The adaptive response of skeletal muscle: What is the evidence?

Heme oxygenase-1 therapy attenuates muscle atrophy following global brachial plexus avulsion in juvenile rats

INTRODUCTION/AIMS

Brachial plexus injury can seriously affect distal target muscle function, and long-term denervation leads to irreversible structural damage. In the present study, we examined the effect of hemin, a heme oxygenase-1 (HO-1) inducer, on intrinsic forepaw muscle atrophy induced by pan-plexus injury in juvenile rats, as well as its underlying mechanism.

METHODS

A global brachial plexus avulsion (GBPA) model of rat was established, and thirty 6-wk-old male rats were randomly divided into five groups: control, GBPA plus scramble small intering RNA (siRNA), GBPA plus scramble siRNA plus hemin, GBPA plus HO-1 siRNA, and GBPA plus HO-1 siRNA plus hemin. Hemin (50 mg/kg) was administered intraperitoneally once daily and the siRNA (5 μg) was injected intramuscularly twice a week. Intrinsic forepaw muscles were used for analysis. Myofiber cross-sectional area (CSA), capillary-to-fiber ratio (C/F), and fiber-type composition were assessed. The levels of inflammatory factors, ubiquitin-protein ligases, and autophagy-related proteins were also measured.

RESULTS

We found that hemin treatment could effectively ameliorate denervated intrinsic forepaw muscle atrophy and suppress type I to II myofiber-type conversion. Hemin treatment failed to prevent muscle capillary loss after denervation. The levels of inflammatory factors (tumor necrosis factor alpha [TNFα] and interleukin 6 [IL-6]), ubiquitin-protein ligases (MuRF-1 and MAFbx), and autophagy-related proteins (BNIP3 and LC3B-II/I ratio) were increased by denervation and HO-1 therapy attenuated the increment.

DISCUSSION

Upregulation of HO-1 might potentially be an effective strategy to alleviate denervation-related muscle atrophy and might be a promising adjunctive treatment to improve hand function in children with pan-plexus injury.

A Prediction Model for Various Treatment Pathways of Upper Extremity in Tetraplegia

Upper extremity function is essential for the autonomy in patients with cervical spinal cord injuries and consequently a focus of the rehabilitation and treatment efforts. Routinely, an individualized treatment plan is proposed to the patient by an interprofessional team. It dichotomizes into a conservative and a surgical treatment pathway. To select an optimal pathway, it is important to define predictors that substantiate the treatment strategy. Apart from standard assessments (Standards for Neurological Classification of Spinal Cord Injury (ISNCSCI), the manual muscle test (MRC), and lower motoneuron integrity of key actuators for hand function performed by motor point (MP) mapping might serve as a possible predictor. Type of damage (upper motor neuron (UMN) or lower motor neuron (LMN) lesion) influences hand posture and thus treatment strategy as positioning and splinting of fingers, hands, arms, and surgical reconstructive procedures (muscle-tendon or nerve transfers) in choice and timing of intervention. For this purpose, an analysis of a database comprising 220 patients with cervical spinal cord injury is used. It includes ISNCSCI, MRC, and MP mapping of defined muscles at selected time points after injury. The ordinal regression analysis performed indicates that MP and ASIA impairment scale (AIS) act as predictors of muscle strength acquisition. In accordance with the innervation status defined by MP, electrical stimulation (ES) is executed either via nerve or direct muscle stimulation as a supplementary therapy to the traditional occupational and physiotherapeutic treatment methods. Depending on the objective, ES is applied for motor learning, strengthening, or maintenance of muscle contractile properties. By employing ES, hand and arm function can be predicted by MP and AIS and used as the basis for providing an individualized treatment plan.

Electrical stimulation alters muscle morphological properties in denervated upper limb muscles

Background

Damage to lower motor neuron causes denervation and degeneration of the muscles affected. Experimental and clinical studies of muscle denervation in lower extremities demonstrated that direct electrical stimulation (ES) of muscle can prevent denervation atrophy and restore contractility. The aim of this study was to identify possible myogenic effect of ES on denervated forearm and hand muscles in persons with spinal cord injury (SCI) and tetraplegia.

Methods

This prospective interventional study with repeated measurement design included 22 patients aged 48·6 (± 15·7), 0·25 (0·1/46) years after spinal cord lesion, AIS A-D. In each patient, two electrophysiologically-confirmed denervated muscles in the hand and forearm were analyzed – one extrinsic (Extensor Carpi Ulnaris - ECU) and one intrinsic (1st Dorsal Interosseus - IOD1). Muscles were stimulated for 33 min, five times per week over a 12-weeks period. Using ultrasonography (USG), muscle thickness (MT) and pennation angle (PA) of these muscles were determined at start and end of the stimulation period.

