Activation of protein kinase B/Akt by urocortin is essential for its ability to protect cardiac cells against hypoxia/reoxygenation-induced cell death

Urocortin Role in Ischemia Cardioprotection and the Adverse Cardiac Remodeling

Despite the considerable progress in strategies of myocardial protection, ischemic heart diseases (IHD) and consequent heart failure (HF) remain the main cause of mortality worldwide. Several procedures are used routinely to guarantee the prompt and successful reestablishment of blood flow to preserve the myocardial viability of infarcted hearts from ischemia injuries. However, ischemic heart reperfusion/revascularization triggers additional damages that occur when oxygen-rich blood re-enters the vulnerable myocardial tissue, which is a phenomenon known as ischemia and reperfusion (I/R) syndrome. Complications of I/R injuries provoke the adverse cardiac remodeling, involving inflammation, mishandling of Ca²⁺ homeostasis, apoptotic genes activation, cardiac myocytes loss, etc., which often progress toward HF. Therefore, there is an urgent need to develop new cardioprotective therapies for IHD and HF. Compelling evidence from animal studies and pilot clinical trials in HF patients suggest that urocortin (Ucn) isoforms, which are peptides associated with stress and belonging to the corticotropin releasing factor family, have promising potential to improve cardiovascular functions by targeting many signaling pathways at different molecular levels. This review highlights the current knowledge on the role of urocortin isoforms in cardioprotection, focusing on its acute and long-term effects.

GPCR-ErbB transactivation pathways and clinical implications

Cell surface receptors including the epidermal growth factor receptor (EGFR) family and G-protein coupled receptors (GPCRs) play quintessential roles in physiology, and in diseases, including cardiovascular diseases. While downstream signaling from these individual receptor families has been well studied, the cross-talk between EGF and GPCR receptor families is still incompletely understood. Including members of both receptor families, the number of receptor and ligand combinations for unique interactions is vast, offering a frontier of pharmacologic targets to explore for preventing and treating disease. This molecular cross-talk, called receptor transactivation, is reviewed here with a focus on the cardiovascular system featuring the well-studied GPCR receptors, but also discussing less-studied receptors from both families for a broad understanding of context of expansile interactions, repertoire of cellular signaling, and disease consequences. Attention is given to cell type, level of chronicity, and disease context given that transactivation and comorbidities, including diabetes, hypertension, coronavirus infection, impact cardiovascular disease and health outcomes.

Stress hormones mediate developmental plasticity in vertebrates with complex life cycles

The environment experienced by developing organisms can shape the timing and character of developmental processes, generating different phenotypes from the same genotype, each with different probabilities of survival and performance as adults. Chordates have two basic modes of development, indirect and direct. Species with indirect development, which includes most fishes and amphibians, have a complex life cycle with a free-swimming larva that is typically a growth stage, followed by a metamorphosis into the adult form. Species with direct development, which is an evolutionarily derived developmental mode, develop directly from embryo to the juvenile without an intervening larval stage. Among the best studied species with complex life cycles are the amphibians, especially the anurans (frogs and toads). Amphibian tadpoles are exposed to diverse biotic and abiotic factors in their developmental habitat. They have extensive capacity for developmental plasticity, which can lead to the expression of different, adaptive morphologies as tadpoles (polyphenism), variation in the timing of and size at metamorphosis, and carry-over effects on the phenotype of the juvenile/adult. The neuroendocrine stress axis plays a pivotal role in mediating environmental effects on amphibian development. Before initiating metamorphosis, if tadpoles are exposed to predators they upregulate production of the stress hormone corticosterone (CORT), which acts directly on the tail to cause it to grow, thereby increasing escape performance. When tadpoles reach a minimum body size to initiate metamorphosis they can vary the timing of transformation in relation to growth opportunity or mortality risk in the larval habitat. They do this by modulating the production of thyroid hormone (TH), the primary inducer of metamorphosis, and CORT, which synergizes with TH to promote tissue transformation. Hypophysiotropic neurons that release the stress neurohormone corticotropin-releasing factor (CRF) are activated in response to environmental stress (e.g., pond drying, food restriction, etc.), and CRF accelerates metamorphosis by directly inducing secretion of pituitary thyrotropin and corticotropin, thereby increasing secretion of TH and CORT. Although activation of the neuroendocrine stress axis promotes immediate survival in a deteriorating larval habitat, costs may be incurred such as reduced tadpole growth and size at metamorphosis. Small size at transformation can impair performance of the adult, reducing probability of survival in the terrestrial habitat, or fecundity. Furthermore, elevations in CORT in the tadpole caused by environmental stressors cause long term, stable changes in neuroendocrine function, behavior and physiology of the adult, which can affect fitness. Comparative studies show that the roles of stress hormones in developmental plasticity are conserved across vertebrate taxa including humans.

Urocortin-2 in Acute Heart Failure: Role as a Marker of Volume Overload and Pulmonary Hypertension

Urocortin (Ucn)-2 has shown promising therapeutic effects on heart failure (HF). However, there are still significant knowledge gaps regarding the role and modulation of the endogenous Ucn-2 axis in the cardiovascular system and, specifically, in acute HF. We evaluated Ucn-2 levels in admission serum samples of 80 acute HF patients and assessed their association with clinical, analytical and echocardiographic parameters. Median age was 76.5 years, and 37 patients (46%) were male. Median serum Ucn-2 was 2.3ng/mL. Ucn-2 levels were positively associated with peripheral edemas (P = 0.022), hepatomegaly (P = 0.007) and sodium retention score (ρ = 0.37, P = 0.001) and inversely correlated with inferior vena cava collapse at inspiration (ρ = -0.37, P = 0.001). Additionally, patients with higher Ucn-2 levels had a higher prevalence of right atrial dilation (P = 0.027), right ventricle dilation (P = 0.008), and higher systolic pulmonary artery pressure (ρ = 0.34, P = 0.002). Regarding analytical parameters, Ucn-2 correlated positively with log BNP (r = 0.22, P = 0.055) and inversely with uric acid (r = 0.24, P = 0.029) and total (r = -0.30, P = 0.007) and low-density lipoprotein cholesterol (r = -0.23, P = 0.038). No associations were found between Ucn-2 and age, sex or left heart structure or function. In conclusion, Circulating Ucn-2 was associated with clinical and echocardiographic markers of volume overload and pulmonary hypertension in acute HF patients.

