Adult neurogenesis in the subventricular zone: studies on the role of purinergic signalling

Background and Purpose - Under physiological conditions in the adult rodent brain, neurogenesis persists in two restricted regions: the subventricular zone (SVZ) of the lateral ventricles and the dentate gyrus of the hippocampus. Within the SVZ, three main cell types are morphologically and functionally distinguished: astrocyte-like stem cells give rise to clusters of transit-amplifying progenitors, which in turn generate migrating neuroblasts. Among various molecules already known to modulate adult neurogenesis, increasing evidence suggests that nucleotides can play a role in controlling proliferation, self-renewal, and differentiation of precursor cells; although no definitive data are available so far. Aim of our study was to investigate the role of ADPβS, acting as agonist at the P2Y1,12,13 receptor subtypes, in modulating adult neurogenesis in the mouse SVZ both in vitro (by the neurosphere assay), and in vivo by its intracerebroventricular (i.c.v.) administration. Methods and Results - Neurospheres (NS) were obtained by mouse SVZ, as described in literature (Doetsch et al., 1999. Cell 97:703-716), and kept in culture up to the 3rd generation in the absence or presence of ADPβS. When cells derived from the dissociation of secondary NS were plated in presence of ADPβS an increased number of tertiary NS paralleled by a reduction of their size and of the total number of viable cells was observed. No changes in the progression through the cell cycle were detected. Since progenitor cells have limited proliferative and self-renewal capacity with respect to stem cells, and therefore give rise to small-sized neurospheres, it can be envisaged that ADPβS acts on this specific cell population. Moreover, ADPβS is able to stimulate cell differentiation in undissociated neurospheres resulting in an increased appearance of both astrocytic and neuronal (GFAP and βTUB) markers. In vivo, ADPβS was administered by minipumps i.c.v. for one week. Animals received a short pulse of BrdU on the last two days, to detect the proliferation of progenitors. Confirming in vitro data, ADPβS treatment increased both GFAP immunostaining and promoted the generation of new born DCX+ neuroblasts. Conclusions - ADPβS stimulates the self-renewal and differentiative capability of neural progenitor cells. This effect could be exploited, since to increase the pool of neural progenitor cells and their differentiation towards neuroblasts for the restoration of brain functions following injury.