Inflammation is a key phase in the cutaneous wound repair process. The activation of inflammatory cells is critical for preventing infection in contaminated wounds and results in the release of an array of mediators, some of which stimulate the activity of keratinocytes, endothelial cells, and fibroblasts to aid in the repair process. However, there is an abundance of data suggesting that the strength of the inflammatory response early in the healing process correlates directly with the amount of scar tissue that will eventually form. This review will summarize the literature related to inflammation and cutaneous scar formation, highlight recent discoveries, and discuss potential treatment modalities that target inflammation to minimize scarring. Scar tissue is generated from activated fibroblasts, which produce excess levels of irregularly organized collagen. Clinically significant scars can develop from surgical, traumatic, or thermal  injury. Scars essentially function as a quick patch for damaged dermal tissue, but they can be problematic in many ways. Compared to normal skin, scar tissue is weaker in terms of tensile strength and it is also more rigid,6, which adversely affects the biomechanical properties of the skin. The replacement of normal tissue with scar tissue reduces the functional capacity of the skin in that area as well, and this can cause problems such as limiting joint motion and impairing normal tissue growth. Scars can also have significant psychosocial implications and can negatively impact a patient’s quality of life.The repair of wounds in mature skin has been studied extensively. This process is highly complex and interactive, and it is made up of a series of well-defined stages that include inflammation, proliferation, and remodeling/scar formation. However, many of the mediators produced by activated inflammatory cells can stimulate fibroblasts, which drives the production of scar tissue and consequently shapes the final outcome of repair. Several innate immune cells have been linked to scar formation, including neutrophils, mast cells, and macrophages. In addition, a variety of inflammatory mediators have been shown to influence scar formation. This review will summarize what is known about the role of inflammation in scar formation and discuss some potentially useful approaches to reduce scar formation by modulating inflammation.Although inflammation occurs relatively early after injury, it can impact later stages of repair such as scar formation. In the early stages of repair, the primary functions of inflammation are to clean the wound site, clear debris, and prevent infection–13. Furthermore, a wide range of studies have shown that high levels of inflammation are associated with excessive scarring or abnormal scars such as keloids and hypertrophic scars (HTS), whereas inflammation is significantly blunted in wounds that heal without scars [A large number of studies suggest that the level of inflammation in injured skin correlates directly with scar formation. A direct association between the extent of injury (and hence the levels of inflammation) and the amount of scarring that will ultimately result from the wound healing process has been established. For example, larger/deeper wounds or injuries that cause more severe damage are associated with higher levels of inflammation and heal with more scar tissueut scars . EvidencKeloids are abnormal, raised scars that develop after injury. These scars display some similarities with tumors, as they tend to invade the adjacent skin and extend beyond the initial site of injury. There are no widely accepted experimental animal models of keloid disease, so studies on keloid pathogenesis are generally limited to experiments on tissue from human patients. A number of studies have examined inflammation in keloid tissue and the vast majority have indicated that keloids are associated with an increase in pro-inflammatory mediators and inflammatory cells.et al. suggested that a pro-inflammatory niche exists in keloids, based on observations that interleukin (IL)-6 and IL-17 were increased in keloid tissue compared to normal skin. Another group reported an increase in chemokine-like factor 1 and other pro-inflammatory cytokines, such as IL-6, IL-8, and IL-18, in keloid tissue compared to normal skin and normal scars. Jumper et al. performed a site-specific gene expression profiling study and found that keloid tissue was enriched for pro-inflammatory genes and pro-inflammatory signaling pathway members, including IL-1β, IL-8, and IL-17, among others. Interestingly, the data pointed to a possible role for the overlying epidermal cells in keloid lesions in the regulation of inflammation.Several studies have suggested an increase in pro-inflammatory mediator expression in keloids. A study by Zhang et al. suggested that the total number of mast cells and the number of mast cells expressing chymase, a serine protease found primarily in mast cells, are higher in keloid tissue compared to normal skin. An increase in chymase activity in keloids was also observed, and chymase was shown to stimulate collagen production in cultured fibroblasts. Another study found a low number of mast cells expressing tryptase, another mast cell-related serine protease, in keloids compared to tissue from several other organs; however, the sample size was small (n = 3 keloids) and there was no direct analysis of or comparison to normal skin. Several studies have also shown an increase in macrophages in keloids compared to normal skin,20. A study by Shaker et al. showed that both macrophages and mast cells are frequently found in close proximity to fibroblasts in keloid tissue, and another study by Arbi et al. showed a close association between mast cells and fibroblasts in keloid samples by transmission electron microscopy. Although these studies were limited in scope, they do suggest the possibility that direct cell-cell interactions between inflammatory cells and fibroblasts could be important for fibrosis.In addition to pro-inflammatory mediators, several inflammatory cell types are prominent in keloids, particularly mast cells and macrophages. A study by Dong et al. In this study, the number of mast cells and degranulated (activated) mast cells were found to be increased in keloids compared to normal skin and normal scar tissue, as were the number of M1 and M2 macrophages. M1  and M2  macrophages express different biomarkers, and this general classification system is commonly used to delineate different macrophage phenotypes. Interestingly, inflammatory cell enrichment was more closely associated with intralesional and perilesional keloid sites as opposed to extralesional sites.A more comprehensive analysis of inflammatory and immune cells was performed by Bagabir . Two other studies suggested either minimal differences or fewer mast cells in keloids,27. While the reasons for the discrepancies between the studies are not entirely clear, the observations by Bagabir et al. described earlier showed that the number of inflammatory cells varied across different sites within a keloid lesion. Also, in some of the studies, granule markers were the sole staining method used, which could underestimate the number of mast cells if they have degranulated. Therefore, the specific locations at which the cells were quantified, in addition to differences in staining methods, sample sizes, and patient populations, could contribute to the inconsistent results.While most published studies indicate an increase in mast cells and macrophages in keloid scars, one study comparing human keloids and equine exuberant granulation tissue (a fibrotic condition suggested to have some similarities to human keloids) reported minimal mast cells and macrophages in both fibrotic conditionsHTS, which are raised red scars, also fall into the category of abnormal scars. Unlike keloids, HTS are confined to the borders of the original wound. A wide range of studies in both small and large animal models as well as human clinical samples have