Infection of epithelial cells with H. pylori induced an inflammatory

The co-cultivation of gastric stromal cells with the epithelial counterpart reconstituted the gastric mucosa in vitro. As the results have shown, stromal cells influence the epithelial monolayer under homeostatic conditions. Thus, it was of interest to investigate also the interplay and communication of these two cell populations under pathophysiologic conditions i.e. acute H. pylori infection. The human pathogen H. pylori colonize and infect epithelial cells mainly in the antrum of the human stomach. This bacterium is equipped with the Type IV secretion system (T4SS) that translocate with an injection the virulence factor CagA into the host cells. The phosphorylation of CagA (pCagA) inside the host cell and the consequent detection of pCagA (PY99) in epithelial cells is, therefore, a hallmark of a successful H. pylori infection. Hence, antral mucosoid cultures were infected with H. pylori strain P12 for three days to prove the susceptibility of this culture model for infection studies.

Confocal images of infected mucosoid cultures immunolabeled with an antibody against

3.3 Communication between epithelium and stroma adhered to the epithelial cells yet (Figure 49A*) or were attached to the epithelial surface (Figure 49A**). The western blot analysis of pCagA (PY99) in infected mucosoid cultures and non-infected control showed the detection of pCagA (PY99) in infected mucosoid culture (Figure 49B) similarly as in the positive control of the same cells infected in 2D but not in the non-infected control.

Figure 49: H. pylori attached to the epithelial surface and translocated CagA into the host cell.

(A) Antral mucosoid cultures infected with isogenic H. pylori P12 (MOI 100) for 72 hours were labeled by IF against H. pylori CagA (red) to visualize bacteria and epithelial cell marker E-Cadherin (green).

Enlarged images below show groups of bacteria that (*) have not yet adhered to the epithelial cells or (**) attached to the epithelial surface. Scale bar: 10 µm. (B) Western Blot analysis of pCagA detected with an antibody against PY99 (phosphorylated CagA) and total CagA in cell lysates of non-infected mucosoid culture (left lane), antral mucosoid culture infected with P12 at MOI 100 for 72 hours (middle lane) and the same cells seeded planar in 2D on collagen-coated plastic and infected with P12 at MOI 25 for 18 hours (right lane).

As the mucosoid cultures are responsive to stromal cells under physiological conditions and also to infection with H. pylori the next step was to explore the impact of infection in the communication between epithelial and stromal cells by differential gene profiling.

For this purpose, epithelial cells of mucosoids alone or co-cultured with GSC were infected with H. pylori strain P12 (MOI 100) for three days as depicted in the schematic in Figure 50.

3.3 Communication between epithelium and stroma

Figure 50: Schematic representation of the H. pylori infection of co-cultured mucosoids. Only EPCs were in contact with bacteria.

Differential gene expression of the infected cultures and co-cultures was analyzed by microarray and the gene expression was compared to their non-infected mucosoid culture and co-culture counterparts. The differential gene expression of the co-cultured GSC from this experiment was also analyzed in parallel. In general obtained results shown in Figure 51A revealed that the infection of EPCs with H. pylori induced the expression of NFκB target genes in mucosoids as well as in co-cultured mucosoids.

Most of the analyzed NFκB target genes were similarly regulated in both EPC cultures, although co-cultured mucosoids showed a stronger induction for certain genes like interleukin (IL) 11, IL15, IL18, CXCL3, CXCL5, CXCL8 (IL8) or tumor necrosis factor (TNF) (Figure 51A). A small panel of genes was differently regulated in co-cultured mucosoids compared to mucosoids alone i.e. CSF2 (colony stimulating factor 2), IL11 (interleukin 11), IL1RN (interleukin 1 receptor antagonist), IGFBP1 (insulin growth factor binding protein 1), MMP1 (matrix metalloproteinase 1), IL1A (interleukin 1 alpha) and IL1B (interleukin 1 beta, IL1β). Selected candidates of the gene profiling were further validated by RT-PCR using the same RNA as for the microarray. RT-PCR analysis results revealed that IL1β (Figure 51B) indeed is higher expressed in infected co-cultured mucosoids. For CSF2 (Figure 51C) instead, the differences observed in the gene profiling were not confirmed. Furthermore, mRNA expression levels of IL8 (Figure 51D) and TNFα (Figure 51E) were analyzed and showed higher induction in H. pylori infected co-cultured mucosoids, confirming the differences observed in the gene profiling in Figure 51A.

