Altered Ca2+ homeostasis and endoplasmic reticulum stress in myotonic dystrophy type 1 muscle cells

Area of Science:

• Muscle cell biology
• Calcium homeostasis
• Genetic disorders

Background:

• Myotonic Dystrophy type 1 (DM1) pathogenesis involves unstable CTG repeats in the DMPK gene.
• This leads to aberrant splicing of transcripts, affecting cellular calcium (Ca2+) homeostasis.
• Understanding Ca2+ dysregulation is crucial for DM1 research.

Purpose of the Study:

• To investigate the splicing of Ca2+ transporter genes (RyR1, SERCA1, CACN1S) during DM1 muscle cell maturation.
• To assess the functional consequences on excitation-contraction (EC) coupling and Ca2+ handling.
• To explore the link between Ca2+ homeostasis, ER stress, and DM1 muscle degeneration.

Main Methods:

• Monitoring splicing of RyR1, SERCA1, and CACN1S during primary DM1 muscle cell differentiation.
• Assessing the functionality of the EC coupling machinery and cytosolic Ca2+ response.
• Measuring intracellular Ca2+ stores, RyR1 protein levels, and ER stress markers.

Main Results:

• DM1 myotubes exhibited higher fetal isoforms of SERCA1 and CACN1S mRNA at 15 days.
• Cytosolic Ca2+ response to depolarization failed to increase in DM1 myotubes during differentiation.
• Reduced RyR1 protein, uncoupled Ca2+ release, and induced ER stress markers were observed in DM1 cells.

Conclusions:

• Perturbed Ca2+ homeostasis, driven by altered splicing and ER stress, contributes to muscle degeneration in DM1.
• These findings suggest a premature senescence phenotype in DM1 muscle cells.
• Targeting Ca2+ handling and ER stress pathways may offer therapeutic strategies for DM1.