神經軸的生長對於神經系統的建立是一項必需的條件。Brain-derived neurotrophic factor (BDNF) 和它的受器 TrkB 結合並且透過訊息傳遞和基因表現去調節神經軸突和樹突的型態。訊息橋接蛋白 SH2B1β 在先前已被證實能夠調節各種訊息傳遞途徑。我們初步的結果指出高度表現 SH2B1β 能夠促進BDNF 所誘導的海馬迴神經軸生長。但是，對於 SH2B1β 促進BDNF 所誘導神經軸生長的機制卻不清楚。在此論文研究當中，我們顯示了 SH2B1β 促進了海馬迴神經細胞的樹突數目。為了檢視 SH2B1β 如何去促進 BDNF 所誘導的神經軸生長，我們已建立了穩定表現 SH2B1β 與 TrkB 的大鼠腎上腺髓質嗜鉻細胞瘤細胞株 (簡稱 PC12 cells) 去研究它在 BDNF 誘導的訊息傳遞中所扮演的角色。我們的實驗結果顯示相對於控制組的細胞，高度表現 SH2B1β的 PC12-SH2B1β+TrkB 細胞能夠促進 BDNF 誘導的神經軸生長。SH2B1β 能夠增強 BDNF 誘導的 MEK-ERK1/2、PI3K-AKT 和 PLCγ1 訊息傳遞途徑。利用專一的抑制劑去抑制 MEK-ERK1/2 和 PI3K-AKT訊息傳遞途徑更進一步地顯示了 SH2B1β 所促進的 BDNF 誘導的神經軸生長需要這兩條訊息傳遞途徑的參與。除此之外，SH2B1β 也會增強 BDNF 誘發的 signal transducer and activator of transcription 3 (STAT3) 在絲胺酸上的磷酸化。我們更進一步地證實了 SH2B1β 的 SH2 domain 及酪胺酸磷酸化參與了 BDNF 誘發的訊息傳遞和神經軸生長。總結我們的實驗結果顯示了 SH2B1β 能夠透過增強 MEK-ERK1/2、PI3K-AKT 和 PLCγ1 訊息傳遞途徑和 STAT3 上的絲胺酸磷酸化去促進 BDNF 所誘導的神經軸生長。

Neurite outgrowth is essential for the establishment of a functional nervous system. Brain-derived neurotrophic factor (BDNF) binds to its receptor TrkB and regulates axonal and dendritic morphology through signaling transduction and gene expression in neurons. SH2B1β, a signaling adaptor protein, has previously been shown to regulate several signaling pathways. Our preliminary results suggest that overexpression of SH2B1β promotes BDNF-induced neurite outgrowth in hippocampal neurons. However, little is known about the underlying mechanisms by which SH2B1β promotes BDNF-induced neurite outgrowth. In this study, we showed that SH2B1β promotes the number of dendrites in hippocampal neurons. To examine how SH2B1β promotes BDNF-induced neurite outgrowth, we have established PC12 cells stably expressing SH2B1β and TrkB to investigate its role in BDNF-induced signaling pathways. Our data demonstrated that overexpressing SH2B1β promotes BDNF-induced neurite outgrowth in PC12-SH2B1β+TrkB cells compared with the control cells. SH2B1β enhances BDNF-induced MEK-ERK1/2, PI3K-AKT and PLCγ1 signaling pathways. Inhibition of MEK-ERK1/2 and PI3K-AKT pathway by specific inhibitors further suggest that these two pathways are required for SH2B1β-promoted BDNF-induced neurite outgrowth. Moreover, SH2B1β enhances BDNF-stimulated signal transducer and activator of transcription 3 (STAT3) phosphorylation at serine 727. We further demonstrate that SH2 domain and tyrosine phosphorylation of SH2B1β are involved in BDNF-induced signaling pathways and neurite outgrowth. Taken together, our results demonstrate that SH2B1β promotes BDNF-induced neurite outgrowth through enhancing pathways involving MEK-ERK1/2, PI3K-AKT, PLCγ1 and phosphorylation of STAT3 at serine 727.

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