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

AimsThe 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 (1S) subunit of voltage-gated Ca2+ channels (Ca(v)1.1). 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. MethodsWe analysed the expression of RYR1, SERCA and Ca(v)1.1 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(v)1.1 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. ConclusionThe aberrant splicing of RYR1, SERCA1 and Ca(v)1.1 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.