Decoding LRH-1 Activity in Gut Regeneration and Differentiation

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Project Summary/Abstract Background: The primary epithelial stem cell in the intestine has been known for over a decade, leading to important observations in epithelial renewal and injury recovery. These fundamental studies have demonstrated that the intestinal epithelium is a balanced continuum between stemness in the crypt base and differentiation towards the mucosal surface, with complex signaling networks influencing stemness and fate of the differentiating progenitor cells. Several groups have now shown that destruction of intestinal stem cells and/or extensive epithelial damage can be repaired by the dedifferentiation of progenitor cells. Thus, the balance between stemness and differentiation can be tipped by as yet undefined molecular mechanisms. We discovered that the nuclear receptor Liver Receptor Homolog-1 (LRH-1; NR5A2) is essential for both stem cell maintenance and for directing differentiation of the highly specialized enteroendocrine cell lineage. Therefore, this unusual transcription factor has dual roles promoting stemness and cell differentiation, making it an attractive target for elucidating the mechanisms responsible for gut epithelial renewal and healing. Approach: In this application, we will 1) determine the contribution of LRH-1 to epithelial repair and stem cell restitution in enteritis models, 2) determine how SUMOylation of LRH-1 modulates receptor function in stem and progenitor cells, and 3) determine and validate the cell-specific gut LRH-1 “targetome.” We will accomplish this through the use of lineage-traced mouse models and novel implementations of the intestinal organoid platform. Following successful completion of our aims, we will have mechanistically evaluated the contribution of a druggable nuclear receptor to 1) balancing stem cell renewal, differentiation, and restitution of damaged epithelium 2) provided the first ever detailed evaluation of SUMOylated LRH-1 in the gut, and 3) generated a bona fide LRH-1 gut targetome that will be invaluable for receptor drug development. Goals: This proposal is designed to expand upon a key finding uncovered during my funded K08 investigation and advance our mechanistic understanding of how the gut balances stemness vs differentiation during normal and diseased states. Underlying this work is our hypothesis that LRH-1 is differentially modulated within unique cellular contexts in stem and progenitor cells to drive diverse gene programs simultaneously supporting cell renewal and specialized cell differentiation. Our experiments are designed to maximally exploit the extraordinary confluence of intestinal epithelial physiology and nuclear receptor biology framed by LRH-1.