Cardiac cells differentiated from human induced pluripotent stem cells produce exosomes that improve recovery from myocardial infarction in pigs.

Rationale: Clinical application of mesenchymal stem cells (MSCs) and MSC-derived exosomes (MSC-Exos) to alleviate myocardial ischemia/reperfusion (I/R) injury is compromised by the low cell engraftment rate and uncontrolled exosomal content. As one of their active ingredients, single-component microRNA therapy may have more inherent advantages. We sought to find an ideal microRNA candidate and determine whether it could reproduce the cardioprotective effects of MSCs and MSC-Exos.

Background: Human induced pluripotent stem cell-derived endothelial cells (hiPSC-ECs) exhibit the potential to repair the injured heart after myocardial infarction (MI) by promoting neovascularization and cardiomyocyte survival. However, because of the low cellular retention and poor engraftment efficacy, cell therapy of MI is partly mediated by exosomes secreted from the transplanted cells. In this study, we investigated whether exosomes secreted from hiPSC-ECs could become a promising acellular approach to repair the infarcted heart after MI and elucidated the underlying protective mechanism.Methods: The hiPSC-ECs were differentiated, and exosomes were isolated in vitro. Then, hiPSC-EC exosomes were delivered by intramyocardial injection in a murine MI model in vivo. Echocardiography, combined with hemodynamic measurement, histological examination, Ca²⁺transient and cell shortening assessment, and Western blot, was used to determine the protective effects of hiPSC-EC exosomes on the infarcted heart. Furthermore, microRNA sequencing, luciferase activity assay, and microRNA gain–loss function experiments were performed to investigate the enriched microRNA and its role in exosome-mediated effects.Results: In vitro, the hiPSC-EC exosomes enhanced intracellular Ca²⁺transients, increased ATP content, and improved cell survival to protect cardiomyocytes from oxygen–glucose deprivation injury. Congruously, hiPSC-EC exosome administration in vivo improved the myocardial contractile function and attenuated the harmful left ventricular remodeling after MI without increasing the frequency of arrhythmias. Mechanistically, the hiPSC-EC exosomes notably rescued the protein expression and function of the sarcoplasmic reticulum Ca²⁺ATPase 2a (SERCA-2a) and ryanodine receptor 2 (RyR-2) to maintain intracellular Ca²⁺homeostasis and increase cardiomyocyte contraction after MI. The microRNA sequencing showed that miR-100-5p was the most abundant microRNA in exosomes. miR-100-5p could target protein phosphatase 1β (PP-1β) to enhance phospholamban (PLB) phosphorylation at Ser¹⁶and subsequent SERCA activity, which contributes to the hiPSC-EC exosome-exerted cytoprotective effects on maintaining intracellular Ca²⁺homeostasis and promoting cardiomyocyte survival.Conclusion: The hiPSC-EC exosomes maintain cardiomyocyte Ca²⁺homeostasis to improve myocardial recovery after MI, which may provide an acellular therapeutic option for myocardial injury.

Rationale: Cardiac fibrosis is an adverse consequence of aberrant fibroblast activation and extracellular matrix (ECM) deposition following myocardial infarction (MI). Recently, long noncoding RNAs (lncRNAs) have been reported to participate in multiple cardiac diseases. However, the biological functions of lncRNA rhabdomyosarcoma 2-associated transcript (RMST) in cardiac fibrosis remain largely unknown.

Myocardial infarction (MI) causes excessive damage to the myocardium, including the epicardium. However, whether pluripotent stem cell‐derived epicardial cells (EPs) can be a therapeutic approach for infarcted hearts remains unclear. Here, the authors report that intramyocardial injection of human embryonic stem cell‐derived EPs (hEPs) at the acute phase of MI ameliorates functional worsening and scar formation in mouse hearts, concomitantly with enhanced cardiomyocyte survival, angiogenesis, and lymphangiogenesis. Mechanistically, hEPs suppress MI‐induced infiltration and cytokine‐release of inflammatory cells and promote reparative macrophage polarization. These effects are blocked by a type I interferon (IFN‐I) receptor agonist RO8191. Moreover, intelectin 1 (ITLN1), abundantly secreted by hEPs, interacts with IFN‐β and mimics the effects of hEP‐conditioned medium in suppression of IFN‐β‐stimulated responses in macrophages and promotion of reparative macrophage polarization, whereas ITLN1 downregulation in hEPs cancels beneficial effects of hEPs in anti‐inflammation, IFN‐I response inhibition, and cardiac repair. Further, similar beneficial effects of hEPs are observed in a clinically relevant porcine model of reperfused MI, with no increases in the risk of hepatic, renal, and cardiac toxicity. Collectively, this study reveals hEPs as an inflammatory modulator in promoting infarct healing via a paracrine mechanism and provides a new therapeutic approach for infarcted hearts.