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

Mitochondrial Kinase Signaling for Cardioprotection

Myocardial ischemia/reperfusion injury is reduced by cardioprotective adaptations such as local or remote ischemic conditioning. The cardioprotective stimuli activate signaling cascades, which converge on mitochondria and maintain the function of the organelles, which is critical for cell survival. The signaling cascades include not only extracellular molecules that activate sarcolemmal receptor-dependent or -independent protein kinases that signal at the plasma membrane or in the cytosol, but also involve kinases, which are located to or within mitochondria, phosphorylate mitochondrial target proteins, and thereby modify, e.g., respiration, the generation of reactive oxygen species, calcium handling, mitochondrial dynamics, mitophagy, or apoptosis. In the present review, we give a personal and opinionated overview of selected protein kinases, localized to/within myocardial mitochondria, and summarize the available data on their role in myocardial ischemia/reperfusion injury and protection from it. We highlight the regulation of mitochondrial function by these mitochondrial protein kinases.

KATP channels are regulators of programmed cell death and targets for the creation of novel drugs against ischemia/reperfusion cardiac injury

BACKGROUND

The use of percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI) is associated with a mortality rate of 5%-7%. It is clear that there is an urgent need to develop new drugs that can effectively prevent cardiac reperfusion injury. ATP-sensitive K+ (KATP ) channel openers (KCOs) can be classified as such drugs.

RESULTS

KCOs prevent irreversible ischemia and reperfusion injury of the heart. KATP channel opening promotes inhibition of apoptosis, necroptosis, pyroptosis, and stimulation of autophagy. KCOs prevent the development of cardiac adverse remodeling and improve cardiac contractility in reperfusion. KCOs exhibit antiarrhythmic properties and prevent the appearance of the no-reflow phenomenon in animals with coronary artery occlusion and reperfusion. Diabetes mellitus and a cholesterol-enriched diet abolish the cardioprotective effect of KCOs. Nicorandil, a KCO, attenuates major adverse cardiovascular event and the no-reflow phenomenon, reduces infarct size, and decreases the incidence of ventricular arrhythmias in patients with acute myocardial infarction.

CONCLUSION

The cardioprotective effect of KCOs is mediated by the opening of mitochondrial KATP (mitoKATP ) and sarcolemmal KATP (sarcKATP ) channels, triggered free radicals' production, and kinase activation.

Chondroprotection by urocortin involves blockade of the mechanosensitive ion channel Piezo1

Osteoarthritis (OA) is characterised by progressive destruction of articular cartilage and chondrocyte cell death. Here, we show the expression of the endogenous peptide urocortin1 (Ucn1) and two receptor subtypes, CRF-R1 and CRF-R2, in primary human articular chondrocytes (AC) and demonstrate its role as an autocrine/paracrine pro-survival factor. This effect could only be removed using the CRF-R1 selective antagonist CP-154526, suggesting Ucn1 acts through CRF-R1 when promoting chondrocyte survival. This cell death was characterised by an increase in p53 expression, and cleavage of caspase 9 and 3. Antagonism of CRF-R1 with CP-154526 caused an accumulation of intracellular calcium (Ca2+) over time and cell death. These effects could be prevented with the non-selective cation channel blocker Gadolinium (Gd3+). Therefore, opening of a non-selective cation channel causes cell death and Ucn1 maintains this channel in a closed conformation. This channel was identified to be the mechanosensitive channel Piezo1. We go on to determine that this channel inhibition by Ucn1 is mediated initially by an increase in cyclic adenosine monophosphate (cAMP) and a subsequent inactivation of phospholipase A2 (PLA2), whose metabolites are known to modulate ion channels. Knowledge of these novel pathways may present opportunities for interventions that could abrogate the progression of OA.

