Brn4 and TH synergistically promote the differentiation of neural stem cells into dopaminergic neurons

Neural stem cells (NSCs) are pluripotent cells capable of differentiation into dopaminergic (DA) neurons, which are the major cell types damaged in Parkinson's disease (PD). Therefore, NSCs are considered the most promising cell source for cell replacement therapy of PD. However, the poor differentiation and maturation of DA neurons and decreased cell survival after transplantation are a challenge. We have previously demonstrated that Brn4, a member of the POU domain family of transcription factors, induced the differentiation of NSCs into neurons and promoted their maturation. In this study, we directly transduced tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine biosynthesis, into NSCs to induce DA neuronal differentiation. However, these DA neurons were morphologically immature and seldom expressed dopamine transporter (DAT), a late marker of mature DA neurons. In contrast, TH co-transfected with Brn4 generated increased number of mature DA neurons. Furthermore, Brn4 significantly induced the expression of glial cell line-derived neurotrophic factor (GDNF) with its receptors GFRα-1 and Ret, which may contribute to the maturation and survival of differentiated DA neurons. Our findings may be of future importance for the use of NSCs in cell replacement therapy of PD.