p38 mitogen-activated protein kinase regulates chamber specific perinatal growth in heart.

In mammalian heart, left ventricle (LV) rapidly becomes more dominant in size and function over right ventricle (RV) after birth. The molecular regulators responsible for this chamber specific differential growth are largely unknown. We found the cardiomyocytes in neonatal mouse RV had lower proliferation, more apoptosis and smaller sizes comparing to the LV. Such chamber specific growth pattern was associated with a selective activation of p38 MAPK activity in the RV and simultaneous inactivation in the LV. Cardiomyocyte-specific deletion of both mapk14 and mapk11 genes in mice results in loss of p38 MAP kinase expression and activity in the neonatal heart. Inactivation of p38 activity led to marked increase in myocytes proliferation and hypertrophy but diminished myocyte apoptosis, specifically in the RV. Consequently, the p38 inactivated hearts showed RV specific enlargement postnatally, progressing to pulmonary hypertension and right heart failure at adult stage. Chamber-specific p38 activity was associated with differential expression of dual-specific phosphatases (DUSPs) in neonatal hearts, including Dusp26. Unbiased transcriptome analysis revealed IRE1/XBP mediated gene regulation contributed to p38 MAPK dependent regulation of neonatal myocyte proliferation and binucleation. These findings establish an obligatory role of DUSP-p38-IRE1 signaling in myocytes for chamber specific growth in postnatal heart.