In vivo exposure to lipopolysaccharide inhibits STAT1 signaling

Abstract The present study investigates the impact of lipopolysaccharide (LPS) preconditioning on signaling transduction and downstream gene expression of the murine transcription factor STAT1 (Signal Transducer and Activator of Transcription 1). Wild‑type and transgenic mice expressing an amino-terminal deletion mutant of STAT1 (STAT1-ΔN) received an intraperitoneal injection of either LPS (5 mg kg⁻ 1 ) or phosphate‑buffered saline (PBS) used as a control, and twenty‑four hours later, isolated splenocytes were subjected ex vivo to a 30‑minute stimulation with interferon‑γ (IFNγ), LPS, or a combination of both agents. Splenocytes derived from LPS‑treated mice displayed a significant attenuation of STAT1 tyrosine phosphorylation upon IFNγ stimulation relative to PBS‑treated animals, whereas tyrosine phosphorylation of the homologous STAT3 remained unchanged. Moreover, LPS pre‑exposure was associated with a significant down‑regulation of STAT1‑target genes, including Socs1 and Socs3 encoding suppressor of cytokine signaling (SOCS) proteins, which are known negative feedback regulators. Transcriptomic profiling identified 190 differentially expressed genes (DEGs) between LPS- and PBS‑pretreated samples, and 399 DEGs after combined LPS/IFNγ stimulation. Flow‑cytometric analysis corroborated these findings, revealing a substantial reduction in tyrosine-phosphorylated STAT1 levels in CD4⁺ T cells, macrophages, B cells, and myeloid‑derived cells from LPS‑pretreated mice following IFNγ stimulation, compared to PBS‑treated controls. In summary, these results demonstrate that LPS preconditioning suppresses STAT1 signaling and reshapes the functional responsiveness of diverse immune cell subsets. The data suggest that an initial innate immune activation can diminish subsequent cytokine‑driven signaling, thereby modulating inflammatory pathways. This work advances our understanding of the complex interplay between LPS‑induced tolerance and STAT1‑dependent inflammatory signaling.