Pkc Delta Silencing Alleviates Saturated Fatty Acid Induced Er Stress By Enhancing Serca Activity

Protein kinase C delta (PKC delta) plays an important role in nonalcoholic fatty liver disease (NAFLD), however, the mechanism remains unknown. The present study explored the role of PKCd in NAFLD development and investigated the relationships between PKCd, calcium homeostasis, and endoplasmic reticulum (ER) stress (ERS). Hepatic steatosis cell model was induced by palmitic acid (PA) in L02 cells. Lipid accretion was evaluated using Oil Red O staining and a triglyceride (TG) detection kit. PKCd was down-regulated by siRNA. RT-PCR and Western blotting were used to detect the expression of ERS markers. The fluorescence of Ca2+ influx was recorded using confocal microscopy. Sarco-ER Ca2+-ATPase (SERCA) activity was measured by ultramicro-ATP enzyme test kit. PA treatment induced lipid accretion in L02 cells, destroyed the ER structure, and increased PKCd activation in a time-dependent manner. Further, PA treatment significantly increased the expression of ERS markers, Ig heavy chain binding protein (Bip), and homologous proteins of CCAAT-enhancer binding proteins (CHOP). PKCd silencing down-regulated Bip and CHOP expression, indicating a successful alleviation of ERS. The increased calcium storage induced by PA stimulation was significantly decreased in L02 cells treated with PKCd siRNA compared with the negative control. Moreover, diminished SERCA activity caused by PA was recovered in PKCd siRNA transfected cells. To the best of our knowledge, this is the first report demonstrating that the inhibition of PKCd alleviates ERS by enhancing SERCA activity and stabilizing calcium homeostasis.