Internalization of dead cells governs intestinal stem cell activity - ABSTRACT Appropriate response to injury is critical for epithelial barrier function and organismal health. In order to restore tissue homeostasis after injury, stem cells must receive signals from their surrounding niche to adjust their proliferation and differentiation at defined stages of repair. The dynamic mammalian intestinal epithelium is a well-suited barrier to approach this problem, as it constitutes the first line of host defense against diverse forms of potentially disease-causing environmental insults and is rapidly replenished by defined populations of intestinal stem cells (ISCs). Located at the base of crypts of Lieberkühn, ISCs are relatively protected from these insults, yet need to sense external factors in order to regulate functions including stem cell state, turnover, and lineage allocation, each critical for maintaining barrier integrity. While certain signaling mechanisms that maintain some ISCs decisions are known, how ISCs adapt to environment influences that are durable and communicative to other ISCs is unclear. This proposal tests the hypothesis that ISCs engage in phagocytosis of dead cells as a means for sensing the health of intestinal tissues in which they reside, and that this mechanism underlies durable and widespread alterations in stem cell function. The supporting idea is built off of a surprising, but still untested discovery made half a century ago by pioneers in this field – that ISCs can engulf dead neighboring cells. Using modern techniques, my preliminary data support this capability and indicate that ingestion of apoptotic intestinal epithelial cells impacts ISC proliferation and differentiation. In Aim 1, I will determine the mechanism of ISC uptake of dead cells by employing discrete and bioactive cargo, spheroids derived from mouse and de-identified human samples, as well as in vivo mouse models. In Aim 2, I will test the mechanisms by which dead cell engulfment alters ISC function through cutting- edge lysosomal purification techniques, genetic models, and in vivo models of epithelial injury. The proposed research will lay the groundwork for understanding fundamental intestinal stem cell biology that forms the basis of sensing environmental cues that can trigger adaptive responses for maintaining optimal tissue and organismal health. This knowledge will pave the way for future efforts to understand and leverage key intestinal stem cell biology as therapeutic targets to address a wide range of disease states.
