Neurite outgrowth from hippocampal neurons is promoted by choroid plexus ependymal cells in vitro

Choroid plexus ependymal cells (CPECs) were known to promote axonal growth when choroid plexus is grafted into the adult rat spinal cord. The present study was carried out to examine whether CPECs promote axonal outgrowth from neurons derived from the CNS in vitro. Hippocampal neurons were cocultured on CPEC monolayers. After 24 h, neurite extension was evaluated using various parameters in comparison with cultures grown on poly-L-lysine (PLL)-coated plates and cocultures grown on astrocyte monolayers. The primary neurite length and total neurite length were longest in the cocultures with CPECs. The number of primary neurites and the number of branches were larger in the cultures with CPECs than in the cultures on PLL-coated plates, but almost the same as in the cocultures with astrocytes. Next, we examined whether the neurite extension-promoting effect occurring within 24 h is due primarily to contact with the CPECs or to factors secreted by CPECs into the culture medium. The CPEC monolayers were killed by ethanol fixation, and neurons cultured on them. The neurons extended long neurites with elaborate branching, as in the case of cocultures grown on living CPECs. On the other hand, CPEC-conditioned medium exhibited less promoting effect on neurite outgrowth from hippocampal neurons. These results indicate that CPECs have a capacity to promote neurite outgrowth from CNS neurons in vitro , and that surface plasma membrane-bound components of CPECs strongly contribute to the enhancement of neurite outgrowth in the present coculture system.