Urocortin-II and Urocortin-III Are Cardioprotective against Ischemia Reperfusion Injury: An Essential Endogenous Cardioprotective Role for Corticotropin Releasing Factor Receptor Type 2 in the Murine Heart

Abstract

Corticotropin-releasing factor (CRF) receptor type 2beta (CRFR2beta) is expressed in the heart. Urocortin (Ucn)-I activation of CRFR2beta is cardioprotective against ischemic reperfusion (I/R) injury by stimulation of the ERKs1/2 p42, 44. However, by binding CRF receptor type 1, Ucn-I can also activate the hypothalamic stress axis. Ucn-II/stresscopin related peptide and Ucn-III/stresscopin are two new members of the CRF/Ucn-I gene family and are selective for CRFR2beta. We propose that CRFR2beta selective Ucn-II or Ucn-III will protect cardiomyocytes and the ex vivo Langendorff perfused rat heart from I/R injury by activation of ERK1/2-p42, 44. Ucn-II is expressed in mouse cardiomyocytes, and Ucn-II or Ucn-III can bind to CRFR2beta, resulting in ERK1/2-p42, p-44 phosphorylation and cAMP stimulation. Phosphorylation of ERK1/2-p42, p-44 is regulated by the Ras/Raf-1 kinase pathway, independent of adenylate cyclase and, therefore, cAMP activation. Ucn-II and Ucn-III protect cardiomyocytes from I/R injury and reduce the percentage of infarct size:risk ratio in Langendorff perfused rat hearts exposed to regional I/R (P<0.001). The CRFR2 selective antagonist astressin2-B and an ERK1/2-p42, 44 inhibitor abolish the cardioprotective actions of Ucn-II and Ucn-III in reperfusion. Cardiomyocytes isolated from CRFR2-null mice are less resistant to I/R injury, compared with wild-type cardiomyocytes. We propose the use of CRFR2 selective agonists, Ucn-II and Ucn-III, to treat ischemic heart disease because of their potent cardioprotective effects in the murine heart and their minimal impact on the hypothalamic stress axis. We emphasize an important endogenous cardioprotective role for CRFR2beta in the murine heart.

Urocortin 2 autocrine/paracrine and pharmacologic effects to activate AMP-activated protein kinase in the heart

“…Ucn2 treatment had a preconditioning action to prevent injury during ischemia in our mouse model, consistent with prior studies (14). Interestingly, AMPK is also activated during ischemic preconditioning (40,41), the physiologic phenomenon by which preceding short durations of ischemia decrease the susceptibility to necrosis during more prolonged and potentially injurious ischemia.…”

“…1A). To determine the mechanism by which Ucn2 treatment stimulates heart AMPK, we used the CRFR2 antagonist anti-sauvagine-30 (a-SVG-30), an N-terminally truncated version of Ucn2 (14). Preincubation with a-SVG-30 abolished Ucn2-stimulated AMPK and downstream ACC phosphorylation (Fig.…”

“…Ucn2 binds with high affinity to the CRFR2 in cardiomyocytes (14). Thus, we hypothesized that an endogenous cardiac Ucn2 autocrine/paracrine pathway might modulate AMPK activation during ischemia.…”

erbB2 is required for G protein-coupled receptor signaling in the heart

“…Adult mouse cardiac myocytes were isolated from 3-to 6-month-old controls, heart-specific erbB2 mutants (13), or CRFR2␤ mutants (19) as described (18). Cells were stimulated with Ucn 2 (100 nM), glucagon (100 nM), vasoactive intestinal peptide (100 nM), angiotensin II (100 nM), ISO (10 M), and phenylephrine (50 M) for 5 min or 5 ng͞ml NRG1 or EGF for 15 min.…”

“…Differences among means were compared within the treatment groups by using Student's t test. Intracellular cAMP levels were measured by an RIA as described previously (18).…”