Human spontaneous labor without histologic chorioamnionitis is characterized by an acute inflammation gene expression signature

Abstract

Objective: The purpose of this study was to identify which biological processes may be involved in normal labor.

Study design: Transcriptional profiles for chorioamniotic membranes (n = 24) and blood (n = 20) were generated from patients at term with no labor (TNL) and in labor (TIL).

Results: Expression of 197 transcripts (P < or = .02) differentiated TIL and TNL chorioamniotic membrane samples. Gene Ontology analysis indicated that TIL samples had increased expression of multiple chemokines and transcripts associated with neutrophil and monocyte recruitment. Microarray results were verified using quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) with independent samples. Transcriptional profiles from blood RNA revealed no Gene Ontology category enrichment of discriminant probe sets.

Conclusion: Labor induces gene expression changes consistent with localized inflammation, despite the absence of histologically detectable inflammation.

Figure 1. Hierarchical clustering of probe sets that discriminate the chorioamniotic membrane samples of TIL patients from their TNL counterparts

A permutation based t-test was used to find genes with altered expression between TIL and TNL samples. The top 224 probe sets (P ≤ 0.02) with a minimum average expression difference of 1.4-fold are shown.

Figure 2. Subcluster of discriminant probe sets with the lowest P values

A sub-cluster of probe sets taken from the hierarchical clustering shows genes previously implicated in parturition and genes involved in the acute inflammatory response. Row labels correspond to the permuted t-test P value followed by the HUGO Gene Nomenclature Committee (HGNC) official gene symbol and include the most commonly used alternative gene symbol. The color scale and column labels follow the same conventions as Figure 1.

Figure 3. Analysis of microarray data from chorioamniotic membranes using Gene Ontology categories

A, Graph of Gene Ontology (GO) Biological Process categories that are over-represented in the 224 discriminant probe sets. Significantly enriched GO Biological Processes from hierarchical level 4 are indicated below each set of bars. Black bars represent the number of observed, and grey bars represent the number of expected genes for that category. Symbols: ***: P < 0.00059; **: P < 0.0049; and *: P < 0.019. B, Hierarchical clustering of discriminant probe sets from selected GO categories. Discriminant probe sets either belonged to significantly enriched GO Biological Processes categories (shown in Figure 3A), or GO Molecular Activities corresponding to chemokine, cytokine, or cytokine binding (Table III). The color scale, row and column labels follow the same conventions as Figure 1. Sub-clusters of the array samples on the top dendrogram have been colored for clarity. The central gene cluster has been colored red on the left dendrogram and is discussed in the text. C, Venn diagram illustrating the relatedness of all significantly enriched GO Biological Process categories. The square box represents probe sets that were chosen by their Molecular Function. Colored gene symbols: dark blue, neutrophil chemotaxis and activation; red, monocyte chemotaxis and activation; and green, transition of acute inflammation from a predominantly neutrophilic to monocytic infiltration.