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Natural history of a mouse model of X-linked myotubular myopathy

ABSTRACT: X-linked myotubular myopathy (XLMTM) is a severe monogenetic disorder of the skeletal muscle. It is caused by loss-of-expression/function mutations in the myotubularin (MTM1) gene. Much of what is known about the disease, as well as the treatment strategies, has been uncovered through experimentation in pre-clinical models, particularly the Mtm1 gene knockout mouse line (Mtm1 KO). Despite this understanding, and the identification of potential therapies, much remains to be understood about XLMTM disease pathomechanisms, and about the normal functions of MTM1 in muscle development. To lay the groundwork for addressing these knowledge gaps, we performed a natural history study of Mtm1 KO mice. This included longitudinal comparative analyses of motor phenotype, transcriptome and proteome profiles, muscle structure and targeted molecular pathways.We identified age-associated changes in gene expression, mitochondrial function, myofiber size and key molecular markers, including DNM2. Importantly, some molecular and histopathologic changes preceded overt phenotypic changes, while others, such as triad structural alternations, occurred coincidentally with the presence of severe weakness. In total, this study provides a comprehensive longitudinal evaluation of the murine XLMTM disease process, and thus provides a critical framework for future investigations.

ORGANISM(S): Mus musculus

PROVIDER: GSE207447 | GEO | 2022/07/08

REPOSITORIES: GEO

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Project description:Purpose: The goal of this study was to investigate the transcriptional profile of genes expressed in the quadriceps muscle of myotubularin deficient (Mtm1-/-) mice, and determine whether improvements in the pathophysiology of tamoxifen treated Mtm1-/- mice are a consequence of ER-dependent transcriptional modulation. Methods: Muscle mRNA profiles from quadriceps of 36-day-old wild-type (WT), myotubularin deficient (Mtm1-/-) mice, and tamoxifen treated WT and Mtm1-/- mice were generated by deep sequencing, in triplicate or quadruplicate, using Illumina HiSeq 2500. Read sets from each of the 14 samples across the four conditions were aligned to the reference genome (GRCm38/MM10 version of the Mus musculus genome) and transcriptome using STAR (Dobin et al. Bioinformatics 2013 PMID: 23104886) two-step alignment to generate a Binary Alignment Map file (BAM file). Coordinate sorted BAM files were used to quantify transcript abundance (count data) using HTSeq (Anders et al. Bioinformatics 2014, PMID: 25260700). Raw read counts generated were used as input for differential gene expression analysis, carried out using both DESeq (Anders and Huber 2010) and edgeR (Robinson, McCarthy, and Smyth 2010) R/Bioconductor packages. This was carried out in a pair-wise manner between any two conditions that were considered. FDR adjusted p-values from both edgeR and DESeq was used to determine genes that are significantly differentially expressed between the conditions tested. Finally, we used the GoSeq R/Bioconductor package (Young MD, et al Genome Biology, 11, pp. R14) to identify pathways that were significantly enriched for differentially expressed genes between any two conditions. Results: Using an established data analysis workflow, 65 million reads were aligned per sample (>90% exonic). We observed 849 differentially expressed transcripts in untreated mtm1-/-mice (p< 0.01) in comparison to wild-type (WT) controls. Furthermore, we identified 29 differentially expressed genes (p<0.01) between mtm1-/- mice and their TAM-treated mtm1-/- mice. In particular, we observed that the transcriptional profiles of mtm1 -/- mice and tamoxifen-treated mtm1-/- mice cluster together and are distinct from wild-type contros. Moreover, no significant changes were observed in the expression of estrogen-response genes that are known gene targets of tamoxifen; no significant transcriptional changes were observed in well-known MTM-related genes.This strongly indicates that, contrary to its well-established function as a transcriptional modulator, tamoxifen improves the pathophysiology of myotubular myopathy in a post-transcriptional manner. Concusions: Our study represents the first comprehensive analysis of the whole transcriptome of the Mtm1-/- and tamoxifen treated Mtm1-/- mouse, generated by RNA-seq technology. The data reported here provides a framework a comparative investigation of the expression profiles in Mtm1-/- mice and tamoxifen treated Mtm1-/- mice. Importantly, our results demonstrate that in our MTM murine model, tamoxifen does not appear to alter the transcriptional profile of many estrogen-receptor (ER) related genes, and moreover does not appear to alter the transcriptional profile of genes that are abnormally expressed in Mtm1-/- mice alone. This suggests that tamoxifen is acting to improve the pathophysiology of the MTM mouse model in a transcriptionally-indepedent manner.

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Natural history of a mouse model of X-linked myotubular myopathy

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