Halofuginone and muscular dystrophy

Abstract

Muscular dystrophies (MDs) include different inherited diseases that all result in progressive muscle degeneration, impaired locomotion and often premature death. The major focus of MD research has been on alleviating the primary genetic deficit - using gene therapy and myoblast-transfer approaches to promote expression of the deficient or mutated genes in the muscle fibers. Although promising, these approaches have not yet entered into clinical practice and unfortunately for MD patients, there is currently no cure. Thus, the development of complementary and supportive therapies that slow disease progression and improve patients' quality of life is critically important. The main features of MDs are sarcolemmal instability and increased myofiber vulnerability to mechanical stress, resulting in myofiber degeneration. Fibrosis, with progressive replacement of muscle tissue, is a prominent feature in some MDs, preventing complete regeneration and hampering muscle functions. TGFß is the leading candidate for activating fibroblasts and eliciting overproduction of extracellular matrix (ECM) proteins. Halofuginone, an inhibitor of Smad3 phosphorylation downstream of TGFß signaling, inhibits the activation of fibroblasts and their ability to synthesize ECM, regardless of their origin or location. In animal models of MDs with prominent muscle fibrosis, halofuginone treatment has resulted in both prevention of collagen production in young animals and resolution of established fibrosis in older ones: the reduction in muscle collagen content was associated with improved muscle histopathology and major improvements in muscle function. Recently, these halofuginonedependent improvements were also observed in MD with minor fibrosis involvement, probably due to a direct effect of halofuginone on muscle cells, resulting in myotube fusion that is dependent on Akt and MAPK pathway activation. In summary, halofuginone improves muscle histopathology and muscle functions in various MDs, via inhibition of muscle fibrosis on the one hand, and increased myotube fusion on the other.