Aging, sex and NLRP3 inflammasome in cardiac ischaemic disease

Experimentally, many strong cardioprotective treatments have been identified in different animal models of acute ischaemia/reperfusion injury (IRI) and coronary artery disease (CAD). However, the translation of these cardioprotective therapies for the benefit of the patients into the clinical scenario has been very disappointing. The reasons for this lack are certainly multiple. Indeed, many confounding factors we must deal in clinical reality, such as aging, sex and inflammatory processes are neglected in many experiments. Due to the pivotal role of aging, sex and inflammation in determining cardiac ischaemic disease, in this review, we take into account age as a modifier of tolerance to IRI in the two sexes, dissecting aging and myocardial reperfusion injury mechanisms and the sex differences in tolerance to IRI. Then we focus on the role of the gut microbiota and the NLRP3 inflammasome in myocardial IRI and on the possibility to consider NLRP3 inflammasome as a potential target in the treatment of CAD in relationship with age and sex. Finally, we consider the cardioprotective mechanisms and cardioprotective treatments during aging in the two sexes.

Angiotensin-converting enzyme 2: a key enzyme in key organs

2020 marked the 20th anniversary of the discovery of the angiotensin-converting enzyme 2 (ACE2). This major event that changed the way we see the renin-angiotensin system today could have passed quietly. Instead, the discovery that ACE2 is a major player in the severe acute respiratory syndrome coronavirus 2 pandemic has blown up the literature regarding this enzyme. ACE2 connects the classical arm renin-angiotensin system, consisting mainly of angiotensin II peptide and its AT1 receptor, with a protective arm, consisting mainly of the angiotensin 1-7 peptide and its Mas receptor. In this brief article, we have reviewed the literature to describe how ACE2 is a key protective arm enzyme in the function of many organs, particularly in the context of brain and cardiovascular function, as well as in renal, pulmonary and digestive homeostasis. We also very briefly review and refer to recent literature to present an insight into the role of ACE2 in determining the course of coronavirus diseases 2019.

Regulation of STAT3 and its role in cardioprotection by conditioning: focus on non-genomic roles targeting mitochondrial function

Ischemia–reperfusion injury (IRI) is one of the biggest challenges for cardiovascular researchers given the huge death toll caused by myocardial ischemic disease. Cardioprotective conditioning strategies, namely pre- and post-conditioning maneuvers, represent the most important strategies for stimulating pro-survival pathways essential to preserve cardiac health. Conditioning maneuvers have proved to be fundamental for the knowledge of the molecular basis of both IRI and cardioprotection. Among this evidence, the importance of signal transducer and activator of transcription 3 (STAT3) emerged. STAT3 is not only a transcription factor but also exhibits non-genomic pro-survival functions preserving mitochondrial function from IRI. Indeed, STAT3 is emerging as an influencer of mitochondrial function to explain the cardioprotection phenomena. Studying cardioprotection, STAT3 proved to be crucial as an element of the survivor activating factor enhancement (SAFE) pathway, which converges on mitochondria and influences their function by cross-talking with other cardioprotective pathways. Clearly there are still some functional properties of STAT3 to be discovered. Therefore, in this review, we highlight the evidence that places STAT3 as a promoter of the metabolic network. In particular, we focus on the possible interactions of STAT3 with processes aimed at maintaining mitochondrial functions, including the regulation of the electron transport chain, the production of reactive oxygen species, the homeostasis of Ca²⁺ and the inhibition of opening of mitochondrial permeability transition pore. Then we consider the role of STAT3 and the parallels between STA3/STAT5 in cardioprotection by conditioning, giving emphasis to the human heart and confounders.

Extracellular vesicles (EVs) in ischemic conditioning and angiogenesis: Focus on endothelial derived EVs

During myocardial ischemia, timely reperfusion is critical to limit infarct area and the overall loss of cardiac contractile function. However, reperfusion further exacerbates the damage of the ischemic heart. This type of injury is known as ischemia-reperfusion injury (IRI). Ischemic conditioning is a procedure which consists of brief cycles of ischemia and reperfusion in order to protect the myocardium against IRI. Remote ischemic conditioning (RIC), namely transient brief episodes of ischemia at a remote site before a subsequent damaging ischemia/reperfusion procedure of the target organ (e.g., the heart), protects against IRI. However, how the stimulus of RIC is transduced from the remote organ to the ischemic heart is still unknown. Recently, extracellular vesicles (EVs) have been proposed to have a role in the RIC procedure. The endothelium releases EVs and is also one of the tissues mostly exposed to EVs during their journey to the target organ. Moreover, EVs may have important roles in angiogenesis and, therefore, in the remodeling of post-ischemic organs. Here we analyze how EVs may contribute to the overall cardioprotective effect and the implication of the endothelium and its EVs in RIC mediated acute cardioprotection as well as in angiogenesis.

Extracellular Vesicles in Comorbidities Associated with Ischaemic Heart Disease: Focus on Sex, an Overlooked Factor

Extracellular vesicles (EV) are emerging early markers of myocardial damage and key mediators of cardioprotection. Therefore, EV are becoming fascinating tools to prevent cardiovascular disease and feasible weapons to limit ischaemia/reperfusion injury. It is well known that metabolic syndrome negatively affects vascular and endothelial function, thus creating predisposition to ischemic diseases. Additionally, sex is known to significantly impact myocardial injury and cardioprotection. Therefore, actions able to reduce risk factors related to comorbidities in ischaemic diseases are required to prevent maladaptive ventricular remodelling, preserve cardiac function, and prevent the onset of heart failure. This implies that early diagnosis and personalised medicine, also related to sex differences, are mandatory for primary or secondary prevention. Here, we report the contribution of EV as biomarkers and/or therapeutic tools in comorbidities predisposing to cardiac ischaemic disease. Whenever possible, attention is dedicated to data linking EV to sex differences.

