Per2 deficiency in microglia alleviates motor dysfunction by inhibiting ferroptosis in spinal cord injury

Microglia are specialized resident immune cells of the central nervous system parenchyma that mediate reactions such as the inflammatory response to spinal cord injury (SCI) and play significant roles in exacerbating or alleviating disease progression. Previous studies have suggested that ferroptosis, a newly discovered form of regulated necrotic cell death, plays a crucial role in exacerbating neuronal dysfunction and loss following SCI; however, the role of microglial ferroptosis in SCI and the underlying mechanisms remain elusive. Here, we elucidate that lipid droplets accumulate in microglia to facilitate ferroptosis of microglia after SCI. Notably, microglial ferroptosis peaks at 3 days post-injury, after which it decreases. Microglial Period 2 (Per2) expression is elevated after SCI in vivo, this change is highly synchronized with the changes in microglial ferroptosis. Using conditional knockout mice, we observed that microglia-specific Per2 knockout promoted neurological function recovery by suppressing microglial ferroptosis. In vitro, Per2 overexpression and deficiency amplified and mitigated microglial ferroptosis, respectively. Using RNA-seq analysis, we found that Gpx4 was downregulated by Per2. Coimmunoprecipitation (Co-IP) demonstrated that Per2 directly interacted with PPARα to further regulate Gpx4. Furthermore, we demonstrated that the degree of microglial ferroptosis was decreased and that the number of microglia was increased by treatment with a ferroptosis inhibitor, which indicated that reducing microglial ferroptosis during the acute phase of SCI may be beneficial for alleviating neurological dysfunction. Overall, our results indicate that Per2 determines the susceptibility of microglia to ferroptosis via the PPARα-Gpx4 axis, and suggest that Per2 has potential as a therapeutic strategy to alleviate motor dysfunction by inhibiting microglial ferroptosis following SCI.