Carboxy-terminal 24-amino-acid peptide of integral membrane protein 2A is produced in the heart and stimulates atrial natriuretic peptide release

Humoral factors regulating cardiac myocytes have not yet been fully elucidated. Using mass spectrometry, we analyzed peptides released from primary neonatal rat cardiac fibroblasts to identify a 24-amino-acid peptide with an intramolecular disulfide bond. It is derived from the C-terminal end of integral membrane protein 2A (ITM2A), a single-pass type II membrane protein; the peptide sequence is identical between humans and rodents and N-terminally flanked by conserved dibasic residues KR. The ITM2A peptide stimulated secretion of atrial natriuretic peptide (ANP), the predominant hormone produced by cardiac myocytes, in a Langendorff rat heart perfusion system as well as a primary culture of neonatal rat ventricular myocytes. These ANP secretion changes were not accompanied by an alteration in the beating rate, a key determinant of ANP secretion. In a mouse cardiac infarction model, both plasma ANP concentration and ITM2A gene expression in heart tissue reached a peak level on day 7 after operation. Our findings provide new insight into cardiac cell-to-cell communication that regulates ANP secretion.