Endothelial cell-derived extracellular vesicles exert cardio-protective effect via their protein cargo

Background

Extracellular vesicles (EV) are recognized as carriers of relevant biological effects and have been identified as regulators of cell-to-cell communication contributing to several patho-physiological processes. These processes include angiogenesis/coagulation/tissue repair/inflammation. In ischemia/reperfusion (I/R) settings, along with the direct effects of the I/R itself, paracrine mechanisms associated with the activation of the inflammatory response, primary involving endothelial cells, are crucial drivers of both vessel and cardiomyocyte damage.

Purpose

Since in models of myocardial I/R injury the role of EV released from endothelial cells is still unclear, our hypothesis was to provide insight on this specific topic. To this end, naïve endothelial cell (EC)-derived EV (eEV) and eEV released in response to the pro-inflammatory cytokine interleukin-3 (IL-3) (eEV-IL-3) have been evaluated on different I/R models.

Methods

eEV were characterized by MACSPlex-Exosome-Kit and western blot analysis. For the in-vitro hypoxia-reoxygenation (H/R) experiments, H9c2 or EC were pretreated with eEV, eEV-IL-3 (1x104 EV/cell) or IL-3 (10ng/ml) for 2 hours and then exposed to hypoxia (1% O2, 5% CO2) for additional 2 hours in the presence of eEV, eEV-IL-3 or IL-3 and subsequently reoxygenated (21% O2 and 5% CO2) for 1 hour. To verify the effect of EC treated with eEV, eEV-IL-3 or IL-3 on H9c2 and subjected to H/R protocol, transwell assay was used. At the end of the H/R protocol, cell viability was assessed. For ex-vivo experiments, isolated rat hearts, pretreated with a buffer containing EV (from EC pretreated or not with IL-3), were subjected to 30 minutes global normothermic ischemia and 1 hour reperfusion. Triton infusion was also used as a model of endothelial damage. At the end of I/R, the infarct size was measured and expressed as a percentage of total left ventricular mass (LVM). The role of eNOS/guanylyl-cyclase/MEK1/2 pathways in mediating eEV biological effects was also evaluated using different inhibitors both in in-vitro and ex-vivo models. Finally, protein profiles of eEV and eEV-IL-3 were analyzed using label free mass spectrometry.

Results

eEV and eEV-IL-3 protect EC, but not H9c2 exposed to H/R protocol, while eEV, but not eEV-IL-3-treatment limits I/R injury in the rat heart. Rat hearts pre-treated with triton significantly avoid eEV-induced cardio-protection. Transwell assay showed a reduction of H9C2 mortality after treatment with both eEV and eEV-IL-3. Proteomic analysis revealed that MEK1/2 and the endothelial-NOS (eNOS)-antagonist caveolin-1 were differentially expressed in eEV and eEV-IL-3. The use of eNOS/guanylyl-cyclase/MEK1/2 inhibitors prevented eEV-induced cardio-protection.

Conclusions

These observations indicate that eEV, but not eEV-IL-3, have cardio-protective effects when given as preconditioning agents. We have also shown that the activation of eNOS/GC/MEK1/2 pathway is crucial for eEV-mediated cardio-protection.

Funding Acknowledgement

Type of funding source: None

Mechanisms Involved in Cardioprotection Induced by Physical Exercise

Significance: Regular exercise training can reduce myocardial damage caused by acute ischemia/reperfusion (I/R). Exercise can reproduce the phenomenon of ischemic preconditioning, due to the capacity of brief periods of ischemia to reduce myocardial damage caused by acute I/R. In addition, exercise may also activate the multiple kinase cascade responsible for cardioprotection even in the absence of ischemia. Recent Advances: Animal and human studies highlighted the fact that, besides to reduce risk factors related to cardiovascular disease, the beneficial effects of exercise are also due to its ability to induce conditioning of the heart. Exercise behaves as a physiological stress that triggers beneficial adaptive cellular responses, inducing a protective phenotype in the heart. The factors contributing to the exercise-induced heart preconditioning include stimulation of the anti-radical defense system and nitric oxide production, opioids, myokines, and adenosine-5'-triphosphate (ATP) dependent potassium channels. They appear to be also involved in the protective effect exerted by exercise against cardiotoxicity related to chemotherapy. Critical Issues and Future Directions: Although several experimental evidences on the protective effect of exercise have been obtained, the mechanisms underlying this phenomenon have not yet been fully clarified. Further studies are warranted to define precise exercise prescriptions in patients at risk of myocardial infarction or undergoing chemotherapy.

Metaflammation: Tissue-Specific Alterations of the NLRP3 Inflammasome Platform in Metabolic Syndrome

In the last decades, the extension of life expectancy and the increased consumption of foods rich in saturated fats and added sugars have exposed the general population to emerging health problems. The prevalence of metabolic syndrome (MS), composed of a cluster of factors as obesity, dyslipidemia, hyperglycemia, and hypertension, is rapidly increasing in industrialized and developing countries leading to precocious onset of age-related diseases. Indeed, oxidative stress, accumulation of advanced glycation endproducts, and a chronic low-grade inflammation are common features of MS and physiological ageing. In particular, the entire set of MS factors contributes to the development of an inflammatory status named metaflammation, which has been associated with activation of early innate immune response through the assembling of the multiprotein complex inflammasome. The most investigated family of inflammasome platforms is the NOD-like receptor pyridine containing (NLRP) 3, which is activated by several exogenous and endogenous stimuli, leading to the sequential cleavage of caspase-1 and IL-1β, followed by secretion of active IL-1β. We here collect the most recent findings on NLRP3 activation in MS providing evidence of its central role in disease progression and organ dysfunction in target tissues of metaflammation, in particular in cardiovascular, hepatic and renal complications, with a focus on oxidative stress and advanced glycation endproducts. A wide overview of the most promising strategies for the modulation of NLRP3 activation and related metabolic repercussions is also provided, since the finding of specific pharmacological tools is an urgent requirement to reduce the social and economic burden of MS- and elderly-associated diseases.