Urocortin increased endothelial ICAM1 by cPLA2-dependent NF-κB and PKA pathways in HUVECs

Urocortin (Ucn1), a member of the corticotrophin-releasing hormone (CRH) family, has been reported to participate in inflammation. The increased expression of intercellular adhesion molecule 1 (ICAM1) plays important roles in inflammation and immune responses. Our previous results demonstrated that Ucn1 significantly enhanced the expression of ICAM1. However, the underlying mechanisms are still unknown. The purpose of this study is to investigate the detailed mechanisms of Ucn1-induced upregulation of ICAM1. Here, we characterized the mechanisms of Ucn1 usage to regulate ICAM1 expression in human umbilical vein endothelial cells (HUVECs). Our data revealed that Ucn1 increased ICAM1 and cyclooxygenase 2 (COX2) expressions in a time-dependent manner via CRH receptor 2 (CRHR2). In addition, COX2 was involved in ICAM1 upregulation. Furthermore, Ucn1 could increase the expression and phosphorylation of cytosolic phospholipases A2 (cPLA2) in a time-dependent manner via CRHR2 and CRHR1. Moreover, ablation of cPLA2 by the inhibitor pyrrophenone or siRNA attenuated the ICAM1 increase induced by Ucn1. In addition, nuclear factor κB (NF-κB) was activated, indicated by the increase in nuclear p65NF-κB expression and phosphorylation of p65NF-κB, depending on cPLA2 and CRHR2 activation. Pyrrolidinedithiocarbamic acid, an inhibitor of NF-κB, abolished the elevation of ICAM1 but not COX2. Also, Ucn1 increased the production of prostaglandin E2 (PGE2) which further activated protein kinase A (PKA)-CREB pathways dependent of cPLA2 via CRHR2. Moreover, the increase in NF-κB phosphorylation was not affected by the selective COX2 inhibitor NS-398 or the PKA inhibitor H89. In conclusion, these data indicate that Ucn1 increase the ICAM1 expression via cPLA2-NF-κB and cPLA2-COX2-PGE2-PKA-CREB pathways by means of CRHR2.

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

Urocortin 2 (Ucn2), a peptide of the corticotropin-releasing factor (CRF) family, binds with high affinity to type 2 CRF receptors (CRFR2) on cardiomyocytes and confers protection against ischemia/reperfusion. The mechanisms by which the Ucn2-CRFR2 axis mitigates against ischemia/reperfusion injury remain incompletely delineated. Activation of AMP-activated protein kinase (AMPK) also limits cardiac damage during ischemia/reperfusion. AMPK is classically activated by alterations in cellular energetics; however, hormones, cytokines, and additional autocrine/paracrine factors also modulate its activity. We examined the effects of both the endogenous cardiac Ucn2 autocrine/paracrine pathway and Ucn2 treatment on AMPK regulation. Ucn2 treatment increased AMPK activation and downstream acetyl-CoA carboxylase phosphorylation and glucose uptake in isolated heart muscles. These actions were blocked by the CRFR2 antagonist anti-sauvagine-30 and by a PKCε translocation-inhibitor peptide (εV1-2). Hypoxia-induced AMPK activation was also blunted in heart muscles by preincubation with either anti-sauvagine-30, a neutralizing anti-Ucn2 antibody, or εV1-2. Treatment with Ucn2 in vivo augmented ischemic AMPK activation and reduced myocardial injury and cardiac contractile dysfunction after regional ischemia/reperfusion in mice. Ucn2 also directly activated AMPK in ex vivo-perfused mouse hearts and diminished injury and contractile dysfunction during ischemia/reperfusion. Thus, both Ucn2 treatment and the endogenous cardiac Ucn2 autocrine/paracrine pathway activate AMPK signaling pathway, via a PKCε-dependent mechanism, defining a Ucn2-CRFR2-PKCε-AMPK pathway that mitigates against ischemia/reperfusion injury.

Urocortin protects chondrocytes from NO-induced apoptosis: a future therapy for osteoarthritis?

