芳香烴接受器2之內生性配體於斑馬魚神經分化的角色

Abstract

戴奧辛經由芳香烴接受器 (aryl hydrocarbon receptor, AHR) 調控不同的訊號傳遞路徑影響細胞的行為，例如，胚胎發育，腫瘤生成以及發炎反應。然而能與芳香烴接受器結合並影響細胞的生理反應之內生性配體仍有待更多發現與深深入研究。藉由本實驗室所開發之戴奧辛檢測法，我們在斑馬魚胚胎中找到可能的芳香烴接受器內生性配體，四氫皮質甾酮 (Tetrahydrocorticosterone, THB)，於此研究當中，我們希望能進一步透過四氫皮質甾酮所激活的芳香烴接受器的功能。在細胞實驗中四氫皮質甾酮可以誘導芳香烴接受器進入細胞核，並且激活下游基因CYP1A1的表現。在我們先前的研究中，證實芳香烴接受器大量表達會導致神經纖維母細胞瘤細胞分化; 而四氫皮質甾酮也同樣展現其促進神經纖維母細胞瘤細胞神經分化的潛力。動物實驗則顯示四氫皮質甾酮透過斑馬魚的芳香烴接受器2 (AHR2)提高芳香烴接受器標的之zCYP1A、髓鞘相關的zMBP以及zOLIG2的表現。此外，我們也發現四氫皮質甾酮透過芳香烴接受器2參與了早期的神經發育，以及不同的神經細胞群系如寡突膠細胞、星狀膠細胞以及小膠質細胞等的分化。由以上結果，我們認為四氫皮質甾酮乃一內生性的芳香烴接受器配體，並且在神經分化的過程中扮演了關鍵的角色。

Activation of aryl hydrocarbon receptor (AHR) by xenobiotic toxic chemicals such as 2,3,7,8-tetrachlorodibenzo-p-dioxin regulates a variety of cellular processes, for example, embryogenesis, tumorigenesis and inflammation. However, the identity of endogenous ligands activating AHR remains unclear. To explore the possibilities, previously developed cell free bioassay for dioxin-like compounds in our laboratory was applied and Tetrahydrocorticosterone (THB) was identified from zebrafish embryos as a potential AHR ligand. In this study, we aim to investigate the functions of THB in AHR activation and further physiological effects. In vitro studies revealed that THB induces AHR translocation into nucleus and activates the expression of downstream cytochrome P450 1A1 (CYP1A1). THB also demonstrated potential to promote neuronal differentiation in neuroblastoma (NB) cells, which corresponds to our previous studies that AHR overexpression lead to NB cells differentiation. On the other hand, In vivo studies indicated that THB treatment enhances AHR-target zCYP1A, myelin-associated myelin basic protein (zMBP) and oligodendrocyte transcription factor 2 (zOLIG2) expression via AHR2-dependent pathway in zebrafish. Moreover, we found that THB is involved in early neurogenesis and neuronal differentiation of oligodendrocyte, astrocyte and microglia via AHR2 pathway. Therefore, our results strongly suggest that THB is an endogenous AHR ligand, and plays a critical role during neuronal differentiation.