Inhibition of permeability transition pore opening by mitochondrial STAT3 and its role in myocardial ischemia/reperfusion

The signal transducer and activator of transcription 3 (STAT3) contributes to cardioprotection by ischemic pre- and postconditioning. Mitochondria are central elements of cardioprotective signaling, most likely by delaying mitochondrial permeability transition pore (MPTP) opening, and STAT3 has recently been identified in mitochondria. We now characterized the mitochondrial localization of STAT3 and its impact on respiration and MPTP opening. STAT3 was mainly present in the matrix of subsarcolemmal and interfibrillar cardiomyocyte mitochondria. STAT1, but not STAT5 was also detected in mitochondria under physiological conditions. ADP-stimulated respiration was reduced in mitochondria from mice with a cardiomyocyte-specific deletion of STAT3 (STAT3-KO) versus wildtypes and in rat mitochondria treated with the STAT3 inhibitor Stattic (STAT3 inhibitory compound, 6-Nitrobenzo[b]thiophene 1,1-dioxide). Mitochondria from STAT3-KO mice and Stattic-treated rat mitochondria tolerated less calcium until MPTP opening occurred. STAT3 co-immunoprecipitated with cyclophilin D, the target of the cardioprotective agent and MPTP inhibitor cyclosporine A (CsA). However, CsA reduced infarct size to a similar extent in wildtype and STAT3-KO mice in vivo. Thus, STAT3 possibly contributes to cardioprotection by stimulation of respiration and inhibition of MPTP opening

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 Ca(2+) 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

Ageing, sex and cardioprotection

Translation of cardioprotective interventions aimed at reducing myocardial injury during ischaemia-reperfusion from experimental studies to clinical practice is an important yet unmet need in cardiovascular medicine. One particular challenge facing translation is the existence of demographic and clinical factors that influence the pathophysiology of ischaemia-reperfusion injury of the heart and the effects of treatments aimed at preventing it. Among these factors, age and sex are prominent and have a recognised role in the susceptibility and outcome of ischaemic heart disease. Remarkably, some of the most powerful cardioprotective strategies proven to be effective in young animals become ineffective during ageing. This article reviews the mechanisms and implications of the modulatory effects of ageing and sex on myocardial ischaemia-reperfusion injury and their potential effects on cardioprotective interventions

Inhibition of STAT3 signaling prevents vascular smooth muscle cell proliferation and neointima formation

Dedifferentiation, migration, and proliferation of resident vascular smooth muscle cells (SMCs) are key components of neointima formation after vascular injury. Activation of signal transducer and activator of transcription-3 (STAT3) is suggested to be critically involved in this process, but the complex regulation of STAT3-dependent genes and the functional significance of inhibiting this pathway during the development of vascular proliferative diseases remain elusive. In this study, we demonstrate that STAT3 was activated in neointimal lesions following wire-induced injury in mice. Phosphorylation of STAT3 induced trans-activation of cyclin D1 and survivin in SMCs in vitro and in neointimal cells in vivo, thus promoting proliferation and migration of SMCs as well as reducing apoptotic cell death. WP1066, a highly potent inhibitor of STAT3 signaling, abrogated phosphorylation of STAT3 and dose-dependently inhibited the functional effects of activated STAT3 in stimulated SMCs. The local application of WP1066 via a thermosensitive pluronic F-127 gel around the dilated arteries significantly inhibited proliferation of neointimal cells and decreased the neointimal lesion size at 3 weeks after injury. Even though WP1066 application attenuated the injury-induced up-regulation of the chemokine RANTES at 6 h after injury, there was no significant effect on the accumulation of circulating cells at 1 week after injury. In conclusion, these data identify STAT3 as a key molecule for the proliferative response of SMC and neointima formation. Moreover, inhibition of STAT3 by the potent and specific compound WP1066 might represent a novel and attractive approach for the local treatment of vascular proliferative diseases

From basic mechanisms to clinical applications in heart protection, new players in cardiovascular diseases and cardiac theranostics: meeting report from the third international symposium on "New frontiers in cardiovascular research"

In this meeting report, particularly addressing the topic of protection of the cardiovascular system from ischemia/reperfusion injury, highlights are presented that relate to conditioning strategies of the heart with respect to molecular mechanisms and outcome in patients' cohorts, the influence of co-morbidities and medications, as well as the contribution of innate immune reactions in cardioprotection. Moreover, developmental or systems biology approaches bear great potential in systematically uncovering unexpected components involved in ischemia-reperfusion injury or heart regeneration. Based on the characterization of particular platelet integrins, mitochondrial redox-linked proteins, or lipid-diol compounds in cardiovascular diseases, their targeting by newly developed theranostics and technologies opens new avenues for diagnosis and therapy of myocardial infarction to improve the patients' outcome

Secretogranin II; a Protein Increased in the Myocardium and Circulation in Heart Failure with Cardioprotective Properties

