Abstract
Multiple trauma can induce sepsis and organ failure, even threaten people’s lives. To further study the mechanisms of multiple trauma, we analyzed microarray of GSE5760. GSE5760 was downloaded from the Gene Expression Omnibus including a total of 58 peripheral blood transcriptome from patients without (WT, n = 30) and carrying (MUT, n = 28) the tumor necrosis factor (TNF) rs1800629 A variant. The differentially expressed genes (DEGs) were screened using the limma package in R and the Benjamin and Hochberg method in a multi-test package. Then, functional enrichment analysis of DEGs was performed. Also, transcription factors significantly related to DEGs were searched using WebGestalt and interaction network of transcription factors and DEGs were constructed using STRING online software. Furthermore, pathway enrichment analysis for the DEGs in the interaction network was conducted using KO-Based Annotation System (KOBAS). We screened 39 DEGs including 27 upregulated and 12 downregulated genes. The enriched functions were associated with biological process (BP) (such as response to hypoxia, P value = 0.039803), cell components (CC) (such as mitochondrial part, P value = 0.043857), and molecular function (MF) (such as structural constituent of ribosome, P value = 0.008735). Besides, RPS7 and RPL17 were associated with ribosome and participated in ribosome pathway. PPP2R2B was related to mitochondrion. KCNMA1, ALAS2 and SOCS3 were associated with hypoxia. Moreover, transcription factors of LEF1, CHX10, ELK1, SP1, and MAZ were significantly related to DEGs. RPS7, RPL17, PPP2R2B, KCNMA1, ALAS2, and SOCS3 might relate to multiple trauma. And TNF-α mutation could cause sepsis in patients with multiple trauma by changing the expression of these genes.
Introduction
Multiple trauma is a serious injury involving multi-sites and organs. Patients with multiple trauma are often suffering from bleeding, shock, and severe physiological disorders, some life-threatening. 1 The injuries can be induced by intentional causes (domestic violence, suicides, homicides, and war) and non-intentional ones (sports-related injuries, falls, traffic crashes, near-drowning, burns, and accidental poisoning). 2 More than 5 million deaths per year resulted from injuries, 3 and about 50% of young children with non-intentional injuries are left with disabilities. 4 Thus, it is very urgent to study the molecular mechanisms of multiple trauma and develop therapeutic schedules.
In multiple trauma, cytokines have many physiological and pathological roles. The major cause of late death after multiple trauma is organ failure, and sepsis is the main reason for organ failure. 5 TNF-α is a cytokine produced by the macrophage and monocyte activation, and plays a key role in the inflammatory response, cell immunity, tumor immunity, and other physiological and pathological processes.6,7 Through the regulation of granulocyte-macrophage colony-stimulating factor (GM-CSF), TNF-α synthesis is elevated in the blood of patients with multiple injuries or sepsis. 8 Angiopoietin-2 (Ang-2) is regulated by proinflammatory stimuli and is associated with sepsis pathophysiology. Furthermore, serum TNF-α has a strong relationship with serum Ang-2 and it may play a role in the regulation of Ang-2 production in sepsis. 9
Menges et al. analyzed serial blood samples from patients on the first day after trauma and during follow-up, patients with sepsis syndrome, and patients with a fatal outcome. They found that carriers of the TNF rs1800629 A allele have higher TNF-α serum concentrations, which are related to sepsis syndrome and death after severe injury. 10 However, they neither have screened differentially expressed genes (DEGs), nor have conducted functional and pathway enrichment analyses, which can further study the mechanisms of how TNF-α mutation affects sepsis syndrome and death after severe injury. The molecular mechanisms of multiple trauma still remain unclear.
Using the data from Menges et al., 10 we screened the DEGs between samples with and without the TNF rs1800629 A variant and their potential functions were analyzed by Gene Ontology (GO) and pathway enrichment analysis. Also, transcription factors significantly related to DEGs were searched, and then the interaction relationships between transcription factors and DEGs were further investigated using network analysis. Key genes identified in this study might have some correlation with multiple trauma and sepsis. However, their potential therapeutic value still needed further validations.
Materials and methods
Microarray data
Expression profile of GSE5760 deposited by Menges et al. 10 was downloaded from Gene Expression Omnibus (GEO, see http://www.ncbi.nlm.nih.gov/geo/). GSE5760 included a collective of 30 peripheral blood transcriptome from patients without the TNF rs1800629 A variant (WT, n = 30) and 28 peripheral blood transcriptome from patients carrying the TNF rs1800629 A variant (MUT, n = 28), which were collected from 12 patients without the TNF rs1800629 A variant and 10 patients carrying the TNF rs1800629 A variant.
