内脏脂肪组织来源外泌体促进结肠上皮细胞增殖及其在肥胖相关结肠癌演变中的作用

Previous studies have indicated that obesity is one of the leading risk factors for colorectal cancer, while the underlying mechanisms remain largely unknown. The applicants have reported that the aberrant expression　and function of RNA binding protein QKI due to external or internal cues are the key mechanisms for dysregulated cell proliferation and differentiation, and thus tumorigenesis in colon (Gastroenterology). Our ongoing work further revealed that the exosomes from the abdominal tissue changed significantly in quantity and components under obesity, especially the expression of lncRNA Hotair. Moreover, these altered exosomes obviously promote colon epithelium proliferation. In view of the fact that Hotair harbors the QKI response elements, we hypothesize that the altered exosomes derived from abdominal adipose tissue under obesity could circulate and endocytosed by the intestinal tissues, resulting in the release of the pro-proliferating molecule Hotair, which in turn inhibits the function of QKI and increases risk of colon cancer. In light of these data, we will first explore the mechanism how exosomes go awry, focusing on the possible involvement of inflammation in exosome secretion and component selective encapsulation of Hotair. Next, we will confirm the pro-proliferation effects of the exosmal Hotair and possible involvement of QKI, by combinatory use of gene knockout mice and engineering the exosomes. Finally, we will confirm the role of visceral fat derived exosomes in promoting colon cancer by analysis of both APCmin mice and clinical samples. The proposed project holds promise to unravel a novel mechanism how obesity increases the colon cancer risk, and thus shedding light on its prevention.

研究表明肥胖是结肠癌独立危险因素，但具体机制不清。申请者前期发现RNA结合蛋白QKI功能异常是结肠癌演变的重要机制（Gastroenterology等）。后续研究又发现肥胖小鼠肠上皮细胞增殖增加，QKI功能降低；与此同时，内脏脂肪外泌体中lncRNA Hotair增加，后者随外泌体进入肠上皮并促进细胞增殖。鉴于Hotair含有能与QKI相互作用的顺式元件，我们推测肥胖条件下内脏脂肪外泌体经循环进入肠道上皮细胞后，内含的Hotair以ceRNA（内源竞争性RNA）方式阻断QKI功能，进而促进肠上皮增殖，增加罹患结肠癌风险。本项目拟在明确肥胖条件下内脏脂肪外泌体Hotair表达变化机制的基础上，探讨肥胖条件下内脏脂肪通过外泌体中Hotair调控结肠上皮（干）细胞命运的具体作用和机制，最后结合APCmin小鼠和临床样本探讨该外泌体途径增加结肠癌风险的可能性，期望发现肥胖增加结肠癌风险的新机制。

流行病学研究发现肥胖是结肠癌的独立危险因素，探讨肥胖增加结肠癌风险的具体机制，有望为肥胖相关结肠癌的防治。本研究旨在阐明肥胖条件下内脏脂肪组织源外泌体被肠道组织细胞内吞的机制；明确上述外泌体调控结肠癌恶性演变中的具体机制；建立肥胖与结肠癌演变之间的分子联系，为结肠癌的防治提供新的思路和可能靶点。主要取得了以下几方面的结果：1）系统分析了内脏脂肪外泌体进入循环后，在小鼠体内不同脏器的分布情况，发现内脏脂肪外泌体在肝中分布最多，脾脏次之，此外在结肠、肺以及心脏中也有明显的分布；2）发现肥胖小鼠内脏脂肪外泌体能够加剧DSS诱导的小鼠急性结肠炎，证实高脂饮食小鼠内脏脂肪来源的外泌体通过促进结肠组织巨噬细胞M1极化，加重结肠炎；3）证明脂肪组织来源的miR-155是肥胖增加肠炎严重程度的关键分子； 4）确立肥胖条件下脂肪组织巨噬细胞是外泌体miR-155的重要来源；5）通过 HFD-VAT-Exo装载miR-155 拮抗剂显著改善DSS诱导的小鼠结肠炎表型；6）探讨了肿瘤来源外泌体对脂肪组织等的影响，发现肿瘤细胞外泌体携带的miR-320进入骨髓间充质细胞后，通过靶向β-catenin，抑制其成骨分化能力，与此类似，肿瘤细胞来源的miR-92能够显著抑制成脂分化相关的基因表达，进而抑制脂肪细胞生成；7）创建了一系列外泌体改构策略，为更好装载核酸药物和靶向递送提供了新策略。我们基于天然外泌体合成和cargo装载的机制，创建了基于RNA结合蛋白-RNA相互作用等外泌体核酸药物装载策略。上述研究相关成果发表于Nano Letters、ACS Nano等权威期刊。