Proteomic identification of virulence-related factors in young and aging C. elegans infected with Pseudomonas aeruginosa.

The molecular mechanisms that distinguish immunosenescence from general age-related decline are poorly understood. We addressed this by exposing Day 1 and Day 5 adults of Caenorhabditis elegans to Pseudomonas aeruginosa strain PA01, an opportunistic pathogen. Day 5 adult C. elegans exhibited greater vulnerability to infection as compared to Day 1 C. elegans. Using TMT6 -plex isobaric labeling and reductive dimethylation, we identified 55 proteins whose levels were altered following infection of Day 1 and Day 5 adults. Proteins whose levels changed in response to infection at both ages were strongly enriched for locomotory functions underscoring the importance of pathogen avoidance mechanisms. In Day 1 C. elegans, proteins with reproductive functions were highly enriched, whereas, Day 5 worms showed elevated levels of factors representing stress response pathways such as unfolded protein response (UPR) and metabolic functions. We also found that PA01 infection is associated with elevated protein carbonylation, an irreversible marker for oxidative stress. We explored the function of UNC-60, a cytoskeletal protein whose levels were changed by both age and infection, and found that mutants of unc-60 have reduced lifespan. Overall, our data provide novel insights into the relationship between age and immunosenescence in metazoans.

SIGNIFICANCE: There are gaps in our knowledge pertaining to how aging influences an organism's response to pathogen exposure. In C. elegans, pathogen exposure to P. aeruginosa PA01 results in shortened lifespan, which is more pronounced in Day 5, compared to Day 1 adult worms. The proteome has age-specific responses to this exposure, and notably affects development, reproduction, metabolism, protein folding/unfolding, locomotion, and response to stress. This study addresses the molecular links between aging and immunosenescence in invertebrates.