Our work implicates exosomes and the miRNAs they

Our work implicates exosomes, and the miRNAs they contain, as crucial mediators of CDC-induced cardiac regeneration. CDCs exert diverse but coordinated effects: they recruit endogenous progenitor chenodeoxycholic acid and coax surviving heart cells to proliferate (Chimenti et al., 2010; Li et al., 2010; Malliaras et al., 2013; Stastna et al., 2010); on the other hand, injected CDCs suppress maladaptive LV remodeling (Lee et al., 2011), apoptosis (Cheng et al., 2012; Li et al., 2010), inflammation (Tseliou et al., 2014), and tissue fibrosis (Tseliou et al., 2014) after MI. While it is possible that CDCs secrete a medley of individual growth factors and cytokines that collectively produce diverse benefits, the involvement of master-regulator miRNAs within exosomes would help tie together the various effects without postulating complex mixtures of numerous secreted protein factors. Moreover, miRNAs are known to confer long-lasting benefits and fundamental alterations of the injured microenvironment (Osman, 2012), helping to rationalize the sustained benefits of CDCs despite their evanescent survival in the tissue (Malliaras et al., 2012). CDC exosomes contain rich signaling information conferred by a cell type that is the first shown to be capable of producing regeneration in a setting of “permanent” injury, and confer the same benefits as CDCs without transplantation of living cells. For all these reasons, CDC exosomes merit further development as cell-free therapeutic candidates.
Experimental Procedures
Acknowledgments We thank Baiming Sun for performing animal surgeries, Geoffrey De Couto for advice on the apoptosis assays, Susmita Sahoo for helpful discussions regarding the experimental protocol used in Figure 1B, and Ryan Middleton and Weixin Liu for technical assistance. This work was supported by a grant from the NIH to E.M. E.M. is founder of, unpaid advisor to, and owns equity in Capricor Therapeutics.
Introduction Spinal cord injury (SCI) affects approximately 1,275,000 people in the United States alone, at a cost of over $40.5 billion annually (Christopher & Dana Reeve Foundation, 2009). Human neural stem cell (hNSC) transplantation has emerged as an approach to promote repair or regeneration of the damaged CNS. However, the role of the transplantation niche in hNSC survival, proliferation, migration, and differentiation has received little attention. A niche provides extrinsic cues that influence many aspects of stem cell biology (Decimo et al., 2012). Accordingly, a transplantation niche in an injured microenvironment could alter both the engraftment dynamics and the availability of differentiation cues. At least two paradigms can be postulated for the dynamics of transplanted cell engraftment (Figure 1A) and migration (Figure 1B) in the spinal cord. The injured microenvironment could alter these dynamics by causing a paradigm shift or enhancing/impairing one paradigm. Furthermore, the injured microenvironment could alter the lineage-specific differentiation or localization of transplanted cells. In previous studies, we tested the transplantation of human CNS stem cells propagated as neurospheres (hCNS-SCns; Uchida et al., 2000) into immediate, subacute, and chronic microenvironments following contusive SCI in NOD-scid mice (Cummings et al., 2005, 2006, 2008; Hooshmand et al., 2009; Salazar et al., 2010), C57Bl/6 mice (Sontag et al., 2013), and athymic nude rats (Piltti et al., 2013a, 2013b). In those studies, we identified robust engraftment, long-term survival, proliferation, differentiation, and extensive migration, along with improved locomotor function, with no evidence of allodynia or hyperalgesia. Although it has been suggested that cell engraftment could be adversely affected by transplantation timing (Okano et al., 2003), we have reported that stereological quantification of engrafted cells after immediate, subacute, or early chronic transplantation revealed similar total numbers of human cells 12–16 weeks posttransplantation (Cummings et al., 2005, 2006, 2008; Hooshmand et al., 2009; Salazar et al., 2010). Our objective in the present study was to investigate the effect of the transplantation niche and injured microenvironment on the spatiotemporal dynamics of hNSC engraftment. For these experiments, we focused on the subacute hCNS-SCns transplantation paradigm, which was previously demonstrated to improve locomotor function (Cummings et al., 2005, 2008; Hooshmand et al., 2009).