Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, Ontario, Canada.
Department of Molecular Genetics, The University of Toronto, Toronto, Ontario, Canada.
J Clin Invest. 2023 Sep 15;133(18):e166275. doi: 10.1172/JCI166275.
X-linked myotubular myopathy (XLMTM) is a fatal congenital disorder caused by mutations in the MTM1 gene. Currently, there are no approved treatments, although AAV8-mediated gene transfer therapy has shown promise in animal models and preliminarily in patients. However, 4 patients with XLMTM treated with gene therapy have died from progressive liver failure, and hepatobiliary disease has now been recognized more broadly in association with XLMTM. In an attempt to understand whether loss of MTM1 itself is associated with liver pathology, we have characterized what we believe to be a novel liver phenotype in a zebrafish model of this disease. Specifically, we found that loss-of-function mutations in mtm1 led to severe liver abnormalities including impaired bile flux, structural abnormalities of the bile canaliculus, and improper endosome-mediated trafficking of canalicular transporters. Using a reporter-tagged Mtm1 zebrafish line, we established localization of Mtm1 in the liver in association with Rab11, a marker of recycling endosomes, and canalicular transport proteins and demonstrated that hepatocyte-specific reexpression of Mtm1 could rescue the cholestatic phenotype. Last, we completed a targeted chemical screen and found that Dynasore, a dynamin-2 inhibitor, was able to partially restore bile flow and transporter localization to the canalicular membrane. In summary, we demonstrate, for the first time to our knowledge, liver abnormalities that were directly caused by MTM1 mutation in a preclinical model, thus establishing the critical framework for better understanding and comprehensive treatment of the human disease.
X 连锁肌小管肌病 (XLMTM) 是一种致命的先天性疾病，由 MTM1 基因突变引起。目前尚无批准的治疗方法，尽管 AAV8 介导的基因转移治疗在动物模型和初步患者中显示出前景。然而，接受基因治疗的 4 名 XLMTM 患者因进行性肝功能衰竭而死亡，并且现在更广泛地认识到与 XLMTM 相关的肝胆疾病。为了试图了解 MTM1 缺失本身是否与肝病理有关，我们在这种疾病的斑马鱼模型中描述了我们认为是一种新的肝脏表型。具体来说，我们发现 mtm1 的功能丧失突变导致严重的肝脏异常，包括胆汁流量受损、胆小管结构异常以及管腔转运蛋白的内体介导运输不当。使用带有报告基因标记的 Mtm1 斑马鱼系，我们确定了 Mtm1 在肝脏中的定位与 Rab11 相关，Rab11 是再循环内体的标志物，以及管腔转运蛋白，并证明了肝细胞特异性重新表达 Mtm1 可以挽救胆汁淤积表型。最后，我们完成了靶向化学筛选，发现 Dynasore（一种 dynamin-2 抑制剂）能够部分恢复胆汁流量和转运蛋白向胆小管膜的定位。总之，我们首次在临床前模型中证明了由 MTM1 突变直接引起的肝脏异常，从而为更好地理解和全面治疗人类疾病奠定了重要框架。
