MicroRNA-20a constrains p300-driven myocardial angiogenic transcription by direct targeting of p300.

OBJECTIVE: To characterize downstream effectors of p300 acetyltransferase in the myocardium. BACKGROUND: Acetyltransferase p300 is a central driver of the hypertrophic response to increased workload, but its biological targets and downstream effectors are incompletely known. METHODS AND RESULTS: Mice expressing a myocyte-restricted transgene encoding acetyltransferase p300, previously shown to develop spontaneous hypertrophy, were observed to undergo robust compensatory blood vessel growth together with increased angiogenic gene expression. Chromatin immunoprecipitation demonstrated binding of p300 to the enhancers of the angiogenic regulators Angpt1 and Egln3. Interestingly, p300 overexpression in vivo was also associated with relative upregulation of several members of the anti-angiogenic miR-17∼92 cluster in vivo. Confirming this finding, both miR-17-3p and miR-20a were upregulated in neonatal rat ventricular myocytes following adenoviral transduction of p300. Relative expression of most members of the 17∼92 cluster was similar in all 4 cardiac chambers and in other organs, however, significant downregulation of miR-17-3p and miR-20a occurred between 1 and 8 months of age in both wt and tg mice. The decline in expression of these microRNAs was associated with increased expression of VEGFA, a validated miR-20a target. In addition, miR-20a was demonstrated to directly repress p300 expression through a consensus binding site in the p300 3'UTR. In vivo transduction of p300 resulted in repression both of p300 and of p300-induced angiogenic transcripts. CONCLUSION: p300 drives an angiogenic transcription program during hypertrophy that is fine-tuned in part through direct repression of p300 by miR-20a.

Quantitative control of adaptive cardiac hypertrophy by acetyltransferase p300.

BACKGROUND: Acetyltransferase p300 is essential for cardiac development and is thought to be involved in cardiac myocyte growth through MEF2- and GATA4-dependent transcription. However, the importance of p300 in the modulation of cardiac growth in vivo is unknown. METHODS AND RESULTS: Pressure overload induced by transverse aortic coarctation, postnatal physiological growth, and human heart failure were associated with large increases in p300. Minimal transgenic overexpression of p300 (1.5- to 3.5-fold) induced striking myocyte and cardiac hypertrophy. Both mortality and cardiac mass were directly related to p300 protein dosage. Heterozygous loss of a single p300 allele reduced pressure overload-induced hypertrophy by approximately 50% and rescued the hypertrophic phenotype of p300 overexpressers. Increased p300 expression had no effect on total histone deacetylase activity but was associated with proportional increases in p300 acetyltransferase activity and acetylation of the p300 substrates histone 3 and GATA-4. Remarkably, a doubling of p300 levels was associated with the de novo acetylation of MEF2. Consistent with this, genes specifically upregulated in p300 transgenic hearts were highly enriched for MEF2 binding sites. CONCLUSIONS: Small increments in p300 are necessary and sufficient to drive myocardial hypertrophy, possibly through acetylation of MEF2 and upstream of signals promoting phosphorylation or nuclear export of histone deacetylases. We propose that induction of myocardial p300 content is a primary rate-limiting event in the response to hemodynamic loading in vivo and that p300 availability drives and constrains adaptive myocardial growth. Specific reduction of p300 content or activity may diminish stress-induced hypertrophy and forestall the development of heart failure.

Reparaçäo miocárdica quando em uso de baixa dosagem e longa duraçäo de inibidor da síntese do óxido nítrico: miofibroblastos, colágeno tipo III e fibronectina / Myocardial repair with long-term and low-dose administration of a nitric oxide synthesis inhibitor: myofibroblasts, type III collagen and fibronectin

Objetivo - Estudar o processo de reparação miocárdica em ratos hipertensos sob inibição da síntese do óxido nítrico. Métodos - Foram estudados dois grupos de animais (controle e L-NAME 12 mg/kg/dia). A presença de colágeno tipo III, fibronectina e células contendo a-cima de músculo liso foi examinada por técnica imuno-histoquímica. Resultados - A fibronectina foi observada em ambas as lesões, recentes e tardias, enquanto que o colágeno tipo III foi observado, principalmente, nas áreas de cicatrização incompleta entre os miócitos e em torno dos ramos das artérias coronárias. As áreas de lesões recentes e tardias mostraram a presença de células fusiformes. A análise imuno-histoquímica demonstrou positividade para a actina de músculo liso nestes células. Conclusão - As células que expressam alpha-actina de músculo liso no miocárdio de ratos hipertensos estão associadas a acúmulo de colágeno tipo III e de fibronectina nas áreas de lesão.