Research has repeatedly shown that a lack of social ties increases risk for poor health. Recent research has demonstrated that poor mental and physical health outcomes are distally associated with social isolation, are more proximally associated with perceived social isolation, and are not explicable in terms of differences in health behaviors. Recent studies have identified alterations in hypothalamic-pituitary-adrenal (HPA) axis regulation of inflammatory biology in leukocytes as a potential mechanism of isolation-related health risks. Individuals reporting chronically high levels of subjective social isolation have shown a heightened rise in morning cortisol levels (Adams et al. 2006), and alterations in genome-wide transcription of glucocorticoid target genes and NF-:B target genes (Cole et al. 2007). These isolation-related alterations in leukocyte biology might stem from a functional desensitization of the glucocorticoid receptor (GR) in isolated people (Cole 2008), which in turn, is reciprocally related to NF-:B expression, a key factor in regulation of cellular responses to infection, cancer, and inflammation. Impaired transcription of glucocorticoid response genes and increased activity of pro-inflammatory transcription control pathways provide a functional genomic explanation for elevated risk of inflammatory disease in individuals who experience chronically high levels of perceived social isolation. Initial genomics analyses tested a relatively small sample and provided preliminary support for this hypothesis. This revised application seeks to extend those initial findings by (1) expanding the range of genomic analyses, (2) identifying the specific aspect of glucocorticoid-mediated transcriptional control driving those effects, (3) determining the plausibility of a causal role for subjective social isolation in predicting transcriptional control in longitudinal studies, and (4) establishing an animal model of subjective social isolation that can provide a platform for experimental studies. Utilizing participants from the Chicago Health, Aging and Social Relations longitudinal study, a population-based sample of middle-aged and older adults, we investigate whether transcriptional alterations occur only in those who show chronically high levels of subjective isolation, or whether similar effects occur even at minimal or variable levels of subjective isolation. Differential expression of GR and/or NF-:B proteins, and/or post-translational modifications of the GR (e.g., GR phosphorylation) will be examined as potential molecular mechanisms of altered glucocorticoid transcriptional control. The plausibility of a causal role for social isolation will be evaluated by examining the extent to which naturally occurring changes in subjective isolation over a two-year period predict changes in transcriptional control. Finally, a non-human primate model will be evaluated by conducting social behavioral assays to distinguish among and determine stability of "sociability" phenotypes in adult male rhesus monkeys, and biological assays will be done to determine relationships between social phenotypes and measures of HPA activity, GR- mediated signal transduction, and genome-wide transcriptional profiles.
Research has repeatedly shown that social isolation increases risk for poor health. We previously found functional genomic differences between individuals high and low in social isolation which could contribute to differences in risk of disease. The proposed research therefore is designed to identify the specific biological mechanisms mediating these genomic effects.
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