Hypoxic preconditioning produces differential expression of hypoxia-inducible factor-1alpha (HIF-1alpha) and its regulatory enzyme HIF prolyl hydroxylase 2 in neonatal rat brain.
Hypoxic preconditioning can protect the brain against a subsequent damaging ischaemic insult. Mild hypoxia alone seems not sufficient to cause neuronal injury, but can induce changes in gene expression and intracellular signalling pathways and the hypoxia-inducible transcription factor (HIF-1) is a key modulator of these genes. Recently, a family of HIF prolyl hydroxylase enzymes (PHDs) has been shown to regulate HIF-1 function by controlling its degradation. Since PHD-2 is thought to be the predominant isoform which regulates HIF-1, we have investigated whether preconditioning with hypoxia can affect levels of PHD-2 and HIF-1alpha proteins to elucidate roles for the HIF-1/PHD-2 system in the neuroprotection conferred by hypoxic preconditioning. Sprague-Dawley rats (postnatal Day 6 (p6)) were exposed to preconditioning with hypoxia (3 h, 8% oxygen) or normoxia (3 h, room air) at various times (0, 0.5, 2, 4, 16 and 24 h) after reoxygenation, brains were obtained for Western blot and immunohistochemical analyses of PHD-2 and HIF-1alpha proteins. Western blotting studies demonstrate a significant increase in the expression of PHD-2 ( approximately 1.8-2-fold increase, at 0.5, 16 and 24 h after reoxygenation; p < 0.01) and HIF-1alpha (approximately 1.7-fold increase immediately after hypoxia; p < 0.05) proteins following hypoxic preconditioning relative to normoxic control tissue. Similar results were observed in immunohistochemical studies examining PHD-2 and HIF-1alpha proteins. Our study demonstrated for the first time that in vivo exposure to systemic hypoxia elevates the expression of PHD-2 protein in brain and it is likely that enhancing HIF-1 function by inhibition of PHD activity is involved in the protective effect conferred by hypoxic preconditioning in neonatal rat brain.
Jones
Nicole M
NM
Brain Injury and Repair Program, Howard Florey Institute, The University of Melbourne, Parkville, Vic., Australia. n.jones@hfi.unimelb.edu.au
Lee
Elizabeth M
EM
Brown
Timothy G
TG
Jarrott
Bevyn
B
Beart
Philip M
PM
D000818:Animals; D000831:Animals, Newborn; D015153:Blotting, Western; D002540:Cerebral Cortex / Q000378:metabolism / Q000503:physiopathology*; D002534:Hypoxia, Brain / Q000378:metabolism / Q000503:physiopathology*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis*; D007150:Immunohistochemistry; D007700:Kinetics; D011393:Procollagen-Proline Dioxygenase / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values
D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D011393:Procollagen-Proline Dioxygenase