Comprehensive Expression Analysis of mRNA and microRNA for Investigation of Compensatory Mechanisms in the Rat Kidney after Unilateral Nephrectomy (Male_miRNA)

Compensation is a physiological response that occurs during chemical exposure to maintain homeostasis. Because compensatory responses are not usually considered adverse effects, it is important to understand compensatory mechanisms for chemical risk assessment. Although the kidney is a major target organ for toxicity, there is controversy over whether hyperplasia or hypertrophy contributes to the compensatory mechanism, and there is limited information to apply for chemical risk assessment. In the current study, compensatory mechanisms of the kidney were investigated in a unilateral nephrectomy (UNx) model using adult male and female rats. In residual kidneys of male and female rats after UNx, 5-bromo-2'-deoxyuridine-labeling indices and mRNA expression of cell cycle-related genes were increased, although there were no fluctuations in mRNA expression of transforming growth factor-β1, which contributes to hypertrophy in renal tubules. Pathway analysis using mRNA expression data from a cDNA microarray revealed that canonical pathways related to cell proliferation were mainly activated and that forkhead box M1 (FOXM1) was an upstream regulator of compensatory cell proliferation in residual kidneys of male and female rats. cDNA microarray for microRNAs (miRNAs) demonstrated that 9 miRNAs were downregulated in residual kidneys, and mRNA/miRNA integrated analysis indicated that miRNAs were associated with the expression of factors downstream of FOXM1. Overall, these results suggested that FOXM1-mediated hyperplasia rather than hypertrophy contributed to compensatory mechanisms in the kidney and that miRNAs regulated downstream FOXM1 signaling. These results will be beneficial for evaluating nephrotoxicity in chemical risk assessment and for developing new biomarkers to predict nephrotoxicity.代偿是化学暴露期间为维持机体内稳态而发生的生理反应。由于代偿反应通常不被视为不良效应，因此明晰化学风险评估中的代偿机制具有重要意义。肾脏是毒性作用的主要靶器官之一，但关于细胞增生（hyperplasia）或肥大（hypertrophy）是否参与代偿机制仍存在争议，且可用于化学风险评估的相关研究数据较为有限。本研究采用成年雌雄大鼠构建单侧肾切除术（unilateral nephrectomy, UNx）模型，对肾脏的代偿机制展开系统性探究。结果显示，在UNx术后雌雄大鼠的残留肾脏中，5-溴-2'-脱氧尿苷（5-bromo-2'-deoxyuridine）标记指数及细胞周期相关基因的mRNA表达水平均显著升高；而对肾小管肥大具有调控作用的转化生长因子-β1（transforming growth factor-β1）的mRNA表达未出现明显波动。通过cDNA微阵列的mRNA表达数据进行通路富集分析发现，与细胞增殖相关的经典通路主要被激活，且叉头框蛋白M1（forkhead box M1, FOXM1）是雌雄大鼠残留肾脏中代偿性细胞增殖的核心上游调控因子。针对微小RNA（microRNAs, miRNAs）的cDNA微阵列检测表明，残留肾脏中有9种miRNAs表达显著下调；mRNA与miRNA整合分析显示，这些差异表达的miRNAs与FOXM1下游靶因子的表达水平密切相关。综上，本研究结果提示，肾脏代偿机制依赖FOXM1介导的细胞增生而非肥大，且miRNAs可通过调控FOXM1下游信号通路参与肾脏代偿过程。上述研究成果可为化学风险评估中的肾毒性评价以及预测肾毒性的新型生物标志物开发提供重要理论参考与数据支持。