The Molecular Effects of a High Fat Diet on Endometrial Tumour Biology

We sought to validate the BDII/Han rat model as a model for diet-induced obesity in endometrial cancer (EC) and determine if transcriptomic changes induced by a high fat diet (HFD) in an EC rat model can be used to identify novel biomarkers in human EC. Nineteen BDII/Han rats were included. Group A (n = 7) were given ad lib access to a normal calorie, normal chow diet (NCD) while Group B (n = 12) were given ad lib access to a calorie rich HFD for 15 months. RNAseq was performed on endometrial tumours from both groups. The top-ranking differentially expressed genes (DEGs) were examined in the human EC using The Cancer Genome Atlas (TCGA) to assess if the BDII/Han rat model is an appropriate model for human obesity-induced carcinogenesis. Weight gain in HFD rats was double the weight gain of NCD rats (50 g vs. 25 g). The incidence of cancer was similar in both groups (4/7-57% vs. 4/12-33%; p = 0.37). All tumours were equivalent to a Stage 1A, Grade 2 human endometrioid carcinoma. A total of 368 DEGs were identified between the tumours in the HFD group compared to the NCD group. We identified two upstream regulators of the DEGs, mir-33 and Brd4, and a pathway analysis identified downstream enrichment of the colorectal cancer metastasis and ovarian cancer metastasis pathways. Top-ranking DEGs included Tex14, A2M, Hmgcs2, Adamts5, Pdk4, Crabp2, Capn12, Npw, Idi1 and Gpt. A2M expression was decreased in HFD tumours. Consistent with these findings, we found a significant negative correlation between A2M mRNA expression levels and BMI in the TCGA cohort (Spearman's Rho = -0.263, p < 0.001). A2M expression was associated with improved overall survival (HR = 0.45, 95% CI 0.23-0.9, p = 0.024). Crabp2 expression was increased in HFD tumours. In human EC, CRABP2 expression was associated with reduced overall survival (HR = 3.554, 95% CI 1.875-6.753, p < 0.001). Diet-induced obesity can alter EC transcriptomic profiles. The BDII/Han rat model is a suitable model of diet-induced obesity in endometrial cancer and can be used to identify clinically relevant biomarkers in human EC.本研究旨在验证BDII/Han大鼠（BDII/Han rat）作为子宫内膜癌（endometrial cancer, EC）饮食诱导肥胖模型的适用性，并探究在该子宫内膜癌大鼠模型中，高脂饮食（high fat diet, HFD）诱导的转录组变化能否用于识别人类子宫内膜癌的新型生物标志物。本研究共纳入19只BDII/Han大鼠。A组（n=7）自由采食正常热量普通饲料饮食（normal chow diet, NCD），B组（n=12）自由采食高热量高脂饮食（high fat diet, HFD），造模周期为15个月。对两组大鼠的子宫内膜肿瘤样本进行RNA测序（RNAseq）。通过癌症基因组图谱（The Cancer Genome Atlas, TCGA）数据库分析人类子宫内膜癌样本，对两组间排名靠前的差异表达基因（differentially expressed genes, DEGs）进行验证，以评估BDII/Han大鼠模型是否适用于人类肥胖相关致癌机制的研究。高脂饮食组大鼠的体重增重为正常饲料组的2倍（50g vs 25g）。两组大鼠的肿瘤发生率无显著差异（4/7，57% vs 4/12，33%；p=0.37）。所有大鼠子宫内膜肿瘤均对应人类子宫内膜样癌1A期2级分型。相较于正常饲料组，高脂饮食组大鼠的子宫内膜肿瘤中共鉴定出368个差异表达基因。本研究鉴定出差异表达基因的两个上游调控因子mir-33与Brd4；通路富集分析显示，差异表达基因下游显著富集结直肠癌转移与卵巢癌转移相关通路。排名靠前的差异表达基因包括Tex14、A2M、Hmgcs2、Adamts5、Pdk4、Crabp2、Capn12、Npw、Idi1及Gpt。高脂饮食组肿瘤中A2M的表达水平显著下调。与上述结果一致，本研究在癌症基因组图谱队列中发现，A2M的mRNA表达水平与体质量指数（body mass index, BMI）呈显著负相关（斯皮尔曼相关系数Spearman's Rho=-0.263，p<0.001）。A2M的高表达与患者总生存期延长显著相关（风险比HR=0.45，95%置信区间CI=0.23-0.9，p=0.024）。高脂饮食组肿瘤中Crabp2的表达水平显著上调。在人类子宫内膜癌样本中，CRABP2的高表达与患者总生存期缩短显著相关（HR=3.554，95%CI=1.875-6.753，p<0.001）。饮食诱导的肥胖可改变子宫内膜癌的转录组特征。BDII/Han大鼠模型可作为子宫内膜癌饮食诱导肥胖的合适模型，且可用于识别与临床相关的人类子宫内膜癌生物标志物。