Altered Ca2+ Homeostasis and Endoplasmic Reticulum Stress in Myotonic Dystrophy Type 1 Muscle Cells

Annalisa Botta,Gyorgy Szabadkai,Boris Pantic,Adriana Malena,Matteo Suman,Lodovica Vergani,Emanuele Loro,Giulia Del Moro

doi:10.3390/genes4020275

Annalisa Botta, Gyorgy Szabadkai + Show 6 more

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https://doi.org/10.3390/genes4020275

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Abstract

The pathogenesis of Myotonic Dystrophy type 1 (DM1) is linked to unstable CTG repeats in the DMPK gene which induce the mis-splicing to fetal/neonatal isoforms of many transcripts, including those involved in cellular Ca2+ homeostasis. Here we monitored the splicing of three genes encoding for Ca2+ transporters and channels (RyR1, SERCA1 and CACN1S) during maturation of primary DM1 muscle cells in parallel with the functionality of the Excitation-Contraction (EC) coupling machinery. At 15 days of differentiation, fetal isoforms of SERCA1 and CACN1S mRNA were significantly higher in DM1 myotubes compared to controls. Parallel functional studies showed that the cytosolic Ca2+ response to depolarization in DM1 myotubes did not increase during the progression of differentiation, in contrast to control myotubes. While we observed no differences in the size of intracellular Ca2+ stores, DM1 myotubes showed significantly reduced RyR1 protein levels, uncoupling between the segregated ER/SR Ca2+ store and the voltage-induced Ca2+ release machinery, parallel with induction of endoplasmic reticulum (ER) stress markers. In conclusion, our data suggest that perturbed Ca2+ homeostasis, via activation of ER stress, contributes to muscle degeneration in DM1 muscle cells likely representing a premature senescence phenotype.

Highlights

Myotonic dystrophy (Steinert¶s disease, 1909) is the most prevalent form of adult muscular dystrophy with a frequency of 1 in 8,000 individuals worldwide [1]
Cellular and endoplasmic reticulum (ER)/SR Ca2+ Homeostasis Is Altered in Primary DM1 Myotubes
To determine whether altered Ca2+ homeostasis plays a role in triggering cellular dysfunction, primary cultures of muscle cells were established from biopsies of five DM1 patients and five age-matched healthy individuals

Summary

Introduction

Myotonic dystrophy (Steinert¶s disease, 1909) is the most prevalent form of adult muscular dystrophy with a frequency of 1 in 8,000 individuals worldwide [1]. The genetic defect in DM1, identified in 1992, results from the expansion of a CTG repeat in the 3' untranslated region (UTR) of dystrophia myotonica protein kinase MIM #605377), a gene which maps to the chromosome 19q13.3 and encodes a serine/threonine protein kinase [4]. Repeat length correlates directly with disease severity and inversely with the age of onset [5]. Amplification is frequently observed after parent-to-child transmission, but extreme amplifications are not transmitted through the male line. This mechanism explains genetic anticipation [6,7] and the occurrence of the severe congenital form almost exclusively in the offspring of affected women [3]

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