GUCY2D Cone–Rod Dystrophy-6 Is a “Phototransduction Disease” Triggered by Abnormal Calcium Feedback on Retinal Membrane Guanylyl Cyclase 1
GUCY2D Cone–Rod Dystrophy-6 Is a “Phototransduction Disease” Triggered by Abnormal Calcium Feedback on Retinal Membrane Guanylyl Cyclase 1
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DOI：
10.1523/jneurosci.2985-17.2018
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发表时间：
2018-02
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通讯作者：
Shinya Sato;I. Peshenko;E. Olshevskaya;V. Kefalov;A. Dizhoor
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作者：
Shinya Sato;I. Peshenko;E. Olshevskaya;V. Kefalov;A. Dizhoor
视网膜膜鸟苷酸环化酶 1 (RetGC1) 中的 Arg838Ser 突变与常染色体显性锥杆营养不良 6 型 (CORD6) 有关。据信，光感受器变性是由 RetGC1 通过鸟苷酸环化酶激活蛋白 (GCAP) 对钙调节的敏感性改变引起的。为了确定这种突变导致变性的机制，我们研究了表达 R838S RetGC1 的两个转基因小鼠品系 362 和 379 中杆光感受器的结构和功能。在这两个品系中，到3-4周龄时，即最终光感受器退化之前，视杆细胞外节都变得比非转基因同胞短。尽管其外节缩短，但转基因视杆细胞的暗电流比非转基因对照高 1.5-2.2 倍。类似地，R838S+视杆中的暗淡闪光响应幅度更大，达到峰值的时间延迟，并且闪光敏感性增加，所有这些都表明转基因视杆中的暗适应游离cGMP升高。在表达 R838S RetGC1 的视杆细胞中，暗电流噪声增加，并且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 Ca2+ 光转导反馈被破坏，并且外节中游离 Ca2+ 浓度异常高。值得注意的是，在 GCAP1,2+/+ 或 GCAP1,2+/- 背景下的 R838S RetGC1 转基因小鼠中，光感受器变性通常发生在 3 月龄后，但在缺乏鸟苷酸环化酶 Ca2+ 反馈的 GCAP1,2−/− 小鼠中，光感受器变性得到了预防。总之，RetGC1 连接的 CORD6 中鸟苷酸环化酶的失调是一种“光转导疾病”，这意味着它与光感受器中游离 cGMP 和 Ca2+ 水平增加有关。意义声明 在表达人膜鸟苷酸环化酶 1（RetGC1、GUCY2D）的小鼠模型中，这种突变与早期进展性先天性失明、锥杆营养不良 6 型（CORD6）相关，可解除鸟苷酸环化酶激活蛋白（GCAP）（钙传感器蛋白）介导的光转导对环化酶的钙敏感反馈的调节。环化酶异常的钙敏感性会增加视杆外节中 cGMP 门控暗电流，重塑视杆光响应，并引发光感受器死亡。这项工作首次证明了 GUCY2D CORD6 连锁突变对体内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。
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 R838S+ 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 Ca2+ phototransduction feedback and abnormally high free-Ca2+ concentration in the outer segments. Notably, photoreceptor degeneration, which typically occurred after 3 months of age in R838S RetGC1 transgenic mice in GCAP1,2+/+ or GCAP1,2+/− backgrounds, was prevented in GCAP1,2−/− mice lacking Ca2+ 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 Ca2+ levels in photoreceptors. SIGNIFICANCE STATEMENT In a mouse model expressing human membrane guanylyl cyclase 1 (RetGC1, GUCY2D), 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 GUCY2D CORD6-linked mutation on photoreceptor physiology in vivo. It also identifies the abnormal regulation of the cyclase by calcium-sensor proteins as the main trigger for the photoreceptor death.