Title

Brain regional angiogenic potential at the neurovascular unit during normal aging

Date of Completion

January 2011

Keywords

Biology, Cell|Biology, Neurobiology

Degree

Ph.D.

Abstract

While mounting evidence indicates angiogenesis is impaired during normal aging, this has largely been investigated in peripheral organs, with much less effort focused on the aging brain. Given the strong regional specialization of the brain and increased vulnerability of certain brain regions to age-related deficits, the broad hypothesis of this dissertational research was cerebral angiogenic potential is regionally modified during normal aging. To test this, the expression of a broad group of angiogenesis-associated genes was assayed at the neurovascular unit (NVU) in discrete brain regions of normal aging mice by immunohistochemistry-guided laser capture microdissection (Immuno-LCM) coupled to quantitative real-time PCR (qRT-PCR). Complementary quantitative microvascular density/branching studies were performed as well. Effects of physical exercise on gene expression and microvascular density/branching were assayed to determine if such an intervention could reverse age-related regional cerebral angiogenic trends. Additionally, the response in gene expression to chronic mild hypoxia, which is normally a strong stimulus for angiogenesis in young healthy subjects, was further probed in the cortex to highlight any age-associated weaknesses in adaption to this stress. Normal aging was found to significantly impact resting expression of angiogenesis-associated genes at the NVU in a region-dependent manner—implying regional adaptation to the aging process. Physical exercise reversed some of these age-associated regional gene trends, as well as positively influenced cerebral capillary density and branching in a region-dependent way. Lastly, hypoxia revealed the angiogenic response to be weakened in aged brain, which displayed significantly muted changes in gene expression. Collectively, these results suggest a picture of heterogeneous changes in angiogenic capacity of the brain that accompany normal aging, and suggest a therapeutic benefit of physical exercise that acts at the NVU. Furthermore, a pilot study on the feasibility of coupling Immuno-LCM to a downstream mass spectrometric platform to study the brain microvascular endothelial proteome was also done, setting the stage for future analysis of brain regional angiogenic potential in the aged NVU, at the protein level. ^