Role of sepsis in the development of limb muscle weakness in a porcine intensive care unit model

Severe muscle wasting and loss of muscle function in critically ill mechanically ventilated intensive care unit (ICU) patients have significant negative consequences on their recovery and rehabilitation that persist long after their hospital discharge; moreover, the underlying mechanisms are unclear. Mechanical ventilation (MV) and immobilization-induced modifications play an important role in these consequences, including endotoxin-induced sepsis. The present study aims to investigate how sepsis aggravates ventilator and immobilization-related limb muscle dysfunction. Hence, biceps femoris muscle gene expression was investigated in pigs exposed to ICU intervention, i.e., immobilization, sedation, and MV, alone or in combination with sepsis, for 5 days. In previous studies, we have shown that ICU intervention alone or in combination with sepsis did not affect muscle fiber size on day 5, but a significant decrease was observed in single fiber maximal force normalized to cross-sectional area (specific force) when sepsis was added to the ICU intervention. According to microarray data, the addition of sepsis to the ICU intervention induced a deregulation of >500 genes, such as an increased expression of genes involved in chemokine activity, kinase activity, and transcriptional regulation. Genes involved in the regulation of the oxidative stress response and cytoskeletal/sarcomeric and heat shock proteins were on the other hand downregulated when sepsis was added to the ICU intervention. Thus, sepsis has a significant negative effect on muscle function in critically ill ICU patients, and chemokine activity and heat shock protein genes are forwarded to play an instrumental role in this specific muscle wasting condition.