利用转基因和条件基因敲除小鼠研究多不饱和脂肪酸影响大肠癌发生及其机制

The decreased proportion of dietary n-3/n-6 polyunsatuated fatty acids(PUFAs) is a major cause of obesity and and colorectal tumorigenesis. However, the underlying molecular mechanisms are not clearn. Our prelimiary data demonstrated that n-6 PUFAs strongly activated mammalian target of rapamycin (mTOR) signaling while n-3 PUFAs inhibited mTOR in colorectal cancer cells. Importantly, reduced mTOR activity, plasma lipids level and colorectal tumorigenesis were observed in fat-1 (desaturase that converts n-6 to n-3 PUFAs endogenously) transgenic APCmin/+ mice compared with littermate controls. These results implicate that n-3/n-6 PUFAs may regulate colorectal tumorigenesis through mTOR signaling and plasma lipids. Using large intestine-specific TSC1 and Raptor knockout mice (mTOR is specifically activated or inhibited in colorectal epithelial cells), fat-1 transgenic SCID and fat-1 transgenic APCmin/+ mice and colorectal cancer cells as models, this project aims to investigate the role and mechanisms of mTOR signaling and plasma lipids in regulation of colorectal tumorigenesis by n-3/n-6 PUFAs. This study will provide novel mechanisms for potentiation of colorectal tumorigenesis by dietary factors, and provide evidence for prevention and treatment of colorectal cancer by dietary n-3 PUFAs.

N-3/n-6多不饱和脂肪酸（PUFAs）在膳食中的比例减少是引起肥胖和大肠癌发生的重要原因，但PUFAs影响这一过程的机制尚未阐明。课题组前期研究中发现n-6或n-3 PUFAs可分别激活或抑制大肠癌细胞哺乳动物雷帕霉素靶蛋白（mTOR）信号通路，fat-1(使n-6转化为n-3 PUFAs的酶)转基因可明显抑制APCmin/+小鼠mTORC1活性、降低血脂并减少大肠癌发生，提示n-3或n-6 PUFAs可通过调节mTOR通路与血脂水平抑制或促进大肠癌发生。本项目拟通过大肠上皮特异敲除TSC1、Raptor小鼠(使mTORC1过度激活或抑制)、fat-1转基因APCmin/+与fat-1-SCID小鼠与细胞模型，探讨mTORC1与血脂在介导PUFA影响大肠癌发生中的作用与机制，为n-3PUFAs抑制大肠癌的机制提出新观点，为饮食中增加n-3 PUFAs防治大肠癌提供依据。

N-3/n-6多不饱和脂肪酸（PUFAs）在膳食中的比例减少是引起肥胖和大肠癌发生的重要原因，但PUFAs影响这一过程的机制尚未阐明。课题组前期研究中发现n-6或n-3 PUFAs可分别激活或抑制大肠癌细胞哺乳动物雷帕霉素靶蛋白（mTOR）信号通路，fat-1(使n-6转化为n-3 PUFAs的酶)转基因可明显抑制APCmin/+小鼠mTORC1活性、降低血脂并减少大肠癌发生，提示n-3或n-6 PUFAs可通过调节mTOR通路与血脂水平抑制或促进大肠癌发生。本项目通过fat-1-APCmin/+(内源性转化n-6 PUFAs为n-3 PUFAs的肠癌小鼠),大肠上皮特异敲除TSC1、Raptor小鼠(使mTORC1过度激活或抑制)与细胞模型，探讨了PUFAs通过mTORC1抑制溃疡性结肠炎和结肠癌的作用和机制。 .本研究发现，fat-1- APCMin/+双转基因小鼠相对于APCMin/+小鼠结肠癌发生率显著降低，贫血症状明显缓解。此外，无论在APC突变的结肠癌细胞系及敲低APC的正常肠上皮细胞系中，内源性和外源性的n-3 PUFAs均可通过显著抑制mTORC1的活性从而抑制细胞的增殖并促进其凋亡。fat-1- APCMin/+双转基因小鼠相对于APCMin/+小鼠血脂水平更低，而体外实验也证实n-3 PUFAs可抑制脂肪前体细胞中的mTORC1活性并抑制其成脂分化。本研究还发现，结肠上皮细胞特异性的mTORC1活性可通过环氧合酶2(COX-2)促进IL-1、IL-6和IL-23等炎症因子的表达，从而加剧溃疡性结肠炎。反之，n-3 PUFAs则可抑制结肠上皮细胞中的mTORC1活性并缓解溃疡性结肠炎。本研究为在饮食中增加n-3 PUFAs防治溃疡性结肠炎及大肠癌提供了理论依据。