Connection between the Gut Microbiome, Systemic Inflammation, Gut Permeability and FOXP3 Expression in Patients with Primary Sjögren's Syndrome

Abstract

The aims of this study were to explore intestinal microbial composition and functionality in primary Sjögren's syndrome (pSS) and to relate these findings to inflammation, permeability and the transcription factor Forkhead box protein P3 (FOXP3) gene expression in peripheral blood. The study included 19 pSS patients and 19 healthy controls matched for age, sex, and body mass index. Fecal bacterial DNA was extracted and analyzed by 16S rRNA sequencing using an Ion S5 platform followed by a bioinformatics analysis using Quantitative Insights into Microbial Ecology (QIIME II) and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt). Our data suggest that the gut microbiota of pSS patients differs at both the taxonomic and functional levels with respect to healthy controls. The gut microbiota profile of our pSS patients was characterized by a lower diversity and richness and with Bacteroidetes dominating at the phylum level. The pSS patients had less beneficial or commensal butyrate-producing bacteria and a higher proportion of opportunistic pathogens with proinflammatory activity, which may impair intestinal barrier function and therefore contribute to inflammatory processes associated with pSS by increasing the production of proinflammatory cytokines and decreasing the release of the anti-inflammatory cytokine IL-10 and the peripheral FOXP3 mRNA expression, implicated in the development and function of regulatory T cells (Treg) cells. Further studies are needed to better understand the real impact of dysbiosis on the course of pSS and to conceive preventive or therapeutic strategies to counteract microbiome-driven inflammation.

Keywords: FOXP3 expression; gut microbiota; inflammation; intestinal permeability; primary Sjögren’s syndrome.

Figure 1

Comparison of alpha diversity in primary Sjögren’s syndrome (pSS) patients and healthy controls (HC). (A) Shannon and Simpson’s diversity indices; (B) Chao1 and ACE richness indices.

Figure 2

Principal Coordinates Analysis (PCoA) of bacterial communities from primary Sjögren’s syndrome (pSS) patients and healthy controls using Bray-Curtis similarity index at the genus level. Blue dot (pSS patients) and red dot (healthy controls).

Figure 3

Composition of fecal microbiota at the phylum levels in primary Sjögren’s syndrome (pSS) patients and healthy controls (HC). (A) Data are shown as a percentage of the total identified sequences per group. (B) Differentially abundant phyla in the stool samples of pSS patients compared to HC * p < 0.05, ** p <0.001. The bars indicate mean ± standard deviation (SD).

Figure 4

Family-level microbial classification of bacteria from stool samples of primary Sjögren’s syndrome (pSS) patients and healthy controls (HC). (A) Data are shown as a percentage of the total identified sequences per group. (B) Differentially abundant families in the stool samples of pSS patients compared to HC. * p < 0.05, ** p < 0.001. The bars indicate mean ± standard deviation (SD).

Figure 5

Relative abundance of bacterial genera in the microbiota of primary Sjögren’s syndrome (pSS) patients and healthy controls (HC). (A) Data are shown as a percentage of the total identified sequences per group. (B) Differentially abundant genera in the stool samples of pSS and HC. * p < 0.05, ** p < 0.001. The bars indicate mean ± standard deviation (SD).

Figure 6

Heatmap of bacterial gene functional predictions using the Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) algorithm from fecal samples from primary Sjögren’s syndrome (pSS) patients and healthy controls (HC).