Obestatin regulates cardiovascular function and promotes cardioprotection through the nitric oxide pathway

Patients with ischaemic heart disease or chronic heart failure show altered levels of obestatin, suggesting a role for this peptide in human heart function. We have previously demonstrated that GH secretagogues and the ghrelin gene-derived peptides, including obestatin, exert cardiovascular effects by modulating cardiac inotropism and vascular tone, and reducing cell death and contractile dysfunction in hearts subjected to ischaemia/reperfusion (I/R), through the Akt/nitric oxide (NO) pathway. However, the mechanisms underlying the cardiac actions of obestatin remain largely unknown. Thus, we suggested that obestatin-induced activation of PI3K/Akt/NO and PKG signalling is implicated in protection of the myocardium when challenged by adrenergic, endothelinergic or I/R stress. We show that obestatin exerts an inhibitory tone on the performance of rat papillary muscle in both basal conditions and under β-adrenergic overstimulation, through endothelial-dependent NO/cGMP/PKG signalling. This pathway was also involved in the vasodilator effect of the peptide, used both alone and under stress induced by endothelin-1. Moreover, when infused during early reperfusion, obestatin reduced infarct size in isolated I/R rat hearts, through an NO/PKG pathway, comprising ROS/PKC signalling, and converging on mitochondrial ATP-sensitive potassium [mitoK(ATP)] channels. Overall, our results suggest that obestatin regulates cardiovascular function in stress conditions and induces cardioprotection by mechanisms dependent on activation of an NO/soluble guanylate cyclase (sGC)/PKG pathway. In fact, obestatin counteracts exaggerated β-adrenergic and endothelin-1 activity, relevant factors in heart failure, suggesting multiple positive effects of the peptide, including the lowering of cardiac afterload, thus representing a potential candidate in pharmacological post-conditioning.

Platelets, diabetes and myocardial ischemia/reperfusion injury

Mechanisms underlying the pathogenesis of ischemia/reperfusion injury are particularly complex, multifactorial and highly interconnected. A complex and entangled interaction is also emerging between platelet function, antiplatelet drugs, coronary diseases and ischemia/reperfusion injury, especially in diabetic conditions. Here we briefly summarize features of antiplatelet therapy in type 2 diabetes (T2DM). We also treat the influence of T2DM on ischemia/reperfusion injury and how anti-platelet therapies affect post-ischemic myocardial damage through pleiotropic properties not related to their anti-aggregating effects. miRNA-based signature associated with T2DM and its cardiovascular disease complications are also briefly considered. Influence of anti-platelet therapies and different effects of healthy and diabetic platelets on ischemia/reperfusion injury need to be further clarified in order to enhance patient benefits from antiplatelet therapy and revascularization. Here we provide insight on the difficulty to reduce the cardiovascular risk in diabetic patients and report novel information on the cardioprotective role of widely used anti-aggregant drugs.

Endogenous Cardioprotective Agents: Role in Pre and Postconditioning

Cardiovascular diseases (CVD) are the leading cause of death, chronic illness and disability in Western countries. The most common cause of CVD derives from the harmful effects of acute myocardial ischemia and subsequent reperfusion injury. Cardioprotection against acute ischemia/ reperfusion injury is made possible by the "conditioning protocols." Conditioning is obtained by applying a few periods of brief ischemia and reperfusion in the event of prolonged (index) ischemia that may cause myocardial infarction. Whilst the conditioning stimulus is applied before the index ischemia in ischemic pre-conditioning, it is applied after the event in post-conditioning. Pre and post- conditioning stimuli can be applied in a different/remote organ (remote pre- and post-conditioning); in this case conditioning stimulus can also be applied during the index event, in the so called remote per-conditioning. All these endogenous cardioprotective strategies recruit endogenous cytoprotective agents and factors that elicit specific cardioprotective pathways. Here, we discuss many of these cardioprotective factors compared to literature and highlight their main characteristics and mechanisms of action. Enphasis is given to endogenous cardioprotective agents acting or not on surface receptors, including chromogranin A derivatives, ghrelin-associated peptides, growth factors and cytokines, and to microvesicles and exosomes. Moreover the cardioprotective effects of gasotransmitters nitric oxide, hydrogen sulphide and carbon monoxide are reviewed. The possible clinical translation of these knowledge for future successful therapies is briefly and critically discussed.

Catestatin exerts direct protective effects on rat cardiomyocytes undergoing ischemia/reperfusion by stimulating PI3K-Akt-GSK3β pathway and preserving mitochondrial membrane potential

Catestatin (Cst) is a 21-amino acid peptide deriving from Chromogranin A. Cst exerts an overall protective effect against an excessive sympathetic stimulation of cardiovascular system, being able to antagonize catecholamine secretion and to reduce their positive inotropic effect, by stimulating the release of nitric oxide (NO) from endothelial cells. Moreover, Cst reduces ischemia/reperfusion (I/R) injury, improving post-ischemic cardiac function and cardiomyocyte survival. To define the cardioprotective signaling pathways activated by Cst (5 nM) we used isolated adult rat cardiomyocytes undergoing simulated I/R. We evaluated cell viability rate with propidium iodide labeling and mitochondrial membrane potential (MMP) with the fluorescent probe JC-1. The involvement of Akt, GSK3β, eNOS and phospholamban (PLN) cascade was studied by immunofluorescence. The role of PI3K-Akt/NO/cGMP pathway was also investigated by using the pharmacological blockers wortmannin (Wm), L-NMMA and ODQ. Our experiments revealed that Cst increased cell viability rate by 65% and reduced cell contracture in I/R cardiomyocytes. Wm, L-NMMA and ODQ limited the protective effect of Cst. The protective outcome of Cst was related to its ability to maintain MMP and to increase AktSer473, GSK3βSer9, PLNThr17 and eNOSSer1179 phosphorylation, while treatment with Wm abolished these effects. Thus, the present results show that Cst is able to exert a direct action on cardiomyocytes and give new insights into the molecular mechanisms involved in its protective effect, highlighting the PI3K/NO/cGMP pathway as the trigger and the MMP preservation as the end point of its action.

