Hexosamine Biosynthetic Pathway 對於脂肪細胞分化過程中所扮演的角色

The role of Hexosamine Biosynthetic Pathway in Adipocyte Differentiation

林芷(Tzu Lin)

指導教授 ： 謝翠娟

高雄醫學大學/醫學院/醫學遺傳學研究所/碩士(2008年)

https://doi.org/10.6832/KMU.2008.00131

摘要

WHO指出肥胖已經成為全球危害健康最大的挑戰，而全球肥胖人口仍在持續上升，肥胖所帶來的併發症包括新陳代謝症候群、呼吸功能障礙、癌症及阿茲海默症等。肥胖是由脂肪細胞的增加和增大所造成，脂肪細胞所分泌的細胞激素，也是引起肥胖併發症的主要因素之一。研究指出O-GlcNAcylation (O-linked N-acetylglucosamine)醣基化修飾能夠調節細胞週期、基因表現、蛋白質活性及訊號傳遞路徑，O-GlcNacylation的上游路徑為Hexosamine biosynthetic pathway (HBP)，HBP的速率決定酵素為GFAT-1 (glucosamine : fructose-6-phosphate amidotransferase 1 )，當細胞受到高糖或氧化壓力的刺激，會活化HBP而增加蛋白質O-GlcNacylation修飾，脂肪組織中過量表現GFAT-1酵素的小鼠，會產生嚴重的葡萄糖不耐性，以及過重的現象；O-GlcNAclytion在脂肪細胞中，藉由抑制胰島素傳遞路徑分子，而造成胰島素抗性，顯示HBP和蛋白質O-GlcNAc修飾在肥胖形成的過程中可能扮演者重要的病理角色。然而對於HBP以及蛋白質O-GlcNAc修飾是否及如何參與脂肪細胞分化過程，則還沒有深入的研究報告。
因此本論文想要探討HBP以及蛋白質O-GlcNAc修飾是否能參與並調控脂肪細胞分化過程、早期分化基因表現以及脂肪細胞激素的分泌。實驗結果顯示，脂肪細胞分化的過程中，蛋白質O-GlcNAcylation的程度大為提高，並隨著時間而增加；分化過程中早期基因SREBP-1c, PPAR-γ, C/EBP-α, C/EBP-β, 和C/EBP-δ表現增加；以及在3T3-L1細胞分化為成熟脂肪細胞時期，會大量表現adiponectin, visfatin, apelin, retinol-binding protein-4 和 angiotensinogen mRNAs。利用GFAT-1的抑制劑AZA或DON，可以降低HBP的活性，減少蛋白質O-GlcNAcylation，並且抑制3T3-L1細胞分化為脂肪細胞，另外可以顯著減少脂肪細胞早期分化過程所需要的基因，以及脂肪細胞激素的表現。
本研究證實HBP的活化和蛋白質O-GlcNAc修飾程度的提高在脂肪細胞早期分化過程中扮演很重要的角色。脂肪細胞分化的過程需要HBP的活化使下游蛋白質O-GlcNAc修飾增加，影響早期分化過程基因表現，並且調控脂肪細胞激素的分泌。

關鍵字

肥胖 ； 脂肪細胞分化 ； 分化 ； 脂肪細胞激素 ； 脂泌素 ； 新陳代謝症候群 ； 胰島素抗組性 ； 脂肪 ； 醣基化 ； 糖基化 ； 己糖胺 ； 胺基己糖

並列摘要

Obesity is a rapidly growing global threat against public health. The World Health Organisation (WHO) has defined obesity as a condition with excessive fat accumulation in the body. Increasing adipose tissue relates in adipokines secretion and involves in development of metabolic complications. However, regulation of adipocyte differentiation and adipokines secretion still need further clarified. O-linked N acetyl-glucosamine (O-GlcNAc) modification has been implicated in regulation of signaling pathway, cell function, cell cycle and gene expression in several cell types. Hexosamine biosynthetic pathway (HBP) generates the sugar nucleotide UDP-GlcNAc, which is the donor for O-GlcNAc modification of nucleocytoplasmic proteins. When the GFAT-1 (rate limiting enzyme of HBP) was overexpressed in mice, the mice developed fat cell hypertrophy and excess weight. The aim of this study is to investigate the pathophysiological role of HBP and protein O-GlcNAc modification on adipocyte by observing the expression of genes involving in early stage of differentiation and adipokines affecting late stage complications.
Our results demonstrate that the O-GlcNAc modified proteins are increased in the process of 3T3-L1 preadipocyte differentiation since very early stage after induction. Genes involve in early stage of differentiation such as SREBP-1c, PPAR-γ, C/EBP-α, C/EBP-β, and C/EBP-δ are upregulated. Adiponectin, visfatin, apelin, retinol-binding protein-4 and angiotensinogen mRNAs are increased in mature adipocytes. However, blocking HBP by AZA or DON can decrease the end product of HBP—O-GlcNAc modification and prevents the differentiation of 3T3-L1 cells. Decreasing HBP activity also diminishes gene expressions which are necessary for adipocyte differentiation in early stage and prevents mRNA overexpression of above adipokines. The results suggest that HBP activation and change of protein O-GlcNAc modification maybe a novel pathway mediating differentiation and adipokine expression in adipocytes.

並列關鍵字

obesity ； adipocyte differentiation ； adipokines ； adipocytokine ； adipose ； diabetes ； WAT ； DM ； Insulin resistance ； metabolic syndrome ； 3T3-L1 ； 3T3 ； hexosamine ； O-GlcNAcylation ； GlcNAc ； O-GlcNAc ； GFAT ； HBP ； PPAR ； C/EBP ； SREBP

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