A2B5+ and O4+ Cycling progenitors in the adult forebrain white matter respond differentially to PDGF-AA, FGF-2, and IGF-1.

Cycling glial progenitors reside within subcortical white matter of the mammalian adult forebrain. Either A2B5 or O4 expression defines two of the major classes of cycling progenitors. We examined the growth factor receptor profiles of these progenitor populations and their capability to proliferate and differentiate in response to PDGF-AA, FGF-2, and IGF-1. FGF-2 and IGF-1 enhance the acquisition of O1 by the O4+ progenitors, but have no significant effect on the acquisition of O4 and/or O1 by the A2B5+ progenitors. In contrast, PDGF-AA enhances the acquisition of O1 by the A2B5+ progenitors, while having no significant affect on the acquisition of O1 by the O4+ progenitors unless combined with FGF-2. In addition, PDGF-AA and FGF-2 promote the proliferation of A2B5+ progenitors, while having no mitogenic effect on the O4+ progenitors unless the two factors are combined with IGF-1. Interestingly, not all of the progenitors within the A2B5 or O4 populations express the same growth factor receptors nor respond similarly to growth factors. Thus, there are substantial differences between the two populations and heterogeneity within each of these populations may exist.