Endothelium dependent cardiovascular effects of the Chromogranin A-derived peptides Vasostatin-1 and Catestatin

The involvement of Chromogranin A (CgA) in the cardiovascular function regulation is attributed to its function as a prohormone. Several studies indicated that CgA-derived peptides, particularly Vasostatin-1 (VS-1) and Catestatin (CST), exert signaling effects in numerous organs/systems, including the cardiovascular system. This review focuses on the recently described signaling pathways activated by VS-1 and CST, giving insights into the mechanisms at the basis of their cardiac negative inotropic action, their vasodilator effects and their cardioprotective role observed in different experimental conditions. Accumulated evidences provided convincing support for VS-1 and CST as vasoactive peptides indirectly acting on cardiomyocytes through a Ca(2+)-independent/PI3-K-dependent NO release from endothelial cells. This pathway is supposed to be triggered by the interaction of these peptides with the plasma membrane. The premise of these studies grounds on the biochemical features of VS-1 and CST, which are structurally characterized by amphipathic properties and the ability to interact with mammalian and microbial membranes. On the other hand, recent data obtained in both isolated heart and isolated cardiomyocytes suggest that the VS-1 and CST-mediated cardioprotective effects are primarily direct on the myocardium, rather than endothelium-dependent. Anyway, both direct and indirect pathways seem to be characterized by the absence of specific membrane receptors on target cells, highlighting intriguing novelties in the topic of cell signaling, in particular respect to an hypothetical receptor-independent eNOS activation.

A novel catestatin-induced antiadrenergic mechanism triggered by the endothelial PI3K-eNOS pathway in the myocardium

AIMS

Catestatin (CST) is a chromogranin A (CgA)-derived peptide (hCgA352-372) with three identified human variants (G364S/P370L/R374Q-CST) that show differential potencies towards the inhibition of catecholamine release. Although CST affects several cardiovascular parameters, the mechanisms underlying CST action in the heart have remained elusive. Therefore, we sought to determine the mechanism of action of CST and its variants on ventricular myocardium and endothelial cells.

METHODS AND RESULTS

Contractile force and Ca(2+) transients were measured, respectively, on rat papillary muscles and isolated cardiomyocytes (CC) under basal conditions and after β-adrenergic stimulation. Nitric oxide (NO) production and endothelial nitric oxide synthase (eNOS) phosphorylation (P(Ser1179)eNOS) were studied in bovine aortic endothelial (BAE-1) cells. Under basal conditions, wild-type CST (WT-CST, 10-50 nM) transiently enhanced myocardial contractility. CST variants (G364S and P370L) exerted a comparable positive inotropic effect. The H(1) histamine receptor antagonist mepyramine abolished the increase of contractile force induced by WT-CST. Moreover, WT-CST dose-dependently (5-50 nM) reduced the effect of β-adrenergic stimulation. This anti-adrenergic effect was not mediated by a direct action on CC, but involved a PI3K-dependent NO release from endocardial endothelial cells. Indeed, CST induced a wortmannin-sensitive, Ca(2+)-independent increase in NO production and eNOS phosphorylation on BAE-1 cells. While the anti-adrenergic and NO release effects of P370L-CST were comparable with those of WT-CST, the G364S variant was ineffective on the same parameters.

CONCLUSION

Our results suggest that the anti-adrenergic action of CST depends on the endothelial PI3K-Akt-eNOS pathway and that its structural alterations entail functional features that correlate with the different anti-hypertensive potential described in humans.

Vasostatin 1 activates eNOS in endothelial cells through a proteoglycan-dependent mechanism

