POS0303 CROSSING THE BARRIERS: DYSBIOSIS AND SUBCLINICAL UTERINE INFLAMMATION IN THE PATHOGENESIS OF AxSpA IN FEMALES. ANOTHER BREAK IN THE WALL?

Background: Spondyloarthritis (SpA) presents a distinct phenotype among sexes with females experiencing delayed diagnosis but also a higher functional burden and poorer outcomes compared to males, underscoring the need to investigate sex-specific factors in SpA pathogenesis. While the role of gut dysbiosis in SpA and the gut-joint axis is well-established, the specific contribution of the female genital immune system remains underexplored. Data in animal models suggest an interplay between the uterus and joints. We explored this novel dimension in SpA pathogenesis which may have specific implications for female patients. Objectives: The primary aim of this study is to investigate the existence of a uterine-gut axis contributing to the pathogenesis of SpA in female patients. Methods: Vaginal, cervical, and uterine swabs were collected from 25 premenopausal, newly diagnosed SpA patients and 25 age-matched healthy controls (HC), excluding individuals with recent antibiotic usage, known gynaecological diseases, or contraceptive medication use. The microbial composition of these swabs was analyzed using 16S rRNA sequencing to identify distinct microbial patterns associated with SpA. To investigate genital inflammation in the context of arthritis, we employed the SKG preclinical model of SpA, synchronizing menstrual cycles via progesterone administration. A total of 15 SKG mice were assessed at baseline and at 1 and 2 weeks post-curdlan intraperitoneal administration. Uterine samples from SKG mice were assessed histologically for the presence of inflammation, scoring from 0, normal histopathologic findings to 3, diffuse increase of inflammatory cells with epithelial abnormalities (squamous metaplasia, epithelial apoptosis, infiltration of neutrophils, and micro-abscesses). Bulk RNA sequencing were also performed on SKG uterine samples. Additionally, we conducted an in-depth genomic and molecular characterization of uterine resident immune cells in SpA and HC (n=2 each), applying 10X Genomics technology to huAN menstrual blood for precise cellular profiling. Results: Our study revealed significant dysbiosis in the genital tract of newly diagnosed female SpA patients, characterized by a reduced abundance of eubiotic lactobacilli and a notable presence of the genus Gardnerella in 83% of SpA samples, compared to 16% in controls (p < 0.001). In the SKG mouse model, we observed genital inflammation, more pronounced 1 week post-curdlan, characterized by the presence of inflammatory infiltrate, microabscesses, epithelial apoptosis, and squamous metaplasia (histological score median 1, 3, 2 at baseline, 1 week, and 2 weeks post-curdlan, respectively; p < 0.001). Preliminary bulk RNA sequencing of SKG uterine samples identified four gene subclusters, with one distinctly differentiating curdlan-treated mice from controls. Preliminary single-cell transcriptomics from menstrual blood (n=2) identified eight immune cell populations and a decreased abundance of monocytes and an expansion of T cells, particularly memory T-cells in SpA vs HC. Differential expression of innate immune cell genes (e.g., IL7R, IL10, IL6, IL1B) was also observed. Conclusion: This study suggests that the uterine barrier may axis plays a role in female SpA pathogenesis. Our findings of significant genital tract dysbiosis and distinct immune cell profiles in female SpA patients compared to healthy controls, underscore the importance of sex-specific factors in SpA. A comprehensive approach utilizing preclinical models, metagenomics, transcriptomics, and immunohistochemistry has begun to unravel the intricate relationship between the cervicovaginal immune landscape and SpA, highlighting potential pathways that contribute to sexual dimorphism in the disease. This sets the stage for future investigations into targeted therapies that address these sex-specific differences in SpA. REFERENCES: [1] Zaiss et al. Nat Rev Rheumatol 2021. [2] Romand et al. Arthritis Rheumatol, 2021. [3] Baillet et al. Arthritis and Rheumatism, 2015. Acknowledgements: NIL. Disclosure of Interests: None declared.