Deletion of Fas in adipocytes relieves adipose tissue inflammation and hepatic manifestations of obesity in mice

Abstract

Adipose tissue inflammation is linked to the pathogenesis of insulin resistance. In addition to exerting deathpromoting effects, the death receptor Fas (also known as CD95) can activate inflammatory pathways in several cell lines and tissues, although little is known about the metabolic consequence of Fas activation in adipose tissue. We therefore sought to investigate the contribution of Fas in adipocytes to obesity-associated metabolic dysregulation. Fas expression was markedly increased in the adipocytes of common genetic and diet-induced mouse models of obesity and insulin resistance, as well as in the adipose tissue of obese and type 2 diabetic patients. Mice with Fas deficiency either in all cells or specifically in adipocytes (the latter are referred to herein as AFasKO mice) were protected from deterioration of glucose homeostasis induced by high-fat diet (HFD). Adipocytes in AFasKO mice were more insulin sensitive than those in wild-type mice, and mRNA levels of proinflammatory factors were reduced in white adipose tissue. Moreover, AFasKO mice were protected against hepatic steatosis and were more insulin sensitive, both at the whole-body level and in the liver. Thus, Fas in adipocytes contributes to adipose tissue inflammation, hepatic steatosis, and insulin resistance induced by obesity and may constitute a potential therapeutic target for the treatment of insulin resistance and type 2 diabetes.

Fas activation in adipocytes impairs insulin‐stimulated glucose uptake by reducing Akt

“…Likewise, we previously reported that activation of the Fas signalling pathway in 3T3-L1 adipocytes increased the production of pro-inflammatory cytokines such as IL-6 and KC, without affecting cell viability [5]. Moreover, FasL-treated 3T3-L1 adipocytes became insulin resistant, as revealed by decreased insulin-stimulated glucose uptake and increased basal lipolysis [5]. However, the molecular mechanism involved in FasL-induced reduction in insulin-stimulated glucose uptake in 3T3-L1 adipocytes is not clear, and the present study seeks to unravel this mechanism.…”

“…1). However since Fas is still expressed in the stromal vascular fraction of adipose tissue, Fas is still present in adipose tissue of AFasKO mice [5], while it is almost completely absent in isolated adipocytes (Fig. 1A).…”

“…Adipocyte-specific Fas knockout (AFasKO) mice were generated as described [5]. All mice were housed in a specific pathogen-free environment on a 12-hour light-dark cycle and fed a high fat diet (HFD) (D12331, Research Diets, New Brunswick, USA).…”

“…White adipose tissue (retroperitoneal) was collected from wild-type and AFasKO mice [5]. Pads were rinsed in DMEM (4.5 g/L D-glucose, Invitrogen, Basel, Switzerland) containing 0.5% bovine serum albumin (Merck, Geneva, Switzerland) and minced into pieces of 2 cm 2 size and incubated for an hour at 37°C and 5% CO 2 .…”

“…Cell lysates and tissue samples were homogenized and Western blotting was performed as described previously [5]. The following primary antibodies were used: Anti-phospho-Akt (Thr308), antiphospho-Akt (Ser473), anti-Akt (Cell signalling, Beverly, MA, USA); anti-phospho-AS160, anti-IRS-1, anti-IR, anti-PPARc 2 (Santa Cruz Biotechnology, Santa Cruz, CA, USA); anti-GLUT4 and anti-GLUT1 (gift from Dr. A. Klip, The Hospital for Sick Children, Toronto, ON, Canada); anti-Fas, anti-AS160 and anti-phospho IRS-1 (Ser 307) (Upstate, Lake Placid, NY, USA).…”