Department of Ophthalmology and The Neuroscience Center of Excellence, LSU Health Sciences Center, 2020 Gravier Street, Suite D, New Orleans, LA 70112, USA.
Exp Eye Res. 2013 Mar;108:59-67. doi: 10.1016/j.exer.2012.12.008. Epub 2012 Dec 26.
Our previous study on retinal light exposure suggests the involvement of zinc (Zn(2+)) toxicity in the death of RPE and photoreceptors (LD) which could be attenuated by pyruvate and nicotinamide, perhaps through restoration of NAD(+) levels. In the present study, we examined Zn(2+) toxicity, and the effects of NAD(+) restoration in primary retinal cultures. We then reduced Zn(2+) levels in rodents by reducing Zn(2+) levels in the diet, or by genetics and measured LD. Sprague Dawley albino rats were fed 2, or 61 mg Zn(2+)/kg of diet for 3 weeks, and exposed to 18 kLux of white light for 4 h. We light exposed (70 kLux of white light for 50 h) Zn(2+) transporter 3 knockout (ZnT3-KO, no synaptic Zn(2+)), or RPE65 knockout mice (RPE65-KO, lack rhodopsin cycling), or C57/BI6/J controls and determined light damage and Zn(2+) staining. Retinal Zn(2+) staining was examined at 1 h and 4 h after light exposure. Retinas were examined after 7 d by optical coherence tomography and histology. After LD, rats fed the reduced Zn(2+) diet showed less photoreceptor Zn(2+) staining and degeneration compared to a normal Zn(2+) diet. Similarly, ZnT3-KO and RPE65-KO mice showed less Zn(2+) staining, NAD(+) loss, and RPE or photoreceptor death than C57/BI6/J control mice. Dietary or ZnT3-dependent Zn(2+) stores, and intracellular Zn(2+) release from rhodopsin recycling are suggested to be involved in light-induced retinal degeneration. These results implicate novel rhodopsin-mediated mechanisms and therapeutic targets for LD. Our companion manuscript demonstrates that pharmacologic, circadian, or genetic manipulations which maintain NAD(+) levels reduce LD.
我们之前的视网膜光暴露研究表明，锌（Zn(2+)）毒性参与了 RPE 和光感受器（LD）的死亡，而丙酮酸和烟酰胺可以减轻这种毒性，可能是通过恢复 NAD(+)水平。在本研究中，我们检查了原发性视网膜培养物中的 Zn(2+)毒性和 NAD(+)恢复的影响。然后，我们通过降低饮食中的 Zn(2+)水平、通过遗传学方法降低 Zn(2+)水平，并测量 LD，来降低啮齿动物的 Zn(2+)水平。Sprague Dawley 白化大鼠喂食 2 或 61mg Zn(2+)/kg 的饮食 3 周，并暴露于 18 kLux 的白光下 4 小时。我们用光照射（70 kLux 的白光照射 50 小时）Zn(2+)转运蛋白 3 敲除（ZnT3-KO，没有突触 Zn(2+)）、或视黄醛循环缺乏的 RPE65 敲除（RPE65-KO）、或 C57/BI6/J 对照小鼠，并确定光损伤和 Zn(2+)染色。在光暴露后 1 小时和 4 小时检查视网膜 Zn(2+)染色。光损伤后 7 天通过光学相干断层扫描和组织学检查视网膜。与正常 Zn(2+)饮食相比，喂食低 Zn(2+)饮食的大鼠在光暴露后显示出较少的光感受器 Zn(2+)染色和变性。同样，ZnT3-KO 和 RPE65-KO 小鼠比 C57/BI6/J 对照小鼠显示出较少的 Zn(2+)染色、NAD(+)损失、RPE 或光感受器死亡。饮食或 ZnT3 依赖性 Zn(2+)储存，以及视黄醛循环释放的细胞内 Zn(2+)，被认为参与了光诱导的视网膜变性。这些结果表明了新的视黄醛介导的机制和 LD 的治疗靶点。我们的配套研究表明，维持 NAD(+)水平的药理学、昼夜节律或遗传学操作可减少 LD。