3.3 Communication between epithelium and stroma

Figure 51: H. pylori infection induced an early NFκB driven immune response in epithelial cells independent of GSC co-culture. Mucosoids alone (-GSC) or co-cultured with GSC for seven days (+GSC) were infected for three days with H. pylori (MOI 100; P12 (3days)). Non-infected counterparts were used as controls. (A) RNA from two biological replicates per group was used to perform microarray analysis. Displayed are the gene expression levels (Log10 fold change) of target genes of the NFκB signaling pathway in EPCs. Microarray data processing and visualization as a heat map were performed by Dr. Hilmar Berger. (B-E) RT-PCR analyses were performed to validate observations from microarray using the RNA from the two biological replicates of each group. mRNA expression levels of (B) IL1β, (C) CSF2, (D) IL8 and (E) TNFα were determined using specific primers. The mRNA expression was normalized to the housekeeping gene GAPDH.

3.3 Communication between epithelium and stroma

The differential gene expression of corresponding GSC of non-infected and H. pylori infected mucosoids was also analyzed in the microarray. In Figure 52A an overview of regulated NFκB pathway target genes in GSCs is displayed in a heat map. The infection of EPCs induced an NFκB driven immune response also in GSCs. A panel of cytokines and chemokines especially IL1β, IL6, CXCL8 (IL8), was upregulated in GSCs upon epithelial infection indicating paracrine signaling between epithelium and stroma. To validate the obtained differential gene expression data for selected candidates, RT-PCR analyses were performed to determine the mRNA expression levels of IL6, IL1β, IL8 (Figure 52B), CXCL12 and IL18 (Figure 52C). The results demonstrate that specifically IL1β is highly induced in GSC when EPCs were infected with H. pylori. The upregulation of IL8 and IL6 was confirmed by RT-PCR, but the induction was lower compared to IL1β (Figure 52B). The mRNA expression level of CXCL12 was analyzed as the microarray data revealed that CXCL12 is downregulated in GSCs during infection. RT-PCR data did not confirm this observation because the CXCL12 mRNA expression did not change between non-infected and infected samples (Figure 52C).

IL18 instead was upregulated in GSC during infection confirming the microarray data.

3.3 Communication between epithelium and stroma

Figure 52: GSCs respond to the H. pylori infection of overlaying EPCs. Co-cultured mucosoids were infected for three days with H. pylori (MOI 100; EPC: P12 (3days)). Non-infected counterparts served as control (EPC: NI). (A) RNA from GSCs from two biological replicates per group was used to perform microarray analysis. Displayed are the gene expression levels (Log10 fold change) of target genes of the NFκB signaling pathway in GSCs. Microarray data processing and visualization as a heat map were performed by Dr. Hilmar Berger. (B-C) RT-PCR analyses were performed to validate observations from microarray using the RNA from the two biological replicates of each group. mRNA expression levels of (B) IL6, IL1β and IL8 and (C) CXCL12 and IL18 were determined using specific primers. The mRNA expression levels were normalized to the housekeeping gene GAPDH.

3.3 Communication between epithelium and stroma

In summary infection of co-cultured epithelial cells led to higher expression in a selected panel of NFκB target genes, while a small subset of NFκB target genes was only specifically induced in co-cultured mucosoids against infection. Furthermore, gastric stromal cells actively participate in the modulation of the immune response by inducing the expression of inflammatory cytokines specifically IL1β, IL6, and IL8.

Infection with H. pylori for analyzing the differential gene expression was performed for three days. It was shown in cell lines that the NFκB subunit p65 translocation from the cytoplasm into the nucleus is oscillating during H. pylori infection (Bartfeld et al.

