Role of gut microbiota dysbiosis on the development of spondyloarthritis – MICROSPA

Relationship between gut microbiota and joint inflammation has remained scarcely studied until now. Our recent studies in spondyloarthritis (SPA) -high throughput sequencing of fecal samples from 350 patients and healthy controls - revealed intestinal dysbiosis specific for this disorder, characterized by decreased diversity and decreased abundance of several taxa, contrasting with increased abundance of few anaerobes that positively correlated with disease activity, including Ruminococcus gnavus. We hypothesize that bacterial species expanded during active disease could play a direct pathogenic role in SPA. This concerns in particular R. gnavus a species highly variable at the genome level, with strains already shown to associate with inflammatory bowel disease or Lupus and harboring genes that could contribute to pathogenicity by various mechanisms. In particular, some R. gnavus strains display mucolytic activity that may weaken the epithelial barrier or produce pro-inflammatory constituents (i.e. cell wall polysaccharide or B cell superantigens).
This project will be realized by a Consortium of academic partners already engaged in mutual collaboration. Its goals will be: i.) to isolate strains of bacterial species of interest and characterize their microbial genes/products specifically associated with SpA; ii.) to address the pathogenicity of those strains in vitro using biological samples from SpA patients; iii.) to characterize in vivo the pathogenic role of microbiota in HLA-B27 transgenic rat model of SpA (B27-rat).
Task 1 concerns administration of the project, follow-up of achievements, exploitation of results with regard to valorization and intellectual property.
Task 2 will establish a collection of R. gnavus -and other species of interest- strains from SpA patients and HC (fecal samples, intestinal biopsies). Isolated strains will be characterized genetically and metabolically to identify features characteristic of SpA that could confer pathogenicity. This will be complemented by analysis of available metagenomic data for genes/metabolic pathways and by metabolomic study of fecal and plasma sample from SpA vs. HC to infer biological consequences specific for SpA.
Task 3 will test in vitro the pro-inflammatory effect of candidate bacterial genes on cell line, using a dedicated high throughput Metafun pipeline and of specific strains on intestinal organoids and gut-on-chips derived from intestinal biopsies, on monocytes and on intestinal T lymphocytes from 50 pairs of SpA/HCs. R. gnavus strains closely associated with intestinal mucosa will be quantified by RT-q-PCR.
Task 4 candidate bacterial strains causality will be tested in a murine model of SPA (B27-rat) both in vivo and in vitro. In vivo: B27-rats will be colonized with selected strains -from R. gnavus and others- isolated from SPA patients to test their pathogenicity; pro-inflammatory effect of bacterial strains will be tested in conventional B27-rats treated at weaning with antibiotics or polyethylene glycol and fed daily for several weeks with candidate strains and further in germ-free B27-rats mono-associated with candidate bacteria. In vitro: B27-rat T cells reactivity will be tested against bacterial used to feed them.
In summary, this project will provide extensive characterization of gut resident bacteria species suspected to be pathogenic in SpA. It is designed to bring a proof of concept that gut microbiota could play direct pathogenic role in the development of SpA by studying their consequences on metabolome and on immune and epithelial cells reactivity in intestinal tissue, as well as addressing causality in the B27-rat model of SpA. If the conclusions that specific gut bacterial strains could play a causal role in the pathogenesis of SpA can be drawn, it may open the track for therapeutic interventions, trying to correct gut dysbiosis by the mean of vaccination, prebiotic or probiotic use, phagotherapy, or fecal microbiota transplantation.