ABSTRACT
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-1beta during their terminal dopaminergic specification. We showed that IL-1beta 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-1beta were specific for mdNPCs and were not observed in striatal neural precursor cells (NPCs). Surprisingly, IL-1beta did not activate the NF-kappaB pathway or the transcription factor activating protein 1 (AP-1), but inhibition of nuclear translocation of NF-kappaB by SN50 facilitated IL-1beta-induced Nurr1 expression and dopaminergic differentiation of mdNPCs. Incubation of mdNPCs with IL-1beta 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-1beta. 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-1beta 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-1beta depends on activation of the ERK1/2 and p38 MAP kinase pathway.
Subject(s)
MAP Kinase Signaling System/physiology , Mesencephalon/cytology , Mitogen-Activated Protein Kinases/metabolism , Neurons/cytology , Neurons/enzymology , Animals , Cell Differentiation/physiology , Cell Growth Processes/physiology , Cells, Cultured , DNA-Binding Proteins/metabolism , Immunohistochemistry , Interleukin-1beta/pharmacology , Mesencephalon/drug effects , Mesencephalon/metabolism , NF-kappa B/metabolism , Neurons/drug effects , Nuclear Receptor Subfamily 4, Group A, Member 2/deficiency , Nuclear Receptor Subfamily 4, Group A, Member 2/metabolism , Phenotype , Rats , Receptors, Interleukin-1 Type I/biosynthesisABSTRACT
In previous studies, we demonstrated functional neuronal and dopaminergic differentiation of fetal mesencephalic neural precursor cells. The major factors for orienting their progeny towards a dopaminergic phenotype are forskolin and interleukin-1beta. Here, we investigated the effects of dexamethasone (10 microM) on neuronal and glial differentiation. Exposure of mesencephalic neural precursor cells to dexamethasone significantly reduces the amount of glial fibrillary acidic protein astroglia, but not of galactocerebrosidase C oligodendroglia, MAP2ab neurons and tyrosine hydroxylase dopaminergic cells. Presuming a possible involvement of the nuclear factor-kappaB pathway, we examined the effects of wortmannin (phosphatidylinositol 3'-kinase inhibitor) and SN50 (nuclear factor-kappaB inhibitor) on gliogenesis. Both wortmannin and SN50 mimicked the effects of dexamethasone suggesting that dexamethasone specifically blocks astroglial differentiation from mesencephalic neural precursor cells most likely via inhibition of the nuclear factor-kappaB pathway.
