Expression of BMP-2 and BMP-4 proteins by type-1 and type-2 astrocytes induced from neural stem cells under different differentiation conditions

Bone morphogenetic proteins (BMPs), a subgroup of the TGF-beta superfamily, play critical roles in neural progenitor cell fate determination. Neural stem cells (NSCs) are multipotent progenitor cells that can differentiate into neurons, oligodendrocytes and astrocytes under certain conditions. In our recent report, using an antibody that can recognize both BMP-2 and BMP-4 (BMP-2/4), we showed that BMP-2/4 is only expressed in astrocytes differentiated from NSCs in a medium containing 1 percent fetal bovine serum (FBS). In this in vitro model, the astrocytic differentiation of NSCs was mainly toward type-2. When NSCs were cultured in a medium containing 10 percent FBS, most of the cells differentiated into type-1 astrocytes. However, little information is available for BMP-2 and BMP-4 expression in type-1 and type-2 astrocytes induced from NSCs under these different culture conditions. In this study, using two antibodies specific for BMP-2 and BMP-4, respectively, we discriminated the presence of BMP-2 and BMP-4 in NSCs and their derivatives under 1 percent and 10 percent FBS culture conditions by RT-PCR, western blot and immunofluorescence staining. We found that BMP-2 and BMP-4 are highly expressed in both type-1 and type-2 astrocytes, and no detectable expression in NSCs, neurons and oligodendrocytes. This suggests that the astrocytes might be one source of BMPs during the differentiation of NSCs. However, in our model, we cannot exclude the possibility that microglia or endothelial cells could also be a source of BMPs.