Aims Recent evidence suggests that cardiac progenitor cells (CPCs) may improve cardiac function after injury. The underlying mechanisms are indirect, but their mediators remain unidentified. Exosomes and other secreted membrane vesicles, hereafter collectively referred to as extracellular vesicles (EVs), act as paracrine signalling mediators. Here, we report that EVs secreted by human CPCs are crucial cardioprotective agents. Methods and results CPCs were derived from atrial appendage explants from patients who underwent heart valve surgery. CPC-conditioned medium (CM) inhibited apoptosis in mouse HL-1 cardiomyocytic cells, while enhancing tube formation in human umbilical vein endothelial cells. These effects were abrogated by depleting CM of EVs. They were reproduced by EVs secreted by CPCs, but not by those secreted by human dermal fibroblasts. Transmission electron microscopy and nanoparticle tracking analysis showed most EVs to be 30–90 nm in diameter, the size of exosomes, although smaller and larger vesicles were also present. MicroRNAs most highly enriched in EVs secreted by CPCs compared with fibroblasts included miR-210, miR-132, and miR-146a-3p. miR-210 down-regulated its known targets, ephrin A3 and PTP1b, inhibiting apoptosis in cardiomyocytic cells. miR-132 down-regulated its target, RasGAP-p120, enhancing tube formation in endothelial cells. Infarcted hearts injected with EVs from CPCs, but not from fibroblasts, exhibited less cardiomyocyte apoptosis, enhanced angiogenesis, and improved LV ejection fraction (0.8 ± 6.8 vs. −21.3 ± 4.5%; P < 0.05) compared with those injected with control medium. Conclusion EVs are the active component of the paracrine secretion by human CPCs. As a cell-free approach, EVs could circumvent many of the limitations of cell transplantation.

In the advanced stages of heart failure, many key enzymes involved in myocardial energy substrate metabolism display various degrees of down-regulation. The net effect of the altered metabolic phenotype consists of reduced cardiac fatty oxidation, increased glycolysis and glucose oxidation, and rigidity of the metabolic response to changes in workload. Is this metabolic shift an adaptive mechanism that protects the heart or a maladaptive process that accelerates structural and functional derangement? The question remains open; however, the metabolic remodelling of the failing heart has induced a number of investigators to test the hypothesis that pharmacological modulation of myocardial substrate utilization might prove therapeutically advantageous. The present review addresses the effects of indirect and direct modulators of fatty acid (FA) oxidation, which are the best pharmacological agents available to date for ‘metabolic therapy’ of failing hearts. Evidence for the efficacy of therapeutic strategies based on modulators of FA metabolism is mixed, pointing to the possibility that the molecular/biochemical alterations induced by these pharmacological agents are more complex than originally thought. Much remains to be understood; however, the beneficial effects of molecules such as perhexiline and trimetazidine in small clinical trials indicate that this promising therapeutic strategy is worthy of further pursuit.

Cell therapy trials using cardiac-resident progenitor cells (CPCs) and bone marrow-derived mesenchymal stem/progenitor cells (BMCs) in patients after myocardial infarction have provided encouraging results. Exosomes, nanosized extracellular vesicles of endosomal origin, figure prominently in the bioactivities of these cells. However, a head-to-head comparison of exosomes from the two cell types has not been performed yet. CPCs and BMCs were derived from cardiac atrial appendage specimens and sternal bone marrow, respectively, from patients (n = 20; age, 69.9 ± 10.9) undergoing heart surgery for aortic valve disease and/or coronary artery disease. Vesicles were purified from cell conditioned media by centrifugation/filtration and ultracentrifugation. Vesicle preparations were predominantly composed of exosomes based on particle size and marker expression (CD9, CD63, CD81, Alix, and TSG-101). CPC-secreted exosomes prevented staurosporine-induced cardiomyocyte apoptosis more effectively than BMC-secreted exosomes. In vivo, CPC-secreted exosomes reduced scar size and improved ventricular function after permanent coronary occlusion in rats more efficiently than BMC-secreted exosomes. Both types of exosomes stimulated blood vessel formation. CPC-secreted exosomes, but not BMC-derived exosomes, enhanced ventricular function after ischaemia/reperfusion. Proteomics profiling identified pregnancy-associated plasma protein-A (PAPP-A) as one of the most highly enriched proteins in CPC vs. BMC exosomes. The active form of PAPP-A was detected on CPC exosome surfaces. These vesicles released insulin-like growth factor-1 (IGF-1) via proteolytic cleavage of IGF-binding protein-4 (IGFBP-4), resulting in IGF-1 receptor activation, intracellular Akt and ERK1/2 phosphorylation, decreased caspase activation, and reduced cardiomyocyte apoptosis. PAPP-A knockdown prevented CPC exosome-mediated cardioprotection both in vitro and in vivo. These results suggest that CPC-secreted exosomes may be more cardioprotective than BMC-secreted exosomes, and that PAPP-A-mediated IGF-1 release may explain the benefit. They illustrate a general mechanism whereby exosomes may function via an active protease on their surface, which releases a ligand in proximity to the transmembrane receptor bound by the ligand.

