The relationship between socioeconomic status and poverty and mRNA expression in immune cells

The contributors to the observed health disparities in cardiovascular diseases (CVDs) in Baltimore City are multifactorial and include socioeconomic status (SES), psychosocial stress, genetics and ancestry, and access to health care and nutrition, but how these factors influence the biological onset of these disparate conditions remains to be solved. The long-term goal of the laboratory is to elucidate how poverty influences differential gene expression (DGE) patterns in the immune system and how these patterns may predispose individuals to diseases of the immune and cardiovascular systems. There is a gap in our knowledge in what genes and genetic pathways in the immune system are influenced by living in poverty. Examining this
association in a diverse cohort will help identify novel genetic pathways linking environmental stress to immune cell gene expression and function and help overcome critical barriers in our understanding of how disparate conditions develop in at-risk, impoverished communities.

This project will use RNA-sequencing (RNA-seq) to examine mRNA expression patterns in peripheral blood mononuclear cells (PBMCs) isolated from participants of the Healthy Aging in Neighborhoods of Diversity Across the Life Span (HANDLS) study, a diverse, longitudinal cohort of Baltimore City residents. While we will not generate a new drug or other therapeutic intervention, this project will generate new knowledge on how longitudinal DGE is related to poverty, and this can be built upon for further investigation into the understanding of the biological mechanisms of disparate conditions. DGE of mRNAs have been observed in inflammatoryrelated diseases of the immune and cardiovascular systems, including hypertension, and have previously been associated with disease progression and outcome in African Americans (AAs) and other traditionally underrepresented minority groups.

We hypothesize that poverty is associated with differential mRNA expression in PBMCs and these patterns are linked with biological mechanisms related to the development of inflammatory conditions in PBMCs. Preliminary data in our laboratory using microarray gene profiling indicate that poverty status, gender, and race are associated with differential mRNA expression patterns in cardiovascular- and inflammatory-related pathways
in PBMCs.

We will validate these results and investigate our hypotheses in the following aims:

Aim #1: Validate the effect of poverty status on differential mRNA expression in immune cells. Our working hypothesis is that mRNA gene expression patterns in inflammatory-related or other gene pathways in PBMCs from HANDLS participants are differentially-expressed in those living in poverty compared with those living above poverty. We will also examine if these patterns are influenced by gender or race in sub-group comparative analyses. We will perform RNA-seq on PBMCs isolated from HANDLS participants during Wave 1 of the study (August '04 - March '09) who are AA or white, male or female, and living above or below the poverty line (n=30/group, 260 total). We anticipate this cross-sectional analysis will validate the mRNAs and related gene-networks identified in our discovery microarray and identify additional mRNAs that exhibit differential expression in the context of poverty. We will use multiple, stringent bioinformatic programs and analyses to identify relevant pathways including gene ontology analysis, iPathwayGuide, among others. We will validate the expression of the most significantly upregulated and downregulated genes and related pathways by genespecific
RT-qPCR to confirm our bioinformatic analysis.

Aim #2: Identify the longitudinal effect of poverty on mRNA expression in immune cells. Our working hypothesis is that living for extended periods in poverty influences global mRNA expression in PBMCs, particularly in pathways related to cytokine and chemokine production and other inflammatory response pathways compared with those living above poverty. Our RNA-seq strategy will include PBMCs isolated from HANDLS participants during Wave 3 of the study (June '09 - July '13; mean follow-up 4.8 yrs; n=520) for the same individuals from Wave 1 (outlined in Aim 1). We will identify relevant genes and pathways that exhibit longitudinal expression patterns associated with poverty, and identify any associations with gender and race.
We will validate the expression of the most significantly upregulated and downregulated genes by RT-qPCR. We anticipate identifying unique and overlapping pathways as determined in our cross-sectional analysis (Aim 1).

Aim #3: Examine the biological effects of candidate gene differential expression ex vivo and in vitro. Our working hypothesis is that differential mRNA expression due to living in poverty influences inflammatory response in PMBCs. We will evaluate the correlation between specific differentially-expressed pathways in PMBCs and circulating serum factors isolated from HANDLS participants, including C-reactive protein, cholesterol, HDL, LDL, and others. This will determine if circulating factors in participants living in poverty serve as potential biomarkers for poverty-related gene expression in PBMCs. Candidate genes and pathways identified in our analysis will be examined in immune and endothelial cell culture models to understand whether the DGE pattern observed in HANDLS participants influences cellular inflammatory signaling pathways.

Impact: This is a novel approach to understanding gene-environmental interactions related to poverty in Baltimore City residents and will further our understanding of the influences of social determinants of health.