CELLULAR SENESCENCE IMPLICATED IN SEPSIS-INDUCED MUSCLE WEAKNESS AND AMELIORATED WITH METFORMIN

Background: Sepsis is a life-threatening medical emergency, frequently complicated with intensive care unit-acquired weakness syndrome (ICU-AW). ICU-AW patients display flaccid weakness of the limbs, especially in the proximal limb muscles. However, little is known regarding its pathogenesis. Here, we aimed to identify the potential signaling pathway involved in ICU-AW regulation and identify a potential therapeutic drug for intervention. Methods: Both in vivo and in vitro septic mice were used. For the in vivo septic mice, either cecum ligation and puncture or intraperitoneal injection of LPS was conducted in mice. The body weight and muscle mass were then measured and recorded. Muscle strength was evaluated by limb grip strength test. The expression of proteins extracted from cells and muscles was checked through Western blot analysis. Quantitative reverse transcription-polymerase chain reaction was carried out to test the transcriptional level of genes. Senescence-associated β-galactosidase (SA-β-gal) staining and Sirius red for collagen staining were conducted. Metformin, as an antiaging agent, was then tested for any attenuation of sepsis-related symptoms. For in vitro sepsis modeling, myoblasts were treated with LPS, analyzed for senescence-related protein expression, and subsequently retested upon metformin treatment. Results: We found that both the weight and strength of muscle were dramatically reduced in cecum ligation and puncture- or LPS-induced septic mice. RNA-seq analysis revealed that various cellular senescent genes were involved in sepsis. In line with this, expression of senescence-related genes, p53 and p21 were both upregulated. Both SA-β-gal and Sirius red for collagen staining were enhanced in tibialis anterior muscles. Notably, inhibition of p53 expression by siRNA prominently reduced the number of SA-β-gal-positive myoblasts upon LPS treatment. This indicated sepsis-induced cellular senescence to be dependent on p53. Consistent with the function of metformin in antiaging, metformin attenuated cellular senescence in both murine myoblasts and skeletal muscles during sepsis. Muscle strength of septic mice was improved upon metformin treatment. Metformin intervention is therefore proposed as a potential therapeutic strategy for ICU-AW. Conclusion: Taken together, we revealed a previously unappreciated linkage between cellular senescence and sepsis-induced muscle weakness and propose metformin as a potential therapeutic drug for the treatment of ICU-AW.