Role and Regulation of Nox4 in the retina during diabetes

2型糖尿病的患病率正在以惊人的速度增长，全球约有9300万人受到影响，其中2800万人患有威胁视力的糖尿病视网膜病变(DR)，这是糖尿病的主要眼部并发症。利用生长因子血管内皮生长因子(VEGF)抗体的治疗已经极大地改善了增殖性糖尿病视网膜病变和黄斑水肿的治疗，这是DR的两个晚期阶段，但仍然没有针对疾病早期阶段的治疗方法来防止神经视网膜的改变，从而保护视觉功能。几篇综述总结认为，与糖尿病相关的视网膜功能障碍可能被视为视网膜神经血管单位的改变。神经血管单位是指血管内皮细胞和周细胞、星形胶质细胞、Müler神经胶质细胞和神经元之间的生理生化关系，这些细胞与血视网膜屏障密切相关。因此，需要解决血管功能障碍和神经变性的新的治疗方法。已知高血糖依赖的反应性代谢物的产生会导致过多的活性氧(ROS)产生，这可能是DR NADPH(烟酰胺腺嘌呤二核苷酸磷酸)酶产生ROS的关键因素，并且已知它们广泛分布于整个视网膜。NOx-4是NOx家族的7种异构体之一，参与信号转导、细胞分化和死亡等多种途径。一项研究表明，在糖尿病啮齿动物中，NOX4的缺失显著降低了ROS的产生，降低了血管内皮生长因子的表达，降低了血管通透性，从而证明了NOX4是DR期间视网膜ROS的重要来源。到目前为止，大多数关于NOX4在视网膜中的作用的研究利用了视网膜或其他器官衍生的内皮细胞，这些细胞促成了与DR相关的血管变化。时至今日，对于NOX4在血管系统外的视网膜中的作用和调控仍然知之甚少，这些细胞类型特别容易受到代谢变化的影响，并导致DR的早期病理生理变化。因此，我的目标是通过评估NOX4作为糖尿病条件下培养的视网膜神经元、Müler细胞和周细胞中ROS的主要来源以及两种糖尿病啮齿动物模型(1型和2型)中NOX4在视网膜中的作用和调控，来全面了解NOX4在糖尿病期间视网膜的活动情况。我还想进一步评估抑制NOX4在预防氧化应激诱导的DR早期神经退行性变化方面的原理。如果能够实现这种治疗，那么有可能在DR发育的最早阶段促进视网膜细胞的存活。

The prevalence of type 2 diabetes is increasing at an alarming rate with approximately 93 million people affected worldwide and 28 million of them having vision-threatening diabetic retinopathy (DR), the major ocular complication of diabetes. Therapies utilizing antibodies against the growth factor Vascular endothelial growth factor (VEGF) have tremendously improved the treatment of proliferative diabetic retinopathy and macular edema, the two late stages of DR, but there are still no therapies targeting early stages of the disease to prevent alterations of the neural retina and thereby preserve visual function. Several reviews have summarized that retinal dysfunction associated with diabetes may be viewed as a change in the retinal neurovascular unit. The neurovascular unit refers to the physiological and biochemical relationship among blood-vessel endothelial cells and pericytes, astrocytes, Müller glial cells, and neurons which are intimately associated to influence the blood– retina barrier. Therefore, new therapeutic approaches that address vascular dysfunction and neural degeneration are required. Hyperglycemia-dependent generation of reactive metabolites are known to cause excessive reactive oxygen species (ROS) production, which are likely to be a key contributor to the development of DR. NADPH (nicotinamide adenine dinucleotide phosphate) enzymes generate ROS and they are known to be widely distributed throughout the retina. Nox 4, one of the 7 isoforms of the Nox family, has been implicated in numerous pathways such as signal transduction, cell differentiation and death. Evidence that Nox4 is an important source of ROS in the retina during DR was provided by a study demonstrating that depletion of Nox4 significantly decreased ROS production, VEGF expression and reduced vascular permeability in diabetic rodents. To date most studies on the role of Nox4 in the retina utilized retinal or other organ derived endothelial cells, which contribute to the vascular changes associated with DR. Still today, there is a gap of knowledge regarding the role and regulation of Nox4 in the retina outside of the vasculature, celltypes which are particularly susceptible to metabolic changes and contribute to the early pathophysiological changes in DR. Thus, I aim to develop a complete picture of Nox4 activity in the retina during diabetes by evaluating the role and regulation of Nox4 as major source of ROS in the retinal neurons, Müller cells and pericytes under diabetic conditions in culture and in two rodent models of diabetes (type 1 & 2). I further want to evaluate the rationale of Nox4 inhibition in preventing oxidative stress induced early neurodegenerative changes in DR. If such a treatment could be realized, it may be possible to promote retinal cell survival in DR at the earliest stages of its development.