Effects of Electrical Muscle Stimulation on Skeletal Muscle During Lipopolysaccharide-Induced Inflammation: A Controlled Murine Study.

Interleukin-1 signaling contributes to endurance training-induced skeletal muscle adaptations.

Interleukin (IL)-1 is widely recognized as an inflammatory cytokine induced in response to muscle injury, where it contributes to the clearance of damaged fibers and supports subsequent regenerative and reparative processes. In contrast, IL-1 derived from infiltrating neutrophils in response to transient, non-damaging exercise has been reported to regulate energy metabolism during endurance exercise. Therefore, in the present study, we investigated the role of IL-1 in skeletal muscle endurance adaptations induced by chronic endurance training (ET). Thirteen-week-old BALB/c wild-type (WT) mice and mice deficient in both IL-1α and IL-1β (IL-1 knockout; IL-1 KO) were used. The left hindlimb was subjected to ET induced by electrical stimulation of the triceps surae muscle three times per week for five weeks, while the right hindlimb served as a control. Baseline muscle endurance did not differ between WT and IL-1 KO mice. Following ET, muscle endurance and mitochondria respiration were significantly increased in WT mice but not in IL-1 KO mice. Moreover, ET induced increases in citrate synthase activity and the expression of PGC-1α, mitochondrial respiratory chain complexes I and III, and hexokinase 2 exclusively in WT mice. A single bout of exercise significantly increased IL-1β mRNA, but not IL-1α mRNA, in WT mice. In addition, exercise-induced phosphorylation of p38 MAPK and increases in PGC-1α-b and hexokinase 2 mRNA expression were attenuated in IL-1 KO mice. These findings suggest that IL-1 signaling is associated with ET-induced improvements in muscle endurance and mitochondrial quantity and quality, possibly through activation of the p38 MAPK pathway.

Whole Muscle Physiology for the Assessment of Skeletal Muscle Function in Mice

Adenosine 5'-monophosphate prevents sepsis-associated muscle wasting by activating AMPK and suppressing IL-1β inflammatory cytokines

Sepsis-associated muscle wasting (SAMW) causes long-term functional decline, even after recovery. Emerging evidence indicates that adenosine 5'-monophosphate (AMP) confers organ-protective effects in response to physiological stress or injury, potentially through the activation of AMP-activated protein kinase (AMPK) signalling pathways. In this study, we investigated the effects of AMP on SAMW to evaluate its efficacy as a therapeutic agent to alleviate SAMW. In vivo, a mouse model of cecum ligation and puncture sepsis was established using male C57BL/6 mice, which received intraperitoneal AMP (0.5 mg/g) or saline as a control. In vitro, C2C12 myoblasts and RAW264.7 macrophages were cultured under standard conditions and treated with AMP. Forelimb grip strength, blood and muscle sampling, western blotting, AMP assays, RNA sequencing, ELISA, flow cytometry, real-time PCR, immunohistochemistry, histology, and computed tomography imaging were performed to assess molecular, cellular, and physiological responses. In addition, plasma samples from patients with sepsis were analysed to explore translational relevance. AMP suppressed sepsis-induced inflammatory cytokine production and improved muscle strength by attenuating mammalian target of rapamycin complex 1 activation and modulating AMPK signaling, thereby contributing to the preservation of muscle mass and a reduction in systemic inflammation. In vitro, AMP suppressed LPS- induced IL-1β production in RAW264.7 macrophages and attenuated LPS- or IL-1β-induced myotube atrophy in C2C12 cells and shifted the cells towards a fast-twitch phenotype. Evaluation of clinical samples revealed elevated inflammatory cytokines in patients with sepsis exhibiting muscle wasting. This study demonstrates that AMP effectively mitigates SAMW by activating AMPK and suppressing IL-1β-mediated molecular pathways. These findings highlight the potential of AMP as a novel therapeutic agent for preserving skeletal muscle functionality and morphology in sepsis.

Elevation of body temperature during exercise enhances protection against dexamethasone‑induced skeletal muscle atrophy