Urocortin Induces Phosphorylation of Distinct Residues of Signal Transducer and Activator of Transcription 3 (STAT3) via Different Signaling Pathways

BACKGROUND Urocortin (Ucn) is a member of the hypothalamic corticotrophin-releasing factor family and has been shown to reduce cell death in the heart caused by ischemia/reperfusion (I/R) injury. Signal transducer and activator of transcription 3 (STAT3) is a transcription factor known to function as a pro-survival and anti-apoptotic factor, whose activation depends on a variety of cytokines, including IL-6. A recent study demonstrated that urocortin induced IL-6 release from cardiomyocytes in a CRF-R2-dependent manner, suggesting a possible link between CRF-R2 stimulation and STAT3 activation. MATERIAL AND METHODS Experimental work was carried out in HL-1 cardiac myocytes exposed to serum starvation for 16-24 h. RESULTS Ucn stimulation led to IL-6 expression and release from mouse atrial HL-1 cardiomyocytes. Ucn treatment led to rapid phosphorylation of JAK2, which was blocked by the protein synthesis inhibitor cycloheximide or the JAK inhibitor AG490. Urocortin treatment induced STAT3 phosphorylation at Y705 and S727 through transactivation of JAK2 in an IL-6-dependent manner, but had no effect on STAT1 activity. Kinase inhibition experiments revealed that urocortin induces STAT3 S727 phosphorylation through ERK1/2 and Y705 phosphorylation through Src tyrosine kinase. In line with this finding, urocortin failed to induce phosphorylation of Y705 residue in SYF cells bearing null mutation of Src, while phosphorylation of S727 residue was unchanged. CONCLUSIONS Here, we have shown that Ucn induces activation of STAT3 through diverging signaling pathways. Full understanding of these signaling pathways will help fully exploit the cardioprotective properties of endogenous and exogenous Ucn.

Natural and synthetic peptides in the cardiovascular diseases: An update on diagnostic and therapeutic potentials

Several peptides play an important role in physiological and pathological conditions into the cardiovascular system. In addition to well-known vasoactive agents such as angiotensin II, endothelin, serotonin or natriuretic peptides, the vasoconstrictor Urotensin-II (Uro-II) and the vasodilators Urocortins (UCNs) and Adrenomedullin (AM) have been implicated in the control of vascular tone and blood pressure as well as in cardiovascular disease states including congestive heart failure, atherosclerosis, coronary artery disease, and pulmonary and systemic hypertension. Therefore these peptides, together with their receptors, become important therapeutic targets in cardiovascular diseases (CVDs). Circulating levels of these agents in the blood are markedly modified in patients with specific CVDs compared with those in healthy patients, becoming also potential biomarkers for these pathologies. This review will provide an overview of current knowledge about the physiological roles of Uro-II, UCN and AM in the cardiovascular system and their implications in cardiovascular diseases. It will further focus on the structural modifications carried out on original peptide sequences in the search of analogues with improved physiochemical properties as well as in the delivery methods. Finally, we have overviewed the possible application of these peptides and/or their precursors as biomarkers of CVDs.

Urocortin-2 improves right ventricular function and attenuates pulmonary arterial hypertension

Aims

Pulmonary arterial hypertension (PAH) is a devastating disease and treatment options are limited. Urocortin-2 (Ucn-2) has shown promising therapeutic effects in experimental and clinical left ventricular heart failure (HF). Our aim was to analyse the expression of Ucn-2 in human and experimental PAH, and to investigate the effects of human Ucn-2 (hUcn-2) administration in rats with monocrotaline (MCT)-induced pulmonary hypertension (PH).

Methods and results

Tissue samples were collected from patients with and without PAH and from rats with MCT-induced PH. hUcn-2 (5 μg/kg, bi-daily, i.p., for 10 days) or vehicle was administered to male wistar rats subjected to MCT injection or to pulmonary artery banding (PAB) to induce right ventricular (RV) overload without PAH. Expression of Ucn-2 and its receptor was increased in the RV of patients and rats with PAH. hUcn-2 treatment reduced PAH in MCT rats, resulting in decreased morbidity, improved exercise capacity and attenuated pulmonary arterial and RV remodelling and dysfunction. Additionally, RV gene expression of hypertrophy and failure signalling pathways were attenuated. hUcn-2 treatment also attenuated PAB-induced RV hypertrophy.

Conclusions

Ucn-2 levels are altered in human and experimental PAH. hUcn-2 treatment attenuates PAH and RV dysfunction in MCT-induced PH, has direct anti-remodelling effects on the pressure-overloaded RV, and improves pulmonary vascular function.

CRF and urocortin 3 protect the heart from hypoxia/reoxygenation-induced apoptosis in zebrafish

Fish routinely experience environmental hypoxia and have evolved various strategies to tolerate this challenge. Given the key role of the CRF system in coordinating the response to stressors and its cardioprotective actions against ischemia in mammals, we sought to characterize the cardiac CRF system in zebrafish and its role in hypoxia tolerance. We established that all genes of the CRF system, the ligands CRFa, CRFb, urotensin 1 (UTS1), and urocortin 3 (UCN3); the two receptor subtypes (CRFR1 and CRFR2); and the binding protein (CRFBP) are expressed in the heart of zebrafish: crfr1 > crfr2 = crfbp > crfa > ucn3 > crfb > uts1 In vivo, exposure to 5% O2 saturation for 15 min and 90 min of recovery resulted in four- to five-fold increases in whole heart crfb and ucn3 mRNA levels but did not affect the gene expression of other CRF system components. In vitro, as assessed by monitoring caspase 3 activity and the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling-positive cells, pretreatment of excised whole hearts with CRF or UCN3 for 30 min prevented the increase in apoptosis associated with exposure to 1% O2 saturation for 30 min with a 24-h recovery. Lastly, the addition of the nonselective CRF receptor antagonist αh-CRF(9-41) prevented the cytoprotective effects of CRF. We show that the CRF system is expressed in fish heart, is upregulated by hypoxia, and is cytoprotective. These findings identify a novel role for the CRF system in fish and a new strategy to tolerate hypoxia.

