AFAP-120基因突变导致腓骨肌萎缩症的分子机制研究

Charcot-Marie-Tooth (CMT) disease, also called Hereditary Motor and Sensory neuropathy (HMSN), is the most common inherited neurological disorde. CMT phenotype is characterized by distal weakness, progressive distal muscle atrophy, foot deformities (pes cavus and hammer toes), sensory loss, and so on. CMT is generally not fatal or life threatening, but the quality of patient life is affected severely. We found previously a family from Shandong Province with five affected individuals with an autosomal dominant pattern of inheritance. To detect the gene associated with this ICMT family, whole-exome sequencing was done. The heterozygous c.1621C>T change in the AFAP-120 gene, which was predicted to cause the amino acid substitution p.P541S, was identified be the pathogenic mutation. We generated a transgenic mouse line expressing mutated AFAP-120 (P542S) protein and found some mouse showed a sensory loss and a gait defect. Micrographs of both heterozygous and homozygous AFAP-120P542S mice showed many blank bulbs appeared in axonal compartment of myelinated fibres. To explore the molecular mechanism of AFAP-120 mutation leading to ICMT, we decide to promote our study.

腓骨肌萎缩症又称为CMT，是最常见的遗传性神经系统疾病。CMT在幼年及成年都可发病，患者常伴有四肢无力、四肢远端肌肉进行性萎缩、足部骨骼畸形、轻度感觉受累等症状，患者生活质量受到严重影响。前期，我们实验室在山东省发现了一个ICMT遗传病家系，通过外显子组捕获与二代测序技术筛查，发现该家系患者基因组中AFAP-120基因的第1621位发生错义突变（c.1621C>T）。利用AFAP-120（P542S）点突变小鼠进行行为学及病理学分实验分析，我们发现AFAP-120发生突变后，小鼠表现出步态失调、四肢感觉能力减弱等异常，其轴索出现与ICMT患者类似的萎缩、缺失病变。然而，对于对AFAP-120（P541S）突变后如何导致ICMT发生的分子机制，至今未能查明。为进一步探索AFAP-120发生突变后如何影响外周神经功能，进而导致ICMT发生，我们决定开展此项研究。

腓骨肌萎缩症是一种常见的遗传性周围神经系统疾病，患者四肢远端进行性肌肉萎缩，形成“鹤形腿”、高弓足、爪形手等畸形，严重影响患者生活。我们前期研究了一个CMT遗传家系，通过基因测序发现该家系患者AFAP-120基因发生c.1621C>T（p.P541S）点突变。我们对患者CMT的发生及小鼠CMT表型的出现与AFAP-120c.1621C>T（p.P541S）突变发生的关联性进行了研究。然而对于该突变引起外周神经轴索病变，进而导致 CMT发生的具体机制仍然不清楚，也未检索到相关文献报道。因此，立项该课题进行探索。 . 课题开展后，我们首先利用生物信息学方法对AFAP-120发生P541S突变后其结构与功能的变化进行了分析，发现突变发生后疏水的脯氨酸被亲水的丝氨酸替代，蛋白结构和功能发生变化。在细胞水平，通过过表达突变蛋白AFAP-120（P541S）的方法，发现突变后细胞微丝发生缠结，成团；伪足数量增多；轴突长度变短。在分子水平，我们对蛋白AFAP-120（P541S）突变后与结合蛋白的相互作用变化进行了探索，发现突变后AFAP-120与F-actin 的相互作用增强。. 该课题的顺利开展，进一步明确了AFAP-120 错义突变 c.1621C>T（p.P541S）与CMT发生之间的因果关系，并探索了该突变导致CMT发生的具体分子机制，推动了AFAP-120突变导致CMT发生的分子机制这一科学问题地解决，为AFAP-120突变家系的基因治疗及相关药物的开发奠定了基础。