| 摘要: | Obestatin是23個胺基酸胜肽類的荷爾蒙，一種新型的能量調節荷爾蒙，其真正的功能還不清楚。Obestatin可促進或抑制胰島素的分泌，其對於胰島素的分泌及血糖的調控並不清楚。
AMP-activated protein kinase (AMPK)為一種能量感應器，是調節細胞代謝的指標，改變AMPK的活性，對於胰島素分泌，飽和脂肪酸的攝入及高胰島素血症有調節作用。在脂肪形成的過程中，acetyl-CoA carboxylase (ACC)蛋白參與其中反應，並且ACC蛋白為AMPK蛋白的下游，因此AMPK蛋白磷酸化與ACC蛋白具有密切的關係。
本研究中，我們主要探討obestatin對於INS-1細胞株在葡萄糖培養液下經由AMPK蛋白、p-ACC蛋白的表現和胰島素分泌(GSIS)的調控作用。以及INS-1細胞株在棕櫚酸(palmitate)的作用之下，研究obestatin對於誘導p-AMPK、p-ACC蛋白的表現和胰島素分泌的影響。INS-1 細胞株培養在不同濃度的葡萄糖溶液中，分別有加與沒加obestatin於短時間(60分鐘)及長時間(48 小時)的作用。當高濃度葡萄糖(28 mM)培養液短時間作用下會誘導p-AMPK的抑制作用及促進胰島素分泌。然而加入10-6 M obestatin則可增加p-AMPK、p-ACC蛋白的表現和抑制胰島素的分泌(約由1.2 0.06 μg/L下降至0.8 0.06 μg/L)。長時間(48 小時)暴露在高濃度(28 mM)葡萄糖培養液之下會抑制p-AMPK、p-ACC蛋白的表現。 Obestatin則有顯著意義增加INS細胞株的p-AMPK、p-ACC蛋白的表現和增加胰島素分泌(當葡萄糖濃度為28 mM時，胰島素的濃度約由0.3 0.01 μg/L上升至0.4 0.03 μg/L)。另一方面長時間暴露在0.2 mM棕櫚酸(palmitate)中則會抑制p-AMPK、p-ACC蛋白的表現及胰島素分泌(約由0.7 0.03 μg/L下降至0.6 0.01 μg/L)，但經由10-6 M obestatin處理後，有意義刺激p-AMPK、p-ACC蛋白的表現及調節胰島素分泌(約由0.6 0.01 μg/L上升至0.7 0.02 μg/L)。
綜合上述結果發現，obestatin對於INS-1 細胞株具有調節胰島素分泌的作用，無論與葡萄糖培養液短時間或長時間作用和葡萄糖長時間培養下(有無棕櫚酸存在時)，都是經由AMPK、ACC此訊息傳遞路徑。
Abstract
Obestatin is a 23 amino acid peptide hormone and a new type of hormonal regulation of energy, whose biological functions are poorly understood. Up to now, all available data have suggested that obestatin may promote or inhibit insulin secretion, but the effects of insulin secretion and glucose regulation is not clear.
AMP-activated protein kinase (AMPK), which serves as a metabolic master switch in response to alterations in cellular energy charge, changes in AMPK activity contribute to the regulation of insulin secretion, saturation fatty acid intake and hyperinsulinemia. In the process of fat formation, acetyl-CoA carboxylase (ACC) protein involves reactions, and ACC is the downstream of AMPK. Therefore, phosphorylated AMPK (p-AMPK) and ACC proteins are a close relationship.
In the present study, we aimed to investigate the effect of obestatin on AMPK activity, p-ACC expression and glucose-stimulated insulin secretion (GSIS) in INS-1 cells, as well as p-AMPK, p-ACC and GSIS in INS-1 cells treated with palmitate. INS-1 cells were couture in the different concentrations of glucose then which were treated acutely (60 min) or chronically (48 h) with and without obestatin. The acute effects of glucose included p-AMPK inhibition and augmentation in insulin secretion. Obestatin increased p-AMPK, p-ACC expression and regulated GSIS (about 1.2 0.06 μg/L decreased to 0.8 0.06 μg/L) on INS-1 cells. Chronic glucose exposure inhibited the expression of p-AMPK and p-ACC protein levels. Obestatin increased p-AMPK, p-ACC expression and regulated GSIS (when the glucose concentration of 28 mM and the concentration of insulin from about 0.3 0.01 μg/L increased to 0.4 0.03 μg/L) on INS-1 cells. Chronic palmitate exposure inhibited the expression of p-AMPK and p-ACC protein levels. And obestatin stimulated p-AMPK and p-ACC expression, which induced insulin release (about 0.6 0.01 μg/L increased to 0.7 0.02 μg/L). On the other hand, we examined the effects of obestatin on secretion of insulin, signal transduction whether the maintenance role, then in the regulation of lipotoxicity achieve the integrity of β-cell.
Our findings suggest that obestatin may regulate insulin secretion in INS-1 cells on acute and chronic glucose exposure through AMPK and ACC signaling. |
