Aims. The decrease in the number of satellite cells (SCs), contributing to myofibre formation and reconstitution, and their proliferative capacity, leads to muscle loss, a condition known as sarcopenia. Resistance training can prevent muscle loss; however, the underlying mechanisms of resistance training effects on SCs are not well understood. We therefore conducted a comprehensive transcriptome analysis of SCs in a mouse model. Methods. We compared the differentially expressed genes of SCs in young mice (eight weeks old), middle-aged (48-week-old) mice with resistance training intervention (MID+ T), and mice without exercise (MID) using next-generation sequencing and bioinformatics. Results. After the bioinformatic analysis, the PI3K-Akt signalling pathway and the regulation of actin cytoskeleton in particular were highlighted among the top ten pathways with the most differentially expressed genes involved in the young/MID and MID+ T/MID groups. The expression of Gng5, Atf2, and Rtor in the PI3K-Akt signalling pathway was higher in the young and MID+ T groups compared with the MID group. Similarly, Limk1, Arhgef12, and Araf in the regulation of the actin cytoskeleton pathway had a similar bias. Moreover, the protein expression profiles of Atf2, Rptor, and Ccnd3 in each group were paralleled with the results of NGS. Conclusion. Our results revealed that age-induced muscle loss might result from age-influenced genes that contribute to muscle development in SCs. After resistance training, age-impaired genes were reactivated, and age-induced genes were depressed. The change fold in these genes in the young/MID mice resembled those in the MID + T/MID group, suggesting that resistance training can rejuvenate the self-renewing ability of SCs by recovering age-influenced genes to prevent sarcopenia. Cite this article: Bone Joint Res 2022;11(2):121–133

Our aim was to accurately determine whether muscle atrophy and fatty infiltration are reversible following cuff repair. Patients with a repairable cuff-tear were recruited and assessed clinically and radiologically (Magnetic Resonance Imaging). At surgery, supraspinatus was biopsied. Post-operatively, patients underwent clinical evaluation at standardised intervals, with further MRI and an ultrasound guided biopsy of supraspinatus at 12 months. MRI was used to characterize cuff-tears and determine the degree of muscle atrophy and fatty infiltration. Biopsy samples were fixed on-site and transported for processing. Morphometric assessments of myofibres were made and mean cross-sectional areas calculated using validated techniques. The pathologist was blinded to sample details. Statistical analysis was performed to assess differences in mean myofibre area following cuff repair and correlated with radiological findings. Eight patients were available for completed histological and radiological analysis. Six (two re-tears) demonstrated sizeable and highly statistically significant improvements in mean myofibre cross-sectional area (P=0.000–0.0253). Of the two not showing any increase in myofibre area, neither result was statistically significant (P=0.06, 0.2); one was a re-tear and one was a repair of a partial-thickness tear. Radiologically, the muscle and fatty changes had not demonstrably changed. Our finding that myofibre cross-sectional area increases following cuff repair suggests muscle atrophy is a potentially reversible process. Even with re-tears, improvements were seen. MRI features of fatty infiltration and muscle atrophy were not seen to improve however. It is likely that radiological assessment is not sensitive enough to demonstrate the reversibility of muscle atrophy seen on histological analysis at one year

Objectives. Traumatic brachial plexus injury causes severe functional impairment of the arm. Elbow flexion is often affected. Nerve surgery or tendon transfers provide the only means to obtain improved elbow flexion. Unfortunately, the functionality of the arm often remains insufficient. Stem cell therapy could potentially improve muscle strength and avoid muscle-tendon transfer. This pilot study assesses the safety and regenerative potential of autologous bone marrow-derived mononuclear cell injection in partially denervated biceps. Methods. Nine brachial plexus patients with insufficient elbow flexion (i.e., partial denervation) received intramuscular escalating doses of autologous bone marrow-derived mononuclear cells, combined with tendon transfers. Effect parameters included biceps biopsies, motor unit analysis on needle electromyography and computerised muscle tomography, before and after cell therapy. Results. No adverse effects in vital signs, bone marrow aspiration sites, injection sites, or surgical wound were seen. After cell therapy there was a 52% decrease in muscle fibrosis (p = 0.01), an 80% increase in myofibre diameter (p = 0.007), a 50% increase in satellite cells (p = 0.045) and an 83% increase in capillary-to-myofibre ratio (p < 0.001) was shown. CT analysis demonstrated a 48% decrease in mean muscle density (p = 0.009). Motor unit analysis showed a mean increase of 36% in motor unit amplitude (p = 0.045), 22% increase in duration (p = 0.005) and 29% increase in number of phases (p = 0.002). Conclusions. Mononuclear cell injection in partly denervated muscle of brachial plexus patients is safe. The results suggest enhanced muscle reinnervation and regeneration. Cite this article: Bone Joint Res 2014;3:38–47

