Metabolic Reprogramming: A Byproduct or a Driver of Cardiomyocyte Proliferation?

Defining mechanisms of cardiomyocyte proliferation should guide the understanding of endogenous cardiac regeneration and could lead to novel treatments for diseases such as myocardial infarction. In the neonatal heart, energy metabolic reprogramming (phenotypic alteration of glucose, fatty acid, and amino acid metabolism) parallels cell cycle arrest of cardiomyocytes. The metabolic reprogramming occurring shortly after birth is associated with alterations in blood oxygen levels, metabolic substrate availability, hemodynamic stress, and hormone release. In the adult heart, myocardial infarction causes metabolic reprogramming but these changes cannot stimulate sufficient cardiomyocyte proliferation to replace those lost by the ischemic injury. Some putative pro-proliferative interventions can induce the metabolic reprogramming. Recent data show that altering the metabolic enzymes PKM2 [pyruvate kinase 2], LDHA [lactate dehydrogenase A], PDK4 [pyruvate dehydrogenase kinase 4], SDH [succinate dehydrogenase], CPT1b [carnitine palmitoyl transferase 1b], or HMGCS2 [3-hydroxy-3-methylglutaryl-CoA synthase 2] is sufficient to partially reverse metabolic reprogramming and promotes adult cardiomyocyte proliferation. How metabolic reprogramming regulates cardiomyocyte proliferation is not clearly defined. The possible mechanisms involve biosynthetic pathways from the glycolysis shunts and the epigenetic regulation induced by metabolic intermediates. Metabolic manipulation could represent a new approach to stimulate cardiac regeneration; however, the efficacy of these manipulations requires optimization, and novel molecular targets need to be defined. In this review, we summarize the features, triggers, and molecular regulatory networks responsible for metabolic reprogramming and discuss the current understanding of metabolic reprogramming as a critical determinant of cardiomyocyte proliferation.

The novel antibody fusion protein rhNRG1-HER3i promotes heart regeneration by enhancing NRG1-ERBB4 signaling pathway.

Stimulating cardiomyocyte proliferation in the adult heart has emerged as a promising strategy for cardiac regeneration following myocardial infarction (MI). The NRG1-ERBB4 signaling pathway has been implicated in the regulation of cardiomyocyte proliferation. However, the therapeutic potential of recombinant human NRG1 (rhNRG1) has been limited due to the low expression of ERBB4 in adult cardiomyocytes. Here, we investigated whether a fusion protein of rhNRG1 and an ERBB3 inhibitor (rhNRG1-HER3i) could enhance the affinity of NRG1 for ERBB4 and promote adult cardiomyocyte proliferation. In vitro and in vivo experiments were conducted using postnatal day 1 (P1), P7, and adult cardiomyocytes. Western blot analysis was performed to assess the expression and activity of ERBB4. Cardiomyocyte proliferation was evaluated using Ki67 and pH 3 immunostaining, while fibrosis was assessed using Masson staining. Our results indicate that rhNRG1-HER3i, but not rhNRG1, promoted P7 and adult cardiomyocyte proliferation. Furthermore, rhNRG1-HER3i improved cardiac function and reduced cardiac fibrosis in post-MI hearts. Administration of rhNRG1-HER3i inhibited ERBB3 phosphorylation while increasing ERBB4 phosphorylation in adult mouse hearts. Additionally, rhNRG1-HER3i enhanced angiogenesis following MI compared to rhNRG1. In conclusion, our findings suggest that rhNRG1-HER3i is a viable therapeutic approach for promoting adult cardiomyocyte proliferation and treating MI by enhancing NRG1-ERBB4 signaling pathway.

Chemokine CCL2 promotes cardiac regeneration and repair in myocardial infarction mice via activation of the JNK/STAT3 axis.

