Reactivating endogenous mechanisms of cardiac regeneration via paracrine boosting using the human amniotic fluid stem cell secretome

Background: The adult mammalian heart retains residual regenerative capability via endogenous cardiac progenitor cell (CPC)activation and cardiomyocyte proliferation. We previously reported the paracrine cardioprotective capacity of human amniotic fluid-derived stem cells (hAFS)following ischemia or cardiotoxicity. Here we analyse the potential of hAFS secretome fractions for cardiac regeneration and future clinical translation. Methods: hAFS were isolated from amniotic fluid leftover samples from prenatal screening. hAFS conditioned medium (hAFS-CM)was obtained following hypoxic preconditioning. Anti-apoptotic, angiogenic and proliferative effects were evaluated on rodent neonatal cardiomyocytes (r/mNVCM), human endothelial colony forming cells (hECFC)and human CPC. Mice undergoing myocardial infarction (MI)were treated with hAFS-CM, hAFS-extracellular vesicles (hAFS-EV), or EV-depleted hAFS-CM (hAFS-DM)by single intra-myocardial administration and evaluated in the short and long term. Results: hAFS-CM improved mNVCM survival under oxidative and hypoxic damage, induced Ca 2+ -dependent angiogenesis in hECFC and triggered hCPC and rNVCM proliferation. hAFS-CM treatment after MI counteracted scarring, supported cardiac function, angiogenesis and cardiomyocyte cell cycle progression in the long term. hAFS-DM had no effect. hAFS-CM and hAFS-EV equally induced epicardium WT1+ CPC reactivation. Although no CPC cardiovascular differentiation was observed, our data suggests contribution to local angiogenesis by paracrine modulation. hAFS-EV alone were able to recapitulate all the beneficial effects exerted by hAFS-CM, except for stimulation of vessel formation. Conclusions: hAFS-CM and hAFS-EV can improve cardiac repair and trigger cardiac regeneration via paracrine modulation of endogenous mechanisms. While both formulations are effective in sustaining myocardial renewal, hAFS-CM retains higher pro-angiogenic potential, while hAFS-EV particularly enhances cardiac function.