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

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 ofthe 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, ofthe 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-inducec
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.
RELEVANCE (See instructions):
We propose to clarify molecular mechanisms by which hypertension may be affecting cognition.
Understanding of these molecular mechanisms will help define potential therapeutic targets aimed at
alleviating the undesirable effects of hypertension on cognitive status.
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