Aims

Rotator cuff muscle atrophy and fatty infiltration affect the clinical outcomes of rotator cuff tear patients. However, there is no effective treatment for fatty infiltration at this time. High-intensity interval training (HIIT) helps to activate beige adipose tissue. The goal of this study was to test the role of HIIT in improving muscle quality in a rotator cuff tear model via the β3 adrenergic receptor (β3AR).

The health of a synovial joint is relied on normal function and coordination of a group of tissues such as articular cartilage (AC), ligaments, tendons and muscles. Osteoarthritis (OA), which is the most common joint disease, is clinically characterised by lesion of AC. Despite this, injury of a ligament or tendon or muscle generates a joint instability, which accelerates deterioration of AC and progression of OA. Traditional histology is often used to study the pathology of biological tissues. It requires tissue biopsy, which traumatises the donor tissues. Therefore, it is not an idea method for assessing AC, ligaments and tendons as the tissues have a poor healing capability. There is a worldwide demand of an imaging technique that diagnoses the microstructural changes of chondral and connective tissues without biopsy. Confocal arthroscopy (Optiscan Pty Ltd, Australia) possesses a Ø 6.3 mm probe and offers a 0.7 µm lateral imaging resolution and 7 µm axial resolution. It has been successfully used for examining the internal microstructural disorders in rotator cuff tendons of human cadavers without tissue biopsy (WU et al., 2015). This study investigates the capability of confocal arthroscopy as optical histology for assessing the internal microstructure of AC, ligaments, tendons and muscles in a knee joint. Four sheep keen joints were freshly donated by other research unrelated to this study. After 5 ml clinical grade fluorescein solution at 0.05 g/L was injected into the joint cavity of a knee joint, the joint was passively exercising for about 10 minutes. The joint was then open collaterally and washed thoroughly using PBS for acquiring the microstructure of AC, ligaments, tendons and muscles using the confocal arthroscopy. Results: without biopsy, confocal arthroscopy offers an imaging resolution for onsite distinguishing the subtle microstructural difference of AC in the weight-bearing and non-weight bearing region. It also permitted visualising the hierarchical collagen structure in ligaments and tendons at a fibre level, and characterising the muscle nuclei, motor-neurons, moto-neuron synapse and striates of myofibres. Confocal arthroscopy showed the early promise to act as optical histology for studying the microstructure of chondral and a range of connective tissues, which allows understand better the health status of a knee joint. Since a sheep knee joint is very small for operating a normal procedure of an arthroscopic examination, an open knee joint surgery was performed in this study to allow imaging the microstructure of AC and a range of connective tissues. This is accounted as a limitation in the study. Nevertheless, this study demonstrated the development of confocal arthroscopy may lead to optical histology of the internal microstructure of AC and a group of connective tissues, which offers understanding more comprehensively the healthy status of a knee joint

MicroRNAs (miRNAs) are a class of small non-coding RNAs that have emerged as potential predictive, prognostic, and therapeutic biomarkers, relevant to many pathophysiological conditions including limb immobilization, osteoarthritis, sarcopenia, and cachexia. Impaired musculoskeletal homeostasis leads to distinct muscle atrophies. Understanding miRNA involvement in the molecular mechanisms underpinning conditions such as muscle wasting may be critical to developing new strategies to improve patient management. MicroRNAs are powerful post-transcriptional regulators of gene expression in muscle and, importantly, are also detectable in the circulation. MicroRNAs are established modulators of muscle satellite stem cell activation, proliferation, and differentiation, however, there have been limited human studies that investigate miRNAs in muscle wasting. This narrative review summarizes the current knowledge as to the role of miRNAs in the skeletal muscle differentiation and atrophy, synthesizing the findings of published data.

Cite this article: Bone Joint Res 2020;9(11):798–807.