Accumulating evidences point to a significant role for the chromogranin A (CgA)-derived peptide vasostatin 1 (VS-1) in the protective modulation of the cardiovascular activity, because of its ability to counteract the adrenergic signal. We have recently shown that VS-1 induces a PI3K-dependent-nitric oxide (NO) release by endothelial cells, contributing to explain the mechanism of its cardio-suppressive and vasodilator properties. However, the cellular processes upstream the eNOS activation exerted by this peptide are still unknown, as typical high-affinity receptors have not been identified. Here we hypothesize that in endothelial cells VS-1 acts, on the basis of its cationic and amphipathic properties, as a cell penetrating peptide, binding to heparan sulfate proteoglycans (HSPGs) and activating eNOS phosphorylation (Ser1179) through a PI3K-dependent, endocytosis-coupled mechanism. In bovine aortic endothelial cells (BAE-1 cells) endocytotic vesicles trafficking was quantified by confocal microscopy with a water-soluble membrane dye; caveolin 1 (Cav1) shift from plasma membrane was studied by immunofluorescence staining; VS-1-dependent eNOS phosphorylation was assessed by immunofluorescence and immunoblot analysis. Our experiments demonstrate that VS-1 induces a marked increase in the caveolae-dependent endocytosis, (115 +/- 23% endocytotic spots/cell/field in VS-1-treated cells with respect to control cells), that is significantly reduced by both heparinase III (HEP, 17 +/- 15% above control) and Wortmannin (Wm, 7 +/- 22% above control). Heparinase, Wortmannin, and methyl-beta-cyclodextrin (MbetaCD) abolish the VS-1-dependent eNOS phosphorylation (P(Ser1179)eNOS). These results suggest a novel signal transduction pathway for endogenous cationic and amphipathic peptides in endothelial cells: HSPGs interaction and caveolae endocytosis, coupled with a PI3K-dependent eNOS phosphorylation.

Neuregulin-1beta1 rapidly modulates nitric oxide synthesis and calcium handling in rat cardiomyocytes

AIMS

The ErbB-neuregulin-1β1 (Nrg1β1) pathway is required for cardiac development and exerts chronic effects on the postnatal adult heart. Long-term application of Nrg1β1 results in hypertrophy and protection against oxidative stress and cytotoxic agents. We performed experiments with acute Nrg1β1 treatment to find evidence for a further protective role due to rapid modulation of adult cardiomyocyte function.

METHODS AND RESULTS

In confocal fluorimetric measurements, Nrg1β1 induced a calcium-independent increase in nitric oxide (NO) production in isolated adult rat ventricular myocytes (ARVCMs) that was blocked by the phosphoinositide-3-kinase (PI3K) inhibitor Wortmannin. Western blot analysis showed enhancement of endothelial nitric oxide synthase phosphorylation in Nrg1β1-treated ARVCMs, which was attenuated by Wortmannin. Nrg1β1 induced a significant increase in calcium transient amplitude (indo-1 ratiometric measurement) and accelerated the recovery of cytosolic calcium in the sarcoplasmic reticulum without affecting whole-cell L-type calcium current. Wortmannin or the protein kinase G inhibiting peptide (DT-2) abolished the increase in calcium transient amplitude and the acceleration of calcium recovery induced by Nrg1β1 treatment. Immunofluorescence analysis revealed that Nrg1β1 treatment increased phospholamban phosphorylation, and the effect was blocked by PI3K and protein kinase G inhibition. Caffeine-releasable sarcoplasmic reticulum calcium content was also higher during Nrg1β1 administration.

CONCLUSION

Rapid activation of PI3K, endothelial nitric oxide synthase and protein kinase G and a consequent improvement in diastolic calcium can be added to established Nrg1 protective roles.

Thrombopoietin modulates cardiac contractility in vitro and contributes to myocardial depressing activity of septic shock serum

Thrombopoietin (TPO) is a humoral growth factor that has been shown to increase platelet activation in response to several agonists. Patients with sepsis have increased circulating TPO levels, which may enhance platelet activation, potentially participating to the pathogenesis of multi-organ failure. Aim of this study was to investigate whether TPO affects myocardial contractility and participates to depress cardiac function during sepsis. We showed the expression of the TPO receptor c-Mpl on myocardial cells and tissue by RT-PCR, immunofluorescence and western blotting. We then evaluated the effect of TPO on the contractile function of rat papillary muscle and isolated heart. TPO did not change myocardial contractility in basal conditions, but, when followed by epinephrine (EPI) stimulation, it blunted the enhancement of contractile force induced by EPI both in papillary muscle and isolated heart. An inhibitor of TPO prevented TPO effect on cardiac inotropy. Treatment of papillary muscle with pharmacological inhibitors of phosphatidylinositol 3-kinase, NO synthase, and guanilyl cyclase abolished TPO effect, indicating NO as the final mediator. We finally studied the role of TPO in the negative inotropic effect exerted by human septic shock (HSS) serum and TPO cooperation with TNF-alpha and IL-1beta. Pre-treatment with the TPO inhibitor prevented the decrease in contractile force induced by HSS serum. Moreover, TPO significantly amplified the negative inotropic effect induced by TNF-alpha and IL-1beta in papillary muscle. In conclusion, TPO negatively modulates cardiac inotropy in vitro and contributes to the myocardial depressing activity of septic shock serum.

