Objective  To observe the effect of sepsis on skeletal muscle function and to explore the role of skeletal muscle mitochondrial calcium uptake protein 1 (MICU1).

  Methods  A total of 40 specific-pathogen-free (SPF) healthy male C57BL/6J mice were randomly assigned to 4 groups, a sham operation group (Sham group, n=8), a sepsis modeling 6 h group (cecal ligation and puncture CLP-6 h group, n=10), a sepsis modeling 12 h group (CLP-12 h group, n=10), and a sepsis modeling 24 h group (CLP-24 h, n=12). The sepsis model was established by CLP. Mice in the Sham group only underwent laparotomic exploration of the cecum. Another 20 SPF mice were selected. The tibialis anterior muscle on one side was empty-transfected with adeno-associated virus (AAV) as controls (AAV-C), and the tibialis anterior muscle on the other side was transfected with AAV to enhance MICU1 expression (AAV-M). The mice were randomly assigned to two groups, a sham operation group (AAV-C-Sham and AAV-M-Sham, n=8) and a sepsis model 24 h group (AAV-C-CLP and AAV-M-CLP, n=12). The grip strength and compound muscle action potential (CMAP) of the tibialis anterior muscle were measured in each group at the corresponding time points. The levels of inflammatory factors, including tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6), in the skeletal muscle were measured by ELISA. The morphological changes of skeletal muscle cells were observed through H&E staining. The expression levels of MICU1 and muscle atrophy-related proteins, including muscle RING-finger containing protein 1 (MuRF1) and muscle atrophy Fbox protein (MAFbx), were determined by Western blot. The expression levels of MICU1 mRNA in skeletal muscle were determined by RT-qPCR.

  Results  Compared with mice in the Sham group, mice in the CLP group showed decreased body weight (P<0.05); their grip strength decreased with the prolongation of CLP modeling time (P<0.05); the amplitude of CMAP decreased, showing prolonged duration and latency (P<0.05); the expression levels of inflammatory factors, including TNF-α and IL-6, in skeletal muscle increased gradually (P<0.05); the fiber diameter and cross-sectional area of skeletal muscle decreased gradually with the prolongation of modeling time (P<0.05); the protein expression levels of MuRF1and MAFbx proteins increased gradually (P<0.05); the expression levels of MICU1 protein and mRNA decreased gradually (P<0.05). There was no significant difference in all indices between AAV-M-Sham and AAV-C-Sham groups (P>0.05). Compared with mice in the AAV-C-CLP group, mice in the AAV-M-CLP group showed increased grip strength (P<0.05); the amplitude of CMAP increased, showing shortened duration and latency (P<0.05); the fiber diameter and cross-sectional area of skeletal muscle increased (P<0.05); the expression levels of MuRF1and MAFbx decreased (P<0.05).

  Conclusion  Sepsis leads to skeletal muscle dysfunction, which is related to the decrease in mitochondrial MICU1 expression.