Differential effects of three canonical Toxoplasma strains on gene expression in human neuroepithelial cells

Abstract

Strain type is one of the key factors suspected to play a role in determining the outcome of Toxoplasma infection. In this study, we examined the transcriptional profile of human neuroepithelioma cells in response to representative strains of Toxoplasma by using microarray analysis to characterize the strain-specific host cell response. The study of neural cells is of interest in light of the ability of Toxoplasma to infect the brain and to establish persistent infection within the central nervous system. We found that the extents of the expression changes varied considerably among the three strains. Neuroepithelial cells infected with Toxoplasma type I exhibited the highest level of differential gene expression, whereas type II-infected cells had a substantially smaller number of genes which were differentially expressed. Cells infected with type III exhibited intermediate effects on gene expression. The three strains also differed in the individual genes and gene pathways which were altered following cellular infection. For example, gene ontology (GO) analysis indicated that type I infection largely affects genes related to the central nervous system, while type III infection largely alters genes which affect nucleotide metabolism; type II infection does not alter the expression of a clearly defined set of genes. Moreover, Ingenuity Pathways Analysis (IPA) suggests that the three lineages differ in the ability to manipulate their host; e.g., they employ different strategies to avoid, deflect, or subvert host defense mechanisms. These observed differences may explain some of the variation in the neurobiological effects of different strains of Toxoplasma on infected individuals.

FIG. 1.

Venn analysis of the overlap of deregulated RefSeq genes in SK-N-MC cells due to different Toxoplasma infections. In the SK-N-MC cells infected by Toxoplasma type I compared to controls, type II compared to controls, and type III compared to controls, respectively, 1,122, 78, and 344 RefSeq gene transcripts were differentially expressed. The intersections of the circles indicate the number of genes in common between contrasts.

FIG. 2.

Transcriptional changes of biological processes involved in nervous system development affected by type I strain infection. Shown are the biological processes with significant P value changes in SK-N-MC cells altered by Toxoplasma type I infection. NC, no significant change.

FIG. 3.

Transcriptional changes of biological processes involved in nerve impulse transmission affected by type I strain infection. Shown are the biological processes with significant P value changes in SK-N-MC cells altered by Toxoplasma type I infection. NC, no significant change.

FIG. 4.

Transcriptional changes of biological processes involved in the nucleotide metabolic process affected by type III strain infection. Shown are the biological processes with significant P value changes in SK-N-MC cells altered by Toxoplasma type III infection. LSU, large subunit.

FIG. 5.

Ingenuity signaling-related networks depicting interactions among molecules. Merged network based on the top 5 signaling-related networks (107 differentially expressed genes [DEGs] and 66 interconnecting molecules) altered by Toxoplasma type I infection. Red denotes upregulation, and green denotes downregulation of the gene. The intensity of the gene color (red or green) indicates the degree of up- or downregulation. White indicates interconnecting molecules. Lines between molecules indicate a direct molecular connection between molecules. Gold lines indicate connectivity between the merged networks. Asterisks indicate duplicates. The gene shapes denote the functional class of the gene product. CoA, coenzyme A; ORF, open reading frame. The networks were generated through the use of Ingenuity Pathways Analysis (Ingenuity Systems).

FIG. 6.

Correlation between microarray and real-time PCR data. The scatter plot compares ratios of mean expression levels of infected cells to those of controls for 15 genes. Each point represents the infected cell/control ratio from microarray (x axis) and real-time PCR (y axis) analyses. The Pearson correlation coefficient is indicated on the scatter plot.