Abstract 693: TLR3 Modulates Inflammation and Lipolysis in Visceral Adipose Tissue in High Fat Diet-fed Mice

Abstract

Inflammation in insulin sensitive tissues, the visceral adipose tissue (VAT), is a central abnormality in obesity/insulin resistance (IR), with recruitment of innate immune cells such as monocytes into adipose tissue driving the development of glucose and lipoprotein dysregulation. We evaluated the role of Toll like receptor 3 (TLR3) in high fat diet-induced obesity and IR. Wild-type C57BL/6 and TLR3 -/- male mice were fed a high fat diet for 15 weeks. High fat feeding resulted in increased TLR3 expression in VAT. TLR3 deficiency attenuated the high fat diet-increased body weight, fasting blood glucose, whole body IR and impaired glucose tolerance. Morphologically, high fat diet induced adiposity and enlarged adipocyte area in VAT, which were attenuated in TLR3 -/- mice. Functionally, high fat diet induced dysregulation of adipocytokines such as downregulation of adiponectin and resistin, upregulation of leptin in VAT, with the disturbance of adiponectin and leptin was corrected in TLR3-/- mice. In addition, high fat diet inhibited insulin pathway, accompanied with decreased phosphorylation of AMPK and lowered expression of lipolysis-related enzymes such as HSL and ATGL, both at the mRNA levels and protein levels, all of which was corrected by TLR3 deficiency. Finally, TLR3 deletion suppressed the high fat feeding-mediated macrophage polarization, evidenced by increased type M1 macrophage (F4/80+/CD11c+/CD206-) infiltration and upregulation of M1 genes such as IL-6 and TNFα. TLR3 modulates high fat diet-induced IR and obesity by suppressing M1 macrophage-mediated VAT inflammation, facilitating secretion of adipocyte-derived hormones, thus enhanced AMPK activity and adipose lipolysis. These findings provide new mechanistic links between dietary factors-mediated IR and associated abnormalities in lipid metabolism and adipose inflammation.