PROJECT SUMMARY
Muscular dystrophies (MDs) are heritable neuromuscular diseases that cause progressive weakness and loss
of muscle as regenerative processes fail to adequately respond to progressive muscle damage. This ultimately
results in the replacement of functional musculature with a pathological extracellular matrix (ECM) composed of
fibrosis and fat, known as a fibro-matrix, which is a prominent feature of the most common of the MDs, Duchenne
MD (DMD). Effective therapeutics to combat fibro-matrix development and facilitate muscle regeneration are a
major unmet clinical need for MD patients, however, the mechanisms responsible for these issues are not well
understood. This project investigates cellular mechanisms contributing to the failed regeneration and fibrosis
development in dystrophic muscle. Specifically, NAD(P)H oxidase 4 (NOX4) has been identified as an anti-
fibrotic and pro-regenerative target in muscle. This was demonstrated by marked reductions in muscle fibrosis
and beneficial muscle remodeling of severely dystrophic muscle that models DMD, where NOX4 was targeted
using genetic and pharmacological approaches. It is hypothesized that NOX4 expression in myofibroblasts, cells
that produce ECM following tissue injury, contributes to muscle fibrosis by preventing myofibroblast clearance
following muscle regeneration. This phenomenon is known as myofibroblast persistence. The experiments of
this project will rigorously investigate the mechanisms leading to and the pathological consequences resulting
from the development of myofibroblast persistence using innovative genetic models, in vitro assays, and
transcriptomic analyses. Aim 1 will investigate myofibroblast dynamics in dystrophic skeletal muscle using
myofibroblast fate-mapping and conditional ablation of NOX4. Myofibroblast persistence will be assessed in a
newly-developed assay using cells isolated from dystrophic muscle, and several in vitro assays will be employed
to investigate myofibroblast behavior during differentiation and development of persistence. Aim 2 will evaluate
the influence that myofibroblasts exert on gene expression and cellular behavior of myogenic, fibroblastic, and
immune cells in dystrophic and regenerating muscle. In vitro models will be used to discern physical versus
diffusible cues responsible for these myofibroblast-driven phenotypes. The ultimate goal of the current project is
to define the pathological consequences of myofibroblasts in chronic muscle disease and provide solid
mechanistic insight responsible for the efficacious impact of NOX4-targeting as a beneficial remodeling
therapeutic strategy for the treatment of MDs and, potentially, other forms of muscle pathology.