Brain-derived extracellular vesicles circUsp32 polarized macrophages causing acute kidney injury after traumatic brain injury.

Brain-kidney cross-talk following traumatic brain injury (TBI) can induce acute kidney injury (AKI), but mechanisms remain unclear. Extracellular vesicles derived from injured brain tissue (TBI-EVs) may mediate brain-kidney interactions. In vivo experiments demonstrated that TBI-EVs causes AKI by promoting pro-inflammatory macrophage polarization. TBI-EVs markedly increased AKI markers and proportion of pro-inflammatory-polarized macrophages. Mechanistically, transcriptomics of TBI-EVs revealed high circUsp32 expression. Subsequent in vitro assays showed that circUsp32 competitively binds to the SH2 domain of suppressor of cytokine signaling 1 (Socs1), affecting interferon regulator factor 7 (IRF7) ubiquitination and promoting pro-inflammatory polarization. CircUsp32 knockdown reduced pro-inflammatory polarization and alleviated AKI in TBI mice. In addition, circUsp32 is homologous to hsa_circ_0044940, which may serve as a predicted biomarker of AKI after TBI. Notably, AKI following TBI may contribute to neuroinflammation via uremic toxins. Collectively, these findings suggest that circUsp32 mediates macrophage polarization through the Socs1/IRF7 axis and could be a potential biomarker for AKI following TBI.