Retinoic acid and neurotrophins collaborate to regulate neurogenesis in adult-derived neural stem cell cultures

TLDR

Adult rat hippocampal stem cells can self‑renew and generate neurons and glia in vitro, yet the molecular cues governing their differentiation are poorly understood. The authors employed hippocampal stem cell clones to assess how retinoic acid modulates neuronal differentiation. Retinoic acid rapidly up‑regulates NeuroD and p21, induces cell‑cycle exit, triples immature neuron numbers, and increases Trk receptor expression, and subsequent neurotrophin treatment drives maturation of these neurons into diverse transmitter phenotypes, showing that RA and neurotrophins act at distinct neurogenesis stages. © 1999 John Wiley & Sons, Inc., J Neurobiol 38:65–81.

Abstract

The adult rat hippocampus contains fibroblast growth factor 2–responsive stem cells that are self-renewing and have the ability to generate both neurons and glia in vitro, but little is known about the molecular events that regulate stem cell differentiation. Hippocampus-derived stem cell clones were used to examine the effects of retinoic acid (RA) on neuronal differentiation. Exposure to RA caused an immediate up-regulation of NeuroD, increased p21 expression, and concurrent exit from cell cycle. These changes were accompanied by a threefold increase in the number of cells differentiating into immature neurons. An accompanying effect of RA was to sustain or up-regulate trkA, trkB, trkC, and p75NGFR expression. Without RA treatment, cells were minimally responsive to neurotrophins (NTs), whereas the sequential application of RA followed by brain-derived neurotrophic factor or NT-3 led to a significant increase in neurons displaying mature γ-a-minobutyric acid, acetylcholinesterase, tyrosine hydroxylase, or calbindin phenotypes. Although NTs promoted maturation, they had little effect on the total number of neurons generated, suggesting that RA and neurotrophins acted at distinct stages in neurogenesis. RA first promoted the acquisition of a neuronal fate, and NTs subsequently enhanced maturation by way of RA-dependent expression of the Trk receptors. In combination, these sequential effects were sufficient to stimulate stem cell–derived progenitors to differentiate into neurons displaying a variety of transmitter phenotypes. © 1999 John Wiley & Sons, Inc. J Neurobiol 38: 65–81, 1999