Role Of Fibroblast Growth Factor 13 In The Postnatal And Adult Hippocampal Neurogenesis In Mouse

Development of the nervous system plays a crucial role in the whole development process. Abnormal neurodevelopment not only causes a variety of neurological disorders, including mental retardation, language disorders, autism, epilepsy, but also affects peripheral tissue and organs. Compared with embryonic development, postnatal neurodevelopment has important physiological significance in the further differentiation and maturation of various organs and tissues. Fibroblast growth factor (FGF) family plays a vital role in cell proliferation and differentiation course, and it is widely involved in nervous system development and maintenance of normal physiological function. Although FGF11 subfamily (FGF11-14) has some homology with other members of FGFs, they can not be secreted and activate FGF receptors because of lacking the N-terminal signal peptide, and thus they have some features which are different from the other FGFs. FGF13 mRNA is expressed widely in a variety of tissues during development and the expression levels are much higher than other FGF 11 subfamily members, suggesting that it may play important function in the brain development. Meanwhile FGF 13 gene defects are also closely associated with a variety of X-linked mental retardation, further suggesting its importance during neural development. However, the function of FGF13 in the central nervous system and its relationship with X-linked mental retardation remains unclear.In the present study, we used FGF13 gene conditional knockout mouse model to investigate the functions and molecular mechanisms of FGF13 in mouse postnatal neurodevelopment. Our findings laid the foundation for the clarification of FGF function in X-linked mental retardation.AIM:To investigate the functions and mechanisms of FGF 13 in mouse neurodevelopment.METHODS:1. FGF13fl/fl;hGFAP-Cre+ mice and littermate controls were injected with 100 mg/kg BrdU intraperitoneally for 5 consecutive days and were killed 2h after the last BrdU injection to identify BrdU-positive cells.2. Immunohistochemistry was carried out to determine the number of BrdU, Ki67, Ascl1, GFAP, Dcx, S100β, NeuN positive cells in the SGZ and SVZ of FGF13fl/fl;hGFAP-Cre+ mice and littermate controls, as well as the number and the fluorescence intensity of NG2 positive cells in FGF13fl/fl;NG2-Cre+ mice and the control mice.3. PCNA, Ascll, GFAP, ARID1B, GSK3β, p-GSK3p(Y216), NG2, MBP and Olig2 were semi-quantified by western blotting.4. mRNA of FGF13A, FGF13B and NG2 were detected by real-time PCR.RESULTS:1. FGF13 gene deletion causes structural abnormalities in hippocampal dentate gyrusAverage thickness and the numbers of hippocampal granule cell layer were significantly reduced in P30 and P60 FGF13fl/fl;hGFAP-Cre+ mice.2. FGF13 gene deletion reduces the number of neural stem cells/neural precursor cells in the SGZThe numbers of Brdu+ cells and Ki67+ cells were decreased in the SGZ of P30/P60 FGF13fl/fl;hGFAP-Cre+ mice. Concomitantly, the levels of PCNA protein expression were also reduced in hippocampal tissue. However, there was no such change in P0/P7 FGF13fl/fl;hGFAP-Cre+ mice. Compared with the SGZ, the number of Brdu+ cells and Ki67+ cells in the SVZ did not altered markedly compared with control. Moreover, the number of GFAP+/S100β- Type 1 aNSCs in the SGZ was also reduced in P30/P60 FGF13fl/fl;hGFAP-Cre+ mice. The number of Ascll+ TAPs decreased in SGZ of P30 FGF13fl/fl;hGFAP-Cre+ mice as well as the level of Ascll protein declined in hippocampal tissue. Meanwhile, there was a reduction in the number of Dcx+/Ki67+ neuroblasts FGF13 gene deficient mice.3. FGF13 gene deletion causes in a decline in the generation of neurons in the SGZThe number of Dcx+ and Dcx+Ki67" immature neurons was significantly decreased in the SGZ of P30/P60 FGF13hGFAPcKO mice with reduction in the generation of NeuN+ mature neurons.4. FGF13 gene deletion doesn’t affect astrocyte genesis in SGZThere was no significant change in the number of GFAP+/S100β+ astrocytes in the SGZ of P30/P60 FGF13hGFAPcKO mice and in the level of GFAP protein in hippocampus of P0/P60 FGF13hGFAPcKO mice.5. FGF13 gene deletion in OPCs upregulates the levels of NG2 proteinThe fluorescence intensity of NG2 was increased in the cortex and hippocampus of FGF13NG2cKO mice by immunohistochemistry with no significant change in the number of OPCs. The levels of NG2 protein and mRNA also rose mildly in FGF13NG2cKO mice. FGF13 gene deletion didn’t affect the protein levels of MBP and Olig2.6. FGF13 interaction with ARID1B and FGF13 gene deletion reduced ARID1B expressionYeast two-hybrid analysis reveals that FGF13 interacted directly with ARID1B and the levels of ARID1B expression were decreased in response to FGF13 deletion.7. FGF13 is associated with Wnt signaling pathwayPO mice hippocampal neurospheres were cultured for 5 days, with incubation of LiCl (20 and 50 mM) for 2 days. The mRNA levels of FGF13 were increased in a dose-dependent manner. The levels of p-GSK3β(Y216) protein rose in the hippocampal tissue of P0/P60 FGF13hGFAPcKO mice. CONCLUSION:FGF13 gene deletion may lead to a decrease in the number of NSCs/neural progenitor cells and neurons through ARID1B and Wnt signaling pathway. FGF13 gene deletion in OPC upregulates the expression levels of NG2 protein, but does not affect OPC proliferation and postnatal myelination.