Osteoarthritis (OA) is characterized by a loss of joint mobility and pain resulting from progressive destruction and loss of articular cartilage secondary to chondrocyte death and/ or senescence. Certain stimuli including nitric oxide (NO) and the pro-inflammatory cytokine tumor necrosis factor α (TNF-α have been implicated in this chondrocyte death and the subsequent accelerated damage to cartilage. In this study, we demonstrate that a corticotrophin releasing factor (CRF) family peptide, urocortin (Ucn), is produced by a human chondrocyte cell line, C-20/A4, and acts both as an endogenous survival signal and as a cytoprotective agent reducing the induction of apoptosis by NO but not TNF-α when added exogenously. Furthermore, treatment with the NO donor S-nitroso-N-acetyl-D-L-penicillamine upregulates chondrocyte Ucn expression, whereas treatment with TNF-α does not. The chondroprotective effects of Ucn are abolished by both specific ligand depletion (with an anti-Ucn antibody) and by CRF receptor blockade with the pan-CRFR antagonist α-helical CRH(9-41). CRFR expression was confirmed by reverse transcription-PCR with subsequent amplicon sequence analysis and demonstrates that C-20/A4 cells express both CRFR1 and CRFR2, specifically CRFR1α and CRFR2β. Protein expression of these receptors was confirmed by western blotting. The presence of both Ucn and its receptors in these cells, coupled with the induction of Ucn by NO, suggests the existence of an endogenous autocrine/paracrine chondroprotective mechanism against stimuli inducing chondrocyte apoptosis via the intrinsic/mitochondrial pathway.

Intermittent hypobaric hypoxia improves postischemic recovery of myocardial contractile function via redox signaling during early reperfusion

Intermittent hypobaric hypoxia (IHH) protects hearts against ischemia-reperfusion (I/R) injury, but the underlying mechanisms are far from clear. ROS are paradoxically regarded as a major cause of myocardial I/R injury and a trigger of cardioprotection. In the present study, we investigated whether the ROS generated during early reperfusion contribute to IHH-induced cardioprotection. Using isolated perfused rat hearts, we found that IHH significantly improved the postischemic recovery of left ventricular (LV) contractile function with a concurrent reduction of lactate dehydrogenase release and myocardial infarct size (20.5 ± 5.3% in IHH vs. 42.1 ± 3.8% in the normoxic control, P < 0.01) after I/R. Meanwhile, IHH enhanced the production of protein carbonyls and malondialdehyde, respective products of protein oxidation and lipid peroxidation, in the reperfused myocardium and ROS generation in reperfused cardiomyocytes. Such effects were blocked by the mitochondrial ATP-sensitive K(+) channel inhibitor 5-hydroxydecanoate. Moreover, the IHH-improved postischemic LV performance, enhanced phosphorylation of PKB (Akt), PKC-ε, and glycogen synthase kinase-3β, as well as translocation of PKC-ε were not affected by applying H(2)O(2) (20 μmol/l) during early reperfusion but were abolished by the ROS scavengers N-(2-mercaptopropionyl)glycine (MPG) and manganese (III) tetrakis (1-methyl-4-pyridyl)porphyrin. Furthermore, IHH-reduced lactate dehydrogenase release and infarct size were reversed by MPG. Consistently, inhibition of Akt with wortmannin and PKC-ε with εV1-2 abrogated the IHH-improved postischemic LV performance. These findings suggest that IHH-induced cardioprotection depends on elevated ROS production during early reperfusion.

Relevance of urocortins to cardiovascular disease

Acquired cardiovascular diseases such as coronary heart disease, peripheral artery disease and related vascular problems contribute to more than one-third of worldwide morbidity and mortality. In many instances, particularly in the under developed world, cardiovascular diseases are diagnosed at a late stage limiting the scope for improving outcomes. A range of therapies already exist for established cardiovascular disease, although there is significant interest in further understanding disease pathogenesis in order to improve diagnosis and achieve primary and secondary therapeutic goals. The urocortins are a group of recently defined peptide members of the corticotrophin-releasing factor family. Previous pre-clinical work and human association studies suggest that urocortins have potential to exert some beneficial and other detrimental effects on the heart and major blood vessels. More current evidence however favours beneficial effects of urocortins, for example these peptides have been shown to inhibit production of reactive oxygen species and vascular cell apoptosis, and thus may have potential to antagonise the progression of cardiovascular disease. This review summarises published data on the potential role of urocortins in cardiovascular disease.

