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.

Lipid signaling and lipotoxicity in metaflammation: indications for metabolic disease pathogenesis and treatment

“…The limitations of the human studies with existing anti-cytokine reagents were recently reviewed in an excellent article (230). There are also exciting, but not yet fully exploited, possibilities by antagonizing lipid-sensing pathways, i.e., using TLR4 antagonists (231) or PKR inhibitors (232) to alleviate inflammation along with other beneficial effects associated with the target functions. In these areas, studies in humans are also highly limited at the moment.…”

Cooperative stimulation of atherogenesis by lipopolysaccharide and palmitic acid-rich high fat diet in low-density lipoprotein receptor-deficient mice

“…Slides were fixed in 10% of formaline for 10 minutes, stained with Harris modified hematoxylin (Fisher Scientific, Pittsburgh, PA) for 10 minutes and then rinsed in deionized water. Histological analysis of atherosclerotic lesions was performed as described previously 13 .…”

“…Immunohistochemical analysis was performed as described previously 13 with anti-F4/80 (Bio-Rad Laboratories, Inc., Hercules, CA), anti-CD68 (AbD Serotec, Raleigh, NC) and anti-intercellular adhesion molecule (ICAM-1) antibodies (Santa Cruz Biotechnology, Inc. Dallas, TX).…”

“…It has been shown consistently that administration of low dose LPS (10–50 μg/mouse) in atherosclerosis-prone mice induces atherosclerosis 6–11 . Our laboratory has demonstrated that antagonizing Toll-like receptor (TLR)4, the receptor for LPS, reduces atherosclerosis 12, 13 . Furthermore, it has been shown that deficiency of either TLR4 or myeloid differentiation primary response 88 (MyD88), an adaptor protein that links TLR4 to downstream signaling pathways, attenuated atherosclerosis 14–16 .…”

Epigenetics and innate immunity: the ‘unTolld’ story

“…In addition, polymorphisms in tlr4 have also been associated with psoriatic arthritis 34 and the development of rheumatoid arthritis 35 . Although recent mouse studies have shown that TLR4 antagonists can reduce atherogenesis in mice with type‐2 diabetes 36 …”