Résumé :
|
Communication n° 86. Duchenne Muscular Dystrophy (DMD), and mdx mouse and grmd dog dystrophies result from X-linked genetic defects leading to a lack of dystrophin. Dystrophin is involved in the dystrophin-glycoprotein complex (DGC). Until now, experimental studies have failed to detect the DGC in the dystrophin-deficient skeletal muscles. Hence, this complex was assumed to be disrupted in the absence of dystrophin, and appeared to be involved in the development of the disease. The present work shows for the first time that the DGC proteins are present as insoluble proteins in dystrophin-deficient muscle plasma membrane. Muscle plasma membranes from normal and dystrophic muscles were obtained by tissue fractionation using differential centrifugations. Plasma membrane preparations (CSM) containing markers of the plasma membrane were obtained after a final density gradient centrifugation of total microsomes (TM). Beta-dystroglycan and the other proteins of the DGC are actually present at normal levels in TM obtained from mdx mouse and grmd dog muscles: a pre-treatment with cholate detergent is able to reveal their presence by SDS-PAGE and immunoblotting (Cluchague, FEBS lett, 2004, 572, 216-220). Surprisingly, the density gradient centrifugation is also able to reveal the presence of all DGC proteins at high levels in CSM without a detergent treatment. beta-DG is this case appeared as a double band migrating at 43 and 30 kDa. The latter is predominant in dystrophic muscles and may contain the transmembrane and intracellular domains of the protein. The presence of orthovanadate, an inhibitor of phosphatases during the fractionation procedure reveals that beta-dystroglycan from mdx mouse muscle and specifically the 30 kDa band is highly phosphorylated. These results give new insights about the development of the dystrophic process involved in mdx mouse and grmd dog as well as in DMD.
|