Intermedin 1-53 inhibits rat cardiac fibroblast activation induced by angiotensin II

Intermedin (IMD) is a novel peptide related to calcitonin gene-related peptide (CGRP) and adrenomedullin (ADM). Proteolytic processing of a larger precursor of IMD yields a biologically active C-terminal fragment IMD(1-53). We aimed to observe the cardioprotective antifibrotic effects of IMD(1-53) and its mechanism. Radioimmunoassay and Western blot analysis was used to determine IMD content in angiotensin II (AngII)-treated rat cardiac fibroblasts (CFs). Real-time PCR was used to measure mRNA levels of IMD and the IMD receptor components calcitonin receptor-like receptor (CRLR) and receptor activity modifying protein (RAMP) 1, 2 and 3. AngII was a powerful stimulator of CF activation. It decreased the production and secretion of IMD and increased the mRNA levels of the IMD receptor components CRLR, RAMP2 and RAMP3, but not IMD and RAMP1. Moreover, IMD(1-53) (10(-8) or 10(-7) mol/l) exerted a 25% and 45% respective inhibition in [(3)H]-thymidine incorporation and 16% and 36% respective inhibition in [(3)H]-proline incorporation in rat CFs incubated with AngII, and the actions of IMD(1-53) could be blocked by CGRP(8-37) and ADM(22-52). Immunofluorescence and Western blot analysis revealed that IMD(1-53) inhibited the increase of alpha-SMA in CFs induced by AngII, and the above effects of IMD(1-53) were similar to or more potent than those of an equivalent dose of ADM. Otherwise, IMD(1-53) resulted in dose-dependent increases of cAMP production in CFs, and co-incubated with H89 blocked the inhibition effect of IMD(1-53) on AngII-induced [(3)H]-thymidine, [(3)H]-proline incorporation and alpha-SMA expression. Collectively, these results show that IMD and its receptor components could be involved in an onset of cardiac fibrosis, and like ADM, IMD(1-53) exerts an antifibrotic effect in CFs, and the effect can be mediated by cAMP-PKA pathway and implicated with the ADM and CGRP receptors.