Prolonged sepsis triggers abnormal mitochondrial dynamics in the limb muscles and diaphragm

Mitochondrial dysfunction is considered as a major trigger of sepsis-induced intensive care unit-acquired weakness (ICU-AW), but the precise role of impaired mitochondrial dynamics in sepsis-induced ICU-AW remains unclear. The cecal ligation and puncture (CLP) model was used to induce sepsis in mice. Fluid resuscitation and antibiotic treatment were used to establish a 5-day duration sepsis model, with sham-operated animals serving as controls. The muscle function of the diaphragm (DM) and tibialis anterior (TA) was assessed individually. Transmission electron microscopy (TEM) was used to observe changes in mitochondrial ultrastructure and measure the morphological parameters. Western blot analysis and quantitative real-time polymerase chain reaction were used to examine the expression of mitochondrial fusion and fission proteins and genes in DM and TA muscles. Additionally, inflammation and apoptosis were assessed in these muscles by measuring the level of pro-inflammatory cytokines and apoptotic DNA degradation, respectively. Mice subjected to CLP developed severe sepsis. Limb muscle dysfunction was more severe than that of the DM, as indicated by a greater reductions in compound muscle action potential, strength, fatigue index, and muscle fiber cross-sectional area. TEM analysis revealed sepsis-induced intermyofibrillar mitochondrial fragmentation and accumulation of injury. Both muscles showed reduced levels of Opa1 and Mfn2 mRNA and protein, and increased levels of Fis1 mRNA and protein. Correlation analysis revealed significant associations between muscle strength and Opa1, Mfn2, and Opa1/Drp1 at 5 days post-sepsis. Surviving mice at 5 days showed persistent inflammation, injury, and apoptosis in both muscles, but were more pronounced in the TA muscle. Prolonged sepsis leads to an impairment in mitochondrial dynamics, resulting in skeletal muscle weakness and atrophy, which may be one of the possible mechanisms of sepsis-induced ICU-AW.