CRH-like peptides protect cardiac myocytes from lethal ischaemic injury

Corticotropin-releasing factor is cytoprotective in Xenopus tadpole tail: coordination of ligand, receptor, and binding protein in tail muscle cell survival

Upon metamorphosis, amphibian tadpoles lose their tails through programmed cell death induced by thyroid hormone (T3). Before transformation, the tail functions as an essential locomotory organ. The binding protein for the stress neuropeptide corticotropin-releasing factor (CRF; CRF-BP) is strongly up-regulated in the tail of Xenopus tadpoles during spontaneous or T3-induced metamorphosis. This finding led us to investigate physiological roles for CRF and CRF-BP in tadpole tail. We found CRF, CRF-BP, and functional CRF1 receptor in tail and CRF and functional CRF1 receptors, but not CRF-BP, in the tail muscle-derived cell line XLT-15. CRF, acting via the CRF1 receptor, slowed spontaneous tail regression in explant culture and caused a reduction in caspase 3/7 activity. CRF increased, but stable CRF-BP overexpression decreased, [3H]thymidine incorporation in XLT-15 cells. Overexpression of CRF-BP in vivo accelerated the loss of tail muscle cells during spontaneous metamorphosis. Lastly, exposure of tail explants to hypoxia increased CRF and urocortin 1 but strongly decreased CRF-BP mRNA expression. We show that CRF is expressed in tadpole tail, is up-regulated by environmental stressors, and is cytoprotective. The inhibitory binding protein for CRF is regulated by hormones or by environmental stressors and can modulate CRF bioactivity.

Mechanisms of the protective effects of urocortin on coronary endothelial function during ischemia-reperfusion in rat isolated hearts

1 Urocortin is a vasodilator peptide related to corticotrophin-releasing factor, which may protect endothelial function during coronary ischemia-reperfusion (I-R). The aim of this study was to study the mechanisms of this protective effect. 2 Hearts from Sprague-Dawley rats were isolated and perfused at constant flow and then exposed to 15 min global zero-flow ischemia, followed by 15 min reperfusion. The relaxation to acetylcholine (10 nM-10 microM) was recorded after pre-constriction of the coronary vasculature with U46619 (100-300 nM) in ischemic-reperfused or time-control hearts. 3 After I-R, the coronary relaxation to acetylcholine was reduced and this reduction was attenuated by treatment with urocortin (10 pM), administered before ischemia and during reperfusion. 4 This urocortin-induced improvement of the relaxation to acetylcholine was not modified by tetraethylammonium (10 mM), blocker of Ca2+ dependent-potassium channels; glibenclamide (10 microM), blocker of K(ATP) channels; N(w)-nitro-L-arginine methyl ester (L-NAME, 100 microM), blocker of nitric oxide synthesis; or meclofenamate (10 microM), blocker of cyclooxygenase, but it was abolished by chelerythrine (3 microM), blocker of protein kinase C (PKC). 5 These results suggest that urocortin may protect coronary endothelial function during I-R by activation of PKC.

Urocortin: a cardiac protective peptide?

Urocortin (UCN), a member of the corticotropin-releasing hormone (CRH)-related peptides, has been reported to play biologically diverse roles in several systems such as cardiovascular, reproductive, appetite, stress, inflammatory responses, etc. In heart, it was reported to have protective effects. On the other hand, it was also reported to have cardiac inotropic and hypertrophic effects and hence to cause cardiac remodeling. This paper will review the effects of UCN in cardiac system.

Four-day urocortin-I administration has sustained beneficial haemodynamic, hormonal, and renal effects in experimental heart failure

AIMS

To investigate the subacute effects of a sustained intravenous infusion of urocortin-I (Ucn-I) in experimental heart failure (HF).

