Abstract
We report the first systems biology investigation of regulators controlling arterial plaque macrophage transcriptional changes in response to lipid lowering in vivo in two distinct mouse models of atherosclerosis regression. Transcriptome measurements from plaque macrophages from the Reversa mouse were integrated with measurements from an aortic transplant-based mouse model of plaque regression. Functional relevance of the genes detected as differentially expressed in plaque macrophages in response to lipid lowering in vivo was assessed through analysis of gene functional annotations, overlap with in vitro foam cell studies, and overlap of associated eQTLs with human atherosclerosis/CAD risk SNPs. To identify transcription factors that control plaque macrophage responses to lipid lowering in vivo, we used an integrative strategy – leveraging macrophage epigenomic measurements – to detect enrichment of transcription factor binding sites upstream of genes that are differentially expressed in plaque macrophages during regression. The integrated analysis uncovered eight transcription factor binding site elements that were statistically overrepresented within the 5′ regulatory regions of genes that were upregulated in plaque macrophages in the Reversa model under maximal regression conditions and within the 5′ regulatory regions of genes that were upregulated in the aortic transplant model during regression. Of these, the TCF/LEF binding site was present in promoters of upregulated genes related to cell motility, suggesting that the canonical Wnt signaling pathway may be activated in plaque macrophages during regression. We validated this network-based prediction by demonstrating that β-catenin expression is higher in regressing (vs. control group) plaques in both regression models, and we further demonstrated that stimulation of canonical Wnt signaling increases macrophage migration in vitro. These results suggest involvement of canonical Wnt signaling in macrophage emigration from the plaque during lipid lowering-induced regression, and they illustrate the discovery potential of an epigenome-guided, systems approach to understanding atherosclerosis regression.
Highlights
Underlying many cardiovascular diseases is atherosclerosis, an arterial accumulation of lipid-laden macrophages with attendant chronic inflammation [1]
REMINISCE leverages macrophage epigenomic and chromatin measurements, such as histone acetylation [38,39] and DNase I hypersensitive sites [40], in the analysis of the 59 regulatory regions of differentially expressed genes, including enhancers as well as promoters. In both the Reversa and aortic transplant regression models, we found that the consensus binding site sequence for the T-cell specific, HMG-box factors (TCF) and lymphoid enhancer factors (LEF), together known as the TCF/ LEF family of transcription factors, was overrepresented within the 59 regulatory regions of genes that are upregulated in plaque macrophages during regression
Reversa mice were maintained on Western diet for 16 weeks, which allowed for the development of hypercholesterolemia (903671 mg/dL total cholesterol [mean 6 standard error, SE]) and substantial, macrophage-rich plaques at the aortic root, as determined by immunostaining with the macrophage marker Cluster of Differentiation 68 (CD68)
Summary
Underlying many cardiovascular diseases is atherosclerosis, an arterial accumulation of lipid-laden macrophages (foam cells) with attendant chronic inflammation [1]. There is significant interest in finding new therapies to promote the regression of atherosclerotic plaques [6,7,8], with particular emphasis on the plaque macrophage as a potential target because of its roles in lipoprotein uptake and vascular inflammation [9,10,11,12], plaque destabilization [13,14], and plaque remodeling in response to dietary changes [15]. Plaque regression has been achieved through expression [16,17,18] or inactivation [19,20] of lipid metabolismmodifying genes; aortic tissue grafting [21,22,23]; and treatment with small-molecule therapeutics [24,25,26] or biologics [27,28], frequently in conjunction with a diet alteration. Reversa mice are Ldlr2/2 Apob100/100 [32,33] and they possess a loxP-flanked allele of the gene encoding microsomal triglyceride transfer protein (Mttp) and a drug-inducible Cre recombinase (Cre) transgene
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
