UNIVERSITY OF WASHINGTON
The focus of this grant is to establish Drosophila melanogaster as a model system to study sphingolipid signaling as it relates to muscle regeneration as well as to test a wunen/LPP3 based strategy that suggested itself from our studies in Drosophila to ameliorate muscle function in dystrophic mice. Muscular Dystrophy is a muscle wasting disease that at present has no cure. As mentioned, our studies have produced a possible new inroad into treatment for this disease and it involves wunen. We will exhaustively characterize wunen, a suppressor isolated in our previous forward genetic screens for modifiers of the Dystrophin-associated Glycoprotein Complex mutant phenotypes. Wunen is a homolog of human lipid phosphate phosphatase 3 (LPP3) which many studies have shown is involved in the regulation of levels of bioactive lipids, particularly sphingosine 1-phosphate (S1P). S1P is implicated in pre-myoblast (adult muscle stem cell) maintenance as well as myoblast differentiation into myotubes. The possibility of a muscle regenerative strategy for suppressing the muscular dystrophy phenotype through the alteration of sphingolipid signaling may be fruitful. We will determine if wunen acts through S1P to inhibit apoptosis and/or increase muscle generation through either increasing proliferation of adult muscle precursor cells or increasing proliferation of adult muscle satellite stem cells which have yet to be defined in Drosophila. We will determine if muscle satellite stem cells exist in the same physical niche as mammalian muscle satellite stem cells which is between the basal lamina and the sarcolemma of existing muscle fibers. In toto, we will establish and extend the role of sphingolipid signaling in muscle formation in Drosophila and determine whether this alleviates the disease phenotype of dystrophic flies. Furthermore, as mentioned, we will attempt to extend the relationship that we have observed between Wunen/LPP3 and muscular dystrophy to mammalian animal models of the disease, particularly the mdx mouse. We hope to produce regenerative therapeutic strategies to alleviate the disease phenotype in this model. These strategies will include reducing LPP3 function as well as increasing the presence of its downstream effector S1P.