METHODS AND RESULTS

In eight sheep with pacing-induced HF, a 4-day infusion of Ucn-I (0.3 microg/kg/h) induced prompt (30 min) and sustained (4-day) increases in cardiac output (CO, Day 4: 1.8+/-0.2 vs. 2.3+/-0.2 L/min, P<0.001) and stroke volume (7.8+/-0.8 vs. 10.2+/-1.0 mL/beat, P=0.0011), and reductions in mean arterial pressure (MAP, 72+/-3 vs. 70+/-3 mmHg, P=0.0305), left atrial pressure (26+/-1 vs. 11+/-2 mmHg, P<0.001), and total calculated peripheral resistance (43+/-6 vs. 32+/-4 mmHg/L/min, P<0.001). Ucn-I also induced persistent falls in plasma renin (1.34+/-0.23 vs. 0.77+/-0.10 nmol/L/min, P=0.048), aldosterone (3273+/-1172 vs. 382+/-44 pmol/L, P=0.0098), endothelin-1 (4.6+/-0.3 vs. 2.7+/-0.3 pmol/L, P<0.001), vasopressin (24+/-4 vs. 14+/-2 pmol/L, P=0.0028) and atrial (184+/-14 vs. 154+/-29 pmol/L, P=0.0226) and brain (43+/-5 vs. 32+/-6 pmol/L, P=0.0016) natriuretic peptides. Plasma adrenocorticotrophic hormone and cortisol rose transiently on Day 0. Ucn-I enhanced urinary sodium excretion (5.3-fold, P=0.0001) and creatinine clearance (1.3-fold, P=0.0055) long-term, and tended to increase urine output (P=0.0748). Food intake was attenuated over the first 2 days of treatment (P=0.0283).

CONCLUSION

Four-day administration of Ucn-I induces sustained reductions in cardiac preload and MAP, improvements in CO and renal function, and inhibition of a range of vasoconstrictor/volume-retaining factors. These findings support Ucn-I's therapeutic potential in HF.

The neuroprotective actions of corticotropin releasing hormone

Corticotropin-releasing hormone (CRH) modulates the activity of the hypothalamic-pituitary-adrenal (HPA) axis, and has a key role in mediating neuroendocrine effects that occur in response to stressful stimuli. Disruption of the CRH system however has been shown to be closely associated with the progression of Alzheimer's disease (AD), and these observations prompted an investigation into the potential neuroprotective effects of the hormone. In addition to its regulatory affects on the molecular processes that underlie AD i.e., amyloid precursor protein (APP) processing and potentially tau phosphorylation, evidence is provided that the neuroprotective effects of CRH are mediated by a number of diverse mechanisms. These stem from activation of its high affinity receptor, the CRH type 1 receptor, and involve the induction of protective intracellular pathways including PKA-CREB that eventually lead to expression of neurotrophic factors. Conversely, inhibition of harmful events, such as caspase activation during apoptosis may also occur. Taken together, an impressive amount of evidence has accumulated recently, highlighting this new and potentially important function of CRH.

Effect of hypoxia on urocortin production in human gestational trophoblasts in vitro

PROBLEM

Urocortin is produced by the placenta throughout pregnancy but its regulation remains unknown. The effect of hypoxia on placental urocortin production is not known. The aim of this study was to determine the effect of in vitro hypoxia on human trophoblastic urocortin production.

METHOD OF STUDY

Placental explants and primary cultures were incubated in anaerobe hypoxic bags for 24 h in a humidified incubator. Urocortin peptide secretion and mRNA (messenger RNA) production was determined by enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction, respectively. Morphological and functional integrity was verified by immunohistochemical analysis of urocortin expression. Vascular endothelial growth factor expression was used to verify the generation of cellular hypoxia in our in vitro system.

RESULTS

Hypoxia did not affect urocortin secretion or mRNA expression in explant and single-cell cultures. Production was greater from first trimester than term explants and from single-cell primary cultures more than from explant cultures.

CONCLUSIONS

Hypoxia does not influence human placental urocortin secretion or mRNA expression in vitro.

