Insulin inhibits IL-10-mediated regulatory T cell function: implications for obesity

Area of Science:

• Immunology
• Metabolic Syndrome
• Endocrinology

Background:

• Chronic inflammation is linked to metabolic dysfunction in obesity and type 2 diabetes.
• Overproduction of proinflammatory cytokines by innate immune cells impacts metabolism, with TNF-α impairing insulin sensitivity.

Purpose of the Study:

• To investigate if hyperinsulinemia, a state of high insulin levels, contributes to chronic adipose inflammation.
• To determine the effect of insulin on regulatory T cells (Tregs) and their inflammatory suppression capabilities.

Main Methods:

• Examined insulin receptor expression on Tregs.
• Investigated the impact of high insulin levels on Treg-mediated suppression of inflammatory responses via the AKT/mTOR pathway.
• Analyzed Treg function in a diet-induced obesity mouse model.

Main Results:

• Tregs express the insulin receptor.
• High insulin levels inhibit IL-10 production and Treg-mediated suppression of TNF-α production by macrophages.
• Insulin's effect on Tregs was specific to IL-10 production, not altering CTLA-4, CD39, or TGF-β.
• Obese mice showed decreased IL-10 and increased IFN-γ production by Tregs in visceral adipose tissue.

Conclusions:

• Hyperinsulinemia impairs Treg function, specifically IL-10 production.
• This impaired Treg function may contribute to obesity-associated inflammation through a novel insulin-mediated pathway.
• Findings suggest a feedback loop where hyperinsulinemia exacerbates inflammation in obesity.