Monday, April 29, 2024
4/29/2024
Project Summary Inflammatory bowel disorders and necrotizing enterocolitis represent insufficient epithelial repair, stemming from failure of proper maintenance and expansion of resident intestinal stem cells (ISCs). ISCs are housed in invaginations called crypts that expand during development and repair after damage in a process called crypt fission. Little is understood of how crypt fission is mediated, however, signaling factors including BMP inhibitors and non-canonical Wnts are implicated. ISCs are regulated and maintained by similar signaling factors secreted by a surrounding mesenchymal environment called “the niche”. It is unclear what role the niche plays in mediating crypt fission. The niche is composed of a myriad of different cell types, including PDGFRA+ intestinal subepithelial myofibroblasts (ISEMFs) and smooth muscle, that are anatomically, molecularly, and functionally distinct. ISEMFs occur closest to the epithelial-mesenchymal barrier, express both BMPs and non-canonical Wnts; smooth muscle populations occur beneath crypts and express abundant BMP inhibitors. Preliminary data suggests that signaling from both ISEMFs and smooth muscle is required for proper crypt fission. Smooth muscle ablation reduces crypt fission during development; however, functional co-culture assays show limited smooth muscle support of organoid growth in vitro. ISEMFs, on the other hand, promote different organoid co-culture phenotypes depending on level of BMP inhibitor added: in low levels, ISEMFs promote differentiation, and in high levels, promote increased crypt budding, aka fission. My hypothesis is that crypt fission is a process coordinated by the signaling activities of both ISEMFs and smooth muscle. In Aim 1, I will investigate the anatomical and functional profiles of ISEMFs and smooth muscle in crypt fission. I will determine when these cells occur during instances of crypt fission, including postnatal development and repair after damage, test the requirement of ISEMFs in promoting crypt fission in vivo, and sufficiency of ISEMFs and smooth muscle in directing crypt fission in vitro. In Aim 2, I will test whether ISEMFs direct crypt fission via non-canonical Wnt signaling. Using both in vitro and in vivo methods, I will determine the specific function of ISEMFs in directing crypt fission via non-canonical Wnt5a. Together, these studies will provide fundamental insights into the collective regulation of crypt fission via distinct mesenchymal niche populations during development and epithelial repair, aiding our understanding of fundamental intestinal biology and disease.
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