- 學位論文
脂締素訊息傳導對葡萄糖和脂質代謝及骨質生成探討
Modulation of glucose and lipid metabolism, and osteogenesis by adiponectin signaling
摘要
脂肪組織除做為多餘能量的儲存場所外，亦可分泌多種脂肪細胞激素調節體內能量恆定及發炎反應等生理現象。脂締素為一與葡萄糖代謝及脂質代謝高度相關之脂肪細胞激素，其功能透過脂締素一型受體 (AdipoR1) 和脂締素二型受體 (AdipoR2) 媒介。本研究以全身型過度表現豬脂締素一型受體之小鼠為動物模式，在高脂及高蔗糖飼糧誘導的肥胖小鼠模式中發現過度表現脂締素一型受體能夠抑制胰島素不敏感、肥胖及脂肪肝現象；我們進一步地建立骨髓間葉幹細胞分離系統，並利用此轉基因小鼠的骨髓間葉幹細胞做為改善高脂高糖飼料引起的胰島素阻抗、葡萄糖耐受性及脂肪肝的治療策略，結果顯示過度表現脂締素一型受體之骨髓間葉幹細胞，確實可做為代謝性症候群的治療途徑。此外，代謝性症候群及老化所伴隨的骨質疏鬆症及骨質代謝性疾病也是近年研究所關注的議題，脂締素及其受體亦表現在骨髓、骨組織及成骨細胞中，而脂締素訊息在骨骼代謝及成骨細胞分化上扮演的角色尚未釐清，本論文以過度表現脂締素一型受體之小鼠為動物模式，發現過度表現脂締素一型受體可增加小鼠的骨密度、骨小樑容積及骨小樑數目，酵素結合免疫吸附法結果顯示過度表脂締素一型受體可增加 osteocalcin 及 osteoprotegrin 在血漿中濃度並減少蝕骨作用激素TRAP5b在血漿中的濃度。體外試驗結果顯示，利用慢病毒感染方法降低脂締素一型受體表現後，會減少骨髓間葉幹細胞及 MC3T3-E1 細胞在成骨細胞分化過程中osteocalcin, osteoprotegrin, alkaline phosphatase 及 msh homeobox 2 基因表現並降低礦化作用的生成。 除此之外，細胞訊息傳導路徑分析及即時定量PCR分析顯示脂締素一型受體可能透過 GSK-3 β 及 β-Catenin 訊息傳導路徑影響骨骼發育及成骨細胞的分化。綜合上述試驗結果顯示，脂締素一型受體在成骨細胞分化及骨骼形成過程中扮演重要角色，並具有潛力成為治療骨質疏鬆症或代謝性相關之骨生成疾病的治療方針。
並列摘要
Adiponectin and its receptors have been demonstrated to play important roles in regulating glucose and lipid metabolism in mice. Obesity, type II diabetes and cardiovascular diseases are tightly correlated with down-regulation of adiponectin signaling. Our AdipoR1 transgenic mice with fluorescent proteins serve as a great model to investigate the involvement of adiponectin signaling in the biological processes. Mice overexpressing porcine adiponectin receptor 1 (pAdipoR1) fed with high fat/high sucrose diet for 24 weeks, exhibited no change in weight gain and demonstrated amelioration of insulin resistance. In this current study, we isolated the mesenchymal stem cells from wild-type (WT-MSC) and adiponectin receptor 1-transgenic mice (pR1-tMSC) and transplanted the cells into the diet-induced obese (DIO) mice, which exhibited diabetic and insulin insensitive. After once-a-week cell transplantation for 8 weeks, WT-MSC and pR1-tMSC treatments improved fatty acid oxidation and alleviate lipid accumulation in the liver, with pR1-tMSC further enhancing glucose metabolism in DIO mice. Our current study, for the first time, demonstrated therapeutic application of pR1-tMSC to improve diet-induced metabolic complications. Metabolic syndrome and aging - associated osteoporosis and metabolic bone diseases is also an active field in recent years. Adiponectin and its receptors are expressed in bone marrow-derived osteoblasts. We used pAdipoR1 transgenic mice as a model to evaluate the role of AdipoR1 on bone physiology at different ages. pAdipoR1 transgenic mice had higher bone mineral density than wild-type mice in both genders at 56 weeks of age. The bone volume and trabecular number, measured by micro-computed tomography (μCT) were significantly greater in transgenic mice than those of wild-type female mice at both 8 and 56 weeks of age. ELISA analysis revealed that both serum osteocalcin and osteoprotegerin (OPG) were significantly increased in 8-week old pAdipoR1 transgenic mice of both genders. Furthermore, serum OPG was elevated at 32 and 56 weeks of age pAdipoR1 transgenic mice of both sex. Serum TRAP5b concentration was reduced in 8 and 56 weeks old male pAdipoR1 mice compared with wild-type male mice. Knock-down of AdipoR1 significantly decreased gene expression of osteocalcin, OPG, alkaline phosphatase and msh homeobox 2 and suppressed the mineralization in MC3T3-E1 cells and mesenchymal stem cells. In addition, pathscan analysis, and real-time PCR analysis suggested AdipoR1 regulates osteoblast differentiation through GSK-3 β and β-Catenin signaling. Consequently, the lack of AdipoR1 impaired osteoblast differentiation and bone formation. We concluded that AdipoR1 is a critical factor for the osteoblast differentiation and bone homeostasis.
參考文獻
延伸閱讀
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