EFFECT OF PROTEASE INHIBITORS AND CLENBUTEROL ON THE IN-VITRO DEGRADATION OF DYSTROPHIN BY ENDOGENOUS PROTEASES IN HUMAN SKELETAL-MUSCLE

The in vitro degradation of dystrophin protein by endogenous proteases in human skeletal muscle has been investigated using a tissue homogen ate assay system with subsequent protein analysis via SDS polyacrylami de electrophoresis and immunoblotting (using a monoclonal antibody to the central rod region of dystrophin). The rate of dystrophin degradat ion and nature of the proteolytic fragments formed at pH 5.5 and pH 7. 5 (corresponding to the two major protease groups of relevance to intr acellular protein catabolism) were broadly similar, incorporation of p rotease inhibitors in the above system suggested that Ca2+ activated p roteinase and cathepsin D are principally responsible for the degradat ion of dystrophin at pH 7.5 and pH 5.5 respectively. The rate of dystr ophin degradation at pH 7.5 was reduced by approximately 20% in the pr esence of 10(-5) M clenbuterol, a beta-adrenoceptor agonist with thera peutic potential in the treatment of human muscle wasting diseases.