Dietary fat-activated colonocyte-macrophage ketone shuttle drives intestinal inflammation

PROJECT SUMMARY An estimated 3 million US adults suffer from inflammatory bowel disease (IBD), a group of conditions primarily including ulcerative colitis (UC) and Crohn's disease (CD) and are characterized by chronic or recurring inflammation of the gastrointestinal tract. While anti-inflammatory and immunosuppressant drugs are available to control symptoms (remission), the relapsing rate can be as high as 75% and challenges exist to effectively maintain remission and improve quality of life. Prebiotic fibers and short-chain fatty acids (SCFAs) generally have beneficial effects on intestinal physiology, and butyrate is the preferred oxidizable fuel for colonocytes. On the other hand, dietary fat exacerbates experimental colitis, and its overconsumption is associated with the global increase in the prevalence of UC. The proposed project aims to understand how excessive fat in diet perturbs colonic metabolism of butyrate and subsequently leads to elevated mucosal inflammation. One notable alternative fate of butyrate in colonocytes is to generate ketone bodies including acetoacetate (AcAc) and D-β- hydroxybutyrate (D-βHB). There is a significant knowledge gap regarding the pathophysiological function of mucosal ketone bodies. In Aim 1, we propose to test the hypothesis that terminal oxidation of butyrate in colonocytes suppresses while ketogenesis promotes intestinal inflammation. We will first perform stable isotope tracing experiments to determine butyrate’s fate during colitis. Using genetic mouse models, we will determine functional outcomes of terminally oxidative vs. ketogenic metabolism of butyrate in colitis. In Aim 2, we seek to understand how high-fat diet (including ketogenic diet) promotes the colonocyte-macrophage ketone shuttle to drive inflammation. We will test the hypothesis that the fat-sensitive PPARα signaling, by counteracting the tissue-reparative type 2 immune response, activates colonic beta-oxidation and ketogenesis to potentiate gut inflammation. Intestinal macrophages, predominantly derived from monocytes via a “waterfall” differentiation process, are the gatekeepers of mucosal homeostasis. In Aim 3, we hypothesize that the utilization of locally produced ketone body, specifically AcAc, induce the formation of Spp1+ macrophages to drive inflammation. Taken together, we expect to find that dietary fat induces the metabolic switch from butyrate terminal oxidation to ketogenesis in colonocytes, which reprograms intestinal macrophages to form a pro-inflammatory milieu. The proposed study will provide valuable insights into the metabolic underpinnings of UC etiopathogenesis and the development of future therapies and dietary advice for UC patients.