Abstract：
Trigeminal neuralgia (TN) is a unique pain disorder characterized by intense paroxysmal facial pain within areas innervated by the trigeminal nerve. Although most cases of TN are sporadic, familial clusters of TN suggest that genetic factors may contribute to this disorder. Whole-exome sequencing in patients with TN reporting positive family history demonstrated a spectrum of variants of ion channels including TRP channels. Here, we used patch-clamp analysis and Ca2+ and Na+ imaging to assess a rare variant in the TRPM7 channel, p.Ala931Thr, within transmembrane domain 3, identified in a man suffering from unilateral TN. We showed that A931T produced an abnormal inward current carried by Na+ and insensitive to the pore blocker Gd3+. Hypothesizing that replacement of the hydrophobic alanine at position 931 with the more polar threonine destabilizes a hydrophobic ring, near the voltage sensor domain, we performed alanine substitutions of F971 and W972 and obtained results suggesting a role of A931-W972 hydrophobic interaction in S3-S4 hydrophobic cleft stability. Finally, we transfected trigeminal ganglion neurons with A931T channels and observed that expression of this TRPM7 variant lowers current threshold and resting membrane potential, and increases evoked firing activity in TG neurons. Our results support the notion that the TRPM7-A931T mutation located in the S3 segment at the interface with the transmembrane region S4, generates an omega current that carries Na+ influx in physiological conditions. A931T produces hyperexcitability and a sustained Na+ influx in trigeminal ganglion neurons that may underlie pain in this kindred with trigeminal neuralgia.
摘要：
三叉神经痛（TN）是一种独特的疼痛障碍，其特征是在三叉神经支配的区域内出现剧烈的阵发性面部疼痛。虽然大多数TN病例是零星的，TN家族簇表明遗传因素可能导致这种疾病。报告阳性家族史的TN患者的全外显子组测序显示了一系列离子通道变体，包括TRP通道。这里,我们使用膜片钳分析和Ca2+和Na+成像来评估TRPM7通道中的罕见变异，p.Ala931Thr,在跨膜结构域3内，在患有单侧TN的男性中鉴定。我们表明，A931T产生了Na携带的异常内向电流，并且对孔阻断剂Gd3不敏感。假设用极性更大的苏氨酸替换931位的疏水丙氨酸会使疏水环不稳定，在电压传感器域附近，我们对F971和W972进行了丙氨酸取代,获得的结果表明A931-W972疏水相互作用在S3-S4疏水裂隙稳定性中的作用.最后,我们用A931T通道转染三叉神经节神经元，观察到这种TRPM7变体的表达降低了电流阈值和静息膜电位，并增加TG神经元的诱发放电活动。我们的结果支持这样的观点，即位于S3区段与跨膜区S4的界面处的TRPM7-A931T突变会产生欧米茄电流，该欧米茄电流在生理条件下携带Na内流。A931T在三叉神经节神经元中产生过度兴奋和持续的Na流入，这可能是这种三叉神经痛的疼痛的基础。
