In cardiomyocytes, Ca2+ not only regulates excitation–contraction coupling, but also mitochondrial metabolism and oxidative stress signaling, thereby controlling the function and actual destiny of the cell. Understanding the mechanisms of mitochondrial Ca2+ uptake and the molecular pathways involved in the regulation of increased mitochondrial Ca2+ influx is an ongoing challenge in order to identify novel therapeutic targets to alleviate the burden of heart failure. In this review, we discuss the mechanisms underlying altered mitochondrial Ca2+ handling in heart failure and the potential therapeutic strategies.Heart failure is a serious global health challenge, affecting more than 6.2 million people in the United States and is projected to reach over 8 million by 2030. Independent of etiology, failing hearts share common features, including defective calcium (Ca Heart failure (HF) is a complex clinical syndrome characterized by the inability of the heart to pump blood at a rate and with adequate force to meet the metabolic demands of the body. This condition can result from various underlying causes, including damage to the heart muscle (such as from a heart attack), hypertension, valvular heart disease, or other cardiac conditions. HF can affect either the left, right, or both ventricles of the heart and can manifest as systolic dysfunction (impaired ability of the heart to contract and eject blood) or diastolic dysfunction (impaired ability of the heart to relax and fill with blood). The hallmark symptoms of HF include shortness of breath, fatigue, fluid retention (edema), and reduced exercise tolerance. It is a chronic condition that requires ongoing management and treatment to improve the patient’s quality of life and reduce morbidity and mortality. HF shows a steadily growing prevalence and remains the leading cause of death in developed countries ,2. Altho2+) and reactive oxygen species (ROS) are generally considered the main transduction signals linking the SR and mitochondrion and permit them to adapt their responses to external stress in a highly regulated manner [2+ dyshomeostasis, altered bioenergetics, changes in mitochondrial respiration, increased oxidative stress, and impaired energy production and consumption [2+ uptake due to dysregulation in several calcium cycling proteins and increased SR Ca2+ leak through type-2 ryanodine receptors (RyR2) resulting in reduced intracellular Ca2+ stores required for cardiomyocyte contraction and increased baseline cytosolic Ca2+ [2+ uptake follows, which contributes to mitochondrial Ca2+ overload, dysfunction, and oxidative stress [The heart consumes a significant amount of energy supplied almost entirely by mitochondrial ATP production derived from oxidative metabolism . Nearly d manner ,38,39,40sumption ,42,43,44lic Ca2+ ,48,49,50e stress . Mitochoe stress ,54,55,562+ overload in inducing oxidative stress during HF and highlight the potential therapeutic targets as well as new outlooks for future studies.In this review, we summarize the recent evidence demonstrating the crucial role of mitochondrial CaThe heart primarily depends on mitochondrial oxidative metabolism to fulfill approximately 95% of its energy demands , with a 2+ ions are essential to this process. Indeed, increased cytosolic Ca2+ levels with elevated cardiac contractions allow Ca2+ to enter the mitochondria and stimulate pyruvate dehydrogenase, α-ketoglutarate, and isocitrate dehydrogenase to regenerate reducing equivalents [2+ entry into the mitochondria, as in HF, may be deleterious, leading to mitochondrial Ca2+ overload, increased ROS production, and oxidative stress [2+ overload during HF are discussed in the following sections.Increased ATP consumption in cardiomyocytes requires additional reducing equivalents, and Caivalents , as wellivalents . Howevere stress . The fun2+ stored and released within cardiomyocytes in EC coupling. During the depolarizing phase of the cardiac action potential, Ca2+ enters the cardiomyocyte through voltage-activated L-type Ca2+ channels and triggers RyR2 to open and release Ca2+ from SR Ca2+ stores through calcium-induced calcium release (CICR), raising cytosolic Ca2+ levels about ten-fold to ~1 μM [2+ then activates specific proteins of the contractile apparatus and induces contraction of cardiac cells [2+ is removed from the cytosol via three primary mechanisms: type-2a SR Ca2+-ATPase (SERCA2a) transport, sarcolemmal Na+/Ca2+ exchanger (NCX) extrusion, and mitochondrial Ca2+ uptake [Cardiac muscle contraction is regulated beat-to-beat by Cato ~1 μM . Ca2+ thac cells ,69,70. S+ uptake ,73,74,752+ cycling leading to significant increases in cytosolic baseline Ca2+ has been observed [2+ channels in failing compared with non-failing human ventricles was confirmed, which resulted in an excessive calcium influx into the cytosol [2+ leak, was also shown in human and mice cardiomyocytes of failing hearts [+/Ca2+ exchanger (NCX) in extruding cytosolic calcium was demonstrated in a mouse model of heart failure [2+ and potentially increase Ca2+ entry into the mitochondria, causing a detrimental mitochondrial Ca2+ overload in cardiomyocytes [During HF, the widespread dysregulation of Caobserved . First,  cytosol ,78. Moreg hearts . Further failure . Finally failure ,81. Thesmyocytes ,83.2+ dyshomeostasis [2+ cycling proteins [2+ overload [2·−) and resulting in an SR Ca2+ leak [2+ and mitochondrial Ca2+ overload, leading to ROS formation and oxidative stress. The signaling cascades associating the inflammatory response to SR/mitochondrial dysfunction in HF still remain to be elucidated.Inflammation has emerged as a major pathophysiological feature of HF progression, regardless of etiology. Numerous pro-inflammatory signaling molecules are produced and released in HF, initiating vicious cascades involving oxidative stress, mitochondrial dysfunction, myocardial weakened contractility, and, importantly, Caeostasis ,85. Elevproteins ,85. TNF-proteins ,87. Seveoverload ,87. Incroverload ,89. Finaoverload ,85. Wania2+ leak . The ele2+ influx occurs primarily via the mitochondrial Ca2+ uniporter (MCU), whereas Ca2+ efflux occurs mainly via the mitochondrial Na+-Ca2+—Li+ exchanger (mNCLX) [2+ channel in the mitochondrial inner membrane that facilitates Ca2+ transport down its electrochemical gradient without coupling Ca2+ transport with the movement of other ions [2+ uptake channel is a large holocomplex consisting of MCU as the pore-forming unit and multiple regulatory proteins, including the essential MCU regulator (EMRE) [Mitochondrial Ca (mNCLX) ,92,93,94her ions ,108,109.r (EMRE) ,112,113,r (EMRE) ,123,124,r (EMRE) ,127,128,r (EMRE) ,131,132.r (EMRE) . These rr (EMRE) . Howeverr (EMRE) ,135; howr (EMRE) .2+ leads to excessive Ca2+ entry into the mitochondria and causes mitochondrial Ca2+ overload, which is detrimental to the cardiomyocyte [2+ uptake causes mitochondrial Ca2+ overload and oxidative stress, MCU modulators can be an interesting therapeutic option to rescue the subsequent detrimental signaling cascades observed in HF [2+ uptake during acute stress can be reduced by the deletion of the MCU gene or by the MCU blocker, Ru360 [2+ levels remain unchanged [2+ uptake [2+ uptake with different levels of sensitivity to cytosolic Ca2+. Possible mediators of MCU-independent mitochondrial Ca2+ uptake include the Ca2+/H+ exchanger Leucine Zipper And EF-Hand Containing Transmembrane Protein 1 (Letm1) [2+ sensitivity has been shown [d~20–30 μMol) and, as such, resting cytosolic Ca2+ can be insufficient to trigger MCU activity [2+ concentration in cardiomyocytes is, as well as the difference between basal cytosolic Ca2+ in normal versus failing cardiomyocytes when associated with a defective RyR2 leak or reduced SERCA2a activity. Nonetheless, is basal cytosolic Ca2+ in HF sufficient to enter mitochondria and cause Ca2+ overload? This dilemma represents an important question that needs to be clarified by future investigations.During HF, increased cytosolic Caomyocyte ,83,137. ed in HF ,145,146.r, Ru360 ,148, whinchanged ,135. Fur+ uptake . These f (Letm1) ,155,156  (Letm1) ,162,163.en shown  to be quactivity ,165,166.2+ homeostasis [2+ uptake has to be balanced with extrusion in homeostatic conditions, they hypothesized that the key channel responsible for mitochondrial efflux Ca2+, mNCLX [2+ handling [2+ efflux by 38%, displayed an attenuated infarct size after MI or I/R injury, improved cardiac function, and reduced superoxide generation [2+ overload in HF is due to enhanced Ca2+ uptake or repressed extrusion has yet to be further elucidated. Furthermore, the following queries need to be investigated: does increased mNCLX expression/activity affect cytosolic Ca2+ levels by increasing mitochondrial Ca2+ extrusion? Moreover, what are the long-term outcomes of enhanced mNCLX activity in mice? Will those mice be more vulnerable to arrhythmias due to cytosolic Ca2+ overload? We believe that the long-term outcomes of this enhanced mNCLX activity are deteriorated when cardiac disease is associated with leaky RyR2 channels. Although, these hypotheses remain to be verified, recent studies by Garbincius point towards the deleterious effect of mNCLX cardiomyocyte-specific overexpression in mice. Indeed, survival was reduced when mNCLX cardiomyocyte-specific overexpressing mice were subjected to severe neurohormonal stress with angiotensin II and phenylephrine [Recently, Luongo and collaborators revealed a novel mechanism, independent of MCU, responsible for mitochondrial Caeostasis . Since m+, mNCLX ,167, woulephrine .2+ when the Ca2+ concentration is below a threshold of 200 nM [2+ release channels RyR2 and/or 1,4,5-trisphosphate receptors (IP3Rs) [2+ concentrations (10–100 µM) are required to activate Ca2+ uptake into isolated mitochondria; however, in intact cardiomyocytes, the cytosolic Ca2+ concentration after Ca2+ release from the SR remains less than 10 µM, yet Ca2+ is still internalized by mitochondria [It is well established that MCU does not transport Caf 200 nM . However (IP3Rs) ,170,171.chondria ,173.2+ concentrations in microdomains between mitochondria and the SR. For example, RyR2 Ca2+ release during systole creates microdomains of high, localized Ca2+ concentrations (~30 µM) in the vicinity of the mitochondrial membrane, leading to mitochondrial Ca2+ uptake [2+ transfer puzzle that mostly concern the complexity of this highly regulated process, which involves two dynamic organelles. Due, in part, to the low Ca2+ affinity of the MCU, we believe that the formation of Ca2+-rich microdomains alone is not sufficient to allow Ca2+ to enter the mitochondria, especially in the presence of competing sarcolemmal NCX and SERCA2a pumps with a higher Ca2+ affinity and faster uptake rate.Such a discrepancy between isolated mitochondria and intact cells was partially resolved by the finding of high cytosolic Ca+ uptake ,182,183.2+ to transfer to the mitochondria. This hypothesis was recently investigated and two major, non-mutually exclusive interactions between the SR and mitochondria were identified. The functional, tight coupling between the SR and mitochondria is attributed to the inter-organelle tether protein involving mitofusin2 (MFN2) [2+ overload observed in HF is discussed below.Thus, a very close proximity between