examined inflammation in hypertrophic scarring.. In this model, the scars were shown to have a high number of mast cells, similar to human HTS. The HTS-like lesions were also shown to have higher numbers of macrophages compared to control wounds with no mechanical loading. Several other studies have been published using models of HTS formation in which human skin is grafted onto nude mice. In these studies, higher numbers of mast cells and macrophages,31 were observed in the HTS-like lesions compared to control tissue. Upon further examination of macrophage subtypes, M2 macrophages were found to be elevated, and higher levels of pro-inflammatory cytokines were noted in HTS-like samples. An increase in both mast cells and macrophages has also been reported in a mouse model of hypertrophic scar contracture.Several rodent models of HTS have been described. One such model uses the application of a mechanical loading device to apply tension to wounds, inducing a HTS-like phenotype reminiscent of human HTSet al. examined mast cells in human HTS samples and samples from a large animal model of HTS, the red Duroc pig. The authors found an increase in mast cells in HTS from both humans and red Duroc pigs compared to the corresponding normal skin controls.Large animal models, such as pigs, are considered by many to be an ideal wound healing model based on similarities in skin anatomy between pig and human. A study by Harunari et al. reported higher numbers of mast cells in HTS compared to granulation tissue or mature scar tissue samples using toluidine blue, a metachromatic stain that binds mast cell granules. A study by Beer et al. did not see differences in tryptase-positive mast cells when comparing among keloids, HTS, and surgical scars; however, normal skin samples were not included for comparison. Another study by Niessen et al. found no significant differences in tryptase-positive mast cells in HTS compared to normal scars, although they did note a trend toward increased subepidermal mast cells in HTS. There are several possible explanations for the contradictory results between the studies. The use of different techniques to identify mast cells could have played a role, as toluidine blue should indiscriminately stain all mast cell subtypes (including chymase- and tryptase-positive mast cells), whereas tryptase staining may not easily identify mast cells if they predominately express chymase. In addition, the age of the scars examined may play a role. The study by Beer et al. showed a direct correlation between mast cell density and scar age in surgical scar samples and the study by Niessen et al. noted an overall increase in mast cells between 3 and 12 month scar samples, so standardization of scar age may be needed to properly compare studies from different investigators.In human HTS, there are conflicting results regarding whether inflammation is enhanced or reduced in HTS. Early studies by Kischer . In another study looking at scars from cardiothoracic surgery patients, an increase in macrophages was observed in normal scars compared to HTS at earlier time points, but total macrophage and M2 macrophage numbers were increased in HTS at later time points and remained elevated for a longer period of time.There are only a few reports examining macrophages in human HTS. In one study comparing normal scars and HTS from breast surgeries, no differences were found in macrophages between scar types. The authors reported reduced expression of inflammatory genes  in HTS, but the downregulated genes contained both pro- and anti-inflammatory genes. Similarly, another prospective study compared various parameters of inflammation at a very early time point (3 h post-injury) in patients that healed with normal scarring or HTS. The authors reported reduced protein levels of IL-6, IL-8, and CCL2 in wounds from HTS patients compared to normal scar patients and suggested that reduced inflammation is associated with HTS formation. However, increases in P-selectin mRNA were found in HTS compared to normal scar samples. In addition, TNF-α, CXCL4, VCAM, and TLR4 mRNA were significantly increased after surgery only in HTS and there were more M2 macrophages in pre-operative HTS samples.The data on pro-inflammatory cytokine expression in human HTS also appears to be somewhat mixed. One study compared inflammatory gene expression in a small prospective study comparing patients that developed normal scars or HTSTaken together, the data suggest that more detailed analysis of inflammatory cells and inflammatory mediators is needed to definitively show whether inflammation is associated with hypertrophic scarring in humans.–41. One of the key differences between scarless and fibrotic fetal wound healing is the level of inflammation. Many studies have shown that there are few, if any, of the traditional features of inflammation in scarless fetal wounds, but fibrotic fetal wounds that occur later in gestation heal with a strong inflammatory response. In addition, artificially inducing inflammation in fetal wounds that would normally heal scarlessly causes them to heal with a scar.It is well established that developing fetal skin is capable of healing wounds in a scarless, regenerative manner at certain gestational stages. Fetal skin heals scarlessly at early stages of development (until about the third trimester), but as the skin matures at later stages of development it heals through a fibrotic repair process that produces a permanent scar2), cytokines –47, and alarmins (HMGB-1) have been shown to be lower while anti-inflammatory mediators (IL-10) has been shown to be higher in fetal skin or scarless wounds. Fetal fibroblasts produce less IL-6 and IL-8 compared to adult fibroblasts,46 and microarray studies showed that expression of inflammatory genes is reduced in fibroblasts from less developed fetal skin (scarless) compared to more developed fetal skin (fibrotic).Several studies have been performed to identify specific differences in the inflammatory response between scarless and fibrotic wounds. Levels of pro-inflammatory mediators, such as lipids  has fewer macrophages, mast cells, dendritic cells, and other immune cell types compared to adult skin. Because there was an adequate number of immune cells in the lymph nodes, the authors speculated that the reduced immune cell numbers present in the skin was due to a deficiency in homing signals. Indeed, they found reduced levels of chemokines such as CCL17, CCL21, and CCL27 in fetal skin.Studies examining human fetal skin also support the idea that less developed skin has a suppressed inflammatory response. An early study by Rowlatt described a lack of an acute inflammatory reaction and granulation tissue formation at the site of limb amputations caused by amniotic constriction bands in a 20 week human fetus. There is also evidence that oral mucosal wounds have a blunted inflammatory response compared to other tissues that heal with scarring. In a mouse model, Szpaderska et al. showed fewer macrophages, less myeloperoxidase (a marker of neutrophil presence), and lower pro-inflammatory cytokine production in oral mucosal wounds (scarless) compared to cutaneous wounds (scar-forming). Similarly, in a porcine model, Mak et al. compared oral and skin wounds in red Duroc pigs and found reduced macrophage and mast cell numbers in oral wounds, which also displayed accelerated resolution of inflammation. In healthy human oral and skin tissue (uninjured), fewer neutrophils and macrophages have been reported. Global transcriptome analysis by multiple groups suggests that several pro-inflammatory genes and regulatory pathways are suppressed or are less persistent in oral mucosal wounds compared to skin wounds,67.Besides fetal skin, scarless healing has also been described in mucosal tissues, such as the oral mucosaAcomys). Acomys was shown to completely regenerate and heal without scarring in response to large dorsal skin wounds. Follow up studies compared transcription profiles of scar-forming wounds from standard laboratory mice (Mus) and