Sepsis in the ageing population carries a high morbidity and mortality, thus requires better pre-clinical models for improved therapies. Insect-based methods have been used in understanding innate immunity as well as ageing; however Drosophila has not been used to study ageing and sepsis. Sepsis causes impaired mitochondrial activity similar to ageing, but in an accelerated time period. In Drosophila, ageing has been demonstrated to produce a decline in geotaxis; an objective metric of mobility, however it is unknown if sepsis also does. Furthermore, it is unknown how ageing affects the response to sepsis in Drosophila.
We hypothesized that sepsis mimics an accelerated process of aging as assessed by geotaxis, and mitochondrial activity, with this hypothesis we also tested the fidelity and candidacy of this model to mimic human disease.
We used 360 male Drosophila melanogaster flies, half were 3-5 days old and the other half 18-20 days old. We divided each age strata in 3 groups a) infected, b) sham needle pricked, c) control. Group A was infected by thoracic needle pricking with a bacterial solution containing 5 x10^7/ml of S. aureus. We measured geotaxis and cytochrome c oxidase activity (COX). Geotaxis was measured before and 18 hours after intervention with automated digital images. Mitochondrial COX was measured by colorimetric assay. All data was analyzed with parametric tests.
At baseline geotaxis in mature flies was 28.1% lower than in young flies (p<0.001). Infection also caused a decline in geotaxis in both age groups of 26.8% (p=0.001) in mature and 31.5% (p<0.001) in young flies from baseline. There was no difference in COX between age groups after infection (p=0.37). Compared to control group, infected young and mature flies had declining trends in COX but only significant in the young (20.64%, p=0.006; 7.65%, p=0.09, respectively).
Sepsis profoundly affects cellular and systemic end points as shown by a decline in cytochrome C oxidase activity and geotaxis in young flies. In the mature flies, we found a significant impairment of motor function but not of mitochondrial activity as was expected, suggesting age-specific differences in response to injury.
University of Pittsburgh
University of Pittsburgh Critical Care Medicine CRISMA Laboratory
University of Pittsburgh Medical Center