Treg cells protect astrocytes from ferroptosis after subarachnoid hemorrhage by activating the HIF-1α/Hmox1 pathway

Background: Foxp3+ regulatory T (Treg) cells play a central role in maintaining immune homeostasis by suppressing excessive immune responses to prevent autoimmune damage. Within the nervous system, they actively inhibit neuroinflammation and promote tissue repair. Current studies have demonstrated that the number of Tregcells significantly increases following subarachnoid hemorrhage (SAH). Tregcells infiltrating into the brain after SAH can exert critical anti-inflammatory and neuroprotective effects by modulating microglia polarization. Although they are the most abundant and functionally diverse glial cells in the central nervous system, there is only limited research on the direct and specific interactions of astrocytes and Tregcells in SAH. This knowledge gap motivated us to conduct the present studies. Methods: experiments, Tregcells were co-cultured with astrocytes, using oxygenated hemoglobin (OxyHb) to induce a pathological environment mimicking SAH. Key signaling pathways were identified through transcriptome sequencing. The effects of Tregcells on astrocytes were evaluated through AAV-mediated gene overexpression and knockdown, drug agonists and antagonists, plasmid transfection, SAH grading, neurobehavioral testing, western blotting, and immunofluorescence. Results: Following SAH, the HIF-1α/Hmox1 signaling axis was activated in the brain, predominantly in astrocytes. However, this compensatory response was insufficient to prevent progressive ferroptotic injury, as indicated by sustained lipid peroxidation and iron accumulation. Tregcells rapidly accumulated after SAH, and enhancement of their function significantly improved neurological outcomes.Transcriptomic profiling of astrocytes revealed that the interaction between Tregcells and astrocyte selectively enriched ferroptosis pathways, with prominent activation of HIF-1α signaling and robust upregulation of Hmox1. Mechanistically, Tregcells promoted a distinct regulatory pattern characterized by moderate stabilization of HIF-1α but disproportionately enhanced Hmox1 expression. Importantly, Tregcells did not induce excessive activation of the HIF-1α/Hmox1 axis, indicating that they maintain this pathway within a defined protective range to suppress ferroptosis without exacerbating toxicity dependent on iron. Conclusion: This study identified a previously unrecognized immunometabolic mechanism by which Tregcells constrain astrocytic ferroptosis after SAH. By reinforcing an otherwise insufficient endogenous stress response, Tregcells fine tune the HIF-1α/Hmox1 axis to a protective range. They thereby limit oxidative damage that depends on iron and preserve astrocyte integrity.