Key result
In Duchenne muscular dystrophy dogs, skeletal muscle SERCA and its regulators were down-regulated at the active disease stage, whereas calcium-binding proteins were upregulated at the terminal stage, with nominal differences in the heart.
Why the study?
Cytosolic calcium overload drives muscle degradation in DMD, making understanding sarcoplasmic reticulum calcium handling critical in translational canine DMD models.
Downregulation of SERCA regulators in active-stage DMD muscle warrants no clinical change; leaves open whether these shifts drive progression or compensation in canine models.
BACKGROUND: Cytosolic calcium overload contributes to muscle degradation in Duchenne muscular dystrophy (DMD). The sarcoplasmic reticulum (SR) is the primary calcium storage organelle in muscle. The sarco-endoplasmic reticulum ATPase (SERCA) pumps cytosolic calcium to the SR during muscle relaxation. Calcium is kept in the SR by calcium-binding proteins. METHODS: Given the importance of the canine DMD model in translational studies, we examined transcriptional changes of SERCA (SERCA1 and SERCA2a), SERCA regulators (phospholamban, sarcolipin, myoregulin, and dwarf open reading frame), and SR calcium-binding proteins (calreticulin, calsequestrin 1, calsequestrin 2, and sarcalumenin) in skeletal muscle (diaphragm and extensor carpi ulnaris) and heart (left ventricle) in normal and affected male dogs by droplet digital PCR before the onset (≤ 2-m-old), at the active stage (8 to 16-m-old), and at the terminal stage (30 to 50-m-old) of the disease. Since many of these proteins are expressed in a fiber type-specific manner, we also evaluated fiber type composition in skeletal muscle. RESULTS: In affected dog skeletal muscle, SERCA and its regulators were down-regulated at the active stage, but calcium-binding proteins (except for calsequestrin 1) were upregulated at the terminal stage. Surprisingly, nominal differences were detected in the heart. We also examined whether there exists sex-biased expression in 8 to 16-m-old dogs. Multiple transcripts were significantly downregulated in the heart and extensor carpi ulnaris muscle of female dogs. In fiber type analysis, we found significantly more type I fiber in the diaphragm of 8 to 16-m-old affected dogs, and significantly more type II fibers in the extensor carpi ulnaris of 30 to 50-m-old affected dogs. However, no difference was detected between male and female dogs. CONCLUSIONS: Our study adds new knowledge to the understanding of muscle calcium regulation in normal and dystrophic canines.
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Morales et al. (2024) studied Duchenne muscular dystrophy (n=30). Duchenne muscular dystrophy (dystrophin deficiency) vs. Normal dogs was evaluated on Transcript levels of SR calcium-binding proteins, SERCAs, and SERCA regulators. In Duchenne muscular dystrophy dogs, skeletal muscle SERCA and its regulators were down-regulated at the active disease stage, whereas calcium-binding proteins were upregulated at the terminal stage, with nominal differences in the heart.
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