Toll-like receptor-2 deficiency enhances non-alcoholic steatohepatitis

Abstract

BackgroundPreviously we reported that mice deficient in toll-like receptor 4 (TLR-4) signalling were protected from diet-induced non-alcoholic steatohepatitis (NASH). Another member of the toll-like receptor family, TLR-2, has been shown to play a role in lipid trafficking via uptake of diacylated lipoproteins. However, a role for TLR-2 in NASH has not been elucidated. The objectives of the current study were to examine the influence of dietary fat quality and TLR-2 on NASH pathogenesis.MethodsSteatohepatitis was induced in male Db, C57BL/6 and TLR-2-/- mice by feeding an L-amino acid-defined diet that was deficient in methionine and choline (MCDD). Mice fed the base diet supplemented with methionine and choline (control diet; CD) were used as controls. To determine the role of fat quality, MCDD was enriched with polyunsaturated corn oil (PUFA) or coconut oil that is comprised mostly of saturated fat (SAFA); the total amount of each fat was 112.9 g/kg of diet. After 8 weeks of feeding CD or MCDD, hepatic steatosis, inflammation and necrosis were evaluated in histological sections. Total RNA was extracted from frozen liver samples and mRNA expression of TNFα, collagen α1, IL-10, peroxisome proliferator-activated receptor-γ (PPAR-γ), TLR-4, and CD14, was analyzed via real-time PCR. Protein levels of TLR-2 were analyzed by western blot.ResultsPanlobular macrovessicular steatosis and diffuse leukocyte infiltration were noted in PUFA-fed Db mice. Histological scores demonstrated significantly less steatosis, inflammation and necrosis in SAFA-fed mice of all mouse strains. However, compared to wild type mice, hepatocellular damage was notably more severe in TLR-2-/- mice. Consistent with histological findings, mRNA expression of TNFα was elevated by approximately 3-fold in TLR-2-/- mice; PPAR-γ expression was blunted in this strain compared to wild type. Expression of the matrix protein collagen αI was also significantly higher in TLR-2-/- mice, indicating a pro-fibrogenic state. Sensitivity to steatohepatitis due to dietary fat or TLR-2 deficiency correlated significantly with alterations in the expression of TLR-4 as well as the co-receptor CD-14.ConclusionsOur findings suggest that dietary saturated fat plays a protective role against MCDD-induced steatohepatitis, whereas TLR-2 deficiency exacerbated NASH. The mechanism underlying the response to dietary fat and TLR-2 likely involves altered signalling via the TLR-4 pathway.

Influence of dietary saturated fat content on adiposity, macrophage behavior, inflammation, and metabolism: composition matters

“…Additionally, our data and that of others suggest that isocaloric diets with a greater content of omega-6 PUFAs can produce greater IR, result in a poorer TC/HDL-C ratio, and may even increase infl ammation ( 46,55 ), more so than an isocaloric diet composed of signifi cantly more SF. Meanwhile, others have shown that high consumption of omega-6 FAs has been associated with reduced infl ammation, a more favorable TC/HDL-C ratio ( 55 ), and no negative effects on infl ammatory markers ( 61,62 ).…”

“…al. ( 46 ) reported that a MCFA-rich diet more effectively attenuated nonalcoholic steatohepatitis and reduced hepatic TLR-4 expression versus a PUFA-rich diet. These convergent fi ndings may be explained by the inclination of lauric acid to be oxidized in vivo, thus limiting its ability to serve as a ligand for TLRs ( 16 ).…”

Excess iron modulates endoplasmic reticulum stress-associated pathways in a mouse model of alcohol and high-fat diet-induced liver injury

“…27 Mice deficient in TLR2 and TLR4 display attenuation in diet-induced hepatic steatosis and alcoholic liver injury. [48][49][50] Although this study did not thoroughly examine the role of specific TLRs in detail, the increased expression of multiple TLRs in Hfe À / À mice following ethanol and HFD suggests a possible role of iron in modulating TLR signaling in liver diseases. The mechanisms behind this remain unclear, but may involve LPS-independent pathways as there is currently no evidence that Hfe deficiency or iron overload affects hepatic responses to portal endotoxemia.…”

Nonalcoholic Fatty Liver Disease in Children: Role of the Gut Microbiota

“…In comparison to wild-type mice, TLR2-deiciency animals are substantially protected from high-fat diet-induced adiposity, insulin resistance, hypercholesterolemia, and hepatic steatosis [39]. In contrast, increased hepatic inlammation and TNFmRN" expression were observed in TLR2-deiciency mice fed with MCDD [33,40]. The conlicting results of the role of TLR2 signaling in those studies could be due to diferent animal models used, diferent gut microbial ligands involved or compensation by other TLRs.…”