Using ESNPs to repair damaged tissue in neurodegenerative

Using ESNPs to repair damaged tissue in neurodegenerative diseases is an attractive option, as these G418 are more readily obtained than fetal material. Recent work on the relationship between neural stem cells and blood vessels (reviewed in (Bjornsson et al., 2015) as well as our own transplant work (Hartman et al., 2010), prompted us to investigate the interaction of ESNPs with the host vasculature. We demonstrate here that transplanted ESNPs migrate extensively after initial injection, using the blood vessel-astroglial niche as a scaffold. The migration of endogenous SVZ neural precursors on blood vessels has been well documented (Kokovay et al., 2010; Ottone et al., 2014; Saha et al., 2013; Shen et al., 2008). In contrast, in the SGZ, neural progenitors are closely associated with the vascular plexus of the DG, but their migration on blood vessels has only recently been described (Sun et al., 2015). Activated radial glia-like neural stem cells in the adult SGZ, clonally labeled using an inducible Ascl1 knockin mouse line, migrate tangentially on a bed of blood vessels in the SGZ (Sun et al., 2015). This was the first report of tangential, as opposed to radial migration, by granule neuron progenitors in the hippocampus. Intriguingly, there are a number of parallels between the migration of these endogenous neural progenitors and the migration of mESNPs we described previously (Hartman et al., 2010), and in this report. The activated endogenous SGZ neural stem cells migrate optimally between 3 and 7 days following lineage labeling, and less extensively over the next 1-2 months (Sun et al., 2015). We observe optimal migration of mESNPs transplanted to the DG by 7 days post-injection, with little additional movement at one month (Hartman et al., 2010). We also note a strong association with blood vessels for both mESNPs and hESNPs (Figs. 2, 3 and 5). The blood vessel association is seen, for both endogenous progenitors and ESNPs, at both the nestin-positive neural stem cell and DCX-positive neuroblast stages. We also observe the blood vessel juxtaposition for both neural progenitor somas and processes, as reported for endogenous progenitors (Sun et al., 2015). These similarities suggest that ESNPs nicely model an endogenous event. The chemokine CXCL12 plays a role in neural progenitor migration in a number of settings during development and following injury. Our prior work established a role for CXCL12 in migration of mESNPs transplanted to the hippocampus, by demonstrating that AMD3100 could limit the extent of migration (Hartman et al., 2010). We now show that endothelial cells and associated astrocytes can serve as a source of this chemokine. We previously demonstrated that mESNPs migrate towards CXCL12 in a Boyden Chamber assay, and that this migration was inhibited by AMD3100 (Hartman et al., 2010). Using hESNPs, we observed similar results, with cells migrating towards CXCL12 protein and BECs in vitro, and this migration is significantly inhibited by AMD3100. This suggests that endothelial cell-derived CXCL12, acting via the CXCR4 receptor, plays a significant role in promoting ESNP migration. In the Boyden Chamber assay using BECs, however, residual migration is observed in the presence of AMD3100, suggesting that additional BEC-derived chemokines play a role, an idea supported by the literature (reviewed in (Segarra et al., 2015)). Glioma cells use blood vessels as a migratory substrate to metastasize, and a role for CXCL12 has been established (Zagzag et al., 2008). Inhibiting the glioma cell-blood vessel interaction using AMD3100 is currently being considered as part of a combinatorial approach to inhibiting glioma metastasis (NCT01339039). As we progress towards clinical application, it is essential to have a complete understanding of the fate of neural progenitors post-transplantation, including an understanding of interactions with the host vasculature. Our observations that ESNPs migrate on host vasculature raise the concern that transplanted neural stem cells may relocate to distant sites, where they may form neural stem cell tumors if they remain undifferentiated (Germain et al., 2013), or disrupt the existing circuitry if they differentiate into mature neurons. These concerns suggest that measures need to be taken to retain transplanted cells at the injection site, and prevent subsequent migration, though tumor formation at the initial injection site remains a concern.