Abstract 450: Brg1 Attenuates Cardiac Dysfunction by Activating Sonic Hedgehog Pathway in Acute Myocardial Infarction

Abstract

Background: Brahma-related gene 1 (Brg1), the core ATPase subunit of a large chromatin remodeling complex, plays critical role in the regulation of gene expression during cardiac growth, differentiation. In adults, Brg1 is turned off in cardiomyocytes and reactivated by cardiac stress. How Brg1 in myocardial infarction (MI) is poorly understood. The sonic hedgehog (Shh) pathway was activated to protect the injured cardiomyocytes during the development of MI. However, by which Shh activation is mediated in MI still remains to be determined. Methods and results: Adult male C57BL/6 mice were subjected to ligation of the left anterior descending coronary artery for MI model. We investigated Brg1 activation and how it regulated the gene expressions of Shh pathway in peri-infarct zone in MI mice. Our data demonstrated that in peri-infarct zone, the protein of Brg1 was significantly increased 7 days after MI compared with the sham group in control mice, accompanied by upregulation of shh, patched-1 (Ptch1), and glioma-associated oncogene-1(Gli1). We further revealed that with adenoviral intramyocardial injection, the Brg1 overexpression reduced the percentage myocardial infarct, improved cardiac dysfunction, decreased the number of apoptotic cells and upregulated the ratio of Bcl-2/Bax in MI mice. Conversely, shRNA-mediated knockdown of Brg1 enlarged the percentage myocardial infarct, exacerbated cardiac dysfunction, increased the apoptotic cells and downregulated the ratio of Bcl-2/Bax. More importantly, the Brg1 overexpression increased Shh, Ptch1 and Gli1 expressions, whereas Brg1 knockdown suppressed Shh, Ptch1 and Gli1 expressions. Chromatin immunoprecipitation confirmed that Brg1 were recruited to the regulatory elements of Shh, Ptch1 and Gli1. This recruitment was associated with transcriptional upregulation of these three genes. Conclusions: This study indicated that in MI mice, the myocardial Brg1 is upregulated and that the upregulated Brg1 contributes to protection of cardiac function and activation of Shh pathway. Strategies that are aimed at augment the Brg1-Shh pathway may offer useful means for preventing and treating cardiac dysfunction in patients with MI. Key words: Acute myocardial infarction, Brg1, Shh pathway