基質金屬蛋白酶9（MMP 9）在酒精誘發脂肪肝過程中所扮演之角色

The Role of Matrix Metalloproteinase 9 (MMP9) in Development of Alcoholic Fatty Liver

廖珮瑄(Pei-Hsuan Liao)

指導教授 ： 邱智賢

共同指導教授 ： 陳億乘(Yi-Chen Chen)

國立臺灣大學/生物資源暨農學院/動物科學技術學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.02806

摘要

由於基質金屬蛋白酶9（MMP 9）主要調節胞外基質的重組，因而在酒精性肝病發展中扮演重要的角色。近年來的研究卻發現，MMP 9蛋白質本身也具有非酵素的功能。因此，本篇將探討pro-MMP 9是否調控酒精性脂肪肝病（alcoholic fatty liver disease，AFLD）的發展。
本試驗將使用六個月大的B6.FVB(Cg)-Mmp9tm1Tvu/J（KO）及野生型（WT）公鼠進行以下的試驗。由MMP 9的基因型、基因表現、蛋白質表現及活性發現，KO小鼠中的MMP 9會因為缺乏第二內插子，而導致蛋白質失去活性。若以含酒精的Lieber-DeCarli液態飼糧餵食KO小鼠，在肝臟中所誘導的脂質堆積及TG含量皆會明顯高於WT小鼠。推測pro-MMP 9具有調控AFLD發展及脂質代謝的功能。
透過即時聚合酶鏈鎖反應的分析，KO小鼠中Srebp-1的基因表現會明顯高於WT小鼠，推測pro-MMP 9會透過促進Srebp1的表現，增加肝臟內的脂質生合成。然而，KO小鼠中調控脂質運輸（Mttp、Fabp1與Lrp）及beta-氧化作用（Ppar alpha、Acox-1與Cpt-1a）的基因，其表現皆有明顯被抑制的現象；此外，促進發炎反應相關的基因（Tlr 4、Tnf alpha、Il-6及Mcp-1）在KO小鼠肝臟中雖然有明顯的上升，但由於肝切片的結果並沒有免疫細胞湧入，因此推測這些基因有可能是調控發炎以外的作用如脂質堆積。
綜上所述，MMP 9具有酵素及非酵素的功能，而此二種功能皆在AFLD發展中扮演重要的角色。不具活性的MMP 9在長期攝取酒精的情況下，會使脂質累積在肝臟中，其機制可能為增加pro-MMP 9蛋白質表現，並與LDL receptor- related protein （LRP）結合，啟動下游的訊息傳遞如促進SREBP1蛋白質表現、抑制beta-氧化作用及減少脂質運輸蛋白，最後使脂質堆積在肝臟中；此外，促進發炎反應的物質也有可能造成肝臟中脂質的累積。由以上的結果推測，MMP 9有可能透過調控脂質堆積，而促進AFLD發展，然而其詳細機制仍需更進一步的研究再證實。

關鍵字

酒精性脂肪肝 ； 基質金屬蛋白酶9

並列摘要

Matrix metalloproteinase 9 (MMP 9) was thought to play the central role in ethanol-induced fibrogenesis by regulating ECM remodeling. However, its non-enzymatic functions were also highlighted in recent studies. In this study, we aimed to investigate whether pro-MMP 9 also contributes to alcoholic fatty liver disease (AFLD) development by regulating lipid metabolism.
B6.FVB(Cg)-Mmp9tm1Tvu/J (KO) and wild type (WT) C57BL/6 male mice (six-month-old) were used. The results of genotype, mRNA, protein expression and enzyme activity in KO mice show that partial deletion of Mmp 9 exon 2 does not affect the protein expression but enzymatic functions. After fed with Lieber-DeCarli liquid control or ethanol diet for 4 weeks, KO mice developed hepatic steatosis induced by ethanol which is consistent with the hepatic triglyceride (TG) content. These data confirmed the regulatory function of pro-MMP 9 in lipid metabolism.
By real-time PCR analyses, the level of Srebp1, lipogenesis-related gene, were significantly increased in KO mice compared to WT mice. This suggests that pro-MMP 9 may increase hepatic steatosis via up-regulating Srebp1 expression. In addition, the gene expression of transport protein including Mttp, Fabp1 and Lrp were down-regulated in KO mice which may lead to decreased fatty acid and intermediate density lipoprotein uptake from circulation under ethanol consumption. Also, beta- oxidation related genes including Ppar alpha, Cpt1a and Acox1 were lower in KO mice. More interestingly, the inflammatory related genes such as Tlr4, Tnf alpha, Il-6, Mcp-1, and Tgf beta were up-regulated in ethanol-fed KO mice; no obvious immune cell infiltration was observed suggesting that these cytokines may provide other non-immune regulatory functions such as lipid metabolism.
In summary, our results demonstrated both the enzymatic and non-enzymatic MMP9 functions play important roles in AFLD development. Lacking of MMP9 enzymatic functions increased hepatic steatosis under chronic ethanol consumption, and this result may be caused by increasing levels of pro-MMP 9. Increased pro-MMP 9 may act as a ligand to activate LRP downstream targets including SREBP1 and down-regulate beta-oxidation and lipid transport to promote lipid accumulation in liver. Also, we consider the increased inflammatory cytokine may also contribute to hepatic steatosis by unknown pathways. Our current results suggest the potential of MMP 9 to be the target for AFLD therapy. However, detailed mechanisms of pro-MMP 9 mediated lipid metabolism regulations in AFLD progression need further studies to be clarified.

並列關鍵字

alcoholic fatty liver ； MMP 9

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