Department of Ophthalmology and Visual Sciences, Washington University in St. Louis, St. Louis, Missouri 63110, and.
Pennsylvania College of Optometry, Salus University, Elkins Park, Pennsylvania 19027.
J Neurosci. 2018 Mar 21;38(12):2990-3000. doi: 10.1523/JNEUROSCI.2985-17.2018. Epub 2018 Feb 12.
The Arg838Ser mutation in retinal membrane guanylyl cyclase 1 (RetGC1) has been linked to autosomal dominant cone-rod dystrophy type 6 (CORD6). It is believed that photoreceptor degeneration is caused by the altered sensitivity of RetGC1 to calcium regulation via guanylyl cyclase activating proteins (GCAPs). To determine the mechanism by which this mutation leads to degeneration, we investigated the structure and function of rod photoreceptors in two transgenic mouse lines, 362 and 379, expressing R838S RetGC1. In both lines, rod outer segments became shorter than in their nontransgenic siblings by 3-4 weeks of age, before the eventual photoreceptor degeneration. Despite the shortening of their outer segments, the dark current of transgenic rods was 1.5-2.2-fold higher than in nontransgenic controls. Similarly, the dim flash response amplitude in rods was larger, time to peak was delayed, and flash sensitivity was increased, all suggesting elevated dark-adapted free cGMP in transgenic rods. In rods expressing R838S RetGC1, dark-current noise increased and the exchange current, detected after a saturating flash, became more pronounced. These results suggest disrupted Ca phototransduction feedback and abnormally high free-Ca concentration in the outer segments. Notably, photoreceptor degeneration, which typically occurred after 3 months of age in R838S RetGC1 transgenic mice in or backgrounds, was prevented in mice lacking Ca feedback to guanylyl cyclase. In summary, the dysregulation of guanylyl cyclase in RetGC1-linked CORD6 is a "phototransduction disease," which means it is associated with increased free-cGMP and Ca levels in photoreceptors. In a mouse model expressing human membrane guanylyl cyclase 1 (RetGC1, ), a mutation associated with early progressing congenital blindness, cone-rod dystrophy type 6 (CORD6), deregulates calcium-sensitive feedback of phototransduction to the cyclase mediated by guanylyl cyclase activating proteins (GCAPs), which are calcium-sensor proteins. The abnormal calcium sensitivity of the cyclase increases cGMP-gated dark current in the rod outer segments, reshapes rod photoresponses, and triggers photoreceptor death. This work is the first to demonstrate a direct physiological effect of CORD6-linked mutation on photoreceptor physiology It also identifies the abnormal regulation of the cyclase by calcium-sensor proteins as the main trigger for the photoreceptor death.
视网膜膜鸟苷酸环化酶 1（RetGC1）中的 Arg838Ser 突变与常染色体显性遗传的 cones-rod 营养不良 6 型（CORD6）有关。据信，视蛋白变性是由于 RetGC1 对钙调节的敏感性通过鸟苷酸环化酶激活蛋白（GCAPs）发生改变而引起的。为了确定该突变导致变性的机制，我们研究了在表达 R838S RetGC1 的两个转基因小鼠系 362 和 379 中的 rod 光感受器的结构和功能。在这两条线中，rod 外段在 3-4 周龄时比其非转基因兄弟姐妹短，然后最终出现光感受器变性。尽管 rod 外段缩短，但转基因 rod 的暗电流仍比非转基因对照高 1.5-2.2 倍。同样，在 rods 中暗闪光反应幅度较大，峰值时间延迟，闪光敏感性增加，所有这些都表明转基因 rods 中暗适应游离 cGMP 升高。在表达 R838S RetGC1 的 rods 中，暗电流噪声增加，在饱和闪光后检测到的交换电流变得更加明显。这些结果表明 Ca 光转导反馈中断，外段中异常高的游离 Ca 浓度。值得注意的是，在或背景下，通常在 3 个月大时发生 R838S RetGC1 转基因小鼠的光感受器变性，在缺乏对鸟苷酸环化酶的 Ca 反馈的 小鼠中被阻止。总之，与 RetGC1 相关的 CORD6 中的鸟苷酸环化酶失调是一种“光转导疾病”，这意味着它与光感受器中游离 cGMP 和 Ca 水平升高有关。在表达人膜鸟苷酸环化酶 1（RetGC1，）的小鼠模型中，一种与早期进展性先天性失明相关的突变，cone-rod 营养不良 6 型（CORD6），调节由鸟苷酸环化酶激活蛋白（GCAPs）介导的光转导对环化酶的钙敏感反馈，GCAPs 是钙传感器蛋白。环化酶的异常钙敏感性增加了 rod 外段中 cGMP 门控暗电流，重塑了 rod 光反应，并触发光感受器死亡。这项工作首次证明了与 CORD6 相关的突变对光感受器生理学的直接生理影响。它还确定了钙传感器蛋白对环化酶的异常调节是光感受器死亡的主要触发因素。
