Isolation of a persistently quiescent muscle satellite cell population.

Although studies have identified characteristics of quiescent satellite cells (SCs), their isolation has been hampered by the fact that the isolation procedures result in the activation of these cells into their rapidly proliferating progeny (myoblasts). Thus, the use of myoblasts for therapeutic (regenerative medicine) or industrial applications (cellular agriculture) has been impeded by the limited proliferative and differentiative capacity of these myogenic progenitors. Here we identify a subpopulation of satellite cells isolated from mouse skeletal muscle using flow cytometry that is highly Pax7-positive, exhibit a very slow proliferation rate (7.7 ± 1.2 days/doubling), and are capable of being maintained in culture for at least 3 mo without a change in phenotype. These cells can be activated from quiescence using a p38 inhibitor or by exposure to freeze-thaw cycles. Once activated, these cells proliferate rapidly (22.7 ± 0.2 h/doubling), have reduced Pax7 expression (threefold decrease in Pax7 fluorescence vs. quiescence), and differentiate into myotubes with a high efficiency. Furthermore, these cells withstand freeze-thawing readily without a significant loss of viability (83.1 ± 2.1% live). The results presented here provide researchers with a method to isolate quiescent satellite cells, allowing for more detailed examinations of the factors affecting satellite cell quiescence/activation and providing a cell source that has a unique potential in the regenerative medicine and cellular agriculture fields.NEW & NOTEWORTHY We provide a method to isolate quiescent satellite cells from skeletal muscle. These cells are highly Pax7-positive, exhibit a very slow proliferation rate, and are capable of being maintained in culture for months without a change in phenotype. The use of these cells by muscle researchers will allow for more detailed examinations of the factors affecting satellite cell quiescence/activation and provide a novel cell source for the regenerative medicine and cellular agriculture fields.

Discovery-Based Proteomics Identify Skeletal Muscle Mitochondrial Alterations as an Early Metabolic Defect in a Mouse Model of ß-Thalassemia.

Although metabolic complications are common in thalassemia patients, there is still an unmet need to better understand underlying mechanisms. We used unbiased global proteomics to reveal molecular differences between the th3/+ mouse model of thalassemia and wild-type control animals focusing on skeletal muscles at 8 weeks of age. Our data point toward a significantly impaired mitochondrial oxidative phosphorylation. Furthermore, we observed a shift from oxidative fibre types toward more glycolytic fibre types in these animals, which was further supported by larger fibre-type cross-sectional areas in the more oxidative type fibres (type I/type IIa/type IIax hybrid). We also observed an increase in capillary density in th3/+ mice, indicative of a compensatory response. Western blotting for mitochondrial oxidative phosphorylation complex proteins and PCR analysis of mitochondrial genes indicated reduced mitochondrial content in the skeletal muscle but not the hearts of th3/+ mice. The phenotypic manifestation of these alterations was a small but significant reduction in glucose handling capacity. Overall, this study identified many important alterations in the proteome of th3/+ mice, amongst which mitochondrial defects leading to skeletal muscle remodelling and metabolic dysfunction were paramount.

Whole body resistance training on functional outcomes of patients with Stage 4 or 5 chronic kidney disease: A systematic review.

Chronic kidney disease (CKD) causes skeletal muscle wasting, resulting in reduced function and inability to live independently. This systematic review critically appraised the scientific literature regarding the effects of full-body resistance training on clinically-relevant functional capacity measures in CKD. The study population included studies of people with Stage 4 or 5 CKD and a mean age of 40+ years old. Eight databases were searched for eligible studies: Pubmed, Embase, Cochrane, CINAHL, Scopus, Web of Science, MEDLINE, and AGELINE. MeSH terms and keyword combinations were used for screening following the PRISMA conduct. Inclusion criteria were based on PICO principles and no date of publication filter was applied. The intervention was training 2 days/week of structured resistance exercises using major upper and lower muscle groups. Minimum intervention period was 7 weeks. Comparison groups maintained their habitual activity without structured exercise training. Outcome measures of interest were: 6-min walk test, grip strength, timed up-and-go test, and sit-to-stand. Eight randomized controlled trials and one nonequivalent comparison-group study fulfilled the inclusion criteria and underwent data extraction. All studies were of hemodialysis patients. The evidence indicates that full-body resistance exercise significantly improved grip strength, timed up and go and sit to stand tests; metrics associated with enhanced quality and quantity of life.