From Aix-Marseille Université, CNRS, Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille-UMR7286, 13344 Marseille, France.
J Biol Chem. 2014 Mar 14;289(11):7907-18. doi: 10.1074/jbc.M113.528489. Epub 2014 Feb 4.
Cell adhesion molecules (CAMs) play a crucial role in the formation of the nodes of Ranvier and in the rapid propagation of the nerve impulses along myelinated axons. These CAMs are the targets of autoimmunity in inflammatory neuropathies. We recently showed that a subgroup of patients with aggressive chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) shows autoantibodies to contactin (1). The complex of contactin·Caspr·neurofascin-155 (NF155) enables the formation of paranodal junctions, suggesting that antibody attack against paranodes may participate in the severity of CIDP. In the present study, we mapped the molecular determinants of contactin targeted by the autoantibodies. In three patients, immunoreactivity was directed against the Ig domains of contactin and was dependent on N-glycans. The serum of one patient was selectively directed against contactin bearing mannose-rich N-glycans. Strikingly, the oligomannose type sugars of contactin are required for association with its glial partner NF155 (2). To investigate precisely the role of contactin N-glycans, we have mutated each of the nine consensus N-glycosylation sites independently. We found that the mutation of three sites (N467Q/N473Q/N494Q) in Ig domain 5 of contactin prevented soluble NF155-Fc binding. In contrast, these mutations did not abolish cis-association with Caspr. Next, we showed that the cluster of N-glycosylation sites (Asn-467, Asn-473, and Asn-494) was required for immunoreactivity in one patient. Using cell aggregation assays, we showed that the IgGs from the four CIDP patients prevented adhesive interaction between contactin·Caspr and NF155. Importantly, we showed that the anti-contactin autoantibodies induced alteration of paranodal junctions in myelinated neuronal culture. These results strongly suggest that antibodies to CAMs may be pathogenic and induce demyelination via functional blocking activity.
细胞黏附分子（CAMs）在郎飞结的形成和有髓轴突中神经冲动的快速传递中起着至关重要的作用。这些 CAMs 是炎症性神经病中自身免疫的靶标。我们最近表明，一组侵袭性慢性炎症性脱髓鞘性多发性神经病（CIDP）患者的自身抗体针对接触蛋白（1）。接触蛋白· Caspr·神经束蛋白 155（NF155）复合物能够形成连接蛋白结，这表明针对连接蛋白结的抗体攻击可能参与 CIDP 的严重程度。在本研究中，我们绘制了针对自身抗体的接触蛋白的分子决定簇。在三名患者中，免疫反应性针对接触蛋白的 Ig 结构域，并且依赖于 N-糖基化。一名患者的血清选择性针对富含甘露糖的 N-糖基化的接触蛋白。引人注目的是，接触蛋白与其神经束蛋白 155（2）的伴侣结合需要寡甘露糖型糖。为了精确研究接触蛋白 N-糖基化的作用，我们独立地突变了每个 9 个共识 N-糖基化位点。我们发现，Ig 结构域 5 中的三个位点（N467Q/N473Q/N494Q）的突变阻止了可溶性 NF155-Fc 的结合。相比之下，这些突变并没有消除与 Caspr 的顺式结合。接下来，我们表明，一个患者的免疫反应性需要 N-糖基化位点簇（Asn-467、Asn-473 和 Asn-494）。使用细胞聚集测定，我们表明来自四名 CIDP 患者的 IgG 阻止了接触蛋白· Caspr 和 NF155 之间的粘附相互作用。重要的是，我们表明针对接触蛋白的自身抗体诱导了髓鞘神经元培养中连接蛋白结的改变。这些结果强烈表明，针对 CAM 的抗体可能是致病的，并通过功能阻断活性诱导脱髓鞘。