Stimulation of adult cardiomyocyte proliferation is a promising strategy for treating myocardial infarction (MI). Earlier studies have shown increased CCL2 levels in plasma and cardiac tissue both in MI patients and mouse models. In present study we investigated the role of CCL2 in cardiac regeneration and the underlying mechanisms. MI was induced in adult mice by permanent ligation of the left anterior descending artery, we showed that the serum and cardiac CCL2 levels were significantly increased in MI mice. Intramyocardial injection of recombinant CCL2 (rCCL2, 1 µg) immediately after the surgery significantly promoted cardiomyocyte proliferation, improved survival rate and cardiac function, and diminished scar sizes in post-MI mice. Alongside these beneficial effects, we observed an increased angiogenesis and decreased cardiomyocyte apoptosis in post-MI mice. Conversely, treatment with a selective CCL2 synthesis inhibitor Bindarit (30 µM) suppressed both CCL2 expression and cardiomyocyte proliferation in P1 neonatal rat ventricle myocytes (NRVMs). We demonstrated in NRVMs that the CCL2 stimulated cardiomyocyte proliferation through STAT3 signaling: treatment with rCCL2 (100 ng/mL) significantly increased the phosphorylation levels of STAT3, whereas a STAT3 phosphorylation inhibitor Stattic (30 µM) suppressed rCCL2-induced cardiomyocyte proliferation. In conclusion, this study suggests that CCL2 promotes cardiac regeneration via activation of STAT3 signaling, underscoring its potential as a therapeutic agent for managing MI and associated heart failure.

The characteristics of proliferative cardiomyocytes in mammals.

Better understanding of the mechanisms regulating the proliferation of pre-existing cardiomyocyte (CM) should lead to better options for regenerating injured myocardium. The absence of a perfect research model to definitively identify newly formed mammalian CMs is lacking. However, methodologies are being developed to identify and enrich proliferative CMs. These methods take advantages of the different proliferative states of CMs during postnatal development, before and after injury in the neonatal heart. New approaches use CMs labeled in lineage tracing animals or single cell technique-based CM clusters. This review aims to provide a timely update on the characteristics of the proliferative CMs, including their structural, functional, genetic, epigenetic and metabolic characteristics versus non-proliferative CMs. A better understanding of the characteristics of proliferative CMs should lead to the mechanisms for inducing endogenous CMs to self-renew, which is a promising therapeutic strategy to treat cardiac diseases that cause CM death in humans.

Porcupine inhibitor CGX1321 alleviates heart failure with preserved ejection fraction in mice by blocking WNT signaling.

Heart failure with preserved ejection fraction (HFpEF) is highly prevalent, and lacks effective treatment. The aberration of WNT pathway underlies many pathological processes including cardiac fibrosis and hypertrophy, while porcupine is an acyltransferase essential for the secretion of WNT ligands. In this study we investigated the role of WNT signaling pathway in HFpEF as well as whether blocking WNT signaling by a novel porcupine inhibitor CGX1321 alleviated HFpEF. We established two experimental HFpEF mouse models, namely the UNX/DOCA model and high fat diet/L-NAME ("two-hit") model. The UNX/DOCA and "two-hit" mice were treated with CGX1321 (3 mg·kg-1·d-1) for 4 and 10 weeks, respectively. We showed that CGX1321 treatment significantly alleviated cardiac hypertrophy and fibrosis, thereby improving cardiac diastolic function and exercise performance in both models. Furthermore, both canonical and non-canonical WNT signaling pathways were activated, and most WNT proteins, especially WNT3a and WNT5a, were upregulated during the development of HEpEF in mice. CGX1321 treatment inhibited the secretion of WNT ligands and repressed both canonical and non-canonical WNT pathways, evidenced by the reduced phosphorylation of c-Jun and the nuclear translocation of ß-catenin and NFATc3. In an in vitro HFpEF model, MCM and ISO-treated cardiomyocytes, knockdown of porcupine by siRNA leads to a similar inhibitory effect on WNT pathways, cardiomyocyte hypertrophy and cardiac fibroblast activation as CGX1321 did, whereas supplementation of WNT3a and WNT5a reversed the anti-hypertrophy and anti-fibrosis effect of CGX1321. We conclude that WNT signaling activation plays an essential role in the pathogenesis of HFpEF, and porcupine inhibitor CGX1321 exerts a therapeutic effect on HFpEF in mice by attenuating cardiac hypertrophy, alleviating cardiac fibrosis and improving cardiac diastolic function.

Gender Differences in Anxiety, Depression, Insomnia, and Quality of Life in Heart Failure With Preserved Ejection Fraction: A Multicenter, Cross-sectional Study.