Characterization of urocortin as an anti-apoptotic protein in experimental ischemia-reperfusion model of the rat testis

The objective of this study was to investigate the role of urocortin in testicular apoptosis using an experimental ischemia-reperfusion rat model. To evaluate the change in urocortin expression and apoptotic status in the testes following ischemia-reperfusion, the left testes of rats were rotated clockwise by 720° for 1 h, and were then harvested at 0, 1, 3, 6 and 24 h after detorsion (n = 5 in each group). A time-dependent increase in the expression levels of urocortin was noted until 6 h after reperfusion, but the expression of urocortin was markedly decreased 24 h after reperfusion. However, a TUNEL assay showed that the proportion of germ cells undergoing apoptosis significantly increased 24 h after reperfusion compared with that of 6 h after reperfusion. To clarify whether or not urocortin directly regulates the testicular apoptosis induced by ischemia-reperfusion, either astressin, an antagonist of urocortin, or normal saline was injected into the rat testes 15 min before detorsion, followed by the testicular torsion. The testes were then removed 3 h after detorsion (n = 5 in each group). The testicular injection of astressin significantly increased the proportion of TUNEL-positive germ cells, and significantly decreased expression of Bcl-2 and Bcl-xL. In addition, the level of phosphorylated ERK 1/2, but not that of phosphorylated Akt, was significantly reduced by the intratesticular administration of astressin. These findings suggest that urocortin may play a cytoprotective role in the germ cells in response to ischemia-reperfusion injury through the activation of major anti-apoptotic proteins, as well as by the mitogen-activated protein kinase signaling pathway activation.

cJun N-terminal kinase (JNK) phosphorylation of serine 36 is critical for p66Shc activation

p66Shc-dependent ROS production contributes to many pathologies including ischemia/reperfusion injury (IRI) during solid organ transplantation. Inhibiting p66Shc activation may provide a novel therapeutic approach to prevent damage, which is poorly managed by antioxidants in vivo. Previous work suggested that pro-oxidant and a pro-apoptotic function of p66Shc required mitochondrial import, which depended on serine 36 phosphorylation. PKCß has been proposed as S36 kinase but cJun N-terminal kinases (JNKs) may also phosphorylate this residue. To simulate the early stages of ischemia/reperfusion (IR) we either used H2O2 treatment or hypoxia/reoxygenation (HR). As during reperfusion in vivo, we observed increased JNK and p38 activity in mouse embryonic fibroblasts (MEFs) and HL-1 cardiomyocytes along with significantly increased p66ShcS36 phosphorylation, ROS production and cell damage. Application of specific inhibitors caused a pronounced decrease in p66ShcS36 phosphorylation only in the case of JNK1/2. Moreover, S36 phosphorylation of recombinant p66Shc by JNK1 but not PKCß was demonstrated. We further confirmed JNK1/2-dependent regulation of p66ShcS36 phosphorylation, ROS production and cell death using JNK1/2 deficient MEFs. Finally, the low ROS phenotype of JNK1/2 knockout MEFs was reversed by the phosphomimetic p66ShcS36E mutant. Inhibiting JNK1/2-regulated p66Shc activation may thus provide a therapeutic approach for the prevention of oxidative damage.

Reduced expression of CRHR2 and Sp-1 in myocardium of ovariectomized rats is improved by exercise training

Exercise training has been looked on as a non-pharmacologic approach to treating ovariectomy (OVX)-induced dysfunctions. In this study, we investigated whether chronic exercise impacts on expression of urocortins (UCNs) and corticotropin-releasing hormone receptor type 2 (CRHR2) in myocardium of OVX rats. Bilateral OVX or sham-operation was performed under anesthesia. Both groups were then divided into two subgroups, with or without treadmill training for 8 weeks. It was found that OVX as well as exercise did not affect the mRNA levels of UCN, UCN2 and UCN3 in myocardium. OVX caused down-regulation of CRHR2 in myocardium. Exercise training reversed the OVX-induced reduction of CRHR2, but had no influence on CRHR2 level in sham rats. OVX resulted in a decrease in estrogen receptor α (ERα) expression in myocardium, which was restored by exercise. Moreover, exercise training also reversed OVX-induced down-regulation of specific protein-1 (Sp-1) expression in myocardium. CRHR2 expression level correlated with Sp-1 and ERα level in myocardium. These results indicate that exercise training can restore the CRHR2 level in myocardium of OVX rats, which is associated with ERα and Sp-1 expression.

CRFR1 activation protects against cytokine-induced β-cell death

During the development of diabetes β-cells are exposed to elevated concentrations of proinflammatory cytokines, TNFα and IL1β, which in vitro induce β-cell death. The class B G-protein-coupled receptors (GPCRs): corticotropin-releasing factor receptor 1 (CRFR1) and CRFR2 are expressed in pancreatic islets. As downstream signaling by other class B GPCRs can protect against cytokine-induced β-cell apoptosis, we evaluated the protective potential of CRFR activation in β-cells in a pro-inflammatory setting. CRFR1/CRFR2 ligands activated AKT and CRFR1 signaling and reduced apoptosis in human islets. In rat and mouse insulin-secreting cell lines (INS-1 and MIN6), CRFR1 agonists upregulated insulin receptor substrate 2 (IRS2) expression, increased AKT activation, counteracted the cytokine-mediated decrease in BAD phosphorylation, and inhibited apoptosis. The anti-apoptotic signaling was dependent on prolonged exposure to corticotropin-releasing factor family peptides and followed PKA-mediated IRS2 upregulation. This indicates that CRFR signaling counteracts proinflammatory cytokine-mediated apoptotic pathways through upregulation of survival signaling in β-cells. Interestingly, CRFR signaling also counteracted basal apoptosis in both cultured INS-1 cells and intact human islets.

