Finally we observed decreased leukocyte influx

Finally, we observed decreased leukocyte influx in exosome treated animals. It is likely that the reduced influx is secondary to the reduced cardiac injury after exosome treatment, since leukocyte influx did not differ between the groups at 1h reperfusion. In addition, we found that the reduced infarct size and improved cardiac performance were associated with low WBC counts in exosome treated animals. This finding is in line with clinical studies in which infarct size and clinical outcome is directly proportional to WBC count (Barron et al., 2001; Bauters et al., 2007; Chia et al., 2009; Prasad et al., 2007). The identification of exosomes as the cardioprotective factor in MSC secretion provides an attractive safer and less costly ‘off-the-shelf’ therapeutic alternative to cell therapy in the treatment of myocardial infarction. Exosomes will become more attractive if we are able to replicate their efficacy in an ongoing study involving intracoronary injection of exosomes during the reperfusion phase in a porcine model of myocardial I/R injury (Arslan et al., 2012).
Conclusions The following are the supplementary data related to this article.
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Introduction Human mesenchymal stem sulfanilamide (hMSCs) have multilineage differentiation potential. These cells can differentiate to form a variety of tissues such as bone, cartilage, adipose and endothelium (Cao et al., 2005; Phinney and Prockop, 2007; Pittenger et al., 1999; Reyes et al., 2001; Fink et al., 2011). The balance between osteogenic and adipogenic differentiation of human mesenchymal stem cells is disrupted in various human diseases. For example, decreased bone formation accompanied by an increase in bone marrow adipogenesis occurs with aging, immobility or osteoporosis (Kajkenova et al., 1997; Nuttall and Gimble, 2000), whereas increased bone formation or calcification is observed in progressive osseous hyperplasia (Bostrom et al., 1993; Kaplan and Shore, 2000; Parhami and Demer, 1997). Therefore, elucidation of the molecular mechanisms regulating adipogenic and osteogenic differentiation of MSCs is of extreme importance for finding new treatments of these diseases. Adipogenesis is a highly regulated process in which a coordinated cascade of transcription factors leads to the formation of mature adipocytes (Rosen et al., 2000; Sethi and Vidal-Puig, 2007). This cascade begins with the transient expression of C/EBPβ and C/EBPδ which activate C/EBPα and PPARγ. C/EBPα and PPARγ together coordinate the expression of adipogenic genes underlying the phenotype of terminally differentiated adipocytes. Osteogenesis is also a highly coordinated process and is initiated by the transcription factors Runx2 and Osterix (OSX), which lead to the terminal osteoblast phenotype characterized by calcification of the extracellular matrix. The genes involved in this mineralization process include alkaline phosphatase (ALP) and osteopontin (OPN) in early phase, and osteocalcin (OCN) in late differentiation phase (Gallea et al., 2001; Jaiswal et al., 1997; Nakashima and de Crombrugghe, 2003). Mounting evidence showed that multiple pathways are involved in regulating osteogenesis and adipogenesis, such as TGFβ/BMPs/Smads, Wnt/β-catenin, Notch, JAK/STAT, MAPK, PI3K/Akt and Hedgehog pathways (Bellido et al., 1997; Chiba, 2006; Fritzius and Moelling, 2008; Gallea et al., 2001; Ross et al., 2000; Suh et al., 2006; ten Dijke et al., 2003). But what factors are involved and how they orchestrate to regulate the specification of cell fate remain elusive. Therefore, investigating the mechanisms that fine-tune the balance between osteogenic and adipogenic differentiation of MSCs is of high importance. Recent study revealed gene repression to be most prevalent prior to commitment in osteogenesis and adipogenesis, and computational analysis suggested that gene repression before commitment is mediated by miRNAs (Scheideler et al., 2008). Recently, emerging evidence suggests that miRNAs are involved in regulating differentiation and cell fate decisions (Ivey and Srivastava, 2010). miR-196a, -29b, -2861, -3960 and -335-5p were reported to enhance the osteogenic differentiation (Hu et al., 2011; Kim et al., 2009; Li et al., 2009; Zhang et al., 2011a), miR-26a, -133, -135, -141 and -200a could impede osteogenic differentiation (Itoh et al., 2009; Li et al., 2008; Luzi et al., 2008), and miR-143, -24, -31, -30c and -642a-3p were involved in regulating adipogenesis (Esau et al., 2004; Sun et al., 2009; Yang et al., 2011; Zaragosi et al., 2011). But so far, only a few key miRNAs controlling the balance between osteogenesis and adipogenesis had been identified, such as miR-22 and miR-637 (Huang et al., 2012; Zhang et al., 2011b).