TUBB4A mutations result in specific neuronal and oligodendrocytic defects that closely match clinically distinct phenotypes
TUBB4A mutations result in specific neuronal and oligodendrocytic defects that closely match clinically distinct phenotypes
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DOI：
10.1093/hmg/ddx338
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发表时间：
2017-11-15
影响因子：
3.5
通讯作者：
Vanderver, Adeline
中科院分区：
文献类型：
--
作者：
Curiel, Julian;Bey, Guillermo Rodriguez;Vanderver, Adeline
髓鞘减少性白质营养不良是一种遗传性疾病，定义为脑髓鞘发育不足，但其细胞机制通常知之甚少。TUBB4A基因突变编码微管蛋白亚型微管蛋白β类IVA(Tubb4a)，导致髓鞘过少伴基底节和小脑萎缩(H-ABC)的症状复合体。此外，已知TUBB4A突变会导致广泛的表型谱，从原发性肌张力障碍(DYT4)，孤立性髓鞘减少伴痉挛四肢瘫痪，以及婴儿起病，这表明可能涉及多种细胞类型。我们研究了导致H-ABC(p.Asp249Asn)、DYT4(p.Arg2Gly)的TUBB4A突变对细胞的影响，该突变是一种严重的合并髓鞘过少和脑病的表型(p.Asn414Lys)，以及导致孤立的髓鞘过少的较轻表型(p.Val255Ile和p.Arg282Pro)。我们使用了组织病理学、生化和细胞方法的组合来确定这些不同的突变如何在神经元和/或少突胶质细胞中产生不同的细胞效应。我们的结果表明，特定的突变会导致纯神经元、混合神经元和少突胶质细胞或纯少突胶质细胞缺陷，这些缺陷与它们各自的临床表型非常匹配。因此，导致神经元功能障碍表型的DYT4突变导致神经元形态改变，但微管蛋白数量和聚合没有变化，少突胶质细胞形态和髓鞘基因表达正常。相反，与单独的髓鞘过少相关的突变(p.Val255Ile和p.Arg282Pro)和严重的联合表型(p.Asn414Lys)导致正常的神经元形态，但与少突胶质细胞形态、髓鞘基因表达和微管功能障碍相关。H-ABC突变(p.Asp249Asn)表现为神经元和髓鞘相结合的表型，在体外有重叠的细胞缺陷，涉及神经元和少突胶质细胞类型。只有导致髓鞘下化表型的突变才表现出微管动力学改变，并通过显性毒性作用机制发挥作用。DYT4突变对微管动力学没有影响，提示有不同的作用机制。总之，与TUBB4A相关的不同临床表型反映了致病突变的选择性和特异性细胞效应。疾病发病机制的细胞特异性与开发针对这种致残疾病的靶向治疗有关。
Hypomyelinating leukodystrophies are heritable disorders defined by lack of development of brain myelin, but the cellular mechanisms of hypomyelination are often poorly understood. Mutations in TUBB4A, encoding the tubulin isoform tubulin beta class IVA (Tubb4a), result in the symptom complex of hypomyelination with atrophy of basal ganglia and cerebellum (H-ABC). Additionally, TUBB4A mutations are known to result in a broad phenotypic spectrum, ranging from primary dystonia (DYT4), isolated hypomyelination with spastic quadriplegia, and an infantile onset encephalopathy, suggesting multiple cell types may be involved. We present a study of the cellular effects of TUBB4A mutations responsible for H-ABC (p.Asp249Asn), DYT4 (p.Arg2Gly), a severe combined phenotype with hypomyelination and encephalopathy (p.Asn414Lys), as well as milder phenotypes causing isolated hypomyelination (p.Val255Ile and p.Arg282Pro). We used a combination of histopathological, biochemical and cellular approaches to determine how these different mutations may have variable cellular effects in neurons and/or oligodendrocytes. Our results demonstrate that specific mutations lead to either purely neuronal, combined neuronal and oligodendrocytic or purely oligodendrocytic defects that closely match their respective clinical phenotypes. Thus, the DYT4 mutation that leads to phenotypes attributable to neuronal dysfunction results in altered neuronal morphology, but with unchanged tubulin quantity and polymerization, with normal oligodendrocyte morphology and myelin gene expression. Conversely, mutations associated with isolated hypomyelination (p.Val255Ile and p.Arg282Pro) and the severe combined phenotype (p.Asn414Lys) resulted in normal neuronal morphology but were associated with altered oligodendrocyte morphology, myelin gene expression, and microtubule dysfunction. The H-ABC mutation (p.Asp249Asn) that exhibits a combined neuronal and myelin phenotype had overlapping cellular defects involving both neuronal and oligodendrocyte cell types in vitro. Only mutations causing hypomyelination phenotypes showed altered microtubule dynamics and acted through a dominant toxic gain of function mechanism. The DYT4 mutation had no impact on microtubule dynamics suggesting a distinct mechanism of action. In summary, the different clinical phenotypes associated with TUBB4A reflect the selective and specific cellular effects of the causative mutations. Cellular specificity of disease pathogenesis is relevant to developing targeted treatments for this disabling condition.