Skeletal muscle amino acid and myofibrillar protein mRNA response to thermal injury and infection

Cooperation and cheating in Pseudomonas aeruginosa: the roles of the las, rhl and pqs quorum-sensing systems

Pseudomonas aeruginosa coordinates the transcription of hundreds of genes, including many virulence genes, through three hierarchically arranged quorum-sensing (QS) systems, namely las, rhl and pqs. Each system consists of genes involved in autoinducer synthesis, lasI, rhlI and pqsABCDH, as well as cognate-regulatory genes, lasR, rhlR and pqsR. In this study, we analyzed the social behavior of signal-blind (ΔlasR, ΔrhlR, ΔpqsR) and signal-negative (ΔlasI, ΔrhlI, ΔpqsA) mutants from each QS system. As each system controls extracellular common goods but differs in the extent of regulatory control, we hypothesized that all signal-blind mutants can behave as cheaters that vary in their ability to invade a QS-proficient population. We found that lasR and pqsR, but not rhlR, mutants evolve from a wild-type ancestor in vitro under conditions that favor QS. Accordingly, defined lasR and pqsR mutants enriched in wild-type co-culture, whereas rhlR and all signal-negative mutants did not. Both lasR and pqsR mutants enriched with negative frequency dependence, suggesting social interactions with the wild type, although the pqsR mutant also grew well on its own. Taken together, the lasR mutant behaved as a typical cheater, as reported previously. However, the pqsR and rhlR mutants exhibited more complex behaviors, which can be sufficiently explained by positive and negative pleiotropic effects through differential regulation of pqs gene expression in the interconnected QS network. The evolutionary approach adopted here may account for the prevalence of naturally occurring QS mutants.

Gene expression profiling of long-term changes in rat liver following burn injury

The inflammatory response initiated upon burn injury is also associated with extensive metabolic adjustments. While there is a significant body of literature on the characterization of these changes at the metabolite level, little is known on the mechanisms of induction, especially with respect to the role of gene expression. We have comprehensively analyzed changes in gene expression in rat livers during the first 7 d after 20% total body surface area burn injury using Affymetrix microarrays. A total of 740 genes were significantly altered in expression at 1, 2, 4, and 7 d after burn injury compared to sham-burn controls. Functional classification based on gene ontology terms indicated that metabolism, transport, signaling, and defense/inflammation response accounted for more than 70% of the significantly altered genes. Fisher least-significant difference post-hoc testing of the 740 differentially expressed genes indicated that over 60% of the genes demonstrated significant changes in expression either on d 1 or on d 7 postburn. The gene expression trends were corroborated by biochemical measurements of triglycerides and fatty acids 24 h postburn but not at later time points. This suggests that fatty acids are used, at least in part, in the liver as energy substrates for the first 4 d after injury. Our data also suggest that long-term regulation of energy substrate utilization in the liver following burn injury is primarily at the posttranscriptional level. Last, relevance networks of significantly expressed genes indicate the involvement of key small molecules in the hepatic response to 20% total body surface area burn injury.

Proteomic analysis of altered protein expression in skeletal muscle of rats in a hypermetabolic state induced by burn sepsis

mRNA profiling has been extensively used to study muscle wasting. mRNA level changes may not reflect that of proteins, especially in catabolic muscle where there is decreased synthesis and increased degradation. As sepsis is often associated with burn injury, and burn superimposed by sepsis has been shown to result in significant loss of lean tissues, we characterized changes in the skeletal-muscle proteome of rats subjected to a cutaneous burn covering 20% of the total body surface area, followed 2 days later by sepsis induced by CLP (caecal ligation and puncture). EDL (extensor digitorum longus) muscles were dissected from Burn-CLP animals (n=4) and controls (sham-burned and sham-CLP-treated, n=4). Burn-CLP injury resulted in a rapid loss of EDL weight, increased ubiquitin-conjugated proteins and increased protein carbonyl groups. EDL protein profiles were obtained by two-dimensional gel electrophoresis using two immobilized pH gradient strips with overlapping pH range covering a pH 3-8 range. Seventeen spots were significantly altered in the Burn-CLP compared with the control group, representing 15 different proteins identified by peptide mass fingerprinting. The identities of three proteins including transferrin were further confirmed by liquid chromatography-tandem MS. The significant changes in transferrin and HSP27 (heat-shock protein 27) were verified by Western-blot analysis. HSP60, HSP27 and HSPbeta6 were down-regulated, along with HSP70, as detected by Western blotting. Six metabolic enzymes related to energy production were also down-regulated. A simultaneous decrease in chaperone proteins and metabolic enzymes could decrease protein synthesis. Furthermore, decreased HSPs could increase oxidative damage, thus accelerating protein degradation. Using cultured C2C12 myotubes, we showed that H2O2-induced protein degradation in vitro could be partially attenuated by prior heat-shock treatment, consistent with a protective role of HSP70 and/or other HSPs against proteolysis.

Expression profiling analysis of the metabolic and inflammatory changes following burn injury in rats

Burn injury initiates an inflammatory response as part of the healing process that is associated with extensive metabolic adjustments. While most studies have focused on understanding these changes from a biochemical perspective, not much work has been done to characterize these processes at the gene expression level. As a first step, we have comprehensively analyzed changes in gene expression in rat livers during the first 24 h after burn injury using Affymetrix GeneChips, which showed 339 genes to be differentially expressed at a statistical significance of P < 0.05 and changed at least twofold. Functional classification based on gene ontology terms indicated that two categories, metabolism (28%) and inflammation (14%), accounted for nearly 42%. Detailed analysis of the metabolism group of genes indicated that fatty acid (FA) and triglyceride (TG) biosynthesis in the liver were unchanged, whereas TG utilization, FA import, and beta-oxidation increased after burn injury. The increased FA pools after burn injury appear to serve as substrates for ATP production. Following burn injury, the cholesterol biosynthetic pathway was suppressed while cholesterol was increasingly imported and converted into bile acids. The inflammatory genes that were altered included several classic acute phase response markers, as well as genes involved in the complement, kinin, clotting, and fibrinolytic protein systems. These temporally coordinated changes in gene expression were also corroborated by biochemical measurements for FA, TG, cholesterol, and ATP. Together, these data indicate that FA are increasingly imported and oxidized in the liver to meet the enhanced energy demands arising from an inflammatory response during the first 24 h after burn injury.