Mounting evidence indicates that the function of members of the vascular endothelial growth factor (VEGF) family extends beyond blood vessel formation. Here, we show that the prolonged intramyocardial expression of VEGF‐A ₁₆₅ and VEGF‐B ₁₆₇ on adeno‐associated virus‐mediated gene delivery determined a marked improvement in cardiac function after myocardial infarction in rats, by promoting cardiac contractility, preserving viable cardiac tissue, and preventing remodeling of the left ventricle (LV) over time. Consistent with this functional outcome, animals treated with both factors showed diminished fibrosis and increased contractile myocardium, which were more pronounced after expression of the selective VEGF receptor‐1 (VEGFR‐1) ligand VEGF‐B, in the absence of significant induction of angiogenesis. We found that cardiomyocytes expressed VEGFR‐1, VEGFR‐2, and neuropilin‐1 and that, in particular, VEGFR‐1 was specifically up‐regulated in hypoxia and on exposure to oxidative stress. VEGF‐B exerted powerful antiapoptotic effect in both cultured cardiomyocytes and after myocardial infarction in vivo. Finally, VEGFR‐1 activation by VEGF‐B was found to elicit a peculiar gene expression profile proper of the compensatory, hypertrophic response, consisting in activation of αMHC and repression of βMHC and skeletal α‐actin, and an increase in SERCA2a, RYR, PGC1α, and cardiac natriuretic peptide transcripts, both in cultured cardiomyocytes and in infarcted hearts. The finding that VEGFR‐1 activation by VEGF‐B prevents loss of cardiac mass and promotes maintenance of cardiac contractility over time has obvious therapeutic implications.—Zentilin, L., Puligadda, U., Lionetti, V., Zacchigna, S., Collesi, C., Pattarini, L., Ruozi, G., Camporesi, S., Sinagra, G., Pepe, M., Recchia, F. A., Giacca, M. Cardiomyocyte VEGFR‐1 activation by VEGF‐B induces compensatory hypertrophy and preserves cardiac function after myocardial infarction. FASEB J. 24, 1467–1478 (2010). www.fasebj.org

Mechanical ventilation is the main supportive therapy for patients with acute respiratory distress syndrome. As with any therapy, mechanical ventilation has side effects and may induce lung injury. This review will focus on stretch-dependent activation of alveolar epithelial and endothelial cells and polymorphonuclear leukocytes, and apoptosis/necrosis balance. The past year has seen important research in the area of mechanotransduction and lung native immunity, suggesting further mechanisms of lung inflammation and injury in ventilator-induced lung injury. Research in the past year has also stressed the importance of inflammatory response by alveolar cells and role of polymorphonuclear leukocytes in stretch-induced lung injury and has suggested a role for apoptosis in the maintenance of the alveolar epithelium. The proportion of patients receiving protective ventilatory strategies remains modest. If efforts to minimize the iatrogenic consequences of mechanical ventilation are to succeed, there must be a greater understanding of the signal transduction mechanisms and the development of potential pharmacologic targets to modulate the molecular and cellular effects of lung stretch.