RFamide peptides 43RFa and 26RFa both promote survival of pancreatic β-cells and human pancreatic islets but exert opposite effects on insulin secretion

RFamide peptides 43RFa and 26RFa have been shown to promote food intake and to exert different peripheral actions through G-protein-coupled receptor 103 (GPR103) binding. Moreover, 26RFa was found to inhibit pancreatic insulin secretion, whereas the role of 43RFa on β-cell function is unknown, as well as the effects of both peptides on β-cell survival. Herein, we investigated the effects of 43RFa and 26RFa on survival and apoptosis of pancreatic β-cells and human pancreatic islets. In addition, we explored the role of these peptides on insulin secretion and the underlying signaling mechanisms. Our results show that in INS-1E β-cells and human pancreatic islets both 43RFa and 26RFa prevented cell death and apoptosis induced by serum starvation, cytokine synergism, and glucolipotoxicity, through phosphatidylinositol 3-kinase/Akt- and extracellular signal-related kinase 1/2-mediated signaling. Moreover, 43RFa promoted, whereas 26RFa inhibited, glucose- and exendin-4-induced insulin secretion, through Gαs and Gαi/o proteins, respectively. Inhibition of GPR103 expression by small interfering RNA blocked 43RFa insulinotropic effect, but not the insulinostatic action of 26RFa. Finally, 43RFa, but not 26RFa, induced cAMP increase and glucose uptake. In conclusion, because of their survival effects along with the effects on insulin secretion, these findings suggest potential for 43RFa and 26RFa as therapeutic targets in the treatment of diabetes.

GH-releasing hormone induces cardioprotection in isolated male rat heart via activation of RISK and SAFE pathways

GHRH stimulates GH synthesis and release from the pituitary and exerts direct effects in extrapituitary tissues. We have previously shown that pretreatment with GHRH reduces cardiomyocyte apoptosis and improves heart function in isolated rat hearts subjected to ischemia/reperfusion (I/R). Here, we determined whether GHRH given at reperfusion reduces myocardial reperfusion injury and investigated the molecular mechanisms involved in GHRH effects. Isolated rat hearts subjected to I/R were treated at the onset of reperfusion with: 1) GHRH; 2) GHRH+GHRH antagonist JV-1-36; 3) GHRH+mitochondrial ATP-dependent potassium channel inhibitor 5-hydroxydecanoate; 4) GHRH+mitochondrial permeability transition pore opener atractyloside; 5) GHRH+ phosphoinositide 3-kinase/Akt inhibitor Wortmannin (WM); and 6) GHRH+signal transducer and activator of transcription-3 inhibitor tyrphostin-AG490 (AG490). GHRH reduced infarct size at the end of reperfusion and reverted contractility dysfunction in I/R hearts. These effects were inhibited by either JV-1-36, 5-hydroxydecanoate, atractylosid, WM, or AG490. Western blot analysis on left ventricles showed GHRH-induced phosphorylation of either the reperfusion injury salvage kinases (RISK), phosphoinositide 3-kinase/Akt, ERK1/2, and glycogen synthase kinase-3β or signal transducer and activator of transcription-3, as part of the survivor activating factor enhancement (SAFE) pathway. GHRH-induced activation of RISK and SAFE pathways was blocked by JV-1-36, WM, and AG490. Furthermore, GHRH increased the phosphorylation of endothelial nitric oxide synthase and AMP-activated protein kinase and preserved postischemic nicotinamide adenine dinucleotide (NAD(+)) levels. These results suggest that GHRH protects the heart from I/R injury through receptor-mediated mechanisms, leading to activation of RISK and SAFE pathways, which converge on mitochondria and possibly on AMP-activated protein kinase.

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.

Obestatin induced recovery of myocardial dysfunction in type 1 diabetic rats: underlying mechanisms

Background

The aim of this study was to investigate whether obestatin (OB), a peptide mediator encoded by the ghrelin gene exerting a protective effect in ischemic reperfused heart, is able to reduce cardiac dysfunctions in adult diabetic rats.

Methods

Diabetes was induced by STZ injection (50 mg/kg) in Wistar rats (DM). OB was administered (25 μg/kg) twice a day for 6 weeks. Non-diabetic (ND) rats and DM rats were distributed into four groups: untreated ND, OB-treated ND, untreated DM, OB-treated DM. Cardiac contractility and ß-adrenergic response were studied on isolated papillary muscles. Phosphorylation of AMPK, Akt, ERK1/2 and GSK3ß as well ß-1 adrenoreceptors levels were detected by western blot, while α-MHC was measured by RT-PCR.

Results

OB preserved papillary muscle contractility (85 vs 27% of ND), ß-adrenergic response (103 vs 65% of ND), as well ß1-adrenoreceptors and α-MHC levels in diabetic myocardial tissue. Moreover, OB up-regulated the survival kinases Akt and ERK1/2, and enhanced AMPK and GSK3ß phosphorylation. OB corrected oxidative unbalance, reduced pro-inflammatory cytokine TNF-α plasma levels, NFkB translocation and pro-fibrogenic factors expression in diabetic myocardium.

Conclusions

OB displays a significant beneficial effect against the alterations of contractility and ß-adrenergic response in the heart of STZ-treated diabetic rats, which was mainly associated with the ability of OB to up-regulate the transcription of ß1-adrenergic receptors and α-MHC; this protective effect was accompanied by the ability to restore oxidative balance and to promote phosphorylation/modulation of AMPK and pro-survival kinases such as Akt, ERK1/2 and GSK3ß.

