Previous studies demonstrated SPION labeling in a variety of

Previous studies demonstrated SPION-labeling in a variety of human (Niemeyer et al., 2010; Song et al., 2007) and animal (Rice et al., 2007; Zhu et al., 2007) stem cells. We used SPION to track MSC in the QUIN model. SPION were internalized in MSC without affecting cellular viability. These data corroborate previous findings of SPION biosafety (Arbab et al., 2003) and viability maintenance 3 to 7days after labeling, even using high concentrations of SPION (Jasmin et al., 2010). The MRI signal was generated by labeled Regorafenib cost and remained restricted to the injection site 1h after transplantation. MRI signals lasted for at least 60days, and it is likely that it gradually disappeared due to cell proliferation. Previous data showed that inhibition of cell proliferation mediated by Mitomycin-C reduces SPION loss from labeled MSC (Jasmin et al., 2010). Our in vivo tracking of SPION-labeled MSC suggested migration from the injection site to the contralateral lesioned striatum. MSC migration between hemispheres was described earlier (Li et al., 2011; Wang et al., 2002). Because stained cells were located next to blood vessels and cerebral ventricles, we speculate that they migrated through the blood flow and/or the liquor. MSC migration has been associated with SDF-1/CXCR4 pathway (Tyndall et al., 2007), fractalcin and its receptor CX3CR1 (Ji et al., 2004) (Sordi et al., 2005), TNF-α, and MCP-1 (Fu et al., 2009). MSC local permanence seems not to require persistent integration. The “touch and go effect” (Uccelli et al., 2008) has been discussed as a potential therapeutic characteristic of MSC, which includes induction of a neuroprotective microenvironment with subsequent clearance of the lesioned tissue.
Acknowledgments This study was supported by grants from the Ministry of Health (MS/SCTIE/DECIT), from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Instituto Nacional de Ciência e Tecnologia de Biologia Estrutural e Bioimagem (Inbeb), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ). The authors thank Suelen Sério and Felipe Marins for technical assistance, and Janet W. Reid for editing the manuscript.
Introduction The transplantation of neural stem cells is a promising strategy in restoration of lost functions of injured central nervous system (CNS). However, a pronounced immune rejection after transplantation and the difficulty in obtaining sufficient number of NSPCs pose a major challenge in therapeutic application. Therefore, seeking an autologous cell pool is essential for developing therapeutic strategies to treat the traumatic CNS injury. Astrocytes are ubiquitous cells found throughout the CNS. Compelling evidence indicates that astrocytes possess de-differentiation potential (Steindler and Laywell, 2003; Lang et al., 2004; Itoh et al., 2006; Sharif et al., 2007; Yang et al., 2009, 2010, 2011; Costa et al., 2010; Sher et al., 2011; Moon et al., 2011). This unique property of astrocytes makes them a particularly attractive source of cells for cell-replacement therapy. However, maintenance of NSPC characteristics and inefficient generation of NSPCs from de-differentiated astrocytes remain as prominent problems in their use in cell-replacement therapy. The factors that efficiently induce astrocyte de-differentiation into NSPCs remain obscure. Sonic hedgehog (Shh), a paracrine/autocrine morphogen, plays critical roles in regulating the expression of genes involved in cell proliferation, progenitor cell renewal, cell lineage specification, and tissue regeneration in the organs of various species (Ahn and Joyner, 2005; Chari and McDonnell, 2007; Galvin et al., 2007). For example, self-renewal of neurosphere-forming stem cells in adult mouse forebrain requires the presence of Shh (Palma et al., 2005; Huang et al., 2010). In mouse retina, Shh stimulates progenitor cell proliferation and diversification (Ingham and McMahon, 2001; Lang et al., 2004; Jiang and Hui, 2008; Wall et al., 2009). These aforementioned studies suggest a critical role of Shh signaling in cytogenesis and development. Likewise, there is growing evidence to suggest that Shh can stimulate hematopoietic cells to enter the cell cycle by up-regulating the expression of D-type cyclins required to pass the G1 restriction point (Mill et al., 2003; Mandal et al., 2007). Despite extensive studies on shh biofunctions, very little is known to date about the effect of Shh on the de-differentiation of astrocytes. Similarly, our more recent studies strongly suggest that the underlying mechanism of astrocyte de-differentiation and the transitional rejuvenation processes is intimately linked with certain appropriate molecules released from injured astrocytes (Lang et al., 2004; Itoh et al., 2006; Yang et al., 2009, 2010, 2011). The details of the effectors of astrocyte de-differentiation and the underlying molecular mechanism that contributes to the event are still unknown. In this study, we sought to determine the extent of ACM to induce astrocyte to reversion to NSPCs. We found that up-regulation of Shh expression in astrocytes after mechanical injury may not only contribute to the astrocyte rejuvenation process, but is also very important for establishment and maintenance of NSPCs. The latter finding is consistent with previous studies (Beachy et al., 2004; Ahn and Joyner, 2005; Palma et al., 2005). Furthermore we demonstrated that occurrence of this complex event still depends upon the synergistic action of other molecules signaling in ACM, implying existence of a complementing molecular mechanism underlying astrocyte de-differentiation.