Bioactive lipids such as ceramide and its downstream metabolites sphingosine and sphingosine-1-phosphate(S1P) mediate critical biologic responses including inflammation and cancer1. Thus the enzymes regulatinglipid metabolism are intriguing therapeutic targets. The long-term goal of this project is to define the role of thebioactive sphingolipid metabolizing enzyme acid ceramidase (AC) in colitis and colitis-associated cancer (CAC)and determine whether targeting this enzyme could serve as a novel anti-inflammatory/anti-CAC therapy. The PIs laboratory has an established track record of expertise in sphingolipid metabolism and function23.Our recent work has begun to uncover a specific and very unique role for myeloid (Mye) AC in colitis and CAC.Using dextran sodium sulfate (DSS)-induced colitis and azoxymethane (AOM)/DSS-induced CAC in murinemodels we found that AC expression is increased in the inflammatory infiltrate but not in the colon epithelium.Similarly we observed increased AC expresion in tissue macrophages in humans with colitis and colon cancer.In conditional knockout mice deletion of AC in myeloid cells (Mye AC cKO) but not intestinal epithelial cellsdecreased immune infiltrate and protected mice from colitis and CAC. Moreover we found that our AC-specificinhibitor LCL521 attenuates inflammation in a chronic colitis model (IL10 deficient mice). Finally our newestpreliminary data using bone marrow derived macrophages (BMDMs) from Mye AC cKO mice strongly hint thatMye AC may be required for inflammatory responses in these cells. Together these data suggest that Mye ACplays a large role the development of colitis and CAC. Based on our substantial preliminary data we hypothesize that loss of Mye AC activity is protective againstcolitis and CAC by modulating colonic inflammatory infiltrate and that targeting Mye AC may result in noveldisease-modifying therapy in colitis and CAC. This hypothesis will be tested by the following Specific Aims:Specific Aim 1. Establish that Mye AC cKO protects from chronic colitis and CAC in vivo.Specific Aim 2. Determine the mechanisms by which loss of Mye AC protects from chronic colitis in vivoand probe these mechanisms in cells.Specific Aim 3. Advance pharmacologic inhibition of AC as a novel colitis and CAC target.The significance of these studies lies in the unique role of AC as the ceramidase that is clearly important in colitisand CAC and the potential for AC as a novel therapeutic target. Identifying the mechanisms by which ACregulates chronic colitis and CAC with specific focus on Mye AC is a crucial first step in the design of noveltherapies targeting this pathway. In addition the studies that target AC in specific mouse models of colitis andCAC will allow us to begin to translate our studies into clinical therapeutic approaches in the very near future.