Relation of platelet and leukocyte inflammatory transcripts to body mass index in the Framingham heart study

Abstract

Background: Although many genetic epidemiology and biomarker studies have been conducted to examine associations of genetic variants and circulating proteins with cardiovascular disease and risk factors, there has been little study of gene expression or transcriptomics. Quantitative differences in the abundance of transcripts has been demonstrated in malignancies, but gene expression from a large community-based cohort examining risk of cardiovascular disease has never been reported.

Methods and results: On the basis of preliminary microarray data and previously suggested genes from the literature, we measured expression of 48 genes by high-throughput quantitative reverse-transcriptase polymerase chain reaction in 1846 participants of the Framingham Offspring cohort from RNA derived from isolated platelets and leukocytes. A multivariable stepwise regression model was used to assess clinical correlates of quantitative RNA expression. For specific inflammatory platelet-derived transcripts, including ICAM1, IFNG, IL1R1, IL6, MPO, COX2, TNF, TLR2, and TLR4, there were significant associations with higher body mass index (BMI). Compared with platelets, fewer leukocyte-derived transcripts were associated with BMI or other cardiovascular risk factors. Select transcripts were found to be highly heritable, including GPIBA and COX1. Almost uniformly, heritable transcripts were not those associated with BMI.

Conclusions: Inflammatory transcripts derived from platelets, particularly those part of the nuclear factor kappa B pathway, are associated with BMI, whereas others are heritable. This is the first study, using a large community-based cohort, to demonstrate clinical correlates of gene expression and is consistent with the hypothesis that specific peripheral-blood transcripts play a role in the pathogenesis of coronary heart disease and its risk factors.

Figure 1. Platelet and Leukocyte Cluster Analysis

Related expression patterns for platelets (Figure 1a) and leukocytes (Figure 1b) using cluster analysis. Cluster analysis of gene expression was carried out using delta CT values. Clustering by principal components method with criterion max. eigenvalue > 0.80 was used.

Figure 2. BMI and Difference in Mean Gene Expression in Isolated Circulating Cells

Platelet (Figure 2a) and leukocyte (Figure 2b). The blue line (open circle) is difference in predicted delta CT values between overweight (BMI>25) and normal weight. Red line (closed circle) is difference in predicted delta CT values between obese (BMI>30)and normal weight. Delta CT is gene-specific CT – housekeeping CT.

Figure 2. BMI and Difference in Mean Gene Expression in Isolated Circulating Cells

Platelet (Figure 2a) and leukocyte (Figure 2b). The blue line (open circle) is difference in predicted delta CT values between overweight (BMI>25) and normal weight. Red line (closed circle) is difference in predicted delta CT values between obese (BMI>30)and normal weight. Delta CT is gene-specific CT – housekeeping CT.

Figure 3. Summary of genes significantly associated with BMI and their role in the NFκB pathway

Most of the genes found to be significantly associated with BMI are either known to stimulated NFκB activity or are expressed as a result of activation of this pathway. All, except for CCL2, were platelet expressed transcripts.