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.

Cardiovascular actions of the ghrelin gene-derived peptides and growth hormone-releasing hormone

In 1976, small peptide growth hormone secretagogues (GHSs) were discovered and found to promote growth hormone (GH) release from the pituitary. The GHS receptor (GHS-R) was subsequently cloned, and its endogenous ligand ghrelin was later isolated from the stomach. Ghrelin is a 28-amino acid peptide, whose acylation is essential for binding to GHS-R type 1a and for the endocrine functions, including stimulation of GH secretion and subsequent food intake. Unacylated ghrelin, the other ghrelin form, although devoid of GHS-R binding is an active peptide, sharing many peripheral effects with acylated ghrelin (AG). The ghrelin system is broadly expressed in myocardial tissues, where it exerts different functions. Indeed, ghrelin inhibits cardiomyocyte and endothelial cell apoptosis, and improves left ventricular (LV) function during ischemia–reperfusion (I/R) injury. In rats with heart failure (HF), ghrelin improves LV dysfunction and attenuates the development of cardiac cachexia. Similarly, ghrelin exerts vasodilatory effects in humans, improves cardiac function and decreases systemic vascular resistance in patients with chronic HF. Obestatin is a recently identified ghrelin gene peptide. The physiological role of obestatin and its binding to the putative GPR39 receptor are still unclear, although protective effects have been demonstrated in the pancreas and heart. Similarly to AG, the hypothalamic peptide growth hormone-releasing hormone (GHRH) stimulates GH release from the pituitary, through binding to the GHRH-receptor. Besides its proliferative effects in different cell types, at the cardiovascular level GHRH inhibits cardiomyocyte apoptosis, and reduces infarct size in both isolated rat heart after I/R and in vivo after myocardial infarction. Therefore, both ghrelin and GHRH exert cardioprotective effects, which make them candidate targets for therapeutic intervention in cardiovascular dysfunctions.

Platelet activating factor: the good and the bad in the ischemic/reperfused heart

The present review is focused on the dual role played by platelet-activating factor (PAF) in ischemia and reperfusion (I/R) injury of the heart. Although the involvement of PAF in the pathogenesis of myocardial reperfusion injury is well established, in the last few years it has emerged that very low concentrations of PAF exert cardioprotective effects, comparable to that afforded by ischemic preconditioning (IP). PAF is a potent phosphoglyceride involved in different pathophysiological conditions affecting the cardiovascular system, including the development of myocardial I/R injury. PAF is released from the I/R myocardium in concentrations (1-10 nmol/L) high enough to negatively modulate coronary circulation as well as electrical and contractile activities. PAF may act either directly, via generation of secondary mediators, or through the activation of inflammatory cells like platelets and polymorphonuclear neutrophils, which exacerbate postischemic myocardial injury. The effects of PAF are mediated through specific receptors (PAFRs) that belong to the superfamily of G protein-coupled receptors. Since cardiomyocytes not only produce PAF but also possess PAFRs, it is likely that PAF acts as an autocrine/paracrine mediator. Although the negative effects exerted by high concentrations of PAF are well established, several recent findings from our and other laboratories have demonstrated that very low concentrations (pmol/L) of PAF infused before ischemia induce cardioprotective effects similar to those afforded by IP, and that endogenous PAF production participates in the induction of IP itself. The IP-like action exerted by low concentrations of PAF is due to the activation/phosphorylation of kinases included in the reperfusion injury salvage kinase (RISK) pathway, such as protein kinase C, Akt/PkB and nitric oxide synthase. Together with the activation of mitochondrial K(ATP) channels, these events may allow prevention of mitochondrial permeability transition pores opening at reperfusion. Moreover, the nitric oxide-dependent S-nitrosylation of L-type Ca(2+) channels induced by PAF reduces intracellular Ca(2+) overload.

Obestatin affords cardioprotection to the ischemic-reperfused isolated rat heart and inhibits apoptosis in cultures of similarly stressed cardiomyocytes

Obestatin, a newly discovered peptide encoded by the ghrelin gene, induces the expression of genes regulating pancreatic β-cell differentiation, insulin biosynthesis, and glucose metabolism. It also activates antiapoptotic signaling pathways such as phosphoinositide 3-kinase (PI3K) and ERK1/2 in pancreatic β-cells and human islets. Since these kinases have been shown to protect against myocardial injury, we sought to investigate whether obestatin would exert cardioprotective effects. Both isolated perfused rat heart and cultured cardiomyocyte models of ischemia-reperfusion (I/R) were used to measure infarct size and cell apoptosis as end points of injury. The presence of specific obestatin receptors on cardiac cells as well as the signaling pathways underlying the obestatin effect were also studied. In the isolated heart, the addition of rat obestatin-(1–23) before ischemia reduced infarct size and contractile dysfunction in a concentration-dependent manner, whereas obestatin-(23–1), a synthetic analog with an inverse aminoacid sequence, was ineffective. The cardioprotective effect of obestatin-(1–23) was observed at concentrations of 10–50 nmol/l and was abolished by inhibiting PI3K or PKC by the addition of wortmannin (100 nmol/l) or chelerythrine, (5 μmol/l), respectively. In rat H9c2 cardiac cells or isolated ventricular myocytes subjected to I/R, 50 nmol/l obestatin-(1–23) reduced cardiomyocyte apoptosis and reduced caspase-3 activation; the antiapoptotic effect was blocked by the inhibition of PKC, PI3K, or ERK1/2 pathways. In keeping with these functional findings, radioreceptor binding results revealed the presence of specific high-affinity obestatin-binding sites, mainly localized on membranes of the ventricular myocardium and cardiomyocytes. Our data suggest that, by acting on specific receptors, obestatin-(1–23) activates PI3K, PKC-ε, PKC-δ, and ERK1/2 signaling and protects cardiac cells against myocardial injury and apoptosis induced by I/R.

