TLR4 Antagonist Attenuates Atherogenesis in LDL Receptor-Deficient Mice with Diet-Induced Type 2 Diabetes

Abstract

Although a large number of studies have well documented a key role of toll-like receptor (TLR)4 in atherosclerosis, it remains undetermined if TLR4 antagonist attenuates atherogenesis in mouse model for type 2 diabetes. In this study, we induced type 2 diabetes in low-density lipoprotein receptor-deficient (LDLR ^−/−) mice by high-fat diet (HFD). At 8 weeks old, 20 mice were fed HFD and 20 mice fed regular chow (RC) for 24 weeks. In the last 10 weeks, half HFD-fed mice and half RC-fed mice were treated with Rhodobacter sphaeroides lipopolysaccharide (Rs-LPS), an established TLR4 antagonist. After the treatment, atherosclerotic lesions in aortas were analyzed. Results showed that the HFD significantly increased bodyweight, glucose, lipids including total cholesterol, triglycerides and free fatty acids, and insulin resistance, indicating that the HFD induced type 2 diabetes in LDLR ^−/− mice. Results also showed that Rs-LPS had no effect on HFD-increased metabolic parameters in both nondiabetic and diabetic mice. Lipid staining of aortas and histological analysis of cross-sections of aortic roots showed that diabetes increased atherosclerotic lesions, but Rs-LPS attenuated atherogenesis in diabetic mice. Furthermore, immunohistochemical studies showed that Rs-LPS reduced infiltration of monocytes/macrophages and expression of interleukin (IL)-6 and matrix metalloproteinase-9 in atherosclerotic lesions of diabetic mice. Finally, the antagonistic effect of Rs-LPS on TLR4 was demonstrated by our in vitro studies showing that Rs-LPS inhibited IL-6 secretion from macrophages and endothelial cells stimulated by LPS or LPS plus saturated fatty acid palmitate. Taken together, our study demonstrated that TLR4 antagonist was capable of attenuating vascular inflammation and atherogenesis in mice with HFD-induced type 2 diabetes.