The cardioprotective effect of urocortin during ischaemia/reperfusion involves the prevention of mitochondrial damage

We have previously shown, using Affymetrix gene chip technology, that urocortin induces the expression of several diverse genes in cardiac myocytes. An ATP sensitive inwardly rectifying potassium channel, Katp (Kir6.1), the enzyme calcium independent phospholipase A2 (iPLA2), and protein kinase C epsilon (PKCepsilon) and that these genes are involved in the cardioprotective mechanism of action of urocortin. Here we demonstrate that these gene products are localized to cardiac myocyte mitochondria and for the first time show that urocortin protects cardiac myocytes from ischaemia/reperfusion induced cell death by preventing mitochondrial damage. Using pharmacological agents to Katp channels and iPLA2 and synthetic peptide inhibitors of PKCepsilon, we go on to demonstrate that these three gene products are involved in the urocortin induced protection of cardiac myocyte mitochondria. These proteins may interact at the mitochondria to produce the protective effect.

Localization and physiological roles of urocortin

Urocortin, a 40 amino acid peptide, is a corticotropin-releasing factor (CRF) related peptide, and can bind to all three types of CRF receptors (CRF type 1, type 2a and type 2b receptors) with higher affinities for these receptors than CRF. Immunoreactivity of urocortin is widely distributed in central nervous, digestive, cardiovascular, reproductive, immune and endocrine systems. Urocortin plays important roles in appetite-suppression, immunomodulation, steroidogenesis in the ovary, maintenance of the placental function, labor, and cardioprotection via CRF receptors. Although urocortin has potent adrenocorticotropin (ACTH) releasing activity in vitro, endogenous urocortin does not act on pituitary ACTH secretion in vivo.

Urocortins as cardiovascular peptides

Urocortins (Ucn) 1, 2 and 3, human homologues of fish urotensin I, form the corticotropin-releasing factor (CRF) family, together with CRF, urotensin I and sauvagine. Ucn 3 is a novel member of this family and is a specific ligand for CRF type 2 receptor. CRF type 2 receptor is thought to mediate the stress-coping responses, such as anxiolysis, anorexia, vasodilatation, a positive inotropic action on myocardium and dearousal. Endogenous ligands for the CRF type 2 receptor expressed in the cardiovascular tissues, such as the myocardium, have long been unknown. We have shown expression of Ucn 3 as well as Ucn 1 in the human heart. Ucn 3 is also expressed in the kidney, particularly distal tubules. Studies in various rat tissues showed that high concentrations of immunoreactive Ucn 3 were found in the pituitary gland, adrenal gland, gastrointestinal tract, ovary and spleen in addition to the brain, heart and kidney. These observations suggest that Ucn 3 is expressed in various tissues including heart and kidney, and may regulate the circulation in certain aspects of stress and diseases, such as inflammation. Ucn 1 and 3 appear to have important pathophysiological roles in some cardiovascular diseases.

Warm blood cardioplegic arrest induces mitochondrial-mediated cardiomyocyte apoptosis associated with increased urocortin expression in viable cells

OBJECTIVES

This study assesses the mechanisms of apoptosis in patients after on-pump coronary artery bypass graft surgery and the potential involvement of the endogenous cardiac peptide urocortin as a cardiomyocyte salvage mechanism. We have previously described the mechanisms of apoptosis after ischemia-reperfusion injury in the rat heart and shown that endogenous urocortin is cardioprotective. Here we extend these findings to the human heart exposed to ischemic-reperfusion injury.

METHODS

Two sequential biopsy specimens were obtained from the right atriums of 24 patients undergoing coronary artery bypass grafting at the start of grafting and 10 minutes after release of the aortic clamp. Apoptosis was identified by means of immunocytochemical colocalization between terminal deoxynucleotidyl transferase-mediated nick end-labeling positivity and active caspase-3. Immunostaining for active caspase-9 and caspase-8 was performed to identify the pathways of apoptosis induction. Urocortin and adenosine triphosphate-dependent potassium channel expression was also assessed by means of immunocytochemistry.

RESULTS

Myocyte apoptosis (<0.1% before coronary artery bypass grafting) was increased after coronary artery bypass grafting and reperfusion and was greater in patients with longer periods of cardioplegic arrest (3.3% +/- 0.5% with <55 minutes and 5.1% +/- 0.9% with 85-100 minutes, P <.001). Processing of caspase-9 was always more pronounced than that of caspase-8 (P <.05). Cardioplegic arrest was also associated with increased urocortin expression (up to 29% +/- 3.5% vs <3% in samples obtained before coronary artery bypass grafting, P <.001) but only in nonapoptotic myocytes. These and surrounding viable myocytes also showed increased Kir6.1 adenosine triphosphate-dependent potassium channel expression.