the two organelles seems to be necessary to allow Ca2 (MFN2) ,185,186 2 (MFN2) ,187,188.Recently, the purification of subcellular fractions corresponding to endoplasmic reticulum (ER)–mitochondria contacts, referred to as mitochondria-associated membranes (MAMs), led to the identification of proteins enriched in those membrane domains ,190,191.2+ transfer to the mitochondria. The lack of MFN2 to tether the ER to mitochondria resulted in a significant reduction in mitochondrial Ca2+ uptake, without any impairment of mitochondrial capacity to uptake Ca2+. This impaired uptake reflects an increased distance between the two organelles and, therefore, a limited generation of Ca2+ microdomains. Therefore, MFN2-KO cells provide experimental proof for the importance of Ca2+ microdomains between the ER/SR and mitochondria, a theory postulated by Rizzuto and Pozzan almost 30 years ago [2+ signaling in the myocardium. This is consistent with a requirement for SR–mitochondrial Ca2+ signaling through microdomains to maintain a competent bioenergetic feedback response in cardiomyocytes [MFN2-KO cells were used to investigate how tethering between the ER and mitochondria would impact Caears ago ,197,198.myocytes .2+ signals through inter-organelle microdomains, where the signaling factor is prevented from diffusing into the cytosol. However, as mitochondria are the main source of ATP in cardiomyocytes and the SR is the main source of Ca2+, it is reasonable to postulate the existence of a physical, dynamic interaction that facilitates direct Ca2+ exchange between the two organelles. Increased beat-to-beat SR Ca2+ release can then be rapidly sensed by the mitochondria, inducing mitochondrial Ca2+ uptake, stimulating mitochondrial dehydrogenases, increasing the production of NADH for the ETC, and increasing ATP production according to the physiological demand . This suggests that these channels do not play a role in the malfunctioning of Ca2+ regulation in ventricular cardiomyocytes [2+ overload in HF and the leakage of Ca2+ from RyR2 channels [In the same vein as the close proximity between the SR and mitochondria described above, recent studies have identified several proteins enriched at the SR–mitochondria interface, highlighting the emerging role of inter-organelle interactions within the cell ,201. Onechondria . Specifichondria . The funachinery . This fiachinery . Howeverachinery ,203. Furmyocytes . Interesmyocytes . On anotchannels . This dichannels .2+ overload, the precise quantity of Ca2+ taken up by mitochondria with each heartbeat in both normal and failing hearts remains uncertain. Furthermore, there is an ongoing debate regarding whether the mitochondrion can function as a primary reservoir for Ca2+ ions [2+ homeostasis is manipulated [2+ in various animal models has led to a mitochondrial phenotype resembling that observed in heart failure. This phenotype includes compromised ATP generation, heightened mitochondrial oxidative stress, and, ultimately, the death of cardiomyocytes [Despite the important progress achieved in the investigation of the pathophysiologic implications of mitochondrial Caa2+ ions ,206,207.ipulated ,111. Indmyocytes ,209.2+ fluxes between the ER and mitochondria [2+ leak was not investigated in these models.Other proteins facilitating a physical connection between the ER and mitochondria have been proposed, including PDZ-domain-containing 8 (PDZD8) ,211, prochondria ; however2+ levels lead to the production of mitochondrial reactive oxygen species in various diseases, including heart failure [2·−) and hydroxyl radical (·OH), as well as non-radical species, such as hydrogen peroxide (H2O2) and hypochlorite (OCl−) [2+ stimulates the Krebs cycle, resulting in the generation of NADH and FADH2, both of which provide electrons to the electron transport chain (ETC). As electrons progress through a series of redox reactions along the ETC, a proton gradient is established, facilitating ATP production, as described earlier [2O2) by superoxide dismutase (SOD), with SOD2 being the primary mitochondrial isoform [2O2 is then removed by the antioxidant systems of peroxiredoxin (Prx) and glutathione peroxidase (Gpx) in the mitochondria [2·− generation from complex I of the ETC caused excessive formation of H2O2 and ·OH, which became deleterious when their production overwhelmed detoxification [2+ overload. This overload further amplifies mitochondrial oxidative stress, propagating a vicious cycle.Numerous studies have shown that excessive mitochondrial Ca failure ,68. ROS  failure , protein failure , and nuc failure . This cae (OCl−) ,221. In  earlier . Dependi earlier ,224,225. isoform ,227. Mitchondria ,229. In fication ,231. Sinfication ,232. In 2+ leak through the hyperactivity of RyR2 [2+ leak not only augments cytosolic Ca2+ concentrations by depleting Ca2+ stores but also increases mitochondria Ca2+ overload, which further produces ROS [Increased mitochondrial oxidative stress during HF, in human patients as well as in animal models ,234, is  of RyR2 . As HF p of RyR2 . Increasuces ROS  and wors2O2, RyR undergoes covalent disulfide cross-linking between the N-terminal domains of the four neighboring protomers, adopting an open state conformation and generating an SR Ca2+ leak [2+ leak through the channel [Many cysteine residues in RyR can be subjected to oxidative post-translational modification; however, the exact nature of these modifications for available cysteines and how they affect the activity of the channel remains to be determined. Recent work suggests that, in the presence of Ha2+ leak . We and  channel ,236,237. channel ,240,241 2+ have been implicated as a key factor for the development of age-related cardiac disorders, HF, and atrial fibrillation [2+ release (SOICR) by raising the activation threshold and delaying the termination of Ca2+ release. Furthermore, the C3602A mutation markedly increased fractional Ca2+ release and diminished the inhibitory effect of N-ethylmaleimide on Ca2+ release, but had no effect on the stimulatory action of 4,4′-dithiodipyridine on Ca2+ release [2+ release. Likewise, Nikolaienko et al. reported that this particular residue did not participate in inter-subunit cross-linking and played a limited role in RyR2 regulation by calmodulin during oxidative stress [RyR channels comprise several surface-exposed cysteine residues with free thiol groups prone to oxidation by reactive oxygen and nitrogen species. Oxidized cysteines that render RyR2 channels leaky to Caillation . Assessiillation . On the illation  in RyR1  release . Moreovee stress . Based oe stress  and our e stress , we mappThe other hyper-reactive cysteines C36, C253, and C315 are located in the N-terminal domain (NTD) of RyR1, while only C36 is conserved in RyR2. The N-terminal β-trefoil domains form the central cytosolic vestibule mediating inter-subunit interactions in the resting state of the channel. Since these interactions are disrupted during channel activation, it has been proposed that NTD is involved in the allosteric regulation of channel gating in both RyR1 and RyR2. Importantly, NTD is a known disease hot spot for pathogenic CPVT mutations weakening the RyR2 stability of the closed state ,249,250.2+ release. The RY1&2 domain is highly dynamic and its oxidation at C917 may contribute to the local regulation of this region.The hyper-active cysteine C822 is located in the SPRY1 (SPIa kinase and ryanodine receptor) domain, C917 in the tandem-repeat domain RY1&2, and C1582 in the SPRY3 region of RyR2. The SPRY domains represent important protein–protein interaction scaffolds in the periphery of the cytosolic shell of RyR. Interestingly, C1582 is located near the calstabin-binding site. Its oxidation can be important to modulating calstabin binding to the channel, which is critical for stabilizing the closed state of RyR and reducing spontaneous Ca2+ release by RyR2. Interestingly, helical domain 1 in the BSol1 domain is where C2402, C2572, and C2577 are located, and it exhibits a domain–domain interface with NTD. The disruption of NTD–Bsol interactions leads to inappropriate channel activation [The hyper-active cysteines C2402, C2572, C2577, and C3158 are located in the bridging solenoid (Bsol) of RyR2, another highly flexible and dynamic region of the protein. BSol encompasses the helical domains BSol1, BSol2, and BSol3. Between the first two is the RY3&4 domain that contains the PKA phosphorylation site (S2808) important for the adrenergic regulation of Cativation ,252. Sim2+ leakage [Nonetheless, through the application of genetic techniques to induce specific truncations and modifications in channel residues and domains, a recent study pinpointed that only two cysteine residues within each RyR2 subunit were accountable for nearly half of RyR2’s functional response when exposed to oxidative stress, specifically cysteine 1078 within the Ry1&2-SPRY2 linker and cysteine 2991 in the BSol loop function as a redox-sensitive pair. They engage in the formation of inter-subunit disulfide cross-links between adjacent subunits when confronted with oxidative stress, ultimately leading to an aberrant RyR2 Ca leakage . This fi leakage .2+ leakage due to oxidative stress [2+ leak.Additionally, as previously discussed, while the previous research has pointed to cysteine 3635 in RyR1 or its equivalent, cysteine 3602, as the most hyperactive redox-sensitive residue, Nikolaienko et al. demonstrated that this particular residue did not contribute to channel cross-linking or the activation of Cae stress ,253. In It has been observed that RyR channels self-organize into higher-order clusters forming checkerboard-like arrangements in the terminal cisternae of SR membranes. Peripheral domains likely involved in mediating clustering interactions between RyR channels are SPRY1, RY1&2 domains, and the C-terminal Bsol region ,256. Imp2+/calmodulin-dependent protein kinase II (CamKII), both known to be redox sensitive, have been shown to phosphorylate RyR2 at different sites and promote RyR2 Ca2+ leak. PKA and CamKII regulate RyR2 function and play an important role in regulating cardiac contractility and arrhythmogenesis [2+ leak, which in turn reduces cardiac contractility and ultimately furthers HF progression. Chronic PKA activation in HF is caused by the hyper-adrenergic state observed in HF patients, as well as in animal models of HF [RyR2 is a large scaffold on which several regulatory proteins and enzymes can be assembled. Among them, two major regulatory kinases, protein kinase A (PKA) and Caogenesis ,268,269.ls of HF .2+ leak, which may lead to mitochondrial Ca2+ overload and dysfunction. To date, however, the exact physiological relevance of this ROS-dependent activation of PKA under physiological and pathological conditions, especially in comparison to adrenergic-dependent activation, remains mostly unknown.Furthermore, the type-I negative regulatory subunits of PKA are also subject to oxidation by ROS . The oxi2+/CaM autonomous activity due to T287 auto-phosphorylation [2+ uptake in the heart by phosphorylating the MCU, with subsequent impacts on mPTP activation and programmed cell death [2+ uptake, respiration, or ROS emission in isolated cardiac mitochondria, nor in isolated cardiac myocytes [Since CamKII has also demonstrated autonomous activation