Browsing by Author "Greicius, Gediminas"
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Item Open Access PDGFRα+ pericryptal stromal cells are the critical source of Wnts and RSPO3 for murine intestinal stem cells in vivo.(Proceedings of the National Academy of Sciences of the United States of America, 2018-04) Greicius, Gediminas; Kabiri, Zahra; Sigmundsson, Kristmundur; Liang, Chao; Bunte, Ralph; Singh, Manvendra K; Virshup, David MWnts and R-spondins (RSPOs) support intestinal homeostasis by regulating crypt cell proliferation and differentiation. Ex vivo, Wnts secreted by Paneth cells in organoids can regulate the proliferation and differentiation of Lgr5-expressing intestinal stem cells. However, in vivo, Paneth cell and indeed all epithelial Wnt production is completely dispensable, and the cellular source of Wnts and RSPOs that maintain the intestinal stem-cell niche is not known. Here we investigated both the source and the functional role of stromal Wnts and RSPO3 in regulation of intestinal homeostasis. RSPO3 is highly expressed in pericryptal myofibroblasts in the lamina propria and is several orders of magnitude more potent than RSPO1 in stimulating both Wnt/β-catenin signaling and organoid growth. Stromal Rspo3 ablation ex vivo resulted in markedly decreased organoid growth that was rescued by exogenous RSPO3 protein. Pdgf receptor alpha (PdgfRα) is known to be expressed in pericryptal myofibroblasts. We therefore evaluated if PdgfRα identified the key stromal niche cells. In vivo, Porcn excision in PdgfRα+ cells blocked intestinal crypt formation, demonstrating that Wnt production in the stroma is both necessary and sufficient to support the intestinal stem-cell niche. Mice with Rspo3 excision in the PdgfRα+ cells had decreased intestinal crypt Wnt/β-catenin signaling and Paneth cell differentiation and were hypersensitive when stressed with dextran sodium sulfate. The data support a model of the intestinal stem-cell niche regulated by both Wnts and RSPO3 supplied predominantly by stromal pericryptal myofibroblasts marked by PdgfRα.Item Open Access Wnt signaling suppresses MAPK-driven proliferation of intestinal stem cells.(The Journal of clinical investigation, 2018-08) Kabiri, Zahra; Greicius, Gediminas; Zaribafzadeh, Hamed; Hemmerich, Amanda; Counter, Christopher M; Virshup, David MIntestinal homeostasis depends on a slowly proliferating stem cell compartment in crypt cells, followed by rapid proliferation of committed progenitor cells in the transit amplifying (TA) compartment. The balance between proliferation and differentiation in intestinal stem cells (ISCs) is regulated by Wnt/β-catenin signaling, although the mechanism remains unclear. We previously targeted PORCN, an enzyme essential for all Wnt secretion, and demonstrated that stromal production of Wnts was required for intestinal homeostasis. Here, a PORCN inhibitor was used to acutely suppress Wnt signaling. Unexpectedly, the treatment induced an initial burst of proliferation in the stem cell compartment of the small intestine, due to conversion of ISCs into TA cells with a loss of intrinsic ISC self-renewal. This process involved MAPK pathway activation, as the proliferating cells in the base of the intestinal crypt contained phosphorylated ERK1/2, and a MEK inhibitor attenuated the proliferation of ISCs and their differentiation into TA cells. These findings suggest a role for Wnt signaling in suppressing the MAPK pathway at the crypt base to maintain a pool of ISCs. The interaction between Wnt and MAPK pathways in vivo has potential therapeutic applications in cancer and regenerative medicine.