Circular RNAs are generated from many protein-coding genes, but their role in cardiovascular health and disease states remains unknown. Here we report identification of circRNA transcripts that are differentially expressed in post myocardial infarction (MI) mouse hearts including circFndc3b which is significantly down-regulated in the post-MI hearts. Notably, the human circFndc3b ortholog is also significantly down-regulated in cardiac tissues of ischemic cardiomyopathy patients. Overexpression of circFndc3b in cardiac endothelial cells increases vascular endothelial growth factor-A expression and enhances their angiogenic activity and reduces cardiomyocytes and endothelial cell apoptosis. Adeno-associated virus 9 -mediated cardiac overexpression of circFndc3b in post-MI hearts reduces cardiomyocyte apoptosis, enhances neovascularization and improves left ventricular functions. Mechanistically, circFndc3b interacts with the RNA binding protein Fused in Sarcoma to regulate VEGF expression and signaling. These findings highlight a physiological role for circRNAs in cardiac repair and indicate that modulation of circFndc3b expression may represent a potential strategy to promote cardiac function and remodeling after MI.

Rationale Hypoxia favors stem cell quiescence, while normoxia is required for their activation; but whether cardiac stem cell (CSC) function is regulated by the hypoxic/normoxic state of the cell is currently unknown. Objective A balance between hypoxic and normoxic CSCs may be present in the young heart, although this homeostatic control may be disrupted with aging. Defects in tissue oxygenation occur in the old myocardium, and this phenomenon may expand the pool of hypoxic CSCs, which are no longer involved in myocyte renewal. Methods and Results Here we show that the senescent heart is characterized by an increased number of quiescent CSCs with intact telomeres that cannot reenter the cell cycle and form a differentiated progeny. Conversely, myocyte replacement is controlled only by frequently dividing CSCs with shortened telomeres; these CSCs generate a myocyte population that is chronologically young but phenotypically old. Telomere dysfunction dictates their actual age and mechanical behavior. However, the residual subset of quiescent young CSCs can be stimulated in situ by stem cell factor reversing the aging myopathy. Conclusions Our findings support the notion that strategies targeting CSC activation and growth interfere with the manifestations of myocardial aging in an animal model. Although caution has to be exercised in the translation of animal studies to human beings, our data strongly suggests that a pool of functionally-competent CSCs persists in the senescent heart and this stem cell compartment can promote myocyte regeneration effectively, correcting partly the aging myopathy.

Rationale: Systemic inflammation compromises the reparative properties of endothelial progenitor cell (EPC) and their exosomes on myocardial repair, although the underlying mechanism of loss of function of exosomes from inflamed EPCs is still obscure. Objective: To determine the mechanisms of IL-10 (interleukin-10) deficient-EPC–derived exosome dysfunction in myocardial repair and to investigate if modification of specific exosome cargo can rescue reparative activity. Methods and Results: Using IL-10 knockout mice mimicking systemic inflammation condition, we compared therapeutic effect and protein cargo of exosomes isolated from wild-type EPC and IL-10 knockout EPC. In a mouse model of myocardial infarction (MI), wild-type EPC-derived exosome treatment significantly improved left ventricle cardiac function, inhibited cell apoptosis, reduced MI scar size, and promoted post-MI neovascularization, whereas IL-10 knockout EPC-derived exosome treatment showed diminished and opposite effects. Mass spectrometry analysis revealed wild-type EPC-derived exosome and IL-10 knockout EPC-derived exosome contain different protein expression pattern. Among differentially expressed proteins, ILK (integrin-linked kinase) was highly enriched in both IL-10 knockout EPC-derived exosome as well as TNFα (tumor necrosis factor-α)-treated mouse cardiac endothelial cell–derived exosomes (TNFα inflamed mouse cardiac endothelial cell–derived exosome). ILK-enriched exosomes activated NF-κB (nuclear factor κB) pathway and NF-κB–dependent gene transcription in recipient endothelial cells and this effect was partly attenuated through ILK knockdown in exosomes. Intriguingly, ILK knockdown in IL-10 knockout EPC-derived exosome significantly rescued their reparative dysfunction in myocardial repair, improved left ventricle cardiac function, reduced MI scar size, and enhanced post-MI neovascularization in MI mouse model. Conclusions: IL-10 deficiency/inflammation alters EPC-derived exosome function, content and therapeutic effect on myocardial repair by upregulating ILK enrichment in exosomes, and ILK-mediated activation of NF-κB pathway in recipient cells, whereas ILK knockdown in exosomes attenuates NF-κB activation and reduces inflammatory response. Our study provides new understanding of how inflammation may alter stem cell-exosome–mediated cardiac repair and identifies ILK as a target kinase for improving progenitor cell exosome-based cardiac therapies.

