Elevated hippocampal CD24 in astrocytes participates in neural regeneration possibly via activating SHP2/ERK pathway after experimental traumatic brain injury in mice.

Massive neuron loss is the key reason for poor prognoses in patients with traumatic brain injury (TBI), and astrocytes function as nutrition-providing neurons. Therefore, researchers must determine the potential role of astrocytes in neural regeneration after TBI. Our previous studies established that upregulating CD24 in the hippocampus might improve cognitive functions after TBI. However, whether CD24 in hippocampal astrocytes is involved in neural regeneration after TBI remains unknown. Therefore, we detected the CD24 expression in the ipsilateral hippocampus via western blot and quantitative real-time PCR. We further investigated the CD24 expression patterns in hippocampal astrocytes via immunofluorescence staining. We then injected adeno-associated virus-Gfa2-siRNA-CD24 (AAV-CD24) into the astrocytes to downregulate CD24 and analyzed the related cellular signals. Golgi-Cox staining and the growth associated protein-43 (GAP43) level were used to observe neuronal morphology and neural regeneration around the astrocytes in the ipsilateral hippocampus, and the Morris water maze test was used to assess neural functional recovery. The CD24 protein and mRNA levels in the cornu ammonis and dentate gyrus regions of the ipsilateral hippocampus were elevated after TBI, and high CD24 expression was widespread in the hippocampal astrocytes after TBI. Specific inhibition of CD24 in the hippocampal astrocytes interfered with the activation of Src homology region 2 containing protein tyrosine phosphatase 2 (SHP2) and extracellular signal regulated kinase (ERK), shortened the neuronal dendritic spines, decreased the GAP43 level and impaired the cognitive functions of the TBI-model mice. These results revealed that elevated hippocampal CD24 in astrocytes participated in neural regeneration in mice after TBI, possibly by activating the SHP2/ERK pathway.