Alternative splicing alterations of Ca2+ handling genes are associated with Ca2+ signal dysregulation in myotonic dystrophy type 1 ( DM1) and type 2 ( DM2) myotubes.

Aims The pathogenesis of myotonic dystrophy type 1 ( DM1) and type 2 ( DM2) has been related to the aberrant splicing of several genes, including those encoding for ryanodine receptor 1 ( RYR1), sarcoplasmatic/endoplasmatic Ca²⁺- ATPase ( SERCA) and α_1S subunit of voltage-gated Ca²⁺ channels ( Ca_v1.1). The aim of this study is to determine whether alterations of these genes are associated with changes in the regulation of intracellular Ca²⁺ homeostasis and signalling. Methods We analysed the expression of RYR1, SERCA and Ca_v1.1 and the intracellular Ca²⁺ handling in cultured myotubes isolated from DM1, DM2 and control muscle biopsies by semiquantitative RT-PCR and confocal Ca²⁺ imaging respectively. Results (i) The alternative splicing of RYR1, SERCA and Ca_v1.1 was more severely affected in DM1 than in DM2 myotubes; (ii) DM1 myotubes exhibited higher resting intracellular Ca²⁺ levels than DM2; (iii) the amplitude of intracellular Ca²⁺ transients induced by sustained membrane depolarization was higher in DM1 myotubes than in controls, whereas DM2 showed opposite behaviour; and (iv) in both DM myotubes, Ca²⁺ release from sarcoplasmic reticulum through RYR1 was lower than in controls. Conclusion The aberrant splicing of RYR1, SERCA1 and Ca_v1.1 may alter intracellular Ca²⁺ signalling in DM1 and DM2 myotubes. The differing dysregulation of intracellular Ca²⁺ handling in DM1 and DM2 may explain their distinct sarcolemmal hyperexcitabilities. [ABSTRACT FROM AUTHOR]