Our previous study has shown that the transcription factor Krüppel-like factor 7 (KLF7) promotes peripheral nerve regeneration and motor function recovery after spinal cord injury. KLF7 also participates in traumatic brain injury, but its regulatory mechanisms remain poorly understood. In the present study, an HT22 cell model of traumatic brain injury was established by stretch injury and oxygen-glucose deprivation. These cells were then transfected with an adeno-associated virus carrying KLF7 (AAV-KLF7). The results revealed that, after stretch injury and oxygen-glucose deprivation, KLF7 greatly reduced apoptosis, activated caspase-3 and lactate dehydrogenase, downregulated the expression of the apoptotic markers B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax) and cleaved caspase-3, and increased the expression of βIII-tubulin and the antiapoptotic marker Bcl-2. Furthermore, KLF7 overexpression upregulated Janus kinase 2 (JAK2) and signal transducer and activator of transcription 3 (STAT3) phosphorylation in HT22 cells treated by stretch injury and oxygen-glucose deprivation. Immunoprecipitation assays revealed that KLF7 directly participated in the phosphorylation of STAT3. In addition, treatment with AG490, a selective inhibitor of JAK2/STAT3, weakened the protective effects of KLF7. A mouse controlled cortical impact model of traumatic brain injury was then established. At 30 minutes before modeling, AAV-KLF7 was injected into the ipsilateral lateral ventricle. The protein and mRNA levels of KLF7 in the hippocampus were increased at 1 day after injury and recovered to normal levels at 3 days after injury. KLF7 reduced ipsilateral hippocampal atrophy, decreased the injured cortex volume, downregulated Bax and cleaved caspase-3 expression, and increased the number of 5-bromo-2'-deoxyuridine-positive neurons and Bcl-2 protein expression. Moreover, KLF7 transfection greatly enhanced the phosphorylation of JAK2 and STAT3 in the ipsilateral hippocampus. These results suggest that KLF7 may protect hippocampal neurons after traumatic brain injury through activation of the JAK2/STAT3 signaling pathway. The study was approved by the Institutional Review Board of Mudanjiang Medical University, China (approval No. mdjyxy-2018-0012) on March 6, 2018.
Keywords: JAK2/STAT3; Kruppel-like factor 7; apoptosis; hippocampus; neuroprotection; oxygen-glucose deprivation; stretch; traumatic brain injury.