Abstract Prolonged glucocorticoid exposure induces skeletal muscle atrophy through suppression of protein synthesis and activation of catabolic signalling pathways. Although exercise attenuates glucocorticoid‐induced muscle loss, whether exercise‐induced increases in body temperature contribute remains unclear. In this study, we examined whether exercise in different thermal conditions modulates skeletal muscle atrophy and intracellular signalling during glucocorticoid exposure. Female Sprague–Dawley rats (n = 48) were assigned to six groups: control (CON), dexamethasone‐treated (DEX), cold exercise (∼5°C; CE), cold exercise with dexamethasone (CED), warm exercise (25°C; WE) and warm exercise with dexamethasone. Exercise protocols were matched, and dexamethasone was administered for 5 days. Dexamethasone reduced plantaris muscle mass (by 17%, P < 0.0001) and fibre cross‐sectional area (27%, P < 0.0001). During dexamethasone treatment, exercise in a cold environment provided partial protection, with muscle mass higher than DEX (P = 0.0476), but both muscle mass and fibre CSA remained lower than CON (P = 0.0096 and P = 0.0215, respectively). In contrast, exercise in a warm environment preserved muscle mass and fibre CSA (no difference vs. CON) and resulted in higher muscle mass (P = 0.0070) and fibre CSA (P < 0.0001) than DEX. Exercise‐induced increases in rectal temperature were associated with higher Hsp72 and Hsp25 expression, partial preservation of Akt–FoxO3a signalling and reduced MuRF1 expression, whereas exercise in a cold environment showed minimal heat shock protein response and limited suppression of catabolic signalling. These findings indicate that exercise‐induced elevation of body temperature enhances protection against glucocorticoid‐induced skeletal muscle atrophy and support a role for heat‐associated cellular stress responses in modulating muscle protein turnover during glucocorticoid exposure.

Integrin-β1/FAK signaling is involved in electrical stimulation to prevent disuse muscular atrophy induced by tail suspension in mice.

BACKGROUND Electrical stimulation is a widely used method for preventing and treating disuse muscle atrophy; however, the underlying mechanisms remain incompletely examined. Integrins, a class of transmembrane cell adhesion receptors, are considered primary mechanosensors involved in load-induced muscle growth. However, no previous studies have demonstrated whether integrin β1 and its downstream FAK signaling pathway are involved in the prevention of disuse muscle atrophy via electrical stimulation. Our study hypothesized that mechanical signals generated by electrical induced muscle contraction activate integrins, thereby contributing to muscle atrophy prevention. MATERIALS AND METHODS A disuse muscle atrophy model was constructed by tail suspending C57BL/6 mice for 2 weeks. The average physiological cross-sectional area, muscle strength, muscle fiber type, integrin β1, p-FAK, and p-p70S6K protein expression in the gastrocnemius and soleus muscles were measured following electrical stimulation. RESULTS Mice in the tail suspension with electrical stimulation (TS + E) group exhibited significantly greater physiological cross-sectional area and muscle strength compared with the tail suspension (TS) group (p < 0.05). Additionally, integrin β1 expression was lower in the TS group compared with the control group (p < 0.05). In contrast, in the TS + E group, expression levels of integrin β1, FAK, p-mTOR, and p-p70s6k were elevated compared with the TS group (p < 0.05). In GAS and SOL, the p-p70s6k/p70s6k ratio was significantly higher in the TS + E group compared with the TS group (p < 0.05). In GAS, the p-FAK/FAK ratio was higher in the TS + E group compared with the TS group (p < 0.01). However, no significant difference in p-FAK/FAK ratio was observed between the two groups in SOL. CONCLUSION Electrical stimulation upregulates the expression of the mechanosensor integrin β1 and enhances the phosphorylation of its downstream effector, FAK, in skeletal muscle. These effects may contribute to the attenuation of disuse muscle atrophy, providing preclinical evidence supporting the role of the integrin-β1/FAK signaling pathway in electrical stimulation-mediated muscle preservation.

The impact of stroke on intramuscular connective tissue in mice

Background Previous studies about post-stroke peripheral structural remodeling have been focused on muscle fiber alterations, while extracellular matrix (ECM) remodeling in musculoskeletal tissues remains unclear. This study examines changes in extracellular matrix (ECM), specifically hyaluronan (HA) and collagen, in forelimb muscles following distal middle cerebral artery occlusion (dMCAO) in mice. Methods Twenty-two 8-week-old C57BL/6 mice (10 male, 12 female) were randomly assigned to the control group (n = 10; 4 male, 6 female) or the experimental group (n = 12; 6 male, 6 female). 4 weeks post-stroke, forelimb muscle samples were collected and analyzed for HA and collagen distribution and concentrations. Results HA concentrations were significantly elevated in both the left (stroke affected) forelimb muscles (63.74 ± 11.80 μg/g), and right (unaffected) forelimb muscles (64.16 ± 13.52 μg/g) of stroke mice compared to the controls (left: 50.07 ± 8.84 μg/g, p = 0.022; and right: 49.36 ± 12.22 μg/g, p = 0.015). No significant difference in HA levels was observed between the affected and unaffected sides of stroke mice (p = 0.905). Collagen concentrations did not differ significantly among groups (control left: 8.62 ± 2.91 μg/g; control right: 8.77 ± 1.35 μg/g; stroke-affected: 8.24 ± 2.11 μg/g; stroke-unaffected: 8.28 ± 2.45 μg/g). Conclusion The results revealed a systemic increase in HA concentration in the stroke group, while collagen levels remained unchanged. These findings provide biochemical evidence of early alterations in extracellular matrix composition after stroke.