DEGs screening
After GSE5760 was downloaded, we first transformed the probe numbers into the corresponding gene names. The average value of multiple probes mapped with one gene was obtained as ultimate gene expression value. Then, we conducted Log 2 conversion. 11 After that, the data were analyzed using the limma (linear models for microarray data) package in R language. 12 The Benjamini and Hochberg (BH) method in a multi-test package 13 was used to adjust the raw P values into a false discovery rate (FDR), 14 while, log fold-change (FC) was calculated. The FDR <0.05 and |logFC| >1 were used as the cutoff criteria.
Functional enrichment analysis
The Database for Annotation, Visualization and Integrated Discovery (DAVID), which is used for functional annotation analysis of large gene lists, consists of a comprehensive set of tools. 15 Using the DAVID software, biological process (BP), molecular function (MF), and cell components (CC) enrichment analysis were performed for the DEGs. The P value <0.05 was used as the cutoff criterion.
Searching for transcription factors significantly related to DEGs
As a web-based integrated data mining system, the Web-based Gene Set Enrichment Analysis Toolkit (WebGestalt, see http://genereg.ornl.gov/webgestalt/) includes four modules: information retrieval, organization/visualization, statistics, and gene set management. 16 The WebGestalt software was used to search transcription factors significantly related to DEGs. The P value <0.05 was used as the cutoff criterion.
Network analysis
The STRING (Search Tool for the Retrieval of Interacting Genes/Proteins) online software 17 was used to search interrelationships of all the DEGs. The cutoff criterion was set at 0.4, and the other parameters were set to the default values. Besides, combing with the interactions between the transcription factors and the DEGs, interaction network was constructed and visualized using the Cytoscape. 18
Pathway enrichment analysis of DEGs in network
The KO-Based Annotation System (KOBAS) is a web-based platform for pathway identification and automated annotation. 19 In this study, the KOBAS was used to conduct Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis for the DEGs in the interaction network. The cumulative hypergeometric distribution was used to perform statistical analysis. The P value <0.05 was used as the cutoff criterion.
Results
DEGs analysis
A total of 39 DEGs were screened, including 12 downregulated genes (e.g. suppressor of cytokine signaling 3 [SOCS3], thyroid hormone receptor, beta [THRB], complement component [3b/4b] receptor 1 CR1, and aminolevulinate, delta-, symthase 2 [ALAS2]) and 27 upregulated genes (e.g. ribosomal protein L17 [RPL17], spectrin repeat containing, nuclear envelope 2 [SYNE2], inversin [INVS], and ribosomal protein S7 [RPS7]) (Table 1). Moreover, there were more upregulated genes than downregulated genes.
The screened upregulated and downregulated genes.
Functional enrichment analysis
DAVID was used for functional enrichment analysis of the DEGs. The enriched functions were listed in Table 2. We enriched four functions in BP category, including RNA processing (P value= 0.038809), response to hypoxia (P value = 0.039803), translation (P value = 0.042681), and response to oxygen levels (P value = 0.043641). Functions related to CC included ribosomal subunit (P value = 0.002963), non-membrane-bounded organelle (P value = 0.007812), and mitochondrial part (P value = 0.043857). Functions associated with MF included structural constituent of ribosome (P value = 0.008735) and enoyl-CoA hydratase activity (P value = 0.015157).
The enriched gene ontology (GO) terms for the DEGs.
Some of the DEGs we obtained were associated with the function and structure of ribosome, especially the upregulated ribosome protein RPS7 and RPL17 (such as translation, ribosomal subunit, and ribonucleoprotein). Meanwhile, large conductance calcium-activated potassium channel alpha subunit (KCNMA1), ALAS2, and SOCS3 were related to the functions of response to hypoxia and response to oxygen levels. Also, phosphatase 2 regulatory subunit B-beta isoform (PPP2R2B) was associated with functions associated with CC, such as non-membrane-bounded organelle and mitochondrial part. Moreover, enoyl-CoA hydratase 1, peroxisomal (ECH1) was related to the functions of mitochondrion and enoyl-CoA hydratase activity.
Searching for transcription factors and network analysis
We obtained five transcription factors significantly related to DEGs: lymphoid enhancer-binding factor 1 (LEF1), cation/H(+) antiporter 10 (CHX10), ELK1, member of ETS oncogene family (ELK1), Sp1 transcription factor (SP1), and MYC-associated zinc finger protein (MAZ) (Table 3). Using the STRING online software, we searched inter-relationships of all the DEGs, combing the interactions between the transcription factors and the DEGs, and the interaction network was constructed and visualized using the Cytoscape (Figure 1). In total, we obtained 17 interactions among the DEGs. There were 32 nodes and 51 edges in the network. Also, KCNMA1 was regulated by SP1 and MAZ. Moreover, ECH1 and PPP2R2B, PPP2R2B and RPL17, RPL17 and RPS7 had inter-relationships, respectively. In addition, PPP2R2B were targeted by LEF1, CHX10, SP1, and MAZ.
