The C57BL/10ScSn‐Dmdmdx/J (BL10‐mdx) mouse has been the most commonly used model for Duchenne muscular dystrophy (DMD) for decades. Their muscle dysfunction and pathology is, however, less severe than in patients with DMD, which complicates preclinical studies. Recent discoveries indicate that disease severity is exacerbated when muscular dystrophy mouse models are generated on a DBA2/J genetic background. Knowledge on the natural history of animal models is pivotal for high‐quality preclinical testing. However, for BL10‐mdx mice on a DBA2/J background (D2‐mdx), limited data are available. We addressed this gap in the natural history knowledge. First, we compared histopathological aspects in skeletal muscles of young D2‐mdx, BL10‐mdx, and wild‐type mice. Pathology was more pronounced in D2‐mdx mice and differed in severity between muscles within individuals. Secondly, we subjected D2‐mdx mice to a functional test regime for 34 weeks and identified that female D2‐mdx mice outperform severely impaired males, making females less useful for functional preclinical studies. Direct comparisons between 10‐ and 34‐wk‐old D2‐mdx mice revealed that disease pathology ameliorates with age. Heart pathology was progressive, with some features already evident at a young age. This natural history study of the D2‐mdx mouse will be instrumental for experimental design of future preclinical studies.—Van Putten, M., Putker, K., Overzier, M., Adamzek, W. A., Pasteuning‐Vuhman, S., Plomp, J. J., Aartsma‐Rus, A. Natural disease history of the D2‐mdx mouse model for Duchenne muscular dystrophy. FASEB J. 33, 8110–8124 (2019). http://www.fasebj.org

Limb-girdle muscular dystrophy types 2D and 2F (LGMD 2D and 2F) are autosomal recessive disorders caused by mutations in the alpha- and delta sarcoglycan genes, respectively, leading to severe muscle weakness and degeneration. The cause of the disease has been well characterized and a number of animal models are available for pre-clinical studies to test potential therapeutic interventions. To facilitate transition from drug discovery to clinical trials, standardized procedures and natural disease history data were collected for these mouse models. Implementing the TREAD-NMD standardized operating procedures, we here subjected LGMD2D (SGCA-null), LGMD2F (SGCD-null) and wild type (C57BL/6J) mice to five functional tests from the age of 4 to 32 weeks. To assess whether the functional test regime interfered with disease pathology, sedentary groups were taken along. Muscle physiology testing of tibialis anterior muscle was performed at the age of 34 weeks. Muscle histopathology and gene expression was analysed in skeletal muscles and heart.Muscle histopathology and gene expression was analysed in skeletal muscles and heart. Mice successfully accomplished the functional tests, which did not interfere with disease pathology. Muscle function of SGCA- and SGCD-null mice was impaired and declined over time. Interestingly, female SGCD-null mice outperformed males in the two and four limb hanging tests, which proved the most suitable non-invasive tests to assess muscle function. Muscle physiology testing of tibialis anterior muscle revealed lower specific force and higher susceptibility to eccentric-induced damage in LGMD mice. Analyzing muscle histopathology and gene expression, we identified the diaphragm as the most affected muscle in LGMD strains. Cardiac fibrosis was found in SGCD-null mice, being more severe in males than in females. Our study offers a comprehensive natural history dataset which will be useful to design standardized tests and future pre-clinical studies in LGMD2D and 2F mice.

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Limb girdle muscular dystrophy (LGMD) types 2D and 2F are caused by mutations in the genes encoding for α- and δ-sarcoglycan, respectively, leading to progressive muscle weakness. Mouse models exist for LGMD2D ( Sgca -/- ) and 2F ( Sgcd -/- ). In a previous natural history study, we described the pathology in these mice at 34 weeks of age. However, the development of muscle pathology at younger ages has not been fully characterised yet. We therefore performed a study into age-related changes in muscle function and pathology by examining mice at different ages. From 4 weeks of age onwards, male mice were subjected to functional tests and sacrificed at respectively 8, 16 or 24 weeks of age. Muscle histopathology and expression of genes involved in muscle pathology were analysed for several skeletal muscles, while miRNA levels were assessed in serum. In addition, for Sgcd -/- mice heart pathology was assessed. Muscle function showed a gradual decline in both Sgca -/- and Sgcd -/- mice. Respiratory function was also impaired at all examined timepoints. Already at 8 weeks of age, muscle pathology was prominent, and fibrotic, inflammatory and regenerative markers were elevated, which remained relatively constant with age. In addition, Sgcd -/- mice showed signs of cardiomyopathy from 16 weeks of age onwards. These results indicate that Sgca -/- and Sgcd -/- are relevant disease models for LGMD2D and 2F.