BACKGROUND: Patients with heart failure with preserved ejection fraction (HFpEF) are more often female, but gender differences in psychological distress in patients with HFpEF have not been determined. OBJECTIVE: We aimed to compare anxiety, depression, insomnia, and quality of life (QoL) between women and men with HFpEF. METHODS: A total of 263 consecutive hospitalized patients with HFpEF were enrolled in a multicenter study. Demographic and clinical characteristics were recorded. Anxiety and depression were assessed using the Hospital Anxiety and Depression Scale (HADS), insomnia was assessed by the Insomnia Severity Index and Pittsburgh Sleep Quality Index, and QoL was assessed by the Kansas City Cardiomyopathy Questionnaire. RESULTS: Women accounted for 59% and men accounted for 41% of the patients with HFpEF. Women and men had similar New York Heart Association functional class and N-terminal pro-brain natriuretic peptide levels. Between women and men with HFpEF, similar depression prevalence (HADS-D: 4.9 ± 3.7 vs 4.1 ± 3.6, P = .222), insomnia severity (Insomnia Severity Index: 9.3 ± 6.4 vs 8.0 ± 6.5, P = .120), and QoL (Kansas City Cardiomyopathy Questionnaire: 46.6 ± 12.6 vs 47.6 ± 12.7, P = .738) were found when adjusting for potential confounders. Women had more severe anxiety (HADS-Anxiety: 2.4 ± 2.9 vs 1.6 ± 2.3, P = .025) and worse sleep quality (Pittsburgh Sleep Quality Index: 9.9 ± 4.6 vs 8.7 ± 4.5, P = .046) compared with men after adjustment. CONCLUSIONS: There were no gender differences in depression, insomnia, and QoL in patients with HFpEF when adjusting for confounders. Women with HFpEF suffered more severe anxiety and sleep quality than men after adjustment. Thus, it is recommended that psychological distress in patients with HFpEF be assessed in clinical practice, and gender differences taken into consideration.

Loss of NPPA-AS1 promotes heart regeneration by stabilizing SFPQ-NONO heteromer-induced DNA repair.

The role of long non-coding RNA (lncRNA) in endogenous cardiac regeneration remains largely elusive. The mammalian cardiomyocyte is capable of regeneration for a brief period after birth. This fact allows the exploration of the roles of critical lncRNAs in the regulation of cardiac regeneration. Through a cardiac regeneration model by apical resection (AR) of the left ventricle in neonatal mice, we identified an lncRNA named natriuretic peptide A antisense RNA 1 (NPPA-AS1), which negatively regulated cardiomyocyte proliferation. In neonates, NPPA-AS1 deletion did not affect heart development, but was sufficient to prolong the postnatal window of regeneration after AR. In adult mice, NPPA-AS1 deletion improved cardiac function and reduced infarct size after myocardial infarction (MI), associated with a significant improvement in cardiomyocyte proliferation. Further analysis showed that NPPA-AS1 interacted with DNA repair-related molecule splicing factor, proline- and glutamine-rich (SFPQ). A heteromer of SFPQ and non-POU domain-containing octamer-binding protein (NONO) was required for double-strand DNA break repair, but NPPA-AS1 was competitively bound with SFPQ due to the overlapped binding sites of SFPQ and NONO. NPPA-AS1 deletion promoted the binding of SFPQ-NONO heteromer, decreased DNA damage, and activated cardiomyocyte cell cycle re-entry. Together, loss of NPPA-AS1 promoted cardiomyocyte proliferation by stabilizing SFPQ-NONO heteromer-induced DNA repair and exerted a therapeutic effect against MI in adult mice. Consequently, NPPA-AS1 may be a novel target for stimulating cardiac regeneration to treat MI.

The prognostic utility of GRACE risk score in predictive adverse cardiovascular outcomes in patients with NSTEMI and multivessel disease.

BACKGROUND: GRACE risk score models are capable of predicting all-cause mortality of non-ST elevation myocardial infarction (NSTEMI) patients. However, its utility for evaluating major adverse cardiovascular events (MACE) in NSTEMI patients with multivessel disease (MVD) remains unclear. METHODS AND RESULTS: This study was designed as a retrospective cohort study that recruited patients with NSTEMI and multivessel disease between September 2013 and December 2018 in Daping Hospital, Chongqing, China. The primary outcome was a composite outcome that included all-cause mortality, recurrent angina, non-fatal myocardial infarction, coronary re-vascularization, and non-fatal strokes. Of the 827 patients with NSTEMI, 32 did not complete follow-up and 430 were excluded because of single-vessel disease. The remaining 365 NSTEMI patients with MVD had a median follow-up of 3.0 (IQR 2.6-3.3) years, 78 patients experienced outcomes. The GRACE risk score predicted the MACE (hazard ratio 1.014, 95% CI 1.006-1.021, P < 0.001). The GRACE risk score performed well in predicting all-cause mortality (c-statistic 0.72, 95% CI 0.59-0.85, P = 0.001) in MVD but was less powerful in predicting MACE (c-statistic 0.69, 95% CI 0.62-0.75, P < 0.001). When combining the GRACE risk score with the SYNTAX score, and blood urea nitrogen for predicting all-cause mortality and MACE events, the c-statistic value increased to 0.82 and 0.81 (P < 0.001). CONCLUSION: In NSTEMI patients with MVD, the GRACE score showed an acceptable predictive value for all-cause mortality, but it was less powerful in predicting MACE. Blood urea nitrogen may be valuable in assessing long-term cardiovascular events in patients with MVD.