Urocortin 3 activates AMPK and AKT pathways and enhances glucose disposal in rat skeletal muscle

Insulin resistance (IR) in skeletal muscle is an important component of both type 2 diabetes and the syndrome of sarcopaenic obesity, for which there are no effective therapies. Urocortins (UCNs) are not only well established as neuropeptides but also have their roles in metabolism in peripheral tissues. We have shown recently that global overexpression of UCN3 resulted in muscular hypertrophy and resistance to the adverse metabolic effects of a high-fat diet. Herein, we aimed to establish whether short-term local UCN3 expression could enhance glucose disposal and insulin signalling in skeletal muscle. UCN3 was found to be expressed in right tibialis cranialis and extensor digitorum longus muscles of rats by in vivo electrotransfer and the effects studied vs the contralateral muscles after 1 week. No increase in muscle mass was detected, but test muscles showed 19% larger muscle fibre diameter (P=0.030), associated with increased IGF1 and IGF1 receptor mRNA and increased SER256 phosphorylation of forkhead transcription factor. Glucose clearance into the test muscles after an intraperitoneal glucose load was increased by 23% (P=0.018) per unit mass, associated with increased GLUT1 (34% increase; P=0.026) and GLUT4 (48% increase; P=0.0009) proteins, and significantly increased phosphorylation of insulin receptor substrate-1, AKT, AKT substrate of 160 kDa, glycogen synthase kinase-3β, AMP-activated protein kinase and its substrate acetyl coA carboxylase. Thus, UCN3 expression enhances glucose disposal and signalling in muscle by an autocrine/paracrine mechanism that is separate from its pro-hypertrophic effects, implying that such a manipulation may have promised for the treatment of IR syndromes including sarcopaenic obesity.

Urocortin 2 stimulates nitric oxide production in ventricular myocytes via Akt- and PKA-mediated phosphorylation of eNOS at serine 1177

Urocortin 2 (Ucn2) is a cardioactive peptide exhibiting beneficial effects in normal and failing heart. In cardiomyocytes, it elicits cAMP- and Ca(2+)-dependent positive inotropic and lusitropic effects. We tested the hypothesis that, in addition, Ucn2 activates cardiac nitric oxide (NO) signaling and elucidated the underlying signaling pathways and mechanisms. In isolated rabbit ventricular myocytes, Ucn2 caused concentration- and time-dependent increases in phosphorylation of Akt (Ser473, Thr308), endothelial NO synthase (eNOS) (Ser1177), and ERK1/2 (Thr202/Tyr204). ERK1/2 phosphorylation, but not Akt and eNOS phosphorylation, was suppressed by inhibition of MEK1/2. Increased Akt phosphorylation resulted in increased Akt kinase activity and was mediated by corticotropin-releasing factor 2 (CRF2) receptors (astressin-2B sensitive). Inhibition of phosphatidylinositol 3-kinase (PI3K) diminished both Akt as well as eNOS phosphorylation mediated by Ucn2. Inhibition of protein kinase A (PKA) reduced Ucn2-induced phosphorylation of eNOS but did not affect the increase in phosphorylation of Akt. Conversely, direct receptor-independent elevation of cAMP via forskolin increased phosphorylation of eNOS but not of Akt. Ucn2 increased intracellular NO concentration ([NO]i), [cGMP], [cAMP], and cell shortening. Inhibition of eNOS suppressed the increases in [NO]i and cell shortening. When both PI3K-Akt and cAMP-PKA signaling were inhibited, the Ucn2-induced increases in [NO]i and cell shortening were attenuated. Thus, in rabbit ventricular myocytes, Ucn2 causes activation of cAMP-PKA, PI3K-Akt, and MEK1/2-ERK1/2 signaling. The MEK1/2-ERK1/2 pathway is not required for stimulation of NO signaling in these cells. The other two pathways, cAMP-PKA and PI3K-Akt, converge on eNOS phosphorylation at Ser1177 and result in pronounced and sustained cellular NO production with subsequent stimulation of cGMP signaling.

Targeting urocortin signaling pathways to enhance cardioprotection: is it time to move from bench to bedside?

Despite the exponential growth in medical knowledge, cardiovascular diseases (CVDs) contribute to more than one-third of worldwide morbidity and mortality. A range of therapies already exist for established CVDs, although there is significant interest in further understanding their pathogenesis. The urocortins (Ucns) are peptide members of the corticotrophin-releasing factor family, a group of evolutionary conserved peptides with homologues in fish, amphibians and mammals and considered to play a pivotal role in energy homeostasis and local tissue repair. A number of preclinical studies in vitro, in-vivo and ex-vivo have defined a multifaceted effect of Ucns on the cardiovascular system. Different G-protein coupled signaling and protein-kinase pathways have been shown to be activated by Ucns, together with different transcriptional and translational effects, all of which preferentially converge on the mitochondria, where the modulation of apoptosis is considered their principal action. It has been demonstrated in experimental models, and consequentially suggested in human diseases, that Ucn-mediated inhibition of apoptosis can be exploited for the improvement of both therapeutic and preventative strategies against CVDs. Specifically, some unavoidable iatrogenic ischemia/reperfusion (I/R) injuries, e.g. during cardiac surgery or percutaneous coronary angioplasty, may greatly benefit from the anti-apoptotic effect of Ucns. However, few studies on the topic have been employed in humans to date. Therefore, this review will focus on the different intra-cellular mechanisms of action of Urocortins, and detail the different Ucn-mediated pathways identified so far. It will also highlight the limited evidence already existing in human clinical and surgical settings, as well as emphasize the potential uses of Ucns in human cardiac pathology.

Cardioprotection of 17β-estradiol against hypoxia/reoxygenation in cardiomyocytes is partly through up-regulation of CRH receptor type 2

Estrogens have been suggested to exert cardioprotection through maintaining endogenous cardioprotective mechanisms. In the present study, we investigated whether estrogens protect cardiomyocytes against hypoxia/reoxygenation (H/R) via modulating urocortins (UCNs) and their receptor corticotrophin-releasing hormone receptor type 2 (CRHR2). We found that 17β-estradiol (E2) enhanced UCN cardioprotection against H/R and increased CRHR2 expression in neonatal rat cardiomyocytes. E2 protected cardiomyocytes against H/R, which was impaired by CRHR2 antagonist or knockdown of CRHR2. Estrogen receptor α (ERα) antagonist treatment or ERα knockdown could abolish E2-induced CRHR2 up-regulation. Moreover, knockdown of Sp1 also attenuated E2-induced CRHR2 up-regulation. Ovariectomy resulted in down-regulation of CRHR2 and Sp-1 in myocardium of mice, which was restored by E2 or ERα agonist treatment. These results suggest that estrogens act on ERα to up-regulate CRHR2 expression in cardiomyocytes, thereby enhancing cardioprotection of UCNs against H/R.

