Comparison of longitudinal leukocyte gene expression after burn injury or trauma-hemorrhage in mice

Abstract

A primary objective of the large collaborative project entitled “Inflammation and the Host Response to Injury” was to identify leukocyte genes that are differentially expressed after two different types of injury in mouse models and to test the hypothesis that both forms of injury would induce similar changes in gene expression. We report here the genes that are expressed in white blood cells (WBCs) and in splenocytes at 2 h, 1 day, 3 days, and 7 days after burn and sham injury or trauma-hemorrhage (T-H) and sham T-H. Affymetrix Mouse Genome 430 2.0 GeneChips were used to profile gene expression, and the results were analyzed by dCHIP, BRB Array Tools, and Ingenuity Pathway Analysis (IPA) software. We found that the highest number of genes differentially expressed following burn injury were at day 1 for both WBCs (4,989) and for splenocytes (4,715) and at day 1 for WBCs (1,167) and at day 3 for splenocytes (1,117) following T-H. The maximum overlap of genes that were expressed after both forms of injury were at day 1 in WBCs (136 genes) and at day 7 in splenocytes (433 genes). IPA revealed that the cell-to-cell signaling, cell death, immune response, antiapoptosis, and cell cycle control pathways were affected most significantly. In summary, this report provides a database of genes that are modulated in WBCs and splenocytes at sequential time points after burn or T-H in mice and reveals that relatively few leukocyte genes are expressed in common after these two forms of injury.

Innate immune responses to trauma

“…After severe trauma, a ‘genetic storm’ and functional reprioritizing of leukocytes have been described 22 that seem in other studies to be unique to each injury pattern 23 . Overall, the cellular translation results in largely balanced pro-inflammatory and anti-inflammatory protective effects mediated by targeted chemotaxis, cytokine release (with the systemic appearance of, for example, IL-6, IL-8, IL-1Ra and IL-10), the generation of reactive oxygen species (ROS), phagocytosis, the formation of neutrophil extracellular traps (NETs) and the killing of bacteria 6,24–28 .…”

Abandon the Mouse Research Ship? Not Just Yet!

“…It must be noted that an oral communication by one of the PNAS co-authors indicated that reanalysis of genomic responses in a more narrow PMN population did not markedly improve the overall correlation (20), although a peer-reviewed publication of such a reanalysis has not yet been reported. The risks of imprecise comparison of genomic responses in circulating white blood cells (WBC) are not solely restricted to mouse versus human studies; earlier GLUE GRANT-based reports that analyzed various inflammation/injury scenarios using only mouse models, voiced identical concerns (49;50). Analyses of gene expression in discrete leukocyte subsets are certainly warranted as they provide more precise information regarding individual activation patterns in injury and/or infection.…”

“…It has been suggested that in systemic inflammatory response syndrome (SIRS) and/or infection, compartmentalized synthesis and release of inflammatory cytokines are equally important (63-65) and that cells other than leukocytes may be responsible for morbidity and mortality in trauma (61), inflammatory shock (66), endotoxemia (67-69) and/or infection (70). Studies have also shown that peripheral blood cells fail to reflect what occurs in the tissue fixed cells within the same or different organs (30;49;50;71;72). Furthermore, the concept of compartmentalization pertains to coexistence of differential (and often contrasting) responses that depend on the specific location of the immune-competent machinery and this notion has been supported by numerous preclinical studies.…”

Genomic responses in mouse models poorly mimic human inflammatory diseases

“…The Inflammation and Host Response to Injury, Large Scale Collaborative Research Program has completed multiple studies on the genomic responses to systemic inflammation in patients and human volunteers as well as murine models (14)(15)(16)(17)(18). These datasets include genome-wide expression analysis on white blood cells obtained from serial blood draws in 167 patients up to 28 d after severe blunt trauma (15), 244 patients up to 1 y after burn injury, and 4 healthy humans for 24 h after administration of low-dose bacterial endotoxin (14) and expression analysis on analogous samples from well-established mouse models of trauma, burns, and endotoxemia (16 treated and 16 controls per model) (16)(17)(18).…”

“…These datasets include genome-wide expression analysis on white blood cells obtained from serial blood draws in 167 patients up to 28 d after severe blunt trauma (15), 244 patients up to 1 y after burn injury, and 4 healthy humans for 24 h after administration of low-dose bacterial endotoxin (14) and expression analysis on analogous samples from well-established mouse models of trauma, burns, and endotoxemia (16 treated and 16 controls per model) (16)(17)(18). In humans, severe inflammatory stress produces a genomic storm affecting all major cellular functions and pathways (15) and therefore, provided sufficient perturbations to allow comparisons between the genes in the human conditions and their orthologs in the murine models.…”