Mitochondrial-targeting antioxidant MitoQ modulates angiogenesis and promotes functional recovery after spinal cord injury

Background: In traumatic spinal cord injury (SCI), secondary injuries, including cellular death, mitochondrial dysfunction, and vascular injury, have been considered as important causes of impaired functional recovery after SCI. Postinjury angiogenesis has been considered to be a potential strategy for SCI treatment. New-born vessels may play a key role in nerve regeneration, which indicates the importance of angiogenesis in nerve regeneration. Recent studies have revealed the crosstalk between reactive oxygen species (ROS) and angiogenesis. As the main source of cellular ROS, mitochondria have been proven to be essential to the angiogenesis process. Methods: SCI was established in a T10 clip-compression animal model. Then, the animals received an intraperitoneal injection of MitoQ (5 mg/kg/d) on Days 0, 1, and 2 after surgery. The Basso Mouse Scale (BMS) score and footprint analysis (CatWalk analysis) were performed to evaluate functional recovery after SCI. Immunofluorescence and fluorescence assays (LEL-FITC/CD31/Iba-1/Neurofilament) were performed to evaluate angiogenesis, microglia activation and neural regeneration. RT-qPCR (VEGFR-1, VEGFR-2 and VEGFA) was performed to evaluate angiogenesis-related factor in injured spinal cord. ATP production assay and western-blotting assay (Mfn-1 and Drp-1) were performed to evaluate mitochondrial function in the injured spinal cord. BV2 cells were used as in vitro cell model. After receiving TBHP or TBHP-MitoQ treatment, ELISA and immunofluorescence assays were used to evaluate the level of VEGFA secretion from BV2 cells. A coculture system of HUVECs and BV2 cells was established. Tube formation assays and immunofluorescence assays (CD31) were performed on HUVECs in a coculture system to evaluate angiogenesis promotion. ATP production assays were performed to evaluate mitochondrial function in BV2 cells. MitoSOX Red and DCFH-DA staining were performed to evaluate mitochondrial and cellular ROS.Results: In vitro MitoQ promoted the secretion of VEGFA from BV2 cells, which was verified through ELISA and immunofluorescence assays. The angiogenic promotion of MitoQ-treated BV2 cells was evaluated by tube formation and immunofluorescence assays (CD31) in a coculture system of BV2 cells and HUVECs. MitoQ inhibited cellular and mitochondrial-derived ROS in TBHP-treated BV2 cells. ATP production was increased in MitoQtreated BV2 cells. To verify MitoQ's effect in vivo, a T10 clip-compression animal model was established successfully. MitoQ significantly promoted functional recovery, as shown by the BMS assay and gait analysis. The promotion of neural regeneration was identified through immunofluorescence assay of neurofilament. Immunofluorescence and fluorescence assays (LEL-FITC/CD31/Iba-1) and RT-qPCR (VEGFR-1, VEGFR-2 and VEGFA) indicated that MitoQ could promote angiogenesis and inhibit macrophage/microglia activation in lesion-site after SCI. Enhanced ATP production and increased Mfn-1 with decreased Drp-1 protein expression showed MitoQ could promote mitochondrial function in SCI.Conclusion: The mitochondrial-specific antioxidant MitoQ promotes functional recovery and tissue preservation through the enhancement of angiogenesis with the modification of mitochondrial function after SCI.