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Obesity leads to a switch in subsets of CD4(+) T cell in adipose tissue, characterized by an increase in IFNg producing Th1 cells and a decrease in anti-inflammatory regulatory T (Treg) cells, which impairs systemic insulin sensitivity. What signals these changes is unknown. Herein we demonstrate that genetic deficiency of adipocyte MHCII decreases adipose IFNg expression and increases adipose Treg abundance in obese mice, leading to reduced obesity-induced adipose inflammation and reduced insulin resistance without affecting weight gain. The preserved insulin sensitivity of high fat diet (HFD)-fed adipocyte-specific MHCII knockout (aMHCII(-/-)) mice was substantially attenuated by adipose-specific Treg ablation. Adipocytes of aMHCII(-/-) mice exhibit decreased capacity to stimulate IFNg production in Th1 cells, whereas HFD-fed IFN gamma R1(-/-) mice were more insulin sensitive and had similarly high levels of Tregs in adipose tissue as aMHCII(-/-) mice. We further show that IFNg strongly inhibits IL-33 effects to promote adipose Treg proliferation. Our results identify MHCII in adipocyte as a critical determinant of the obesity-induced adipose T cell subset switch and insulin resistance.