Epigenetic, Neuroimaging & Behavioral Effects of Hypertension in the Aging Brain

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With high prevalence in the community-dwelling elderly population, hypertension may be an important factor influencing the development and progression of cognitive aging. Although hypertension is a major health problem that has been shown to affect cognition, very little is known about its effects on the molecular status, especially the epigenetic status, of brain regions critical to cognition. However, significant literature is accumulating describing effects of selective cognitive tasks on epigenetic mechanisms in rodents. The known effect of hypertension on cognition, and the accumulating literature on the epigenetic bases of selected cognitive capacities leads to the overarching hypothesis to be tested by this project: epigenetic changes induced in a rodent model of hypertension will mirror the known relationships between cognitive tasks and epigenetic mechanisms in rodents. We focus on epigenetic mechanisms since these are major factors in the regulation of gene expression. Specifically, this project is aimed at determining epigenetic changes induced by hypertension in subregions of the brain known to be important to cognition. We will study brains from 20 normotensive controls and 20 hypertensive behaviorally characterized rats, who have also received high resolution in vivo magnetic resonance imaging (MRl) scans of brain structure and white matter integrity. Male Fischer 344 rats have the cytochrome P450 promoter (Cyp1a1) inserted to up-regulate the expression of the mouse renin (Ren2) gene, Administration of 0,15% indole-3-carbinol {I3C) to the diet of these transgenic rats activates the Cyplal promoter to induce a gradual onset of hypertension. Dependent variables will be gene expression and the major epigenetic mechanisms, DNA methylation and histone modifications, as well as measures of cognitive performance and patterns of MRl gray and white matter integrity. Defined sub-regions, of the hippocampus will be isolated by laser capture microdissection. In order to obtain sufficient starting material successive sections from the same brain will be pooled. We will assess DNA methylation on a genome wide basis by bisulfite conversion, amplification and NimbleGen arrays. PCR will be used to assess DNA methylation of specific genes based on previous findings of others and array data produced by this project. We will assess selected histone modifications by chromatin immunoprecipitation followed by PCR of selected genes. The genes we select are those previously shown to be differentially expressed in brain regions, with an emphasis on hippocampus, in association with learning and memory. We will test our major hypothesis by statistical determination of hypertension-induced epigenetic changes in our model and then compare the resulting data with epigenetic changes associated with cognitive behaviors and MRl gray and white matter integrity. We will use multivariate analyses to estimate the extent to which epigenetic variables account for cognitive status in the experimental animals.