K03861 Our findings showing an increase of growth factors ex

Our findings showing an increase of growth factors expression in miR133-CPCs upon stress conditioning and the amelioration of cardiac functions after miR133-CPCs transplantation post-AMI are in agreement with a recent publication that demonstrates that previous supplementation (“priming”) of SCA1+/CD31+ K03861 with recombinant IGF-1+HGF increases their engraftment capacity and survival rate, promoting angiogenesis and favoring regeneration in response to the hostile microenvironment of an infarcted heart, after their transplantation (Wang et al., 2014). Our results demonstrate that miR-133a, without affecting proliferation/differentiation potential, promotes CPCs survival and significantly increases their capacity to protect the heart against hypertrophy and apoptosis after MI. Recently, it has been proposed that exosomes, which resulted to be highly enriched in specific miRNAs, play a critical role in hCPC-driven improvement of cardiac function after injury (Barile et al., 2014). Exosomes secreted by CDCs also contain a distinctive repertoire of miRNAs (Ibrahim et al., 2014) and inhibit apoptosis and promote proliferation of cardiomyocytes, while enhancing angiogenesis. All of these recent evidences support the phenotype that we observed with miR-133a-CPCs. We confirmed that secreted miR-133a was mainly incorporated into the exosomal fraction of miR-133a-CPCs-CM, suggesting that direct transfer of the miRNA might mediate part of miR-133a-CPCs paracrine actions on the damaged tissue. However, the high levels of miR-133a already present in mature cardiomyocytes makes unlikely that CPC-exosomal contribution of miR-133a may provide additional significant effects on damaged cardiomyocytes. Finally, it has been recently demonstrated that the combination of miR-133a with cardiac core transcriptional factors (Gata4, Mef2c, and Tbx5) or GMT plus Mesp1 and Myocd significantly improves direct cardiac reprogramming from human and mouse fibroblasts (Muraoka et al., 2014). Our results on the role of miR-133a in CPCs could be fully compatible with its plausible contribution to transient progenitor survival during the reprogramming process. In summary, we believe that miR-133a protective actions integrate the rescue of endogenous CPCs, early activated progenitors as angioblasts (Malliaras et al., 2014) or endothelial cells, and the secretome/exosome-mediated repair of damaged resident cardiomyocytes via a complex combination of secreted miRNAs and growth and survival factors. Our work provides a detailed dissection of the mechanisms activated by miR-133-CPC transplantation and establishes the basis for a future improvement of therapeutic use of CPCs for regenerating injured myocardium after infarct.
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Introduction In developing mammals, hematopoiesis initially occurs extraembryonically, most prominently in the yolk sac (Silver and Palis, 1997), and later arises within the embryo in the aorta-gonad-mesonephros (AGM) region (Godin et al., 1993; Medvinsky et al., 1993) and developing endocardium (Nakano et al., 2013). Definitive hematopoietic stem cells (HSCs), which are responsible for blood production throughout life, first detectibly emerge in the AGM (Müller et al., 1994) and colonize the fetal liver (FL), ultimately occupying niches in the bone marrow (reviewed in Mikkola and Orkin, 2006). The specification of blood is closely coordinated with the specification of blood vessels, and genetic evidence supports the notion of a shared ontogeny. For example, murine embryos null for Kdr (also known as Flk1) do not develop blood islands or blood vessels and die between embryonic development days 8.5 and 9.5 (Shalaby et al., 1995). In chimeric embryos, Kdr null cells are not detected in later sites of hematopoiesis such as the FL or adult bone marrow but are found in other mesodermal tissues like heart, kidney, and muscle (Shalaby et al., 1997). In fact, endothelial cells and hematopoietic cells can be observed in vitro to arise from the same mesodermal progenitors, called hemangioblasts (Choi et al., 1998).