Increased levels of DHPS and EIF5AHyp in H. pylori-infected patients
Using immunostaining, we evidenced that that the level of DHPS and hypusinated EIF5A were increased overall in the gastric mucosa of endoscopic biopsies from patients with H. pylori gastritis compared to individuals without infection (Fig. 1). Of importance, the staining was abundant in GECs in H. pylori-infected patients but also present in the immune infiltrates, as we reported (Gobert et al. 2020).
Deletion of epithelial hypusination reduces the inflammatory response to H. pylori
To investigate the role of hypusination in epithelial cells during H. pylori infection we utilized a genetic approach by generating C57BL/6 animals with a gastric epithelial-specific knockout of Dhps. First, we verified by immunoblots and densitometry that DhpsΔepi mice exhibited reduced expression of DHPS and EIF5AHyp levels in the gastric epithelium compared to Dhpsfl/+ control mice (Fig. 2A and 2B).
Then, we infected Dhpsfl/+ and DhpsΔepi mice with H. pylori PMSS1 for 8 weeks. We confirmed by immunofluorescence that DHPS and EIF5AHyp were less expressed in GECs from naive DhpsΔepi mice (Fig. 3A). Upon infection, the levels of DHPS and EIF5AHyp were increased in GECs and immune infiltrates of Dhpsfl/+ mice compared to uninfected animals (Fig. 3A); there was markedly less staining in the GECs of DhpsΔepi mice, whereas immune cells were still positive for DHPS (Fig. 3A).
All 30 DhpsΔepi mice were colonized and only 1 of the 21 Dhpsfl/+ mice was not colonized and was thus removed from the analysis. We observed no difference in gastric bacterial burden between both genotypes (Fig. 3B). An inflammatory infiltrate and mild foveolar hyperplasia were mainly observed at the antrocorporal transitional mucosa of H. pylori-infected Dhpsfl/+ mice (Fig. 3C). These parameters were less observed in the stomach of infected DhpsΔepi mice (Fig. 3C). Using a comprehensive score, we found increased inflammation in both genotypes compared to uninfected animals, but also significantly less inflammation in the gastric tissue of infected DhpsΔepi mice compared to the infected Dhps+/fl mice (Fig. 3D).
Proteome of H. pylori-infected animals with Dhps deficiency
To determine the role of the hypusination pathway during H. pylori-mediated inflammation, we performed TMT proteomics on isolated GECs from uninfected and infected Dhpsfl/+and DhpsΔepi mice.
First, we analyzed the proteome in GECs from naïve mice. There were 79 proteins significantly induced by the specific Dhps deletion in epithelial cells (Supplementary Table S1). These proteins were signaling molecules, such as cyclin-dependent kinase 1 (CDK1) or Src substrate cortactin (SRC8), the superoxide dismutase SODM, and numerous heterogeneous nuclear ribonucleoproteins (ROA1/A2/A3/AA), which are RNA-binding proteins playing critical roles in multiple cellular processes such as DNA repair and regulation of gene expression (Fig. 4A and Supplementary Table S1). We also found 183 proteins downregulated in GECs from DhpsΔepi mice. Among them we found numerous ribosomal proteins (e.g., RM24, RS4X, RT33), as expected, different cytochromes P450 (e.g. CP3AB, CP2E1, CP1A2), and one glutathione-S-transferase (MGST1) (Fig. 4A and Supplementary Table S1). The changes in the level of these proteins in GECs were overall associated with a lessening of the pathways associated with organismal injury, cancer, and gastrointestinal diseases in DhpsΔepi mice (Fig. 4B and Supplementary Table S2); pathways associated with cell movement were mainly induced in DhpsΔepi mice (Fig. 4B and Supplementary Table S2).
We identified 110 and 174 proteins significantly induced by H. pylori infection in the GECs from the stomach tissues from Dhpsfl/+ and DhpsΔepi mice, respectively. Among them, 37 were in common to both genotypes (Fig. 5A). These included mediators of adaptive immunity (IGHA, HB2A/2I, HG2A, and TGTP2), and regulators of the innate immune response, such as DOXA2, I23O1, and STAT1 (Fig. 5B and Supplementary Table S1). However overall, the level of expression of these proteins in H. pylori-infected DhpsΔepi mice was lower compared to infected Dhpsfl/+animals (Fig. 5B). Moreover, there were 170 proteins significantly downregulated in GECs from Dhpsfl/+ mice with infection (Fig. 5A), whereas only 61 proteins were less expressed in infected DhpsΔepi GECs (Fig. 5A); only 18 proteins were similar in both genotypes (Fig. 5A). The proteins downregulated by H. pylori infection in Dhpsfl/+animals included numerous cytochromes, e.g., CP2F, CP2E1, CP3AB, CP2DA, and CP240, which are known to be downregulated during infection and inflammation, TFF1, the stabilizer of the mucous gel overlying the gastrointestinal mucosa that provides a physical barrier against bacteria, and the marker of M2/Mreg macrophages, ARGI1 (Fig. 5C and Supplementary Table S1); most of these effectors were less altered in infected DhpsΔepi mice (Fig. 5C and Supplementary Table S1).
When we analyzed the functional clusters corresponding to the proteins differentially expressed between infected DhpsΔepi versus infected Dhpsfl/+ mice (see Supplementary Table S1), we evidenced that numerous pathways related to infections were significantly upregulated, whereas the biological processes related to inflammation were mainly downregulated (Fig. 5D and Supplementary Table S3).