Neurogenesis versus gliogenesis : study on neuronal-glial differentiation switch
Date of Issue2014
School of Biological Sciences
The adult glial precursor cells were recently shown to be able to produce neurons in central nervous system (CNS) and to obtain multipotental ability in vitro. These findings suggest that glial precursors are not irreversibly committed into one distinct fate and still can be converted to other lineages. This is of great significance for neuronal replacement during various neurological disorders by reprogramming of glial progenitors into neuronal differentiation. Although the fate determination of glial precursors was studied extensively, the signals and factors, which could redirect their fate to become neurons, still remained unknown. To elucidate the mechanisms underlying this remarkable ability of glial precursor cells, we modified the gene expression profile in NG2+ glial precursor cells using enhanced retroviral mutagen (ERM) technique followed by phenotype screening to identify possible gene(s) responsible for glial and neuronal cell fate detem1ination. Among the identified molecules, we found the gene named nonmetastatic cell l which encodes a nucleoside diphosphate kinase protein A (Nm23-Ml or NMEl). So far, the Nm23 members have been shown to be involved in various molecular processes including tumor metastasis, cell proliferation, differentiation and cell fate determination. In the present study, we provide evidence suggesting the role of NMEl in glial and neuronal cell fate determination in vitro. We showed that NMEl is widely expressed in neuronal structures throughout adult mouse CNS. Our immunohistochemical results revealed that NME 1 is strongly co locali zed with mature neuronal marker through white matter of spinal cord and brain. Interestingly, NMEl overexpress10n m oligodendrocyte precursor OLN-93 cells potently induced the acquisition of neuronal phenotype, while its silencing was shown to promote oligodendrocyte differentiation. Here we further demonstrate that NME 1 overexpression promotes neuronal differentiation of oligodendrocyte precursor OLN-93 cells through Pcatenin signaling pathway. We found that Wnt agonist (LiCI) treatment inhibits the proliferation and accelerates the neuronal differentiation of induced neuronal cells (iN cells). Moreover, we demonstrate that NMEl overexpression increases the phosphorylation of glycogen synthase kinase 3beta (GSK-3beta) and causes to the beta-catenin stabilisation in a manner similar to Wnt canonical signaling pathway. This effect was further confirmed by dominant negative TCF4 (DN-TCF4) transfection. Since NMEl overexpression does not affect the expression of Wnt molecules and their receptors, our co-immunoprecipitation experiments reveal that NME 1 is able to interact with GSK-3beta directly. Therefore, our findings indicate a novel regulatory role of NME 1 in driving glial precursor cells to neurons through beta-catenin signaling pathway.