Cyp4v3基因敲除小鼠模型的表型分析

目的:构建Cyp4v3^-/-小鼠模型以模拟人类结晶样视网膜变性(Bietti crystalline dystrophy,BCD)患者的临床症状,为进一步探索BCD的致病机制和基因治疗方案奠定基础。方法:利用clustered regularly interspaced short palindromic repeats (CRISPR) /Cas9技术,设计sgRNA,注射入C57BL/6J小鼠受精卵中构建携带定点突变的小鼠模型。提取小鼠DNA确定其基因型,分别在其3、6、12月龄时以野生型(wild type, WT)的C57BL/6J小鼠为对照组,进行眼底彩照检查观察其眼底结晶沉积情况;用视网膜电生理(electroretinogram,ERG)检查视网膜功能;用冰冻切片免疫荧光染色观察视网膜组织结构;视网膜色素上皮(retinal pigment epithelium,RPE)铺片鬼笔环肽染色观察RPE形态结构。结果:Cyp4v3^-/-小鼠随着年龄增长,可模拟BCD患者的一些临床症状。在疾病早期未发现眼底有结晶样沉积,ERG检测其视网膜功能未发现明显下降,神经视网膜及RPE的形态结构及数量均未发生明显变化。随着Cyp4v3^-/-小鼠年龄增长,眼底彩照在6月龄时发现有结晶样沉积,12月龄时沉积消失但色素沉积,RPE萎缩;ERG检查在6月龄时发现有暗适应波幅下降,12月龄时暗适应和明适应波幅均有明显下降;免疫荧光染色显示Cyp4v3^-/-小鼠神经视网膜层形态结构受疾病影响不严重;RPE铺片鬼笔环肽染色显示,12月龄时Cyp4v3^-/-小鼠RPE细胞六边形形态改变,排列松散,与WT小鼠相比同等大小视野范围内RPE细胞数量明显减少且差异有统计学意义(P=0.011)。结论:Cyp4v3^-/-小鼠疾病表型与年龄相关,与人类BCD患者临床症状有相似之处,为进一步研究BCD发病机制和基因治疗策略提供了好的模型;本研究发现BCD病理改变首先发生在RPE,但是具体机制还需进一步研究。

Generation and characterization of Cyp4v3 gene knockout mice

Objective: Bietti crystalline dystrophy (BCD) is a rare degenerative eye disease caused by mutations in the CYP4V2 gene, and Cyp4v3 is the murine ortholog to CYP4V2. To better understand the molecular pathogenesis of this disease and to explore the potential treatment we have established a Cyp4v3 knock-out mouse model. Methods: Cyp4v3 ^-/- mice were generated by clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 in embryonic stem cells of C57BL/6J mice. Ocular morphologic characteristics were evaluated via fundus imaging, histologic analysis of rods and cones via immunofluorescence, and phalloidin stain to observe retinal pigment epithelium (RPE) in whole-mounts, electroretinogram (ERG) was also conducted to examine the retinal function. Results: The characteristic features of BCD recurred in the Cyp4v3 ^-/- mice, including retinal crystalline deposits, atrophy and degeneration of RPE cells, and ERG amplitude decline of dark and light adapted a- and b- wave; however, the immunofluorescence stain of rod and cone cells did not show obvious differences when compared with the wild type (WT) mice. In the early stage of the disease, no crystal-like deposits were found in the fundus, ERG detection of the retinal function did not find a significant decline, and the morphological structure and quantity of the neural retina and RPE did not change significantly. Crystalline deposits occurred and converged when the Cyp4v3 ^-/- mice at the end of 6 months, and the deposits disappeared when the Cyp4v3 ^-/- mice at the end of 12 months. The ERG amplitude started to decline when the Cyp4v3 ^-/- mice at the end of 6 months and deteriorated at the end of 12 months. The RPE cells of the 12-month old Cyp4v3 ^-/- mice showed irregular shape by phalloidin staining of F-actin. The Cyp4v3 ^-/- mice behaved normally and were viable and fertile when maintained under specific pathogen-free (SPF) housing conditions. Conclusion: Just like BCD patients, the disease progress of Cyp4v3 ^-/- mouse is correlated with the age, which provides a good model for pathogenesis and gene therapy study in the future. The atrophy and degeneration of RPE take the lead in progressing of the disease, but the mechanism is not clear yet.