2010) subsequently it is expected that also the NFκB p65 target gene expression should follow this trend. Thus, a time course of infection was performed over 36 hours to analyze eventual changes in cytokine induction. The mRNA expression level of IL8 was chosen as readout and was analyzed in epithelial cells as well as in stromal cells using RT-PCR (Figure 53). Results showed that the IL8 mRNA expression level peaked first 12 hours post-infection (hpi) in epithelial cells (Figure 53A) with declining expression levels at 24 hpi followed by a second peak after 36 hpi. However, in stromal cells (Figure 53B), the highest IL8 mRNA expression was observed after 24 hpi, 12 hours later than in epithelial cells indicating that the stroma starts the inflammatory response obviously after the epithelium.

Figure 53: Time course of IL8 mRNA expression in EPC and GSC after H. pylori infection of co-cultured mucosoids. Mucosoids were co-cultured with GSC for seven days and epithelial cells were infected with H. pylori (MOI 50) for 2 h, 6 h, 12 h, 24 h, and 36 h. Non-infected (NI) co-cultured mucosoids served as a control. RT-PCR analyses of IL8 mRNA expression were performed for the different time points of infection in (A) EPCs and in (B) corresponding GSC. Data were normalized to NI control respectively and are depicted as fold change. Experiment was done once. Error bars represent min and max values of technical triplicate NI: non-infected; hpi: hours post-infection.

3.3 Communication between epithelium and stroma The following experiments were done using an infection time of 24 hours to be able to detect both epithelial and stromal immune responses. Besides IL8, the mRNA expression level of the cytokines IL1β and IL6 were analyzed in stromal cells, 24 hours after H. pylori infection of co-cultured epithelial cells as these were the strongest hits in the microarray analysis.

Results shown in Figure 54 demonstrate that especially mRNA expression level of IL1β (Figure 54A) was upregulated with high statistical significance. For IL6 (Figure 54A) and IL8 (Figure 54A), also an increase in mRNA expression level was observed. To confirm the results a semi-quantitative cytokine array for IL1β and IL6 was performed using the culture medium 24 hours after infection. The supernatant was centrifuged to remove cell debris prior to the cytokine array. Results revealed that epithelial cells alone did not produce IL1β (Figure 54B). Only in the presence of stromal cells, IL1β was detected in the supernatant, while the amount was dependent on the bacterial load; the stronger the infection, the higher the IL1β response. For infection with an MOI 25, the IL1β concentration was lower than for infection with MOI 100. No IL1β was detected in the non-infected control. These results confirm that the stromal cells are the main source of IL1β and not the epithelial cells. Comparable results were observed in the IL6 cytokine array (Figure 54C). Here as well only in the presence of stromal cells, IL6 was detected in the supernatant. The IL6 concentration did not change with increasing MOI suggesting that the maximal threshold was attained or the system was saturated.

Interestingly, also in the supernatant of the non-infected GSC co-cultured control, a high IL6 concentration was detected that was not present in the supernatant of neither non-infected nor infected epithelial cells alone. Again these results strongly confirm that stromal cells were the producer of IL6 and secreted IL6 also under non-infected, homeostatic condition.

3.3 Communication between epithelium and stroma

Figure 54: EPC infection induced a strong immune response in GSC. Mucosoid cultures co-cultured with GSCs were infected with H. pylori (MOI 50) for 24 hours. (A) RT-PCR analyses of mRNA expression levels of IL1β, IL6 and IL8 in GSC were performed in three biological replicates calculated as mean ± SD. Paired Student’s t-test. **, p < 0.01. (B-C) Mucosoids and co-cultured mucosoids were infected with H. pylori (MOI25 and MOI100) and culture medium was used for semi-quantitative cytokine array of (B) IL1β and (C) IL6. Culture medium from non-infected culture and co-culture counterparts were used as controls. The experiment was done once. LOD: limit of detection.

4.1 Development of the mucosoid culture model