Expression of urocortin peptides in canine myocardium and plasma

Urocortin (Ucn) peptides are the endogenous ligands for the corticotropin-releasing factor type 2 receptor (CRFR2). They have potentially important roles in cardiovascular physiology in health and disease, and show promise as therapeutics for congestive heart failure. Analysis of canine heart tissue showed mRNA expression of Ucn 1, Ucn 3 and CRFR2 in all heart chambers. Immunohistochemistry also demonstrated Ucns 1 and 3 expression in cardiomyocytes. To assess the potential usefulness of circulating Ucns as markers of heart disease, plasma samples from 45 dogs with cardiac disease and 15 controls were analysed by radioimmunoassay. Both Ucns 1 and 3 were measurable but the presence of cardiac disease did not alter their concentrations. Therefore, whilst Ucns are expressed in canine myocardium (where they may play a role in the endogenous neurohumoral response to cardiac disease or failure) they do not appear to be sensitive biomarkers of cardiac disease in our canine patient population.

Circulating levels of stress associated peptide Urocortin in heart failure patients

The available data suggest that Urocortin (UCN), a cardioprotective and vasoactive peptide known from fish neuroendocrinology, is involved in cardiac regulation. The aim of this study was to determine UCN plasma concentrations in patients with heart failure (HF). Plasma concentrations of UCN, measured in 42 fully treated HF patients. UCN, were determined using a specific ELISA assay after acidic extraction with Sep-Pak C18 columns. Circulating levels of other neurohormones Nt-proBNP, Nt-proANP and Big ET-1 were also determined. Reference values were obtained from 20 healthy age- and sex-matched subjects. In comparison with controls, UCN plasma concentrations (geometric mean [95% CI]) were significantly increased in HF patients (88 pmol/L [75-105] vs 46 [39-54], p<0.001). As expected, the other neurohormones were also significantly increased in HF patients (Nt-proBNP: 3501 pg/ml [2356-5202] vs 35 [24-51], Nt-proANP: 5498 pg/ml [4336-6971] vs 324 [255-411] and Big ET-1: 15.8 pg/ml [13.6-18.4] vs 5.9 [5.2-6.8]; p<0.01 for all vs controls). No significant correlation was observed between UCN and the other HF biomarkers. Our results demonstrate that plasma concentrations of UCN are significantly increased in patients with HF and that UCN may participate in the neurohumoral response of HF.

Urocortin 2 protects against retinal degeneration following bilateral common carotid artery occlusion in the rat

Urocortin 2 (Ucn 2) is corticotropin-releasing factor (CRF) paralog that preferentially activates CRF(2) receptors. Ucns exert CRF(2)-mediated cytoprotective effects against ischemia-reperfusion injury in cardiomyocytes. However, little is known regarding potential retinoprotective effects of Ucns despite the known presence of CRF family peptides and their receptors (predominantly CRF(2 alpha)) in retina. Therefore, the present study investigated the effects of post-ischemic intravitreal Ucn 2 (2 nmol) administration on ischemia-induced retinal degeneration. Two-month-old rats were subjected to permanent bilateral common carotid artery occlusion, and their retinas were processed histologically after two weeks survival to determine the density of viable cells in the ganglion cell layer and the thickness of all retinal layers. In vehicle-treated subjects, carotid occlusion reduced retina thickness by approximately 60% as compared to sham-operated animals. In contrast, intraocular Ucn 2 treatment led to a marked amelioration of the retinal layers, and the thickness of all layers was significantly increased by 40% compared to ischemic vehicle-treated subjects. Ucn 2 treatment also increased the number of cells by 55% in the ganglion cell layer as compared to those from carotid-occluded retinas of vehicle-treated subjects. These findings suggest that intraocular Ucn 2 treatment may protect against ischemia-induced retinal degeneration, results with potential therapeutic implications for ophthalmic diseases.

