Abstract 12870: Macrophage Toll-like Receptor 9 Signaling Contributes to the Development of Insulin Resistance through the Promotion of Inflammation in Adipose Tissue
Background: Chronic inflammation closely associates with insulin resistance. Toll-like receptor (TLR)9 recognizes bacterial unmethylated DNA and plays a role in innate defense, although it can also provoke inflammation in response to fragmented DNA from mammalian cells, contributing to the pathogenesis of autoimmune diseases. The role of TLR9 in the development of insulin resistance, however, remains unknown. This study tested the hypothesis that TLR9 signal promotes inflammation in adipose tissue and causes insulin resistance in high-fat fed mice.
Methods and Results: We fed TLR9 deficient (TLR9 KO) mice or wild type (WT) mice a high-fat diet (60% fat) for 12 weeks.
High-fat feeding increased TLR9 expression in adipose tissue. Results of quantitative PCR demonstrated macrophage fraction in adipose tissue dominantly expressed TLR9. Weight of epididymal fat pad and liver, and plasma lipid levels were similar between two groups, however results of glucose tolerance test and insulin tolerance test at 10 weeks after initiation of the diet demonstrated that disruption of TLR9 improved insulin resistance (P≤0.05). TLR9 KO mice showed less MCP-1 expression in adipose tissue which resulted in less macrophage infiltration (P≤0.05). Adipocytes obtained from TLR9 KO mice showed higher levels of adiponectin and PPAR-γ compared with those from WT mice (P≤0.05, respectively). In vitro experiments using thioglycolate-stimulated peritoneal macrophages demonstrated that CpG ODN, synthetic oligonucleotides which contain unmethylated CpG, could promote the expression of pro-inflammatory molecules (e.g., MCP-1 and TNF-α) in WT macrophages (P≤0.05) but not in TLR9 KO macrophages. Furthermore, conditioned medium from 3T3-L1 adipocytes promoted the expression of these inflammatory molecules only in WT macrophages (P≤0.05). Conditioned medium from TNF-α treated 3T3-L1 adipocytes further stimulates these inflammatory responses in WT macrophages, however TLR9 KO macrophages did not show these responses.
Conclusion: Our results suggested that TLR9 mediates macrophage-adipocyte interaction and contributes to the development of insulin resistance by promoting inflammation in adipose tissue.
- © 2013 by American Heart Association, Inc.