regenerative wounds from Acomys, and showed Acomys wounds had a diminished cytokine/chemokine response. Acomys has also been reported to be neutropenic (reduced blood neutrophils) and have less pronounced macrophage recruitment to wounds compared to Mus strains. These results fit the general theme observed with scarless oral mucosal and fetal wounds, which have a dampened inflammatory response compared to wounds that heal with scars.Scarless healing has also been documented in a unique mouse species, the African spiny mouse  at early time points post-injury, while reducing scar size and normalizing collagen architecture/collagen fibril density at later time points. Another study showed that oral administration of the mast cell stabilizer ketotifen reduced wound contraction and collagen deposition, causing thinner, less dense collagen fibrils to be produced in a red Duroc pig model.Drugs that act as mast cell stabilizers, which prevent mast cell degranulation, have been used in animal models of wound healing to study the importance of mast cells in scar formation. By preventing mast cell degranulation, these drugs inhibit the release of pre-stored mediators present within the granules. Disodium cromoglycate  has been shown to reduce collagen content in a rat model when injected directly into woundsW/W-v mice are mutant mice that lack mast cells due to functional mutations in the tyrosine kinase receptor c-kit, which binds an important growth factor for mast cells (stem cell factor). Younan et al. used these mice in a study looking at the effects of microdeformation in wounds using a negative pressure wound therapy device. They showed that microdeformation induced higher levels of mast cell degranulation, which correlated with an increase in granulation tissue thickness and collagen deposition. These changes were normalized in KitW/W-v mice, suggesting that the increases in granulation tissue and collagen production from the microdeformation device were mast cell-dependent. KitW/W-v mice were also shown to heal with smaller scars in late-gestation fetal skin wounds compared to control mice and less fibrosis at the wound edge in adult scald wounds, supporting the idea that mast cells promote scar formation and fibrosis. In contrast to these studies, several other mast cell-deficient mouse strains have been shown to heal with similar levels of scar tissue and collagen deposition compared to control mice that have normal mast cell numbers–78. Many of the published studies discussed above used different wound models and different mast cell-deficient strains, which could partially explain the variable results. In addition, most mast cell-deficient strains also have defects in one or more other immune cell types and non-specifically deplete the entire mast cell population, so it will be important to revisit these ideas once we understand more about mast cell heterogeneity and have more precise mouse models to specifically target mast cells and possibly different functional mast cell subtypes.The role of mast cells in scar formation has also been examined in mast cell-deficient mouse strains , and the results seem to differ depending on the mouse strain and wound model used. Kit. PU.1 null mice, which lack macrophages and functional neutrophils, were shown to heal quickly and with minimal scarring. However, the relative importance of macrophages versus neutrophils is unclear since both cell types are absent in wounds from PU.1 null mice. While some studies suggest that the early neutrophil response may be important for scar formation and the presence of neutrophil extracellular traps have been reported in skin scars and other fibrotic conditions, there do not appear to be published studies examining scar formation using animal models in which neutrophils have been specifically depleted.Several mutant mouse strains have been used to examine the importance of neutrophils and macrophages in wound-induced scar formation. One of the first studies of this kind explored wound healing in mice lacking the transcription factor PU.1et al. showed reduced collagen density in wounds from macrophage-depleted mice and Lucas et al. showed that depletion of macrophages at early stages of wound healing reduced the amount of granulation tissue and the size of scars that formed. Several studies have also used clodronate liposomes to deplete macrophages. One study showed that macrophage depletion reduced collagen expression and deposition in wounds and another showed that macrophage depletion reduced scar formation in a xenograft model of HTS. While it is generally accepted that macrophages release mediators that can stimulate collagen production by fibroblasts, several recent studies have suggested the possibility of novel mechanisms. For example, macrophages were shown to support adipocyte-derived myofibroblasts through insulin-like growth factor and platelet-derived growth factor C. A recent report also highlighted the plasticity of myeloid cells, which may be converted directly to collagen-producing fibroblasts in healing wounds. More work will have to be done to understand exactly how macrophages contribute to scar formation.More specific studies examining the role of macrophages in collagen deposition and scar formation have been performed using several approaches. Studies from two groups have used slightly different genetically modified mouse strains in combination with diphtheria toxin to deplete macrophages. Mirza Aside from specific inflammatory cell types, a wide range of inflammatory mediators, including both pro- and anti-inflammatory mediators, have been shown to play a functional role in cutaneous scar formation.,47, pro-inflammatory lipids like PGE2, and alarmins such as HMGB-1. Some of these same mediators have also been studied in adult wound healing models. For example, HMGB-1 has been linked to scar formation and blocking PGE2 production with drugs that inhibit cyclooxygenase-2 activity has been shown to reduce scar formation in adult incisional wound models,90. Other pro-inflammatory cytokines that have been linked to cutaneous scar formation and/or collagen production in adult scar/fibrosis models include IL-17 and monocyte chemoattractant protein-1,93. Additionally, osteopontin (OPN), which has pro-inflammatory cytokine-like properties and is associated with wound-induced inflammation, has been linked to scar formation. Studies in a mouse model showed that osteopontin knockdown in the skin resulted in less inflammation  as well as reduced scar formation compared to control wounds.Both fetal and adult wound healing studies in animal models have implicated specific pro-inflammatory mediators in the stimulation of scar formation. Fetal wound healing models have been useful for identifying inflammatory mediators with fibrogenic potential since a specific mediator can be injected into fetal wounds to determine whether it can convert the scarless healing process into a fibrotic repair process. With this approach, the formation of a scar in a wound that would otherwise heal scarlessly can be used as a readout of pro-fibrotic activity. A number of pro-inflammatory mediators have been shown to promote scar formation in fetal wounds using this system, including cytokines such as IL-6 and IL-33. Furthermore, scar formation is amplified in IL-10 knockout mice and scar formation is reduced when IL-10 levels are artificially enhanced,49,97–99. In addition to IL-10 having anti-inflammatory effects, studies have suggested that IL-10 signaling enhances the production of hyaluronic acid–103, an extracellular matrix molecule associated with scarless healing and regeneration–110. Other anti-inflammatory and pro-resolution mediators have also been linked to scar formation. Mice lacking the chemokine receptor CXCR3, which has been implicated in wound resolution, heal with abnormal scarring, and the pro-resolution mediator chemerin15 has been shown to reduce inflammation and scar formation.In contrast to pro-inflammatory mediators, anti-inflammatory mediators have been