CONCLUSIONS

Cardioplegic arrest and subsequent reperfusion result in cardiomyocyte apoptosis, largely through mitochondrial injury, as well as exclusive urocortin expression in viable cells. This finding might suggest a cardioprotective role for endogenous urocortin in human subjects.

CRF and CRF receptors: role in stress responsivity and other behaviors

Since corticotropin-releasing factor (CRF) was first characterized, a growing family of ligands and receptors has evolved. The mammalian family members include CRF, urocortinI (UcnI), UcnII, and UcnIII, along with two receptors, CRFR1 and CRFR2, and a CRF binding protein. These family members differ in their tissue distribution and pharmacology. Studies have provided evidence supporting an important role of this family in regulation of the endocrine and behavioral responses to stress. Although CRF appears to play a stimulatory role in stress responsivity through activation of CRFR1, specific actions of UcnII and UcnIII on CRFR2 may be important for dampening stress sensitivity. As the only ligand with high affinity for both receptors, UcnI's role may be promiscuous. Regulation of the relative contribution of the two CRF receptors to brain CRF pathways may be essential in coordinating physiological responses to stress. The development of disorders related to heightened stress sensitivity and dysregulation of stress-coping mechanisms appears to involve regulatory mechanisms of CRF family members.

Translational medicine in fish-derived peptides: from fish endocrinology to human physiology and diseases

Recent studies have revealed the importance of fish-derived peptide hormones to human endocrinology. These peptides include melanin-concentrating hormone (MCH), urocortins (human urotensin-I), and urotensin-II. MCH, a hypothalamic peptide, is a potent stimulator on appetite. Urocortins, e.g. urocortin 1 and urocortin 3 (stresscopin), are endogenous ligands for the corticotropin-releasing factor (CRF) receptors, particularly CRF type 2 receptor, that mediates a vasodilator action, a positive inotropic action and a central appetite-inhibiting action. These actions mediated by CRF type 2 receptor may ameliorate the stress response. Human urotensin-II is a potent vasoconstrictor peptide, while it acts as a vasodilator on some arteries. Human urotensin-II is expressed in various types of cells and tissues, including cardiovascular tissues, as well as many types of tumor cells. Thus, these fish-derived peptides appear to play important roles in human physiology, such as appetite regulation, stress response and cardiovascular regulation, and also in diseases, for example, obesity, cardiovascular diseases and tumors. Development of antagonists/agonists against the receptors for these peptides may open new strategies for the treatment of various diseases, including obesity-related diseases, hypertension, heart failure and malignant tumors.

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

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.

Reduced cerebral injury in CRH-R1 deficient mice after focal ischemia: a potential link to microglia and atrocytes that express CRH-R1

Corticotropin releasing hormone (CRH) and its family of related peptides are involved in regulating physiologic responses to multiple stressors, including stroke. Although CRH has been implicated in the exacerbation of injury after stroke, the mechanism remains unclear. After ischemia, both excitotoxic damage and inflammation contribute to the pathology of stroke. CRH is known to potentiate excitotoxic damage in the brain and has been shown to modulate inflammatory responses in the periphery. Here the present authors examine the relative contribution of the two known CRH receptors, CRH-R1 and CRH-R2, to ischemic injury using CRH receptor knockout mice. These results implicate CRH-R1 as the primary mediator of ischemic injury in this mouse model of stroke. In addition, the authors examine a potential role for CRH in inflammatory injury after stroke by identifying functional CRH receptors on astrocytes and microglia, which are cells that are known to be involved in brain inflammation. By single cell PCR, the authors show that microglia and astrocytes express mRNA for both CRH-R1 and CRH-R2. However, CRH-R1 is the primary mediator of cAMP accumulation in response to CRH peptides in these cells. The authors suggest that astrocytes and microglia are cellular targets of CRH, which could serve as a link between CRH and inflammatory responses in ischemic injury via CRH-R1.