NFAT transcription factor regulation by urocortin II in cardiac myocytes and heart failure

Urocortin II (UcnII), a cardioactive peptide with beneficial effects in normal and failing hearts, is also arrhythmogenic and prohypertrophic. We demonstrated that cardiac effects are mediated by a phosphatidylinositol-3 kinase (PI3K)/Akt kinase (Akt)/endothelial nitric oxide synthase (eNOS)/nitric oxide (NO) signaling pathways. Nuclear factor of activated T-cells (NFAT) transcription factors play a key role in the regulation of gene expression in cardiac development, maintenance of an adult differentiated cardiac phenotype, and remodeling processes in cardiac hypertrophy and heart failure (HF). We tested the hypothesis that UcnII differentially regulates NFAT activity in cardiac myocytes from both normal and failing hearts through the PI3K/Akt/eNOS/NO pathway. Isoforms NFATc1 and NFATc3 revealed different basal subcellular distribution in normal and HF rabbit ventricular myocytes with a nuclear NFATc1 and a cytosolic localization of NFATc3. However, in HF, the nuclear localization of NFATc1 was less pronounced, whereas the nuclear occupancy of NFATc3 was increased. In normal myocytes, UcnII induced nuclear export of NFATc1 and attenuated NFAT-dependent transcriptional activity but did not affect the distribution of NFATc3. In HF UcnII facilitated nuclear export of both isoforms and reduced transcriptional activity. NFAT regulation was mediated by a PI3K/Akt/eNOS/NO signaling cascade that converged on the activation of several kinases, including glycogen synthase kinase-3β (GSK3β), c-Jun NH2-terminal kinase (JNK), p38 mitogen-activated kinase (p38), and PKG, resulting in phosphorylation, deactivation, and nuclear export of NFAT. In conclusion, while NFATc1 and NFATc3 reveal distinct subcellular distribution patterns, both are regulated by the UcnII-PI3K/Akt/eNOS/NO pathway that converges on the activation of NFAT kinases and NFAT inactivation. The data reconcile cardioprotective and prohypertrophic UcnII effects mediated by different NFAT isoforms.

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.

The cardioprotective effects of urocortin are mediated via activation of the Src tyrosine kinase-STAT3 pathway

Src tyrosine kinase family was recently identified as a novel upstream modulator of MAP kinase subfamily, p42/p44, whose activation is required for urocortin (Ucn)-mediated cardioprotection. Src kinase was also shown to reduce apoptosis in different cancer cell lines, enhancing phosphorylation and DNA binding affinity of signal transducer and activator of transcription (STAT)3. In order to evaluate the effects of Ucn on the activation status of different STAT family members, HL-1 cardiac cells were incubated with Ucn (10 nM) for increasing periods of time. STAT3 was rapidly phosphorylated at Tyr705, while neither phosphorylation at Ser727 nor induction of total STAT3 was observed. Pretreatment with PP2, a selective inhibitor of Src tyrosine kinase, reduced the pSTAT^−T705 phosphorylation and transcriptional activity induced by Ucn in a dose-dependent manner. Overexpression of STAT3 in HL-1 cardiac myocytes pretreated with Ucn reduced the magnitude of cell death as compared with Ucn treatment alone, while transfection of HL-1 cells with a STAT3 mutant functionally inactive, acting as a dominant negative (DN-STAT3), enhanced the extent of cell death in a dose-dependent manner. In line with this finding, in HL-1 cardiac myocytes overexpressing STAT3 treated with Ucn, addition of the Src kinase inhibitor PP2 reversed the cytoprotective effects of Ucn, proving that the cytoprotective effects of Ucn are also mediated via the Src-pSTAT^−T705 phosphorylation pathway. By immunocytochemistry, Ucn induced nuclear translocation of pST3-T705, which was inhibited by pretreatment with PP2. Together, these data strongly suggest that Ucn can mediate cardioprotection by activating the Src-pSTAT-T705 phosphorylation pathway.

Urocortin is a novel regulator of osteoclast differentiation and function through inhibition of a canonical transient receptor potential 1-like cation channel

This study investigated the role of urocortin (UCN), a member of the corticotrophin-releasing factor (CRF) family of peptides, in osteoclast maturation and function. We found that 10(-7) M UCN significantly (P<0.05) suppressed osteoclast differentiation from bone marrow precursor cells in culture and reduced the expression of several osteoclastic markers. Furthermore, UCN potently suppressed osteoclast bone resorption, by significantly inhibiting both the plan area of bone resorbed by osteoclasts and actin ring formation within osteoclasts at 10(-9) M (P<0.05), with complete inhibition at 10(-7) M (P<0.001). UCN also inhibited osteoclast motility (10(-7) M) but had no effect on osteoclast survival. Osteoclasts expressed mRNA encoding both UCN and the CRF receptor 2β subtype. Pre-osteoclasts however, expressed CRF receptor 2β alone. Unstimulated osteoclasts contained constitutively active cation channel currents with a unitary conductance of 3-4 pS, which were inhibited by over 70% with UCN (10(-7) M). Compounds that regulate calcium signalling and energy status of the cell, both crucial for osteoclast activity were investigated. The non-selective cation channel blockers, lanthanum (La(3)(+)) and gadolinium (Gd(3)(+)), inhibited actin ring formation in osteoclasts, whereas modulators of voltage-dependent Ca(2)(+) channels and K(ATP) channels had no effect. These findings show for the first time that UCN is a novel anti-resorptive molecule that acts through a direct effect on osteoclasts and their precursor cells.

Clinical perspectives of urocortin and related agents for the treatment of cardiovascular disease

The effects of corticotropin-releasing hormone, also known as corticotropin-releasing factor (CRF), on the cardiovascular system have been intensively researched since its discovery. Moreover, the actions of urocortin (Ucn) I on the cardiovascular system have also been intensively scrutinized following the cloning and identification of its receptor, CRF receptor type 2 (CRFR2), in peripheral tissues including the heart. Given the cardioprotective actions of CRFR2 ligands, the clinical potential of not only Ucn I but also Ucn II and III, which were later identified as more specific ligands for CRFR2, has received considerable attention from researchers. In addition, recent work has indicated that CRF type 1 receptor may be also involved in cardioprotection against ischemic/reperfusion injury. Here we provide a historical overview of research on Ucn I and related agents, their effects on the cardiovascular system, and the clinical potential of the use of such agents to treat cardiovascular diseases.

