Roles of insulin and transferrin in neural progenitor survival and proliferation

Abstract Multipotent neural progenitor cells or neural stem cells (NSC) can be propagated in vitro from a variety of sources and have great potential for neural repair. Although it is well known that NSC divide in response to basic fibroblast growth factor (FGF‐2) and epidermal growth factor (EGF), cofactors necessary for survival and maintenance of a multipotent potential are still a matter of debate. In the current study, we examined the requirements for NSC proliferation and survival in vitro using the neurosphere culture system. Apotransferrin (TF), along with EGF and FGF‐2, was sufficient for the formation of primary neurospheres derived from embryonic rat cortices. The addition of low concentrations of insulin or insulin‐like growth factor‐1 (IGF‐1) enhanced neurosphere size and number and was necessary for continued passaging. Both insulin and IGF‐1 acted at low concentrations, suggesting that their effects were mediated by their cognate receptors, both of which were expressed by neurosphere cultures. Sphere‐forming progenitors survived for long periods in culture without EGF or FGF‐2 when either insulin or IGF‐1 was added to the media. Cell cycle analysis determined that surviving progenitors were relatively quiescent during the period without mitogens. Upon the reintroduction of EGF and FGF‐2, surviving progenitors gave rise to new spheres that produced largely glial‐restricted progeny compared with sister cultures. These data indicate that the neurogenic potential of NSC may be intimately linked to a continuous exposure to mitogens. © 2008 Wiley‐Liss, Inc.