Role of Sphingolipids in the Development of Diabetic Nephropathy

描述(申请人提供)：鞘磷脂已经成为参与调节多种细胞功能的关键信号分子。目前对鞘磷脂的研究主要集中在神经酰胺和S1P这两种生物活性鞘脂的细胞内信号转导功能上，而对这两种神经鞘脂胞内信号传递途径的研究较少。拟议的研究将不仅集中在这些鞘磷脂的细胞外运输，而且还将集中在血浆、尿液和分离的脂蛋白中神经鞘磷脂和复合己糖基和乳糖基神经酰胺分子物种的胞外运输，并确定与糖尿病和肾病相关的它们运输的变化。633例参加糖尿病控制和并发症试验(DCCT)的1型糖尿病患者的血浆脂质组学分析表明，几种神经酰胺的低血浆浓度预示着大量白蛋白尿的发生。相比之下，尽管糖尿病患者的鞘氨醇-1-磷酸(S1P)水平比匹配的非糖尿病患者高2.6倍，但并没有。有蛋白尿的1型糖尿病患者血浆载脂蛋白M(ApoM)浓度显著升高，而正常白蛋白尿组则未见。目前尚不清楚血浆鞘磷脂代谢的变化如何导致糖尿病肾病，以及个体脂蛋白在其中所起的作用。 新陈代谢。我们将检验这一假设，即1型糖尿病患者的血浆脂蛋白，尤其是高密度脂蛋白，显著富含S1P，但缺乏选定的神经酰胺。此外，高密度脂蛋白中所选神经酰胺含量的减少会导致它们在血浆和尿液中的浓度降低。最后，通过测量1型糖尿病患者体内神经酰胺的水平，可以发现患者在疾病的不同阶段有发生肾病的高危风险。为了评估这些假说，我们将进行三个具体目标的研究：1)确定在DCCT试验开始和结束时收集的亚组患者的血浆鞘磷脂和载脂蛋白水平是否与糖尿病肾病的发生和进展有关；2)比较匹配的有正常蛋白尿的1型糖尿病患者与大量蛋白尿患者、有大量蛋白尿的非糖尿病患者以及健康对照组的血浆和尿鞘磷脂和载脂蛋白浓度；3)确定观察到的与糖尿病和蛋白尿相关的血浆总鞘脂和载脂蛋白浓度的差异是否局限于极低密度脂蛋白、低密度脂蛋白或高密度脂蛋白。了解糖尿病和肾病患者血浆鞘磷脂转运的知识将指导我们未来研究脂蛋白鞘磷脂改变细胞代谢的可能性，特别是与糖尿病肾脏疾病相关的细胞。

DESCRIPTION (provided by applicant): Sphingolipids have emerged as key signaling molecules involved in the regulation of a variety of cellular functions. Most research investigating sphingolipids has focused on the intracellular signaling functions of two bioactive sphingolipids - ceramide and S1P, but little attention has been given to the source of delivery of these molecules to cells. The proposed studies will focus on the extracellular transport of not only these sphingolipids but also that of sphingomyelin and the complex hexosyl- and lactosylceramide molecular species in plasma, urine, and in isolated lipoproteins and additionally, determine the changes in their transport which are associated with diabetes and nephropathy. The lipidomics profile of plasma obtained from 633 type 1 diabetic patients at their entry into the Diabetes Control and Complications Trial (DCCT), demonstrated that low plasma concentrations of several ceramide species predicted the development of macroalbuminuria. In contrast, the levels of sphingosine-1-phosphate (S1P), although 2.6-fold higher in diabetic patients compared to matched non-diabetic subjects, did not. Plasma concentrations of apolipoprotein M (ApoM), a physiological carrier of S1P, were significantly increased in Type 1 diabetic patients with albuminuria and ApoM was found in urine from these patients but not in normoalbuminuric patients. It is not known how changes in plasma sphingolipid metabolism contribute to nephropathy in diabetes and what role the individual lipoprotein classes play in this metabolism. We will test the hypothesis that plasma lipoproteins from type 1 diabetes patients, but especially HDL, are markedly enriched in S1P but poor in selected ceramides. Additionally, the decreased content of selected ceramides in HDL leads to their decreased concentrations both in plasma and urine. Lastly, measuring the levels of these ceramides in type 1 diabetes will identify patients at high risk to develop nephropathy at different stages of the disease. To evaluate these hypotheses, we will conduct studies with three Specific Aims: 1) Determine whether the levels of sphingolipids and ApoM measured in the plasma collected at the beginning and at the end of the DCCT trial in a subgroup of patients are associated with the development and progression of diabetic nephropathy; 2) Compare the sphingolipid and ApoM concentrations in plasma and urine from matched Type 1 diabetes patients with normoalbuminuria with those with macroalbuminuria, with non-diabetic subjects with macroalbuminuria, and with healthy controls; 3) Determine if the observed differences in plasma total sphingolipid and ApoM concentrations which are associated with diabetes and albuminuria are localized to VLDL, LDL or HDL. Knowledge of plasma sphingolipid transport in diabetes and in nephropathy will direct our future studies investigating the potential for lipoprotein sphingoliid to alter cell metabolism, especially cells associated with diabetic kidney disease.