following the oxidation of its regulatory domain, the role of CamMKII oxidation in cardiovascular disease, including HF, has garnered significant attention . The Andrylation . Recentlll death . Howeverll death . These dmyocytes .2+ uptake into the SR, which may increase mitochondrial Ca2+ overload and further ROS production [In addition to RyR2, PKA, and CamKII, SERCA2a has also been shown to experience dysregulation following oxidation by ROS. By treating cardiomyocytes with various reactive oxygen species, several studies have demonstrated decreased SERCA2a Caoduction ,278,279.2+ triggers the opening of the mitochondrial permeability transition pore (mPTP), a non-specific pore in the inner membrane of the mitochondria [c and SMAC/Diablo into the cytosol and, eventually, apoptosis [2+ overload, production of ROS, depletion of ATP and ADP, and increases in inorganic phosphate [Elevated mitochondrial matrix Cachondria ,281, conchondria . Thus, wpoptosis ,284,285.hosphate , all of 2+ handling, mitochondrial dysfunction, and oxidative stress have been linked to the development and progression of HF, independent of etiology. Therefore, the SR and mitochondria may serve as two of the most promising therapeutic targets for HF [2+ handling, as well as its relation to altered cytosolic Ca2+, appears pivotal. Several strategies targeting mitochondria or the SR, including small molecules, peptides, and antioxidants that have been tested in preclinical and clinical studies in HF, are summarized in As previously discussed, defective Cas for HF ,290,291.2+ overload and subsequent oxidative stress, thereby controlling the function and fate of cardiomyocytes. The impairment of RyR2 Ca2+ release has emerged as a major mechanism underlying HF and arrhythmogenesis as a consequence of genetic mutations and/or stress-mediated RyR2 post-translational modifications, loss of channel stability, and impairment of coupled gating.As mentioned above, RyR2 is an essential player in several functions of cardiomyocytes, from EC coupling to the activation of numerous pathways, gene expression, as well as mitochondrial Ca2+ leak by preventing calstabin2 depletion without blocking the channel pore [A family of compounds known as Rycals, a small, orally available molecule, prevent RyR2 Canel pore ,247. Pronel pore ,293. Thinel pore .2+ homeostasis, known as the major mechanism in cardiomyopathies, arrythmias, and death.SS31, a potent antioxidant peptide with the ability to penetrate cell membranes, is located within the inner mitochondrial membrane, where it exhibits protective properties for mitochondria ,295. Exp2+ reservoirs. They accumulate Ca2+ ions during cytosolic Ca2+ elevations in cardiomyocytes. Elevations in intramitochondrial Ca2+ levels trigger multiple enzymes within the mitochondrial matrix. These enzymes, in turn, boost ATP generation, modify the patterns of intracellular Ca2+ signaling across both space and time, and assume a pivotal role in instigating mitochondrial oxidative stress and pathways leading to cell death. It is clear that, in HF, an excessive SR Ca2+ leak, mainly through RyR2 channels, plays a crucial role in the pathophysiology of mitochondrial Ca2+ accumulation and dysfunction and constitutes a feedback loop of alterations between the SR and mitochondria, which contribute to the impairment of cardiac function. Future investigations should focus on breaking this feedback loop by simultaneously targeting the SR leak and mitochondrial Ca2+ overload/oxidative stress using RyR2 stabilizing drugs and mitochondrial antioxidants.Beyond their crucial role as an energy source, cardiac mitochondria serve as Ca


Curcumin, Emblica and Cassia in counteracting enteric inflammation and motor abnormalities in a mouse model of obesity, induced by a high-fat diet (HFD). Male C57BL/6 mice, fed with standard diet (SD) or HFD, were treated with a natural mixture . After 8 weeks, body weight, BMI, liver and spleen weight, along with metabolic parameters and colonic motor activity were evaluated. Additionally, plasma LBP, fecal calprotectin, colonic levels of MPO and IL-1β, as well as the expression of occludin, TLR-4, MYD88 and NF-κB were investigated. Plant-based food supplement administration (1) counteracted the increase in body weight, BMI and metabolic parameters, along with a reduction in spleen and liver weight; (2) showed strengthening effects on the IEB integrity; and (3) reduced enteric inflammation and oxidative stress, as well as ameliorated the colonic contractile dysfunctions. Natural mixture administration reduced intestinal inflammation and counteracted the intestinal motor dysfunction associated with obesity.Intestinal epithelial barrier (IEB) impairment and enteric inflammation are involved in the onset of obesity and gut-related dysmotility. Dietary supplementation with natural plant extracts represents a useful strategy for the management of body weight gain and systemic inflammation associated with obesity. Here, we evaluate the efficacy of a food supplement containing the dry extract of  Obesity is a pathological condition characterized as excessive fat accumulation, resulting from an imbalance between energy intake and its consumption . At presSeveral lines of evidence well demonstrated that the presence of a low-grade systemic inflammation, commonly defined as “meta-inflammation”, resulting from increased pro-inflammatory cytokine and chemokine secretion from adipocytes and adipose tissue-associated macrophages, seems to contribute to the impairment of insulin signaling, immune function and lipid metabolism, as well as a remarkable morphofunctional remodelling of the enteric neuromuscular compartment, resulting in bowel motor dysfunctions ,4,5. In Curcumin, Emblica and Cassia, might exert anti-obesity activity, counteracting body weight gain and systemic inflammation associated with obesity methyl]-1-piperidinyl]ethyl]-1H-indole , (R)-[[(2-phenyl-4-quinolinyl)carbonyl]amino]-methyl ester benzeneacetic acid  and atropine sulphate , to assess neurogenic contraction, whereas the myogenic activity was detected maintaining the specimens in Krebs solution with the addition of tetrodotoxin  and stimulating with exogenous substance P .The contractile activity of colonic longitudinal smooth muscle preparations was recorded, as previously reported , with miLipopolysaccharide binding protein (LPB) level in plasma was measured by ELISA , as previously described ,19. For g. Aliquots of 100 µL were used to conduct the experiment. IL-1β levels were indicated as picograms per milligram (pg/mg) of protein.Plasmatic myeloperoxidase (MPO) levels, positively linked to obesity-related inflammation and insulin resistance induced by the diet ,21, was g, 10 min, 4 °C), and supernatants were frozen in liquid nitrogen and stocked at −80 °C. Faecal calprotectin levels were determined using mouse calprotectin enzyme-linked immunosorbent assay kit and analyzed in accordance with the manufacturer’s instructions.Calprotectin, a calcium binding protein of neutrophil granulocytes regarded as an index of neutrophil infiltration in the intestinal mucosa, was assessed in faecal samples. Briefly, freeze-dried faecal pellets were reconstituted in 1 mL PBS, along with 50 μL of 1% (wt/vol) ascorbic acid . Samples were then homogenized for ten minutes (4 °C). Homogenates were diluted with 2 mL lysis buffer . Homogenates were further homogenized for 30 s and centrifuged .The statistical analysis was performed only for studies where each group size was at least n = 6. In particular, the results are presented as mean ± standard error of the mean (S.E.M.). Two-way ANOVA or one-way ANOVA was used to assess statistical significance, followed by Tukey’s post hoc tests. Significant differences were obtained with Curcuma L., Cassia M. and P. emblica) significantly counteracted the body weight gain in HFD-fed mice . Electrically elicited responses consisted of phasic contractions which were, in some cases, followed by after-contractions of variable amplitude. Colonic preparations from mice fed with HFD for 8 weeks, maintained in Krebs solution with 10 μM guanethidine, 100 μM L-NAME, 1 μM atropine, 1 μM GR159897 and 1 μM SB218795, showed a significant increment of electrically evoked NK1-mediated tachykininergic contractions, compared to SD animals A. DietarThe stimulation, induced by exogenous substance P (SP) of colonic preparations from SD and HFD mice, untreated and treated with natural mixture, elicited contractions of similar magnitude, suggesting no alterations in SP-induced myogenic contractions B. Obese patients often experience—alongside several associated comorbidities, including cardiovascular disease, non-alcoholic fatty liver disease, type 2 diabetes and cancer— gastrointestinal disturbances, including constipation and delayed gastric emptying ,26,27. ICurcumin, Emblica and Cassia, in counteracting the onset of enteric inflammation and the development of motor abnormalities in a mouse model of diet-induced obesity. In particular, our experiments pointed out three major novel findings. The natural mixture supplementation (1) counteracted the increase in body weight, BMI and metabolic parameters, along with a reduction in spleen and liver weight; (2) exerts strengthening effects on the IEB integrity; and (3) reduces enteric inflammation and oxidative stress, as well as ameliorates the colonic contractile dysfunctions. On these bases, in the present study, we evaluated the efficacy of a food supplement, containing the dry extract of Curcuma L., Cassia M. and P. emblica to counteract body weight gain and oxidative stress associated with obesity, in accordance with previous studies [Curcuma L. and P. emblica showed anti-obesity properties, inhibiting adipogenesis and regulating lipid metabolism, as well as preventing the increase in liver weight. In parallel, Cassia M., besides normalize metabolic parameters such as blood total cholesterol and triglycerides levels, displayed anti-oxidant properties, reducing the levels of reactive oxygen species (ROS) [Curcuma L. and Cassia M., respectively. Indeed, it has been demonstrated that the treatment with curcumin can significantly reduce the circulating LBP levels and improve IEB integrity by upregulating intestinal ZO-1, occludin and claudin-1 expression in murine models of sepsis, intestinal ischemia-reperfusion injury and type 2 diabetes mellitus [Cassia mimosoides normalized the inflammatory parameters, reducing circulating IL-1β and TNF levels in a HFD mouse model [Cassia mimosoides and Curcuma longa. Indeed, it has been demonstrated that the presence of intestinal inflammation determines a reorganization of neurochemical coding on the enteric neurons, resulting in an increase in the tachykinergic contractions with consequent alteration of gut motility in obesity [Cassia M. and Curcuma L. on the mouse ileum and colon. Indeed, it has been described that treatment with Cassia and Curcumin is able to relieve the inflammatory-related intestinal dysmotility through a spasmolytic action on excitatory neurotransmitter pathways [Curcumin, Emblica and Cassia, exerts interesting anti-obesity properties, preventing the increase in body, liver and spleen weight, as well as counteracting the metabolic alterations associated with a hypercaloric diet. In addition, such a natural mixture, besides exerting strengthening effects on the IEB integrity, shows anti-inflammatory properties and relieves the bowel dysmotility associated with obesity through a normalization of excitatory tachykininergic colonic contractions  ,13,14,36es (ROS) ,38,39,40es (ROS) . Of notees (ROS) . Interesmellitus ,43,44. Ise model ,46. In tse model ,17, corrse model . Consist obesity . Therefopathways ,49,50,51ractions . In line


