第二型糖尿病為一常見的代謝異常疾病，異常的高血糖為主要的特徵之ㄧ，目前尚不十分清楚其詳細的致病機轉。研究發現免疫作用及發炎反應對於第二型糖尿病病程之發展扮演了重要角色。許多文獻也指出肝臟的糖質新生作用除了維持空腹時血糖的恆定之外，也是造成糖尿病患者異常高血糖的原因之ㄧ。糖質新生作用主要是受肝臟中phoenolpyruvate carboxykinase (PEPCK)及glucose-6-phosphatase (G-6-Pase)這兩個酵素的調控，而PEPCK及G-6-Pase的表現也會受到一些因子的調控，包括胰島素(insulin)會抑制這些酵素的表現；而昇糖素(glucagon)及糖皮質素(glucocorticoids)則會刺激PEPCK及G-6-Pase的表現。其中，胰島素透過調控PEPCK及G-6-Pase的轉錄活化因子peroxisome proliferator- activated receptor γ coactivator-1α (PGC-1α)進而抑制糖質新生酵素的表現。先前的文獻中指出介白質素-6 (interlukin-6, IL-6)等TH2的細胞激素與糖尿病病程之發展有關，本實驗室先前的研究中發現，第二型糖尿病病患比起未罹患糖尿病之患者通常帶有介白質素-4 (interlukin-4, IL-4)分泌能力較強的基因多型性(gene polymorphism)，而且在動物實驗中發現IL-4分泌量較高的母鼠產生第二型糖尿病的病程進展較快速，病情也較嚴重。因此本篇論文研究重點在於探討IL-4是否會調控肝臟糖質新生酵素的表現，進而影響第二型糖尿病的發病或病程的發展。HepG2細胞在正常葡萄糖濃度中，糖質新生酵素PEPCK及G-6Pase mRNA的表現會隨著IL-4的濃度越高及刺激的時間越長而有增加的趨勢，而且胰島素可抑制由IL-4所刺激之糖質新生酵素PPEPCK及G-6Pase mRNA的表現。此外，為了模擬糖尿患病體內的高血糖環境，本論文也探討高濃度葡萄糖環境中IL-4對糖質新生酵素的影響，結果顯示高濃度葡萄糖環境可加強IL-4所刺激PEPCK及G-6-Pase的基因表現，但高濃度胰島素(acute insulin, AI)之抑制情形會因而減弱。由上述結果推測，在正常葡萄糖濃度環境中，IL-4可能會參與糖尿病致病機轉， IL-4會促進糖質新生酵素的表現，進一步發展成異常高血糖。另外，在糖尿病患體內，分泌發炎激素IL-4的能力增加，IL-4又會受到高血糖環境的影響，更促進了糖質新生酵素的表現，如此惡性循環使病程發展更為嚴重。IL-4可能在糖尿病致病機轉及糖尿病病患之病程發展扮演一重要角色。
Type 2 diabetes mellitus (T2DM) is a metabolic disorder characterized by abnormal hyperglycemia with unknown etiology. Immune response and inflammation are suggested to play important roles in the development of T2DM. Hepatic gluconeogenesis is essential for maintaining blood glucose levels during fasting and is the major contributor to postprandial and fasting hyperglycemia in diabetes. Gluconeogenesis is controlled by the activities of two gluconeogenic key enzymes in the liver, designated phoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G-6-Pase). Both PEPCK and G-6-Pase expression are regulated at the level of transcription, inhibited by insulin, and stimulated by glucagon and glucocorticoids. Specifically, insulin blocks the recruitment of the transcriptional coactivator PGC-1α to the promoter of the PEPCK and G-6-Pase. Previous reports suggested that TH2 cytokines such as interlukin-6 (IL-6) were involved in diabetes development. Our previous studies suggested that individuals carrying genotypes of high interleukin-4 (IL-4) , another TH2 cytokine, secreting ability and thus having higher IL-4 levels were susceptible to diabetic development. We therefore aimed to determine the effect of IL-4 on the expression of hepatic gluconeogenic enzymes by using HepG2 cell. Our results showed that IL-4 treatment can induce PEPCK and G-6-Pase mRNA expression in dose- and time- dependent manners. However, the IL-4-induced PEPCK and G-6-Pase mRNA expression would be quenched by insulin. Our results suggested that IL-4 may be involved in the upregulation of hepatic gluconeogenesis in insulin-resistant state. T2DM is a metabolic disorder characterized by abnormally hyperglycemia. We therefore aimed to determine the effect of IL-4 in the high glucose concentration on the expression of hepatic gluconeogenic enzymes. Our results showed that mRNA expression of key gluconeogenic enzymes was promoted by high glucose concentration in the presence of IL-4 treatment, and impaired insulin function. Our results suggested that IL-4 may play an important role in progression of T2DM.
