Dysfunction of retinal neurons and circuits early in diabetic retinopathy

描述（由申请人提供）：多巴胺能无突神经元是视网膜中多巴胺的唯一来源。多巴胺在突触样变异处局部释放到目标神经元，也以旁分泌的方式扩散影响视网膜，它在调节视网膜从夜间到白天的视力中起着关键作用。来自已发表的研究的有趣数据表明，多巴胺能过程和静脉曲张与视网膜毛细血管密切相关，而不仅仅是神经元，但多巴胺是否在视网膜中像在大脑中一样具有血管活性尚不清楚。在本应用中，我们将验证多巴胺调节视网膜的神经元和血管功能的新假设，以及多巴胺在糖尿病神经元和毛细血管内皮细胞中的作用失调对糖尿病视网膜病变的视力损害有重要影响。我们认为糖尿病视网膜中多巴胺的产生减少，加剧了神经元和血管功能障碍，我们已经确定发生在ins2秋田小鼠糖尿病模型中。这是基于我们的初步数据，多巴胺释放、酪氨酸羟化酶表达和多巴胺能神经元数量在糖尿病秋田视网膜中都减少。此外，我们发现视网膜回路功能、视觉行为和血流的缺陷都与多巴胺减少是一个统一的机制。这对于推进我们对视网膜功能的基本理解具有根本的重要性，重要的是，它代表了一个具有翻译意义的新假设，可以为改善糖尿病视网膜病变的临床治疗带来新的目标。这种假设的多巴胺减少会干扰视网膜功能，因为多巴胺对间隙连接网络的正常解偶联对于匹配视网膜对平均光强的敏感性和调节感受野功能是必要的。我们已经证明糖尿病秋田小鼠的光动力学追踪（OKT）明显受损（Akimov和Renteria， 2012），这是一种需要多巴胺才能达到最佳表现的视觉行为。这些神经缺陷的机制以及它们如何概括人类糖尿病视网膜病变的视觉功能障碍将在Aim 1中详细探讨。这是翻译意义重大的，因为我们的研究将表明，维持多巴胺信号的治疗将改善视觉行为缺陷，多巴胺能功能障碍发生在糖尿病视网膜病变发病的早期。我们进一步假设多巴胺对视网膜内皮细胞的作用是糖尿病视网膜病变中多巴胺减少的第二个关键致病途径。我们在秋田小鼠中发现，多巴胺减少会加剧vegf相关的通透性，并导致眼血流不畅。目的2探讨多巴胺作用于视网膜内皮细胞的新观点及其对视网膜神经元的影响。这一应用具有创新性，因为这一途径可以作为抗VEGF治疗的一种新辅助手段，进一步阻断VEGF的血管渗透活性。这项工作的总体影响是，它为理解糖尿病视网膜病变中视力丧失的发生提供了新的见解，并为治疗提供了新的途径。

DESCRIPTION (provided by applicant): Dopaminergic amacrine neurons are the only source of dopamine in the retina. Released locally at synapse- like varicosities to target neurons and also in a paracrine fashion to diffusely affect the retina, dopamine is critical in adjusting the retina from nighttime to daytime vision. Intriguing data from published studies indicate that dopaminergic processes and varicosities closely associate with the retinal capillaries, not just neurons, but whether dopamine is vasoactive in retina as in brain is unknown. In this application, we will test the novel hypothesis that dopamine regulates both neuronal and vascular function of the retina and that dysregulation of dopamine action at neurons and capillary endothelial cells in diabetes contributes significantly to the visual impairments of diabetic retinopathy. We propose that dopamine production is reduced in diabetic retina, exacerbating the neuronal and vascular dysfunctions that we have determined to occur in the Ins2Akita mouse model of diabetes. This is based on our preliminary data that dopamine release, tyrosine hydroxylase expression, and dopaminergic neuron number are all reduced in diabetic Akita retina. Further, we find deficits in retinal circuit function, visual behavior, and lood flow that are all remarkably consistent with reduced dopamine as a unifying mechanism. This is of fundamental importance for advancing our basic understanding of retinal function and, importantly, represents a translationally significant new hypothesis that could lead to new targets for improved clinical treatment of diabetic retinopathy. This postulated reduction in dopamine would interfere with retinal function because the normal uncoupling of gap junction networks by dopamine is necessary for matching retinal sensitivity to mean light intensity and for modulating receptive field function. We have demonstrated a marked impairment in diabetic Akita mice of optokinetic tracking (OKT) (Akimov and Renteria, 2012), a visual behavior that requires dopamine for optimal performance. The mechanisms of these neural deficits and how they recapitulate visual dysfunctions in human diabetic retinopathy will be explored in detail in Aim 1. This is translationally significant because our studies will show that treatments that maintain dopamine signaling will ameliorate visual behavior deficits and that dopaminergic dysfunction occurs early in the pathogenesis of diabetic retinopathy. We further hypothesize that dopamine action on retinal endothelial cells is a second critical pathogenic pathway of reduced dopamine in diabetic retinopathy. We propose that reduced dopamine exacerbates VEGF-associated permeability and contributes to the poor ocular blood flow we find in Akita mice. Aim 2 pursues these new ideas of dopamine action on endothelial cells in the retina and their outcomes for retinal neurons. This application is innovative because this pathway could be exploited using FDA-approved treatments as a novel adjunct to anti-VEGF therapy to further block the vascular permeabilizing activity of VEGF. The overall impact of the proposed work is that it provides novel insight for understanding how vision loss occurs in diabetic retinopathy and provides a new pathway to target for therapy.