Taken together, our studies demonstrate that anti-miR-375 therapy reduced inflammatory response, decreased cardiomyocyte death, improved LV function, and enhanced angiogenesis by targeting multiple cell types mediated at least in part through PDK-1/AKT signalling mechanisms.

Background Activated fibroblasts (myofibroblasts; myoFBs) play critical role in cardiac fibrosis; however, their origin in the diseased heart remains unclear warranting further investigation. Recent studies suggest the contribution of bone marrow fibroblast progenitor cells (BM-FPC) in pressure overload (PO)-induced cardiac fibrosis. We have earlier shown that interleukin-10 (IL10) suppresses PO-induced cardiac fibrosis; however, the role of IL10 in inhibition of BM-FPC-mediated cardiac fibrosis is not known. We hypothesized that IL10 inhibits PO-induced homing of BM-FPCs to the heart and their trans-differentiation to myoFBs and thus attenuates cardiac fibrosis. Methods Pressure overload was induced in wild-type (WT) and IL10 knockout (IL10KO) mice by transverse aortic constriction (TAC). To determine the bone marrow origin, chimeric mice were created using eGFP WT mice marrow to the IL10KO mice. For mechanistic studies, fibroblast progenitor cells were isolated from mouse bone marrow. Results Pressure overload enhanced bone marrow fibroblast progenitor cell (BM-FPC) mobilization and homing in IL10KO mice compared to WT mice. Furthermore, WT bone marrow (from eGFP mice) transplantation in BM-depleted IL10KO mice (IL10KO chimeric mice) reduced TAC-induced BM-FPC mobilization compared to IL10KO mice. GFP co-staining with αSMA or collagen 1α in left ventricular tissue sections of IL10KO chimeric mice suggest that myofibroblasts were derived from bone marrow post-TAC. Finally, WT-BMT in IL10KO mice inhibited TAC-induced cardiac fibrosis and improved heart function. At the molecular level, IL10 treatment significantly inhibited TGFβ-induced transdifferentiation and fibrotic signaling in WT BM-FPC in vitro. Furthermore, fibrosis-associated miRNAs expression was highly upregulated in IL10KO-FPCs compared to WT-FPCs. PCR-based selective miRNA analysis revealed that TGFβ-induced enhanced expression of fibrosis-associated miRNAs (miRNA-21, -145 and -208) was significantly inhibited by IL10. Restoration of miRNA-21 levels suppressed the IL10 effects on TGFβ-induced fibrotic signaling in BM-FPC. Conclusion Our findings suggest that IL10 inhibits BM-FPC homing and trans-differentiation to myofibroblasts in pressure overloaded myocardium. Mechanistically for the first time we showed that IL10 suppresses Smad-miRNA-21 mediated activation of BM-FPCs and thus modulates cardiac fibrosis.

Background Aging negatively impacts on the function of resident human cardiac progenitor cells (hCPCs). Effective regeneration of the injured heart requires mobilization of hCPCs to the sites of damage. In the young heart, signaling by the guidance receptor EphA2 in response to the ephrin A1 ligand promotes hCPC motility and improves cardiac recovery after infarction. Methods and Results We report that old hCPCs are characterized by cell-autonomous inhibition of their migratory ability ex vivo and impaired translocation in vivo in the damaged heart. EphA2 expression was not decreased in old hCPCs; however, the elevated level of reactive oxygen species in aged cells induced post-translational modifications of the EphA2 protein. EphA2 oxidation interfered with ephrin A1-stimulated receptor auto-phosphorylation, activation of Src family kinases, and caveolin-1-mediated internalization of the receptor. Cellular aging altered the EphA2 endocytic route, affecting the maturation of EphA2-containing endosomes and causing premature signal termination. Over-expression of functionally intact EphA2 in old hCPCs corrected the defects in endocytosis and downstream signaling, enhancing cell motility. Based on the ability of phenotypically young hCPCs to respond efficiently to ephrin A1, we developed a novel methodology for the prospective isolation of live hCPCs with preserved migratory capacity and growth reserve. Conclusions Our data demonstrate that the ephrin A1/EphA2 pathway may serve as a target to facilitate trafficking of hCPCs in the senescent myocardium. Importantly, EphA2 receptor function can be implemented for the selection of hCPCs with high therapeutic potential, a clinically relevant strategy that does not require genetic manipulation of stem cells.

