Organisciak D T, Darrow R M, Barsalou L, Darrow R A, Kutty R K, Kutty G, Wiggert B
Department of Biochemistry and Molecular Biology, Wright State University School of Medicine, Dayton, Ohio 45435, USA.
Invest Ophthalmol Vis Sci. 1998 Jun;39(7):1107-16.
To determine the effects of age and long-term light- or dark-rearing environments on acute, intense-light-mediated retinal degeneration.
Male albino rats were maintained in a dim cyclic light environment or in darkness for as long as 1 year. When aged 2, 4, 8, and 12 months, some rats were given the synthetic antioxidant dimethylthiourea (DMTU) by intraperitoneal injection and were exposed to intense visible light for as long as 24 hours. Uninjected control rats were exposed to light at the same time. Other rats were treated with light of lower intensity for various periods. Two weeks after intense-light treatment, photoreceptor cell degeneration was estimated by determining the level of rhodopsin and by measuring the content of photoreceptor cell DNA. Light-induced changes in retinal DNA were analyzed immediately after exposure by neutral gel electrophoresis and by 8-hydroxy-deoxyguanosine measurements. Expression of the antioxidative stress protein heme oxygenase-1 (HO-1) was determined by northern blot analysis of mRNA in retinal extracts.
At all ages, rats reared in cyclic dim-light conditions had lower rhodopsin levels than did rats reared in darkness; photoreceptor cell DNA levels were unaffected by the rearing environment. Senescent losses in rhodopsin and retinal DNA were significant after rats were 12 months old. Dim-light-reared rats exhibited an age-related increase in retinal light damage susceptibility, whereas dark-reared rats were equally susceptible to damage at all ages. In both types of rats, the mechanism of light-induced cell death involved an apoptotic process, visualized by the pattern of DNA fragments on electrophoretic gels. The process also induced the expression of HO-1 mRNA. Photoreceptor cell loss determined by biochemical measurement, DNA fragmentation, and HO-1 induction were dramatically reduced by the administration of DMTU.
The age-related increase in susceptibility to retinal light damage in rats is influenced by their long-term daily light history. Decreasing retinal irradiance by dark-rearing eliminates the age-related increase in light damage, suggesting a correlation between light environment and retinal gene expression associated with damage. In all rats, retinal light damage resulted in a pattern of DNA fragmentation consistent with apoptotic cell death and in an increased expression of HO-1 mRNA. Antioxidant treatment greatly reduced apoptosis and HO-1 expression. This indicates that light damage involves an oxidative process that may also trigger apoptosis in the retina. The rat aging model may provide useful insights into the role of light environment associated with retinal degeneration in an aging human population.
确定年龄以及长期光照或黑暗饲养环境对急性强光介导的视网膜变性的影响。
雄性白化大鼠在昏暗的循环光照环境或黑暗环境中饲养长达1年。在2、4、8和12月龄时，部分大鼠腹腔注射合成抗氧化剂二甲基硫脲（DMTU），并暴露于强光下长达24小时。未注射的对照大鼠同时接受光照。其他大鼠接受不同时长的低强度光照处理。强光处理两周后，通过测定视紫红质水平和测量光感受器细胞DNA含量来评估光感受器细胞变性。光照后立即通过中性凝胶电泳和8-羟基-脱氧鸟苷测量分析视网膜DNA的光诱导变化。通过对视网膜提取物中mRNA进行Northern印迹分析来确定抗氧化应激蛋白血红素加氧酶-1（HO-1）的表达。
在所有年龄段，在循环弱光条件下饲养的大鼠视紫红质水平均低于在黑暗中饲养的大鼠；光感受器细胞DNA水平不受饲养环境影响。大鼠12月龄后，视紫红质和视网膜DNA的衰老性损失显著。弱光饲养的大鼠视网膜光损伤易感性呈现与年龄相关的增加，而黑暗饲养的大鼠在所有年龄段对损伤的易感性相同。在这两种类型的大鼠中，光诱导细胞死亡的机制涉及凋亡过程，通过电泳凝胶上的DNA片段模式可见。该过程还诱导了HO-1 mRNA的表达。通过生化测量、DNA片段化和HO-1诱导确定的光感受器细胞损失通过给予DMTU显著减少。
大鼠视网膜光损伤易感性与年龄相关的增加受其长期日常光照经历影响。通过黑暗饲养降低视网膜辐照度可消除与年龄相关的光损伤增加，表明光照环境与视网膜损伤相关基因表达之间存在关联。在所有大鼠中，视网膜光损伤导致与凋亡细胞死亡一致的DNA片段化模式以及HO-1 mRNA表达增加。抗氧化治疗大大减少了细胞凋亡和HO-1表达。这表明光损伤涉及一个氧化过程，该过程也可能触发视网膜中的细胞凋亡。大鼠衰老模型可能为了解光照环境在老年人群视网膜变性中的作用提供有用的见解。