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.

Post-ischaemic activation of kinases in the pre-conditioning-like cardioprotective effect of the platelet-activating factor

AIM

Platelet-activating factor (PAF) triggers cardiac pre-conditioning against ischemia/reperfusion injury. The actual protection of ischaemic pre-conditioning occurs in the reperfusion phase. Therefore, we studied in this phase the kinases involved in PAF-induced pre-conditioning.

METHODS

Langendorff-perfused rat hearts underwent 30 min of ischaemia and 2 h of reperfusion (group 1, control). Before ischaemia, group 2 hearts were perfused for 19 min with PAF (2 x 10(-11) M); groups 3-5 hearts were co-infused during the initial 20 min of reperfusion, with the protein kinase C (PKC) inhibitor chelerythrine (5 x 10(-6) M) or the phosphoinositide 3-kinase (PI3K) inhibitor LY294002 (5 x 10(-5) M) and atractyloside (2 x 10(-5) M), a mitochondrial permeability transition pore (mPTP) opener respectively. Phosphorylation of PKCepsilon, PKB/Akappat, GSK-3beta and ERK1/2 at the beginning of reperfusion was also checked. Left ventricular pressure and infarct size were determined.

RESULTS

PAF pre-treatment reduced infarct size (33 +/- 4% vs. 64 +/- 5% of the area at risk of control hearts) and improved pressure recovery. PAF pre-treatment enhanced the phosphorylation/activation of PKCepsilon, PKB/Akappat and the phosphorylation/inactivation of GSK-3beta at reperfusion. Effects on ERK1/2 phosphorylation were not consistent. Infarct-sparing effect and post-ischaemic functional improvement induced by PAF pre-treatment were abolished by post-ischaemic infusion of either chelerythrine, LY294002 or atractyloside.

CONCLUSIONS

The cardioprotective effect exerted by PAF pre-treatment involves activation of PKC and PI3K in post-ischaemic phases and might be mediated by the prevention of mPTP opening in reperfusion via GSK-3beta inactivation.

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.

The platelet activating factor triggers preconditioning-like cardioprotective effect via mitochondrial K-ATP channels and redox-sensible signaling

Endogenous platelet activating factor (PAF) is involved in heart ischemic preconditioning. PAF can also afford pharmacological preconditioning. We studied whether mitochondrial-ATP-sensitive K(+) (mK(ATP)) channels and reactive oxygen species (ROS) are involved in PAF-induced cardioprotection. In Group 1 control hearts, Langendorff-perfused rat hearts underwent 30 min ischemia and 2 hours of reperfusion. Group 2 hearts, before ischemia, were perfused for 19 min with PAF (2x10(-11) M); Groups 3 and 4 hearts were co-infused with PAF and N-acetyl-L-cysteine or 5-hydroxydecanoate to scavenge ROS or to block mK(ATP) channels, respectively. Left ventricular pressure and infarct size were determined. PAF-pretreatment reduced infarct size (33 +/- 4% vs 64 +/- 4.6 % of the area at risk of control hearts) and improved pressure recovery. Infarct-sparing effect of PAF was abolished by N-acetyl-L-cysteine and 5-hydroxydecanoate. Thus, the cardioprotective effect exerted by PAF-pretreatment involves activation of mK(ATP) channels and redox signaling in pre-ischemic phase.

Oxidative stress triggers cardiac fibrosis in the heart of diabetic rats

Diabetic cardiomyopathy is characterized by myocyte loss and myocardial fibrosis, leading to decreased elasticity and impaired contractile function. The study examines the downstream signaling whereby oxidative stress, induced by hyperglycemia, leads to myocardial fibrosis and impaired contractile function in the left ventricle of diabetic rats. It also examines the effects of dehydroepiandrosterone (DHEA), which prevents the oxidative damage induced by hyperglycemia in experimental models. DHEA was administered for 6 wk in the diet [0.02%, wt/wt)] to rats with streptozotocin-induced diabetes. Oxidative balance, advanced glycated end products (AGEs) and AGE receptors, transcription factors nuclear factor-kappaB and activator protein-1, and profibrogenic growth factors (connective tissue growth factor and TGFbeta1) were determined in the left ventricle of treated and untreated streptozotocin-diabetic rats. Structural and ultrastructural changes, and the contractile force developed by electrically driven papillary muscles, under basal conditions and after stimulation with isoproterenol, were also evaluated. Oxidative stress induced by hyperglycemia increased AGEs and AGE receptors and triggered a cascade of signaling, eventually leading to interstitial fibrosis. DHEA treatment, by improving oxidative balance, counteracted the enhanced AGE receptor activation and increase of profibrogenic factors and restored tissue levels of collagen I, collagen IV, and fibronectin to those of control animals. Moreover, DHEA completely restored the contractility of isolated papillary muscle. Oxidative stress led to cardiac fibrosis, the most important pathogenetic factor of the heart's impaired functional integrity in diabetes. Structural and ultrastructural changes and impairment of muscle function induced by experimental diabetes were minimized by DHEA treatment.

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.