The role of G protein-coupled receptor kinase 4 in cardiomyocyte injury after myocardial infarction.

AIMS: G protein-coupled receptor kinase 4 (GRK4) has been reported to play an important role in hypertension, but little is known about its role in cardiomyocytes and myocardial infarction (MI). The goal of present study is to explore the role of GRK4 in the pathogenesis and progression of MI. METHODS AND RESULTS: We studied the expression and distribution pattern of GRK4 in mouse heart after MI. GRK4 A486V transgenic mice, inducible cardiomyocyte-specific GRK4 knockout mice, were generated and subjected to MI with their control mice. Cardiac infarction, cardiac function, cardiomyocyte apoptosis, autophagic activity, and HDAC4 phosphorylation were assessed. The mRNA and protein levels of GRK4 in the heart were increased after MI. Transgenic mice with the overexpression of human GRK4 wild type (WT) or human GRK4 A486V variant had increased cardiac infarction, exaggerated cardiac dysfunction and remodelling. In contrast, the MI-induced cardiac dysfunction and remodelling were ameliorated in cardiomyocyte-specific GRK4 knockout mice. GRK4 overexpression in cardiomyocytes aggravated apoptosis, repressed autophagy, and decreased beclin-1 expression, which were partially rescued by the autophagy agonist rapamycin. MI also induced the nuclear translocation of GRK4, which inhibited autophagy by increasing HDAC4 phosphorylation and decreasing its binding to the beclin-1 promoter. HDAC4 S632A mutation partially restored the GRK4-induced inhibition of autophagy. MI caused greater impairment of cardiac function in patients carrying the GRK4 A486V variant than in WT carriers. CONCLUSION: GRK4 increases cardiomyocyte injury during MI by inhibiting autophagy and promoting cardiomyocyte apoptosis. These effects are mediated by the phosphorylation of HDAC4 and a decrease in beclin-1 expression.

Association of Nonalcoholic Fatty Liver Disease with Ventricular Tachycardia and Sinus Arrest in Patients with Non-ST-Segment Elevation Myocardial Infarction.

Nonalcoholic fatty liver disease (NAFLD) is an emerging driver of cardiac arrhythmias. However, the relationship between NAFLD and malignant arrhythmia in non-ST-segment elevation myocardial infarction (NSTEMI) patients is still unclear.In this study, 358 NSTEMI inpatients were enrolled. They all received 24-hour Holter monitoring after percutaneous coronary intervention. All inpatients were divided into two groups: the non-NAFLD group (236 cases, 65.9%) and the NAFLD group (122 cases, 34.1%). Compared with the non-NAFLD group, the NAFLD group had a significantly higher incidence of PVCs/hour > 5 (premature ventricular complexes, 32.0% versus 9.3%, P < 0.001), ventricular tachycardia (VT, 22.1% versus 5.9%, P < 0.001), and sinus arrest (SA, 7.4% versus 1.3%, P = 0.002). We found that NAFLD was closely associated with the occurrence of VT [unadjusted odds ratio (OR) 4.507, 95% confidence interval (CI) 2.263-8.974, P < 0.001] and SA (OR 6.186, 95%CI 1.643-23.291, P = 0.007). After adjusting for age, sex, body mass index, and other confounding factors, the above differences were still statistically significant (VT: OR 4.808, 95%CI 2.254-10.253, P < 0.001; SA: OR 9.589, 95%CI 2.027-45.367, P = 0.004).NAFLD is associated with the occurrence of VT and SA in NSTEMI patients. It indicates that NAFLD might be a risk factor for malignant arrhythmias in post-NSTEMI patients.