Stress-mediated heart rate dynamics after deletion of the gene encoding corticotropin-releasing factor receptor 2

The objective of the present study was to investigate the potential role of corticotropin-releasing factor receptor subtype 2 (CRFR2) in autonomic regulation of heart rate and heart rate variability under physiological conditions in conscious mice. Heart rate dynamics during novelty exposure and auditory fear conditioning were assessed by radiotelemetry. Heart rate responses and heart rate variability values were not different in CRFR2+/+ and CRFR2-/- mice during novelty exposure, which was associated with similar locomotor activity exhibited by both genotypes. The heart rate responses during retention of conditioned auditory fear were similar and the exponential relationship between heart rate and heart rate variability was independent of genotype. Pharmacological stimulation of the peripheral CRFR2beta by intraperitoneal injection of 200 ng human/rat corticotropin-releasing factor yielded a sustained tachycardia in wildtype control (CRFR2+/+) mice which was absent in CRFR2-deficient (CRFR2-/-) mice. Similarly, the tachycardia was effectively blocked by preinjection of the CRFR2 antagonist antisauvagine-30. In conclusion, the results indicate the involvement of CRFR2 in heart rate dynamics upon pharmacological stimulation but demonstrate that CRFR2 is not involved in baseline heart rate regulation and stress-mediated modulation of heart rate responses.

Beneficial hemodynamic, endocrine, and renal effects of urocortin in experimental heart failure: comparison with normal sheep

OBJECTIVES

The goal of this study was to determine the bioactivity of urocortin (Ucn) in experimental heart failure (HF).

BACKGROUND

Urocortin may participate in cardiovascular function and pressure/volume homeostasis. Its effects in HF are unknown.

METHODS

Eight normal sheep and eight sheep with pacing-induced HF received ovine Ucn (10, 50, and 100 mg intravenous boluses at 2-h intervals) in vehicle-controlled studies.

RESULTS

Urocortin boluses dose-dependently increased plasma Ucn (p < 0.001). Pharmacokinetics were similar in normal and HF sheep with half-lives approximating 1.3 and 19.5 h for the first and second phases, respectively. In HF, cardiac output increased (twofold), while peripheral resistance, left atrial pressure (both 50% falls: p < 0.001), and mean arterial pressure (p < 0.05) fell. In normal sheep, changes in peripheral resistance and atrial pressure were blunted and in arterial pressure were directionally opposite. Urocortin induced persistent, dose-dependent falls (30% to 50%) in plasma vasopressin, renin activity, aldosterone, natriuretic peptides (all p < 0.001), and endothelin-1 (p < 0.05) in HF sheep, while adrenocorticotrophic hormone and cortisol levels rose acutely (both p < 0.001). In comparison, Ucn in normal sheep resulted in a similar rise in cortisol and fall in aldosterone, no significant effects on plasma renin activity and natriuretic peptides, and a rise in vasopressin. Urocortin produced dose-dependent, sustained increases in urine volume (twofold, p < 0.01), sodium excretion (>9-fold rise, p < 0.001), and creatinine clearance (p < 0.001) in HF sheep. No significant renal effects were observed in normal sheep.

CONCLUSIONS

Urocortin has profound and sustained hemodynamic, hormonal, and renal effects in experimental HF. Urocortin may have a role in pressure/volume homeostasis in HF and may provide a novel therapeutic approach to this disease.

K(ATP) channel gene expression is induced by urocortin and mediates its cardioprotective effect

BACKGROUND

Urocortin is a novel cardioprotective agent that can protect cardiac myocytes from the damaging effects of ischemia/reperfusion both in culture and in the intact heart and is effective when given at reperfusion.

METHODS AND RESULTS

We have analyzed global changes in gene expression in cardiac myocytes after urocortin treatment using gene chip technology. We report that urocortin specifically induces enhanced expression of the Kir 6.1 cardiac potassium channel subunit. On the basis of this finding, we showed that the cardioprotective effect of urocortin both in isolated cardiac cells and in the intact heart is specifically blocked by both generalized and mitochondrial-specific K(ATP) channel blockers, whereas the cardioprotective effect of cardiotrophin-1 is unaffected. Conversely, inhibiting the Kir 6.1 channel subunit greatly enhances cardiac cell death after ischemia.