Central urocortin 3 and type 2 corticotropin-releasing factor receptor in the regulation of energy homeostasis: critical involvement of the ventromedial hypothalamus

The vital role of the corticotropin-releasing factor (CRF) peptide family in the brain in coordinating response to stress has been extensively documented. The effects of CRF are mediated by two G-protein-coupled receptors, type 1 and type 2 CRF receptors (CRF(1) and CRF(2)). While the functional role of CRF(1) in hormonal and behavioral adaptation to stress is well-known, the physiological significance of CRF(2) remains to be fully appreciated. Accumulating evidence has indicated that CRF(2) and its selective ligands including urocortin 3 (Ucn 3) are important molecular mediators in regulating energy balance. Ucn 3 is the latest addition of the CRF family of peptides and is highly selective for CRF(2). Recent studies have shown that central Ucn 3 is important in a number of homeostatic functions including suppression of feeding, regulation of blood glucose levels, and thermoregulation, thus reinforcing the functional role of central CRF(2) in metabolic regulation. The brain loci that mediate the central effects of Ucn 3 remain to be fully determined. Anatomical and functional evidence has suggested that the ventromedial hypothalamus (VMH), where CRF(2) is prominently expressed, appears to be instrumental in mediating the effects of Ucn 3 on energy balance, permitting Ucn 3-mediated modulation of feeding and glycemic control. Thus, the Ucn 3-VMH CRF(2) system is an important neural pathway in the regulation of energy homeostasis and potentially plays a critical role in energy adaptation in response to metabolic perturbations and stress to maintain energy balance.

Myocardial AKT: the omnipresent nexus

One of the greatest examples of integrated signal transduction is revealed by examination of effects mediated by AKT kinase in myocardial biology. Positioned at the intersection of multiple afferent and efferent signals, AKT exemplifies a molecular sensing node that coordinates dynamic responses of the cell in literally every aspect of biological responses. The balanced and nuanced nature of homeostatic signaling is particularly essential within the myocardial context, where regulation of survival, energy production, contractility, and response to pathological stress all flow through the nexus of AKT activation or repression. Equally important, the loss of regulated AKT activity is primarily the cause or consequence of pathological conditions leading to remodeling of the heart and eventual decompensation. This review presents an overview compendium of the complex world of myocardial AKT biology gleaned from more than a decade of research. Summarization of the widespread influence that AKT exerts upon myocardial responses leaves no doubt that the participation of AKT in molecular signaling will need to be reckoned with as a seemingly omnipresent regulator of myocardial molecular biological responses.

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.

Urocortin-induced cardiomyocytes hypertrophy is associated with regulation of the GSK-3β pathway

Urocortin-1 (UCN), a member of the corticotropin-releasing factor, is a cardioprotective peptide, and is also involved in cardiac hypertrophy. The involvement of GSK-3β, a pivotal kinase in cardiac hypertrophy, in response to UCN is not yet documented. Cardiomyocytes from adult rats were stimulated for 48 h with UCN. Cell size, protein, and DNA contents were determined. Phosphorylated and total forms GSK-3β and the total amount of β-catenin were quantified by Western immunoblots. The effects of astressin, a UCN competitive receptor antagonist, were also evaluated. UCN increased cell size and the protein-to-DNA ratio, in accordance with a hypertrophic response. This effect was associated with increased phosphorylation of GSK-3β and marked accumulation of β-catenin, a downstream element to GSK-3β. All these effects were prevented by astressin and LY294002, an inhibitor of the phosphatidyl-inositol-3-kinase. UCN-induced cardiomyocytes hypertrophy is associated with regulation of GSK-3β, a pivotal kinase involved in cardiac hypertrophy, in a PI3K-dependent manner. Furthermore, the pharmacological blockade of UCN receptors was able to prevent UCN-induced hypertrophy, which leads to inhibition of the Akt/GSK-3β pathway.

Molecular determinants and feedback circuits regulating type 2 CRH receptor signal integration

In most target tissues, the adenylyl cyclase/cAMP/PKA, the extracellular signal regulated kinase and the protein kinase B/Akt are the main pathways employed by the type 2 corticotropin-releasing hormone receptor to mediate the biological actions of urocortins (Ucns) and CRH. To decipher the molecular determinants of CRH-R2 signaling, we studied the signaling pathways in HEK293 cells overexpressing recombinant human CRH-R2β receptors. Use of specific kinase inhibitors showed that the CRH-R2β cognate agonist, Ucn 2, activated extracellular signal regulated kinase in a phosphoinositide 3-kinase and cyclic adenosine monophosphate/PKA-dependent manner with contribution from Epac activation. Ucn 2 also induced PKA-dependent association between AKAP250 and CRH-R2β that appeared to be necessary for extracellular signal regulated kinase activation. PKB/Akt activation was also mediated via pertussis toxin-sensitive G-proteins and PI3-K activation but did not require cAMP/PKA, Epac or protein kinase C for optimal activation. Potential feedback mechanisms that target the CRH-R2β itself and modulate receptor trafficking and endocytosis were also investigated. Indeed, our results suggested that inhibition of either PKA or extracellular signal regulated kinase pathway accelerates CRH-R2β endocytosis. Furthermore, Ucn 2-activated extracellular signal regulated kinase appeared to target β-arrestin1 and modulate, through phosphorylation at Ser412, β-arrestin1 translocation to the plasma membrane and CRH-R2β internalization kinetics. Loss of this "negative feedback" mechanism through inhibition of the extracellular signal regulated kinase activity resulted in significant attenuation of Ucn 2-induced cAMP response, whereas Akt phosphorylation was not affected by altered receptor endocytosis. These findings reveal a complex interplay between the signaling molecules that allow "fine-tuning" of CRH-R2β functional responses and regulate signal integration. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.

cAMP- and Ca²(+) /calmodulin-dependent protein kinases mediate inotropic, lusitropic and arrhythmogenic effects of urocortin 2 in mouse ventricular myocytes

BACKGROUND AND PURPOSE

Urocortin 2 is beneficial in heart failure, but the underlying cellular mechanisms are not completely understood. Here we have characterized the functional effects of urocortin 2 on mouse cardiomyocytes and elucidated the underlying signalling pathways and mechanisms.