Gastrin, via activation of PPARα, protects the kidney against hypertensive injury.

Hypertensive nephropathy (HN) is a common cause of end-stage renal disease with renal fibrosis; chronic kidney disease is associated with elevated serum gastrin. However, the relationship between gastrin and renal fibrosis in HN is still unknown. We, now, report that mice with angiotensin II (Ang II)-induced HN had increased renal cholecystokinin receptor B (CCKBR) expression. Knockout of CCKBR in mice aggravated, while long-term subcutaneous infusion of gastrin ameliorated the renal injury and interstitial fibrosis in HN and unilateral ureteral obstruction (UUO). The protective effects of gastrin on renal fibrosis can be independent of its regulation of blood pressure, because in UUO, gastrin decreased renal fibrosis without affecting blood pressure. Gastrin treatment decreased Ang II-induced renal tubule cell apoptosis, reversed Ang II-mediated inhibition of macrophage efferocytosis, and reduced renal inflammation. A screening of the regulatory factors of efferocytosis showed involvement of peroxisome proliferator-activated receptor α (PPAR-α). Knockdown of PPAR-α by shRNA blocked the anti-fibrotic effect of gastrin in vitro in mouse renal proximal tubule cells and macrophages. Immunofluorescence microscopy, Western blotting, luciferase reporter, and Cut&tag-qPCR analyses showed that CCKBR may be a transcription factor of PPAR-α, because gastrin treatment induced CCKBR translocation from cytosol to nucleus, binding to the PPAR-α promoter region, and increasing PPAR-α gene transcription. In conclusion, gastrin protects against HN by normalizing blood pressure, decreasing renal tubule cell apoptosis, and increasing macrophage efferocytosis. Gastrin-mediated CCKBR nuclear translocation may make it act as a transcription factor of PPAR-α, which is a novel signaling pathway. Gastrin may be a new potential drug for HN therapy.

Cardiomyocyte PKA Ablation Enhances Basal Contractility While Eliminates Cardiac ß-Adrenergic Response Without Adverse Effects on the Heart.

RATIONALE: PKA (Protein Kinase A) is a major mediator of ß-AR (ß-adrenergic) regulation of cardiac function, but other mediators have also been suggested. Reduced PKA basal activity and activation are linked to cardiac diseases. However, how complete loss of PKA activity impacts on cardiac physiology and if it causes cardiac dysfunction have never been determined. OBJECTIVES: We set to determine how the heart adapts to the loss of cardiomyocyte PKA activity and if it elicits cardiac abnormalities. METHODS AND RESULTS: (1) Cardiac PKA activity was almost completely inhibited by expressing a PKA inhibitor peptide in cardiomyocytes (cPKAi) in mice; (2) cPKAi reduced basal phosphorylation of 2 myofilament proteins (TnI [troponin I] and cardiac myosin binding protein C), and one longitudinal SR (sarcoplasmic reticulum) protein (PLB [phospholamban]) but not of the sarcolemmal proteins (Cav1.2 α1c and PLM [phospholemman]), dyadic protein RyR2, and nuclear protein CREB (cAMP response element binding protein) at their PKA phosphorylation sites; (3) cPKAi increased the expression of CaMKII (Ca2+/calmodulin-dependent kinase II), the Cav1.2 ß subunits and current, but decreased CaMKII phosphorylation and CaMKII-mediated phosphorylation of PLB and RyR2; (4) These changes resulted in significantly enhanced myofilament Ca2+ sensitivity, prolonged contraction, slowed relaxation but increased myocyte Ca2+ transient and contraction amplitudes; (5) Isoproterenol-induced PKA and CaMKII activation and their phosphorylation of proteins were prevented by cPKAi; (6) cPKAi abolished the increases of heart rate, and cardiac and myocyte contractility by a ß-AR agonist (isoproterenol), showing an important role of PKA and a minimal role of PKA-independent ß-AR signaling in acute cardiac regulation; (7) cPKAi mice have partial exercise capability probably by enhancing vascular constriction and ventricular filling during ß-AR stimulation; and (8) cPKAi mice did not show any cardiac functional or structural abnormalities during the 1-year study period. CONCLUSIONS: PKA activity suppression induces a unique Ca2+ handling phenotype, eliminates ß-AR regulation of heart rates and cardiac contractility but does not cause cardiac abnormalities.

Wnt signaling pathways in myocardial infarction and the therapeutic effects of Wnt pathway inhibitors.

