Probiotic interventions maintain intestinal barrier function and alleviate necrotizing enterocolitis by inhibiting ferroptosis in intestinal PMN-MDSCs.

Circulating polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) and gut probiotics are crucial for alleviating experimental necrotizing enterocolitis (NEC) in mice, yet the mechanisms linking intestinal PMN-MDSCs (iPMN-MDSCs) to specific microbiota remain unclear. Herein, we identified Lactobacillus (L.) reuteri and L. rhamnosus as two key strains significantly reduced under NEC conditions; their combined supplementation increased iPMN-MDSC abundance and olfactomedin 4 (OLFM4) expression, thereby improving intestinal epithelial cell (IEC) function and attenuating NEC. Olfm4 deficiency in neutrophils exacerbated NEC, disrupted intestinal barrier integrity, and induced microbial dysbiosis. Mechanistically, OLFM4 inhibited iPMN-MDSC ferroptosis by enhancing activating transcription factor 4 (ATF4) activity and upregulating its targets solute carrier family 7a member 11 (Slc7a11) and glutathione peroxidase 4 (Gpx4). Downregulation of Atf4 or Gpx4 recapitulated the phenotypic alterations observed in Olfm4-deficient mice, including aggravated NEC and impaired iPMN-MDSC function. Treatment with indole-3-aldehyde, an effector metabolite of probiotics, alleviated NEC by restoring the OLFM4-driven anti-ferroptosis axis in iPMN-MDSCs. In patients with NEC, reduced intestinal LOX1+PMN-MDSCs and a weakened anti-ferroptosis pathway were associated with disease progression. These findings offer a therapeutic strategy for NEC by targeting iPMN-MDSC ferroptosis via probiotic- or metabolite-based interventions.