Loss of Mtm1 causes cholestatic liver disease in a model of X-linked myotubular myopathy
Sophie Karolczak, … , Chunyue Yin, James J. Dowling
Sophie Karolczak, … , Chunyue Yin, James J. Dowling
Published July 25, 2023
Citation Information: J Clin Invest. 2023;133(18):e166275. https://doi.org/10.1172/JCI166275.
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Research Article Hepatology Muscle biology

Loss of Mtm1 causes cholestatic liver disease in a model of X-linked myotubular myopathy

Abstract

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.

Authors

Sophie Karolczak, Ashish R. Deshwar, Evangelina Aristegui, Binita M. Kamath, Michael W. Lawlor, Gaia Andreoletti, Jonathan Volpatti, Jillian L. Ellis, Chunyue Yin, James J. Dowling

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Figure 5

Livers from mtm zebrafish exhibit widespread transcriptional changes.

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Livers from mtm zebrafish exhibit widespread transcriptional changes. Co...
Comparative RNA-Seq from isolated livers from 7 dpf larvae from the following conditions: WT, mtm mutants, WT exposed to a high-fat diet (overfed), WT exposed to alcohol (EtOH-treated), and abcb11b mutants (panel F and Supplemental Figure 2). (A) PCA shows that transcriptomes from mtm zebrafish segregated together and were distinct when compared with WT and the other pathologic conditions. (B) Volcano plot showing differential expression between mtm and WT livers. There were 797 transcripts upregulated and 561 transcripts downregulated in the mtm mutants (absolute [log2 fold change (FC)] >2 vs. WT, adjusted P = 0.05). (C) Venn diagrams comparing mtm fish with abcb11b-knockout fish. These transcriptomes had little overlap. (D) Venn diagrams showing comparisons between mtm zebrafish and fish treated with a high-fat diet or alcohol. In general, the individual transcriptomes were distinct and with little overlap. (E) Direct interrogation of transcripts from genes encoding canalicular transport proteins. There were no statistically significant changes between WT and mtm zebrafish, indicating that the expression changes seen in bsep (abcb11b) and mdr1 (pgp) were at the posttranscriptional level. (F) Pathway analyses of the various conditions using the fgsea (version 1.10.1 R package) analytic tool. The most striking differences were found in pathways representing inflammation and immune responses, which are shared in part between mtm and abcb11b mutants.