Growth hormone-releasing hormone promotes survival of cardiac myocytes in vitro and protects against ischaemia-reperfusion injury in rat heart

AIMS

The hypothalamic neuropeptide growth hormone-releasing hormone (GHRH) stimulates GH synthesis and release in the pituitary. GHRH also exerts proliferative effects in extrapituitary cells, whereas GHRH antagonists have been shown to suppress cancer cell proliferation. We investigated GHRH effects on cardiac myocyte cell survival and the underlying signalling mechanisms.

METHODS AND RESULTS

Reverse transcriptase-polymerase chain reaction analysis showed GHRH receptor (GHRH-R) mRNA in adult rat ventricular myocytes (ARVMs) and in rat heart H9c2 cells. In ARVMs, GHRH prevented cell death and caspase-3 activation induced by serum starvation and by the beta-adrenergic receptor agonist isoproterenol. The GHRH-R antagonist JV-1-36 abolished GHRH survival action under both experimental conditions. GHRH-induced cardiac cell protection required extracellular signal-regulated kinase (ERK)1/2 and phosphoinositide-3 kinase (PI3K)/Akt activation and adenylyl cyclase/cAMP/protein kinase A signalling. Isoproterenol strongly upregulated the mRNA and protein of the pro-apoptotic inducible cAMP early repressor, whereas GHRH completely blocked this effect. Similar to ARVMs, in H9c2 cardiac cells, GHRH inhibited serum starvation- and isoproterenol-induced cell death and apoptosis through the same signalling pathways. Finally, GHRH improved left ventricular recovery during reperfusion and reduced infarct size in Langendorff-perfused rat hearts, subjected to ischaemia-reperfusion (I/R) injury. These effects involved PI3K/Akt signalling and were inhibited by JV-1-36.

CONCLUSION

Our findings suggest that GHRH promotes cardiac myocyte survival through multiple signalling mechanisms and protects against I/R injury in isolated rat heart, indicating a novel cardioprotective role of this hormone.

The homologous rat chromogranin A1-64 (rCGA1-64) modulates myocardial and coronary function in rat heart to counteract adrenergic stimulation indirectly via endothelium-derived nitric oxide

Chromogranin A (CGA), produced by human and rat myocardium, generates several biologically active peptides processed at specific proteolytic cleavage sites. A highly conserved cleavage N-terminal site is the bond 64-65 that reproduces the native rat CGA sequence (rCGA1-64), corresponding to human N-terminal CGA-derived vasostatin-1. rCGA1-64 cardiotropic activity has been explored in rat cardiac preparations. In Langendorff perfused rat heart, rCGA1-64 (from 33 nM) induced negative inotropism and lusitropism as well as coronary dilation, counteracting isoproterenol (Iso) - and endothelin-1 (ET-1) -induced positive inotropic effects and ET-1-dependent coronary constriction. rCGA1-64 also depressed basal and Iso-induced contractility on rat papillary muscles, without affecting calcium transients on isolated ventricular cells. Structure-function analysis using three modified peptides on both rat heart and papillary muscles revealed the disulfide bridge requirement for the cardiotropic action. A decline in Iso intrinsic activity in the presence of the peptides indicates a noncompetitive antagonistic action. Experiments on rat isolated cardiomyocytes and bovine aortic endothelial cells indicate that the negative inotropism observed in rat papillary muscle is probably due to an endothelial phosphatidylinositol 3-kinase-dependent nitric oxide release, rather than to a direct action on cardiomyocytes. Taken together, our data strongly suggest that in the rat heart the homologous rCGA1-64 fragment exerts an autocrine/paracrine modulation of myocardial and coronary performance acting as stabilizer against intense excitatory stimuli.

