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1.  Hypoxia Inducible Factor-1 (HIF-1) Independent Microvascular Angiogenesis in the Aged Rat Brain 
Brain Research  2010;1366:101-109.
Angiogenesis is a critical component of mammalian brain adaptation to prolonged hypoxia. Hypoxia-induced angiogenesis is mediated by hypoxia inducible factor-1 (HIF-1) dependent transcriptional activation of growth factors, such as vascular endothelial growth factor (VEGF). Microvascular angiogenesis occurs over a three week period in the rodent brain. We have recently reported that HIF-1α accumulation and transcriptional activation of HIF target genes in the aged cortex of 24 month F344 rats is significantly attenuated during acute hypoxic exposure. In the present study, we show that cortical HIF-1α accumulation and HIF-1 activation remains absent during chronic hypoxic exposure in the aged rat brain (24 month F344). Despite this lack of HIF-1 activation, there is no significant difference in baseline or post-hypoxic brain capillary density counts between the young (3 month F344) and old age groups. VEGF mRNA and protein levels are significantly elevated in the aged cortex despite the lack of HIF-1 activation. Other HIF-independent mediators of hypoxia inducible genes could be involved during chronic hypoxia in the aged brain. PPAR-γ coactivator (PGC)-1α, a known regulator of VEGF gene transcription, is elevated in the young and aged cortex during the chronic hypoxic exposure. Overall, our results suggest a compensatory HIF-1 independent preservation of hypoxic-induced microvascular angiogenesis in the aged rat brain.
PMCID: PMC3378376  PMID: 20875806
Aging; Angiogenesis; Brain; Hypoxia; HIF-1; Microvessels; PGC-1α; VEGF

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