Roles of phosphatidylinositol 3-kinase and osteopontin in steatosis and aminotransferase release by hepatocytes treated with methionine-choline-deficient medium

Sahai, Atul; Pan, Xiaomin; Paul, Rachelle; Malladi, Padmini; Kohli, Rohit; Whitington, Peter F.

doi:10.1152/ajpgi.00360.2005

Cited by 30 publications

(33 citation statements)

References 39 publications

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“…These results suggest that conditions causing PI3K activation will cause SHP repression. It has been shown that mitochondrial ROS induces hepatocyte steatosis by upregulating the PI3K pathway (Kohli et al, 2007) and that hepatocytes exposed to the MCD medium developed significant and progressive steatosis along with activation of PI3K/Akt (Sahai et al, 2006). Moreover, PI3K (p85) was significantly higher in NAFLD patients (Xu et al, 2011).…”

Section: Discussionmentioning

confidence: 98%

Repression of the Nuclear Receptor Small Heterodimer Partner by Steatotic Drugs and in Advanced Nonalcoholic Fatty Liver Disease

et al. 2015

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The small heterodimer partner (SHP) (NR0B2) is an atypical nuclear receptor that lacks a DNA-binding domain. It interacts with and inhibits many transcription factors, affecting key metabolic processes, including bile acid, cholesterol, fatty acid, and drug metabolism. Our aim was to determine the influence of steatotic drugs and nonalcoholic fatty liver disease (NAFLD) on SHP expression and investigate the potential mechanisms. SHP was found to be repressed by steatotic drugs (valproate, doxycycline, tetracycline, and cyclosporin A) in cultured hepatic cells and the livers of different animal models of NAFLD: iatrogenic (tetracycline-treated rats), genetic (glycine N-methyltransferase-deficient mice), and nutritional (mice fed a methionine-and choline-deficient diet). Among the different transcription factors investigated, CCAATenhancer-binding protein a (C/EBPa) showed the strongest dominant-repressive effect on SHP expression in HepG2 and human hepatocytes. Reporter assays revealed that the inhibitory effect of C/EBPa and steatotic drugs colocalize between 2340 and 2509 base pair of the SHP promoter, and mutation of a predicted C/EBPa response element at 2473 base pair abolished SHP repression by both C/EBPa and drugs. Moreover, inhibition of major stress signaling pathways demonstrated that the mitogen-activated protein kinase kinase 1/2 pathway activates, while the phosphatidylinositol 3 kinase pathway represses SHP in a C/EBP-dependent manner. We conclude that SHP is downregulated by several steatotic drugs and in advanced NAFLD. These conditions can activate signals that target C/EBPa and consequently repress SHP, thus favoring the progression and severity of NAFLD.

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Section: Discussionmentioning

confidence: 98%

Repression of the Nuclear Receptor Small Heterodimer Partner by Steatotic Drugs and in Advanced Nonalcoholic Fatty Liver Disease

et al. 2015

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“…Cells incubated with MCD medium in the presence of serum, a lipid source, store TG and exhibit hepatocyte dysfunction (35,36). It is unclear if saturated or unsaturated fatty acids contributed to the dysfunction observed.…”

Section: Discussionmentioning

confidence: 99%

“…TG Accumulation and ALT Induction in McA Cells-McA cells have been used as a model of steatosis (29,34), and it has been demonstrated that short term culture of hepatic derived cells in MCD medium with serum results in steatosis and release of ALT (35,36). McA cells were incubated for 16 h in serum-free BSA-containing medium (control) or MCD medium without or with palmitic, oleic, or linoleic acid complexed to BSA.…”

Section: Time Course Of Steatohepatitis Inmentioning

confidence: 99%

PKCδ Is Activated in a Dietary Model of Steatohepatitis and Regulates Endoplasmic Reticulum Stress and Cell Death

Greene

Burrington

Ruhoff

et al. 2010

Journal of Biological Chemistry

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“…Hepatocyte Cell Culture-AML-12 cells, a mouse hepatocyte cell line that has been stably transfected with human transforming growth factor-␣ (American Type Culture Collection, Manassas, VA), were treated as previously described (12). In brief, these cells are grown to 70 -80% confluence in Dulbecco's modified Eagle's medium/Ham's nutrient mixture F-12 containing 10% fetal bovine serum (for growth factors) and then made quiescent by incubating for 24 h in standard medium without fetal bovine serum.…”

Section: Methodsmentioning

confidence: 99%

“…To further explore the possibility that the MCD diet represented a signal leading to steatosis and other expressions of experimental NASH, including the overexpression of OPN, we examined the effects of substituting medium deficient in methionine and choline (MCD medium) on AML-12 mouse hepatocytes in vitro (12). Substituting MCD medium for control medium produced significant hepatocyte steatosis by 18 h of exposure.…”

mentioning

confidence: 99%

Mitochondrial Reactive Oxygen Species Signal Hepatocyte Steatosis by Regulating the Phosphatidylinositol 3-Kinase Cell Survival Pathway

Kohli

Pan

Malladi

et al. 2007

Journal of Biological Chemistry

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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.Innumerable epidemiologic studies demonstrate that inappropriate intake of macronutrients and a sedentary lifestyle conspire to produce rampant obesity in the United States. Hepatic steatosis (the accumulation of excess neutral fat within hepatocytes) in obese persons is thought to result from metabolic disturbances attendant to obesity. An estimated 30 million adults and 1.6 million children in the United States have nonalcoholic fatty liver disease (NAFLD), 2 of which an estimated 30% have nonalcoholic steatosis (NASH), which can lead to chronic debilitating liver injury, including cirrhosis (1). Hepatic steatosis is the defining feature of NAFLD (2). It is commonly held that steatosis is the precursor of events that lead to the transition of NAFLD to NASH, including the induction of oxidative stress and activation of inflammatory pathways (3, 4). The development of hepatic steatosis is therefore considered to be the necessary first effect of disturbed nutrition that induces the cascade of events leading to NASH. How disturbed nutrition causes hepatic steatosis is not well understood.Experimental NASH can be produced in laboratory rodents by dietary manipulation, including both restricted intake (i.e. methionine-choline deficient (MCD) diet) (5) and excess ...

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Roles of phosphatidylinositol 3-kinase and osteopontin in steatosis and aminotransferase release by hepatocytes treated with methionine-choline-deficient medium

Abstract: Sahai, Atul, Xiaomin Pan, Rachelle Paul, Padmini Malladi, Rohit Kohli, and Peter F. Whitington. Roles of phosphatidylinositol 3-kinase and osteopontin in steatosis and aminotransferase release by hepatocytes treated with methionine-choline-deficient medium.

Cited by 30 publications

References 39 publications

Repression of the Nuclear Receptor Small Heterodimer Partner by Steatotic Drugs and in Advanced Nonalcoholic Fatty Liver Disease

Repression of the Nuclear Receptor Small Heterodimer Partner by Steatotic Drugs and in Advanced Nonalcoholic Fatty Liver Disease

PKCδ Is Activated in a Dietary Model of Steatohepatitis and Regulates Endoplasmic Reticulum Stress and Cell Death

Mitochondrial Reactive Oxygen Species Signal Hepatocyte Steatosis by Regulating the Phosphatidylinositol 3-Kinase Cell Survival Pathway

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