TGFβ1 alleviates axonal injury by regulating microglia/macrophages alternative activation in traumatic brain injury

Traumatic brain injury (TBI) causes substantial mortality and long-term disability worldwide. TGFβ1 is a unique molecular and functional signature in microglia, but the role of TGFβ1 in TBI is not clear. The purpose of this study was to investigate the role of TGFβ1 in TBI. The weight dropping device was used to establish TBI model of rats. Hematoxylin eosin staining and Bielschowsky silver staining were used to assess tissue loss. Beam walking and muscle strength tests were used to assess neurological deficits. Immunohistochemical staining was used to assess axonal injures. Western blotting was used to detect expression of related proteins. RT-PCR was used to detect expression of cytokines. Immunofluorescence staining was used to assess the microglia/macrophages activation. We observed obvious axonal injury and microglia/macrophages activation in the peri-lesion cortex. The expression of inflammatory cytokines was markedly high after TBI. The expression of TGFβ1 and TGFβRI were significantly reduced after TBI. TGFβ1 promoted the functional recovery and alleviated axonal injury 1 day after TBI. TGFβ1 promoted microglia/macrophages polarizing to alternative activation and alleviated neuroinflammation. These effects of TGFβ1 could be inhibited by LY2109761, the inhibitor of TGFRI/II. These results suggested that TGFβ1 played a protective role in axonal injury and could be a potential therapeutic target in early stages following TBI.