Western diet increases HMGB1 levels and activates cardiac and hepatic Toll‐like receptor 4 (TLR4) signaling in male mice

Abstract

BackgroundOverconsumption of a Western diet (WD), characterized by a high amount of fats and carbohydrates, is a major contributor to the epidemic of non‐alcoholic liver and cardiovascular disease in the United States. Our laboratory has recently demonstrated that WD causes endothelial dysfunction via vascular TLR4 signaling activation, a key component of innate immunity linked to inflammation. Based on these findings, we hypothesized that WD triggers inflammatory responses in the livers and hearts of male mice via activation of TLR4 signaling. We also investigated whether WD elevates high‐mobility group box 1 protein (HMGB1) levels, a pro‐inflammatory factor known to be an endogenous ligand for TLR4.MethodsAdult male C57BL/J mice were randomized in two experimental groups: Control Group received a regular chow diet and WD group received WD (40% fat, 43% carbohydrates, and 17% protein) for 28 weeks. Prior to terminal experiments, body weights were measured weekly. After euthanasia with isoflurane (via nasal 5% in 100% O2), livers, hearts, and adipose tissue were removed and processed for further molecular assays. Blood samples were also obtained for biochemical analysis.ResultsAs expected, WD group exhibited increased body weight (31.1 ± 3.2 vs. 25.2 ± 1.4g, p<0.01), adipocyte size (7724.2 ± 1745.8 vs. 2727.3 ± 927.1 μm2, p<0.05) and elevated serum free fatty acids (0.20 ± 0.02 vs. 0.14 ± 0.024 mM, p<0.05) compared to controls. Next, to test the hypothesis that WD activates TLR4 signaling in hepatic and cardiac tissue, Western blot analysis was performed. Hepatic expression of TLR4 (2.8 fold increase vs. controls, p<0.001) and its downstream protein TNF receptor‐associated factor 6 (TRAF6) (1.8 fold increase vs. controls, p<0.01) were markedly elevated in the WD group. Similarly, cardiac expression of TLR4 (2.2 fold increase vs. controls, p<0.01) and TRAF6 (2.8 fold increase vs. controls, p<0.001) were increased in the WD group. Strikingly, we found that serum HMGB1 expression was significantly increased in WD group in comparison to the controls (70% elevation vs control, p<0.05).ConclusionOur results suggest that upregulation of HMGB1 may contribute to TLR4/TRAF6 signaling activation in hepatic and cardiac tissue of western diet fed mice. To expand this investigation, we will utilize pharmacological and molecular approaches to target HMGB1 and confirm its role in WD‐induced inflammation.Support or Funding InformationIn‐house Grant NYITThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.