Calcium homeostasis and cell death in Sol8 dystrophin-deficient cell line in culture

Abnormalities of calcium homeostasis are involved in the process of cell injuries such as Duchenne muscular dystrophy characterized by the absence of the protein dystrophin. But how the absence of dystrophin leads to cytosolic calcium overload is as yet poorly understood. This question has been addressed with skeletal muscle cells from human DMD muscles or mdx mice. Although easier to obtain than human muscles, mdx muscle cells have provided controversial data concerning the resting intracellular calcium level ([Ca2+](i)). This work describes the culture of So18 cell line that expresses neither dystrophin nor adhalin, a dystrophin-associated protein. The [Ca2+](i) and intracellular calcium transients induced by different stimuli (acetylcholine, caffeine and high potassium) are normal during the first days of culture. At later stages, calcium homeostasis exhibits drastic alterations with a breaking down of the calcium responses and a large [Ca2+](i) elevation. Concomitantly, So18 cells exhibit morphological signs of cell death like cytoplasmic shrinkage and incorporation of propidium iodide. Cell death could be significantly reduced by blocking the activity of calpains, a type of calcium-regulated proteases. These results suggest that So18 cell line provides an alternative model of dystrophin-deficient skeletal muscle cells for which a clear disturbance of the calcium homeostasis is observed in culture in association with calpain-dependent cell death. It is shown that transfection with a plasmid cDNA permits the forced expression of dystrophin in So18 myotubes as well as a correct sorting of the protein. This approach could be used to explore possible interactions between dystrophin deficiency, calcium homeostasis alteration, and dystrophic cell death. (C) 2001 Harcourt Publishers Ltd.