Saccharomyces boulardii Alleviates Colitis by Regulating FXR-NLRP3 Mediated Macrophage Pyroptosis

Background: Ulcerative colitis (UC), a typical inflammatory bowel disease (IBD), is pathologically defined by mucosal inflammation confined to the colonic mucosa. Saccharomyces boulardii (Sb), a commonly utilized probiotic yeast for managing digestive disorders like UC, has not been thoroughly investigated regarding its precise mechanisms for alleviating colitis. Increasing evidence indicates the involvement of FXR in UC. Meanwhile, the regulatory role of FXR on NLRP3 has garnered increasing attention. This study investigated the therapeutic effects of Sb supernatant (SbS) on colitis and elucidated the role of the FXR-NLRP3 signaling pathway in this process.

Methods: A murine model of colitis was established through administration of dextran sulfate sodium (DSS), followed by oral gavage with either SbS or the control Sabouraud dextrose broth (SDB) culture medium. The FXR activation, NLRP3 inflammasome inhibition, and macrophage Pyroptosis were evaluated both in vivo and in vitro. The effects of SbS in activating FXR, suppressing NLRP3 inflammasome and alleviating the colitis were assessed.

Results: SbS ameliorated symptoms of DSS-induced colitis. Our data demonstrated that SbS elicited activation of FXR and concomitantly suppressed NLRP3 expression within the colonic tissue samples. Additionally, SbS was further observed to suppress the expression of cleaved Caspase-1, a key effector protein in Pyroptosis process, within the F4/80⁺ macrophage population. Moreover, SbS modulated the expression of genes and proteins associated with Pyroptosis, collectively suggesting its potential to ameliorate intestinal Pyroptosis, potentially via its direct impact on macrophage. Consistently, SbS ameliorated Pyroptosis of macrophages in vitro through activating FXR and inhibiting NLRP3 inflammasome. However, the therapeutic effect of SbS was reversed by the FXR inhibitor, guggulsterone, resulting in increased levels of pyroptosis-related proteins.

Conclusion: SbS demonstrated a beneficial effect in alleviating UC by modulating the FXR-NLRP3 signaling pathway, thereby mitigating macrophage Pyroptosis. This discovery presents new insights into effects of Sb on alleviating UC.

Farnesoid X receptor; NLRP3 inflammasome; Saccharomyces boulardii; colitis; macrophages; pyroptosis.