Sepsis triggers more severe and sustained muscle fiber atrophy in limb muscles when compared with respiratory muscle. This response is associated with enhanced proteasomal and autophagic proteolytic pathway activities and is triggered by inhibition of the AKT and complex 1 of the mammalian target of rapamycin pathways and activation of the AMPK pathway.

Background: Pulmonary Pseudomonas aeruginosa infection in cystic fibrosis patients is associated with skeletal muscle atrophy. In this study, we investigated the effects of P. aeurginosa infection and a whey protein-rich diet on skeletal muscle proteolytic pathways.Design: An agar bead model of pulmonary P. aeurginosa infection was established in adult C57/Bl6 mice. Protein ubiquitinaiton, lipidation of LC3B protein and expressions of autophagy-related genes and ubiquitin E3 ligases were quantified using immunoblotting and qPCR. The effects of pressure-treated whey protein diet on muscle proteolysis were also evaluated.Results: Pulmonary P. aeurginosa infection reduced diaphragm, tibialis anterior, and soleus muscle weights and increased protein ubiquitination, LC3B protein lipidation, and the expressions of Lc3b, Gabarapl1, Bnip3, Parkin, Atrogin-1, and MuRF1 genes in each muscle. These changes were greater in the tibialis as compared to soleus and diaphragm. Proteolysis indicators increased within one day of infection but were not evident after seven days of infection. A pressurized whey diet attenuated LC3B protein lipidation, expressions of autophagy-related genes (BNIP3), pro-inflammatory cytokines, and protein ubiquitination.Conclusions: We conclude that pulmonary P. aeruginosa infection activates the autophagy, and the proteasome pathways in skeletal muscles and that a pressurized whey protein diet attenuates muscle proteolysis in this model.

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