Ca2+ toxicity due to reverse Na+/Ca2+ exchange contributes to degeneration of neurites of DRG neurons induced by a neuropathy-associated Nav1.7 mutation
Ca2+ toxicity due to reverse Na+/Ca2+ exchange contributes to degeneration of neurites of DRG neurons induced by a neuropathy-associated Nav1.7 mutation
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DOI：
10.1152/jn.00195.2015
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发表时间：
2015-09-01
影响因子：
2.5
通讯作者：
Waxman, S. G.
中科院分区：
文献类型：
--
作者：
Estacion, M.;Vohra, B. P. S.;Waxman, S. G.
电压门控钠通道Nav1.7中的功能获得性错义突变与小纤维神经病有关，其特征在于烧灼痛、自主神经功能障碍和表皮内神经纤维的丧失。然而，连接Nav1.7突变轴突变性的机制级联并不完全清楚。Nav1.7中的G856 D突变产生通道生物物理性质的稳健变化，包括超极化激活、去极化失活以及增强的斜坡电流和持续电流，这有助于含有Nav1.8的神经元表现出的超兴奋性。我们在这里报告，与野生型（WT）Nav1.7表达神经元相比，G856 D转染的背根神经节（DRG）神经元的胞体和神经突显示出高[K+]刺激后细胞内Na+浓度（[Na+]）和细胞内[Ca 2 +]水平的增加。阻断钠/钙交换器（NCX）或钠通道的反向模式可减弱G856 D表达DRG细胞体和神经突中高[K+]诱发的[Ca 2 +]瞬变。我们还发现，用高[K+]或2-脱氧葡萄糖（2-DG）处理WT或G856 D表达的神经突不会引起这些神经突的变性，但是高[K+]和2-DG的组合引起G856 D神经突的变性，而不是WT神经突。我们的研究结果还表明，0 Ca 2+或阻断NCX的反向模式保护G856 D表达的神经突在暴露于高[K+]和2-DG时免于变性。这些结果表明，表达突变体G856 D Nav1.7的DRG神经元中的[Na+]过载，其触发NCX的反向模式并导致Ca 2+毒性，并表明亚型特异性阻断Nav1.7或抑制反向NCX作为可能减缓或预防小纤维神经病中轴突变性的策略。
Gain-of-function missense mutations in voltage-gated sodium channel Nav1.7 have been linked to small-fiber neuropathy, which is characterized by burning pain, dysautonomia and a loss of intraepidermal nerve fibers. However, the mechanistic cascades linking Nav1.7 mutations to axonal degeneration are incompletely understood. The G856D mutation in Nav1.7 produces robust changes in channel biophysical properties, including hyperpolarized activation, depolarized inactivation, and enhanced ramp and persistent currents, which contribute to the hyperexcitability exhibited by neurons containing Nav1.8. We report here that cell bodies and neurites of dorsal root ganglion (DRG) neurons transfected with G856D display increased levels of intracellular Na+ concentration ([Na+]) and intracellular [Ca2+] following stimulation with high [K+] compared with wild-type (WT) Nav1.7-expressing neurons. Blockade of reverse mode of the sodium/calcium exchanger (NCX) or of sodium channels attenuates [Ca2+] transients evoked by high [K+] in G856D-expressing DRG cell bodies and neurites. We also show that treatment of WT or G856D-expressing neurites with high [K+] or 2-deoxyglucose (2-DG) does not elicit degeneration of these neurites, but that high [K+] and 2-DG in combination evokes degeneration of G856D neurites but not WT neurites. Our results also demonstrate that 0 Ca2+ or blockade of reverse mode of NCX protects G856D-expressing neurites from degeneration when exposed to high [K+] and 2-DG. These results point to [Na+] overload in DRG neurons expressing mutant G856D Nav1.7, which triggers reverse mode of NCX and contributes to Ca2+ toxicity, and suggest subtype-specific blockade of Nav1.7 or inhibition of reverse NCX as strategies that might slow or prevent axon degeneration in small-fiber neuropathy.