CGRP and specific CGRP receptors are found in the heart where they produce positive-inotropic and anti-apoptotic effects, key adaptations to exercise and cardiovascular disease. PI3K/Akt and MAPK signaling imbalances are associated with cardiomyocyte pathologies; however, the effects of CGRP on these pathways are unclear. Therefore, we hypothesized that CGRP modulates inotropic and apoptotic adaptations of cardiomyocytes by regulating PI3K/Akt and MAPK/ERK signaling balances. We treated cardiomyocytes with combinations of CGRP, PI3K/Akt and MAPK signaling agonists and antagonists. We evaluated expression of the mRNA and proteins levels of survival signaling molecules related to the PI3K/Akt and MAPK and measured apoptosis by caspase 3/7 activity. CGRP1-37 decreased Akt, NFκB, SOD-3 and increased ERK1/2 and p38 MAPK expressions, which was antagonized by CGRP8-37. Akt-negative construct transfection, Ad.Akt(K179M), inhibited the CGRP1-37-induced increment in MAPK expressions. A PI3K-antagonist treatment with LY294002 or CGRP1-37/Ad.Akt(K179M) co-treatment alleviated the CGRP-increased caspase activity and -decrements in SOD-3. These findings demonstrate a CGRP negative effect on the PI3K/Akt signaling pathway and CGRP receptor-induced crosstalk between PI3K/Akt and MAPK in normal cardiomyocytes. Future studies to differentiate CGRP effects on intracellular signal transduction mechanisms in pathological conditions will elucidate the significance of CGRP in, and provide novel therapeutic targets for, heart failure.
Keywords: CGRP; Cardiac myocytes; MAPK/ERK signaling; PI3K/Akt signaling; Rat.