Fetuin-A Alleviates Neuroinflammation Against Traumatic Brain Injury-Induced Microglial Necroptosis By Regulating Nrf-2/HO-1 Pathway

Background: The microglia-mediated inflammatory response is a vital mechanism of secondary damage following traumatic brain injury (TBI), but its underlying mechanism of microglial activation is unclear. Methods: Controlled cortical impact (CCI) was induced in adult male C57BL/6J mice, and we also used glutamate to construct a classical in vitro injury model in BV2 cell line. The activation of microglia was determined by western blot assessments and immunostaining. The inflammatory factors were determined by ELLSA. The oxidative stress marker and mitochondrial ROS were determined by immunoblotting and MitoSox Red staining. Transmission electron microscopy (TEM) was used to observe a typical morphology of necroptotic cells. Results: Our quantitative proteomics identified 2499 proteins, 157 were significantly differentially expressed between brain tissues at 6 hours after CCI (CCI6h) and sham groups, and 109 were significantly differentially expressed between CCI24h and sham brain tissues. Moreover, compared with sham groups, the terms “acute-phase response”, “inflammation”, and “protein binding” were significantly enriched in CCI groups. Interestingly, fetuin-A, a liver-secreted acute-phase glycoprotein, was involved in these biological processes. Using experimental TBI models, we found that the fetuin-A level peaked at 6 h and then decreased gradually. Importantly, we showed that fetuin-A reduced the cortical lesion volume and edema area and inhibited the inflammatory response, which was associated with suppressing microglial necroptosis, thus decreasing microglial polarization to the M1 phenotype. Furthermore, administration of fetuin-A attenuated mitochondrial oxidative stress in glutamate-treated BV2 cells, which is a critical mechanism of necroptosis suppression. In addition, we demonstrated that fetuin-A treatment promoted translocation of nuclear factor erythroid 2-related factor 2 (Nrf-2) from the cytoplasm to the nucleus in vivo; however, the Nrf-2 inhibitor ML385 and si-heme oxygenase-1 (HO-1) disrupted the regulation of oxidative stress by fetuin-A and induced increased ROS levels and necroptosis in glutamate-treated BV2 cells. Interestingly, the mechanism of fetuin-A in BV2 cells also protects neurons from adverse factors in co-culture assays.Conclusions: Our results demonstrate that fetuin-A activates Nrf-2/HO-1, suppresses oxidative stress and necroptosis levels, and thereby attenuates the abnormal inflammatory response following TBI, providing a potential therapeutic strategy for TBI treatment.