In vivo role of the fibroblast in muscular dystrophy-Renewal

Abstract Congenital muscular dystrophies (CMDs) are a group of genetic disorders that lead to neuromuscular degeneration and profound muscle wasting with early morbidity and mortality, often in adolescence. The more common mutations leading to CMD are in the LAMA2 gene, although mutations in the 3 genes encoding collagen VI (COL6A1, COL6A2 and COL6A3) is next most common where it leads to Ullrich and Bethlam myopathy. While these CMDs have been studied at the molecular levels for over 3 decades now, the field still lacks an appropriate therapy to treat afflicted individuals. The field also lacks a complete understanding of how this disease is initiated and propagated, although the overarching mechanism appears to be associated with how the skeletal muscle myofiber attaches to the overriding basement membrane. Here we will attempt to elucidate the greater underlying molecular and cellular mechanisms of Ullrich CMD by using a mouse model of Col6a2 deficiency. We hypothesize that detachment of the myofiber from its basement membrane due to collagen VI deficiency is sensed by integrin complexes where it also leads to TGFβ activation, leading to skeletal muscle fibroblast (FAP) activation and continued defective ECM generation that generates a reinforcing disease circuit that furthers the disconnection of the myofiber from the overriding basement membrane and ECM. To dive deeply into the molecular mechanisms of Ullrich CMD we propose 3 specific aims: Aim #1, to genetically increase/decrease myofibroblast activity in skeletal muscle of Ullrich CMD mice. Aim #2, to examine if loss of collagen VI leads to altered myofiber - ECM coupling in Ullrich CMD. Aim #3, to examine TGFβ as a mediator of myofibroblast-ECM-dependent disease in Ulrich CMD. A strength of this application is the use of genetically modified mouse models to directly assess the effects of the myofibroblast, TGFβ and myofiber-basement membrane detachment as primary disease initiating components of CMD in vivo, together generating a 3-way reinforcing feedback circuit. Finally, this work will suggest obvious translational approaches with gene therapy or biologics for treating Ullrich CMD (and related CMDs) based on the most proximal disease initiating mechanisms. For example, Aim #1 would suggest the use of reprogrammed CAR T-cells against activated fibroblasts, which was recently shown to antagonize fibrotic heart disease. Aim #2 would suggest gene therapy with a version of the Thbs4 cDNA that broadly upregulates integrins and the DGC to strengthen myofiber connectivity to the basement membrane broadly. Aim #3 would suggest the use of a selective TGFβ1 antagonizing monoclonal antibody (mAb) in patients.