Mitochondrial reactive oxygen species signal hepatocyte steatosis by regulating the phosphatidylinositol 3-kinase cell survival pathway.
Abnormal dietary intake of macronutrients is implicated in the development of obesity and fatty liver disease. Steatosis develops in cultured hepatocytes exposed to medium containing either a high concentration of long chain free fatty acids (HFFA) or medium deficient in methionine and choline (MCD). This study examined the mitochondrial reactive oxygen species (ROS)-dependent regulation of the phosphoinositol (PI) 3-kinase pathway in steatosis induced by exposure of AML-12 mouse hepatocytes to MCD or HFFA medium. Exposure to either MCD or HFFA medium resulted in increased production of superoxide anions and H(2)O(2), transduction of the PI 3-kinase pathway and steatosis. Inhibition of PI 3-kinase with LY294002 prevented steatosis. Pharmacologically inhibiting electron transport chain complex III production of ROS prevented activation of PI 3-kinase during macronutrient perturbation, whereas pharmacologically promoting electron transport chain complex III ROS production activated PI 3-kinase independent of nutrient input. The data suggest that H(2)O(2) is the ROS species involved in signal transduction; promoting the rapid conversion of superoxide to H(2)O(2) does not inhibit PI 3-kinase pathway activation during nutrient perturbation, and exogenous H(2)O(2) activates it independent of nutrient input. In addition to transducing PI 3-kinase, the ROS-dependent signal cascade amplifies the PI 3-kinase signal by maintaining phosphatase and tensin homolog in its inactive phosphorylated state. Knockdown of phosphatase and tensin homolog by small interfering RNA independently activated the PI 3-kinase pathway. Our findings suggest a common path for response to altered nutrition involving mitochondrial ROS-dependent PI 3-kinase pathway regulation, leading to steatosis.
Kohli
Rohit
R
Department of Pediatrics, Children's Memorial Hospital, Children's Memorial Research Center, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60614, USA.
Pan
Xiaomin
X
Malladi
Padmini
P
Wainwright
Mark S
MS
Whitington
Peter F
PF
D000818:Animals; D017209:Apoptosis; D002470:Cell Survival; D002867:Chromones / Q000494:pharmacology; D005230:Fatty Acids, Nonesterified / Q000378:metabolism; D005234:Fatty Liver / Q000473:pathology; D015971:Gene Expression Regulation, Enzymologic; D022781:Hepatocytes / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000737:chemistry; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D008954:Models, Biological; D009025:Morpholines / Q000494:pharmacology; D051059:PTEN Phosphohydrolase / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism; D015398:Signal Transduction
D002867:Chromones; D005230:Fatty Acids, Nonesterified; D009025:Morpholines; D017382:Reactive Oxygen Species; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D006861:Hydrogen Peroxide; D019869:Phosphatidylinositol 3-Kinases; D051059:PTEN Phosphohydrolase; C487757:Pten protein, mouse