Previous studies have reported that the fetal pial capillaries penetrate the cerebral cortex and differentiate into the intracerebral vascular components. These pial and intracerebral vasculars express not only CD31 but also nestin, a neural stem cell marker. We have already reported that fetal leptomeninges can be a resource of neural stem cells. Few have been revealed about neurogenesis from CD31-positive cells in the brain.
We examined whether CD31-positive cells derived from the fetal cerebral cortex have a potential to differentiate into neural lineage.
The localization of CD31-positive cells in the embryonic (E17) mouse brain was analyzed by immunohistochemistry and immunoelectron microscopy. Cells isolated from E17 cerebral cortex and MACS-sorted for CD31 were cultured for a week in adhering medium and then in neurosphere-producing medium, and differented into neural lineage. Total RNA extracted from the cultured cells was subjected to RT-PCR.
Immunohistochemistry for CD31, PDGFR-beta, NG2 and nestin showed that cells close to the pial and cerebral microvessels expressed nestin. These vessel-associated nestin-positive cells co-expressed CD31 and NG2, a pericyte marker. Immunoelectron microscopy confirmed that CD31 was localized not only to the endothelial cell (EC) membranes but also to the pericyte-like cell (PC) at the adhering site to ECs. The cultured CD31-positive cells could differentiate into neural lineage. The adhesive environment reduced CD31-expression in the cells, but spheroid formation retained CD31. Nestin was constantly expressed throughout the culture.
These results indicate that CD31-positive cerebral ECs and PCs also express nestin and have a potential to differentiate into neural cells limited in fetal and neonatal stage. It is well known that the interaction of neurogenesis and angiogenesis is coordinated in postnatal brain. The present study suggests the new mechanism for regulating neurogenesis of post-injured brain.