We recently generated a knock-in mouse model (PYGM p.R50X/p.R50X) of the McArdle disease (myophosphorylase deficiency). One mechanistic approach to unveil the molecular alterations caused by myophosphorylase deficiency, which is arguably the paradigm of “exercise intolerance,” is to compare the skeletal muscle tissue of McArdle, heterozygous, and healthy (wild-type [wt]) mice.
We analyzed in quadriceps muscle of p.R50X/p.R50X (n = 4), p.R50X/wt (n = 6), and wt/wt mice (n = 5) (all male, 8 wk old) molecular markers of energy-sensing pathways, oxidative phosphorylation and autophagy/proteasome systems, oxidative damage, and sarcoplasmic reticulum Ca2+ handling.
We found a significant group effect for total adenosine monophosphate-(AMP)-activated protein kinase (tAMPK) and ratio of phosphorylated (pAMPK)/tAMPK (P = 0.012 and 0.033), with higher mean values in p.R50X/p.R50X mice versus the other two groups. The absence of a massive accumulation of ubiquitinated proteins, autophagosomes, or lysosomes in p.R50X/p.R50X mice suggested no major alterations in autophagy/proteasome systems. Citrate synthase activity was lower in p.R50X/p.R50X mice versus the other two groups (P = 0.036), but no statistical effect existed for respiratory chain complexes. We found higher levels of 4-hydroxy-2-nonenal–modified proteins in p.R50X/p.R50X and p.R50X/wt mice compared with the wt/wt group (P = 0.011). Sarco(endo)plasmic reticulum ATPase 1 levels detected at 110 kDa tended to be higher in p.R50X/p.R50X and p.R50X/wt mice compared with wt/wt animals (P = 0.076), but their enzyme activity was normal. We also found an accumulation of phosphorylated sarco(endo)plasmic reticulum ATPase 1 in p.R50X/p.R50X animals.
Myophosphorylase deficiency causes alterations in sensory energetic pathways together with some evidence of oxidative damage and alterations in Ca2+ handling but with no major alterations in oxidative phosphorylation capacity or autophagy/ubiquitination pathways, which suggests that the muscle tissue of patients is likely to adapt overall favorably to exercise training interventions.
1Mitochondrial and Neuromuscular Diseases Laboratory and “MITOLAB-CM,” Research Institute of Hospital “12 de Octubre” (“i + 12”), Madrid, SPAIN; 2Neuromuscular and Neuropediatric Research Group, Neurosciences Department, Germans Trias i Pujol Research Institute and Campus Can Ruti, Autonomous University of Barcelona, Badalona, SPAIN; 3Department of Research and Doctorate Studies, European University, Madrid, SPAIN; 4Neuromuscular and Mitochondrial Pathology Department, Vall d’Hebron University Hospital, Research Institute (VHIR), Autonomous University of Barcelona, Barcelona, SPAIN; and 5Spanish Network for Biomedical Research in Rare Diseases (CIBERER), U723, Madrid, SPAIN
Address for correspondence: María Morán, Ph.D., Laboratorio de Enfermedades Raras, Mitocondriales y Neuromusculares, Instituto de Investigación Hospital Universitario 12 de Octubre (i + 12), Centro de Actividades Ambulatorias, 6a planta. Avenida de Córdoba s/n, Madrid 28041, Spain; E-mail: email@example.com.
Submitted for publication February 2016.
Accepted for publication March 2016.
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