Myocardial infarction (MI) is one of the most serious health threats, resulting in huge physical and economic burdens worldwide. Wnt signaling pathways play an important role in developmental processes such as tissue patterning, cell differentiation and cell division. Appropriate regulation of the activities of Wnt signaling pathways is also important for heart development and healing in post-MI heart. Moreover, Wnt pathway inhibitors have been identified as novel antitumor drugs and applied in ongoing clinical trials. This research progress has generated increasing interests for investigating the effects of Wnt pathway inhibitors on MI healing. In this short review, we summarize the roles of Wnt signaling pathways in post-MI heart and the therapeutic effects of Wnt pathway inhibitors on MI, and discuss the underlying mechanisms of Wnt pathway inhibitors in cardiac repairing.

Irisin exerts a therapeutic effect against myocardial infarction via promoting angiogenesis.

Irisin, a myokine, is cleaved from the extracellular portion of fibronectin domain-containing 5 protein in skeletal muscle and myocardium and secreted into circulation as a hormone during exercise. Irisin has been found to exert protective effects against lung and heart injuries. However, whether irisin influences myocardial infarction (MI) remains unclear. In this study we investigated the therapeutic effects of irisin in an acute MI model and its underlying mechanisms. Adult C57BL/6 mice were subjected to ligation of the left anterior descending coronary artery and treated with irisin for 2 weeks after MI. Cardiac function was assessed using echocardiography. We found that irisin administration significantly alleviated MI-induced cardiac dysfunction and ventricular dilation at 4 weeks post-MI. Irisin significantly reduced infarct size and fibrosis in post-MI hearts. Irisin administration significantly increased angiogenesis in the infarct border zone and decreased cardiomyocyte apoptosis, but did not influence cardiomyocyte proliferation. In human umbilical vein endothelial cells (HUVEC), irisin significantly increased the phosphorylation of ERK, and promoted the migration of HUVEC detected in wound-healing and transwell chamber migration assay. The effects of irisin were blocked by the ERK inhibitor U0126. In conclusion, irisin improves cardiac function and reduces infarct size in post-MI mouse heart. The therapeutic effect is associated with its pro-angiogenic function through activating ERK signaling pathway.

Dedifferentiation, Proliferation, and Redifferentiation of Adult Mammalian Cardiomyocytes After Ischemic Injury.

BACKGROUND: Adult mammalian hearts have a limited ability to generate new cardiomyocytes. Proliferation of existing adult cardiomyocytes (ACMs) is a potential source of new cardiomyocytes. Understanding the fundamental biology of ACM proliferation could be of great clinical significance for treating myocardial infarction (MI). We aim to understand the process and regulation of ACM proliferation and its role in new cardiomyocyte formation of post-MI mouse hearts. METHODS: ß-Actin-green fluorescent protein transgenic mice and fate-mapping Myh6-MerCreMer-tdTomato/lacZ mice were used to trace the fate of ACMs. In a coculture system with neonatal rat ventricular myocytes, ACM proliferation was documented with clear evidence of cytokinesis observed with time-lapse imaging. Cardiomyocyte proliferation in the adult mouse post-MI heart was detected by cell cycle markers and 5-ethynyl-2-deoxyuridine incorporation analysis. Echocardiography was used to measure cardiac function, and histology was performed to determine infarction size. RESULTS: In vitro, mononucleated and bi/multinucleated ACMs were able to proliferate at a similar rate (7.0%) in the coculture. Dedifferentiation proceeded ACM proliferation, which was followed by redifferentiation. Redifferentiation was essential to endow the daughter cells with cardiomyocyte contractile function. Intercellular propagation of Ca2+ from contracting neonatal rat ventricular myocytes into ACM daughter cells was required to activate the Ca2+-dependent calcineurin-nuclear factor of activated T-cell signaling pathway to induce ACM redifferentiation. The properties of neonatal rat ventricular myocyte Ca2+ transients influenced the rate of ACM redifferentiation. Hypoxia impaired the function of gap junctions by dephosphorylating its component protein connexin 43, the major mediator of intercellular Ca2+ propagation between cardiomyocytes, thereby impairing ACM redifferentiation. In vivo, ACM proliferation was found primarily in the MI border zone. An ischemia-resistant connexin 43 mutant enhanced the redifferentiation of ACM-derived new cardiomyocytes after MI and improved cardiac function. CONCLUSIONS: Mature ACMs can reenter the cell cycle and form new cardiomyocytes through a 3-step process: dedifferentiation, proliferation, and redifferentiation. Intercellular Ca2+ signal from neighboring functioning cardiomyocytes through gap junctions induces the redifferentiation process. This novel mechanism contributes to new cardiomyocyte formation in post-MI hearts in mammals.

