Segregation of a Missense Variant in Enteric Smooth Muscle Actin γ-2 With Autosomal Dominant Familial Visceral Myopathy
Segregation of a Missense Variant in Enteric Smooth Muscle Actin γ-2 With Autosomal Dominant Familial Visceral Myopathy
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DOI：
10.1053/j.gastro.2012.08.045
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发表时间：
2012-12-01
期刊：
影响因子：
29.4
通讯作者：
Tuupanen, Sari
中科院分区：
文献类型：
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作者：
Lehtonen, Heli J.;Sipponen, Taina;Tuupanen, Sari
背景与目的：家族性内脏肌病是一种罕见的遗传性肌病假性梗阻，其遗传因素尚不清楚。FVM的特点是肠道平滑肌细胞功能受损，导致肠道运动异常、剧烈腹痛、营养不良，甚至死亡。我们寻找可能导致这种疾病的遗传因素。方法：我们对一个有7名成员被诊断为FVM的家庭中的2个个体的血液样本进行了全外显子组序列分析。Sanger测序被用来分析额外的家庭成员和280名没有这种疾病的个体(对照)。采用免疫组织化学方法对4例患者和2例正常对照的肠组织标本进行分析。使用CRL-1976和U2OS肉瘤细胞株进行功能研究，包括免疫荧光、细胞收缩和肌动球蛋白结构分析。结果：来自两个兄弟姐妹的DNA全外显子组序列分析确定了83个基因变异，这些基因变异在兄弟姐妹之间共享，被认为是可能导致疾病的变化。肠道平滑肌肌动蛋白γ-2(ACTG2)中的R148S杂合变异体，与疾病表型分离。与对照组相比，FVM患者的肠平滑肌(固有肌层)胞浆ACTG2水平降低，ACTG2蛋白异常积聚到细胞内包涵体中。与表达ACTG2(Wt)的细胞相比，表达外源ACTG2(R148S)的肉瘤细胞在肌动蛋白细丝中掺入的这种蛋白数量减少(P<；.001)。ACTG2(R148S)还干扰肌动蛋白的细胞骨架组织和细胞的收缩活动，呈显性-负性作用。这些发现以及蛋白质的变异位置表明，ACTG2 R148S干扰了肌动蛋白细丝的组装。结论：我们发现ACTG2中的R148S变异是一个家系中FVM的原因。改变的ACTG2蛋白似乎聚集在肠道平滑肌组织中，而不是形成肌动蛋白细丝。这种缺陷会损害内脏平滑肌细胞的收缩，降低肠道动力。
BACKGROUND & AIMS: Familial visceral myopathy (FVM) is a rare inherited form of myopathic pseudo-obstruction; little is known about the genetic factors that cause this disorder. FVM is characterized by impaired functions of enteric smooth muscle cells, resulting in abnormal intestinal motility, severe abdominal pain, malnutrition, and even death. We searched for genetic factors that might cause this disorder. METHODS: We performed whole-exome sequence analysis of blood samples from 2 individuals in a family that had 7 members diagnosed with FVM. Sanger sequencing was used to analyze additional family members and 280 individuals without this disorder (controls). Intestinal tissue samples from 4 patients and 2 controls were analyzed by immunohistochemistry. Functional studies, including immunofluorescence, cell contractility, and actomyosin structure analyses, were performed using CRL-1976 and U2OS sarcoma cell lines. RESULTS: Whole-exome sequence analysis of DNA from 2 siblings identified 83 gene variants that were shared between the siblings and considered as possible disease-causing changes. A heterozygous variant, R148S in enteric smooth muscle actin gamma-2 (ACTG2), segregated with disease phenotype. Intestinal smooth muscle (muscularis propria) from individuals with FVM had reduced levels of cytoplasmic ACTG2 and abnormal accumulation of the protein into intracellular inclusions compared with controls. Sarcoma cells that expressed exogenous ACTG2(R148S) incorporated reduced amounts of this protein into actin filaments compared with cells expressing ACTG2(wt) (P < .001). ACTG2(R148S) also interfered with actin cytoskeleton organization and the contractile activities of the cells, indicating a dominant-negative effect. These findings, along with the site of the variation in the protein, indicate that ACTG2 R148S interferes with actin filament assembly. CONCLUSIONS: We identified the R148S variant in ACTG2 as a cause of FVM in one family. The altered ACTG2 protein appears to aggregate, rather than form actin filaments, in intestinal smooth muscle tissue. This defect could impair contraction of the visceral smooth muscle cells and reduce bowel motility.