G 蛋白偶合受體 (G Protein Coupled Receptor) 是人體中最大的一群表現在細胞膜上的受體家族，它與配體 (Ligand) 結合後產生的訊息傳遞路徑調控了多種重要的人體生理功能。而目前已經開發的 GPCR 作為標靶藥物的僅佔人體內所有GPCR 家族成員的 5~6%，顯示 GPCR 在新藥研究領域中仍具有非常大的開發潛力。而最近幾年研究中提出GPCR中OGR1 subfamily (TDAG8、OGR1、GPR4、G2A)能雙配對 (Double-pairing)兩種不同的化學物質，分別是質子和lysolipid。其中目前對於T-cell death-associated gene 8 (TDAG8)受體目前是受爭議性的，有人發現在單獨使用氫離子來刺激TDAG8受體時，發在在pH值接近6.2時有發現有最大量環單磷酸腺苷(cAMP)的累積；但也有人發現在透過半乳糖腦苷脂(psychosine)刺激TDAG8受體時，有發現在鈣離子的累積。所以說明氫離子和半乳糖腦苷脂為TDAG8受體的配體。是屬於促進劑(agonist)的角色。但特別的另外也有人發現在含有半乳糖腦苷脂的環境下，氫離子所引發的環單磷酸腺苷的量有受到抑制的情形，推測半乳糖腦苷脂可能為抑制劑(antagonist)的角色。所以在本篇論文主要是探討半乳糖腦苷脂在何種環境下對TDAG8受體，為促進劑或者抑制劑的角色。而在結果部分發現到，透過RNAi方式半乳糖腦苷脂確實能刺激活化TDAG8，但也發現在小鼠神經瘤母細胞上，對於半乳糖腦苷脂和氫離子的刺激，有相互抑制的情形；另外也觀察到對於氫離子的刺激主要是走Gq反應途徑，半乳糖腦苷脂則為Gi。 T-cell death-associated gene 8 (TDAG8) is a member of proton-sensing G-protein coupled receptors, which are sensitive to acid stimulation. TDAG8 can also respond to the lysophospholipid, 1-β-D-Galactosylacyosylsphingosine (Psychosine), an intermediate of cerebrosides biosynthesis. A model was proposed in which the receptors have two ligand-binding sites, one for protons and the other for lipids. The liplids were suggested to interact with both sites, as agonist and antagonist, respectively. The aim of this study is toinvestigate whether psychosine acts on TDAG8 as an agonist and antagonized proton response. We stimulated cells with psychosine in the presence or absence of proton. Cells were stimulated with psychosine in presence or the absence of proton. The results have demonstrated that psychosine in presence or the absence of proton. The results have demonstrated that psychosine can act on TDAG8. Psychosine can inhibit proton-induced [Ca2+] increase in N2A cells, and vice versa.
