Treg-microglia partnership in the injured spinal cord preserves Treg cells function and regulates microglial cholesterol metabolism

The quantitative variations and specific roles of regulatory T cells (Treg cells) within spinal cord injury (SCI) remain elusive. Utilizing single-cell RNA sequencing, flow cytometry, and immunofluorescence, we discovered that Treg cells began to infiltrate the injured spinal cords in mice approximately three days after SCI. Selective depletion of Treg cells resulted in an expansion of the injury area, reduction in neuronal survival, and a decrease in long-term functional recovery post-SCI. Transcriptomic analyses of Treg cells unveiled potent anti-inflammatory functions and the potential to influence neighboring immune cells within the spinal cord after SCI. Adoptive transfer of Treg cells demonstrated measurable improvement in SCI recovery and increased neuronal retention in mice. However, selective depletion of microglia inhibited the neuroprotective effects of Treg cells, indicating that the effect of Treg cells in the spinal cord depends on the presence of microglia. Mechanistically, Treg cells promoted spinal cord functional recovery by upregulating microglial Abcg1 receptor expression, enhancing cholesterol transport, reducing microglial lipid droplet formation, and moderating the M1 phenotype after SCI. In summary, our study elucidates the spatiotemporal distribution of Treg cells after SCI and their unique transcriptomic features, clarifying the impact of Treg cells on microglial cholesterol metabolism and inflammatory phenotype. These findings indicate that Treg cells may serve as a potential target for SCI treatment.