Pseudomonas Aeruginosa Infection Augments Burn-Induced Hepatic ER Stress
Author(s):
Mile Stanojčić, Sunnybrook Research Institute, University of Toronto, Toronto, Canada; Bogdan Stanković, Sunnybrook Research Institute, University of Toronto, Toronto, Canada; Marc Jeschke, Sunnybrook Research Institute
Background: Thermal injury is a trauma that is characterized by a severe hypermetabolic response and increased susceptibility to infection if not resolved. The unfolded protein response (UPR) initiated by the endoplasmic reticulum (ER) is an adaptive process to manage organelle stress preventing further dysfunction. Activation of the UPR/ER stress response pathway has been implicated in promoting a persistent hypermetabolic response following thermal injury by not facilitating but rather promoting infections.
Hypothesis: Using the two-hit model of burn + Pseudmonas aeruginosa (PA) infection, we sought to investigate the activation of this signalling pathway in a time dependent manner during the pathogenesis of injury.
Methods: Mice were divided into three treatment groups (control, burn and burn + PA infection). Burned mice received a full-thickness, 30% scald burn (98ºC for 10 seconds), with infectious mice receiving PA topically at a dose of (1-1.5 x 107 CFU), 3-days after insult. All mice were sacrificed during the following time points with respect to insult, (relative to burn for the burn group and infection for burn+PA group): 1, 12, 24 and 48 hours. Multiplex analysis was used to characterize chemokine and inflammatory cytokine expression.
Results: Here we show that both burn and burn + infection groups have distinct and time dependent hepatic ER stress activation profiles. Specifically, both groups had upregulation of all markers relative to controls with characteristic expression observed for BiP, PERK, JNK and eIF2α at all time points (1, 12, 24 and 48hrs after insult, respectively). The infectious burn group was best distinguished by BiP with elevated expression present during the acute time points and peaking at 12 hours; 4.8 and 2.2-times higher than controls (p<0.01) and burn (p<0.05), respectively. Chemokines began to distinguish themselves at 12hr after infection with elevated expression at 24hours (G-CSF, MCP-1, KC, MIP-1α/β, MIP-2). Similarly, inflammation was also elevated at the 24hr mark relative to both control and burn mice (TNF- α & IL-1β).
Conclusions: Our findings indicate that burn plus PA infection results in augmented hepatic ER stress and further highlights the importance of selecting appropriate time points and pathways to best reflect the phenotype. Furthermore, the time-dependant immune-responsiveness suggests that hepatic ER stress may be driving the systemic inflammatory response. Therapeutic interventions need to be further explored to determine the impact of alleviating this response following injury, which may act to minimize systemic pathology.