CONCLUSIONS

This is, to our knowledge, the first report of the altered expression of a K(ATP) channel subunit induced by a cardioprotective agent and demonstrates that K(ATP) channel opening is essential for the effect of this novel cardioprotective agent.

Urocortin has cell-proliferative effects on cardiac non-myocytes

Urocortin (Ucn) is a member of the corticotropin-releasing hormone (CRH)-related peptides that has been reported to have cardiac inotropic and hypertrophic effects. In addition, Ucn mRNA was expressed in cardiac myocytes (MCs) and Ucn was suggested to have cardioprotective effects. Recently, it was reported that Ucn mRNA was expressed in cardiac non-myocytes (NMCs). Based on these facts, Ucn is assumed to affect not only MCs but also NMCs in an autocrine fashion. The present study was designed to elucidate a pathophysiological role of Ucn on NMCs. NMCs were prepared by the discontinuous Percoll gradient and adhesion method. Ucn increased [(3)H]-thymidine uptake into NMCs. Ucn also enhanced endothelin-1-induced increase of [(3)H]-thymidine uptake into NMCs. Effects of Ucn on [(3)H]-thymidine uptake into NMCs were significantly abolished by the protein kinase A inhibitor, H89 (10(-5) M), but not by a competitive antagonist of CRH receptors, astressin (10(-5) M). Ucn also increased intracellular cAMP accumulation more potently than CRH on a molar basis. Finally, both MCs and NMCs also secreted Ucn. Together with the recent findings, at least in NMCs, these data suggest that Ucn could exert its own actions via the cAMP signaling pathway, but not through known CRH type 2 receptors, in an autocrine fashion. In conclusion, the present study indicated that Ucn was secreted not only from MCs but also from NMCs and that the primary source of Ucn acting on heart was the heart itself. On the other hand, Ucn could proliferate NMCs as well as MCs, suggesting that Ucn could be involved in cardiac hypertrophy and fibrosis, i.e., cardiac remodeling, in spite of its putative cardioprotective actions.

Urocortin

Urocortin (Ucn) is a 40 amino acid peptide which is closely related to corticotrophin-releasing factor (CRF). It is expressed in specific regions of the brain but is also detectable in other organs notably the heart. Although some of the effects of Ucn in the nervous system such as enhanced anxiety and activity mimic those of CRF, Ucn is a much more potent suppressor of appetite/feeding behaviour. Moreover, Ucn has much more potent effects on the cardiovascular system than CRF, including enhanced cardiac contractility/heart rate and enhanced resistance of cardiac cells to injury induced, for example, by ischaemia/reperfusion. This suggests Ucn may play a key role in the response of the cardiovascular system to stress. In addition, Ucn represents a novel cardioprotective agent which may be of therapeutic use in treating the damaging effects of cardiac ischaemia and subsequent reperfusion.

Urocortin promotes hemodynamic and bioenergetic recovery and improves cell survival in the isolated rat heart exposed to ischemia/reperfusion

OBJECTIVES

This study evaluates the hemodynamic, bioenergetic and cytoprotective effects of urocortin (Ucn) in the isolated rat heart exposed to ischemia (I)/reperfusion (R).

BACKGROUND

We have previously demonstrated that administration of exogenous Ucn reduces infarct size in ischemic-reperfused rat hearts.

METHODS

Urocortin 10(-8)M was added to the perfusate before I, before I and during R, and during R alone in the isolated pulsed rat heart exposed to 35 min I followed by 60 min R.

RESULTS

Partial to complete recovery of diastolic pressure and developed pressure was seen irrespective of when Ucn was perfused. In particular, beneficial effects are observed when Ucn is only given during R. Urocortin given only before I, and before I and over R, although not during R alone, also produces significant recovery of high-energy phosphate pools. In each group, improvement in ventricular function is associated with reduction both in myocardial damage, assessed by creatine phosphokinase release, and in endothelial cell and cardiomyocyte apoptosis, assessed by caspase 3 activity and fluorescent-based terminal deoxynucleotidyl transferase mediated nick end labelling enhanced with counterstains. These improvements in ventricular performance, bioenergetics and cell survival are not secondary to any inotropic effects of Ucn.