Phosphoinositide 3-kinasegamma (PI3Kgamma) controls L-type calcium current (ICa,L) through its positive modulation of type-3 phosphodiesterase (PDE3)

The modulation of L-type calcium current (ICa,L) is mainly due to mediators acting through activation of G protein-coupled receptors (GPCR) and different protein kinases; among them, phosphoinositide 3-kinasegamma (PI3Kgamma) has been recently discovered to play an important role in the regulation of cardiac contractility and beta-adrenergic signal transduction. Recent reports have demonstrated that, in the heart, different subtypes of beta-adrenergic receptors are coupled to both Gi and/or Gs proteins. While beta1-adrenergic receptors (beta1-AR) couple only to Gs and evoke a strong ICa,L, beta2-adrenergic receptors (beta2-AR) can activate both Gs and Gi proteins and trigger only a limited ICa,L. Here we demonstrate that (i) PI3Kgamma-/- ventricular myocytes are characterized by an higher basal ICa,L density, even if the responsiveness of adenylyl cyclase to Forskolin is comparable to that observed in PI3Kgamma+/+ cardiomyocytes; (ii) both in basal conditions and after beta-AR stimulation, the activity of phosphodiesterase (PDE) type 3 depends on PI3Kgamma; (iii) in PI3Kgamma-/- cardiac myocytes, specific stimulation of beta2-AR is followed by a increase in ICa,L stronger than in wild-type controls. Taken together, our results suggest that the higher values of ICa,L observed both in basal conditions and after beta-AR stimulation in PI3Kgamma-/- ventricular myocytes are mainly due to a positive modulation of PDE3 activity exerted by PI3Kgamma. As observed in PI3Kgamma-/- neonatal cardiomyocytes, cells lacking PI3Kgamma are more sensitive to stimulation of beta2-adrenergic receptors.

Platelet-activating factor induces cardioprotection in isolated rat heart akin to ischemic preconditioning: role of phosphoinositide 3-kinase and protein kinase C activation

Ischemic preconditioning (IP) is a cardioprotective mechanism against myocellular death and cardiac dysfunction resulting from reperfusion of the ischemic heart. At present, the precise list of mediators involved in IP and the pathways of their mechanisms of action are not completely known. The aim of the present study was to investigate the role of platelet-activating factor (PAF), a phospholipid mediator that is known to be released by the ischemic-reperfused heart, as a possible endogenous agent involved in IP. Experiments were performed on Langendorff-perfused rat hearts undergoing 30 min of ischemia followed by 2 h of reperfusion. Treatment with a low concentration of PAF (2 × 10−11 M) before ischemia reduced the extension of infarct size and improved the recovery of left ventricular developed pressure during reperfusion. The cardioprotective effect of PAF was comparable to that observed in hearts in which IP was induced by three brief (3 min) periods of ischemia separated by 5-min reperfusion intervals. The PAF receptor antagonist WEB-2170 (1 × 10−9 M) abrogated the cardioprotective effect induced by both PAF and IP. The protein kinase C (PKC) inhibitor chelerythrine (5 × 10−6 M) or the phosphoinositide 3-kinase (PI3K) inhibitor LY-294002 (5 × 10−5 M) also reduced the cardioprotective effect of PAF. Western blot analysis revealed that following IP treatment or PAF infusion, the phosphorylation of PKC-ε and Akt (the downstream target of PI3K) was higher than that in control hearts. The present data indicate that exogenous applications of low quantities of PAF induce a cardioprotective effect through PI3K and PKC activation, similar to that afforded by IP. Moreover, the study suggests that endogenous release of PAF, induced by brief periods of ischemia and reperfusion, may participate to the triggering of the IP of the heart.

Phosphoinositide 3-kinase gamma controls autonomic regulation of the mouse heart through Gi-independent downregulation of cAMP level

Cardiac beta-adrenergic and the muscarinic receptors control contractility and heart rate by triggering multiple signaling events involving downstream targets like the phosphoinositide 3-kinase gamma (PI3Kgamma). We thus investigated whether the lack of PI3Kgamma could play a role in the autonomic regulation of the mouse heart. Contractility and ICaL of mutant cardiac preparations appeared increased in basal conditions and after beta-adrenergic stimulation. However, basal and beta-adrenergic stimulated heart rate were normal. Conversely, muscarinic inhibition of heart rate was reduced without alteration of the Gbetagamma-dependent stimulation of IK,ACh current. In addition, muscarinic-mediated anti-adrenergic effect on papillary muscle contractility and ICaL was significantly depressed. Consistently, cAMP level of PI3Kgamma-null ventricles was always higher than wild-type controls. Thus, PI3Kgamma controls the cardiac function by reducing cAMP concentration independently of Gi-mediated signaling.

Phosphoinositide 3-kinase gamma: kinase-dependent and -independent activities in cardiovascular function and disease

Cardiac function is controlled by GPCRs (G-protein-coupled receptors) which exert their function by triggering numerous signalling pathways, including the activation of PI3K (phosphoinositide 3-kinase). The GPCR-activated PI3Kgamma is weakly expressed in the heart, but the deletion of its expression in mice causes remarkable phenotypes. Indeed, the lack of PI3Kgamma does not modify heart rate and blood pressure, but does increase contractility, particularly in response to stimuli that enhance cardiac contractile force, such as catecholamines. Consistently, treatment of mutant cardiomyocytes with beta-adrenergic agonists causes an abnormal increase in the elevation of cAMP production. On the other hand, PI3Kgamma appears to play a role in mediating the contractile depression exerted by other GPCR agonists, such as PAF (platelet-activating factor), that are released in pathological conditions, such as after an ischaemic insult. The receptor for PAF coupled to G(i) activates PI3Kgamma, which, in turn, is essential to promote Akt phosphorylation, NOSIII (nitric oxide synthase isoform III) activation and the production of nitric oxide, a well characterized cardiodepressing agent. As a whole, PI3Kgamma appears to negatively control cardiac contractility through different signalling mechanisms, thus becoming a possible drug target for the treatment of critical human cardiac pathologies, such as infarction or heart failure.

