In nearly all tissues, there is a continual turnover of cells, usually by the process of apoptosis. In healthy tissues, the dying cells are quickly recognized and cleared by phagocytes. However, failure to promptly clear apoptotic cells leads to their secondary necrosis, release of toxic cytoplasmic contents, and inflammation within tissues. Current evidence suggests that the apoptotic cells `advertise' their presence early on in the death process, via soluble factors termed `find-me signals' to attract phagocytes, and thereby promote their prompt clearance. Initial studies from the Principal Investigators of this proposal have identified the nucleotides ATP and UTP as one type of `find-me signal' that is critical for apoptotic cell clearance in vitro and in vivo; subsequent studies led to a key discovery that the membrane protein pannexin 1 (Panx1) is the channel mediating nucleotide release from apoptotic cells. The overall hypothesis tested in this proposal is that pannexin channel-dependent release of nucleotide find-me signal from apoptotic cells, and subsequent sensing by phagocytes is important for proper cell clearance in vivo, and that disruption of the Panx1-mediated find-me signal pathway would contribute to diseases. Based on our preliminary studies, in Aim 1, we study the molecular basis of a novel Panx1 activation mechanism, seeking new understanding that will allow manipulation of `find- me` signal release via these channels.
In Aim 2, we use conditional cell-specific Panx1 knockout mice and conditional transgenic mice to determine if manipulation of Panx1 channels affects cell clearance in vivo. For this, we take advantage of a model where evidence suggests cell clearance is important in normal tissue homeostasis and in disease ? i.e., thymic development. Collectively, we expect these studies to yield new mechanistic understanding on how the regulated release of find-me signals influence cell clearance, and better define this mode of inter-cellular communication between dying cells and phagocytes, with implications for autoimmunity. These studies can also provide a rationale for considering Panx1 channels as a suitable target for therapeutic development.
Failure to promptly clear dying cells in tissues has been linked to many diseases including autoimmunity, and lung inflammation. This proposal aims to provide new mechanistic understanding on how the regulated release of find-me signals from the dying cells mediate attraction of phagocytes, and in turn, influence cell clearance, with implications for inflammation. The results from the proposed studies may also help selective and beneficial pharmacological targeting of pannexin channels in promoting cell clearance in vivo.
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