shown to limit scar formation in fetal and adult wound healing models. The most well-documented example of this is the anti-inflammatory cytokine IL-10. Studies have shown that IL-10 levels are higher in scarless fetal wounds compared to scar-forming woundsGiven the evidence supporting the idea that inflammation promotes scar formation, it seems logical that targeting inflammation might be a viable therapeutic strategy for restricting scar tissue production and enhancing the cosmetic and functional clinical outcomes resulting from skin injury. There are data supporting various anti-inflammatory approaches that could be effective for minimizing the appearance of scars and several other proposed scar therapies may reduce scarring in part by altering inflammation. These will be discussed below.. The use of steroids for scar therapy has been reviewed previously–116.Steroids and nonsteroidal anti-inflammatory drugs (NSAIDs) are traditional anti-inflammatory drugs that may be beneficial for preventing or treating scars. Corticosteroids are anti-inflammatory drugs commonly used in clinical settings to treat raised scars such as HTS and keloids. Steroid therapy can be used in an attempt to induce scar regression, but may be more effective when used to prevent recurrence after scar revision surgery2, by inhibiting the function of one or more cyclooxygenase enzymes. These drugs are commonly used to treat pain, fever, and inflammation. Some of these drugs have been suggested to reduce collagen deposition and scar formation in animal models of wound healing. In an incisional murine wound model, topical application of celecoxib resulted in decreased PGE2 production, inhibition of neutrophil recruitment, and significantly reduced scar size. In a rabbit ear model of HTS formation, celecoxib treatment was shown to reduce scarring (measured by scar elevation index score), and a combination of celecoxib and the angiotensin-converting enzyme inhibitor captopril reduced inflammation and scar height. Studies have also suggested that dressings incorporated with anti-inflammatory drugs, such as electrospun fibrous scaffolds loaded with ibuprofen and emulgel dressings containing the anti-inflammatory drug acetylsalicylic acid along with stratifin , may lead to reduced scarring.NSAIDs are another class of anti-inflammatory drugs that block the production of inflammatory lipid mediators, such as PGE. High TLR4 expression has been documented in human HTS tissue and HTS fibroblasts. TLR4 has also been suggested to play a role in HTS development in a mouse model, where treatment with the TLR4 inhibitor TAK-242 (restorvid) was found to reduce scar formation. The data were very limited in this study, with only 3 mice per group and no quantitative scar data; however, TLR4 has been linked to fibrosis previously and TAK-242 has been shown to reduce fibrosis in several organs, including the skin, in other animal studies–127. Together, these studies suggest TLR4 inhibitors may be a promising strategy to minimize scarring. In addition, the fact that this drug has been used topically to reduce ultraviolet light-induced inflammation and skin carcinogenesis,129 and has been used in clinical trials for other diseases, suggests that TLR4 inhibitors may be a worthwhile pursuit.Drugs that target innate immune receptors have the potential to be used to limit scar formation based on their anti-inflammatory mechanism of action. TLR4 inhibitors are one example. TLR4 is a pattern recognition receptor that binds to many different pathogen-associated molecular patterns as well as damage-associated molecular patterns  that stimulate inflammation in response to microbes or tissue damage, respectively,132. An increase in SDF-1 is believed to stimulate recruitment of CXCR4-positive leukocytes, and possibly collagen-producing fibrocytes, from the circulation, thereby promoting HTS formation,132. Similar results have been reported in keloid tissue, with an increase in SDF-1 expression and CXCR4-positive cells in keloids compared to normal tissue. In a small animal HTS model, a CXCR4 antagonist was found to reduce the number of macrophages and myofibroblasts, inhibit contraction, and reduce scar formation. Although more work is needed, the results thus far suggest potential for CXCR4 antagonists in preventing scar tissue deposition.Another potential target is the chemokine receptor CXCR4, which binds to stromal-derived factor-1 (SDF-1), also known as CXCL12. Upregulation of SDF-1/CXCR4 signaling has been reported in human burn patients and in HTS tissue, as well as fibroblast contraction,136. Pirfenidone has also been shown to reduce proliferation and inhibit epithelial-mesenchymal transition in keloid keratinocytes. In wound healing studies, pirfenidone has been shown to reduce pro-inflammatory cytokine production, neutrophil infiltration, and collagen synthesis,139, and in a clinical trial topical application of an 8% pirfenidone gel induced scar regression to a greater degree than control pressure therapy in burn-induced HTS in pediatric patients.Pirfenidone is an anti-fibrotic drug with anti-inflammatory properties used to treat idiopathic pulmonary fibrosis. Although the ability of pirfenidone to treat or prevent skin scarring has not been thoroughly investigated, several studies suggest that it may be a promising option. Multiple studies have shown that pirfenidone can inhibit the pro-fibrotic behavior of cultured dermal fibroblasts. For example, pirfenidone can reduce TGF-β-induced fibroblast proliferation, migration, collagen expression, and myofibroblast formation–144. More recently, the potential for EGCG to inhibit inflammation and scar formation in skin wounds has been described. EGCG has been shown to inhibit mast cell-stimulated collagen protein expression by keloid fibroblasts, likely through alterations in PI3K/Akt signaling. EGCG also inhibited proliferation, migration, and collagen expression in keloid fibroblasts via STAT3 inhibition. In a study using a model in which human keloid fibroblasts were injected into nude mice, EGCG treatment reduced keloid nodule formation and inhibited collagen production. Another study tested the effects of EGCG in long-term keloid organ cultures and showed that EGCG reduced mast cell numbers in the keloid tissue and reduced keloid volume. Recently, a clinical trial examining the effects of a topical formulation of EGCG in human skin wounds showed that EGCG treatment reduced mast cell numbers and improved scar outcomes, as indicated by a reduction in scar thickness and increases in hydration and elasticity. Together, the data suggest that EGCG could be a promising therapeutic to prevent excessive scarring.Epigallocatechin-3-gallate (EGCG) is a green tea polyphenol known to have antioxidant, anti-inflammatory, and anti-tumor effects. The ability of EGCG to be photoprotective and inhibit cutaneous inflammation in response to ultraviolet light-induced skin damage is well documented. Additionally, fibromodulin levels increase during healing in scarless fetal wounds, which have minimal inflammation, but remain low in scar-forming wounds which display a typical inflammatory response. Lower fibromodulin levels have been reported in HTS from human subjects and animal models compared to normal tissue,151, and mice lacking fibromodulin heal with more inflammation and more scar formation,154. Increasing fibromodulin levels via adenoviral overexpression or treating with recombinant fibromodulin has been shown to reduce scar formation in rabbit, mouse, and red Duroc pig wounds–156. Based on these studies, a fibromodulin-based peptide has been developed and is currently being tested in clinical trials.Fibromodulin is a member of the small leucine-rich proteoglycan family that has been shown to have an inverse relationship with scar formation. Fibromodulin levels are initially high in fetal skin at stages associated with scarless healing, then levels decrease during development as the skin starts to heal with a scar–160. Additionally, occlusive dressings, which