Although no genetic associations with advanced NAFLD have been replicated in large studies, preliminary data suggest that polymorphisms in the genes encoding microsomal triglyceride transfer protein, superoxide dismutase 2, the CD14 endotoxin receptor, tumor necrosis factor-alpha, transforming growth factor-beta, and angiotensinogen may be associated with steatohepatitis and/or fibrosis.
The TM6SF2 E167K substitution promotes steatosis and lipid abnormalities in part by altering TM6SF2 and microsomal triglyceride transfer protein expression and differentially impacts CHC and chronic hepatitis B viral load, while effects on fibrosis are marginal.(Hepatology 2016;64:34-46).
Circulating concentrations of adipokines (ie, tumor necrosis factor-alpha, adiponectin, resistin, leptin, and interleukin-6), markers of nitrosative stress (nitrotyrosine), dietary habits, and MTP-493G/T polymorphism were cross-sectionally related to the presence and severity of insulin resistance (homeostasis model assessment index for insulin resistance: >or=2), the metabolic syndrome, and fatty liver in 64 nonobese nondiabetic patients with NAFLD (33 insulin-sensitive and 31 insulin-resistant subjects) and 74 control subjects without liver disease who were matched for sex, BMI, homeostasis model assessment index for insulin resistance status, and the various features of the metabolic syndrome.
The presence of at least one T allele in the -129 C/T polymorphism of the GCLC gene was independently associated with NASH (odds ratio 12.14, 95% confidence interval 2.01-73.35; P = 0.007), whereas, the presence of at least one G allele in the -493 G/T polymorphism of the MTP gene differed slightly between biopsy-proven NASH and simple steatosis.
A polymorphism in the microsomal triglyceride transfer protein (MTP) is associated with hepatic fibrosis, and carriers showed higher levels of steatosis, higher levels of hepatitis C virus (HCV) RNA and advanced fibrosis.
This steatosis was associated with aberrant microsomal apolipoprotein (apo) B-100 and microsomal triglyceride transfer protein (MTP) content, hypotriglyceridemia, hypocholesterolemia and abnormalities in both circulating lipoprotein composition and size.
Intestine-specific inhibitors of MTP decrease chylomicron biogenesis and improve insulin sensitivity in experimental animals and, while overcoming hepatic steatosis, may have significant gastrointestinal side effects that could limit their use in humans.
Our results lead us to propose a new pathophysiological animal model for induction of viral-related steatosis whereby the core protein of HCV targets microsomal triglyceride transfer protein activity and modifies hepatic VLDL assembly and secretion.
We conclude that 1) HFD leads to ApoB100/MTP suppression reducing export of lipids; 2) castration promotes progression to steatohepatitis through activation of the ER stress pathway and enhancement of macrovesicular droplet protein expression; and 3) testosterone suppresses ER stress, inhibits the formation of macrovesicular lipid droplets, promotes lipid export, and ameliorates steatohepatitis induced by HFD and castration.
These results suggest that reduced MTP activity is crucial to development of alcoholic fatty liver, while promotion of MTP activity by HGF might serve as a therapeutic measure against alcoholic liver steatosis.