Deficiency in myeloid differentiation factor-2 and toll-like receptor 4 expression attenuates nonalcoholic steatohepatitis and fibrosis in mice

Abstract

Deficiency in myeloid differentiation factor-2 and toll-like receptor 4 expression attenuates nonalcoholic steatohepatitis and fibrosis in mice. Am J Physiol Gastrointest Liver Physiol 300: G433-G441, 2011. First published January 13, 2011; doi:10.1152/ajpgi.00163.2009.-Toll-like receptor 4 (TLR4) and its coreceptor, myeloid differentiation factor-2 (MD-2), are key in recognition of lipopolysaccharide (LPS) and activation of proinflammatory pathways. Here we tested the hypothesis that TLR4 and its coreceptor MD-2 play a central role in nonalcoholic steatohepatitis (NASH) and liver fibrosis in nonalcoholic fatty liver disease. Mice of control genotypes and those deficient in MD-2 or TLR4 [knockout (KO)] received methionine choline-deficient (MCD) or methionine choline-supplemented (MCS) diet. In mice of control genotypes, MCD diet resulted in NASH, liver triglycerides accumulation, and increased thiobarbituric acid reactive substances, a marker of lipid peroxidation, compared with MCS diet. These features of NASH were significantly attenuated in MD-2 KO and TLR4 KO mice. Serum alanine aminotransferase, an indicator of liver injury, was increased in MCD diet-fed genotype controls but was attenuated in MD-2 KO and TLR4 KO mice. Inflammatory activation, indicated by serum TNF-␣ and nictoinamide adenine dinucleotide phosphate oxidase complex mRNA expression and activation, was significantly lower in MCD diet-fed MD-2 KO and TLR4 KO compared with corresponding genotype control mice. Markers of liver fibrosis [collagen by Sirius red and ␣-smooth muscle actin (SMA) staining, procollagen-I, transforming growth factor-␤1, ␣-SMA, matrix metalloproteinase-2, and tissue inhibitor of matrix metalloproteinase-1 mRNA] were attenuated in MD-2 and TLR4 KO compared with their control genotype counterparts. In conclusion, our results demonstrate a novel, critical role for LPS recognition complex, including MD-2 and TLR4, through NADPH activation in liver steatosis, and fibrosis in a NASH model in mice.

Role of gut microbiota: Obesity and NAFLD

“…MyD88 deficiency prevents steatohepatitis in mice fed a choline-deficient (CD) diet, attributing a novel role to the MyD88 signaling pathway (63). TLR4 and MD-2 knockout mice fed MCD diet exhibit lower serum TNF-α levels than wild-type mice, explaining the pivotal role of the LPS recognition complex in NAFLD inflammation (64). Recently, Kanuri et al reported that the higher expression of TLR 1-5 mRNA in the livers of NAFLD patients was associated with an induction of higher expression of their intracellular adapter molecule, MyD88, but not IRF3 (65).…”

Dietary Influence of the Gut Microbiome Potential Hazards and Benefits

“…Interestingly, HFD-fed TLR4-deficient mice appear to be protected from NAFLD [37][38][39]. Several other murine studies have shown that injection of LPS into NAFLD afflicted mice further promotes hepatic damage via elevated proinflammatory cytokines [40,41].…”

Non-alcoholic Fatty Liver Disease and the Gut Microbiota: Exploring the Connection

“…46 Additionally, a number of other studies have shown that TLR4 mutant mice are resistant to the development of NAFLD. [47][48][49] Similar models using a Methionine choline-deficient (MCD) diet were able to induce NASH, evidenced by increased liver triglyceride accumulation, lipid peroxidation, serum ALT, TNF-α, NADPH, and markers of liver fibrosis. 48 When knockout mice deficient for TLR4 and its co-receptor MD-2 (Myeloid Differentiation factor) were also placed on the MCD diet, however, these increases were attenuated.…”

“…[47][48][49] Similar models using a Methionine choline-deficient (MCD) diet were able to induce NASH, evidenced by increased liver triglyceride accumulation, lipid peroxidation, serum ALT, TNF-α, NADPH, and markers of liver fibrosis. 48 When knockout mice deficient for TLR4 and its co-receptor MD-2 (Myeloid Differentiation factor) were also placed on the MCD diet, however, these increases were attenuated. The authors of this study suggest that these results demonstrate a role for LPS recognition via TLR4 and MD-2 for inducing liver steatosis and fibrosis in a NASH model in mice.…”