MMP13 Inhibition Does Not Rescue GMPPB-Deficient Skeletal Muscle in Zebrafish

The dystroglycan protein is one of many that attach skeletal muscle fibers to the basement membrane at the myotendinous junction. In the alpha-subunit of the dystroglycan molecule, there are sugar chains that help with the adhesion of the molecule to the basement membrane. A mutation in any gene that codes for an enzyme that adds these sugar chains can result in a form of congenital muscle disease called secondary dystroglycanopathy. One of the genes that codes for an enzyme that adds sugar chains is GMPPB and a mutation in this gene results in GMPPB-associated dystroglycanopathy. Using zebrafish as a model for studying dystroglycanopathies has become popular due to their high fecundity, low cost of maintenance, and transparency during early developmental stages. We confirmed through in situ hybridization that matrix metalloproteinase-13 (mmp13a) is upregulated in gmppb mutants and is thought to be a contributor to the progression of the disease. We used a mutant gmppb line of zebrafish to see if chemical inhibition of Mmp13 in the embryos would rescue the mutant phenotypes. We also used a morpholino knockdown strategy when the phenotypes of the gmppb mutants became too variable. We found that chemical inhibition of Mmp13 did not rescue either the gmppb mutant or morphant phenotype. Based off of our results from these experiments, we can conclude that chemical inhibition of Mmp13 does not appear to be a viable treatment for patients diagnosed with GMPPB-associated dystroglycanopathy. We also checked to see if there was co-localization of Mmp13 with macrophages using a fluorescent macrophage reporter transgenic zebrafish line and antibody staining for Mmp13 protein. After staining and imaging the embryos via confocal microscopy, we did not see any co-localization of Mmp13 with macrophages. From the results of this experiment, we can conclude that macrophages are likely not the source of Mmp13