Role of Ca2+-independent phospholipase A2 and store-operated pathway in urocortin-induced vasodilatation of rat coronary artery

Urocortin has been shown to produce vasodilatation in several arteries, but the precise mechanism of its action is still poorly understood. Here we demonstrate the role of store operated Ca2+ entry (SOCE) regulated by Ca2+-independent phospholipase A2 (iPLA2) in phenylephrine hydrochloride (PE)-induced vasoconstriction, and we present the first evidence that urocortin induces relaxation by the modulation of SOCE and iPLA2 in rat coronary artery. Urocortin produces an endothelium independent relaxation, and its effect is concentration-dependent (IC50 approximately = 4.5 nmol/L). We show in coronary smooth muscle cells (SMCs) that urocortin inhibits iPLA2 activation, a crucial step for SOC channel activation, and prevents Ca2+ influx evoked by the emptying of the stores via a cAMP and protein kinase A (PKA)-dependent mechanism. Lysophophatidylcholine and lysophosphatidylinositol, products of iPLA2, exactly mimic the effect of the depletion of the stores in presence of urocortin. Furthermore, we report that long treatment with urocortin downregulates iPLA2 mRNA and proteins expression in rat coronary smooth muscle cells. In summary, we propose a new mechanism of vasodilatation by urocortin which involves the regulation of iPLA2 and SOCE via the stimulation of a cAMP/PKA-dependent signal transduction cascade in rat coronary artery.

Urocortin prevents mitochondrial permeability transition in response to reperfusion injury indirectly by reducing oxidative stress

Urocortin (UCN) protects hearts against ischemia and reperfusion injury whether given before ischemia or at reperfusion. Here we investigate the roles of PKC, reactive oxygen species, and the mitochondrial permeability transition pore (MPTP) in mediating these effects. In Langendorff-perfused rat hearts, acute UCN treatment improved hemodynamic recovery during reperfusion after 30 min of global ischemia; this was accompanied by less necrosis (lactate dehydrogenase release) and MPTP opening (mitochondrial entrapment of 2-[(3)H]deoxyglucose). UCN pretreatment protected mitochondria against calcium-induced MPTP opening, but only if the mitochondria had been isolated from hearts after reperfusion. These mitochondria also exhibited less protein carbonylation, suggesting that UCN decreases levels of oxidative stress. In isolated adult and neonatal rat cardiac myocytes, both acute (60 min) and chronic (16 h) treatment with UCN reduced cell death following simulated ischemia and re-oxygenation. This was accompanied by less MPTP opening as measured using tetramethylrhodamine methyl ester. The level of oxidative stress during reperfusion was reduced in cells that had been pretreated with UCN, suggesting that this is the mechanism by which UCN desensitizes the MPTP to reperfusion injury. Despite the fact that we could find no evidence that either PKC-epsilon or PKC-alpha translocate to the mitochondria following acute UCN treatment, inhibition of PKC with chelerythrine eliminated the effect of UCN on oxidative stress. Our data suggest that acute UCN treatment protects the heart by inhibiting MPTP opening. However, the mechanism appears to be indirect, involving a PKC-mediated reduction in oxidative stress.