Endoplasmic reticulum (ER) stress and its adaptive mechanism, the unfolded protein response (UPR), are triggered by the accumulation of unfolded and misfolded proteins. During osteoclastogenesis, a large number of active proteins are synthesized. When an imbalance in the protein folding process occurs, it causes osteoclasts to trigger the UPR. This close association has led to the role of the UPR in osteoclastogenesis being increasingly explored. In recent years, several studies have reported the role of ER stress and UPR in osteoclastogenesis and bone resorption. Here, we reviewed the relevant literature and discussed the UPR signaling cascade response, osteoclastogenesis-related signaling pathways, and the role of UPR in osteoclastogenesis and bone resorption in detail. It was found that the UPR signal  promoted the expression of the receptor activator of the nuclear factor-kappa B ligand (RANKL) in osteoblasts and indirectly enhanced osteoclastogenesis. IRE1 promoted osteoclastogenesis via promoting NF-κB, MAPK signaling, or the release of pro-inflammatory factors . CREBH promoted osteoclast differentiation by promoting NFATc1 expression. The PERK signaling pathway also promoted osteoclastogenesis through NF-κB and MAPK signaling pathways, autophagy, and RANKL secretion from osteoblasts. However, salubrinal (an inhibitor of eIF2α dephosphorylation that upregulated p-eIF2α expression) directly inhibited osteoclastogenesis by suppressing NFATc1 expression and indirectly promoted osteoclastogenesis by promoting RANKL secretion from osteoblasts. Therefore, the specific effects and mechanisms of p-PERK and its downstream signaling on osteoclastogenesis still need further experiments to confirm. In addition, the exact role of ATF6 and BiP in osteoclastogenesis also required further exploration. In conclusion, our detailed and systematic review provides some references for the next step to fully elucidate the relationship between UPR and osteoclastogenesis, intending to provide new insights for the treatment of diseases caused by osteoclast over-differentiation, such as osteoporosis. The endoplasmic reticulum (ER) is responsible for the synthesis, folding, and modification of secretory and transmembrane proteins through various chaperone proteins and enzymes in ER organelles. Its function is extremely precisely regulated, but a variety of internal factors and changes in the external environment will destroy the protein folding ability of the organelles and trigger ER stress, which is characterized by the accumulation of misfolded or unfolded proteins ,2. Notab2+-nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), and Src.Bone is a dynamic, metabolically active, and functionally diverse organ that is mainly composed of extracellular matrix proteins and calcium phosphate. The bone remodeling process, mainly consisting of bone formation by osteoblasts and bone resorption by osteoclasts, maintains the dynamic balance of the bone mineral density and minerals . It is wDuring osteoclastogenesis, large amounts of active proteins are synthesized and secreted to promote osteoclast differentiation and bone resorption functions, which may activate ER stress and UPR. Interestingly, in addition to being proven to be an adaptive mechanism to alleviate ER stress and promote cell survival, UPR is also involved in osteoclast differentiation and bone resorption. In recent years, several studies on ER stress, UPR, and osteoclasts have been conducted, and scholars have found that ER stress plays an extremely important role in the mechanism of osteoclastogenesis. Therefore, we herein present a detailed review and discussion of ER stress-related mechanisms, signaling pathways of osteoclast differentiation, and the role of branches  of UPR signaling in osteoclastogenesis.As one of the largest organelles in eukaryotic cells, the ER consists of reticular and tubular structures that span the cell and collaborate with other organelles to maintain normal physiological functions. ER has two main domains: the smooth ER, without ribosome attachment, is involved in lipid synthesis, metabolism, and calcium storage; the rough ER, with ribosome attachment, is responsible for the synthesis and transport of secretory proteins, integral membrane proteins, and cytoplasmic protein. At least a third of all proteins, including calcium-handling proteins, the transmembrane receptors, growth factors, and hormones, are synthesized, modified, folded, and matured by the ER, and then transported to various membrane compartments or secreted ,8,9,10.2+ concentration, increased rates of protein synthesis, missense polymorphisms in individual proteins, depletion of energy (ATP), altered osmolarity, nutritional deficiencies, oxidative stress, viral infections, and elevated temperatures all lead to the accumulation of unfolded and misfolded proteins in the ER, resulting in ER stress [The ER is a complex organelle with many different functions and must be tightly regulated to perform its correct function. The disruption of protein folding processes or calcium homeostasis in the ER leads to the accumulation of unfolded and misfolded proteins, triggering ER stress . NotablyR stress ,13.In response to ER stress, an adaptive mechanism known as the UPR is activated in cells to reduce unfolded or misfolded proteins . In addiERN1 gene, is the most evolutionarily conserved of the three ER stress sensors and is widely expressed in a variety of species, from yeast to humans [BIP), disulfide isomerases, glycosylases, ER and Golgi structural components, HERP (homocysteine-induced ER protein), DNAJB9 (DnaJ heat shock protein family (Hsp40) member B9)/ERDJ4) in the nucleus and the ER-related degradation (ERAD) pathway, thereby promoting ER lipid synthesis, peptide folding, and membrane expansion to reduce ER stress [IRE1, encoded by the o humans ,19. Thero humans . When uno humans . IRE1α tR stress ,22,23,24R stress .EIF2AK3 gene), also referred to as PEK, EIF2AK3, like IRE1α, is an ER-resident type I transmembrane protein, one of the four known eukaryotic initiation factor 2 alpha (eIF2α) protein kinases, and the other three are PKR (protein kinase double-stranded RNA-dependent), GCN2 , and HRI (heme-regulated inhibitor) [CHOP  is among them, which is upregulated by ATF4 expression and tends to equalize the unbalanced ER by inducing the expression of many corrective genes, including XBP1 and chaperone proteins [PERK (encoded by the hibitor) ,25,26,27hibitor) . When ERhibitor) ,30,31. Phibitor) . ATF4 behibitor) ,34,35. CBIP, ER degradation-enhancing α-mannosidase-like protein 1 (EDEM1), and protein disulphide isomerase-associated 6 (PDIA6), thereby promoting ER expansion and protein quality control [XBP1 is also a substrate for ATF6α, and ATF6 and XBP1s, the active forms of XBP1, cooperate to promote ER protein folding for quality control in response to ER stress, and thus promote cell survival [ATF6 (activating transcription factor 6) includes ATF6α and ATF6β. The most studied is ATF6α, an ER-resident type II transmembrane protein in the inactivated state, characterized by a cytoplasmic N-terminal bZip transcription factor domain and a large ER luminal domain ,36,37,38survival ,42.Furthermore, five other transcription factors in the ER: LUMAN , old astrocyte specifically induced substance , BBF2 human homolog on chromosome 7 , cyclic AMP-responsive element-binding protein hepatocyte , and CREB4 , have a similar structure to ATF6 and also contain transcription factors (bZIP) in their cytoplasmic domains. When exposed to ER stress, they are transferred to the Golgi apparatus, cleaved by S1P and S2P, and release active structures to the nucleus, where they exert their effects ,43.Normal adults have 213 bones (excluding seed bones). Bones not only provide structural support for the torso to protect important internal organs and tissues but also act as levers to allow movement and mobility of the torso through muscles. In addition, bones maintain mineral homeostasis and the acid–base balance in the body, provide growth factors and cytokines, and serve as the microenvironment for hematopoiesis in the bone marrow .Although at the macroscopic level the skeleton appears to remain stationary, it is a dynamic and active tissue that is constantly transforming, a process that involves a variety of bone cells, such as osteoblasts, osteoclasts, osteocytes, etc. . Bone tiTNFSF11) gene on chromosome 13 (13q14.11). RANKL is mainly expressed by osteoblasts, osteocytes, and immune cells. It has an extracellular domain at the carboxyl terminal and is released into the extracellular environment in the form of soluble RANKL after being cleaved by matrix metalloproteinases and other enzymes [TNFRSF11A gene on chromosome 18 (18q21.33), is mainly expressed in osteoclast precursors, mature osteoclasts, and immune cells such as DC, macrophages, and microglia. Its carboxyl terminal contains three TNF receptor-associated factor (TRAF) binding domains. OPG, a receptor encoded by the TNFRSF11B gene on chromosome 8 (8q24.12), is a soluble decoy receptor without any transmembrane structure, which negatively regulates osteoclastogenesis by binding RANKL [2+-NFATc1 signaling pathways, resulting in the activation of osteoclast differentiation, survival, proliferation, and bone resorption functions  receptor (TNFR)/TNF-like proteins: RANKL, RANK, and osteoprotegerin (OPG) ,54. RANK enzymes ,56. RANKng RANKL ,58. In ang RANKL . CSF1R , NF-κB2 (p52), RelA p65), RelB, and c-Rel . RANKL–R, RelB, aTRAF6 recruitment also induces the formation of complexes containing TGF-β-activated kinase (TAK) 1 and TAK-1-binding protein (TAB) 2 to activate all three MAPK pathways, including JNK (by MKK4/7), ERK (by MEK1/2), and p38 (by MKK3/6) ,68,69. A•−), and non-free radicals such as hydrogen peroxide (H2O2) [phox) [2+ release  receptor regulation) and synergizes with Ca2+ to enhance transcription of the key osteoclast transcription factor NFATc1 , promoting osteoclast precursor fusion and functional gene expression [NQO1, HO-1, SOD2, and GSH reductase 1) to diminish the enhancement of osteoclastogenesis by ROS [RANKL–RANK binding also induces the production of ROS to stimulate osteoclast differentiation ,71. ROS e (H2O2) . It is d) [phox) ,74. It i) [phox) . After Rpression ,76,77,78s by ROS ,76,79.2+ stored in the ER to be released into the cytoplasm, thereby inducing Ca2+ oscillations [2+ released into the cytoplasm subsequently binds to calmodulin (CaM), leading to the activation of CaM-dependent enzymes, such as the phosphatase calcineurin, which induces NFATc1 translocation into the nucleus and promotes the transcription of osteoclast-specific genes [2+ from the ER and activates NFATc1 [ATP6V0D2, TRAP, MMP9, CTSK, and DC-STAMP, thereby contributing to osteoclast survival, maturation, and degradation of the bone matrix [In