Hypoxia-induced angiogenesis is delayed in aging mouse brain

Abstract

Chronic moderate hypoxia results in systemic and central nervous system adaptations that allow acclimatization. Long-term responses to hypoxia involve systemic physiological changes, metabolic regulation, and vascular remodeling. To investigate whether aging affects systemic and cerebral angiogenic adaptational changes in response to prolonged hypoxia, the present study assessed the responses of 4month old ("young") C57BL/6 mice and 24month old ("aged") C57BL/6 mice to chronic hypobaric hypoxia of 0.4atm (290torr). Compared to young mice, delayed body weight-loss recovery and a lag in polycythemic response were observed in aged mice. As previously shown, hypoxia inducible factor-1α (HIF-1α) accumulation was attenuated and vascular endothelial growth factor (VEGF) expression was decreased in the cerebral cortex of aged mice. Conversely, cyclooxygenase-2 (COX-2), angiopoietin-2 (Ang-2), and peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) protein upregulation were not affected in the aged mice. Despite an initial delay in cerebral angiogenic response in aged mice in the first week of hypoxia, no significant differences were observed in microvascular density between young and aged mice in normoxia and at 2 and 3weeks of hypoxia. Taken together, these observations indicate that, even though the HIF-1 response to hypoxia is greatly attenuated, HIF-1 independent compensatory pathways are eventually able to maintain baseline and cerebral angiogenic adaptational changes to chronic hypoxia in aged mice. The delayed adaptive response, however, may result in decreased survival in the aged cohort.