? ? This proposal describes studies on the regulation of expression of cyclic nucleotide phosphodiesterases in dystrophic skeletal muscle. Cyclic 3',5'- adenosine monophosphate (cAMP) is a universally utilized intracellular second messenger. cAMP is an important regulator of energy metabolism in skeletal muscle, and its metabolism is altered in degenerative muscular diseases such as Duchenne muscular dystrophy. Whether this is due to alterations in the catalytic activity or the expression level of enzymes responsible for cAMP synthesis or degradation, or both, is unknown. The signaling action of cAMP is terminated when it is hydrolyzed by phosphodiesterase (PDE). There are eleven known families of mammalian PDE, differentiated by their substrate specificity, kinetics, allosteric regulation and sensitivity to pharmacologic agents. A given tissue or cell will typically express multiple PDE families, each of which contribute to the tissue's total PDE activity. The proposed studies will examine a mechanism for previously reported decreases in PDE expression in skeletal muscle from the mdx mouse, a model with the same defect in the dystrophin gene that causes Duchenne muscular dystrophy. Previous work has shown an increase in total cAMP and cGMP PDE activity in young mdx hind leg muscle. An age-related decrease in particulate but not soluble PDE4 activity suggests that the loss of the dystrophin-glycoprotein complex leads to altered expression of membrane- associated PDE4, perhaps due to the loss of a specific interaction between the two. The studies proposed here would extend this work to examine possible mechanisms of this alteration in PDE4 activity. PDE4 mRNA and protein levels will be quantified in normal and diseased muscle, looking for the cause of declining expression related to the dystrophic state. In vivo localization studies using confocal microscopy and fluorescence-labeled antibodies directed against PDE4 isozymes will examine whether PDE4 activity in the particulate fraction is co-localized with dystrophin such that the loss of dystrophin in mdx mice leads to a concurrent loss in membrane-associated PDE4 protein. The proposed project is aimed at examining the possibility that muscle degeneration and weakness associated with muscular dystrophy can be diminished or their onset slowed by manipulation of a family of enzymes altered in muscular dystrophy. ? ? ? ?
