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 discovey 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 to determine if manipulation of Panx1 channels affects cell clearance in vivo. For this, we take advantage of two models for which new evidence suggests cell clearance is important in normal tissue homeostasis and in disease - i.e., thymic development and airway inflammation. 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 and airway inflammation. These studies can also provide a rationale for considering Panx1 channels as a suitable target for therapeutic development.

Public Health Relevance

Failure to promptly clear dying cells in tissues has been linked to many diseases including autoimmunity, and more recently, 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 airway inflammation. The results from the proposed studies may also help selective and beneficial pharmacological targeting of pannexin channels in promoting cell clearance in vivo.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Research Project (R01)
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Neurotransporters, Receptors, and Calcium Signaling Study Section (NTRC)
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Dunsmore, Sarah
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University of Virginia
Schools of Medicine
United States
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Poon, Ivan K H; Chiu, Yu-Hsin; Armstrong, Allison J et al. (2014) Unexpected link between an antibiotic, pannexin channels and apoptosis. Nature 507:329-34
Chiu, Yu-Hsin; Ravichandran, Kodi S; Bayliss, Douglas A (2014) Intrinsic properties and regulation of Pannexin 1 channel. Channels (Austin) 8:103-9
Poon, Ivan K H; Lucas, Christopher D; Rossi, Adriano G et al. (2014) Apoptotic cell clearance: basic biology and therapeutic potential. Nat Rev Immunol 14:166-80