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RBP4 activates antigen-presenting cells, leading to adipose tissue inflammation and systemic insulin resistance.

ABSTRACT: Insulin resistance is a major cause of diabetes and is highly associated with adipose tissue (AT) inflammation in obesity. RBP4, a retinol transporter, is elevated in insulin resistance and contributes to increased diabetes risk. We aimed to determine the mechanisms for RBP4-induced insulin resistance. Here we show that RBP4 elevation causes AT inflammation by activating innate immunity that elicits an adaptive immune response. RBP4-overexpressing mice (RBP4-Ox) are insulin resistant and glucose intolerant and have increased AT macrophage and CD4 T cell infiltration. In RBP4-Ox, AT CD206(+) macrophages express proinflammatory markers and activate CD4 T cells while maintaining alternatively activated macrophage markers. These effects result from direct activation of AT antigen-presenting cells (APCs) by RBP4 through a JNK-dependent pathway. Transfer of RBP4-activated APCs into normal mice is sufficient to induce AT inflammation, insulin resistance, and glucose intolerance. Thus, RBP4 causes insulin resistance, at least partly, by activating AT APCs that induce CD4 T cell Th1 polarization and AT inflammation.

SUBMITTER: Moraes-Vieira PM

PROVIDER: S-EPMC4078000 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature

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RBP4 activates antigen-presenting cells, leading to adipose tissue inflammation and systemic insulin resistance.

Moraes-Vieira Pedro M PM Yore Mark M MM Dwyer Peter M PM Syed Ismail I Aryal Pratik P Kahn Barbara B BB

Cell metabolism 20140301 3

Insulin resistance is a major cause of diabetes and is highly associated with adipose tissue (AT) inflammation in obesity. RBP4, a retinol transporter, is elevated in insulin resistance and contributes to increased diabetes risk. We aimed to determine the mechanisms for RBP4-induced insulin resistance. Here we show that RBP4 elevation causes AT inflammation by activating innate immunity that elicits an adaptive immune response. RBP4-overexpressing mice (RBP4-Ox) are insulin resistant and glucose ...[more]

PMID: 24606904

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Project description:Obesity is accompanied by numerous systemic and tissue-specific derangements, including systemic inflammation, insulin resistance, and mitochondrial abnormalities in skeletal muscle. Despite growing recognition that adipose tissue dysfunction plays a role in obesity-related disorders, the relationship between adipose tissue inflammation and other pathological features of obesity is not well-understood. We assessed macrophage populations and measured the expression of inflammatory cytokines in abdominal adipose tissue biopsies in 39 nondiabetic adults across a range of body mass indexes (BMI 20.5-45.8 kg/m2). Skeletal muscle biopsies were used to evaluate mitochondrial respiratory capacity, ATP production capacity, coupling, and reactive oxygen species production. Insulin sensitivity (SI) and β cell responsivity were determined from test meal postprandial glucose, insulin, c-peptide, and triglyceride kinetics. We examined the relationships between adipose tissue inflammatory markers, systemic inflammatory markers, SI, and skeletal muscle mitochondrial physiology. BMI was associated with increased adipose tissue and systemic inflammation, reduced SI, and reduced skeletal muscle mitochondrial oxidative capacity. Adipose-resident macrophage numbers were positively associated with circulating inflammatory markers, including tumor necrosis factor-α (TNFα) and C-reactive protein (CRP). Local adipose tissue inflammation and circulating concentrations of TNFα and CRP were negatively associated with SI, and circulating concentrations of TNFα and CRP were also negatively associated with skeletal muscle oxidative capacity. These results demonstrate that obese humans exhibit increased adipose tissue inflammation concurrently with increased systemic inflammation, reduced insulin sensitivity, and reduced muscle oxidative capacity and suggest that adipose tissue and systemic inflammation may drive obesity-associated metabolic derangements.NEW AND NOTEWORTHY Adipose inflammation is proposed to be at the nexus of the systemic inflammation and metabolic derangements associated with obesity. The present study provides evidence to support adipose inflammation as a central feature of the pathophysiology of obesity. Adipose inflammation is associated with systemic and peripheral metabolic derangements, including increased systemic inflammation, reduced insulin sensitivity, and reduced skeletal muscle mitochondrial respiration.

Project description:AIMS/HYPOTHESIS:Absent in melanoma 2 (AIM2) is a cytosolic sensor for double-stranded DNA and a tumour suppressor. Binding of double-stranded DNA to AIM2 forms the AIM2 inflammasome, leading to activation of caspase-1 and production of IL-1? and IL-18. Although inflammasome-independent effects of AIM2 have been reported, its role in energy metabolism is unknown. We aimed to evaluate the effect of AIM2 in energy metabolism and glucose homeostasis. METHODS:Male and female whole body Aim2 knockout (Aim2-/-) mice were used in the current study. Body weight, food intake, body composition, energy expenditure, fasting blood glucose levels, GTT and body temperature were measured at indicated time points. RNA sequencing was carried out on gonadal white adipose tissue (gWAT) in 14-month-old female mice. mRNA and protein levels in tissues were analysed by quantitative real-time PCR and immunoblot. Immune cell infiltration in gWAT was examined by flow cytometry. Stromal vascular fractions isolated from gWAT were used to investigate adipocyte differentiation. RESULTS:Male and female Aim2-/- mice were obese compared with wild-type controls from 7 weeks of age until 51 weeks of age, with increased adiposity in both subcutaneous and visceral fat depots. While there were no differences in food intake, Aim2-/- mice demonstrated decreased energy expenditure and impaired brown adipose tissue function compared with wild-type controls. Fasting glucose and insulin levels were elevated, and Aim2-/- mice were glucose intolerant on intraperitoneal GTT. RNA sequencing revealed marked upregulation of the IFN-inducible gene Ifi202b, which encodes protein 202 (p202) and elevated inflammatory signalling in gWAT of Aim2-/- mice. Increased infiltration of total and Ly6Clow monocytes was noted at 8 weeks of age in gWAT, before the onset of obesity and insulin resistance. Ifi202b knockdown blocked adipogenesis in stromal vascular fractions and reduced inflammation in bone marrow-derived macrophages, demonstrating a key role of p202 in mediating the increased adipogenesis and inflammation in Aim2-/- mice. CONCLUSIONS/INTERPRETATION:These results demonstrate a fundamental role for AIM2 in energy metabolism, inflammation and insulin resistance. Our studies establish a novel link between the innate immunity proteins, AIM2 and p202, and metabolism.

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Dataset Information

RBP4 activates antigen-presenting cells, leading to adipose tissue inflammation and systemic insulin resistance.

Publications

RBP4 activates antigen-presenting cells, leading to adipose tissue inflammation and systemic insulin resistance.

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