The Brain Microvasculature, Hyaluronan, and Aging
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DESCRIPTION (provided by applicant): The vasculature of the aged brain is more vulnerable to injury than that of young brain. Vascular injury can result in less effective perfusion and increased risk of exposure of brain to deleterious substances from the systemic circulation. Brain microvasculature is surrounded by extracellular matrix (ECM) that is necessary for vascular integrity. However, little is known as to how the ECM of brain microvasculature changes with aging. In histologic studies of the cortex of mouse brains, there was a significant increase with aging in Hyaluronan (HA), a disaccharide that is the primary ECM component of microvasculature. Aged cortex also had significantly less expression of the hyaladherin, tumor necrosis factor-inducible gene-6 protein (TSG-6), relative to the young brains. Both HA and TSG-6 were found throughout brain ECM, but were concentrated at the microvasculature. The increased expression of HA, in conjunction with decreased expression of TSG-6, is a key finding, as hyaladherins can reduce the rate at which HA is degraded. HA is generally synthesized by HA Synthases 1,2, or 3 as a large polymer (i.e.,>1,000kDa) of high molecular weight (MW), but is rapidly degraded as a result of hyaluronidase (HYALases 1,2,3) activity to smaller sizes, which at low MW HA (i.e.,<50kDa) promotes inflammation. Notably, there were no differences between the aged and young cortices in HA Synthases, HYALases or other hyaladherins. These findings suggest that decreased TSG-6 with age could affect HA size that, in turn, has important regulatory effects on cellular functions in brain aging. This application uses brains from young, middle-aged, and aged mice to define vascular-associated HA and TSG-6 in vivo (HA thickness/distribution and HA/TSG-6 cellular localization), and then uses brain microvessels (that maintain cell-cell and cell-ECM contacts) for biochemistry. The objective is to address the following hypothesis: Aged brain vasculature has more HA, but decreased expression of TSG-6 that confers stability to HA. These changes are associated with increased degradation of HA and a higher ratio of LMW to total HA. Aim 1. To define the expression of HA and TSG-6 in the vasculature of the cerebral cortex of mouse brains with aging. HA localization and thickness in the brain vasculature will be measured using transmission electron microscopy (TEM). HA and TSG-6 expression will be co-localized with endothelial cells and/or pericytes using dual-labeling immunofluorescence staining of brain cortical sections. Aim 2. To utilize microvessel explants from the cortex of mice to measure mediators of HA, changes in TSG-6, and HA content/size with aging. Expression of HA Synthases, HYALases, and hyaladherins will be examined in the microvessels by qRT-PCR and dual label immunofluorescence. Synthesis of HA and TSG-6, and HA size will be measured using ELISA and 3[H] glucosamine metabolic labeling of microvessels. The long-term goal is to develop interventions, such as TSG-6, that can modify age-related changes in HA content and MW to improve the function of brain vasculature with aging.
