Sexual dimorphism in the response to (-)-Epicatechin on PDGFRα and diaphragm damage in a murine model of muscular dystrophy

Abstract

Introduction: Skeletal muscle has the ability to regenerate after injury through the coordinated action of satellite cells (SCs), fibroadipogenic progenitors (FAPs), which express PDGFRα, and immune system cells. In recent years, sexual dimorphism in muscle regeneration has been described, with female mice showing a greater number of satellite cells and type I fibers compared with males. Among the diseases affecting skeletal muscle are muscular dystrophies (MD), which are characterized by progressive weakness and the replacement of muscle tissue by fibroadipose tissue. The diaphragm is one of the most affected muscles in MD due to its higher connective tissue content, which makes its microenvironment particularly susceptible to structural damage. During regeneration, dysregulation of the muscle microenvironment promotes the differentiation of FAPs into myofibroblasts and adipocytes, contributing to the accumulation of fibroadipose tissue. In this context, several palliative strategies have been proposed to mitigate muscle damage, including the use of the flavonol (-)-epicatechin (Epi), a compound that has been shown to reduce the damaged area and fibrosis, while also promoting muscle hypertrophy. However, most studies have been conducted in males, and therefore knowledge about the response to Epi in females remains limited. In this study, we analyzed the effect of Epi on PDGFRα expression and the damaged area in the diaphragm, comparing the response between male and female mice. Methodology: A total of 64 12-week-old mice were used, including 28 females and 36 males, distributed into four groups of 7 females and 9 males each. Animals received DMSO (0.01% vehicle) or Epi (1 mg/kg), as appropriate. For histological analysis, tissue sections were stained with hematoxylin-eosin to evaluate the damaged area. In addition, total proteins were extracted for Western blot analysis to determine PDGFRα expression as a marker of FAPs. Results: A greater damaged area was observed in the diaphragm of males compared with females. Epi treatment reduced damage in males; in females, its effect was mainly reflected as an improvement in fascicular architecture and greater homogeneity in muscle fiber size. Regarding PDGFRα, females showed higher expression of this marker; however, no significant differences were detected after Epi treatment in either sex. Conclusions: The diaphragm of males exhibited greater damage than that of females. Epi reduced damage mainly in males and improved histological organization in females without significantly modifying PDGFRα expression. These findings demonstrate a sex-dependent response and support the inclusion of sex as a biological variable in studies of muscular dystrophy.