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

BACKGROUND: Electrical muscle stimulation (EMS) is used in critically ill patients to prevent intensive care unit-acquired weakness. It promotes anabolic responses partly through interleukin-6 (IL-6) signaling under non-inflammatory conditions; however, its effects during systemic inflammation remain unclear. We hypothesized that EMS applied during lipopolysaccharide (LPS)-induced systemic inflammation exacerbates skeletal muscle atrophy through activation of IL-6-mediated catabolic signaling. METHODS: Male C57BL/6J mice were randomly assigned to control, EMS, LPS, or EMS/LPS groups. Intraperitoneal LPS (2 mg/kg) or phosphate-buffered saline was administered, followed by EMS applied to the left hindlimb 8 h later (80 Hz, 5 mA, 30 min). Gastrocnemius muscle fiber cross-sectional area (CSA) was measured as an index of muscle atrophy, with three mice analyzed per group. Gastrocnemius muscles and blood samples were collected after treatment, and muscle morphology and CSA were analyzed histologically. Protein expression of Atrogin-1, MuRF1, C/EBPδ, phosphorylated mTOR, p70S6K, and STAT3 was assessed by Western blot, and IL-6 expression by qRT-PCR and ELISA. Data are presented as mean ± standard deviation (SD). RESULTS: Compared with control, EMS alone increased CSA (mean ± SD,1610 ± 468 vs 1350 ± 437 μm2; P < .0001), and the phosphorylation of mTOR (1.72 ± 0.234-fold; P < .0001) and p70S6K (2.34 ± 0.559-fold; P < .0001). In contrast, compared with LPS alone, EMS applied under LPS did not enhance the phosphorylation of mTOR or p70S6K, but reduced muscle fiber CSA (680 ± 327 vs 991 ± 453 μm2; P < .0001), and upregulated Atrogin-1 (13.1 ± 3.72 vs 7.85 ± 2.26-fold; p = 0.0014) and MuRF1 (3.77 ± 1.45 vs 2.50 ± 0.998 -fold; p = 0.0094) expression. These catabolic changes were accompanied by increased STAT3 phosphorylation and C/EBPδ expression (8.28 ± 4.16 vs 4.56 ± 1.88 -fold; p = 0.0098, 39.2 ± 16.4 vs 22.8 ± 12.3-fold; p = 0.0107). Additionally, IL-6 expression was elevated in both stimulated muscle (335 ± 242 vs 140 ± 23.1-fold; p = 0.0095) and serum (28.5 ± 4.60 vs 9.35 ± 3.19 ng/mL; P < .0001) in the EMS/LPS group. Similar atrophic changes were observed in the contralateral, non-stimulated limb. CONCLUSIONS: EMS applied during LPS-induced systemic inflammation exacerbated skeletal muscle atrophy and was associated with activation of IL-6/STAT3-C/EBPδ signaling and proteolytic pathways. These findings provide mechanistic insight into the effects of EMS under inflammatory conditions and warrant further investigation.