RATIONALE: The vasoactive peptide angiotensin II (Ang II) is a potent cardiotoxic hormone whose actions have been well studied, yet questions remain pertaining to the downstream factors that mediate its effects in cardiomyocytes. OBJECTIVE: The in vivo role of the myocyte enhancer factor (MEF)2A target gene Xirp2 in Ang II-mediated cardiac remodeling was investigated. METHODS AND RESULTS: Here we demonstrate that the MEF2A target gene Xirp2 (also known as cardiomyopathy associated gene 3 [CMYA3]) is an important effector of the Ang II signaling pathway in the heart. Xirp2 belongs to the evolutionarily conserved, muscle-specific, actin-binding Xin gene family and is significantly induced in the heart in response to systemic administration of Ang II. Initially, we characterized the Xirp2 promoter and demonstrate that Ang II activates Xirp2 expression by stimulating MEF2A transcriptional activity. To further characterize the role of Xirp2 downstream of Ang II signaling we generated mice harboring a hypomorphic allele of the Xirp2 gene that resulted in a marked reduction in its expression in the heart. In the absence of Ang II, adult Xirp2 hypomorphic mice displayed cardiac hypertrophy and increased beta myosin heavy chain expression. Strikingly, Xirp2 hypomorphic mice chronically infused with Ang II exhibited altered pathological cardiac remodeling including an attenuated hypertrophic response, as well as diminished fibrosis and apoptosis. CONCLUSIONS: These findings reveal a novel MEF2A-Xirp2 pathway that functions downstream of Ang II signaling to modulate its pathological effects in the heart.
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