Abnormal expression of TIP30 and arrested nucleocytoplasmic transport within oligodendrocyte precursor cells in multiple sclerosis
Jin Nakahara, Kohsuke Kanekura, Mikiro Nawa, Sadakazu Aiso, Norihiro Suzuki
Jin Nakahara, Kohsuke Kanekura, Mikiro Nawa, Sadakazu Aiso, Norihiro Suzuki
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Research Article

Abnormal expression of TIP30 and arrested nucleocytoplasmic transport within oligodendrocyte precursor cells in multiple sclerosis

Abstract

Oligodendrocyte precursor cells (OPCs) persist near the demyelinated axons arising in MS but inefficiently differentiate into oligodendrocytes and remyelinate these axons. The pathogenesis of differentiation failure remains elusive. We initially hypothesized that injured axons fail to present Contactin, a positive ligand for the oligodendroglial Notch1 receptor to induce myelination, and thus tracked axoglial Contactin/Notch1 signaling in situ, using immunohistochemistry in brain tissue from MS patients containing chronic demyelinated lesions. Instead, we found that Contactin was saturated on demyelinated axons, Notch1-positive OPCs accumulated in Contactin-positive lesions, and the receptor was engaged, as demonstrated by cleavage to Notch1-intracellular domain (NICD). However, nuclear translocalization of NICD, required for myelinogenesis, was virtually absent in these cells. NICD and related proteins carrying nuclear localization signals were associated with the nuclear transporter Importin but were trapped in the cytoplasm. Abnormal expression of TIP30, a direct inhibitor of Importin, was observed in these OPCs. Overexpression of TIP30 in a rat OPC cell line resulted in cytoplasmic entrapment of NICD and arrest of differentiation upon stimulation with Contactin-Fc. Our results suggest that extracellular inhibitory factors as well as an intrinsic nucleocytoplasmic transport blockade within OPCs may be involved in the pathogenesis of remyelination failure in MS.

Authors

Jin Nakahara, Kohsuke Kanekura, Mikiro Nawa, Sadakazu Aiso, Norihiro Suzuki

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Figure 5

TIP30-positive cells are substantially increased in chronically demyelinated plaques.

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TIP30-positive cells are substantially increased in chronically demyelin...
(A and B) Two consecutive sections were chosen for each MS case, and 1 was stained with LFB plus NFR to identify chronically demyelinated plaques and remyelinating shadow plaques (demarcated by broken line), while the other was double-labeled against NICD and TIP30 (occipital lobe cerebral lesion from 51-year-old female with secondary progressive MS is shown). (C) A photograph at higher magnification from a remyelinating shadow plaque in B showing nuclear NICD–positive cells (arrows; the majority of these cells were positive for nuclear Olig1, an OPC marker [ref. 24] as shown in inset). (D) A photograph at higher magnification from a chronically demyelinated plaque in B, showing cytoplasmic TIP30 (cytoplasmic NICD–aggregated) cells (arrowheads). (E and F) Graphs showing results of statistical analysis for the densities of nuclear NICD–positive cells and cytoplasmic TIP30–positive (cytoplasmic NICD–aggregated) cells, respectively. Data representing the same specimens are connected with lines. Bold lines indicate the average of results from 9 specimens. Circles indicate relapse-remitting MS, triangles indicate secondary-progressive MS, and X’s indicate primary-progressive MS. The difference in the density of nuclear NICD–positive cells between chronically demyelinated plaques and remyelinating shadow plaques was not statistically significant (P = 0.069; note that nuclear NICD is rapidly turned over and therefore difficult to detect; see main text), whereas a significant increase in the density of TIP30-positive cells was noted in chronically demyelinated plaques when compared with remyelinating shadow plaques (P = 0.024). Scale bars: 200 μm (A and B); 50 μm (C and D); 20 μm (insets in C).