Sarcolipin deletion in mdx mice impairs calcineurin signalling and worsens dystrophic pathology

Abstract

Duchenne muscular dystrophy (DMD) is the most severe form of muscular dystrophy affecting 1 in 3500 live male births. Although there is no cure for DMD, therapeutic strategies aimed at enhancing calcineurin signalling and promoting the slow fibre phenotype have shown promise in mdx mice, which is the classical mouse model for DMD. Sarcolipin (SLN) is a small protein that regulates the sarco(endo)plasmic reticulum Ca2+-ATPase pump and its expression is highly upregulated in dystrophic skeletal muscle. We have recently shown that SLN in skeletal muscle amplifies calcineurin signalling thereby increasing myofibre size and the slow fibre phenotype. Therefore, in the present study we sought to determine the physiological impact of genetic Sln deletion in mdx mice, particularly on calcineurin signalling, fibre-type distribution and size and dystrophic pathology. We generated an mdx/Sln-null (mdx/SlnKO) mouse colony and hypothesized that the soleus and diaphragm muscles from these mice would display blunted calcineurin signalling, smaller myofibre sizes, an increased proportion of fast fibres and worsened dystrophic pathology compared with mdx mice. Our results show that calcineurin signalling was impaired in mdx/SlnKO mice as indicated by reductions in utrophin, stabilin-2 and calcineurin expression. In addition, mdx/SlnKO muscles contained smaller myofibres, exhibited a slow-to-fast fibre-type switch that corresponded with reduced expression of mitochondrial proteins and displayed a worsened dystrophic pathology compared with mdx muscles. Altogether, our findings demonstrate a critical role for SLN upregulation in dystrophic muscles and suggest that SLN can be viewed as a potential therapeutic target.

Variable cytoplasmic actin expression impacts the sensitivity of different dystrophin‐deficient mdx skeletal muscles to eccentric contraction

“…Surprisingly, utrophin ablation only partially rendered the Sol susceptible to ECC suggesting the mechanism of ECC force drop is multifactorial. While the mdx /utrophin −/− mouse is a compound phenotype with other complications and other mdx mouse models with decreased utrophin expression exist , the simplest interpretation of our data is that complete loss of utrophin in the mdx /utrophin −/− Sol only partially compromised its resistance to ECC. Also curious, the utrophin‐deficient PL from C57BL/10 showed greater protection than wild‐type control muscles, which further suggests that utrophin is not the sole determinant in effecting resistance to ECC.…”

Low‐dose lithium feeding increases the SERCA2a‐to‐phospholamban ratio, improving SERCA function in murine left ventricles

“…Ionophore (A23187; Sigma)‐supported SERCA activity was measured across a range of Ca 2+ concentrations (pCa 7.3–5.2) using an enzyme‐linked spectrophotometric assay fitted onto a 96‐well plate as previously described (Fajardo, Fajardo, LeBlanc, & MacPherson, 2018; Fajardo, Mikhaeil, Leveille, Tupling, & LeBlanc, 2018). Similar to the GSK3 activity assay, the SERCA activity assay links ATP hydrolysis to the disappearance of NADH using PK and LDH (18 U l −1 for both).…”

Progerin in muscle leads to thermogenic and metabolic defects via impaired calcium homeostasis

“…Researchers have linked the upregulation of Sln to a variety of muscle‐related diseases, including muscular dystrophy (Fajardo et al, ). In this study, we determined that Sln is significantly upregulated in the skeletal muscle that expresses mutant lamin A (Figures b and a).…”

“…Researchers have observed increased Sln expression levels in various forms of muscular dystrophy (Bal et al, 2012;Fajardo et al, 2018Fajardo et al, , 2017Pant, Bal, & Periasamy, 2016). To characterize the physiological role of Sln upregulation in Lmna −/− mice, we created Sln knockout (Sln −/− ) mice ( Figure 1c) using the CRISPR/Cas9-mediated genome engineering technique (Zhou et al, 2014).…”