Proliferative capacity of neural stem cells in hippocampus of rats after traumatic brain injury and its relationship with Janus kinase 2/signaling and transcriptional activation factor 3 signaling pathway

Abstract

Objective To investigate the proliferative capacity of neural stem cells (NSCs) in rat hippocampus after traumatic brain injury (TBI) and its relationship with Janus kinase 2/signaling and transcriptional activation factor 3 (JAK2/STAT3) signaling pathway activity. Methods A total of 108 SD rats were randomly divided into control group (36 rats) and TBI group (72 rats). The TBI model was constructed by PinPoint™ Precision Cortical Impactor. At 1, 3, 7, 14, 21 and 28 days after injury, the brain tissues were taken for immunofluorescence staining to detect the proliferation of NSCs [5-bromodeoxyuridine (BrdU)+ /stem cell key protein-2 (Sox2)+ ] in hippocampus, and phosphorylated JAK2 (p-JAK2) and phosphorylated STAT3 (p-STAT3) were detected by Western blot. The expression level of p-JAK2 and p-STAT3 as well as the changing trend were analyzed. On the basis of preliminary analysis of the proliferation of NSCs and the change of JAK2/STAT3 signaling pathway activity in hippocampus, another 24 SD rats were randomly divided into TBI+ normal saline group and TBI+ AG490 (JAK2 specific inhibitor) group, with 12 rats in each group. At 7 days after injury, the proliferation of NSCs in hippocampus was detected by immunofluorescence staining, and the expression levels of p-JAK2 and p-STAT3 were detected by Western blot, so as to further confirm the correlation between the proliferation ability of NSCs in hippocampus and JAK2/STAT3 signaling pathway. Results Compared with the control group, the number of NSCs in the hippocampus of the TBI group and the expression of p-JAK2 and p-STAT3 increased. And the most significant increase occurred at 7 days after injury [number of NSCs: 31.2±4.7 in the control group, 111.4±8.1 in the TBI group (P<0.01); p-JAK2: 1.11±0.09 in the control group, 2.16±1.01 in the TBI group (P <0.01); p-STAT3: 1.05±0.06 in the control group and 2.06±0.09 in the TBI group (P<0.01)]. The proliferation of NSCs in hippocampus of TBI group was consistent with the change of p-JAK2 and p-STAT3 expression. Seven days after injury, the expression levels of p-JAK2 and p-STAT3 and the proliferation ability of NSCs in the TBI+ AG490 were significantly decreased [p-JAK2: 2.18 ± 0.15 in the TBI + isotonic saline group, 1.24±0.10 in the TBI+ AG490 group (P<0.01); p-STAT3: 2.21±0.12 in the TBI+ isotonic saline group, 1.25±0.11 in the TBI+ AG490 group (P<0.01); NSCs number: 112.8±8.6 in the TBI+ isotonic saline group, 75.5±6.4 in the TBI+ AG490 group (P<0.05)]. Conclusions The proliferation of NSCs in hippocampus of rats increased after TBI, and the activity of JAK2/STAT3 signaling pathway also increased, following the same trend. JAK2 inhibitor AG490 can reduce the activity of JAK2/STAT3 signaling pathway and the proliferation of NSCs. This can provide reference for researches on TBI promoting nerve regeneration and function repair. Key words: Brain injuries; Neural stem cells; Hippocampus; Signal transduction