Endothelium-derived nitric oxide mediates the antiadrenergic effect of human vasostatin-1 in rat ventricular myocardium

Vasostatins (VSs) are vasoactive peptides derived from chromogranin A (CgA), a protein contained in secretory granules of chromaffin and other cells. The negative inotropic effect and the reduction of isoproterenol (Iso)-dependent inotropism induced by VSs in the heart suggest that they have an antiadrenergic function. However, further investigation of the mechanisms of action of VSs is needed. The aim of the present study was to define the signaling pathways activated by VS-1 in mammalian ventricular myocardium and cultured endothelial cells that lead to the modulation of cardiac contractility. Ca(2+) and nitric oxide (NO) fluorometric confocal imaging was used to study the effects induced by recombinant human VS-1 [STA-CgA-(1-76)] on contractile force, L-type Ca(2+) current, and Ca(2+) transients under basal conditions and after beta-adrenergic stimulation in rat papillary muscles and ventricular cells and the effects on intracellular Ca(2+) concentration and NO production in cultured bovine aortic endothelial (BAE-1) cells. VS-1 had no effect on basal contractility of papillary muscle, but the effect of Iso stimulation was reduced by 27%. Removal of endocardial endothelium and inhibition of NO synthesis and phosphatidylinositol 3-kinase (PI3K) activity abolished the antiadrenergic effect of VS-1 on papillary muscle. In cardiomyocytes, 10 nM VS-1 was ineffective on basal and Iso (1 microM)-stimulated L-type Ca(2+) current and Ca(2+) transients. In BAE-1 cells, VS-1 induced a Ca(2+)-independent increase in NO production that was blocked by the PI3K inhibitor wortmannin. Our results suggest that the antiadrenergic effect of VS-1 is mainly due to a PI3K-dependent NO release by endothelial cells, rather than a direct action on cardiomyocytes.

Limited plasticity of mesenchymal stem cells cocultured with adult cardiomyocytes

In order to assess, in a controlled in vitro model, the differentiation potential of adult bone marrow derived stem cells we have developed a coculture procedure using adult rat cardiomyocytes and mesenchymal stem cells (MSCs) from transgenic GFP positive rats. We investigated in the cocultured MSCs the time course of cellular processes that are difficult to monitor in in vivo experiments. Adult rat cardiomyocytes and adult rat MSCs were cocultured for up to 7 days and analyzed by confocal microscopy. Several markers were studied by immunofluorescence technique. The fluorescent ST-BODIPY-Dihydropyridine was used to label calcium channels in living cells. Intracellular calcium was monitored with the fluorescent probe X-Rhod-1. Immunofluorescence experiments showed the presence of connexin-43 between cardiomyocytes and MSCs and between MSCs, while no sarcomeric structures were observed at any time of the coculture. We looked at the expression of calcium channels and development of voltage-dependent calcium signaling in cocultured MSCs. MSCs showed a time-dependent increase of labeling of ST-BODIPY-Dihydropyridine, reaching a relatively strong level after 72 h of coculture. The treatment with a non-fluorescent DHP, Nifedipine, completely abolished ST-BODIPY labeling. We investigated whether depolarization could modulate intracellular calcium. Depolarization-induced calcium transients increased in MSCs in relation to the coculture time. We conclude that MSCs cocultured with adult cardiomyocytes present preliminary evidence of voltage-dependent calcium modulation uncoupled with the development of nascent or adult myofibrils, thus showing a limited lineage specification and a low plasticity to differentiate in a full cardiomyocyte-like phenotype.

An analysis of the changes in the surfaces of metallic femoral components in hip prostheses. A study of 60 prostheses removed after 1-20 years

A study of 60 femoral prosthetic components removed after 1-20 years allowed us to study the behaviour of the metallic surface in real life conditions. Changes were observed exclusively in cemented prostheses. They consisted of corrosion phenomena characteristic of the components of steel EN 58 J and 316 S, and wear phenomena secondary to mobilisation. The latter were observed in steel components as well as in those in Co-Cr alloy. The areas of corrosion in the steel prostheses were characteristically distributed, indicating a combination of causal factors, including an insufficient capacity of passivation of the metal and the particular situation of the cement-to-metal interface.

The effect of practice and temporal location of knowledge of results on the motor performance of older adults

An investigation was conducted to compare the effect of practice on the motor performance of older adults with that of college-aged adults. The temporal location of knowledge of results was varied during the practice in an attempt to ascertain the relationship between information storage/processing capacity and practice effect. Analysis of variance revealed motor performance proficiency differences favoring the younger adults but no difference between age groups in the pattern of performance change associated with practice. The proficiency differences could partially be explained in terms of older adults' information processing limitations.