Changes in the abundance and phenotypes of adipose tissue immune cells are a major determinant of systemic inflammation and insulin resistance during excess weight gain. Adipocyte expression of the class II major histocompatibility complex (MHCII) occurs early during high-fat diet (HFD) challenge and parallels pro- inflammatory changes in MHCII-activated CD4+ adipose resident T cells (ARTs) implicating the adipocyte as an instigator of obesity-induced inflammation. Adipocyte-specific MHCII null (aMHCII-/-) mice created to test this hypothesis 1) developed substantially less visceral adipose tissue (VAT) inflammation than their wild-type (WT) littermates when challenged with HFD, despite identical changes in body weight and %body fat, 2) had markedly more VAT regulatory T cells (Tregs), but not in other peripheral sites; 3) were more insulin sensitive with better glucose homeostasis and 4) when bred into an atherosclerosis prone LDLR-/- background, attenuated accelerated atherosclerosis without affecting plasma cholesterol and triglyceride levels. Tregs are a major component of the CD4+ ART population in lean mice, where they suppress inflammation to maintain normal VAT metabolism, but dramatically decrease during HFD-challenge. However, VAT Tregs are preserved in HFD-fed aMHCII-/- mice, which likely explains the improved metabolic and cardiovascular phenotype in these mice. The aMHCII-/- mutation, thus, provides a unique opportunity to specifically alter adipose inflammation, independent of obesity, dyslipidemia, and changes in peripheral T cells to investigate its impact on obesity- induced complications, particularly atherosclerosis. We hypothesize that decreased adipose inflammation attenuates atherosclerosis even in the presence of obesity.
Specific Aims will address: 1) the effect of A) aMHCII-deficiency and B) visceral adipose tissue (VAT)-specific Treg depletion (via cells with defective VAT Treg homeostasis or an IL-33 receptor blocking antibody which inhibits IL-33-induced VAT Treg proliferation) on diet-induced atherosclerosis; 2) whether A) constitutive, adipocyte-specific MHCII overexpression promotes adipose inflammation to enhance atherosclerosis, and B) administration of IL-33 attenuates atherosclerosis through a VAT Treg-dependent mechanism; and 3) changes in the immune cell composition and molecular phenotypes in aortic lesions in mice with and without aMHCII mutations using T cell flow analyses of aorta, laser capture microdissection of plaque macrophages, and investigation of macrophage trafficking from VAT to aorta. The results of this investigation using adipocyte MHCII knock-in/knock-out models and several novel approaches to specifically alter VAT, but not peripheral, Tregs will determine the contributions of adipose tissue inflammation and VAT Tregs to the pathogenesis of obesity-associated atherosclerosis. This mechanistic insight sets the stage for development of better immune-based therapeutic strategies to combat CVD in the setting of obesity.
Each year cardiovascular disease (CVD) claims the lives of millions of people who are overweight or obese, particularly if they have metabolic syndrome or diabetes, which contribute to an even earlier CVD demise. CVD is a major pro-inflammatory disease aggravated by inflammatory signals from adipose tissue. Our goal is to define the adipose tissue immune microenvironment and decipher its communication with blood vessels to accelerate atherosclerosis. The results of this investigation could identify new immune-based treatment modalities for CVD in the setting of obesity.