Résumé :
|
Evidence is presented for the involvement of IP3-dependent release calcium pathway in the contribution of calcium overload in dystrophin-deficient cells. Our previous results presented that global calcium release during stimulation (K+-evoked calcium increase) was found higher in dystrophin-deficient SolC1(-) myotubes than in mini-dystrophin transfected SolD(+) myotubes. SolC1(-) myotubes also displayed higher activity of spontaneous calcium release as compared to SolD(+) myotubes. Moreover, dystrophin-deficient myotubes were naturally dying faster than mini-dystrophin transfected myotubes. These features prompted us to conduct experiments with cyclosporine A (CsA), known to, among other effects, modulate IP3 pathway, in order to investigate its effects on both cell death and calcium signaling. Cell survival assays, performed with MTT test, revealed a protective effect of both 2-APB (IP3R inhibitor) and CsA against natural cell death occurring in mature dystrophin-deficient myotubes. The area under the curve and kinetics parameters of K+-evoked calcium increase were significantly reduced with the incubation of SolC1(-) myotubes with 2-APB. In the same way, 2-APB exposure was significantly decreasing spontaneous calcium release at rest in SolC1(-) myotubes. Interestingly, for both K+-evoked calcium increases and spontaneous release events, similar results were obtained with CsA exposure with SolC1(-) myotubes. Furthermore, CsA reduced IP3-R1 mRNA levels in SolC1(-), leading to levels measured in mini-dystrophin transfected myotubes (SolD(+)) in control conditions. Taken together, these data suggest that CsA could modulate calcium releases in dystrophin-deficient cells by direct IP3Rs inhibition and/or by reduction of IP3R-1 mRNA expression via the calcineurin pathway, leading to the regulation of the calcium overload in dystrophin-deficient cells. On that account, these data underline a strong involvement of IP3 pathway in calcium-dependent cell death in dystrophin deficiency, and that a modulation of calcineurin pathway could be a therapeutic approach to counteract the calcium overload in dystrophin-deficient myopathies.
|