maintain hydration, reduce both inflammation and scarring. Occlusion reduces the production pro-inflammatory cytokines and lipids by epidermal keratinocytes, the release of pro-inflammatory alarmin molecules such as S100A8, S100A9, and S100A12, and the infiltration of inflammatory cells,162–165. It is likely, then, that maintaining hydration mitigates scar formation in part by diminishing inflammation.Studies have shown that maintaining hydration and allowing healing to occur in a moist environment can be beneficial for healing and reducing scar formation. The underlying mechanisms appear to be related to reduced inflammation. Saline-filled polyurethane or vinyl chambers used to maintain a moist healing environment caused wounds to heal with less inflammation and less scarring compared to dry, air-exposed wounds,166. Mechanically-loaded wounds have also been shown to have a stronger inflammatory response,29,93. In addition, it has been suggested that higher levels of mechanical strain in keloid tissue is associated with inflammation and may contribute to keloid progression. Focal adhesion kinase (FAK) signaling, which controls mechanosignaling in fibroblasts, has been suggested to mediate the enhanced inflammatory reaction associated with mechanical strain,167. Mechanosensing has also been shown in recent studies to regulate inflammatory cell migration using sophisticated in vitro approaches. Here, the authors demonstrated that deformations in collagen matrices caused by contractile activity of fibroblasts provides a strong signal for macrophage migration.Fibroblast behavior is known to be influenced by mechanical signals, and wounds that heal under tension typically heal with more scar tissue. Data from animal models have illustrated this concept, as devices which increase mechanical loading on a wound increase scar formation,169,170. Microarray studies have shown that this device reduces the transcription of genes related to inflammatory pathways. Another strategy to reduce scar formation by affecting mechanotransduction is to inhibit FAK signaling with a small molecule inhibitor. Several small animal studies have suggested that FAK inhibitors can reduce scarring,172, and treatment with FAK inhibitors and genetic ablation of FAK in fibroblasts have been reported to reduce inflammatory mediator production and inflammatory cell recruitment. Collectively, the data suggest that altering mechanical signaling pathways may reduce scar formation at least in part by influencing inflammation.Several approaches have been tested to target mechanosignaling as a way to prevent or reduce scarring. A stress-shielding device, which reduces the tension on a healing wound, has been shown to improve scarring in large animal pre-clinical models as well as human clinical trialsThere is a large body of evidence suggesting that the magnitude of the inflammatory response influences the amount of scar tissue that will result from the healing process . This liDespite the large number of studies on inflammation and scar formation, more research is needed to fully understand this relationship. Conflicting data from some studies demonstrates the complexity of the relationship between inflammation and scar formation and highlights the lack of standardized approaches for studying this relationship experimentally. In particular, variability in experimental models can make it difficult to draw broad conclusions; these models include the use of human tissue, large animal models , and small animal models . More precise characterization of inflammation that includes an expanded view of different inflammatory cell types as well as the specific subtypes of each cell and how changes in these cells over time affect scar formation are needed, especially in human specimens. In addition, further investigation is needed to determine how beneficial various anti-inflammatory approaches could be for minimizing scar formation in human skin.


The extracellular matrix (ECM) is a complex network of secreted proteins which provides support for tissues and organs. Additionally, the ECM controls a plethora of cell functions, including cell polarity, migration, proliferation, and oncogenic transformation. One of the hallmarks of cancer is altered cell metabolism, which is currently being exploited to develop anti-cancer therapies. Several pieces of evidence indicate that the tumor microenvironment and the ECM impinge on tumor cell metabolism. Therefore, it is essential to understand the contribution of the complex 3D microenvironment in controlling metabolic plasticity and responsiveness to therapies targeting cell metabolism. In this mini-review, we will describe how the tumor microenvironment and cancer-associated fibroblasts dictate cancer cell metabolism, resulting in increased tumor progression. Moreover, we will define the cross-talk between nutrient signaling and the trafficking of the ECM receptors of the integrin family. Finally, we will present recent data highlighting the contribution of nutrient scavenging from the microenvironment to support cancer cells growth under nutrient starvation conditions. Cancer-associated fibroblasts (CAFs) are a heterogenous and plastic population of activated fibroblasts, which represent a significant proportion of the tumor microenvironment. For instance, CAFs can account up to 70 and 90% of breast and pancreatic cancer tumor mass, respectively , 2. The Cells interact with the ECM through plasma membrane receptors. Integrins are transmembrane receptors that regulate cell adhesion, migration, and mechanotransduction through mediating cell-ECM interaction , 5. InteIn cancer cells, the activation of oncogenic signaling has a profound effect on cell metabolism. Indeed, aberrant activation of phosphatidyl inositol 3 kinase (PI3K)/AKT and Ras signaling pathways facilitates constant glucose uptake through GLUT1 receptor , 15. In In this mini-review, we will highlight how CAFs control cancer cell metabolism, through metabolite secretion and the generation of a stiffer microenvironment. We will then summarize the cross-talk between integrin trafficking, metabolism and nutrient signaling and we will describe the different mechanisms through which cancer cells can exploit unconventional nutrient sources.The activation of fibroblasts to CAFs is coupled with a metabolic shift to glycolysis, increased catabolic activity and autophagy . As a reIn prostate cancer, CAFs promote the so-called reverse Warburg effect, whereby lactate secretion and mitochondria transfer from CAFs to cancer cells (CCs) lead to an increase in mitochondrial activity and oxidative phosphorylation (OXPHOS) in CCs . This prin vivo in an orthotopic mouse model of breast cancer, where ECM stiffness is coupled with increased glycolysis, glutamine metabolism and aspartate production. Importantly, a reduction in intratumoral levels of aspartate and glutamine leads to a decrease in cell proliferation -bound α5β1, resulting in tensin and Arf4-dependent endocytosis and lysosomal delivery of FN-bound α5β1. This internalization pathway leads to mTORC1 lysosomal recruitment and activation . Mimickiecretion . AltogetAMP-activated protein kinase (AMPK) is a serine/threonine kinase that also works as a sensor for the availability of nutrients. Lack of energy and cell exposure to certain levels of stress activate AMPK, which inhibits anabolic pathways and induces catabolic pathways to provide more energy or source of nutrition for the cells . It has In addition to signaling pathways that directly deal with nutrient availability around the cells, a link between integrin mechanosensing and cell metabolism has also been proposed. CD98hc is an integrin co-receptor and amino acid transporter sensing mechanical forces and causing cell stiffening through integrin and RhoA activation. It has been demonstrated that there is a cross-talk between mechanosensing interruption and sphingolipid synthesis in fibroblasts bearing C330S mutation in CD98hc. Sphingolipids are essential membrane components that can regulate