PDF(Pubmed)
Abstract：
Defective lysosomal acidification is responsible for a large range of multi-systemic disorders associated with impaired autophagy. Diseases caused by mutations in the VMA21 gene stand as exceptions, specifically affecting skeletal muscle (X-linked Myopathy with Excessive Autophagy, XMEA) or liver (Congenital Disorder of Glycosylation). VMA21 chaperones vacuolar (v-) ATPase assembly, which is ubiquitously required for proper lysosomal acidification. The reason VMA21 deficiencies affect specific, but divergent tissues remains unknown. Here, we show that VMA21 encodes a yet-unreported long protein isoform, in addition to the previously described short isoform, which we name VMA21-120 and VMA21-101, respectively. In contrast to the ubiquitous pattern of VMA21-101, VMA21-120 was predominantly expressed in skeletal muscle, and rapidly up-regulated upon differentiation of mouse and human muscle precursors. Accordingly, VMA21-120 accumulated during development, regeneration and denervation of mouse skeletal muscle. In contrast, neither induction nor blockade of autophagy, in vitro and in vivo, strongly affected VMA21 isoform expression. Interestingly, VMA21-101 and VMA21-120 both localized to the sarcoplasmic reticulum of muscle cells, and interacted with the v-ATPase. While VMA21 deficiency impairs autophagy, VMA21-101 or VMA21-120 overexpression had limited impact on autophagic flux in muscle cells. Importantly, XMEA-associated mutations lead to both VMA21-101 deficiency and loss of VMA21-120 expression. These results provide important insights into the clinical diversity of VMA21-related diseases and uncover a muscle-specific VMA21 isoform that potently contributes to XMEA pathogenesis.
摘要：
有缺陷的溶酶体酸化是导致大量与自噬受损相关的多系统疾病的原因。由VMA21基因突变引起的疾病是例外，特别影响骨骼肌（X连锁肌病伴有过度自噬，XMEA）或肝脏（先天性糖基化障碍）。VMA21分子伴侣液泡（v-）ATP酶组装，这是适当的溶酶体酸化所必需的。VMA21缺陷的原因影响具体，但是不同的组织仍然未知。这里,我们显示VMA21编码一个尚未报道的长蛋白同工型，除了前面描述的短同工型，我们分别将其命名为VMA21-120和VMA21-101。与VMA21-101普遍存在的模式相反，VMA21-120主要在骨骼肌中表达，并在小鼠和人类肌肉前体分化后迅速上调。因此，在开发过程中积累的VMA21-120，小鼠骨骼肌的再生和去神经支配。相比之下,既不诱导也不阻断自噬，在体外和体内，强烈影响VMA21同种型表达。有趣的是,VMA21-101和VMA21-120都位于肌细胞的肌浆网，并与v-ATP酶相互作用。而VMA21缺乏会损害自噬，VMA21-101或VMA21-120过表达对肌细胞自噬通量的影响有限。重要的是,XMEA相关突变导致VMA21-101缺陷和VMA21-120表达的丧失。这些结果为VMA21相关疾病的临床多样性提供了重要的见解，并揭示了肌肉特异性VMA21同种型，该同种型有力地促进了XMEA发病机理。
