Background Sex and microbiota dysbiosis affect lupus development/progression. We have found that gut microbiota and metabolomic profiles in adult lupus-prone female and lupus-resistant male NZBxNZWF1 (BWF1) mice differ; male cecal transplants into female mice suppress disease. Here, we identify disease-modulating bacteria and metabolite candidates and characterize potential mechanisms underlying disease suppression mediated by male microbiota transplants.

Methods BWF1 mice were used for all experiments. Fecal microbiota composition in female and male mice was determined by 16S rRNA gene sequencing. Fecal metabolites were identified using mass spectrometry. Cecal contents from adult male or female mice were transplanted by oral gavage into female mice. Disease (proteinuria) and survival, and mesenteric lymph node CD11c⁺CD103⁺ dendritic cell (CD103DC) and splenic CD11b⁺F4/80⁺ macrophage function in in vitro assays and by RNA-seq/RT-PCR were analyzed. In some experiments, female mice were treated with male fecal metabolites in vivo and cell function analyzed ex vivo, or female cells were treated directly with male metabolites in vitro and function analyzed.

Results Microbiota composition analysis in adult female and male mice and recipients of cecal transplants under conditions when male cecal transplants did or did not suppress disease indicated that high Bacteroides and low Clostridium abundances (high Bacteroides/Clostridium ratio) and presence of Alistipes correlated with disease resistance/suppression. Two types of immune cells with different functions were identified as possible mediators of sex-dependent and microbiota-driven differences in disease development. Female CD103DC have decreased ability to convert conventional CD4 cells to Foxp3⁺ Tregs due to defects in retinoic acid (RA) production; female macrophages have decreased ability to mediate efferocytosis and defects in genes associated with PPARγ and LXR signaling. Male cecal transplants can restore function of both CD103DC and macrophages in female recipients. Metabolomics analysis of feces revealed that males have higher phytanic acid (PA), an RXR/PPARγ/LXR agonist. Treatment of female mice in vivo with PA delays disease to some extent and restores both CD103DC and macrophage function. PA also restores CD103DC and macrophage function when added to female cells directly in vitro. PA enhances CD103DC function by restoring RA production via the RXR pathway and macrophage efferocytosis via the PPARγ and LXR pathways in female mice.

Conclusions We have identified specific gut microbiota taxa and metabolite candidates from lupus-resistant male mice that have immunomodulatory activity and the potential to mitigate disease in lupus-prone female mice. Disease mitigation may be mediated through an increase in CD103DC function and macrophages efferocytosis.

Acknowledgments Funded by ALR and NIH-R01AR067188. 16S rRNA gene sequencing was performed by GTAC, Washington University, St. Louis. Mass spectrometry was performed by CREAM, University of Louisville, Louisville.