Abstract 3786: AMPK Mediates the Cardioprotective Effects of Urocortin during Myocardial Ischemia
Urocortin (Ucn), a peptide of the corticotropin-releasing factor (CRF) family, binds with high affinity to type 2 CRF receptors (CRFR2) expressed on the surface of cardiomyocytes and confers protection against acute ischemia/reperfusion injury. The mechanisms by which the Ucn-CRFR2 axis mitigates against myocyte injury in I/R remain incompletely delineated. Some reports have implicated an important role for protein kinase Cϵ (PKCϵ) in mediating urocortin-induced cardioprotection. Mounting evidence supports the beneficial effects of AMP-activated protein kinase (AMPK) in limiting cardiac damage during ischemia/reperfusion. While AMPK is classically regulated by the cellular AMP/ATP ratio, numerous recent data support the modulation of AMPK activity by circulating hormones, cytokines, and other soluble mediators via autocrine, paracrine or endocrine signaling mechanisms. The purpose of this study was to examine whether:
Ucn activates cardiac AMPK;
the Ucn-CRFR2-PKCϵ axis contributes to hypoxic activation of AMPK; and
Ucn-induced cardioprotection is mediated by AMPK.
Incubation of isolated rat left ventricular papillary muscles with Ucn (100 nM) caused significant AMPK activation (2.1-fold, p<0.05 vs. control). A CRFR2 antagonist anti-sauvagine-30 (a-SVG-30) or a PKCϵ translocation-inhibitor peptide (ϵV1–2) eliminated Ucn-stimulated AMPK activation. Furthermore, pre-incubation with a-SVG-30, neutralizing Ucn antibody (Ucn-Ab), or ϵV1–2 partially blocked hypoxia-induced AMPK activation in cardiac muscle (by 21%, 26% and 24%, respectively, all p<0.05 vs. hypoxia alone). In addition, overexpression of kinase-dead (K437R) PKCϵ in H9c2 myoblast cells attenuated hypoxic AMPK activation. Intraperitoneal administration of Ucn (15 μg/kg, i.p.) in wild type C57BL/6 mice significantly reduced myocardial infarct size after in vivo regional ischemia and reperfusion (p<0.05 vs control) and was associated with enhanced cardiac AMPK activation, but Ucn did not have cardioprotection effects in AMPK-deficient transgenic mice. In conclusion, Ucn is released from the heart during ischemia, causes an autocrine/paracrine activation of the AMPK signaling pathway via PKCϵ, and mitigates against ischemia/reperfusion injury.