transmembrane protein dynamics. Loss of CD98hc reduces sphingolipid availability, leading to defects in movement, recruitment and activation of regulatory proteins upstream of RhoA . Therefoin vitro studies showing that cancer cells can use albumin as an alternative source of nutrients, hypoalbuminemia was also seen in some cancer patients (in vivo study directly showed that PDAC cells inside the tumor are able to internalize albumin through macropinocytosis and use albumin derived amino acids for further metabolic pathways, while adjacent normal cells do not have this ability (Even though blood pressure inside the tumors is low due to high interstitial pressure, lymphatic deficiency and leaky blood vessels increase the accessibility of cancer cells to the blood serum or its main protein, albumin , 38. Raspatients . An in v ability . In addi ability . Under g ability . Invasiv ability .Since cancer cells could face different nutrient conditions in various niches during their development, further work is needed to elucidate how ECP and ECM could affect nutrient availability and how Ras and PI3K pathways would interact and affect each other in response to different nutrient conditions.Cancer cells display an elevated metabolic plasticity, allowing them to adapt to different environments and nutrient levels. The TME, in particular CAFs and cell-ECM interaction, are key in controlling this metabolic switch. CAFs secrete several metabolites, including lactate, pyruvate and aspartate, which have been shown to support the growth of different cancer cell types . MoreoveElevated rates of tumor growth and limited blood supply result in a nutrient-deprived TME. These pushes cancer cells to adopt different strategies to obtain metabolic fuels. These include the internalization of ECP, ECM and cell debris. Despite all these processes have been observed, the cross-talk between different nutrient scavenging strategies and how cells can switch between them have not been fully addressed yet. Importantly, it is not known how changes in the TME, including immune cell infiltration and ECM composition and structure, affect the ability of cancer cells to grow under nutrient deprived conditions.Altogether, understanding how cancer cells can thrive within the challenging TME will lead to the identification of cancer vulnerabilities. These could then be exploited for the development of novel strategies for targeting unresponsive tumors.MN and ER wrote this manuscript and generated the figures.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Lumbar spondylolysis is a unilateral or bilateral defect of the pars interarticularis, an isthmus of bone connecting the superior and inferior facet surfaces in the lumbar spine at a given level. Spondylolysis is common in young athletes participating in sports, particularly those requiring repetitive hyperextension movements. The majority of young athletes are able to return to full sport participation following accurate diagnosis and conservative management, including a structured treatment program. Surgical intervention for isolated pars injuries is seldom necessary. A progressive physical therapy (PT) program is an important component of recovery after sustaining an acute pars fracture. However, there is a paucity of literature detailing PT programs specific to spondylolysis. Here, we provide an overview of the epidemiology, natural history, radiographic evaluation, and management of pars fractures in young athletes. In addition, a detailed description of a physiotherapy program for this population that was developed at a spine center within an academic medical center is provided. Spondylolysis is a unilateral or bilateral defect of the pars interarticularis, an isthmus of bone connecting the superior and inferior facet surfaces in the spine at a given level . The parThere are congenital factors such as spina bifida occulta and exaggerated lumbar lordosis that may predispose individuals to pars fractures . In addiThe incidence of lumbar spondylolysis in the general population is 3–10% . All posA review of the natural history of lumbar spondylolysis by the Scoliosis Research Society's Evidence-Based Medicine Committee (SRS EBMC) found that unilateral pars fractures typically heal normally, especially among acute fractures . HoweverIn the short-term following injury, typically defined as six weeks, the majority of patients with spondylolysis will symptomatically improve, and the majority of athletes return to usual sporting activity . One metThe definitive diagnosis of spondylolysis cannot be made with physical examination alone and, therefore, requires imaging for diagnosis. Various studies have evaluated one modality in comparison to a control; however, there is no absolute gold standard for radiographic diagnosis . TypicalAdvanced imaging modalities can be more sensitive than plain film x-rays in the diagnosis of spondylolysis. In comparing MRI with CT, where CT is used as the gold standard for evaluation, the sensitivity of MRI was 83% . Two stuIn analyzing the appropriate diagnostic imaging algorithm, various sequences are reviewed in the literature , 18. TheIn terms of cost of imaging evaluation, a 2013 study evaluated two-view and four-view plain films to CT, bone scan, and MRI. Costs grow multiplicatively from plain film imaging. Two-view and four-view plain films were estimated to cost $350 and $500, respectively; more advanced imaging costs significantly more. Bone scan ($1650), CT ($2000), and MRI ($2900) were significantly more expensive. One can assumes these numbers are higher when accounting for inflation and rising healthcare costs .Our preferred algorithm is as follows: after physical examination, two-view plain films are obtained, and conservative management with activity restriction is recommended. Our advanced imaging modality of choice is MRI in an effort to reduce pediatric radiation exposure. We reserve advanced imaging for longitudinal follow-up in patients that are refractory to conservative treatment.The vast majority of patients with stress fractures of the lumbar pars interarticularis can be managed successfully without surgery. Kurd et al. retrospectively reviewed the medical records of 436 juvenile and adolescent patients with symptomatic spondylolysis confirmed by SPECT or CT . All patIn the small percentage of young patients who fail conservative treatments, direct surgical repair of the spondylolysis has been shown to be highly effective. Reports on direct surgical repair of spondylolysis focus on patients younger than 30 years of age with recommended age cutoffs for improved surgical outcomes stated as 20 or 25 years –25. CritIn 1968, Kimura described bone grafting without internal fixation for the treatment of spondylolytic defects . In the PT participation after the diagnosis of spondylolysis in young athletes is an important component of recovery in order to re-establish strength, provide education, and reintroduce patients back to sports activity. In this population, ample evidence exists to support the development of core-strengthening exercises, specifically activating and isolating the transverse abdominis (TA), internal oblique (IO), and multifidi to structurally stabilize the lumbar segments –32. ThesConflicting recommendations exist relating to the use of external bracing in the setting of spondylolysis, including timing of bracing after diagnosis. However, specific to the diagnosis of spondylolysis, there is good evidence for conservative management, including the restriction of activity/sport combined with PT and implementation of external bracing only if symptoms persist , 3, 33. Understanding of the physiological healing process, timing of treatment intervention, appropriate progression, and graduated application of loads to the healing structure are essential for successful outcomes in any therapeutic intervention. When developing a treatment plan for a young athlete, the physical therapist should also consider other factors related to this age group including physical and emotional