CONCLUSIONS

This is the first report to show enhanced cardiac function induced by Ucn during I/R. Because the cytoprotective and functional benefits are still produced when Ucn is given only at R, these data suggest that Ucn may be useful clinically in the management of myocardial infarction.

Cardiotrophin-1 and urocortin cause protection by the same pathway and hypertrophy via distinct pathways in cardiac myocytes

Cardiotrophin-1 (CT-1) is an Interleukin-6 family cytokine with known hypertrophic and protective effects in cardiac cells. CT-1 and the corticotrophin releasing hormone-like hormone urocortin protect cardiac myocytes by the same p42/44 mitogen activated protein kinase (p42/44 MAPK) dependent pathway. We investigated whether urocortin is also hypertrophic in cardiac myocytes and whether it shares a common pathway with CT-1 for this effect. Moreover, we also investigated, for the first time whether CT-1 and urocortin can induce hypertrophy in cultured adult as opposed to neonatal cardiac cells. Urocortin and CT-1 caused hypertrophy (as measured by an increase in cell area and enhanced protein: DNA ratio) in both adult and neonatal rat cultured cardiac myocytes. The hypertrophic effect of CT-1 was dependent on the signal transducer and activator of transcription 3 (STAT3) pathway but the hypertrophic effect of urocortin was independent of this pathway. In contrast, inhibition of the protective p42/p44 MAPK pathway has no effect on the hypertrophic effect of CT-1 or urocortin. Additionally, inhibition of the STAT3 pathway has no effect on the protective effect of CT-1 or urocortin. These results identify urocortin as a novel hypertrophic and protective agent whose hypertrophic effect is mediated by a distinct pathway to that activated by CT-1, although the two factors mediate protection via the same pathway.

Urocortin-induced endothelium-dependent relaxation of rat coronary artery: role of nitric oxide and K+ channels

1. The mechanisms underlying the vasodilator response to urocortin are incompletely understood. The present study was designed to examine the role of endothelial nitric oxide and Ba(2+)-sensitive K(+) channels in the endothelium-dependent component of urocortin-induced relaxation in the rat left anterior descending coronary artery. 2. Urocortin induced both endothelium-dependent and -independent relaxation with respective pD(2) of 8.64+/-0.03 and 7.90+/-0.10. Removal of endothelium reduced the relaxing potency of urocortin. In rings pretreated with 10(-4) M N(G)-nitro-L-arginine methyl ester, 10(-5) M methylene blue or 10(-5) M ODQ, the urocortin-induced relaxation was similar to that observed in endothelium-denuded rings. L-Arginine (5x10(-4) M) antagonized the effect of N(G)-nitro-L-arginine methyl ester. 3. The relaxant response to urocortin was reduced in endothelium-intact rings preconstricted by 3.5x10(-2) M K(+) and abolished when extracellular K(+) was raised to 5x10(-2) M. Pretreatment with 10(-4) M BaCl(2) significantly inhibited urocortin-induced relaxation. Combined treatment with 10(-4) M BaCl(2) plus 10(-4) M N(G)-nitro-L-arginine methyl ester did not cause further inhibition. In urocortin (10(-8) M)-relaxed rings, BaCl(2) induced concentration-dependent reversal in vessel tone. Tertiapin-Q (10(-6) M) also attenuated urocortin-induced relaxation. In contrast, BaCl(2) did not alter urocortin-induced relaxation in endothelium-denuded rings. 4. In endothelium-denuded rings, hydroxylamine- and nitroprusside-induced relaxation was inhibited by 10(-4) M BaCl(2), but not by 10(-6) M tertiapin-Q. 5. The endothelium of the coronary artery was moderately stained with the antiserum against urocortin. 6. Taken together, the present results indicate that the urocortin-induced endothelium-dependent relaxation of rat coronary arteries is likely attributable to endothelial nitric oxide and subsequent activation of Ba(2+)- or tertiapin-Q-sensitive K(+) channels. The urocortin-induced endothelium-dependent relaxation appears to be mediated by cyclic GMP-dependent mechanisms.

