Mitochondrial free cholesterol loading sensitizes to TNF- and Fas-mediated steatohepatitis

Abstract

The etiology of progression from steatosis to steatohepatitis (SH) remains unknown. Using nutritional and genetic models of hepatic steatosis, we show that free cholesterol (FC) loading, but not free fatty acids or triglycerides, sensitizes to TNF- and Fas-induced SH. FC distribution in endoplasmic reticulum (ER) and plasma membrane did not cause ER stress or alter TNF signaling. Rather, mitochondrial FC loading accounted for the hepatocellular sensitivity to TNF due to mitochondrial glutathione (mGSH) depletion. Selective mGSH depletion in primary hepatocytes recapitulated the susceptibility to TNF and Fas seen in FC-loaded hepatocytes; its repletion rescued FC-loaded livers from TNF-mediated SH. Moreover, hepatocytes from mice lacking NPC1, a late endosomal cholesterol trafficking protein, or from obese ob/ob mice, exhibited mitochondrial FC accumulation, mGSH depletion, and susceptibility to TNF. Thus, we propose a critical role for mitochondrial FC loading in precipitating SH, by sensitizing hepatocytes to TNF and Fas through mGSH depletion.

Lipid-induced oxidative stress causes steatohepatitis in mice fed an atherogenic diet

“…In this study, in addition to cholesterol, the accumulation of TG and FFAs by the addition of a high-fat component accelerated oxidative stress, possibly via the up-regulation of genes involved in the generation of ROS, such as the NADPH oxidase complex, and the down-regulation of genes for antioxidant enzymes. While we were preparing this article, Mari et al 35 reported that the mitochondrial loading of free cholesterol, but not TG and FFA, decreases mitochondrial glutathione and sensitizes it to the TNF-␣-mediated apoptosis of hepatocytes. Therefore, the different kinds of accumulated lipids may cause oxidative stress in the liver additively in different ways.…”

“…34 Because the feeding of cholesterol and cholic acid, which are the main components of the Ath diet, leads to the additive accumulation of cholesterol in the liver, the main pathology in Ath diet-induced steatohepatitis is caused by cholesterol-induced toxicity. 35 In this study, we have shown that Ath diet-induced steatohepatitis with atherosclerosis is a better experimental model of human NASH for the following reasons: (1) this model seems to be a more physiological dietary model of NASH than existing animal models, which require genetic defects, chemical agents such as carbon tetrachloride, or the depletion of nutrients, such as the MCD diet-induced model; (2) the liver pathology involves steatohepatitis with cellular ballooning, a necessary histological feature defining human NASH; (3) the addition of a high-fat component to the Ath diet causes hepatic insulin resistance and promotes oxidative stress, the activation of HSCs, and all components of the liver pathology of NASH (steatosis, inflammation, fibrosis, and cellular ballooning); and (4) there is a molecular signature indicative of lipid-induced oxidative stress in the liver, which may play a causal role in the development of steatohepatitis. To diagnose human NASH, cellular ballooning, in addition to simple steatosis and inflammatory cell infiltration, is one of the most important pathological features.…”

The lysosomal-mitochondrial axis in free fatty acid-induced hepatic lipotoxicity

“…27 Although lipids accumulate mostly in the form of triglycerides, steatosis may results in excess amounts of other lipids such as a variety of FFAs and cholesterol. 11,28 Certain FFAs are potentially cytotoxic, and in vitro studies in different cell lines including hepatocytes have implicated increased cellular FFA levels as a trigger of apoptotic cell death. 12,29,30 Our current data demonstrates that incubation of human and murine hepatocytes with FFAs results in dose-and saturationdependent mitochondrial dysfunction.…”

Reactive oxygen species and vascular biology: implications in human hypertension

“…46 Ang II and endothelin-1 stimulate mitochondrial ROS generation in endothelial and vascular smooth muscle cells and in rat aorta in vivo. [47][48][49][50][51] Mechanisms whereby these vasoactive agents induce such actions are unclear but could involve opening of mitochondrial potassium channels (mitoK ATP ) 52 and mitochondrial permeability transition. 53 Ang II-induced Nox activation has also been shown to induce mitochondrial ROS formation.…”