maturity  and social factors . In the following portion of the paper, we will outline our recommendations for therapy including evaluation considerations, specific exercises, and exercise progression.A thorough subjective history is an essential component of the assessment. In most states, a parent or legal guardian must provide verbal and/or written consent to allow for the treatment of a minor. They can also be a valuable source of information to fully understand the patient's medical and surgical history, psychosocial factors, previous activity, and current functional level. Psychosocial factors can impact rehabilitation outcomes, and therapists should assess patient's beliefs surrounding pain, maladaptive behaviors (avoidance or lack of fear), cultural factors, and lifestyle choices (sleeping and eating habits) . AthleteWhen caring for athletic patients, we recommend documenting a detailed description of the requirements of the individual's sport including the following: type of activity, hours in practice, level of competition, conditioning routine and intensity, and additional training related to performance. Identifying whether the athlete is involved in sports seasonally or year-round is another crucial factor to consider. Most importantly, gathering specifics on provocative movements or activities performed during sports participation will prove valuable when developing a plan for treatment intervention and goal-setting.Outcome measures utilized in the younger population with low back pain include both pain and functional scales. The visual analog pain scale (VAS) and Wong-Baker FACES are both reliable measures of subjective pain in the pediatric population and are simple tools to utilize during exercise sessions . The linIt is important for the physical examination to address all aspects of patient presentation. Adolescents and young adults with the diagnosis of spondylolysis are likely to have a variety of symptoms specific to the bony injury, secondary or compensatory symptoms, postural abnormalities, and movement dysfunction. They may develop habitual movements and postures as a result of functional activity or sport demands that may contribute to LBP. Based on the work of Sahrmann et al., “the conceptual basis of movement system impairment syndromes is that alignment in a nonideal position and repeated movements in a specific direction are thought to be associated with several musculoskeletal conditions”. We belTightness of the proximal hip musculature , increased lumbar muscle tone, painful spine active range of motion (AROM), and inhibition of the lumbopelvic girdle are all frequently recognized symptoms in patients diagnosed with spondylolysis. Recovery is dynamic by nature and oftentimes occurs at an accelerated pace in the young athlete. Frequent reassessment of objective measures, provocative maneuvers, and the patient's subjective complaints  throughout care is essential to capture change and modify treatments appropriately.Observation: posture, spinal alignment, AROM, quadrant motion, and presence of directional preferenceGait: walking and running (if indicated)Palpation: lumbar muscle tenderness and tone, bony landmarks, and step-off deformity of the spineMovement analysis: provocative movements during sport, function, play, and activity ; presence of aberrant movementsLower extremity flexibility: hamstring length and hip flexor tightnessManual muscle testing: gluteal musculature, hamstring, abdominal/trunk strength, and lumbar extensor endurance (if tolerable)Neurological evaluation: reflexes, dermatomal sensory loss, and myotomal strength loss Motor control: ability to contract transverse abdominus and internal obliqueAssessment and documentation of the following are recommended in the physical examination:Poor clinical utility has been found for spondylolysis special testing, for example, the one-legged hyperextension test , 42. TheIn the acute phase, the main focus areas of intervention include (1) pain management and (2) patient education. Resolution of pain and normalized ROM are the initial goals of treatment and are utilized as a benchmark throughout the rehabilitation process to allow for progression of activity . ActivitEliminating specific movements, actions, or sport activities that provoke pain are the initial steps of treatment strategy . Ensure Demonstrate provocative maneuvers  in a way that is practical and understandable for the patient. Practice modification strategies that allow the patient to experience movement without symptom provocation in-session.Initiate an exercise program and ensure that the patient understands the reasoning behind each exercise.Revisit VAS/FACES throughout the sessions, allowing the patient to appropriately identify aggravating factors and pain management strategies without causing fear or anxiety. If the patient is highly pain-focused and excessively cautious, emphasis on pain level should be minimized.Patient education should include the following:Independent of time after diagnosis or previous interventions , we recommend that the patient be introduced or reintroduced to the Level 1 routine specifically for neuromuscular re-education and to confirm that the patient is performing the routine correctly. This is an important consideration in young athletes as their bodies change rapidly and require greater emphasis on adapting to changes during growth periods.Prior to advancement through exercise levels, the patient must demonstrate all of the following: (1) no provocation of pain with current level exercise performance, (2) normalized AROM within activity set, and (3) successful completion of previous level's exercise requirements.Utilization of a tool to provide biofeedback has been recommended to assist in objective and accurate measurement of patient technique throughout treatment and as a guide for exercise progression. , 31.We outline an exercise progression that we believe is comprehensive for the pediatric and young adult patient diagnosed with spondylolysis which is as follows. In addition, a three-level example of home exercise instruction is included for guidance. Please take the following into consideration:(i)Strengthening/neuromuscular control: introduction to isometric TA activation in a comfortable posture, typically supine, and then progressing to variations of static posture with continued isolated TA activation without symptoms .(ii)Precautions: avoid any lumbar range into provocative maneuvers. Avoid compensation from the lumbar spine, gluteals, or hamstrings when isolating the TA.(iii)Stretch: hamstrings, hip flexors, and hip rotators to onset of resistance without pelvic compensation.(iv)Cardiovascular: aquatic and/or land walking and stationary cycling.(v)No increase in symptomsSuccessful isolated TA and multifidi isometric contraction in all postures for 10 repetitions  ×10 second holdsConditions for transition to Level 2:(i)Biofeedback tool is in the form of a pressure monitor that is mildly inflated and placed on the lumbar spine with patient supine, seated, or standing against the wall. Appropriate cocontraction of TA and multifidus can be identified by maintenance of pressure with dynamic movements of the UE and LE, indicating spinal stability with distal movement.Strengthening/neuromuscular control: add upper extremity (UE) and lower extremity (LE) dynamic work to isolated TA/multifidi contraction. Exercises that are easily measured with biofeedback tool are recommended to carry-over from a static to a dynamic routine. Progress to standing LE and UE body-weight resistance with continued incorporation of techniques for lumbopelvic control utilized in lower level exercises .Biofeedb(ii)Stretch: hamstrings, hip flexors, and hip rotators into resistance without noted pelvic compensation.(iii)Cardiovascular: increase the time and intensity of walking, as well as stationary cycling. Cardiovascular exercise should remain low-impact in this phase.