addition, the activation of TRAF6 also stimulates phospholipase Cγ (PLCγ) to produce IP3, which binds to the 1,4,5-trisphosphate receptors (ITPRs) on the ER surface, allowing Callations . Ca2+ reic genes . Furthers NFATc1 ,71. Notas NFATc1 . Eventuae matrix .After the initiation of RANKL signaling in osteoclasts, Src protein binds to TRAF6 and acts on downstream phosphatidylinositol 3-kinase (PI3K) and the serine/threonine protein kinase AKT to promote the survival of osteoclasts ,68.NFATC1, promoting NFATC1 transcription and differentiation of osteoclasts in murine models [RANKL–RANK-induced calcium oscillations are extremely important for osteoclast formation. Interestingly, calcium oscillations also promoted the activation of ER stress (IRE1α-XBP1) through 1,4,5-trisphosphate receptors 2 and 3 (ITPR2 and ITPR3), allowing XBP1 to bind to the promoter region of e models . In the e models ,84,85.2+-ATPase (SERCA) pump [phox, thereby activating ER stress (BiP-IRE1α), which in turn triggered autophagy and stimulated the expression of the osteoclast-specific markers TRAP and CTSK [Thapsigargin (CA) pump . FurtherCA) pump . AnotherCA) pump . A zinc and CTSK . Titaniuand CTSK . It was and CTSK . Liang Zand CTSK .2+-ROS signaling pathways [Notably, the IRE1α signaling pathway also played an essential role in inflammation-mediated bone loss. The inflammatory response at the interface membrane also plays an important role in the loosening of the prosthesis after arthroplasty. ER stress mediated periprosthetic particle-induced inflammatory osteolysis and osteoclastogenesis via BiP-IRE1α and its downstream c-Fos, NF-κB, and Capathways . Rui Wanpathways . TherefoBIP, XBP1, total XBP1, CTSK, and TRAP genes and the increase in the osteoclast number and bone resorption in alveolar bone. This suggested that IRE1α-XBP1 played an active role in alveolar bone resorption induced by pseudomonas gingivalis. In addition, 4-PBA also inhibited the formation of multinucleated osteoclasts from M-CSF and RANKL-induced BMMS in a dose-dependent manner via the IRE1α-XBP1 signaling pathway in vitro. Considering that 4-PBA, as a histone deacetylase inhibitor, may affect gene expression related to bone metabolism and the inflammatory response, the use of another chemical chaperone lacking histone deacetylase inhibitory activity, tauroursodeoxycholic acid, also exhibited similar effects to 4-PBA. However, this study failed to elucidate the relationship between ER stress and osteoclast differentiation and pseudomonas gingivalis-induced periodontitis bone resorption at the protein level. As the gene level usually does not necessarily reflect the protein expression level or protein activation status, this study has some limitations [In the model of periodontitis induced by oral pseudomonas gingivalis in mice, 4-phenylbutyric acid  reversed the significant expression of itations .In addition, IRE1α-XBP1 is commonly activated and upregulated in cancers, such as breast cancer, Burkitt’s lymphoma, oral squamous cell cancer, prostate cancer, lung cancer, liver cancer, etc. . It is wIn summary, IRE1α-XBP1 played a positive role in osteoclastogenesis and associated bone resorption in physiological and pathological bone remodeling states .In the model of periodontitis induced by oral pseudomonas gingivalis in mice, the PERK-eIF2α signaling pathway has been shown to be involved in RANKL-induced osteoclast formation in BMMs . Using RThe role of the PERK-eIF2α signaling pathway on osteoclastogenesis is controversial, depending on the animal and cell model used and the experimental conditions. Jie Li et al. used tail-suspended mice as a model of disuse osteoporosis and investigated the relationship between ER stress and disuse osteoporosis. Their results showed that the expression level of p-eIF2α was positively correlated with the count of osteoblasts and negatively correlated with the count of osteoclasts. Increased osteoclast numbers and reduced bone mass in unloaded mice were reversed by salubrinal, an inhibitor of dephosphorylation of eIF2α. Salubrinal increased p-eIF2α levels and inhibited the expression of RANKL, NFATc1, CTSK, and CHOP in unloaded mice. Moreover, salubrinal lessened the tunicamycin-induced increase in RAW264.7 cell viability, but not apoptosis . Jie Li The role of the PERK-NRF2 signaling pathway in osteoclastogenesis under ER stress has also been reported. Fluoride-involved stimulation of ER stress leads to different degrees of bone formation and bone resorption, in which PERK plays a pivotal role. Fluoride-involved bone resorption is associated with the promotion of RANKL expression by PERK, and NRF2 may be involved, but the exact mechanism has not been elucidated. Scholars suggested that NRF2 may play more of a role in the mechanism of bone formation . In addiIn conclusion, BiP-PERK-eIF2α had a positive effect on osteoclastogenesis . HoweverTherefore, the role of the PERK-eIF2α signaling pathway in osteoclastogenesis and a more detailed mechanism by which PERK-NRF2 regulates osteoclastogenesis need to be further explored and validated.Following UPR initiation, S1P and S2P in Golgi co-cleave ATF6α from the ER. Zheng et al. showed that S1P promotes osteoclastogenesis and bone resorption activity, and the expressions of S1P and ATF6 were significantly reduced in S1P-deficient osteoclasts, but other ER stress-related proteins such as BiP, XBP-1, PERK, ATF4, EDEM1, DNAJB9, and CANX were not significantly changed, while ERN1 was only slightly reduced. Therefore, S1P may regulate osteoclast differentiation and bone resorption through other signaling mechanisms rather than through ER stress .NFATC1 and upregulated its expression, ultimately promoting RANKL-induced osteoclastogenesis [In response to intracellular ER stress, CREBH is activated by S1P and S2P cleavage (similar to ATF6). It has been found that ROS triggered ER stress and thus activated CREBH, which bound to the promoter of ogenesis . In addiogenesis . Howeverogenesis .Therefore, CREBH has a positive effect on osteoclastogenesis, and the regulation of ATF6 on osteoclasts is still controversial and needs further experiments to verify .BiP is defined as a moonlighting protein (intracellular or extracellular protein with different functions) ,124. AltARL6IP5 knockdown promoted RANKL expression in osteoblasts through ER stress and CHOP, thus indirectly promoting osteoclastogenesis [The UPR increased the expression of RANKL in osteoblasts and osteocytes, thus indirectly promoting osteoclast formation and bone resorption . The IREogenesis . In concNFATC1. While PERK also promoted NF-κB, MAPK signaling promoted osteoclast differentiation. Furthermore, as a downstream signal of oxidative stress, PERK promoted autophagy to regulate osteoclast differentiation, but the specific mechanism has not been elaborated, which will be the future research direction. Interestingly, salubrinal (increasing the expression of p-eIF2α) acted directly on osteoclasts to inhibit osteoclastogenesis by inhibiting the expression of NFATc1, and indirectly promoted osteoclastogenesis by acting on osteoblasts (secreting RANKL). In addition, PERK-NRF2 promoted osteoclastogenesis by increasing the expression of RANKL, but the exact mechanism is also unclear. Thus, the specific role and mechanism of p-PERK and its downstream signaling in osteoclastogenesis are open to debate. In addition, CREBH was thought to increase NFATc1 expression to promote osteoclast differentiation, while the role of ATF6 in osteoclastogenesis is controversial. Finally, the role of BiP in osteoclastogenesis remains unaddressed. In summary, the IRE1α signaling pathway and CREBH signaling pathway can promote osteoclastogenesis, providing a new perspective for the treatment of diseases caused by osteoclast over-differentiation, such as osteoporosis. However, the roles and specific mechanisms of other signaling branches of UPR (such as p-PERK and ATF6) and BiP in osteoclastogenesis are still not well-explained, and further in vivo and in vitro experiments are required to elucidate them, which will be the focus of future studies.With the aging of the world’s population, osteoporosis is having an increasing impact on health, causing a huge medical, economic, and family burden to patients and society. The over-differentiation of osteoclasts, as the primary bone-resorbing cells, plays a crucial role in the pathogenesis of osteoporosis. Exploring specific targets for the treatment of osteoclast over-differentiation remains a major research challenge. ER stress and its adaptive mechanism, UPR, occur in the context of the excessive aggregation of misfolded and unfolded proteins in the ER lumen and disturbed calcium ion homeostasis. It is worth noting that there are many common links between ER stress and osteoclasts, such as oxidative stress and an inflammatory reaction. The complex and close relationship between UPR and osteoclasts suggests an important role of UPR in osteoclast-related bone metabolism, and the UPR signaling pathway has been reported to play a crucial role in osteoclastogenesis in both physiological and pathological states. Here, we provided a comprehensive review of UPR, osteoclastogenesis-related signaling pathways, and the role of UPR in osteoclastogenesis and bone resorption. Available evidence suggested that the UPR signaling pathway  indirectly promoted osteoclast differentiation by promoting the secretion of RANKL from osteoblasts. The IRE1α signaling pathway promoted osteoclastogenesis by promoting the NF-κB, MAPK signaling, or the release of pro-inflammatory factors . In addition, RANKL/RANK promoted osteoclastogenesis through the binding of XBP1 to the promoter of


