Department of Perioperative Medicine, Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA.
National Institute of Neurological Disorders and Stroke, Flow and Imaging Cytometry Core Facility, Bethesda, MD 20892, USA.
Exp Neurol. 2023 Dec;370:114552. doi: 10.1016/j.expneurol.2023.114552. Epub 2023 Oct 2.
Inherited painless neuropathies arise due to genetic insults that either block the normal signaling of or destroy the sensory afferent neurons in the dorsal root ganglion (DRG) responsible for transducing noxious stimuli. Complete loss of these neurons leads to profound insensitivity to all sensory modalities including pain. Hereditary sensory and autonomic neuropathy type 2 (HSNAII) is a rare genetic neuropathy characterized by a progressive distal early onset sensory loss. This syndrome is caused by autosomal recessive mutations in the with-no-lysine protein kinase 1 (WNK1) serine-threonine kinase gene. Of interest, disease-associated mutations are found in the large exon, termed "HSN2," which encodes a 498 amino acid domain C-terminal to the kinase domain. These mutations lead to truncation of the HSN2-containing proteins through the addition of an early stop codon (nonsense mutation) leading to loss of the C-terminal domains of this large protein. The present study evaluates the transcripts, gene structure, and protein structure of HSN2-containing WNK1 splice variants in DRG and spinal cord in order to establish the basal expression patterns of WNK1 and HSN2-containing WNK1 splice variants using multiplex fluorescent situ hybridization. We hypothesized that these transcripts would be enriched in pain-sensing DRG neurons, and, potentially, that enrichment in nociceptive neurons was responsible for the painless phenotypes observed. However, our in-depth analyses revealed that the HSN2-WNK1 splice variants were ubiquitously expressed but were not enriched in tachykinin 1-expressing C-fiber neurons, a class of neurons with a highly nociceptive character. We subsequently identified other subpopulations of DRG neurons with higher levels of HSN2-WNK1 expression, including mechanosensory large fibers. These data are inconsistent with the hypothesis that this transcript is enriched in nociceptive fibers, and instead suggest it may be related to general axon maintenance, or that nociceptive fibers are more sensitive to the genetic insult. These findings clarify the molecular and cellular expression pattern of this painless neuropathy gene in human tissue.
遗传性无痛神经病是由于遗传损伤引起的，这些损伤要么阻断了负责转导有害刺激的背根神经节 (DRG) 中感觉传入神经元的正常信号，要么破坏了这些神经元。这些神经元的完全丧失导致对所有感觉模式（包括疼痛）的深度不敏感。遗传性感觉和自主神经病 2 型 (HSNAII) 是一种罕见的遗传性神经病，其特征是进行性远端早期感觉丧失。这种综合征是由常染色体隐性突变引起的无赖氨酸蛋白激酶 1 (WNK1) 丝氨酸-苏氨酸激酶基因。有趣的是，在称为“HSN2”的大外显子中发现了与疾病相关的突变，该外显子编码激酶结构域 C 末端的 498 个氨基酸结构域 C 末端。这些突变通过添加早期终止密码子（无义突变）导致 HSN2 包含的蛋白质截断，从而导致该大蛋白的 C 末端结构域缺失。本研究评估了 DRG 和脊髓中包含 HSN2 的 WNK1 剪接变体的转录物、基因结构和蛋白质结构，以便使用多重荧光原位杂交法确定 WNK1 和包含 HSN2 的 WNK1 剪接变体的基本表达模式。我们假设这些转录物在痛觉感受性 DRG 神经元中丰富，并且，潜在地，在伤害感受神经元中的富集是导致观察到的无痛表型的原因。然而，我们的深入分析表明，HSN2-WNK1 剪接变体广泛表达，但在速激肽 1 表达的 C 纤维神经元中没有富集，C 纤维神经元是一类具有高度伤害感受特性的神经元。随后，我们鉴定了 DRG 神经元中的其他亚群，这些亚群具有更高水平的 HSN2-WNK1 表达，包括机械感觉大纤维。这些数据与该转录物在伤害感受纤维中富集的假说不一致，而是表明它可能与一般轴突维持有关，或者伤害感受纤维对遗传损伤更敏感。这些发现阐明了这种无痛神经病基因在人体组织中的分子和细胞表达模式。
