PROJECT SUMMARY/ABSTRACT Similar to other complications of diabetes mellitus (DM), diabetic gastroenteropathy (DGE) reflects organ- specific dysfunctions likely due to DM-related endocrine, metabolic and immune/inflammatory disturbances. Therapies for DGE are ineffective and address the symptoms, not the disease itself. Hence, and aligned with the mission of RFA-DK-20-030, this proposal seeks to uncover the cellular and molecular mechanisms of DGp and its relative, non-ulcer dyspepsia, in carefully phenotyped patients. We focus on the links between dysimmunity, ICC, glycemia, and mitochondrial dysfunction. The specific aims are as follows: Aim 1. To analyze the relationship between the transcriptome and epigenome of single gastric immune cells, gastric emptying (GE), and glycemia in DM and non-DM patients with upper GI symptoms. Aim 2. To determine the relationship between the transcriptome and epigenome of single circulating PBMCs and single gastric immune cells in DM and non-DM patients with upper GI symptoms. Aim 3. To investigate the relationship between the transcriptome and epigenome of single gastric ICC and immune cells and single circulating PBMCs in DM and non-DM patients with upper GI symptoms. These studies will be investigated with in vivo (i.e., assessment of the DM phenotype, gastrointestinal symptoms, and GE) followed by ex vivo assessments (i.e., transcriptome and epigenome of single circulating PBMCs, single gastric CD45+ cells, and single ICC) in 45 patients undergoing sleeve gastrectomy (i.e., 15 patients in each of 3 groups: non-DM + normal GE, DM + normal GE, DM + delayed GE). This proposal is anchored by, and builds on, an established bench-to-bedside collaboration between Drs. Bharucha and Ordog which, through their complementary expertise, has enhanced our understanding of diabetic gastroparesis. It seeks to better understand the pathogenesis, and through the studies in peripheral immune cells also identify novel biomarkers, of DGE.