Sphingolipid Metabolism and Signaling in the Retina

描述（由申请人提供）：鞘脂是一类膜脂，在调节脂质双分子层的流动性和亚结构域结构中具有重要的结构作用，特别是脂筏。神经酰胺是所有鞘脂生物合成的关键代谢物。Cer及其代谢物鞘鞘醇-1-磷酸（S1P）是鞘脂的信号通路；涉及几种与炎症、肿瘤发生、糖尿病和神经变性相关的人类疾病。Cer信号主要用于细胞凋亡，而S1P在细胞存活中具有相反的细胞内作用。S1P也通过其受体（S1P1-5）在细胞旁发出信号，这些受体主要存在于血管内皮细胞和T细胞中，并发出粘附、迁移、炎症和新生血管的信号。与其在细胞凋亡中的作用一致，神经酰胺最近被证明与光感受器细胞死亡有关。我们的初步数据显示，在遗传性和应激性视网膜变性的几种模型中，神经酰胺水平在视网膜变性期间升高。我们还观察到变性视网膜中S1P水平和表达增加。已知S1P对神经酰胺合成有抑制作用。在初步研究中，我们确定S1P也是鞘磷脂酶（SMase）的竞争性抑制剂，SMase是细胞中另一组负责神经酰胺生成的酶，这表明S1P在Cer生成的调节反馈中起作用。当我们将Cer注射到大鼠玻璃体中时，我们观察到严重的炎症，随后是视网膜功能丧失和光感受器细胞死亡。我们进一步发现FTY720，一种新生的Cer合成抑制剂，可以阻断大鼠视网膜中Cer的产生，并保护视杆细胞免受光诱导的变性。我们的初步结果显示视网膜中神经鞘脂代谢活跃，神经酰胺和S1P之间的微妙平衡对于维持正常的视网膜结构和功能很重要。在本提案中，我们将检验视网膜中Cer和S1P之间失调平衡导致视网膜炎症和细胞死亡的假设。在四个特定目的下提出的实验将集中于阐明Cer在视网膜退行性疾病中的生理作用，了解Cer水平是如何调节的，探索靶向Cer合成的抑制剂或可以降解Cer的酶的治疗潜力，确定S1P与视网膜中Cer代谢的关系，以及Cer和S1P的平衡在维持视网膜稳态和功能中的重要性。本课题将探讨神经酰胺和S1P在视网膜生理和疾病中的作用。这是视网膜研究的一个新领域，与许多形式的人类视网膜营养不良有关，包括年龄相关性黄斑变性、糖尿病性视网膜病变和视网膜色素变性。机制研究可能会为治疗干预确定新的途径和新的靶点。

DESCRIPTION (provided by applicant): Sphingolipids are a family of membrane lipids with important structural roles in the regulation of the fluidity and subdomain structure of the lipid bilayer, especially lipid rafts. Ceramide (Cer) is the key metabolite for all sphingolipid biosynthesis. Cer and its metabolite sphingosine-1-phosphate (S1P) are signaling sphingolipids; implicated in several human diseases associated with inflammation, tumorigenesis, diabetes, and neurodegeneration. Cer signals primarily for apoptosis, whereas S1P has an opposing intracellular role in cell survival. S1P also signals paracellularly via its receptors (S1P1-5), which are mostly present in vascular endothelial cells and T cells and signals for adhesion, migration, inflammation, and neovascularization. Consistent with its role in apoptosis, ceramide has recently been shown to be involved in photoreceptor cell death. Our preliminary data show ceramide levels are increased during retinal degeneration in several models of inherited and stress-induced retinal degeneration. We also observed increased S1P levels and expression in degenerating retinas. S1P is known to have inhibitory effect on ceramide synthesis. In pilot studies, we determined that S1P is a competitive inhibitor of sphingomyelinase (SMase) also, another group of enzymes responsible for ceramide production in cells, suggesting a role for S1P in the regulated feedback of Cer production. When we injected Cer into the rat vitreous, we observed severe inflammation followed by loss of retinal function and photoreceptor cell death. We further found that FTY720, a de novo Cer synthesis inhibitor, blocked Cer production in the rat retina and protected rods from light-induced degeneration. Our preliminary results show an active sphingolipid metabolism in the retina and suggest that the delicate balance between ceramide and S1P is important in maintaining normal retinal structure and function. In this proposal we will test the hypothesis that the dysregulated balance between Cer and S1P in the retina leads to retinal inflammation and cell death. The experiments proposed in four specific aims will focus on elucidating the physiological role of Cer in retinal degenerative diseases, understanding how Cer levels are regulated, exploring the therapeutic potential of inhibitors that target Cer synthesis or the enzymes that can degrade Cer, determining how S1P is related to Cer metabolism in the retina, and how important is the balance of Cer and S1P in maintaining retinal homeostasis and function. This proposal will explore the role of Ceramide and S1P in retinal physiology and diseases. This is a novel and underserved area of retinal research and has relevance to many forms of human retinal dystrophies including age-related macular degeneration, diabetic retinopathy, and retinitis pigmentosa. Mechanistic studies will likely identify novel pathways and novel targets for therapeutic intervention. PUBLIC HEALTH RELEVANCE: Retinal degeneration can cause vision loss at any age. The long-term goal of this project is to understand the role of sphingolipid metabolites that can initiate or potentiate retinal degeneration. This is important because identifying these specific mediators can provide novel targets for therapeutic manipulation to inhibit degeneration.