The adult rat brain subventricular zone (SVZ) contains proliferative precursors that migrate to the olfactory bulb (OB) and differentiate into mature neurons. Recruitment of precursors constitutes a potential avenue for brain repair. We have investigated the kinetics and cellular specificity of transgene expression mediated by AAV2/1 vectors (i.e., adeno-associated virus type 2 pseudotyped with AAV1 capsid) in the SVZ. Self-complementary (sc) and single-stranded (ss) AAV2/1 vectors mediated efficient GFP expression, respectively, at 17 and 24 hr postinjection. Transgene expression was efficient in all the rapidly proliferating cells types, that is, Mash1+ precursors (30% of the GFP+ cells), Dlx2+ neuronal progenitors (55%), Olig2+ oligodendrocyte progenitors (35%), and doublecortin-positive (Dcx+) migrating cells (40%), but not in the slowly proliferating glial fibrillary acidic protein-positive (GFAP+) neural stem cell pool (5%). Because cell cycle arrest by wild-type and recombinant AAV has been described in primary cultures, we examined SVZ proliferative activity after vector injection. Indeed, cell proliferation was reduced immediately after vector injection but was normal after 1 month. In contrast, migration and differentiation of GFP+ precursors were unaltered. Indeed, the proportion of Dcx+ cells was similar in the injected and contralateral hemispheres. Furthermore, 1 month after vector injection into the SVZ, GFP+ cells, found, as expected, in the OB granular cell layer, were mature GABAergic neurons. In conclusion, the rapid and efficient transgene expression in SVZ neural precursors mediated by scAAV2/1 vectors underlines their potential usefulness for brain repair via recruitment of immature cells. The observed transient precursor proliferation inhibition, not affecting their migration and differentiation, will likely not compromise this strategy.
Bockstael and colleagues characterize the kinetics and cell type specificity of recombinant AAV1-mediated gene transfer in the subventricular zone (SVZ) of adult rats. They show that AAV1 effectively transduces rapidly proliferating cell types (i.e., Mash1+ precursors, Dlx2+ neuronal progenitors, Olig2+ oligodendrocyte progenitors) but cannot transduce the slowly proliferating glial fibrillary acidic protein-positive neural stem cell pool.