Control of Anoxia-Reoxygenation Responses by the O2-sensing Enzyme EGL-9 Pathway

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Anoxia (lack of oxygen) followed by reoxygenation causes severe detrimental effects in a wide variety of medical conditions, including ischemic reperfusion injury and myocardial infarction. How animals sense anoxia-reoxygenation and prevent tissue injury are fundamental and unanswered issues. The transcription factor hypoxia inducible factor (HIF) is a key cell protector against anoxia-reoxygenation (A/R)-induced injui^. The discovery of the C. elegans gene egl-9, which encodes an 02-sensing prolyl hydroxylase of HIF- 1, has led to the identification of an evolutionarily conserved pathway central for maintaining 02 homeostasis in organisms from nematodes to humans. Inhibition of mammalian HIF hydroxylase homologs of EGL-9 strongly protects from myocardial ischemia and reperfusion injury. Using automated behavioral tracking under conditions of changing 02 concentrations, I discovered a locomotory behavior called the 02-ON response and have shown that the 02-ON response can model key aspects of mammalian tissue response to ischemia-reperfusion injury. EGL-9 is essential for the 02-ON response and mediates the effect of hypoxic preconditioning on the suppression of the 02-ON response. From a series of genetic screens, I discovered CYSL-1 as a new regulator of EGL-9 and a Cytochrome P450 enzyme CYP-13A12 that generates eicosanoid signaling molecules downstream of EGL-9 to control the 02-ON response. I also performed RNA-seq and isolated C. elegans mutants that define additional novel regulators and targets of the EGL- 9/HIF-1 pathway. The overall goal of this project is to identify and characterize the novel conserved regulators of biological responses to A/R, which is modulated by the EGL-9 pathway, and determine the underlying molecular and cellular mechanisms. In the K99 phase of this project, I have established behavioral and cellular C. elegans models for ischemia-reperfusion injury and characterized CYP-13A12 as a PUFA-epoxygenase in controlling the 02-ON response. In the ROO phase of this project, I will further determine the key mechanisms by which A/R causes the 02-ON response and identify novel regulators and targets of the EGL-9 pathway, which mediates protection from A/R-induced cellular injury and behavioral response to A/R. In my new independent lab in the Cardiovascular Research Institute and Department of Physiology at UCSF in the ROO phase, the outstanding scientific environment will enable me to achieve the research goals and also foster my intellectual interaction and potential collaboration with both biologists and clinicians to seek how identified genes and mechanisms lead to new therapeutics in metabolic and ischemic human disorders. The training and support provided by K99/R00 will facilitate my transition into a fully independent and successful PI.