Systemic Mesenchymal Stem Cell-Derived Exosomes Reduce Myocardial Infarct Size: Characterization With MRI in a Porcine Model.

The observations that mesenchymal stem cells (MSCs) exert cardiac protection and repair via their secretome with the active component(s) identified as exosomes underpinned our test of the efficacy of MSC exosomes in a porcine model of myocardial infarction (MI) when administered systemically by the convenient method of intravenous (IV) bolus injection. Results show that 7 days of IV exosomes results in clear reduction (30-40%) of infarct size measured at both 7 and 28 days post-MI, despite near identical release of hs Troponin T. Together with reduced infarct size, exosome treatment reduced transmurality and lessened wall thinning in the infarct zone. Exosome treated pigs showed relative preservation of LV function with significant amelioration of falls in fractional wall thickening compared with control. However, global measures of LV function were less protected by exosome treatment. It is possible that greater preservation of global LV function may have been attenuated by increased cardiac fibrosis, as T1 values showed significant increase in the exosome pigs compared to control particularly in the infarct related segments. Taken together, these results show clear effects of IV exosomes administered over 7 days to reduce infarct size with relatively preserved cardiac function compared to control treated infarct pigs.

Pleiotropic cardiac functions controlled by ischemia-induced lncRNA H19.

Myocardial ischemia induces a multifaceted remodeling process in the heart. Novel therapeutic entry points to counteract maladaptive signalling include the modulation of non-coding RNA molecules such as long non-coding RNA (lncRNA). We here questioned if the lncRNA candidate H19 exhibits regulatory potential in the setting of myocardial infarction. Initial profiling of H19 expression revealed a dynamic expression profile of H19 with upregulation in the acute phase after murine cardiac ischemia. In vitro, we found that oxygen deficiency leads to H19 upregulation in several cardiac cell types. Repression of endogenous H19 caused multiple phenotypes in cultivated murine cardiomyocytes including enhanced cardiomyocyte apoptosis, at least partly through attenuated vitamin D signalling. Unbiased proteome analysis revealed further involvement of H19 in mRNA splicing and translation as well as inflammatory signalling pathways. To study H19 function more precisely, we investigated the phenotype of systemic H19 loss in a genetic mouse model of H19 deletion (H19 KO). Infarcted heart tissue of H19 KO mice showed a massive increase of pro-inflammatory cytokines after ischemia-reperfusion injury (I/R) without significant effects on scar formation or cardiac function but exaggerated cardiac hypertrophy indicating pathological cardiac remodeling. H19-dependent changes in cardiomyocyte-derived extracellular vesicle release and alterations in NF-κB signalling were evident. Cardiac cell fractionation experiments revealed that enhanced H19 expression in the proliferative phase after MI derived mainly from cardiac fibroblasts. Here further research is needed to elucidate its role in fibroblast activation and function. In conclusion, the lncRNA H19 is dynamically regulated after MI and involved in multiple pathways of different cardiac cell types including cardiomyocyte apoptosis and cardiac inflammation.

A porcine model of heart failure with preserved ejection fraction: magnetic resonance imaging and metabolic energetics.

AIMS: A significant proportion of heart failure (HF) patients have HF preserved ejection fraction (HFpEF). The lack of effective treatments for HFpEF remains a critical unmet need. A key obstacle to therapeutic innovation in HFpEF is the paucity of pre-clinical models. Although several large animal models have been reported, few demonstrate progression to decompensated HF. We have established a model of HFpEF by enhancing a porcine model of progressive left ventricular (LV) pressure overload and characterized HF in this model including advanced cardiometabolic imaging using cardiac magnetic resonance imaging and hyperpolarized carbon-13 magnetic resonance spectroscopy. METHODS AND RESULTS: Pigs underwent progressive LV pressure overload by means of an inflatable aortic cuff. Pigs developed LV hypertrophy (50% increase in wall thickness, P < 0.001, and two-fold increase in mass compared to sham control, P < 0.001) with no evidence of LV dilatation but a significant increase in left atrial volume (P = 0.013). Cardiac magnetic resonance imaging demonstrated T1 modified Look-Locker inversion recovery values increased in 16/17 segments compared to sham pigs (P < 0.05-P < 0.001) indicating global ventricular fibrosis. Mean LV end-diastolic (P = 0.047) and pulmonary capillary wedge pressures (P = 0.008) were elevated compared with sham control. One-third of the pigs demonstrated clinical signs of frank decompensated HF, and mean plasma BNP concentrations were raised compared with sham control (P = 0.008). Cardiometabolic imaging with hyperpolarized carbon-13 magnetic resonance spectroscopy agreed with known metabolic changes in the failing heart with a switch from fatty acid towards glucose substrate utilization. CONCLUSIONS: Progressive aortic constriction in growing pigs induces significant LV hypertrophy with cardiac fibrosis associated with left atrial dilation, raised filling pressures, and an ability to transition to overt HF with raised BNP without reduction in LVEF. This model replicates many aspects of clinical HFpEF with a predominant background of hypertension and can be used to advance understanding of underlying pathology and for necessary pre-clinical testing of novel candidate therapies.

Long Noncoding RNA-Enriched Vesicles Secreted by Hypoxic Cardiomyocytes Drive Cardiac Fibrosis.

Long non-coding RNAs (lncRNAs) have potential as novel therapeutic targets in cardiovascular diseases, but detailed information about the intercellular lncRNA shuttling mechanisms in the heart is lacking. Here, we report an important novel crosstalk between cardiomyocytes and fibroblasts mediated by the transfer of lncRNA-enriched extracellular vesicles (EVs) in the context of cardiac ischemia. lncRNA profiling identified two hypoxia-sensitive lncRNAs: ENSMUST00000122745 was predominantly found in small EVs, whereas lncRNA Neat1 was enriched in large EVs in vitro and in vivo. Vesicles were taken up by fibroblasts, triggering expression of profibrotic genes. In addition, lncRNA Neat1 was transcriptionally regulated by P53 under basal conditions and by HIF2A during hypoxia. The function of Neat1 was further elucidated in vitro and in vivo. Silencing of Neat1 in vitro revealed that Neat1 was indispensable for fibroblast and cardiomyocyte survival and affected fibroblast functions (reduced migration capacity, stalled cell cycle, and decreased expression of fibrotic genes). Of translational importance, genetic loss of Neat1 in vivo resulted in an impaired heart function after myocardial infarction highlighting its translational relevance.