Sab (Sh3bp5) dependence of JNK mediated inhibition of mitochondrial respiration in palmitic acid induced hepatocyte lipotoxicity.
BACKGROUND & AIMS
Sustained c-Jun N-terminal kinase (JNK) activation by saturated fatty acids plays a role in lipotoxicity and the pathogenesis of non-alcoholic steatohepatitis (NASH). We have reported that the interaction of JNK with mitochondrial Sab leads to inhibition of respiration, increased reactive oxygen species (ROS), cell death and hepatotoxicity. We tested whether this pathway underlies palmitic acid (PA)-induced lipotoxicity in hepatocytes.


METHODS
Primary mouse hepatocytes (PMH) from adeno-shlacZ or adeno-shSab treated mice and HuH7 cells were used.


RESULTS
In PMH, PA dose-dependently up to 1mM stimulated oxygen consumption rate (OCR) due to mitochondrial β-oxidation. At ⩾1.5mM, PA gradually reduced OCR, followed by cell death. Inhibition of JNK, caspases or treatment with antioxidant butylated hydroxyanisole (BHA) protected PMH against cell death. Sab knockdown or a membrane permeable Sab blocking peptide prevented PA-induced mitochondrial impairment, but inhibited only the late phase of both JNK activation (beyond 4h) and cell death. In PMH, PA increased p-PERK and its downstream target CHOP, but failed to activate the IRE-1α arm of the UPR. However, Sab silencing did not affect PA-induced PERK activation. Conversely, specific inhibition of PERK prevented JNK activation and cell death, indicating a major role upstream of JNK activation.


CONCLUSIONS
The effect of p-JNK on mitochondria plays a key role in PA-mediated lipotoxicity. The interplay of p-JNK with mitochondrial Sab leads to impaired respiration, ROS production, sustained JNK activation, and apoptosis.
['Win|Sanda|S|', 'Than|Tin Aung|TA|', 'Le|Bao Han Allison|BH|', 'García-Ruiz|Carmen|C|', 'Fernandez-Checa|Jose C|JC|', 'Kaplowitz|Neil|N|']
D048868:Adaptor Proteins, Signal Transducing D000818:Animals D000975:Antioxidants D017209:Apoptosis D002460:Cell Line D002478:Cells, Cultured D004305:Dose-Response Relationship, Drug D055785:Gene Knockdown Techniques D022781:Hepatocytes D006801:Humans D048031:JNK Mitogen-Activated Protein Kinases D008565:Membrane Proteins D051379:Mice D008928:Mitochondria D024101:Mitochondrial Proteins D065626:Non-alcoholic Fatty Liver Disease D010101:Oxygen Consumption D019308:Palmitic Acid D017382:Reactive Oxygen Species
Palmitic acid Hepatocytes Reactive oxygen species Mitochondria Apoptosis