Atherosclerosis is an inflammatory disease with multiple underlying metabolic and physical risk factors including disturbed flow (d-flow), hypercholesterolemia, hypertension and diabetes. However, the mechanisms by which these pro-atherogenic risk factors synergize, leading to initiation and progression of atherosclerosis are still unclear. Recently, we found that BMP Receptor II (BMPR2) plays an unexpected role as an anti- inflammatory and anti-atherogenic protein in endothelial cells. We found that BMPR2 expression was progressively lost as atherosclerosis advances in human coronary arteries. We also found that multiple pro- atherogenic stimuli [d-flow, angiotensin II (Ang II), hypercholesterolemia and TNF?], significantly downregulated BMPR2 expression in endothelium, while anti-atherogenic stimuli such as stable flow (s-flow) upregulated its expression in vivo and in vitro. This suggests that there may be a common mechanism by which pro-atherogenic factors downregulate BMPR2 expression and that protecting it from risk factors or restoring its expression could be a novel avenue for prevention and treatment of atherosclerosis. This application is designed to address these questions to develop a novel therapeutic strategy to prevent the loss of BMPR2 expression as well as to investigate the subsequent mechanism by which it induces endothelial inflammation. Emerging evidence demonstrates that BMPR2 expression can be regulated by microRNAs, although their role in inflammation and atherosclerosis is unclear. Our preliminary studies based on miRNA arrays obtained from mouse arteries subjected to d-flow (by partial carotid ligation) or Ang II have identified 6 miRNAs (miR-17, -21, -25, -93, -106 and -181) as potential pro-atherogenic miRNAs (athero-miRs) that could directly target BMPR2. Current methods to inhibit miRNAs such as anti-miRs affect their target genes (~hundreds) indiscriminately, potentially causing both desired and unwanted effects. Here, we will use a novel approach using ?target site blockers (TSBs)? to avoid the indiscriminate effects of the current methods. Our overarching hypothesis is that pro-atherogenic factors increase endothelial expression of the athero-miRs that directly downregulate BMPR2, which in turn triggers endothelial inflammation and atherosclerosis. We further propose that BR2-TSBs would protect BMPR2 from the athero-miRs, preserving its constitutive anti- inflammatory and anti-atherogenic role without affecting other athero-miR targets. This hypothesis will be tested using two pro-atherogenic conditions (d-flow and Ang II) in vitro (endothelial cells [ECs]) and in vivo.
Aim 1 will determine the functional role of athero-miRs on BMPR2 expression by d-flow and Ang II in ECs in vitro and in vivo.
In Aim 2, we will design BR2-TSBs to prevent BMPR2 downregulation by athero-miRs in ECs in vitro and in vivo.
Aim 3 will determine the therapeutic potential of BR2-TSBs in atherosclerosis in ApoE-/- mice.
Aim 4 will test the hypothesis that loss of BMPR2 leads to ?unleashing? of BMPR2 tail-binding proteins, resulting in endothelial inflammation and atherosclerosis.
Atherosclerosis, the major cause of heart attack and stroke, occurs in response to multiple risk factors such as high cholesterol and diabetes in arterial branches or curved areas where blood flow is unstable. We recently discovered that many of these risk factors commonly reduce expression of a protein called bone morphogenic protein receptor 2 (BMPR2) in blood vessel cells, which in turn induces vascular inflammation and eventual atherosclerosis by unknown mechanisms. This application is designed to determine the mechanism by which BMPR2 expression is regulated by microRNAs and how loss of BMPR2 induces atherosclerosis, and may lead to novel therapeutics that could prevent and treat atherosclerosis.
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