Curcumin prevents strokes in stroke-prone spontaneously hypertensive rats by improving vascular endothelial function.

BACKGROUND: Antioxidants have shown great promise in stroke prevention. Diarylheptanoids (also known as diphenylheptanoids) are a small class of plant secondary metabolites that possess antioxidant activity greater than that of α-tocopherol. Curcumin is the best known member and is mainly extracted from turmeric. This study aimed to explore whether curcumin has a preventive effect on stroke. METHODS: Stroke-prone spontaneously hypertensive rats (SHRsp) were randomly divided into control group (n = 10) and curcumin group (n = 10), and saline or curcumin (100 mg/kg/day) was administrated daily. Vascular endothelial function was examined by the relaxation of the artery in response to acetylcholine (ACH). The levels of reactive oxygen species (ROS) and nitric oxide (NO) were measured by using dihydroethidium (DHE) and 4, 5-diaminofluorescein (DAF-2 DA), respectively. The expression of uncoupling protein 2 (UCP2) was examined by RT-PCR and immunoblotting. RESULTS: Administration of curcumin significantly delayed the onset of stroke and increased the survival of SHRsp, which was ascribed to decreased ROS and improved endothelial dependent relaxation of carotid arteries. In the presence of UCP2 inhibitor genipin, both curcumin-mediated decrease of ROS and increase of NO production were blocked. CONCLUSION: Our study suggests that curcumin exerts a stroke preventive effect by attenuating oxidative stress to improve vascular endothelial function, which might be associated with UCP2 signaling.

Mesenchymal stem cells-derived extracellular vesicles, via miR-210, improve infarcted cardiac function by promotion of angiogenesis.

Mesenchymal stem cells (MSCs) exert therapeutic effect on treating acute myocardial infarction. Recent evidence showed that paracrine function rather than direct differentiation predominately contributes to the beneficial effects of MSCs, but how the paracrine factors function are not fully elucidated. In the present study, we tested if extracellular vesicles (EVs) secreted by MSC promotes angiogenesis in infracted heart via microRNAs. Immunostaining of CD31 and matrigel plug assay were performed to detect angiogenesis in a mouse myocardial infarction (MI) model. The cardiac function and structure was examined with echocardiographic analysis. Capillary-like tube formation, migration and proliferation of human umbilical vein endothelial cells (HUVECs) were determined. As a result, MSC-EVs significantly improved angiogenesis and cardiac function in post-MI heart. MSC-EVs increased the proliferation, migration and tube formation capacity of HUVECs. MicroRNA (miR)-210 was found to be enriched in MSC-EVs. The EVs collected from MSCs with miR-210 silence largely lost the pro-angiogenic effect both in-vitro and in-vivo. The miR-210 target gene Efna3, which plays a role in angiogenesis, was down-regulated by MSC-EVs treatment in HUVECs. In conclusion, MSC-EVs are sufficient to improve angiogenesis and exert therapeutic effect on MI, its pro- angiogenesis effect might be associated with a miR-210-Efna3 dependent mechanism. This article is part of a Special Issue entitled: Genetic and epigenetic control of heart failure - edited by Jun Ren & Megan Yingmei Zhang.

Therapeutic effect of a novel Wnt pathway inhibitor on cardiac regeneration after myocardial infarction.