(iv)No increase in symptomsSuccessful isolated TA/multifidi isometric contraction during dynamic movementAbility to demonstrate 10 repetitions of a full unsupported squat to 90 degrees of knee flexion with good techniqueConditions for transition to Level 3:(i)Progress lumbar range of motion to normal limits without symptoms .(ii)Strengthening: add single-limb and unsupported hip and core exercises to previously double-limb supported activity. Continue with addition of dynamic movements throughout postures.(iii)Stretch: resolution of the hamstring and hip flexor tone should be achieved in this phase as well as normalization of hip AROM symmetry and tolerance for end range stretching without compensation at the pelvis.(iv)Cardiovascular: 30 minutes of walking and progression to cardiovascular exercise equipment.(v)Successful isolation of TA and multifidi activation during asymptomatic dynamic movementElimination of directional preference with single-plane AROMConditions for transition to Level 4:(i)Isolated progressing to multiplanar AROM required for the sport.(ii)Strengthening: add variable surfaces to double-limb exercises followed by progression to single-limb activities.(iii)Neuromuscular control: initiate low-impact, single-direction reaction time activities.(iv)Stretch: continue with previously described hip routine. Addition of lumbar stretches if needed to achieve pain-free AROM.(v)Cardiovascular: progress to 40 minutes of elliptical, StairMaster/VersaClimber.(vi)No provocation of symptoms with daily activities or exercise50% return to sport practice under PT supervisionConditions for transition to Level 5:(i)Strengthening/neuromuscular control: progress to combined movements and coordinated range required for the sport. Agility training in multiple directions. Address specific actions that cause fear or hesitation with dynamic tasks.(ii)Stretching and cardiovascular activities should be at practice levels.(iii)Minimal to no supervision required during the PT home programSuccessful return to 100% sport practice under PT supervisionConditions for transition to Level 6:Patient returns to competitive sport without restriction. Continue exercise program independently. Contact medical team  immediately if symptoms return.Core stabilization translation to sport: TA activation and core support will need to be continuously tested, progressed, and applied to ensure sports-specific carry-over prior to full resumption of previous activity.Growth periods: young athletes will invariably undergo growth during and after treatment. Consistently revisiting the basic TA routine is essential to maintain the contractility and responsiveness of this muscle during periods of growth and progression of sport level.Overtraining: patients, parents, and coaches benefit from education on what constitutes “overtraining.” Limitations, guidelines, and recommendations specific to sport  should be clearly communicated in order to avoid recurrence or worsening of symptoms. Overtraining should always be a consideration/concern in single-sport or year-round athletes.Stress injuries and fractures to the lumbar pars interarticularis are common sports-related injuries among young athletes. After diagnosis, an individualized PT rehabilitation program including education, activity modification, and a progressive course of specific exercise will lead to symptom resolution and return to athletic participation in the vast majority of young athletes. Surgery for direct pars repair is rarely necessary; however, it has high success rates when required in refractory patients. A standardized nonoperative treatment algorithm for pediatric spondylolysis is outlined above.


It has become increasingly clear that functional connectivity derived from resting-state functional magnetic resonance imaging (rsfMRI) data is not stationary, but contains ample dynamic information  using a sliding-window method. They found that PD patients exhibited greater temporal variability in both cortical and subcortical networks. Importantly, this dynamic connectivity measure was associated with the severity of clinical symptoms in patients . In another study, by integrating the strength and temporal variability of complex-network properties derived from effective connectivity networks in patients with post-traumatic stress disorder (PTSD), patients with PTSD with comorbid mild-traumatic brain injury (mTBI) and healthy controls, Rangaprakash et al. identified dysregulation of prefrontal regions over subcortical and visual regions in PTSD/mTBI. These patients displayed lower variability over time in all network properties, which can be an indicator of poorer flexibility. Importantly, authors show that network properties, including dynamic ones, of the prefrontal-subcortical pathway are not only significantly correlated to symptom severity and neurocognitive performance, but also provide predicative value in classifying these disorders . Furthermore, using a novel high-order dynamic functional connectivity networks (D-FCNs), Zhao et al. achieved a classification accuracy of 83% for autism spectrum disorder (ASD). This method can overcome the problems of conventional sliding-window-based D-FCNs, such as lack of high-level interactions across regions and the temporal mismatching issue .The utilization of temporal features in rsfMRI data has considerably enhanced our understanding of the neuropathophysiology and improved the diagnosis of brain disorders. Gu et al. reviewed the relationship between rsfMRI and brain arousal. Authors also discussed the potential impact of arousal on spurious relationship between functional connectivity measures and physiology/behavior . In addition, Wang et al. advanced the capacity of individual identification based on rsfMRI data by including temporal features in convolutional recurrent neural networks (ConvRNN). They demonstrate that ConvRNN can achieve a higher identification accuracy than conventional RNN .Temporal features in rsfMRI data are also tightly linked to physiology. For instance, converging evidence suggests that arousal may have profound effects on rsfMRI signals and connectivity dynamics. Zhou et al. proposed a protocol designed to track dynamical whole-brain functional connectivity states, using signed community clustering with the optimized modularity by two-step procedures. This method makes it possible to track rapid dynamical change in functional connectivity . Chen et al. constructed brain networks using unwrapped fMRI phase image, instead of the magnitude of fMRI data conventionally used. The functional network connectivity matrix obtained based on phase fMRI was more sparsely distributed across the brain, with connections having more balanced positive/negative correlations. Their findings open a new avenue to understanding brain function connectivity . Yang et al. went beyond the conventional method of regressing out motion parameters, and developed an automated convolutional neural network (CNN) model to obtain optimal motion regressors, which can better reduce motion-related artifacts.Methodology development continues to improve our capacity to extract temporal features of rsfMRI. Guan et al. studied the linearity and stationarity of fMRI time series in individual resting-state brain networks, and found that different networks had distinct properties of non-stationarity and non-linearity. Nezafati et al. examined the complexity of regional brain activity measured by rsfMRI data using sample entropy. They found that the brain exhibited significant spatial heterogeneity in levels of entropy/complexity. In addition, the entropy of brain activity was also modulated by task performance .Finally, we have a better understanding of temporal features in rsfMRI data. Taken together, the studies in this special issue demonstrate the importance of investigating temporal features in rsfMRI data, and exemplify the potential impact of applying these features to better understand brain function in health and disease.NZ and XH wrote the editorial. Both authors contributed to the article and approved the submitted version.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.