EXPERIMENTAL APPROACH

Mouse ventricular myocytes were field-stimulated at 0.5 Hz at room temperature. Fractional shortening and [Ca²(+)](i) transients were measured by an edge detection and epifluorescence system respectively. Western blots were carried out on myocyte extracts with antibodies against total phospholamban (PLN) and PLN phosphorylated at serine-16.

KEY RESULTS

Urocortin 2 elicited time- and concentration-dependent positive inotropic and lusitropic effects (EC₅₀ : 19 nM) that were abolished by antisauvagine-30 (10 nM, n= 6), a specific antagonist of corticotrophin releasing factor (CRF) CRF₂ receptors. Urocortin 2 (100 nM) increased the amplitude and decreased the time constant of decay of the underlying [Ca²(+)](i) transients. Urocortin 2 also increased PLN phosphorylation at serine-16. H89 (2 µM) or KT5720 (1 µM), two inhibitors of protein kinase A (PKA), as well as KN93 (1 µM), an inhibitor of Ca²(+)/calmodulin-dependent protein kinase II (CaMKII), suppressed the urocortin 2 effects on shortening and [Ca²(+)](i) transients. In addition, urocortin 2 also elicited arrhythmogenic events consisting of extra cell shortenings and extra [Ca²(+)](i) increases in diastole. Urocortin 2-induced arrhythmogenic events were significantly reduced in cells pretreated with KT5720 or KN93.

CONCLUSIONS AND IMPLICATIONS

Urocortin 2 enhanced contractility in mouse ventricular myocytes via activation of CRF₂ receptors in a cAMP/PKA- and Ca²(+)/CaMKII-dependent manner. This enhancement was accompanied by Ca²(+)-dependent arrhythmogenic effects mediated by PKA and CaMKII.

Corticotropin-releasing factor-2 activation prevents gentamicin-induced oxidative stress in cells derived from the inner ear

Generation of reactive oxygen species (ROS) is a common denominator in many conditions leading to cell death in the cochlea, yet little is known of the cochlea's endogenous mechanisms involved in preventing oxidative stress and its consequences in the cochlea. We have recently described a corticotropin-releasing factor (CRF) signaling system in the inner ear involved in susceptibility to noise-induced hearing loss. We use biochemical and proteomics assays to define further the role of CRF signaling in the response of cochlear cells to aminoglycoside exposure. We demonstrate that activity via the CRF(2) class of receptors protects against aminoglycoside-induced ROS production and activation of cell death pathways. This study suggests for the first time a role for CRF signaling in protecting the cochlea against oxidative stress, and our proteomics data suggest novel mechanisms beyond induction of free radical scavengers that are involved in its protective mechanisms.

Activation of Src protein tyrosine kinase plays an essential role in urocortin-mediated cardioprotection

Urocortin is a 40 amino acid peptide of the corticotrophin-releasing factor (CRF) family that is synthesized and released by cardiac myocytes. Endogenous urocortin expression is increased during ischemia/reperfusion (I/R) and addition of exogenous urocortin reduces cell death caused by I/R injury. Studies have also showed that the protective action of urocortin is mediated by the activation of ERK1/2. We discovered that a non-receptor tyrosine kinase, Src, is involved in the urocortin-induced activation of ERK1/2 in mouse atrial HL-1 myocytes. The selective Src family kinase inhibitor, PP2, reduced the urocortin-induced phosphorylation of ERK1/2, and so did the expression of a dominant-negative mutant of Src in transfected HL-1 cells. Inhibition of Src by PP2 also reduced urocortin's protective effects in HL-1 cells after hypoxia/reoxygenation (H/R), as assessed by flow cytometry and caspase-3 activation assay. Titration studies indicated that as little as 10(-8)M urocortin was sufficient to induce Src activation. Maximal phosphorylation/activation of Src and ERK1/2 were both detected after 5 min incubation with urocortin. These effects of urocortin were largely mediated by CRF receptor-1, although a minor contribution of CRF receptor-2 cannot be excluded. Here we report for the first time that short-term treatment with urocortin causes rapid phosphorylation of Src, and that the urocortin-activated Src kinase serves as an upstream modulator of ERK1/2 activation, playing an essential role in urocortin-mediated cardioprotection.

New targets of urocortin-mediated cardioprotection

The urocortin (UCN) hormones UCN1 and UCN2 have been shown previously to confer significant protection against myocardial ischaemia/reperfusion (I/R) injury; however, the molecular mechanisms underlying their action are poorly understood. To further define the transcriptional effect of UCNs that underpins their cardioprotective activity, a microarray analysis was carried out using an in vivo rat coronary occlusion model of I/R injury. Infusion of UCN1 or UCN2 before the onset of reperfusion resulted in the differential regulation of 66 and 141 genes respectively, the majority of which have not been described previously. Functional analysis demonstrated that UCN-regulated genes are involved in a wide range of biological responses, including cell death (e.g. X-linked inhibitor of apoptosis protein), oxidative stress (e.g. nuclear factor erythroid derived 2-related factor 1/nuclear factor erythroid derived 2-like 1) and metabolism (e.g. Prkaa2/AMPK). In addition, both UCN1 and UCN2 were found to modulate the expression of a host of genes involved in G-protein-coupled receptor (GPCR) signalling including Rac2, Gnb1, Dab2ip (AIP1), Ralgds, Rnd3, Rap1a and PKA, thereby revealing previously unrecognised signalling intermediates downstream of CRH receptors. Moreover, several of these GPCR-related genes have been shown previously to be involved in mitogen-activated protein kinase (MAPK) activation, suggesting a link between CRH receptors and induction of MAPKs. In addition, we have shown that both UCN1 and UCN2 significantly reduce free radical damage following myocardial infarction, and comparison of the UCN gene signatures with that of the anti-oxidant tempol revealed a significant overlap. These data uncover novel gene expression changes induced by UCNs, which will serve as a platform to further understand their mechanism of action in normal physiology and cardioprotection.

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.

