New insights in the regulation of calcium transfers by muscle dystrophin-based cytoskeleton: implications in DMD

Calcium mishandling in Duchenne muscular dystrophy (DMD) suggested that dystrophin, a membrane-associated cytoskeleton protein, may regulate calcium-signalling cascades such as calcium entries. Calcium overload in human DMD myotubes is dependent on their contractile activity suggesting the involvement of channels being activated during contraction and/or calcium release. Forced expression of mini-dystrophin in dystrophin-deficient myotubes, reactivates appropriate sarcolemmal expression of dystrophin-associated proteins and restores normal calcium handling in the cytosol. Furthermore, the recombinant mini-dystrophin reduced the store-operated calcium influx across the sarcolemma, and the mitochondrial calcium uptake during this influx. A slow component of calcium release dependent on IP3R, as well as the production of IP3, were also reduced to normal levels by expression of mini-dystrophin. Our studies provide a new model for the convergent regulation of transmembrane calcium influx and IP3-dependent calcium release by the dystrophin-based cytoskeleton (DBC). We also suggest molecular association of such channels with DBC which may provide the scaffold for assembling a multiprotein-signalling complex that modulates the channel activity. This suggests that the loss of this molecular association could participate in the alteration of calcium homeostasis observed in DMD muscle cells.