Urocortin, but not urocortin II, protects cultured hippocampal neurons from oxidative and excitotoxic cell death via corticotropin-releasing hormone receptor type I

Urocortin and urocortin II are members of the corticotropin-releasing hormone (CRH) family of neuropeptides that function to regulate stress responses. Two high-affinity G-protein-coupled receptors have been identified that bind CRH and/or urocortin I and II, designated CRHR1 and CRHR2, both of which are present in hippocampal regions of mammalian brain. The hippocampus plays an important role in regulating stress responses and is a brain region in which neurons are vulnerable during disease and stress conditions, including cerebral ischemia, Alzheimer's disease, and anxiety disorders. Here we report that urocortin exerts a potent protective action in cultured rat hippocampal neurons with concentrations in the range of 0.5-5.0 pm, increasing the resistance of the cells to oxidative (amyloid beta-peptide, 4-hydroxynonenal, ferrous sulfate) and excitotoxic (glutamate) insults. We observed that urocortin is 10-fold more potent than CRH in protecting hippocampal neurons from insult, whereas urocortin II is ineffective. RT-PCR and sequencing analyses revealed the presence of both CRHR1 and CRHR2 in the hippocampal cultures, with CRHR1 being expressed at much higher levels than CRHR2. Using subtype-selective CRH receptor antagonists, we provide evidence that the neuroprotective effect of exogenously added urocortin is mediated by CRHR1. Furthermore, we provide evidence that the signaling pathway that mediates the neuroprotective effect of urocortin involves cAMP-dependent protein kinase, protein kinase C, and mitogen-activated protein kinase. This is the first demonstration of a biological activity of urocortin in hippocampal neurons, suggesting a role for the peptide in adaptive responses of hippocampal neurons to potentially lethal oxidative and excitotoxic insults.

Urocortin protects against ischemic injury via a MAPK-dependent pathway

Urocortin (UCN), is a peptide related to hypothalamic corticotrophin releasing hormone (CRF) and binds with high affinity to the CRF-R2 beta receptor which is expressed in the heart. UCN prevents cell death when administered to primary cardiac myocyte cultures both prior to simulated hypoxia/ischemia and at the point of reoxygenation after simulated hypoxia/ischemia as assayed by trypan blue exclusion. 3'-OH end labeling of DNA (TUNEL), annexin-V and fluorescence activated cell sorting. The protective effect of UCN is dependent on the p42/p44 mitogen-activated protein kinase (MAPK)-pathway. UCN also reduces damage in isolated rat hearts ex vivo, subjected to regional ischemia/reperfusion with the protective effect being observed when UCN is given either prior to ischemia or at the time of reperfusion after ischemia. Hence, UCN is a cardioprotective agent, which acts when given prior to ischemia or after ischemia at reperfusion.

Urocortin protects against ischemic and reperfusion injury via a MAPK-dependent pathway

Urocortin (UCN) is a peptide related to hypothalamic corticotrophin-releasing hormone and binds with high affinity to corticotrophin-releasing hormone receptor-2beta, which is expressed in the heart. In this study, we report that UCN prevented cell death when administered to primary cardiac myocyte cultures both prior to simulated hypoxia/ischemia and at the point of reoxygenation after simulated hypoxia/ischemia. UCN-mediated cell survival was measured by trypan blue exclusion, 3'-OH end labeling of DNA (TUNEL), annexin V, and fluorescence-activated cell sorting. To explore the mechanisms that could be responsible for this effect, we investigated the involvement of MAPK-dependent pathways. UCN caused rapid phosphorylation of ERK1/2-p42/44, and PD98059, which blocks the MEK1-ERK1/2-p42/44 cascade, also inhibited the survival-promoting effect of UCN. Most important, UCN reduced damage in isolated rat hearts ex vivo subjected to regional ischemia/reperfusion, with the protective effect being observed when UCN was given either prior to ischemia or at the time of reperfusion after ischemia. This suggests a novel function of UCN as a cardioprotective agent that could act when given after ischemia, at reperfusion.