Stress hormones mediate environment-genotype interactions during amphibian development

Environments experienced by organisms during early development shape the character and timing of developmental processes, leading to different probabilities of survival in the developmental habitat, and often profound effects on phenotypic expression later in life. Amphibian larvae have immense capacity for plasticity in behavior, morphology, growth and development rate. This creates the potential for extreme variation in the timing of, and size at metamorphosis, and subsequent phenotype in the juvenile and adult stage. Hormones of the neuroendocrine stress axis play pivotal roles in mediating environmental effects on animal development. Corticotropin-releasing factor, whose secretion by hypothalamic neurons is induced by environmental stress, influences the timing of amphibian metamorphosis by controlling the activity of the thyroid and interrenal (adrenal; corticosteroids) glands. At target tissues, corticosteroids synergize with thyroid hormone to promote metamorphosis. Thus, environmental stress acts centrally to increase the activity of the two principle endocrine axes controlling metamorphosis, and the effectors of these axes synergize at the level of target tissues to promote morphogenesis. While stress hormones can promote survival in a deteriorating larval habitat, costs may be incurred such as reduced tadpole growth and size at metamorphosis. Furthermore, exposure to elevated corticosteroids early in life can cause permanent changes in the expression of genes of the neuroendocrine stress axis, leading to altered physiology and behavior in the juvenile/adult stage. Persistent effects of stress hormone actions early in life may have important fitness consequences.

Activation of phosphatidylinositol 3-kinase/protein kinase B by corticotropin-releasing factor in human monocytes

Corticotropin-releasing factor (CRF) exerts proinflammatory effects in peripheral tissues, whereas the intracellular pathways mediating these effects have not been completely characterized yet. We have previously shown that CRF induces nuclear factor-kappaB DNA-binding activity in mouse and human leukocytes. Here we demonstrate that in the human monocytic THP-1 cells, CRF activates the phosphatidylinositol 3-kinase (PI3K)/Akt and ERK1/2 pathways. These effects of CRF are mediated by corticotropin-releasing factor receptor 2 (CRF2), as suggested by their abolishment after treatment with the specific CRF2 antagonist, astressin 2B. The CRF-mediated PI3K/Akt activation induces cell survival as suggested by the stimulation of the antiapoptotic factor Bcl-2. ERK1/2 activation results in up-regulation of IL-8 expression, an effect inhibited by the CRF-induced activation of PI3K/Akt. These studies demonstrate novel effects of CRF in human monocytes mediated by the activation of PI3K/Akt. Moreover, they reveal pathway-specific effects of the CRF/CRF2 system in chemokine activation and cell survival that may be of importance for the development of novel therapeutics for inflammatory diseases.

Urocortin: a protective peptide that targets both the myocardium and vasculature

The urocortins are a family of endogenously produced peptide hormones that show great promise as potential drugs for the treatment of heart disease. They can increase contractility and cardiac output without causing changes in mean arterial blood pressure. As expected, the receptor for these peptides is present in cardiomyocytes, and they can bind and protect these cells from simulated ischemia and reperfusion in vitro. The receptor is present, however, in much higher density in the endothelial cells that form a continuous lining of the coronary vasculature. Functionally, the urocortin peptides have been shown to have potent local vasodilatory effects, and may affect other aspects of vascular function. In this review, we will attempt to distinguish the "cardio" from the "vascular" effects of urocortin and its homologues, including the archetypal family member, corticotrophin releasing hormone.

Structure, function, property, and role in neurologic diseases and other diseases of the sHsp22

Small heat shock proteins are members of the heat shock proteins family. They share important identical features: 1) they form the conserved structure 'alpha-crystallin domain' with about 80-100 residues in the C-terminal part of the proteins; 2) they have monomeric molecular masses ranging in 12-43 kDa; 3) they associate into large oligomers consisting in many cases of subunits; 4) they increase expression under stress conditions; 5) they exhibit a highly dynamic structure; and 6) they play a chaperone-like role. Hsp22 (also known as HspB8, H11, and E2IG1) retains the structural motif of the 'alpha-crystallin' family of Hsps and is a member of the superfamily of sHsps. Hsp22 displays chaperone activity, autokinase activity, and trigger or block apoptosis activity. It differs from canonical family members existing as a monomer. A decrease in the HspB8 activity may contribute to the development of some neurologic diseases and others.

Glycogen synthase kinase 3 alpha and 3 beta have distinct functions during cardiogenesis of zebrafish embryo

Background

Glycogen synthase kinase 3 (GSK3) encodes a serine/threonine protein kinase, is known to play roles in many biological processes. Two closely related GSK3 isoforms encoded by distinct genes: GSK3α (51 kDa) and GSK3β (47 kDa). In previously studies, most GSK3 inhibitors are not only inhibiting GSK3, but are also affecting many other kinases. In addition, because of highly similarity in amino acid sequence between GSK3α and GSK3β, making it difficult to identify an inhibitor that can be selective against GSK3α or GSK3β. Thus, it is relatively difficult to address the functions of GSK3 isoforms during embryogenesis. At this study, we attempt to specifically inhibit either GSK3α or GSK3β and uncover the isoform-specific roles that GSK3 plays during cardiogenesis.

Results

We blocked gsk3α and gsk3β translations by injection of morpholino antisense oligonucleotides (MO). Both gsk3α- and gsk3β-MO-injected embryos displayed similar morphological defects, with a thin, string-like shaped heart and pericardial edema at 72 hours post-fertilization. However, when detailed analysis of the gsk3α- and gsk3β-MO-induced heart defects, we found that the reduced number of cardiomyocytes in gsk3α morphants during the heart-ring stage was due to apoptosis. On the contrary, gsk3β morphants did not exhibit significant apoptosis in the cardiomyocytes, and the heart developed normally during the heart-ring stage. Later, however, the heart positioning was severely disrupted in gsk3β morphants. bmp4 expression in gsk3β morphants was up-regulated and disrupted the asymmetry pattern in the heart. The cardiac valve defects in gsk3β morphants were similar to those observed in axin1 and apc^mcr mutants, suggesting that GSK3β might play a role in cardiac valve development through the Wnt/β-catenin pathway. Finally, the phenotypes of gsk3α mutant embryos cannot be rescued by gsk3β mRNA, and vice versa, demonstrating that GSK3α and GSK3β are not functionally redundant.

Conclusion

We conclude that (1) GSK3α, but not GSK3β, is necessary in cardiomyocyte survival; (2) the GSK3β plays important roles in modulating the left-right asymmetry and affecting heart positioning; and (3) GSK3α and GSK3β play distinct roles during zebrafish cardiogenesis.