Pseudomonas aeruginosa, competence stimulating peptides from Streptococcus mutans, and D-amino acids from Staphylococcus aureus. Taste receptors are an arm of immune surveillance similar to Toll-like receptors and other pattern recognition receptors. Because they are activated by quorum-sensing molecules, taste receptors report information about microbial population density based on the chemical composition of the extracellular environment. This review summarizes current knowledge of bacterial activation of taste receptors and identifies important questions remaining in this field.Bitter and sweet taste G protein-coupled receptors  were originally identified in type II taste cells on the tongue, where they signal perception of bitter and sweet tastes, respectively. Over the past ~15 years, taste receptors have been identified in cells all over the body, demonstrating a more general chemosensory role beyond taste. Bitter and sweet taste receptors regulate gut epithelial function, pancreatic β cell secretion, thyroid hormone secretion, adipocyte function, and many other processes. Emerging data from a variety of tissues suggest that taste receptors are also used by mammalian cells to “eavesdrop” on bacterial communications. These receptors are activated by several quorum-sensing molecules, including acyl-homoserine lactones and quinolones from Gram-negative bacteria such as  The immune system has been referred to as our “sixth sense” ,2. Like In fact, human olfactory receptors have been suggested to predate the human sense of smell . In otheThe focus of this review is on the immune roles of another type of sensory receptor: taste GPCRs. Taste receptors were originally identified on the tongue  but alsoQuorum sensing is a method of intercellular communication used by individuals of a bacterial species to communicate with each other, with other species, and even to coordinate interactions with their host . It is iPseudomonas aeruginosa or Staphylococcus aureus infections [Quorum sensing is notably involved in regulating the formation of complex aggregate communities known as biofilms ,22,23,24fections .P. aeruginosa and Escherichia coli produce and use various acyl-homoserine lactones (AHLs) as their primary quorum-sensing signals. Although they share a common homoserine lactone (HSL) ring, these molecules are structurally diverse. Thus, each AHL is synthetized by a dedicated AHL synthase. P. aeruginosa, for example, produces two AHLs, 3-oxo-C12-HSL and C4-HSL, which are synthesized by two independent enzymes, LasI and RhlI, respectively [Several families of bacterial quorum-sensing molecules have been reported. Gram-negative bacteria such as ectively . AHLs spectively .Streptococcus mutans, Streptococcus pneumoniae, Streptococcus gordonii, and Streptococcus intermedius [S. mutans, the CSP-mediated quorum-sensing system is encoded by the ComCDE genes and includes the pheromone itself (ComC) and a two-component system consisting of a membrane-bound histidine kinase receptor (ComD) and its cytoplasmic cognate response regulator (ComE) [Quorum-sensing signals in Gram-positive bacteria are typically oligopeptides , such as autoinducing peptides (AIP) . Competeermedius ,29. In Sr (ComE) ,30,31. Cr (ComE) .Pseudomonas quinolone signal (PQS), and the diffusible signal factor (DSF) [Other notable examples of quorum-sensing signals include the autoinducer-2 (AI-2) found in both Gram-positive and Gram-negative bacteria, the or (DSF) ,26. The + and H+ ion channels, respectively, expressed in distinct subsets of morphologically defined type III cells of the taste bud [+ channel Otop1 [Our perception of food is referred to as flavor, which is a combination of smell, mouthfeel (texture), taste, and other stimuli. There are only five canonical tastes detected by the taste bud cells of the tongue: bitter, sweet, savory , salty, and sour. The salty and sour tastes are mediated by Naaste bud ,33. Saltel Otop1 ,35,36. Ael Otop1 .Instead of ion channels, GPCRs are used to detect bitter, sweet, and umami compounds ,39. GPCR2+ signaling through its G-protein pathways (3), which binds to and activates the IP3 receptor (IP3R). The IP3R is an endoplasmic reticulum (ER) ion channel that allows calcium (Ca2+) release from intracellular ER Ca2+ stores [3R [3R isoform found in type II taste cells [3R Ca2+ release. While this makes sense in the context of taste, it is somewhat surprising as further studies have suggested that PKA enhances IP3R activity [3R release kinetics [3R activity [3R.Activation of taste GPCRs in the type 2 taste cells likely first results in Capathways . Gβγ act+ stores ,43. Simu+ stores . It is hores [3R ,46, the te cells ,48,49. Tactivity ,51,52 orkinetics  rather tactivity . In the 2+ release from the ER activates a plasma-membrane-localized cation channel, TRPM5 [+) channels [Nonetheless, Cal, TRPM5 ,55. Thischannels  to generchannels  through channels ,59,60. Tchannels ,61. The channels ,63.TAS1R genes. T1Rs form sweet and umami receptors, thought to be “pleasant” tastes because they signal the presence of beneficial nutrients in foods [2+/Mg2+ receptors [- ions at low mM concentrations may bind to T1R3 and evoke some umami and/or sweet taste signaling in mice [There are two main families of taste GPCRs. The taste family 1 (known as Tas1R or T1R) group contains three T1R isoforms, T1R1, T1R2, and T1R3 ,65,66. Tin foods ,67. The in foods ,67. T1Rsin foods . The swein foods ,70,71,72in foods , as wellin foods . The umain foods . Umami ain foods . Some tyin foods , and T1Rin foods ,78,79 oreceptors , though  in mice . Because in mice ) activat in mice ,84, gymn in mice ) inhibitTAS2R genes [The taste family 2 receptors, Tas2R or T2R, mediate bitter taste and are encoded by 2R genes . Twenty-2R genes . Much li2R genes , but the2R genes .TAS1R2 receptors during evolution and are unable to taste sweet sugars, likely because their natural carnivorous diet contains very little of these nutrients [The expression, functionality, number, and diversity of taste receptors in different species have been greatly shaped by evolutionary pressure ,91,92. Tutrients . HerbivoTAS2R38, has several single-nucleotide polymorphisms (SNPs) resulting in proteins with different amino acids at positions 49, 262, and 296 [At the species level, the expression and function of taste receptors between different individuals is influenced by genetic polymorphisms. Within the T2R bitter taste receptors family, T2R38 is the most well documented isoform. The gene encoding for this isoform,  and 296 ,94. Two  and 296 . For the and 296 ,96,97.TAS2R38 polymorphisms resulting in PAV and AVI variants closely follow a Mendelian inheritance pattern. Individuals with the AVI/AVI genotype are “non-tasters” for T2R38-specific agonists such as phenylthiocarbamide (PTC or phenylthiourea PTU) and 6-propyl-2-thiouracil (PROP) [TAS2R38 polymorphisms may therefore have an impact on how people perceive the taste of these vegetables and on their individual preferences.In Caucasian populations, the l (PROP) . They rel (PROP) ,98. Sevel (PROP) , but thel (PROP) . T2R38 iTAS2R38 polymorphisms may have clinical implications beyond taste detection and processing. This observation may also apply to hundreds of other TAS2R and TAS1R polymorphisms described in humans [TASR38. One specific example is the T1R sweet receptor polymorphism involving a valine or isoleucine residue at position 191. Individuals homozygous for the valine variant may be more susceptible to higher absorption of carbohydrate during meals, as well as have an increased risk of hypertriglyceridemia and dental caries [TAS1R polymorphisms as they may influence these functions beyond diet-related sugar ingestion.The expression of T2R38 receptors outside the oral sphere suggests that n humans ,100 whosl caries ,102. Thel caries ,104, meml caries ,108,109,l caries ,112,113 2+-sensing receptor (CaSR) by various food compounds  [In addition to bitter, sweet, and umami, the tongue may also be able to detect other tastes through GPCRs, including fatty ,117,118,inerals) . Kokumi inerals) ,122,123.Taste receptors were first described as sensory receptors located on the tongue, where they are expressed in taste cells of taste buds. However, bitter and sweet G-protein coupled taste receptors have recently been identified in other tissues ranging from the lungs and gut to the brain ,17. In cTAS2R gene expression was detected in both oral cavity (jaws and gills) and other organs (liver and fins) in the teleost cavefish Astyanax mexicanus [TAS1R and TAS2R genes used by vertebrates for bitter, sweet, and umami tastes [The purpose of these seemingly misplaced, extraoral taste receptors was at first baffling, but it is now known that taste is only part of the responsibility of these receptors. Bitter and sweet receptors serve more general chemosensory roles in many tissues, making them potential therapeutic targets or possibly important mediators of off-target drug effects , particuexicanus . Fish ari tastes .It is important to note that these extra-oral taste receptors do not mediate “taste” per se as they are not linked to neuronal perceptive pathways, but they still serve as local chemoreceptors in the body. The known distribution of bitter and sweet taste receptors varies between organs, it is thought that some express only bitter or only sweet receptors, while others express both. We are only beginning to understand the diverse roles of these receptors. For example, sweet taste receptors in the pancreas and intestine may regulate insulin secretion ,111,141,As described in detail in the following sections, one component of extraoral taste receptor function is the detection of bacterial quorum-sensing molecules . We primThe sinonasal cavity, which includes the nose and the four paranasal sinuses, is the entry point of inhaled air into the body. It has the important function of warming the inhaled/inspired air and removing unwanted particles to protect the integrity of the more delicate lower respiratory tract . Thus, iThe defense mechanisms of the sinonasal cavity are both physical and chemical. Inhaled particles and microbes can be removed through mucociliary clearance (MCC): they are trapped into the upper layer of mucus secreted by the mucosa, and subsequently eliminated into the aerodigestive tract by the beating of the epithelial cells’ cilia. MCC is the prime physical defense of the airway. Severe respiratory infections occur when MCC is impaired in primary ciliary dyskinesia through impairment of cilia function  or in cyThe innate immune system also secretes several antimicrobial peptides and molecules, such as defensins and nitric oxide (NO), that neutralize and prevent infections ,171. The2+-dependent increase in ciliary beating frequency [A novel approach in the treatment of CRS and other airway infections could be to explore bitter taste receptors as pharmacological targets by exploiting their role in innate immunity. T2R receptors are now known to be extensively expressed in the ciliated cells of the bronchial and sinonasal epithelia, specifically in the cilia themselves ,182,183.requency . In the requency , the funrequency ,182,183.requency   in ciliated cells, which leads to a strong increase in intracellular NO production, most likely mediated by the endothelial-named isoform eNOS [2+ and NO signaling also involve PLCβ2 and TRPM5, as described above in the canonical type 2 taste cell signaling [P. aeruginosa [In mice, AHLs activate nasal solitary chemosensory cells (SCC), hence their initial discovery as mouse nasal SCC agonists . In humaorm eNOS ,182,183.ignaling ,182,183.ruginosa ,182,183.ruginosa ,189,190.TAS2R38 polymorphisms, it is consistent to hypothesize that TAS2R38 genetics may influence the magnitude of the T2R38-mediated immune response, depending on patient genotypes. In a first step to test this hypothesis, sinonasal epithelial cells from PAV (super-tasters) and AVI homozygous patients (non-tasters), as well as from PAV/AVI (intermediate tasters) patients, were cultured in vitro at the air-liquid interface (ALI), and their level of Ca2+ signaling and NO production were investigated [2+ signaling and NO production, as well as enhanced MCC and bactericidal effect, compared with non-taster (AVI/AVI) and intermediate taster (PAV/AVI) cells [TASR38 taste-altering polymorphisms also modify the sinonasal epithelial cells’ responses to Gram-negative bacteria su8ch as P. aeruginosa. They were subsequently reinforced by clinical studies that showed super-tasters were less likely to develop Gram-negative sinonasal infections than non-tasters and intermediate tasters [Because of the existence of stigated . We demostigated . In addiI) cells . Overall tasters . Regardi tasters ,192, and tasters . AVI/AVI tasters .TASR38 polymorphisms and CRS [TAS2R38 polymorphisms [TAS2R38 genotype and CRS. A Canadian GWAS found that patients with CRS more frequently had SNPs in