1759: Role of a pathogenic bacterial factor produced by a human gut pathobiont in inducing platelet activation and thrombo-inflammation.

Background/Purpose: SLE is an autoimmune disease that causes progressive multi-organ damage, leading to renal injury, or lupus nephritis (LN), in half of patients. Despite treatment, 20% progress to renal failure within 15 years (1). Recent studies show that about 40% of LN flares are linked to intestinal expansions of the human pathobiont Ruminococcus gnavus (RG), which produces an immunogenic pro-inflammatory cell wall lipoglycan (LG) (2). LN patients with gut dysbiosis may represent a distinct endotype, where increased gut permeability and microbial factors contribute to pathogenesis. In murine studies, we have demonstrated gut colonization of mice with human RG strains (3,4). Notably, in Sle1.Sle2.Sle3 B6 congenic lupus-prone mice, colonization with an LG+ strain accelerated disease progression (4). To investigate pathogenic mechanisms, we here used a different lupus-prone murine model to elucidate the pathways connecting RG-driven platelet activation to worsening renal disease progression.

Methods: Using whole-blood transcriptomics, we recently demonstrated that RG intestinal colonization induced platelet and myeloid cell activation (manuscript submitted). Here, lupus-prone FcgRIb^−/− B6 congenic mice were either sham-treated or colonized with RG strains, including isogenic paired strains that differ only in LG production. Colonization was confirmed by fecal qPCR. Splenic megakaryocytes were quantified by CD41+ immunofluorescence. Renal histology was evaluated by H&E.

Results: Colonization with LG+ RG resulted in increased intestinal permeability, as quantified by serum detection of orally administered fluorochrome-labeled dextran (FITC-dextran, Fig. 1B). Increased gut leakiness correlated with prominent lymphoid follicles in the small intestine (Fig. 1C,D). RG colonization with LG-producing strains induced persistent platelet activation (Fig 2C), as well as extramedullary expansions of platelet progenitors (megakaryocytes), in the spleen (Fig 1E & 2A). Renal injury was induced as documented by increased tubulointerstitial lymphoid infiltrates (Fig. 3). To assess the direct pathogenic effects of purified LG, mice were given an intraperitoneal LG injection, which also induced persistent splenic megakaryocytosis that was detected after 6 days (Fig. 1G).

Conclusion: To understand how the RG pathobiont induces systemic platelet activation and neutrophil death extracellular trap release (i.e. NETosis) in a subset of active LN patients, we have here elucidated distinct pathogenic pathways of this newly identified endotype of proliferative LN. In murine models, we have documented that RG strains that produce an immunostimulatory lipoglycan cause the expansion of splenic megakaryocytes and renal disease exacerbation.



References

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3. Silverman GJ et al. Front Immun 2022; Vol 13
4. Ma L et al. ACR Open 2025;7.5;e70033