Project Summary Obesity now affects over 40% of the US population and is considered the most common chronic inflammatory condition. This increase in prevalence can be attributed to more sedentary lifestyles in combination with easy access to highly palatable, calorically dense foods. Health care providers often prescribe lifestyle modifications to combat obesity and the negative metabolic and cardiovascular outcomes associated with this disease; however, keeping adiposity at bay is often the greatest challenge faced by individuals. Many individuals find themselves weight cycling — periods of repeated weight loss and weight regain for a significant portion of their life, which leads to worsened glucose tolerance and cardiometabolic outcomes. The increase in adiposity that accompanies obesity is characterized by recruitment of proinflammatory immune cells into the adipose tissue that is not resolved with weight loss, suggesting that immune memory in adipose tissue contributes to diseases associated with obesity. We have developed and characterized a robust model of weight cycling in mice and observed that animals that weight cycle have worsened glucose tolerance compared to their non-weight cycled, obese, weight-matched counterparts. In obesity, the adipose tissue is characterized by an increase in CD8+ effector memory T-cells that show signs of both exhaustion and memory. In Dr. Hasty’s parent funded Merit award, the contribution of granzyme K expressing T cells to adipocyte senescence will be studied. In other work, we have shown that this memory T cell population is clonally expanded suggesting that adipose tissue “remembers” previous cycles of obesity, which may contribute to the worsened glucose tolerance seen in our weight cycled animals. To test the hypothesis that T cell memory plays a role in the metabolic outcomes we observe in weight cycling mice, Dr. Garcia has focused on the surface protein CD70, a ligand specific to antigen presenting cells that binds to the CD27 receptor on T cells promoting T cell memory formation. Her preliminary findings indicate that CD70-/- weight-cycled animals are protected from worsened glucose tolerance seen in the wild-type littermates. Therefore, this application aims to identify whether inhibiting T cell memory formation during the weight loss phase functions to prevent clonal expansion within the adipose tissue environment leading to overall reduced inflammatory potential and prevention of the impaired metabolic phenotypes seen in wild-type weight cycled mice. To determine the critical timing for memory formation, we will use a CD70 depletion antibody during the weight gain or weight loss phases and observe whether mice treated with this antibody are protected from worsened glucose tolerance. We will also use single cell RNA sequencing via the 10X Genomics Platform on adipose tissue from CD70-/- and wild-type mice to determine how loss of CD70 impacts the immune cell milieu. Ultimately, this work serves ...