Molecular mechanisms of sexually dimorphic traits of interstitial cells of Cajal and their role in gastrointestinal neuromuscular disorders - PROJECT SUMMARY Female sex is a risk factor for gastrointestinal (GI) motor disorders such as gastroparesis (GP) and slow-transit constipation and disorders of gut-brain interaction, which include functional dyspepsia and irritable bowel syndrome and also involve altered motility. Notably, GP, defined by delayed gastric emptying without mechanical obstruction and severe symptoms, nutritional compromise, anxiety, depression, and poor quality of life, is four times more common in women than men, most often complicating diabetes. The molecular basis of female predominance in these disorders remains unclear and a major impediment to finding a cure for the patients. Interstitial cells of Cajal (ICC) are key regulators of the GI neuromuscular apparatus and have been implicated in the pathomechanisms of GP—particularly, diabetic GP—and other GI motor disorders. This project will test the hypothesis that the fundamental cause of women’s high susceptibility to diabetes- associated ICC loss and GP is the contribution of a female-biased gene regulatory circuitry, which is driven by estrogen signaling via the G protein-coupled receptor GPER1 and the noncanonical, activating Polycomb complex ncPRC1.5, to the transcriptional control of mitochondrial and ICC functions and ICC maintenance. This mode of regulation makes female ICC vulnerable to mitochondrial stress, which, if sufficiently severe, causes repression of genes involved in cell type-specific functions (Specific Aim 1). Mitochondrial stress accompanies both diabetes and immune disorders, thus our hypothesis offers a potential link between the metabolic and immune etiologies proposed for GP. In contrast, male ICC are more resistant to the transcriptional consequences of mitochondrial stress due to higher histone serotonylation, which globally amplifies gene transcription, reflecting increased “writing” of this mark due to accentuated hypoxic signaling from the male ICC’s greater reliance on oxidative phosphorylation and epigenetic repression of its “erasers” (Specific Aim 2). We will test our hypotheses by following a rigorous workflow for the discovery-based, mechanistically focused, and translationally relevant interrogation of the proposed molecular pathways. These experiments will include highly multiplexed bulk and spatial transcriptomic and epigenomic studies, which will be performed in tissues from gonadally, pharmacologically, and genetically manipulated female and male mice, in gastric tissues of male and female patients with or without diabetes and GP, and new, scalable ICC models derived from male and female patients. Findings will be mechanistically validated by RNA interference and epigenome editing in vitro and conditional deletion of genes in ICC in vivo. Pharmacological manipulation of the proposed mechanisms with nutritional supplements and repurposed drugs will be performed in previously established disease models using validated tests of gastric motor functions to demonstrate translational relevance. Results from this project will determine the fundamental mechanisms of sexual dimorphisms in ICC that contribute to the prominent sex bias of GP, with a particular focus on diabetic GP.