Physiology, pharmacology, and therapeutic relevance of urocortins in mammals: ancient CRF paralogs

Urocortins, three paralogs of the stress-related peptide corticotropin-releasing factor (CRF) found in bony fish, amphibians, birds, and mammals, have unique phylogenies, pharmacologies, and tissue distributions. As a result and despite a structural family resemblance, the natural functions of urocortins and CRF in mammalian homeostatic responses differ substantially. Endogenous urocortins are neither simply counterpoints nor mimics of endogenous CRF action. In their own right, urocortins may be clinically relevant molecules in the pathogenesis or management of many conditions, including congestive heart failure, hypertension, gastrointestinal and inflammatory disorders (irritable bowel syndrome, active gastritis, gastroparesis, and rheumatoid arthritis), atopic/allergic disorders (dermatitis, urticaria, and asthma), pregnancy and parturition (preeclampsia, spontaneous abortion, onset, and maintenance of effective labor), major depression and obesity. Safety trials for intravenous urocortin treatment have already begun for the treatment of congestive heart failure. Further understanding the unique functions of urocortin 1, urocortin 2, and urocortin 3 action may uncover other therapeutic opportunities.

Role of oxidative/nitrosative stress in the tolerance to ischemia/reperfusion injury in cardiomyopathic hamster heart

We investigated the role of oxidative/nitrosative stress in the tolerance to ischemia/reperfusion (I/R) injury in BIO14.6 cardiomyopathy hamster hearts at 6 weeks of age. These hearts showed no significant morphologic change and left ventricular (LV) dysfunction. However, expression and activity of iNOS, nitrotyrosine (NT) formation, and protein kinase C (PKC)-epsilon activity were increased in these hearts. When the BIO14.6 hamster hearts were isolated and subjected to 40 min of global ischemia, they showed smaller myocardial necrosis and greater recovery of LV function during reperfusion compared with the control hamster heart. All of these effects were abrogated by prolonged treatment with the antioxidant, 2-mercaptopropionylglycine (MPG). Brief preischemic treatment with MPG or the iNOS inhibitor 1400W also abrogated NT formation and activation of PKC-epsilon and inhibited the tolerance to I/R injury in the BIO14.6 hamster heart. Brief preischemic treatment with the PKC inhibitor chelerythrine or the K(ATP) channel blockers, 5-hydroxydecanoate (5-HD) and glibenclamide, had no effect on iNOS activation and NT formation but inhibited the tolerance to I/R injury in the cardiomyopathic heart. These results suggest that oxidative/nitrosative stress plays a role in the tolerance to I/R injury in the cardiomyopathic heart through activation of PKC and the downstream effectors, K(ATP) channels.

Protein kinase Cepsilon interacts with cytochrome c oxidase subunit IV and enhances cytochrome c oxidase activity in neonatal cardiac myocyte preconditioning

We have previously identified a phorbol ester-induced PKCepsilon (protein kinase Cepsilon) interaction with the ( approximately 18 kDa) COIV [CO (cytochrome c oxidase) subunit IV] in NCMs (neonatal cardiac myocytes). Since PKCepsilon has been implicated as a key mediator of cardiac PC (preconditioning), we examined whether hypoxic PC could induce PKCepsilon-COIV interactions. Similar to our recent study with phorbol esters [Ogbi, Chew, Pohl, Stuchlik, Ogbi and Johnson (2004) Biochem. J. 382, 923-932], we observed a time-dependent increase in the in vitro phosphorylation of an approx. 18 kDa protein in particulate cell fractions isolated from NCMs subjected to 1-60 min of hypoxia. Introduction of a PKCepsilon-selective translocation inhibitor into cells attenuated this in vitro phosphorylation. Furthermore, when mitochondria isolated from NCMs exposed to 30 min of hypoxia were subjected to immunoprecipitation analyses using PKCepsilon-selective antisera, we observed an 11.1-fold increase in PKCepsilon-COIV co-precipitation. In addition, we observed up to 4-fold increases in CO activity after brief NCM hypoxia exposures that were also attenuated by introducing a PKCepsilon-selective translocation inhibitor into the cells. Finally, in Western-blot analyses, we observed a >2-fold PC-induced protection of COIV levels after 9 h index hypoxia. Our studies suggest that a PKCepsilon-COIV interaction and an enhancement of CO activity occur in NCM hypoxic PC. We therefore propose novel mechanisms of PKCepsilon-mediated PC involving enhanced energetics, decreased mitochondrial reactive oxygen species production and the preservation of COIV levels.

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.