Insufficient hydrogen sulfide (H2S) has been implicated in Type 2 diabetic mellitus (T2DM) and hyperhomocysteinemia (HHcy)-related cardiovascular complications. We investigated the role of H2S in T2DM and HHcy-induced endothelial dysfunction in small mesenteric artery (SMA) of db/db mice fed a high methionine (HM) diet. HM diet (8 weeks) induced HHcy in both T2DM db/db mice and non-diabetic db/+ mice (total plasma Hcy: 48.4 and 31.3 µM, respectively), and aggravated the impaired endothelium-derived hyperpolarization factor (EDHF)-induced endothelium-dependent relaxation to acetylcholine (ACh), determined by the presence of eNOS inhibitor N(ω)-nitro-L-arginine methyl ester (L-NAME) and prostacyclin (PGI2) inhibitor indomethacin (INDO), in SMA from db/db mice but not that from db/+ mice. A non-selective Ca2+-active potassium channel (KCa) opener NS309 rescued T2DM/HHcy-impaired EDHF-mediated vascular relaxation to ACh. EDHF-induced relaxation to ACh was inhibited by a non-selective KCa blocker TEA and intermediate-conductance KCa blocker (IKCa) Tram-34, but not by small-conductance KCa (SKCa) blocker Apamin. HHcy potentiated the reduction of free sulfide, H2S and cystathionine γ-lyase protein, which converts L-cysteine to H2S, in SMA of db/db mice. Importantly, a stable H2S donor DATS diminished the enhanced O2- production in SMAs and lung endothelial cells of T2DM/HHcy mice. Antioxidant PEG-SOD and DATS improved T2DM/HHcy impaired relaxation to ACh. Moreover, HHcy increased hyperglycemia-induced IKCa tyrosine nitration in human micro-vascular endothelial cells. EDHF-induced vascular relaxation to L-cysteine was not altered, whereas such relaxation to NaHS was potentiated by HHcy in SMA of db/db mice which was abolished by ATP-sensitive potassium channel blocker Glycolamide but not by KCa blockers.ConclusionsIntermediate HHcy potentiated H2S reduction via CSE-downregulation in microvasculature of T2DM mice. H2S is justified as an EDHF. Insufficient H2S impaired EDHF-induced vascular relaxation via oxidative stress and IKCa inactivation in T2DM/HHcy mice. H2S therapy may be beneficial for prevention and treatment of micro-vascular complications in patients with T2DM and HHcy.

Cardiac lymphatic vasculature undergoes substantial expansion in response to myocardial infarction (MI). However, there is limited information on the cellular mechanisms mediating post-MI lymphangiogenesis and accompanying fibrosis in the infarcted adult heart. Using a mouse model of permanent coronary artery ligation, we examined spatiotemporal changes in the expression of lymphendothelial and mesenchymal markers in the acutely and chronically infarcted myocardium. We found that at the time of wound granulation, a three-fold increase in the frequency of podoplanin-labeled cells occurred in the infarcted hearts compared to non-operated and sham-operated counterparts. Podoplanin immunoreactivity detected LYVE-1-positive lymphatic vessels, as well as masses of LYVE-1-negative cells dispersed between myocytes, predominantly in the vicinity of the infarcted region. Podoplanin-carrying populations displayed a mesenchymal progenitor marker PDGFRα, and intermittently expressed Prox-1, a master regulator of the lymphatic endothelial fate. At the stages of scar formation and maturation, concomitantly with the enlargement of lymphatic network in the injured myocardium, the podoplanin-rich LYVE-1-negative multicellular assemblies were apparent in the fibrotic area, aligned with extracellular matrix deposits, or located in immediate proximity to activated blood vessels with high VEGFR-2 content. Of note, these podoplanin-containing cells acquired the expression of PDGFRβ or a hematoendothelial epitope CD34. Although Prox-1 labeling was abundant in the area affected by MI, the podoplanin-presenting cells were not consistently Prox-1-positive. The concordance of podoplanin with VEGFR-3 similarly varied. Thus, our data reveal previously unknown phenotypic and structural heterogeneity within the podoplanin-positive cell compartment in the infarcted heart, and suggest an alternate ability of podoplanin-presenting cardiac cells to generate lymphatic endothelium and pro-fibrotic cells, contributing to scar development.