The transcription factors significantly related to DEGs.
adjP: adjusted P value O: observed DEGs number; rawP: original P value.

Interaction network of transcription factors and their corresponding DEGs. Circles and squares indicate the up- and downregulated genes, respectively. Triangles represent five transcription factors significantly related to DEGs.
Pathway enrichment analysis of DEGs in the network
By the KOBAS, we conduct KEGG pathway enrichment analysis for the DEGs in the interaction network. We obtained a ribosome pathway (FDR = 0.0029), which involved two DEGs (RPS7 and RPL17). Moreover, the two genes were both upregulated genes (Figure 2).

RPS7 and RPL17 expression in samples. The horizontal axis represents the two genes, the vertical axis shows the ratio MUT/WT. MUT: peripheral blood transcriptome from patients carrying the TNF rs1800629 A variant; WT: peripheral blood transcriptome from patients without the TNF rs1800629 A variant.
Discussion
In this study, we screened a total of 39 DEGs, in which there were 12 downregulated genes and 27 upregulated genes. The functional annotations for BP, CC, and MF suggested that the DEGs we obtained were associated with the function and structure of ribosome (such as RNA processing, ribosomal subunit, and structural constituent of ribosome). In particular, the upregulated ribosome proteins RPS7 and RPL17 not only had functions associated with ribosome (such as translation, ribosomal subunit, and ribonucleoprotein), but also participated in the ribosome pathway. Thus, TNF-α mutation caused significant expression changes of genes associated with ribosome functions. Besides, the main function of ribosome is synthesis of proteins, which is the nature of antibody involved in immune response. 20 What’s more, patients with multiple trauma may have inflammatory disorders subsequently. 21 A critical cause of morbidity and mortality in patients with multiple trauma is infection, 22 so RPS7 and RPL17 might be associated with occurrence and aggravation of sepsis in multiple trauma patients. Also, we screened five transcription factors (LEF1, CHX10, ELK1, SP1, and MAZ) significantly related to DEGs.
Besides, RPS7 and RPL17, and RPL17 and PPP2R2B had inter-relationships, respectively. PPP2R2B were targeted by LEF1, CHX10, SP1, and MAZ. The glycine 90 to aspartate alteration in the PPP2R1B causes a deficit in protein function. 23 In this study, PPP2R2B was associated with functions of mitochondrion and non-membrane-bounded organelle (which includes ribosome). Also, PPP2R2B and ECH1 had inter-relationships. Also, ECH1 was related to the functions of mitochondrion and enoyl-CoA hydratase activity. By constantly monitoring intracellular protons, calcium ions, redox stare, nitric oxide, reactive oxygen species, and gate potential to regulate electron transfer activity, mitochondria occupy the primacy position in energy production and metabolism.24,25 In patients with trauma and shock, mitochondria can open pores that leak contents into the host cell’s cytoplasm and trigger necrosis or programmed cell death. 26 Therefore, PPP2R2B might have correlation with multiple trauma.
Additionally, KCNMA1, ALAS2, and SOCS3 were related to functions associated with response to hypoxia and response to oxygen levels. In survivors of severe trauma, increased oxygen delivery index, oxygen consumption index, and cardiac index are primary compensations that have survival value and augmentation of these compensations can decrease mortality. 27 Oxygen consumption and reduction of oxygen delivery to below a critical level produces ischemic metabolic insufficiency and then causes increasing of lactate generation. 28 Furthermore, blood lactate levels are tightly related to outcome in critically ill trauma patients. 29 Thus, KCNMA1, ALAS2, and SOCS3 might have correlation with multiple trauma. Moreover, we speculated that TNF-α mutation could cause sepsis in patients with multiple trauma by changing the expression of these genes.
In conclusion, we performed a comprehensive bioinformatics analysis of genes which may have relation to multiple trauma. We screened a total of 39 DEGs. Besides, RPS7, RPL17, PPP2R2B, KCNMA1, ALAS2, and SOCS3 might have correlation with multiple trauma and be related to occurrence and aggravation of sepsis in multiple trauma patients. Moreover, TNF-α mutation could cause sepsis in patients with multiple trauma by changing the expression of these genes.
Footnotes
Authors’ contributions
GL, XL, and YL participated in the design of this study. ZL and QL both performed the statistical analysis. GC, GL, and NH carried out the study, and together with WW, collected important background information, and drafted the manuscript. YW, YC, and GS conceived of this study, participated in the design, and helped to draft the manuscript. All authors read and approved the final manuscript.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
This study was supported by Shanghai medical key subject construction project (No. ZK2012A28) and Key National Clinical Discipline construction project and Outstanding young medical talents in Pudong district (PWRq2012-13).
