Global gene expression profiling in early-stage polycystic kidney disease in the Han:SPRD Cy rat identifies a role for RXR signaling

Han:SPRD Cy is a spontaneous rat model of polycystic kidney disease (PKD) caused by a missense mutation in Pkdr1. Cystogenesis in this model is not clearly understood. In the current study, we performed global gene expression profiling in early-stage PKD cyst development in Cy/Cy kidneys and normal (+/+) kidneys, at 3 and 7 days of postnatal age. Expression profiles were determined by microarray analysis, followed by validation with real-time RT-PCR. Genes were selected with over 1.5 fold expression changes compared with age-matched +/+ kidneys for canonical pathway analysis. We found 9 pathways in common between 3-day and 7-day Cy/Cy kidneys. Three significantly changed pathways were designated 'VDR/RXR Activation,' 'LPS/IL-1 Mediated Inhibition of RXR Function,' and 'LXR/RXR Activation'. These results suggest that RXR mediated signaling is significantly altered in developing kidneys with mutated Pkdr1. In gene ontology analysis, the functions of these RXR-related genes were found to be involved in regulating cell proliferation and organ morphogenesis. With real-time RT-PCR analysis, the up-regulation of Ptx2, Alox15b, OSP and PCNA, major markers of cell proliferation associated with the RXR pathway, were confirmed in 3- and 7-day Cy/Cy kidneys compared with 3-day +/+ kidneys. The increased RXR protein was observed both in nuclei and cytoplasm of cystic epithelial cells in early-stage Cy/Cy kidneys, and the RXR-positive cells were strongly positive for PCNA staining. Taken together, cell proliferation and organ morphogenesis signals transduced by RXR mediated pathways may have important roles for cystogenesis in early-stage PKD in this Pkdr1-mutated Cy rat.Han:SPRD Cy是一种自发多囊肾病（polycystic kidney disease, PKD）大鼠模型，其致病根源为Pkdr1基因发生错义突变。目前该模型的囊肿发生机制尚未明确。本研究针对出生后3天和7天的Cy/Cy型肾脏（处于多囊肾病囊肿发生的早期阶段）与正常+/+型肾脏，开展了全基因表达谱分析。表达谱通过微阵列分析进行检测，并采用实时荧光定量逆转录聚合酶链反应（real-time RT-PCR）进行验证。以与同龄+/+肾脏相比表达变化超过1.5倍的基因为对象，进行经典信号通路分析。本研究在3天龄与7天龄的Cy/Cy型肾脏中，共发现9条共有异常调控通路。其中3条发生显著变化的通路分别为“维生素D受体/类视黄醇X受体（VDR/RXR）激活通路”、“脂多糖/白细胞介素-1（LPS/IL-1）介导的类视黄醇X受体（RXR）功能抑制通路”以及“肝X受体/类视黄醇X受体（LXR/RXR）激活通路”。上述结果提示，在携带Pkdr1突变的发育肾脏中，RXR介导的信号通路发生了显著改变。通过基因本体论（gene ontology, GO）分析发现，这些与RXR相关的基因功能主要参与细胞增殖与器官形态发生的调控。经实时RT-PCR验证，相较于3天龄正常+/+肾脏，3天龄与7天龄的Cy/Cy型肾脏中，与RXR通路相关的核心细胞增殖标志物Ptx2、Alox15b、OSP及PCNA的表达上调均得到证实。在早期Cy/Cy型肾脏的囊性上皮细胞的细胞核与细胞质中，均检测到RXR蛋白表达升高，且RXR阳性细胞同时呈现强PCNA染色阳性。综上，由RXR介导的通路所转导的细胞增殖与器官形态发生信号，可能在该Pkdr1突变型Cy大鼠早期多囊肾病的囊肿发生过程中发挥关键作用。