Abstract
Macrophage infiltration is a critical determinant of high-fat diet induced adipose tissue inflammation and insulin resistance. The precise mechanisms underpinning the initiation of macrophage recruitment and activation are unclear. Macrophage migration inhibitory factor (MIF), a pro-inflammatory cytokine, displays chemokine-like properties. Circulating MIF levels are elevated during obesity however its role in high-fat diet induced adipose inflammation and insulin resistance remains elusive. Wildtype and MIF−/− C57Bl\\6J mice were fed chow or high-fat diet. Body weight and food intake was assessed. Glucose homeostasis was monitored by glucose and insulin tolerance tests. Adipose tissue macrophage recruitment and adipose tissue insulin sensitivity was evaluated. Cytokine secretion from stromal vascular fraction, adipose explants and bone marrow macrophages was measured. Inflammatory signature and insulin sensitivity of 3T3-L1-adipocytes co-cultured with wildtype and MIF−/− macrophage was quantified. Hepatic triacylglyceride levels were assessed. MIF−/− exhibited reduced weight gain. Age and weight-matched obese MIF−/− mice exhibited improved glucose homeostasis coincident with reduced adipose tissue M1 macrophage infiltration. Obese MIF−/− stromal vascular fraction secreted less TNFα and greater IL-10 compared to wildtype. Activation of JNK was impaired in obese MIF−/−adipose, concomitant with pAKT expression. 3T3-L1-adipocytes cultured with MIF−/− macrophages had reduced pro-inflammatory cytokine secretion and improved insulin sensitivity, effects which were also attained with MIF inhibitor ISO-1. MIF−/− liver exhibited reduced hepatic triacyglyceride accumulation, enhanced pAKT expression and reduced NFκB activation. MIF deficiency partially protects from high-fat diet induced insulin resistance by attenuating macrophage infiltration, ameliorating adipose inflammation, which improved adipocyte insulin resistance ex vivo. MIF represents a potential therapeutic target for treatment of high-fat diet induced insulin resistance.
Highlights
Adipose tissue inflammation is central to the pathogenesis of obesity associated insulin resistance (IR), type 2 diabetes and hepatic steatosis [1,2,3]
migration inhibitory factor (MIF) deficiency partially protects mice from High-fat diet (HFD)-induced obesity and insulin resistance The severity of HFD-induced IR was less in obese MIF2/2 mice, with significantly lower GTT and ITT compared to obese WT mice (Figure 1A–D)
We measured the weight of various organs and observed both liver and epididymal weights were significantly greater in obese WT compared to MIF2/2 mice (Table 1)
Summary
Adipose tissue inflammation is central to the pathogenesis of obesity associated insulin resistance (IR), type 2 diabetes and hepatic steatosis [1,2,3]. High-fat diet (HFD)-induced adipose tissue expansion is accompanied by a progressive infiltration of macrophages [4,5]. Pro-inflammatory cytokines including TNFa [10] and IL-6 produced by adipose tissue macrophages (ATM) exacerbate local inflammation promoting IR via down-regulation of IRS-1 and GLUT-4 [2]. ATM infiltration and subsequent local inflammation is paramount for induction of IR, the signals responsible for triggering macrophage recruitment remain ambiguous. Emerging data has highlighted the significance of adipose tissuederived chemokines in driving macrophage recruitment during obesity. Deletion of CC-chemokine ligand CCL2/monocyte chemoattractant protein-1 (MCP-1) or its receptor CCR2 attenuates ATM recruitment concurrent with improved adipose tissue inflammation and systemic insulin sensitivity in vivo [12,13,14,15].
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