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The Journal of Neuroscience, July 8, 2009, 29(27):8828-8838; doi:10.1523/JNEUROSCI.1779-09.2009

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Neurobiology of Disease
Selective Inhibition of Hypoxia-Inducible Factor (HIF) Prolyl-Hydroxylase 1 Mediates Neuroprotection against Normoxic Oxidative Death via HIF- and CREB-Independent Pathways

Ambreena Siddiq,^1,2 Leila R. Aminova,³ Carol M. Troy,⁴ Kyungsun Suh,^1,2 Zachary Messer,¹ Gregg L. Semenza,⁵ and Rajiv R. Ratan^1,2

¹Department of Neurosciences, Burke Medical Research Institute, White Plains, New York 10605, ²Department of Neurosciences, Weill Medical College of Cornell University, New York, New York 10065, ³Department of Microbiology, University of Illinois at Urbana–Champaign, Urbana, Illinois 61801, ⁴Department of Pathology, Columbia University College of Physicians and Surgeons, New York, New York 10032, and ⁵Institute for Cell Engineering and Department of Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

Correspondence should be addressed to either of the following: Dr. Ambreena Siddiq or Dr. Rajiv R. Ratan, Burke Medical Research Institute, 785 Mamaroneck Avenue, White Plains, NY 10605, Email: ams2028{at}med.cornell.edu or Email: rrr2001{at}med.cornell.edu

Oxidative stress contributes to tissue injury in conditions ranging from cardiovascular disease to stroke, spinal cord injury, neurodegeneration, and perhaps even aging. Yet the efficacy of antioxidants in human disease has been mixed at best. We need a better understanding of the mechanisms by which established antioxidants combat oxidative stress. Iron chelators are well established inhibitors of oxidative death in both neural and non-neural tissues, but their precise mechanism of action remains elusive. The prevailing but not completely substantiated view is that iron chelators prevent oxidative injury by suppressing Fenton chemistry and the formation of highly reactive hydroxyl radicals. Here, we show that iron chelation protects, rather unexpectedly, by inhibiting the hypoxia-inducible factor prolyl 4-hydroxylase isoform 1 (PHD1), an iron and 2-oxoglutarate-dependent dioxygenase. PHD1 and its isoforms 2 and 3 are best known for stabilizing transcriptional regulators involved in hypoxic adaptation, such as HIF-1 and cAMP response element-binding protein (CREB). Yet we find that global hypoxia-inducible factor (HIF)-PHD inhibition protects neurons even when HIF-1 and CREB are directly suppressed. Moreover, two global HIF-PHD inhibitors continued to be neuroprotective even in the presence of diminished HIF-2 levels, which itself increases neuronal susceptibility to oxidative stress. Finally, RNA interference to PHD1 but not isoforms PHD2 or PHD3 prevents oxidative death, independent of HIF activation. Together, these studies suggest that iron chelators can prevent normoxic oxidative neuronal death through selective inhibition of PHD1 but independent of HIF-1 and CREB; and that HIF-2, not HIF-1, regulates susceptibility to normoxic oxidative neuronal death.

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Received April 14, 2009; revised May 22, 2009; accepted June 1, 2009.

Correspondence should be addressed to either of the following: Dr. Ambreena Siddiq or Dr. Rajiv R. Ratan, Burke Medical Research Institute, 785 Mamaroneck Avenue, White Plains, NY 10605, Email: ams2028{at}med.cornell.edu or Email: rrr2001{at}med.cornell.edu

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