Hepatic steatosis inhibits autophagic proteolysis via impairment of autophagosomal acidification and cathepsin expression

• Published in: Biochemical and biophysical research communications Vol. 412; no. 4; pp. 618 - 625
• Main Authors: Inami, Yoshihiro, Yamashina, Shunhei, Izumi, Kousuke, Ueno, Takashi, Tanida, Isei, Ikejima, Kenichi, Watanabe, Sumio
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 09.09.2011
• Subjects: 60 APPLIED LIFE SCIENCES; ACID CARBONATES; ACIDIFICATION; Acids - metabolism; Animals; Autophagy; Cathepsin; CATHEPSINS; Cathepsins - biosynthesis; ENDOPLASMIC RETICULUM; Fatty Liver - metabolism; Fatty Liver - pathology; FLUORESCENCE; Hepatocytes - metabolism; Hepatocytes - pathology; HOMEOSTASIS; Hydrogen-Ion Concentration; LEUCINE; LIPIDS; LIVER; LIVER CELLS; Lysosome; Male; MEMBRANE PROTEINS; METABOLISM; MICE; Mice, Inbred C57BL; MICROTUBULES; Phagosomes - metabolism; Proteins - metabolism; PROTEOLYSIS; Steatosis; NAFLD; Lysosome; LTR; NASH; ER; Autophagy; Steatosis; GFP; Cathepsin; LAMP1; ANOVA; mTOR; KRB; LC3
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/j.bbrc.2011.08.012

► Acidification of autophagosome was blunted in steatotic hepatocytes. ► Hepatic steatosis did not disturb fusion of isolated autophagosome and lysosome. ► Proteinase activity of cathepsin B and L in autolysosomes was inhibited by steatosis. ► Hepatic expression of cathepsin B and L was suppressed by steatosis. Autophagy, one of protein degradation system, contributes to maintain cellular homeostasis and cell defense. Recently, some evidences indicated that autophagy and lipid metabolism are interrelated. Here, we demonstrate that hepatic steatosis impairs autophagic proteolysis. Though accumulation of autophagosome is observed in hepatocytes from ob/ob mice, expression of p62 was augmented in liver from ob/ob mice more than control mice. Moreover, degradation of the long-lived protein leucine was significantly suppressed in hepatocytes isolated from ob/ob mice. More than 80% of autophagosomes were stained by LysoTracker Red (LTR) in hepatocytes from control mice; however, rate of LTR-stained autophagosomes in hepatocytes were suppressed in ob/ob mice. On the other hand, clearance of autolysosomes loaded with LTR was blunted in hepatocytes from ob/ob mice. Although fusion of isolated autophagosome and lysosome was not disturbed, proteinase activity of cathepsin B and L in autolysosomes and cathepsin B and L expression of liver were suppressed in ob/ob mice. These results indicate that lipid accumulation blunts autophagic proteolysis via impairment of autophagosomal acidification and cathepsin expression.