The Inhibitory Role Of TIP30 In Oligodendroglia Differentiation

Myelin enables incontinuous isolation along axons which leads to a decrease in the threshold for neuronal cell activation and an increase in axon conduction velocity. CNS myelinating cells, oligodendrocytes capacitate formation of myelin and transilient nerve conduction. Oligodendrocyte development undergoes three major stages including:A2B5+ progenitor cells, immature platelet-derived growth factor receptor a (PDGFRa)+ and O4+ oligodendrocytes, and mature myelinating oligodendrocytes that express myelinassociated glycoprotein (MAG), MBP and myelin oligodendrocyte glycoprotein (MOG). Most oligodendrocytes develop during embryogenesis and early postnatal life from restricted periventricular germinal regions. Differentiation of oligodendrocyte precursor cells (OPCs) is a prerequisite for both developmental myelination and adult myelination or remyelination in the central nervous system (CNS). Significant advances in our understanding of oligodendrocyte development have taken place in the recent decades. In particular, identification and functional characterization of Oligl and Olig2, a pair of basic helix-loop-helix (bHLH) transcription factors specificly expressed in oligodendroclia that regulate key stages of early oligodendrocyte development, has provided critical insight into the origins of OPCs, as well as their relationship to other CNS lineages. Further investigation of the subcellular localization of these two transcription factors shows that compared with the permanent nuclear localization of Olig2, the subcellular localization of Oligl dynamically changes as the developmental ages. During the embryonic stage and early stage in the postnatal days, Oligl is located in the nucleus of OPCs, and translocated into the cytoplasm as the time going on. While in mature oligodendrocytes in the adult stages, Oligl is predominantly located in the mature oligodendrocyte cytoplasm within the normal brain. In the adult spinal cord, Oligl also exhibits multifarious subcellular localization in oligodendrocyte lineage cells. In cuprizone induced demyelination or experimental autoimmune encephalomyelitis model, Oligl is localized in the nucleus of NG2+cells in demyelinated lesions of corpus callosum or spinal cord. Is there any connection between the intracellular localization of Oligl and the differentiation procedure? This scientific question still remains largely unknown.The thirty-kDa HIV-1 Tat interacting protein (TIP30), also named CC3 or HTIP2, can inhibit Importin β-mediated nuclear import of substrates with different types of import signals and was first identified as a putative metastasis suppressor of variant small cell lung carcinoma. The TIP30 gene localizes in human chromosome 11p15.1, which plays a negative role in tumorigenesis of various kinds of organisms. When proteins need to function in the nucleus, this cytoplasmic-nuclear transportation shouled be precisely regulated. Karyopherin protein Importin β works by interacting with its cargoes directly or indirectly with the help of adapter proteins to transport proteins into the nucleus. The sequence of Oligl contains nuclear localization sequences (NLS), but we have not known whether its nuclear-cytoplasmic localization could be regulated by TIP30.In this study, we have found that the thirty-kDa HIV-1 Tat interacting protein (TIP30) plays a negative role in oligodendrocyte development. Immunocytochemistry reveals that TIP30 expresses in the whole life of oligodendroglia. QPCR analysis indicates that TIP30 mRNA level decrease at postnatal day 21, when myelin formation to the peak point. The TIP30 knock-out mice exhibit significantly high level of myelin protein at postnatal day 14 and 21, compared with the wild type mice. In a primary OPC culture system in vitro, we demonstrated that TIP30 overexpression dramatically inhibited OPC differentiation, while down-regulation of TIP30 promoted the differentiation of oligodendroglia remarkably. What is the mechanism of the inhibitory role for TIP30 in OPC differentiation and myelination? By means of nuclear-cytoplasmic fragment extraction and immunocytochemistry, we found that overexpression of TIP30 was able to sequester Oligl in the cytoplasm and inhibited its nuclear translocation, whereas down-regulation of TIP30 increased the level Olig1 in the nucleus in the early stage during OPC differentiation in vitro. These results may be explained by co-immunoprecipitation assay that the interaction exhists between TIP30 and Oligl. In the end, we studied the role of TIP30 mediating the intracellular localization of Oligl in demyelinated conditions. In the cuprizone-induced demyelination model with the ability of thoroughly remyelination when cuprizone withdraw, NG2+ cells with nuclear location of Oligl largely accumulated in the corpus callosum during remyelination stage. While in chronic demyelinated lesions of multiple sclerosis (MS), there was abnormally high level of TIP30 in NG2+ cells, and few nuclear Oligl was found in these cells.Taken together, our findings suggest that the intracellular regulator TIP30 plays a negative regulatory role in oligodendroglial differentiation via mediating the nuclear-cytoplasmic localization of Oligl. This research will improve our understanding of remyelination mechanism to some extent.