After myocardial infarction (MI), the heart is difficult to repair because of great loss of cardiomyoctyes and lack of cardiac regeneration. Novel drug candidates that aim at reducing pathological remodeling and stimulating cardiac regeneration are highly desirable. In the present study, we identified if and how a novel porcupine inhibitor CGX1321 influenced MI and cardiac regeneration. Permanent ligation of left anterior descending (LAD) coronary artery was performed in mice to induce MI injury. Cardiac function was measured by echocardiography, infarct size was examined by TTC staining. Fibrosis was evaluated with Masson's trichrome staining and vimentin staining. As a result, CGX1321 administration blocked the secretion of Wnt proteins, and inhibited both canonical and non-canonical Wnt signaling pathways. CGX1321 improved cardiac function, reduced myocardial infarct size, and fibrosis of post-MI hearts. CGX1321 significantly increased newly formed cardiomyocytes in infarct border zone of post-MI hearts, evidenced by the increased EdU+ cardiomyocytes. Meanwhile, CGX1321 increased Ki67+ and phosphohistone H3 (PH3+) cardiomyocytes in culture, indicating enhanced cardiomyocyte proliferation. The mRNA microarray showed that CGX1321 up-regulated cell cycle regulating genes such as Ccnb1 and Ccne1 CGX1321 did not alter YAP protein phosphorylation and nuclear translocation in cardiomyocytes. In conclusion, porcupine inhibitor CGX1321 reduces MI injury by limiting fibrosis and promoting regeneration. It promotes cardiomyocyte proliferation by stimulating cell cycle regulating genes with a Hippo/YAP-independent pathway.

Tirofiban induces vasorelaxation of the coronary artery via an endothelium-dependent NO-cGMP signaling by activating the PI3K/Akt/eNOS pathway.

Tirofiban, a glycoprotein IIb/IIIa inhibitor, is an antiplatelet drug extensively used in patients with acute coronary syndrome (ACS) and exerts an therapeutic effect on no-reflow phenomenon during percutaneous coronary intervention (PCI). Previous studies elucidated the vasodilation caused by tirofiban in the peripheral artery. However, whether tirofiban exerts a vasodilator effect on the coronary artery is unclear. Our present study found that tirofiban induced endothelium-dependent vasodilation in a concentration- and time-dependent manner in the isolated rat coronary artery pre-constricted by 5-hydroxytryptamine (5-HT). Further study showed that incubation of human umbilical venous endothelial cells (HUVECs) with tirofiban increased NO production, which was ascribed to the increased eNOS phosphorylation. This was confirmed by the loss of the vasorelaxant effect of tirofiban in the presence of l-NAME (eNOS inhibitor) and L-NMMA (NOS inhibitor) but not SMT (iNOS inhibitor) on isolated rat coronary arteries. The vasorelaxation was also blocked by the PI3K inhibitors, wortmannin and LY294002, as well as the Akt inhibitor SH-5, indicating the role of PI3K and Akt in tirofiban-mediated vasodilation. Moreover, further study showed that soluble guanylyl cyclase (sGC) inhibitor ODQ, or blockers of potassium channel (big-conductance calcium-activated potassium channel) blocked tirofiban-induced vasodilation of the coronary artery. These findings suggest that tirofiban induces vasorelaxation via an endothelium-dependent NO-cGMP signaling through the activation of the Akt/eNOS/sGC pathway.

Cardiac troponin I exacerbates myocardial ischaemia/reperfusion injury by inducing the adhesion of monocytes to vascular endothelial cells via a TLR4/NF-κB-dependent pathway.

Cardiac troponin I (cTnI), a biomarker for myocardial damage and risk stratification, may be involved in the pathogenesis of cardiovascular diseases, which was ascribed to the effect of cTnI auto-antibodies. Whether or not cTnI itself has a direct impact on acute myocardial injury is unknown. To exclude the influence of cTnI antibody on the cardiac infarct size, we studied the effect of cTnI shortly after myocardial ischaemia-reperfusion (I/R) injury when cTnI antibodies were not elevated. Pretreatment with cTnI augmented the myocardial infarct size caused by I/R, accompanied by an increase in inflammatory markers in the blood and myocardium. Additional experiments using human umbilical vein endothelial cells (HUVECs) showed that the detrimental effect of cTnI was related to cTnI-induced increase in vascular cell adhesion molecule-1 (VCAM-1) expression and VCAM-1 mediated adhesion of human monocytes (THP-1) to HUVECs, which could be neutralized by VCAM-1 antibody. Both toll-like receptor 4 (TLR4) and nuclear factor-κB (NF-κB) were involved in the signalling pathway, because blockade of either TLR4 or NF-κB inhibited the cTnI's effect on VCAM-1 expression and adhesion of monocytes to endothelial cells. Moreover, TLR4 inhibition reduced cTnI-augmented cardiac injury in rats with I/R injury. We conclude that cTnI exacerbates myocardial I/R injury by inducing the adhesion of monocytes to vascular endothelial cells via activation of the TLR4/NF-κB pathway. Inhibition of TLR4 may be an alternative strategy to reduce cTnI-induced myocardial I/R injury.