Project Summary/Abstract Black Americans experience disproportionality high rates of obesity, insulin resistance and diabetes and may derive fewer metabolic benefits from weight loss compared to their White counterparts. The mechanisms responsible for these differences are poorly understood as Black men and women are typically underrecruited in clinical studies. Intermuscular adipose tissue (IMAT) is marbled within and next to skeletal muscle and can cause muscle insulin resistance by bathing the muscles in inflammatory cytokines, adipokines, eicosanoids, and free fatty acids (the IMAT secretome). The literature shows that Black individuals have greater IMAT content and adipose tissue inflammation compared to White individuals. Preliminary data show that IMAT has a similar or worse secretome as visceral adipose tissue towards muscle insulin sensitivity, with secretion of inflammatory cytokines and eicosanoids contributing to muscle insulin resistance. Our central hypothesis is that IMAT secretion of inflammatory cytokines is greater in Black than White participants with less improvement following weight loss, contributing to the racial differences in insulin sensitivity. The purposed research addresses the critical need to elucidate disease mechanisms in Black individuals by comparing changes in the IMAT secretome before and after weight loss between Black and White participants. The rationale is that we will generate new information for differences by race in IMAT paracrine signaling and generate new information for changes in the IMAT secretome by race after weight loss. By identifying differences between obese Black and White participants in the IMAT secretome before and after weight loss, this critical research can support development of tailored diabetes interventions and treatments. We propose two specific aims: Aim1: Evaluate the potency of IMAT paracrine signaling to decrease insulin sensitivity in Black and White participants. We hypothesize IMAT secretes greater inflammatory cytokines and eicosanoids linked to decreased insulin sensitivity in Black compared to White participants. In vitro experiments will measure the potency of the IMAT secretome to cause insulin resistance by race. Aim 2: Determine the effect of weight loss on the IMAT content and paracrine signaling in Black versus White participants. We again hypothesize that weight loss will diminish IMAT secretion of inflammatory cytokines and eicosanoids linked to decreased insulin sensitivity, but this decrease will be less in Black compared to White individuals. Participants with obesity will be studied before and after a 12-week weight loss intervention. IMAT will be sampled using an ultrasound-guided IMAT biopsy technique, insulin sensitivity measured using hyperinsulinemic-euglycemic clamps, and IMAT content measured using MRI. IMAT will be cultured to generate conditioned media, followed by conditioned media analyses and testing of its direct metabolic effects in vitro. This...