Progressive Cl- channel defects reveal disrupted skeletal muscle maturation in R6/2 Huntington's mice
Progressive Cl- channel defects reveal disrupted skeletal muscle maturation in R6/2 Huntington's mice
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DOI：
10.1085/jgp.201611603
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发表时间：
2017-01-01
影响因子：
3.8
通讯作者：
Voss, Andrew A.
中科院分区：
文献类型：
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作者：
Miranda, Daniel R.;Wong, Monica;Voss, Andrew A.
亨廷顿氏病（HD）患者患有进行性和衰弱性运动功能障碍。之前，我们发现R6/2转基因HD小鼠骨骼肌氯离子通道（ClC-1）电流、内整流钾离子通道电流和膜电容降低。ClC-1功能丧失与异常mRNA加工增加和全长ClC-1 mRNA （Clcn1基因）水平降低相关。从生理学上讲，由此产生的肌肉过度兴奋性可能有助于解释HD的不自主收缩。在这项研究中，研究了R6/2小鼠的这些缺陷的发生和进展，范围从3周龄（症状前）到9-13周龄（疾病晚期），并与年龄匹配的野生型（WT）兄弟姐妹进行了比较。R6/2 ClC-1电流密度和异常剪接的Clcn1 mRNA水平随年龄保持不变。相反，在WT小鼠中，随着年龄的增长，ClC-1电流密度增加，异常剪接的Clcn1 mRNA水平下降。在运动症状出现之前，R6/2 ClC-1的性质与WT不同，运动症状发生在5周龄。R6/2肌容量的相对下降也开始于5周龄小鼠，且与纤维萎缩无关。与WT肌肉相比，R6/2的Kir电流密度一直较低。不变的R6/2 ClC-1特性表明肌肉成熟中断，我们通过测量晚期R6/2骨骼肌中新生儿肌球蛋白重链（MyHC）水平升高证实了这一点。在发育较慢的Q175 HD小鼠中，ClC-1和MyHC亚型的类似变化表明，成熟状态的改变与成年发病的HD有关。最后，我们在R6/2肌肉中发现了肌盲样蛋白1的核聚集体，没有主要的CAG重复共定位。这与肌强直性营养不良不同，肌强直性营养不良是另一种具有类似ClC-1缺陷的三核苷酸重复疾病，这表明HD中mRNA剪接异常的新机制。这些早期和进行性骨骼肌缺陷揭示了疾病进展急需的周围生物标志物，并更好地阐明了HD肌病的机制。
Huntington's disease (HD) patients suffer from progressive and debilitating motor dysfunction. Previously, we discovered reduced skeletal muscle chloride channel (ClC-1) currents, inwardly rectifying potassium (Kir) channel currents, and membrane capacitance in R6/2 transgenic HD mice. The ClC-1 loss-of-function correlated with increased aberrant mRNA processing and decreased levels of full-length ClC-1 mRNA (Clcn1 gene). Physiologically, the resulting muscle hyperexcitability may help explain involuntary contractions of HD. In this study, the onset and progression of these defects are investigated in R6/2 mice, ranging from 3 wk old (presymptomatic) to 9-13 wk old (late-stage disease), and compared with age-matched wild-type (WT) siblings. The R6/2 ClC-1 current density and level of aberrantly spliced Clcn1 mRNA remain constant with age. In contrast, the ClC-1 current density increases, and the level of aberrantly spliced Clcn1 mRNA decreases with age in WT mice. The R6/2 ClC-1 properties diverge from WT before the onset of motor symptoms, which occurs at 5 wk of age. The relative decrease in R6/2 muscle capacitance also begins in 5-wk-old mice and is independent of fiber atrophy. Kir current density is consistently lower in R6/2 compared with WT muscle. The invariable R6/2 ClC-1 properties suggest a disruption in muscle maturation, which we confirm by measuring elevated levels of neonatal myosin heavy chain (MyHC) in late-stage R6/2 skeletal muscle. Similar changes in ClC-1 and MyHC isoforms in the more slowly developing Q175 HD mice suggest an altered maturational state is relevant to adult-onset HD. Finally, we find nuclear aggregates of muscleblind-like protein 1 without predominant CAG repeat colocalization in R6/2 muscle. This is unlike myotonic dystrophy, another trinucleotide repeat disorder with similar ClC-1 defects, and suggests a novel mechanism of aberrant mRNA splicing in HD. These early and progressive skeletal muscle defects reveal much needed peripheral biomarkers of disease progression and better elucidate the mechanism underlying HD myopathy.