Findings

MT of IOD1 increased from 6·3 mm (± 3·2 mm) to 9·2 mm (± 2·4 mm) (p = 0·004) and the PA from 5·5° (± 3·0°) to 11° (± 2·2°) (p = 0·001). The corresponding values for the ECU were 5·5 mm (± 2·5 mm) to 7·0 mm (± 2·2 mm) (p = 0·039) and 5·5° (± 3·4°) to 9·4° (± 3·8°) (p = 0·005), respectively. The correlation of MT between baseline and completion was r = 0·58 (p = 0·037) for the ECU and r = 0·63 (p = 0·008) for the IOD1.

Interpretation

12 weeks of direct muscle stimulation increases the MT and PA of the denervated intrinsic and extrinsic hand muscles studied.

Funding

Swiss Paraplegic Centre, Switzerland

Chronic electrical stimulation reduces reliance on anaerobic metabolism in locust jumping muscle

Chronic electrical stimulation (CES) is a well-documented method for changing mammalian muscle from more fast-twitch to slow-twitch metabolic and contractile profiles. Although both mammalian and insect muscles have many similar anatomical and physiological properties, it is unknown if CES produces similar muscle plasticity changes in insects. To test this idea, we separated Schistocerca americana grasshoppers into two groups (n = 37 to 47): one that was subjected to CES for 180 min each day for five consecutive days and one group that was not. Each group was then electrically stimulated for a single time period (0, 5, 30, 60, or 180 min) before measuring jumping muscle lactate, a characteristic of fast-twitch type fibers. At each time point, CES led to a significantly reduced jumping muscle lactate concentration. Based on similar short-term CES mammalian studies, the reduction in lactate production was most likely due to a reduced reliance on anaerobic metabolism. Thus, longer stimulation periods should result in greater aerobic enzymatic activities, altered myosin ATPase, and shift fiber types. This is the first study to use electrical stimulation to explore insect muscle plasticity and our results show that grasshopper jumping muscle responds similarly to mammalian muscle.

Firearms-related skeletal muscle trauma: pathophysiology and novel approaches for regeneration

One major cause of traumatic injury is firearm-related wounds (i.e., ballistic trauma), common in both civilian and military populations, which is increasing in prevalence and has serious long-term health and socioeconomic consequences worldwide. Common primary injuries of ballistic trauma include soft-tissue damage and loss, haemorrhage, bone fracture, and pain. The majority of injuries are of musculoskeletal origin and located in the extremities, such that skeletal muscle offers a major therapeutic target to aid recovery and return to normal daily activities. However, the underlying pathophysiology of skeletal muscle ballistic trauma remains poorly understood, with limited evidence-based treatment options. As such, this review will address the topic of firearm-related skeletal muscle injury and regeneration. We first introduce trauma ballistics and the immediate injury of skeletal muscle, followed by detailed coverage of the underlying biological mechanisms involved in regulating skeletal muscle dysfunction following injury, with a specific focus on the processes of muscle regeneration, muscle wasting and vascular impairments. Finally, we evaluate novel approaches for minimising muscle damage and enhancing muscle regeneration after ballistic trauma, which may have important relevance for primary care in victims of violence.

Human skeletal muscle fiber type percentage and area after reduced muscle use: A systematic review and meta-analysis

The main objective of this systematic review was to examine the effect of reduced muscle activity on the relative number of type 1 muscle fibers (%) in the human vastus lateralis muscle. Other objectives were changes in type 2A and 2X percentages and muscle fiber cross-sectional area. We conducted systematic literature searches in eight databases and included studies assessing type 1 fiber percentage visualized by ATPase or immunohistochemical staining before and after a period (≥14 days) of reduced muscle activity. The reduced muscle activity models were detraining, leg unloading, and bed rest. Forty-two studies comprising 451 participants were included. Effect sizes were calculated as the mean difference between baseline and follow-up and Generic Inverse Variance tests with random-effects models were used for the weighted summary effect size. Overall, the mean type 1 muscle fiber percentage was significantly reduced after interventions (-1.94%-points, 95% CI [-3.37, -0.51], P = .008), with no significant differences between intervention models (P = .86). Meta-regression showed no effect of study duration on type 1 fiber percentage (P = .98). Conversely, the overall type 2X fiber percentage increased after reduced muscle activity (P < .001). The CSA of the muscle fiber types decreased after the study period (all P-values < 0.001) with greater reductions in type 2 than type 1 fibers (P < .001). The result of this meta-analysis display that the type 1 muscle fiber percentage decrease as a result of reduced muscle activity, although the effect size is relatively small.