Coordinated matricellular regulation of intestinal injury repair and regeneration - PROJECT SUMMARY The intestinal epithelium, constantly challenged by environmental toxins, chemicals, or pathogens, is continually being renewed and regenerated to maintain gut homeostasis through the proliferation and differentiation of intestinal stem cells (ISCs). When this regenerative process is impaired, particularly in response to injury, chronic inflammation and disease states such as inflammatory bowel disease may result. The matricellular protein CCN1 has emerged as an overarching regulator of multiple functions in intestinal repair and regeneration through its direct interactions with distinct integrin receptors in disparate cell types. Recently, we have shown that CCN1 coordinately regulates ISC proliferation and differentiation into distinct epithelial cell types through the regulation of Wnt and Notch signaling, in part by activating YAP, which contributes to epithelial regeneration in homeostasis. In our new supporting data, we observed that (1) Mice with Ccn1 deletion in Lgr5+ ISCs and knock-in mice expressing integrins αv-binding defective CCN1 suffer high mortality and impaired epithelial regeneration in dextran sulfate sodium (DSS)-induced injury. (2) Moreover, these knock-in mice fail to restore the ISC pool after diphtheria toxin receptor-mediated ablation of the Lgr5+ ISCs, indicating that CCN1 may be required for the reprogramming or dedifferentiation of epithelial cells into ISCs. (3) Although senescent cells are generally thought to be deleterious, mice treated with the senolytic drug ABT-263 to eliminate senescent cells sustain impaired epithelial restitution after DSS injury, and similar defects are observed in knock-in mice in which Ccn1 is unable to bind integrin α6β1 and are therefore unable to induce stromal fibroblast senescence. These findings suggest that senescent fibroblasts promote intestinal epithelial repair and CCN1 may be a key inducer of senescence. Based on these results, we will scrutinize the hypothesis that CCN1 is an overarching regulator of intestinal injury repair by controlling both the dedifferentiation of epithelial cells to restore the ISC pool and the induction of fibroblast senescence in the stroma through integrins αv and α6β1, respectively, with the following specific aims: (Aim 1) To analyze how CCN1 regulates cell dedifferentiation to restore the ISC pool upon injury and dissect the distinct functions of CCN1 and YAP in a regulatory loop to control this process. (Aim 2) To investigate the role of CCN1-induced stromal cell senescence in epithelial regeneration via the release of the senescence regenerative factors (SRFs). These studies will yield new insights into a powerful endogenous repair program that coordinately regulates complex cellular processes in various cell types for intestinal injury repair and pave the way for novel targeted therapeutics that promote intestinal repair and regeneration following injury.
