Computational Models Provide Insight into In Vivo Studies and Reveal the Complex Role of Fibrosis in mdx Muscle Regeneration.

Duchenne muscular dystrophy is a pro-fibrotic, muscle wasting disease. Reducing fibrosis is a potential therapeutic target; however, its effect on muscle regeneration is not fully understood. This study (1) used an agent-based model to predict the effect of increased fibrosis in mdx muscle on regeneration from injury, and (2) experimentally tested the resulting model-derived hypothesis. The model predicted that increasing the area fraction of fibrosis decreased regeneration 28 days post injury due to limited growth factor diffusion and impaired cell migration. WT, mdx, and TGFβ-treated mdx mice were used to test this experimentally. TGFβ injections increased the extracellular matrix (ECM) area fraction; however, the passive stiffness of the treated muscle, which was assumed to correlate with ECM protein density, decreased following injections, suggesting that ECM protein density was lower. Further, there was no cross-sectional area (CSA) difference during recovery between the groups. Additional simulations revealed that decreasing the ECM protein density resulted in no difference in CSA, similar to the experiment. These results suggest that increases in ECM area fraction alone are not sufficient to reduce the regenerative capacity of mdx muscle, and that fibrosis is a complex pathological condition requiring further understanding.