Integrated bulk and single-cell transcriptomics identify heterogeneous NRF2–HO-1–GPX4-related programs in osteoarthritic synovium

Background The NRF2-HO-1-GPX4 axis is biologically relevant to oxidative-stress defense and ferroptosis regulation, but its transcriptomic behavior in knee osteoarthritis (KOA) synovium may vary across cohorts and local tissue microenvironments. Methods We performed a bioinformatics-led integrated analysis of public human KOA synovial transcriptomic datasets, including bulk OA-versus-control comparisons, paired regional synovial analysis, exploratory pain- and stage-related contrasts, and single-cell/single-nucleus localization. NFE2L2, HMOX1 and GPX4 were analyzed as prespecified genes, and compact module scores summarized NRF2-HO-1-GPX4, ferroptosis-related, oxidative-stress/NRF2 and inflammatory programs. Representative HE and immunohistochemical images were included only as exploratory qualitative tissue-level support. Results NFE2L2 showed the most recurrent OA-positive direction across bulk datasets, whereas HMOX1 and GPX4 were cohort dependent. GSE89408 showed coherent increases in axis-related, ferroptosis-related, oxidative-stress/NRF2 and inflammatory signatures, but this pattern was not universal. In GSE46750, paired synovial cell cultures derived from macroscopically inflamed sites showed higher ferroptosis-related and inflammatory transcriptomic module scores than cultures derived from normal/reactive sites of the same osteoarthritic joints. Exploratory pain- and disease-stage-related analyses were inconclusive, particularly because the GSE176223 comparisons involved repeated profiles from the same donors without donor-aware statistical inference. Marker-score-based single-cell analyses detected axis-related transcripts across broad inferred stromal, immune, vascular and perivascular compartments, although precise cell identities were not independently validated. Biological-sample-level pseudobulk analysis did not establish a consistent OA-associated shift in the compact axis score. Histologically, KOA synovium showed denser and more disorganized fibrous stroma; representative IHC images showed an apparent tendency toward stronger NRF2 and HO-1 staining and weaker GPX4 staining in KOA, without semiquantitative scoring. Conclusion NRF2-HO-1-GPX4-related remodeling in KOA synovium is heterogeneous and appears more closely associated with local inflammatory tissue state than with global diagnosis, pain status or disease stage. The pathology findings provide preliminary qualitative support rather than mechanistic proof.