Abstract 3828: miR-17~92 Cluster Regulates the Angiogenic Switch in the Progression to Heart Failure
Failure of compensatory angiogenesis may contribute to decompensation of cardiac hypertrophy. The miR-17~92 cluster is implicated in tumor growth, and members of this cluster target angiogenic genes. The miR-17~92 cluster regulates angiogenic expression during hypertrophy. Hypertrophy was induced by p300 overexpression or left coronary artery ligation in remote non-ischemic myocardium. 29 angiogenic mRNAs and all 7 members of the miR17~92 cluster were quantitated in hypertrophic tissue and in failing and non-failing human myocardium. Chromatin immunoprecipitation (ChIP) was performed on the miR17~92 promoter in wt and p300tg left ventricles. A pcDNA vector expressing the full miR17~92 cluster was transfected into primary cardiac myocytes and levels of Vegfa and p300 mRNA and protein were determined. In p300tg mice, blood vessel density was markedly increased vs wt during adaptive growth. Expression of angiogenic genes including VEGFA, B, and C, HIF1A and ANGPT1 were increased, peaked at 5mo and fell drastically by 9 mo. In parallel, protein levels of VEGF-A were upregulated at 1 mo but fell below wt levels at 9 mo. Mature miR-17~92 transcripts were initially downregulated in p300tg hearts at 1mo but began to increase at 40d and were significantly upregulated at 9 mo (miR-17–3p: 3.03x p=.04). Mir-17~92 members were also significantly downregulated in 2h post-MI heart (miR-17–5p: 0.7x p=.04; miR-19b: 0.7x p=.02), in parallel with upregulation of VEGF mRNA and protein (3.2x ±1.1, p= .01). In failing vs nonfailing human hearts, upregulation of miR-19b (1.6x ±.3, p=.03) was accompanied by downregulation of angiogenic transcripts including VEGFB, FLT1, EGLN2, and DNM2. In ChIP assays, p300tg hearts revealed increased p300 binding and decreased HDAC9 binding to the miR17~92 promoter vs. wt, as well as binding by MEF2 and GATA4. 16-fold overexpression of miR17~92 in cardiomyocytes completely suppressed both Vegfa and p300 expression. Multiple angiogenic gene transcripts as well as anti-angiogenic miRs are primary targets of p300. We propose that activation of miR-17~92 is part of a negative feedback loop that suppresses p300 and eventually blunts compensatory angiogenesis, leading to heart failure.