Initiation of Dopaminergic Differentiation of Nurr1 − Mesencephalic Precursor Cells Depends on Activation of Multiple Mitogen‐Activated Protein Kinase Pathways

Interleukin‐1 (IL‐1) plays a pivotal role in terminal dopaminergic differentiation of midbrain‐derived neural precursor cells already committed to the mesencephalic dopaminergic phenotype (named mdNPCs for mesencephalic dopaminergic neural precursor cells). Here we characterized the molecular events in long‐term expanded rat nuclear receptor related‐1 − (Nurr1 − ) mdNPCs in response to IL‐1β during their terminal dopaminergic specification. We showed that IL‐1β induced a rapid induction of mRNA of dopaminergic key fate‐determining transcription factors, such as Nurr1 and Pitx3, and a subsequent increase of tyrosine hydroxylase protein as an early marker for dopaminergic neurons in vitro. These effects of IL‐1β were specific for mdNPCs and were not observed in striatal neural precursor cells (NPCs). Surprisingly, IL‐1β did not activate the NF‐κB pathway or the transcription factor activating protein 1 (AP‐1), but inhibition of nuclear translocation of NF‐κB by SN50 facilitated IL‐1β‐induced Nurr1 expression and dopaminergic differentiation of mdNPCs. Incubation of mdNPCs with IL‐1β led to a rapid phosphorylation of ERK1/2 and p38 mitogen‐activated protein (MAP) kinases within 1 to 3 hours, whereas Jun kinase was not phosphorylated in response to IL‐1β. Consistently, inhibition of the ERK1/2 pathway or p38 MAP kinase blocked Nurr1 upregulation and further dopaminergic specification of mdNPCs, but not differentiation into MAP2ab + neurons. IL‐1 receptor antagonist did not block early dopaminergic differentiation events, suggesting that the effects of IL‐1β are not mediated through activation of IL‐1 receptor type I. Our results indicate that induction of terminal dopaminergic specification of Nurr1 − mdNPCs by IL‐1β depends on activation of the ERK1/2 and p38 MAP kinase pathway. STEM CELLS 2009;27:2009–2021