Cyclic AMP and cyclic GMP independent stimulation of ventricular calcium current by peroxynitrite donors in guinea pig myocytes

We investigated the potential involvement of peroxynitrite (ONOO(-)) in the modulation of calcium current (I(Ca)) in guinea pig ventricular myocytes with the whole-cell patch clamp technique and with cyclic AMP (cAMP) measurements. Because of the short half-life of ONOO(-) at physiological pH, we induced an increase in its intracellular levels by using donors of the precursors, nitric oxide (NO) and superoxide anion (O(2) (-)). High concentrations of NO donors, SpermineNONOate (sp/NO, 300 microM) or SNAP (300 microM) increased basal I(Ca) (50.3 +/- 4.6%, n = 7 and 46.2 +/- 5.0%, n = 13). The superoxide anion donor Pyrogallol (100 microM) also stimulated basal I(Ca) (44.6 +/- 2.8%, n = 11). At lower concentration sp/NO (10 nM) and Pyrogallol (1 microM), although separately ineffective on I(Ca), enhanced the current if applied together (33.5 +/- 0.7%, n = 7). The simultaneous donor of O(2) (-) and NO, SIN-1 (500 microM), also stimulated basal I(Ca) (22.8 +/- 2.1%, n = 13). In the presence of saturating cyclic GMP (cGMP, 50 microM) in the patch pipette or of extracellular dibutyryl cGMP (dbcGMP, 100 microM), I(Ca) was still increased by SIN-1 (32.0 +/- 6.1%, n = 4 and 30.0 +/- 5.4%, n = 8). Both Manganese(III)tetrakis(4-benzoic acid) porphyrin chloride (MnTBAP, 100 microM) a ONOO(-) scavenger, and superoxide dismutase (SOD) (150 U/ml) reversed the stimulatory effect of SIN-1 on I(Ca) (respectively -0.6 +/- 4.1%, n = 4 and 3.6 +/- 4.3%, n = 4). Intracellular cAMP level was unaltered by SIN-1, while it was enhanced by blocking the NO-cGMP pathway with the NO synthase inhibitor L-NMMA. These results suggest that peroxynitrite donors increase cardiac calcium current without the involvement of cAMP and cGMP.

Phosphoinositide 3-kinase γ-deficient hearts are protected from the PAF-dependent depression of cardiac contractility

OBJECTIVES

Following an ischemic insult, cardiac contractile recovery might be perturbed by the release of autacoids, like platelet-activating factor (PAF), that depress heart function by acting through G protein-coupled receptors (GPCRs). The signaling events downstream the PAF receptor that lead to the negative inotropic effect are still obscure. We thus investigated whether the GPCR-activated phosphoisositide 3-kinase gamma (PI3Kgamma) could play a role in the cardiac response to PAF.

METHODS

The negative inotropic effect of PAF was studied ex vivo, in isolated electrically driven atria and in Langendorff-perfused whole hearts derived from wild-type and PI3Kgamma-null mice. Postischemic recovery of contractility was analyzed in normal and mutant whole hearts subjected to 30 min of ischemia and 40 min of reperfusion in the presence or absence of a PAF receptor antagonist.

RESULTS

While wild-type hearts stimulated with PAF showed increased nitric oxide (NO) production and a consequent decreased cardiac contractility, PI3Kgamma-null hearts displayed reduced phosphorylation of nitric oxide synthase 3 (NOS3), blunted nitric oxide production and a complete protection from the PAF-induced negative inotropism. In addition, Langendorff-perfused PI3Kgamma-null hearts showed a better contractile recovery after ischemia/reperfusion, a condition where PAF is known to be an important player in depressing contractility. In agreement with a role of PI3Kgamma in this PAF-mediated signaling, postischemic contractile recovery in PI3Kgamma-null mice appeared overlapping with that of normal hearts treated with the PAF receptor antagonist WEB 2170.

CONCLUSION

These data indicate a novel PAF-dependent signaling pathway that, involving PI3Kgamma and NOS3, contributes to postischemic contractile depression.

Cardiac effects of ghrelin and its endogenous derivatives des-octanoyl ghrelin and des-Gln14-ghrelin

The mechanisms underlying the cardiac activities of synthetic growth hormone secretagogues (GHS) are still unclear. The natural ligand of the GHS receptors, i.e. ghrelin, classically binds the GHS receptor and exerts endocrine actions in acylated forms only; its cardiovascular actions still need to be investigated further. In order to clarify these aspects, we studied the effects of either the synthetic peptidyl GHS hexarelin (1 microM), or the natural ghrelin (50 nM) and the endogenous ghrelin derivatives des-Gln14-ghrelin (1-100 nM) and des-octanoyl ghrelin (50 nM), on the tension developed by guinea pig papillary muscle and on L-type Ca2+ current (ICa) of isolated ventricular cells. The binding of these molecules to ventricular cell membrane homogenates was also studied. We observed that all peptides reduced the tension developed at low frequencies (60-120 beats/min) in a dose-dependent manner. No alteration in cardiac contractility was induced by des-Gln14-ghrelin or des-octanoylated ghrelin when the endocardial endothelium had been removed or after cyclooxygenase blockade. Pretreatment with tyramine (2 microM) had no effect on the inotropic response induced by des-Gln(14)-ghrelin. No significant effect on I(Ca) of isolated ventricular cells was observed in the presence of des-Gln14-ghrelin (100 nM). The order of potency on the tension of papillary muscle was: des-octanoyl ghrelin > ghrelin = des-Gln14-ghrelin > hexarelin. This gradient of potency was consistent with the binding experiments performed on ventricular membranes where either acylated or unacylated ghrelin forms, and hexarelin, recognized a common high-affinity binding site. In conclusion, ghrelin, des-Gln14-ghrelin and des-octanoyl ghrelin, show similar negative inotropic effect on papillary muscle; as des-octanoyl ghrelin is peculiarly devoid of any GH-releasing activity, the cardiotropic action of these molecules is independent of GH release. The binding studies and the experiments performed both on the isolated cells and on papillary muscle after endothelium removal or cyclooxygenase blockade indicate that the cardiotropic action of natural and synthetic ghrelin analogues reflects the interaction with a novel GHS receptor (peculiarly common for ghrelin and des-octanoyl ghrelin), leading to release of cyclooxygenase metabolites from endothelial cells, as indicated by direct measurement of prostacyclin metabolite 6-keto-PGF(1alpha).