# The D2.B10-Dmdmdx/J Mouse Model of Duchenne Muscular Dystrophy Exhibits a Severe Mitochondrial Deficiency Not Observed in the C57BL/10ScSn-Dmdmdx/J Mouse

## TL;DR

This study compares two mouse models of Duchenne muscular dystrophy and finds that one has severe mitochondrial issues not seen in the other.

## Contribution

The study reveals a severe mitochondrial deficiency in the D2-mdx mouse model of DMD not observed in the B10-mdx model.

## Key findings

- D2-mdx mice show significant mitochondrial respiration decrease and undetectable ATP levels.
- B10-mdx mice exhibit only mild mitochondrial issues like reduced ATP content.
- Gene therapy improved mitochondrial function in B10-mdx but not fully in D2-mdx mice.

## Abstract

Duchenne muscular dystrophy (DMD) is caused by mutations in the DMD gene, resulting in dystrophin deficiency in skeletal/cardiac muscle and progressive loss of function. Although the genetic causes of DMD have been thoroughly investigated, the energetic consequences have not been well examined across animal models. Previously, the laboratory examined mitochondrial function across nemaline myopathy mouse models of varying disease severity; here, mitochondrial phenotypes in DMD are assessed through the comparison of the milder C57BL/10ScSn-Dmdmdx/J (B10-mdx) and the more severe D2.B10-Dmdmdx/J mouse (D2-mdx) mouse models. D2-mdx exhibit a significant decrease in mitochondrial respiration, undetectable ATP concentrations, increased mitochondrial membrane potential, and alterations in electron transport chain enzyme activities. In contrast, B10-mdx show only mild mitochondrial phenotypes, including decreased ATP content. The D2-mdx mouse has genetic modifiers, including latent transforming growth factor-β–binding protein 4 (LTBP4) and annexin A6, that have been shown to alter DMD severity in humans. However, these modifiers did not account for mitochondrial differences seen in mdx mice. Both models were treated with a microdystrophin adeno-associated virus gene therapy to assess whether dystrophin restoration rescued mitochondrial phenotypes. Gene therapy attenuated the ATP deficiency in the B10-mdx mice, but only improved mitochondrial membrane potentials in D2-mdx mice. The exact cause of the D2-mdx mitochondrial phenotypes remains unknown, but secondary disease processes that affect mitochondrial phenotypes should be taken into consideration when choosing an animal model for DMD studies.