Acclimation to decompression: stress and cytokine gene expression in rat lungs

Abstract

Previous studies demonstrated that animals exposed to repeated compression-decompression stress acclimated (i.e., developed reduced susceptibility) to rapid decompression. This study endeavored to characterize inflammatory and stress-related gene expression and signal transduction associated with acclimation to rapid decompression. Rats were divided into four groups: 1) control-sham: pressure naïve rats; 2) acclimation-sham: nine acclimation dives [70 feet seawater (fsw), 30 min]; 3) control-dive: test dive only (175 fsw, 60 min); and 4) acclimation-dive: nine acclimation dives and a test dive. After the test dive, rats were observed for decompression sickness (DCS). Expression of 13 inflammatory and stress-related genes and Akt (or PKB, a serine/threonine protein kinase) and MAPK phosphorylation of lung tissue were examined. The expression of immediate early gene/transcription factor early growth response gene 1 (Egr-1) was observed in both control and acclimation animals with DCS but not in animals without DCS. Increased Egr-1 in control-dive animals with DCS was significantly greater than in acclimation-dive animals with DCS. TNF-α, IL-1β, IL-6, and IL-10 were significantly elevated in control-DCS animals. Acclimation-DCS animals had increased TNF-α, but there was no change in IL-1β, IL-6, and IL-10. High levels of Akt phosphorylation were observed in lungs of acclimation-sham, acclimation-dive, and control-dive animals; phosphorylated ERK1/2 was only observed in animals with DCS. This study suggests that activation of ERK1/2 and upregulation of Egr-1 and its target cytokine genes by rapid decompression may play a role in the initiation and progression of DCS. It may be that the downregulated expression of these genes in animals with DCS is associated with previous exposure to repeated compression-decompression cycles. This study represents an initial step toward understanding the molecular mechanisms associated with acclimation to decompression.