FXR protects against neonatal sepsis via enhancing the immunosuppressive function of MDSCs

The presence of myeloid-derived suppressor cells (MDSCs) during the early postnatal period plays a protective role against neonatal inflammation. However, the mechanisms regulating neonatal MDSCs remain to be fully elucidated. In this study, we report that the bile acid receptor Farnesoid X receptor (FXR) acts as a pivotal positive regulator of neonatal MDSCs. Using FXR-deficient (FXR-/-) mice and FDA-approved FXR agonist obeticholic acid (OCA), we demonstrated that FXR deficiency impairs the immunosuppressive and antibacterial functions of neonatal MDSCs, thereby exacerbating the severity of neonatal sepsis. Adoptive transfer of MDSCs alleviates sepsis severity in FXR-/- neonatal pups. Mechanistic studies reveal that HIF1a, a well-established regulator of MDSCs, is a direct transcriptional target of FXR. Patients with neonatal sepsis displayed reduced MDSC frequencies and impaired expression of FXR and HIF-1α, which was negatively correlate with the clinical parameters. These observations highlight the important role of FXR in neonatal MDSCs and its therapeutic potential in neonatal sepsis. PMN-MDSCs sorted from spleens of FXR-/- and WT neonatal mice (7 days). PMN-MDSCs were resuspended in TRIzol for RNA extraction. Library preparation was performed using a SMARTer Ultra low RNA kit, and sequencing was conducted on an Illumina NovaSeq platform (150-bp paried-end).