Respiration in vivo in the Retina and RPE

项目总结/摘要 来自脉络膜血液的代谢燃料必须通过视网膜色素上皮（RPE） 到达视网膜中的光感受器。视网膜和RPE具有独特的专门代谢 促进营养物质流动的特征。在以前的研究中，我们发现RPE 最大限度地减少糖酵解，以便更多的葡萄糖可以到达视网膜。最近我们发现， 在活体动物的眼睛中，视网膜是缺氧的， 呼吸到富马酸，生成琥珀酸，而不是将电子转移到氧， 让水。我们还发现视网膜产生和释放的琥珀酸可以为氧气提供燃料 消费的RPE。我们提出了一个脊椎动物能量代谢的模型 琥珀酸盐将还原力从缺氧视网膜转移到富氧视网膜色素上皮的眼睛。 在琥珀酸被RPE细胞氧化后，其碳可以从RPE再循环回到视网膜。 视网膜接受更多的电子并将它们转移到RPE中的氧。 我们最近报道了几条支持琥珀酸介导的 眼睛的新陈代谢周期。到目前为止的证据是基于健康的， 功能性视网膜和RPE/脉络膜活组织。然而，重要的是要建立 这种代谢循环在体内，即在活体动物的眼中发生的程度。 最近，我们建立了一个实验方案，其中我们注入13 C标记的代谢产物， 包括琥珀酸和苹果酸的燃料通过导管进入小鼠的颈静脉。然后我们 测量13 C掺入代谢物中的时程和稳态水平， 视网膜和RPE/脉络膜。在本提案的目标1中，我们将确认我们的初步发现， 琥珀酸循环发生在体内，我们将优化输注方案。在目标2中，我们将使用 体内输注，以显示昼夜节律和昼夜周期如何影响 视网膜和RPE。在目标3中，我们将探索利用琥珀酸循环来减缓 视网膜变性小鼠模型中的光感受器变性。

Project Summary/Abstract Metabolic fuels from the choroidal blood must pass through the retinal pigment epithelium (RPE) to reach photoreceptors in the retina. The retina and RPE have unique specialized metabolic features that facilitate this flow of nutrients. In previous studies we showed that the RPE minimizes glycolysis so that more glucose can reach the retina. More recently we showed that the retina, which is hypoxic in the eye of a living animal, transfers electrons from mitochondrial respiration to fumarate to make succinate instead of transferring the electrons to oxygen to make water. We also showed that succinate made and released by the retina can fuel oxygen consumption by the RPE. We have proposed a model for energy metabolism in the vertebrate eye in which succinate transfers reducing power from the hypoxic retina to the oxygen rich RPE. After succinate is oxidized by RPE cells, its carbons can be recycled from the RPE back to the retina to accept more electrons and transfer them to oxygen in the RPE. We reported recently several lines of evidence that support this model for a succinate-mediated metabolic cycle in the eye. The evidence so far is based on ex vivo analyses of healthy, functioning retina and RPE/choroid living tissues. However, it also is important to establish to what extent this metabolic cycle occurs in vivo, i.e. in the eyes of living animals. Recently we established an experimental protocol in which we infuse 13C labeled metabolic fuels including succinate and malate through catheters into the jugular veins of mice. We then measure the time course and steady state levels of incorporation of 13C into metabolites in the retina and RPE/choroid. In Aim 1 of this proposal we will confirm our initial findings that the succinate cycle occurs in vivo and we will optimize the infusion protocols. In Aim 2 we will use in vivo infusion to show how circadian and diurnal cycles influence metabolic flux between the retina and RPE. In Aim 3 we will explore strategies to exploit the succinate cycle to slow degeneration of photoreceptors in mouse models of retinal degeneration.