Background: Several beneficial effects have been demonstrated for secretogranin II (SgII) in non-cardiac tissue. As cardiac production of chromogranin A and B, two related proteins, is increased in heart failure (HF), we hypothesized that SgII could play a role in cardiovascular pathophysiology. Methodology/Principal Findings: SgII production was characterized in a post-myocardial infarction heart failure (HF) mouse model, functional properties explored in experimental models, and circulating levels measured in mice and patients with stable HF of moderate severity. SgII mRNA levels were 10.5 fold upregulated in the left ventricle (LV) of animals with myocardial infarction and HF (p<0.001 vs. sham-operated animals). SgII protein levels were also increased in the LV, but not in other organs investigated. SgII was produced in several cell types in the myocardium and cardiomyocyte synthesis of SgII was potently induced by transforming growth factor-beta and norepinephrine stimulation in vitro. Processing of SgII to shorter peptides was enhanced in the failing myocardium due to increased levels of the proteases PC1/3 and PC2 and circulating SgII levels were increased in mice with HF. Examining a pathophysiological role of SgII in the initial phase of post-infarction HF, the SgII fragment secretoneurin reduced myocardial ischemia-reperfusion injury and cardiomyocyte apoptosis by 30% and rapidly increased cardiomyocyte Erk1/2 and Stat3 phosphorylation. SgII levels were also higher in patients with stable, chronic HF compared to age-and gender-matched control subjects: median 0.16 (Q1-3 0.14-0.18) vs. 0.12 (0.10-0.14) nmol/L, p<0.001. Conclusions: We demonstrate increased myocardial SgII production and processing in the LV in animals with myocardial infarction and HF, which could be beneficial as the SgII fragment secretoneurin protects from ischemia-reperfusion injury and cardiomyocyte apoptosis. Circulating SgII levels are also increased in patients with chronic, stable HF and may represent a new cardiac biomarker

Bradykinin and adenosine receptors mediate desflurane induced postconditioning in human myocardium: role of reactive oxygen species

BACKGROUND: Desflurane during early reperfusion has been shown to postcondition human myocardium, in vitro. We investigated the role of adenosine and bradykinin receptors, and generation of radical oxygen species in desflurane-induced postconditioning in human myocardium. METHODS: We recorded isometric contraction of human right atrial trabeculae hanged in an oxygenated Tyrode's solution (34 degrees Celsius, stimulation frequency 1 Hz). After a 30-min hypoxic period, desflurane 6% was administered during the first 5 min of reoxygenation. Desflurane was administered alone or with pretreatment of N-mercaptopropionylglycine, a reactive oxygen species scavenger, 8-(p-Sulfophenyl)theophylline, an adenosine receptor antagonist, HOE140, a selective B2 bradykinin receptor antagonist. In separate groups, adenosine and bradykinin were administered during the first minutes of reoxygenation alone or in presence of N-mercaptopropionylglycine. The force of contraction of trabeculae was recorded continuously. Developed force at the end of a 60-min reoxygenation period was compared (mean +/- standard deviation) between the groups by a variance analysis and post hoc test. RESULTS: Desflurane 6% (84 +/- 6% of baseline) enhanced the recovery of force after 60-min of reoxygenation as compared to control group (51 +/- 8% of baseline, P < 0.0001). N-mercaptopropionylglycine (54 +/- 3% of baseline), 8-(p-Sulfophenyl)theophylline (62 +/- 9% of baseline), HOE140 (58 +/- 6% of baseline) abolished desflurane-induced postconditioning. Adenosine (80 +/- 9% of baseline) and bradykinin (83 +/- 4% of baseline) induced postconditioning (P < 0.0001 vs control), N-mercaptopropionylglycine abolished the beneficial effects of adenosine and bradykinin (54 +/- 8 and 58 +/- 5% of baseline, respectively). CONCLUSIONS: In vitro, desflurane-induced postconditioning depends on reactive oxygen species production, activation of adenosine and bradykinin B2 receptors. And, the cardioprotective effect of adenosine and bradykinin administered at the beginning of reoxygenation, was mediated, at least in part, through ROS production

Connexin-43 prevents hematopoietic stem cell senescence through transfer of reactive oxygen species to bone marrow stromal cells

Hematopoietic stem cell (HSC) aging has become a concern in chemotherapy of older patients. Humoral and paracrine signals from the bone marrow (BM) hematopoietic microenvironment (HM) control HSC activity during regenerative hematopoiesis. Connexin-43 (Cx43), a connexin constituent of gap junctions (GJs) is expressed in HSCs, down-regulated during differentiation, and postulated to be a self-renewal gene. Our studies, however, reveal that hematopoietic-specific Cx43 deficiency does not result in significant long-term competitive repopulation deficiency. Instead, hematopoietic Cx43 (H-Cx43) deficiency delays hematopoietic recovery after myeloablation with 5-fluorouracil (5-FU). 5-FU-treated H-Cx43-deficient HSC and progenitors (HSC/P) cells display decreased survival and fail to enter the cell cycle to proliferate. Cell cycle quiescence is associated with down-regulation of cyclin D1, up-regulation of the cyclin-dependent kinase inhibitors, p21cip1. and p16INK4a, and Forkhead transcriptional factor 1 (Foxo1), and activation of p38 mitogen-activated protein kinase (MAPK), indicating that H-Cx43-deficient HSCs are prone to senescence. The mechanism of increased senescence in H-Cx43-deficient HSC/P cells depends on their inability to transfer reactive oxygen species (ROS) to the HM, leading to accumulation of ROS within HSCs. In vivo antioxidant administration prevents the defective hematopoietic regeneration, as well as exogenous expression of Cx43 in HSC/P cells. Furthermore, ROS transfer from HSC/P cells to BM stromal cells is also rescued by reexpression of Cx43 in HSC/P. Finally, the deficiency of Cx43 in the HM phenocopies the hematopoietic defect in vivo. These results indicate that Cx43 exerts a protective role and regulates the HSC/P ROS content through ROS transfer to the HM, resulting in HSC protection during stress hematopoietic regeneration