Lineage restriction of adult human olfactory-derived progenitors to dopaminergic neurons

Human adult olfactory epithelium contains neural progenitors (hONPs) which replace damaged cellular components throughout life. Methods to isolate and expand the hONPs which form neuronspheres in vitro have been developed in our laboratory. In response to morphogens, the hONPs differentiate along several neural lineages. This study optimized conditions for the differentiation of hONPs towards dopaminergic neurons. The hONPs were treated with Sonic hedgehog (Shh), in the presence or absence of retinoic acid (RA) and/or forskolin (FN). Transcription factors (Nurr1, Pitx3 and Lmx1a) that promote embryonic mouse or chicken dopaminergic development were employed to determine if they would modulate lineage restriction of these adult human progenitors. Four expression vectors (pIRES-Pitx3-Nurr1, pLN-CX2-Pitx3, pLN-CX2-Nurr1 and pLNCX2-Lmx1a) were transfected into the hONPs, respectively. Transcription factor expression and the rate-limiting enzyme in dopamine synthesis tyrosine hydroxylase (TH) were detected in the transfected cells after 4 month-selection with G418, indicating transfected hONPs were stably restricted towards a dopaminergic lineage. Furthermore, a dopamine enzyme immunoassay (EIA) was employed to detect the synthesis and release of dopamine. The most efficient transfection paradigm was determined. Several neurotrophic factors were detected in the pretransfected hONPs which have potential roles in the maintenance, survival and proliferation of dopaminergic neurons. Therefore the effect of transfection on the neurotrophin synthesis was examined. Transfection did not alter synthesis. The use of olfactory progenitors as a cell-based therapy for Parkinson’s disease (PD) would allow harvest without invasive surgery, provide an autologous cell population, eliminate need for immunosuppression and avoid the ethical concerns associated with embryonic tissues. This study suggests that specific transcription factors and treatment with morphogens can restrict human adult olfactory-derived progenitors to a dopaminergic neuronal lineage. Future studies will evaluate the utility of these unique cells in cell-replacement paradigms for the treatment of PD like animal models.