Purinergic signaling modulates adult neurogenesis in the subventricular zone: role of parenchymal astrocytes

Increasing evidence suggests that nucleotides play a role in controlling adult neurogenesis. From the few data published so far, a primary role for the P2Y1 G protein-coupled receptor subtype is clearly emerging. Therefore we examined the role of ADPβS, a P2Y1,12,13 receptor agonist, in modulating neural stem cell (NSC) properties in the mouse subventricolar zone (SVZ) both in vivo and in vitro. A 7-day long i.c.v. administration of ADPβS stimulated reactive astrogliosis in brain parenchima and increased the proliferation of GFAP+ precursors, leading to hypertrophy of the SVZ. Moreover, ADPβS promoted the generation of Mash1+ transit amplifying cells and of doublecortin+ neuroblasts. To confirm our in vivo data, we also performed in vitro experiments by the neurosphere (NS) assay. When cells derived from the dissociation of SVZ were plated in the presence of ADPβS, an increased number of NS was generated. Moreover, ADPβS stimulated the differentiation of undissociated NS towards GFAP+ astrocytes, and βTUB+ neurons. Moreover, to test whether ADPβS was only directly acting on NSCs or whether reactive astrocytes are involved, we grew NS in conditioned media derived from astrocytes cultured under control condition or in presence of ADPβS. The medium from ADPβS-treated astrocytes reduced the number and size of primary NS with respect to control medium. Interestingly, when cells obtained from the dissociation of primary NS grown in medium from ADPβS-treated astrocytes were replated in control medium, an increase in the number and size of secondary NS was instead observed. This suggests that a yet-to-be identified astrocytic mediator directly inhibits NS generations, but primes cells to boost their stem cell potential when removed from the culture medium. Taken together, our data suggest that nucleotides can be used to increase the pool of NSCs and their differentiation towards neuroblasts, either directly or through the activation of parenchymal astrocytes.