the bitter receptor genes TAS2R38 and TASR13 than their non-diseased counterparts [TAS2R38 and TAS2R19 genes [Following the results described above, a growing number of studies have continued to examine the relationship between  and CRS ,200,201.orphisms . These corphisms , an Austorphisms , and anoorphisms . Genomicterparts , and a U19 genes .Recent studies demonstrate that T2Rs are true immune recognition receptors, much like Toll-like receptors (TLRs). Gram-negative AHLs have been shown to be able to activate other T2Rs than T2R38, including isoforms T2R10 and T2R14 when expressed in HEK93 cells . In addiP. aeruginosa and currently unidentified molecules present in media conditioned with Bacillus cereus [Other quorum-sensing molecules that may activate T2R-mediated immune response in airway ciliated cells include two quinolones also produced by s cereus . In the s cereus ,86.P. aeruginosa is a major cause of morbidity and mortality and promotes rapid decline in respiratory function [P. aeruginosa in the natural history of CF and its ability to produce T2R38 ligands led scientists to investigate the relationship between susceptibility to this bacterium and TASR38 genotype in CF patients. Studies on that subject have yielded conflicting results. The initial study, which showed correlation between TAS2R38 genotype and some CRS-related symptoms in CF patients [TASR38 and infection by P. aeruginosa in CF patients [TAS2R38 PAV allele was significantly lower in CF patients who had CRS with nasal polyps and required FESS [P. aeruginosa, especially when this colonization occurred before the age of 14 years [Cystic fibrosis (CF) is a rare and fatal disease caused by a defective mutated cystic fibrosis transmembrane regulator (CFTR) protein, an anion channel that regulates fluid secretion in glandular organs such as the lungs, pancreas, and reproductive organs . In CF pfunction . The invpatients , was notpatients . Anotherred FESS . It also14 years .P. aeruginosa in CF patients. The low impact of TAS2R38 genotypes in CF may be rooted in the altered NO responses that have been described in CF patients [TASR38 genotype, contributing to their high susceptibility to P. aeruginosa and reducing the influence of TAS2R38 on CF-related infections. With current CF treatments using CFTR modulators to restore the ion channel function in patients [TASR38 genetics on the susceptibility of CF patients to P. aeruginosa infections.Overall, these previous studies suggest that the PAV allele may confer subtle protection against CRS and possibly infection by patients . In thispatients ,214. Thepatients . Alteredpatients ,215, we T2R-mediated NO production is also reduced during co-stimulation of NPY, which activates inhibitory protein kinase C phosphorylation of eNOS through NPY2R receptors in ciliated epithelial cells . As leveStreptococcus mutans [S. mutans CSP-1 activated intracellular Ca2+ signaling and secretion of IL-8 (CXCL-8), TNF-α, and IL-6 in gingival cells. This was blocked by a T2R14 antagonist (6-methoxyflavone) or CRISPR/Cas9 knockout of T2R14 [S. aureus but not S. mutans in their gingival epithelial cell model [S. mutans CSP-1, they observed inhibition of growth for S. aureus, but not for S. mutans [S. aureus but not S. mutans [S. mutans induced T2R14 dependent IL-8 secretion [Gingival epithelial cells express T2R14, which was recently identified to be involved in detecting competence stimulating peptides (CSPs) from Gram-positive s mutans , a commos mutans . S. mutaof T2R14 . Interesll model . When gi. mutans . This wa. mutans . Insteadecretion .S. aureus internalization [S. mutans and S. pneumoniae share similar CSP quorum-sensing mechanisms [S. pneumoniae infections [Furthermore, they showed that T2R14 knockout reorganizes the cytoskeleton in gingival cells, potentially explaining the inhibition of lization . While tchanisms , there mfections ,219.TAS2R43 and TAS2R14 gene expression levels are associated with early childhood dental caries [TAS2R3, TAS2R4, TAS2R5, and TAS2R60 are also associated with severe early childhood caries [TAS2R38 PAV and AVI polymorphisms have been liked to oral microbial composition by 16S rRNA sequencing [Nonetheless, these data suggest that T2R14 in the oral cavity might be a target for stimulation of innate immune responses in patients with gingivitis or certain types of gingival infections. This may extend to other bitter receptors. A meta-analysis of GWAS data suggested that l caries . Anotherd caries , findingd caries . TAS2R38quencing . T2R16 aquencing .Solitary chemosensory cells (SCCs) are a type of specialized, elongated chemosensory cell that makes up about 1–10% of the cells in the sinonasal cavity ,229,230.Upper airway SCCs have been shown to co-express both bitter (T2R) and sweet (T1R2/3) taste receptors in a single cell, in contrast to type II taste bud cells that only express one type of taste receptor each ,239. ActSweet taste receptors in SCCscan be activated by several types of molecules, including artificial sweeteners and glucose at defined concentrations (0.5–5 mM). Interestingly, this activation counteracts T2R signaling in the same cell and reduces the antimicrobial response by decreasing the release of β-defensins ,134. SciWhile the mechanism described above may be beneficial in healthy patients, it may negatively impact airway disease in CRS patients with comorbidities that can also alter the physiological concentration of glucose in the ASL. Healthy ASL glucose concentration, which is about 0.5 mM, arises from tonic leakage of epithelial glucose from the serous fluid and is 10 times lower than the resting serum glucose concentration. CRS patients with an impaired epithelial barrier due to inflammation ,242 and A key distinguishing mechanistic factor between the nasal SCC T2R responses and the nasal ciliated cell T2R responses is the requirement for the taste- and tuft-cell specific Gα-gustducin, the transducin-like Gα involved in taste signaling ,243,244.Bacillus subtilis and Vibrio Cholerae, typically produce a wide variety of D-amino acids for the synthesis of their cell wall peptidoglycans, and these molecules may also serve as quorum-sensing signals [P. aeruginosa [S. aureus [Staphylococcus epidermidis [B. subtilis [P. aeruginosa [S. epidermidis [S. aureus, or in mixed-species systems [P. aeruginosa and S. aureus sensitivity to rifampicin may be increased by D-amino-acids [Besides glucose and artificial sweeteners, some bacterial D-amino acids have also been identified as T1R2/3 agonists in human sinonasal SCCs. Gram-positive and -negative bacteria, such as  signals . While truginosa ,250, S. . aureus ,252, anddermidis , and dissubtilis , P. aeruruginosa , S. epiddermidis , S. aure systems ,257. In no-acids .B. subtilis biofilm formation by interfering with protein synthesis instead of disrupting the pre-formed biofilm [Mycobacterium tuberculosis, but found no such influence of D-amino acids at 1mM in S. aureus, B. subtilis, or S. epidermidis [Among studies that temper or even contradict those described above, one suggests that D-amino acids indirectly inhibit  biofilm . Anotherdermidis . This stdermidis , and thadermidis  or combidermidis  may poteS. aureus and coagulase-negative Staphylococcus cultures isolated from the sinonasal cavities of CRS patients produced D-Leucine and D-Phenylalanine in concentrations sufficient to activate T1R2/3 in SCCs. This activation resulted in a decrease in T2R-mediated response in SCCs and in the overall immune response of the airway epithelium in vitro. One theory is that this repression of immune response may be another “safeguard” mechanism to prevent clearance of commensal Staphylococcus species in vivo. This theory is supported by the apparently crucial role of bacterial D-amino acids in communication between bacteria and host cells [Staphylococcus to escape immune detection in the respiratory tract. For the moment, neither of these two hypotheses has been proven to be the most probable.Bacteria typically produce D-amino acid at high concentration ranges (µM-to-low mM) ,266,267 st cells . HoweverTAS1R genetics in airway disease, including how it alters D-amino acid activation of the T1R SCCs, innate immunity, and CRS outcomes, should therefore also be investigated.Bacterial D-amino acids may have a broader implication in the regulation of human immunity. In a recent preprint, we reported that D-amino acids’ interaction with T1R3 in ciliated cells may reduce ASL glucose, potentially resulting in impeded bacterial growth . AnotherFinally, SCCs appear to be major effectors of CRS inflammation by producing IL-25, an early signal for type 2 airway inflammatory responses ,271. TheThe idea of immune cell receptors surveilling bacteria is not new. The ubiquitous Toll-like receptors (TLRs) and other pattern recognition receptors detect bacterial-specific components such as lipopolysaccharide (TLR4) or flagellin (TLR5) . In lighOne area that is lagging in taste receptor research is specific antagonists. While a recent study has developed promising antagonists for T2R14 , most knS. aureus vs. S. epidermidis) also interact with host T2Rs. It may be that T2Rs contribute to detection of “good” vs. “bad” bacteria. An alternative is that T2Rs could be activated by any bacteria that reach a density high enough to secrete enough bitter metabolites that activate T2Rs. While many diverse compounds can activate these receptors, T2R isoforms expressed in various tissues might create some degree of specificity for certain molecules. All of these questions need to be examined in the future to better understand how T2Rs fit into host–pathogen interactions. Another class of metabolites that should be investigated include various “quorum quenching” molecules [It is likely that more currently unknown bacterial compounds activate T2Rs. An important question is whether only potentially pathogenic bacteria activate T2Rs or if generally non-infectious related bacteria (e.g., olecules ,24 whichAn important remaining question is whether fungi or viruses also activate bitter taste receptors. Like bacteria, fungi produce a host of metabolites, many of which are likely to be bitter. Whether they reach sufficiently high concentrations to activate T2Rs or T1Rs remains to be determined. Given that taste-receptor-expressing tuft cell/SCC abundance in the upper airway is increased with Th2/type 2 immunity and fungal exposure ,272,292,Do T2Rs play any role in viral infection? SCC/tuft cell abundance has been shown to increase in the distal lung after viral infection . HoweverTAS2R genes associated with improved overall survival in head and neck squamous cell carcinoma [TAS2R and TAS1R genes are also associated with survival in many solid tumor types [Pseudomonas AHLs or quinolone with T2R4, T2R14, or T2R38. Several other studies have shown functional expression of T2Rs in cancer and/or genetic associations of TAS2R or TAS1R genes with cancer [The localization of T2R14 and other T2Rs in oral epithelial cells may also have implications for host–microbe interactions in oral cancer. We showed that bitter receptors, including T2R14, are expressed in oral keratinocyte-derived cancer cells, where they activate apoptosis . Moreovearcinoma . TAS2R aor types , suggestor types , such inh cancer ,303. Furh cancer ,305.


