Background Retinitis pigmentosa (RP)is a common hereditary blinding eye disease in ophthalmology.Current researches documented that RP may have the common pathophysiologic basis to Alzheimer disease and chronic neurodegenerative disease.Understanding this mechanism will offer a new therapeutic target for RP.Objective The purpose of the present study was to investigate the roles of cyclin-dependent kinase 5 (Cdk5)/P25 activation in the apoptosis of retinal neural cells of RCS rats.Methods Eighteen SPF RCS rats and 18 RCS-rdy+ rats were randomized into 17-,25-and 35-day groups respectively and 6 rats for each.The rats were sacrificed at corresponding time points and retinal hemogenete was prepared.Expressions of CdkS,P35,P25 and tau phosphorylation in the retinas were detected by Western blot,and the kinase activity of Cdk5/P25 was analyzed by quantitative colorimetric assay.Results The expressing level of P35 protein(A340) in the retinas of 17-day-old RCS rats was near that of 17-day-old RCS-rdy+ rats(t =0.52,P＞0.05).In 25-and 35-day-old RCS rats,the expressing levels of P35 protein were 2.20±0.48 and 1.23±0.14,which were higher than those of RCS-rdy+ rats(1.43±0.13 and 0.93±0.10),showing significant differences between them(t =3.78,4.28,P＜0.05).The expression of P25 was undetectable at postnatal 17 days in RCS rats and RCS-rdy+ rats,but it showed significantly higher in RCS rats(0.300±0.003 and 0.230±0.004) than that in RCS-rdy+ rats(0.040±0.004 and 0.070±0.004) at postnatal 25 days and 35 days(t=121.81,77.51,P＜0.01).No significant difference was found in the expression of Cdk5 in RCS rats and RCS-rdy+ rats at different ages (t =-0.60,0.19,1.62,P＞ 0.05).The kinase activity of Cdk5/P25 did not show significantly different between RCS and RCS-rdy+ rats at postnatal 17 days(t =0.19,P＞0.05),but significantly higher kinase activity of Cdk5/P25 was seen in RCS rats (0.0058 ±0.0005 and 0.0056±0.0004) than that in RCS-rdy+ rats(0.0038±0.0003 and 0.0032 ±0.0007) at postnatal 25 days and 35 days (t =8.07,5.97,P＜ 0.01).No expression of tau phosphorylation was detected in RCS rats at postnatal 17 days,but significantly higher tau phosphorylation level was seen in RCS rats at postnatal 25 days and 35 days(1.80±0.22 and 1.23±0.17),which were significant different in comparison with RCS-rdy+ rats at postnatal 25 days and 35 days(1.60 ±0.20 and 1.04 ±0.12)(t=4.71,3.17,P＜0.05).Conclusions The Cdk5/P25 kinase activity shows a consistent trend with theexpressions of P25 and tau phosphorylation in the RCS rats,indicating that the upregulation of P25 induces the enhance of enzyme activity of Cdk5,which phosphorylate its substrates to result in more apoptosis of retinal neural cells.%背景 视网膜色素变性(RP)是眼科常见的遗传性、致盲性眼病,可能与阿尔茨海默病等慢性神经退行性疾病具有共同的病理生理机制,细胞周期依赖性蛋白激酶5(Cdk5)与光感受器细胞及视网膜神经节细胞正常功能的维持相关,可能是引起RP光感受器细胞凋亡的途径,有可能成为新的治疗靶点. 目的 探讨Cdk5/P25激酶活性在RCS大鼠视网膜神经细胞凋亡中的作用.方法 SPF级RCS变性大鼠及RCS-rdy+正常对照大鼠各18只,按随机数字表法亚分至出生后17、25、35 d组,每亚组各6只大鼠.各组大鼠分别在相应时间点直接处死后摘除眼球,并取视网膜组织,以Western blot法检测大鼠视网膜组织中Cdk5、P35、P25蛋白的表达和tau蛋白磷酸化水平,并利用紫外分光光度计用光谱法测定两组不同日龄大鼠视网膜组织吸光度(A340)峰值的变化,定量分析各组Cdk5/P25激酶的活性. 结果 P35蛋白在17日龄的RCS大鼠和RCS-rdy+大鼠的视网膜组织中表达水平(A340)差异无统计学意义(t=0.52,P＞0.05),25日龄和35日龄RCS大鼠视网膜组织中P35蛋白表达水平分别为2.20±0.48、1.23±0.14,明显高于RCS-rdy+大鼠的1.43±0.13和0.93±0.10,差异均有统计学意义(t=3.78、4.28,P＜0.05)；P25蛋白在17日龄的RCS大鼠及RCS-rdy+大鼠的视网膜组织中均未检测到,但在25日龄和35日龄的RCS大鼠视网膜组织中表达水平(A340)为0.300±0.003、0.230±0.004,明显高于RCS-rdy+大鼠的0.040±0.004和0.070±0.004,差异均有统计学意义(t=121.81、77.51,P＜0.01)；Cdk5蛋白在各日龄的RCS大鼠视网膜组织中的表达水平与RCS-rdy+大鼠相比差异均无统计学意义(t=-0.60、0.19、1.62,P＞0.05)；17日龄RCS大鼠和RCS-rdy+大鼠视网膜组织中Cdk5/P25激酶活性差异无统计学意义(t=0.19,P＞0.05),25日龄和35日龄的RCS大鼠视网膜组织中Cdk5/P25激酶活性分别为0.0058±0.0005、0.0056±0.0004,明显高于RCS-rdy+大鼠的0.0038±0.0003和0.0032±0.0007,差异均有统计学意义(t=8.07、5.97,P＜0.01)；25日龄和35日龄RCS大鼠视网膜组织中tau蛋白磷酸化水平明显高于RCS-rdy+大鼠,差异均有统计学意义(t=4.71、3.17,P＜0.05). 结论 RCS大鼠视网膜组织中CdkS/P25激酶活性与P25蛋白表达水平和tau蛋白磷酸化水平的变化趋势一致,提示P25表达增加可能诱导Cdk5/P25激酶活性升高,并通过磷酸化其作用底物引起视网膜神经细胞凋亡.
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