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MYTHO is a novel regulator of skeletal muscle autophagy and integrity

Leduc-Gaudet JP, Franco-Romero A, Cefis M, Moamer A, Broering FE, Milan G, et al.

Nat Commun, 2023 Mar 02;14(1):1199.
PMID: 36864049 DOI: 10.1038/s41467-023-36817-1

Autophagy is a critical process in the regulation of muscle mass, function and integrity. The molecular mechanisms regulating autophagy are complex and still partly understood. Here, we identify and characterize a novel FoxO-dependent gene, d230025d16rik which we named Mytho (Macroautophagy and YouTH Optimizer), as a regulator of autophagy and skeletal muscle integrity in vivo. Mytho is significantly up-regulated in various mouse models of skeletal muscle atrophy. Short term depletion of MYTHO in mice attenuates muscle atrophy caused by fasting, denervation, cancer cachexia and sepsis. While MYTHO overexpression is sufficient to trigger muscle atrophy, MYTHO knockdown results in a progressive increase in muscle mass associated with a sustained activation of the mTORC1 signaling pathway. Prolonged MYTHO knockdown is associated with severe myopathic features, including impaired autophagy, muscle weakness, myofiber degeneration, and extensive ultrastructural defects, such as accumulation of autophagic vacuoles and tubular aggregates. Inhibition of the mTORC1 signaling pathway in mice using rapamycin treatment attenuates the myopathic phenotype triggered by MYTHO knockdown. Skeletal muscles from human patients diagnosed with myotonic dystrophy type 1 (DM1) display reduced Mytho expression, activation of the mTORC1 signaling pathway and impaired autophagy, raising the possibility that low Mytho expression might contribute to the progression of the disease. We conclude that MYTHO is a key regulator of muscle autophagy and integrity.

Matched MeSH terms: Myotonic Dystrophy*
Fulltext Deregulation of microRNAs in blood and skeletal muscles of myotonic dystrophy type 1 patients

Ambrose KK, Ishak T, Lian LH, Goh KJ, Wong KT, Ahmad-Annuar A, et al.

Neurol India, 2017 5 11;65(3):512-517.
PMID: 28488611 DOI: 10.4103/neuroindia.NI_237_16

INTRODUCTION: MicroRNAs (miRNAs) are short RNA molecules of approximately 22 nucleotides that function as post-transcriptional regulators of gene expression. They are expressed in a tissue-specific manner and show different expression patterns in development and disease; hence, they can potentially act as disease-specific biomarkers. Several miRNAs have been shown to be deregulated in plasma and skeletal muscles of myotonic dystrophy type 1 (DM1) patients.
METHODS: We evaluated the expression patterns of 11 candidate miRNAs using quantitative real-time PCR in whole blood (n = 10) and muscle biopsy samples (n = 9) of DM1 patients, and compared them to those of normal control samples (whole blood, n = 10; muscle, n = 9).
RESULTS: In DM1 whole blood, miRNA-133a, -29b, and -33a were significantly upregulated, whereas miRNA-1, -133a, and -29c were significantly downregulated in the skeletal muscles compared to controls.
CONCLUSIONS: Our findings align to those reported in other studies and point towards pathways that potentially contribute toward pathogenesis in DM1. However, the currently available data is not sufficient for these miRNAs to be made DM1-specific biomarkers because they seem to be common to many muscle pathologies. Hence, they lack specificity, but reinforce the need for further exploration of DM1 biomarkers.

Matched MeSH terms: Myotonic Dystrophy/blood*; Myotonic Dystrophy/pathology*
Fulltext Analysis of CTG repeat length variation in the DMPK gene in the general population and the molecular diagnosis of myotonic dystrophy type 1 in Malaysia

Ambrose KK, Ishak T, Lian LH, Goh KJ, Wong KT, Ahmad-Annuar A, et al.

BMJ Open, 2017 03 31;7(3):e010711.
PMID: 28363916 DOI: 10.1136/bmjopen-2015-010711

OBJECTIVE: The lack of epidemiological data and molecular diagnostic services in Malaysia has hampered the setting-up of a comprehensive management plan for patients with myotonic dystrophy type 1 (DM1), leading to delayed diagnosis, treatment and support for patients and families. The aim of this study was to estimate the prevalence of DM1 in the 3 major ethnic groups in Malaysia and evaluate the feasibility of a single tube triplet-primed PCR (TP-PCR) method for diagnosis of DM1 in Malaysia.
DESIGN, SETTING AND PARTICIPANTS: We used PCR to determine the size of CTG repeats in 377 individuals not known to be affected by DM and 11 DM1 suspected patients, recruited from a tertiary hospital in Kuala Lumpur. TP-PCR was performed on selected samples, followed by Southern blot hybridisation of PCR amplified fragments to confirm and estimate the size of CTG expansion.
OUTCOME MEASURES: The number of individuals not known to be affected by DM with (CTG)>18 was determined according to ethnic group and as a whole population. The χ2 test was performed to compare the distribution of (CTG)>18 with 12 other populations. Additionally, the accuracy of TP-PCR in detecting CTG expansion in 11 patients with DM1 was determined by comparing the results with that from Southern blot hybridisation.
RESULTS: Of the 754 chromosomes studied, (CTG)>18 frequency of 3.60%, 1.57% and 4.00% in the Malay, Chinese and Indian subpopulations, respectively, was detected, showing similarities to data from Thai, Taiwanese and Kuwaiti populations. We also successfully detected CTG expansions in 9 patients using the TP-PCR method followed by the estimation of CTG expansion size via Southern blot hybridisation.
CONCLUSIONS: The results show a low DM1 prevalence in Malaysia with the possibility of underdiagnosis and demonstrates the feasibility of using a clinical and TP-PCR-based approach for rapid and cost-effective DM1 diagnosis in developing countries.

Matched MeSH terms: Myotonic Dystrophy/genetics*; Myotonic Dystrophy/epidemiology

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