MastigodiaptomusA new species of a Neotropical diaptomid copepod is described based on individuals recovered from a small, almost forgotten collection of unique plankton samples from El Junco, a crater lake in San Cristóbal island, Galápagos archipelago. This copepod was regularly reported (1966–2004) as an abundant zooplankter in the lake, but it was not found in subsequent plankton surveys (2007–2018), and its specific identity remained unknown. In 2020, it was declared extinct because of introduced fish predation, rotenone treatment, and other major disturbances. The taxonomic examination of these invaluable specimens allowed us to recognize them as representing an undescribed species of the freshwater diaptomid genus Here, we describe the new species from El Junco crater lake, located in the San Cristóbal island a part of the Galápagos archipelago, collected with plankton nets. The description is based on detailed morphology, based on SEM and light microscopy.MastigodiaptomusMastigodiaptomus, and the only freshwater calanoid in the Galápagos. The intriguing presence of this chiefly Neotropical copepod genus here could be related either to (1) human agency linked to pirate activities, commercial travelling by Spaniard ships, whaling activities, and intense tortoise hunting in San Cristóbal island. In the past, El Junco was the only freshwater source 600 nautical miles around, or (2) zoochory of resistant dormant stages passively transported by more than 65 migrating bird species known to settle in San Cristóbal. These two hypotheses cannot be properly tested at this time, so the explanation of the presence of this copepod will remain as a new open question in the fascinating natural history of the Galápagos.The taxonomic examination of these invaluable specimens allowed us to recognize them as representing an undescribed species of the freshwater diaptomid genus  Notodiaptomus amazonicus and observed that in July 1966, July 1977, and December 1978, there was a disproportionate large number of adults (up to 80% of the sampled population) compared to nauplii larvae and copepodites, presumably resulting from a slow turnover of the population. According to Tucked away in the drawer of a cabinet holding a research collection at Northern Kentucky University (NKU) are vials containing preserved large red copepods from the Galápagos Islands. All the samples are from a single lake, El Junco, in San Cristóbal Island, the only permanent freshwater lake in the Galápagos archipelago. The copepods were collected in separate expeditions between 1966 and 2004, complementing paleoclimatic studies of the archipelago . PlanktoMastigodiaptomus is the most diverse in the northern Neotropical region; it currently includes about 15 nominal species  as the type species. In different taxonomic accounts of the Neotropical freshwater copepods, this nominal species was deemed as the most widespread and diverse diaptomid from the southern Nearctic region to the northern Neotropics  on September 2, 2004, under permission granted by the Galápagos National Park as part of Project PC 08-04. Samples were collected using a small plankton net with a 63 µm mesh size and fixed with Lugol. The specimens examined were deposited in the Collection of Zooplankton (ECO-CHZ) held at El Colegio de la Frontera Sur (ECOSUR), Chetumal, Mexico, where they are available for further examination. A subsample from the same collection with numerous specimens is also deposited in the same collection (ECO-CHZ). The rest of the collections and original samples are at NKU.The specimens were dissected and drawn in a BX51 microscope with a camera lucida attached. All observations were made under normal illumination, Nomarski and phase contrast techniques. Other six specimens were dried with increasing concentrations  of HDMS (hexamethyldisilazane) and covered with gold. Observations of these individuals were made in a JEOL 6010 scanning electron microscope (SEM) in the Chetumal Unit of ECOSUR.All drawings and SEM photographs are included for the description of this species. The lsid registered in ZooBank for this publication is: urn:lsid:zoobank.org:pub:B1999A13-FD8B-4750-988B-5BE4C7167AA9.http://zoobank.org/. The LSID for the new species nomenclatural act is registered in ZooBank lsid as: urn:lsid:zoobank.org:act:91C915F7-E18F-489D-9D06-DBC0E4201C7DThe electronic version of this article in Portable Document Format will represent a published work according to the International Commission on Zoological Nomenclature (ICZN), and hence the new names contained in the electronic version are effectively published under that Code from the electronic edition alone. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank Life Science Identifiers (LSIDs) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix The online version of this work is archived and available from the following digital repositories: PeerJ, PubMed Central and CLOCKSS.urn:lsid:zoobank.org:pub:B1999A13-FD8B-4750-988B-5BE4C7167AA9Material examined. Adult male holotype, specimen undissected, vial with 1 ml of propylene-glycol, plankton sample, El Junco crater lake, San Cristóbal island, Galápagos archipelago , collected September 2, 2004 by M. Steinitz-Kannan (ECO-CH-Z 11820). Allotype, Adult female, undissected, same locality, date and collector, vial with propylene-glycol (ECO-CHZ-11821). Paratypes: One male specimen, dissected, mounted on semi-permanent slide sealed with DePex mounting medium  (ECO-CH-Z-11822), five males in vial with propylene-glycol (ECO-CH-Z-11822). One female dissected, mounted in semi-permanent slide sealed with DePex mounting medium  (ECO-CH-Z-11823), six adult females in vial with propylene-glycol (ECO-CH-Z-11823). One male and one female, gold-coated, mounted on SEM stub(ECO-CH-Z-11824).Diagnosis. Medium-sized Mastigodiaptomus with 24-segmented female antennules, female fourth pediger with large blunt process on dorsal surface. Male geniculate right antennule 22-segmented, antepenultimate segment with long, straight acute process reaching beyond distal margin of succeeding segment 21. Male right antennule middle section with large spinous processes on segments 13 and 14, process on segment 11 longer than that on segment 10. Segment 16 lacking process. Female fifth leg with inner spiniform process of second exopodal segment with spinulate inner margin, outer margin smooth; endopod 2-segmented, reaching halfway of first exopodal segment. Right male fifth leg with long, slender aculeus about half as long as elongate distal claw. Right endopod as long as first exopodal segment.Female  as: 1, 2, 3 , 4-5(1s), 6 , 7 (1s), 8 (2s), 9(1s), 10 (1s), 11 (2s), 12-13 (1s), 14 , 15(1s), 16, 17-18 (1s), 19 , 20-21 (1s), 22(2s), 23 (2s), 24(2s), 25(4s + 1ae) (s + 1ae) , 3B.Antenna with subquadrate coxa armed with single seta. Basis rectangular, carrying 2 subequally long setae on distal inner margin. Endopod 2-segmented, first segment cylindrical, armed with two subequal setae at distal 1/3; second endopod segment bilobed, proximal lobe armed with 9 setae, distal lobe with 6. Exopodal ramus 8-segmented, second expressed segment with pseudosegments; setal formula as: 1, 2, 1, 1, 1, 1,1, 4. ; M. texensis, M. albuquerquensis  con segment , 4H. Onlnsis see , Fig. 5F 2020 in , M. patzuarensis  , and an endemic species of diatom, Frustulia galapagosaxonica, most abundant during high water periods  were a few individuals of the reported . Other sthe lake .Miconia robinsoniana and removal of exotic species from the lake’s basin. . The earliest human activities associated to the Galápagos islands are related to Pre-colonization commerce , so we cannot conclude whether M. galapagoensis was transported by zoochory from adjacent coastal areas or incidentally introduced by early sailors if it existed previously in the continent.According to M. galapagoensis have been found in the archipelago, but all freshwater ecosystems (temporary or permanent) have not been thoroughly studied, particularly for zooplankton composition. So far, we know only the report on rotifers of Acrocalanus sp. and Clausocalanus sp.) from freshwater temporary ponds, not connected with the sea in San Cristóbal island  which are vulnerable despite governmental protective measures. An example was the illegal introduction of tilapia in the recent past, and the harmful method used for its eradication, its effects being documented only in a bachelor thesis (Because of the biological relevance of this archipelago, we consider a priority to start intensive studies of the zooplankton (in a wide sense, and using modern collecting methods, see r thesis  and a shr thesis .