Authors: M. Mahidur Rahman 1; Chenge Zhang 1; Marco Marchetti 1; Chloe Kraft 1; Collin Clark 1; William Holland 2; Scott Summers 2; Bruce Edgar 1
Affiliations: 1) Huntsman Cancer Institute, University of Utah; 2) Department of Nutrition and Integrative Physiology, Diabetes and Metabolic Research Center, University of Utah, Salt Lake City, Utah, USA
Keywords: d. intestinal stem cells; x. homeostasis
Sphingolipids are an essential component of cellular architecture. Sphingolipid metabolism regulates cellular processes such as proliferation, growth, apoptosis, inflammation, and senescence. Genetic defects in the metabolism of sphingolipids are associated with several metabolic disorders, including colorectal cancer. The molecular mechanisms involved in sphingolipid metabolism-mediated intestinal stem cell (ISC) homeostasis and tumorigenesis are poorly understood. We do not know if and how the intermediate metabolites in the anabolic or catabolic processes of the ceramide metabolism regulate ISC fates in the adult midgut. To check if any of the sphingolipid metabolic enzymes are involved in the ISC homeostasis, we have genetically perturbed these enzymes in the specific cell types of the ISC lineages and the progenitor cells together. We found that the perturbation of different enzymes in the ceramide metabolism affects each cell type differently. Overall, the effects on the progenitors are manifested differently than those on the terminally differentiated enterocytes and enteroendocrine cells. For example, reducing ceramide synthases such as lace strongly affects enteroendocrine cell morphology compared to the ISCs or enteroblasts. Over-expression of the ceramidase bwa in the enteroblasts leads to robust proliferation of the ISCs, besides the increased size of the enteroblasts. On the other hand, the enterocytes are highly sensitive to any perturbation of the enzymes involved in the sphingolipid metabolism. Both increased or decreased levels of the enzymes kill the ECs, which in turn promote ISC proliferation. Since the EGFR signaling pathway is an important driver for ISC proliferation, we probed if the activated EGFR pathway would regulate the sphingolipid metabolism. Transcriptomic and lipidomic analysis of the Spitz activated EGFR pathway in the gut shows that the EGFR pathway can upregulate genes encoding ceramide biosynthesis as well as other sphingolipids. These results suggest that different enzymes and products of the sphingolipid metabolic pathway can act as signaling molecules and interact with major stem cell signaling pathways such as EGFR signaling to affect ISC homeostasis.