Phagocytosis of apoptotic bodies by hepatic stellate cells induces NADPH oxidase and is associated with liver fibrosis in vivo.
Hepatic stellate cell activation is a main feature of liver fibrogenesis. We have previously shown that phagocytosis of apoptotic bodies by stellate cells induces procollagen alpha1 (I) and transforming growth factor beta (TGF-beta) expression in vitro. Here we have further investigated the downstream effects of phagocytosis by studying NADPH oxidase activation and its link to procollagen alpha1 (I) and TGF-beta1 expression in an immortalized human stellate cell line and in several models of liver fibrosis. Phagocytosis of apoptotic bodies in LX-1 cells significantly increased superoxide production both in the extracellular and intracellular milieus. By confocal microscopy of LX-1 cells, increased intracellular reactive oxygen species (ROS) were detected in the cells with intracellular apoptotic bodies, and immunohistochemistry documented translocation of the NADPH oxidase p47phox subunit to the membrane. NADPH oxidase activation resulted in upregulation of procollagen alpha1 (I); in contrast, TGF-beta1 expression was independent of NADPH oxidase activation. This was also confirmed by using siRNA to inhibit TGF-beta1 production. In addition, with EM studies we showed that phagocytosis of apoptotic bodies by stellate cells occurs in vivo. In conclusion, these data provide a mechanistic link between phagocytosis of apoptotic bodies, production of oxidative radicals, and the activation of hepatic stellate cells.
Department of Internal Medicine, Division of Gastroenterology and Hepatology, Clinical Nutrition and Vascular Medicine, UC Davis Medical Center, Sacramento, CA 95817, USA.
Shan-Shan
SS
Zhan
Joy X
JX
Jiang
Jian
J
Wu
Charles
C
Halsted
Scott L
SL
Friedman
Mark A
MA
Zern
Natalie J
NJ
Torok
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002460:Cell Line; D024042:Collagen Type I / Q000096:biosynthesis / Q000235:genetics; D004195:Disease Models, Animal; D006526:Hepatitis C / Q000503:physiopathology; D006801:Humans; D008099:Liver / Q000166:cytology* / Q000378:metabolism* / Q000503:physiopathology; D008103:Liver Cirrhosis / Q000378:metabolism*; D008297:Male; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D019255:NADPH Oxidases / Q000378:metabolism* / Q000502:physiology; D018384:Oxidative Stress / Q000502:physiology; D010587:Phagocytosis / Q000502:physiology*; D014176:Protein Biosynthesis; D034622:RNA Interference; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D013552:Swine; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000235:genetics; D053773:Transforming Growth Factor beta1; D015854:Up-Regulation
D024042:Collagen Type I; D017382:Reactive Oxygen Species; C508960:TGFB1 protein, human; C508962:Tgfb1 protein, rat; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D019255:NADPH Oxidases; C060505:neutrophil cytosolic factor 1