A FOS/NFKB1-associated Hofbauer cell subset mediates placental niche dysregulation in early-onset fetal growth restriction

Background/Objective Early-onset fetal growth restriction (FGR) is a severe pregnancy complication caused by placental dysfunction. Although superficial trophoblast invasion and sterile inflammation are recognized as characteristics, the specific cellular driving factors and molecular mechanisms that lead to the dysregulation of the immune-trophoblast microenvironment remain unclear. Methods We constructed a high-resolution single-nucleus transcriptomic (snRNA-seq) atlas of placental tissues from patients with early-onset FGR and their matched normal controls. By integrating bioinformatics methods, such as pseudotime trajectory inference, gene regulatory network analysis (SCENIC), and intercellular communication modeling (CellChat), along with in vitro validation approaches, such as hypoxia-induced macrophage models, recombinant protein stimulation, and RT-qPCR, we identified specific changes associated with this disease. Results Our research revealed impaired differentiation trajectories of trophoblast cells, characterized by the absence of a critical intermediate state essential for acquiring invasiveness. At the same time, we identified a pathogenic Hofbauer cell subset (HBC5), which increases in number in FGR and exhibits high regulon activity of FOS and NFKB1. In vitro experiments have confirmed that hypoxia triggers the polarization of HBC5-like macrophages, leading to the upregulation of pro-inflammatory factors such as CCL4. Furthermore, the CellChat analysis combined with functional validation indicates that the CCL4 produced by HBC5 significantly induces mitochondrial stress markers GDF15 and APP in trophoblast cells, resulting in dysregulation of the placental microenvironment. Mechanistically, unlike physiological HBC that provide trophic support, HBC5 shows impaired secretion of IGF1, and implements dual blockade of inflammation and metabolism on Extravillous Trophoblasts (EVT) and the vascular system through CCL chemokines and NAMPT signaling pathways. Moreover, we have elucidated a vicious cycle: trophoblast cells under stress conditions release danger signals such as GDF15 and APP, which may continuously maintain the pathogenic immune polarization state of HBC5, and polarized HBC5 in turn stimulates trophoblast cells. Conclusion Our study reveals that the HBC5 subset with high FOS/NFKB1 regulon activity acts as a key mediator of placental niche dysregulation. The identified HBC5-CCL4-Trophoblast stress axis provides a potential therapeutic target for early-onset FGR.