The effects of allelic variation in Pparg on skeletal metabolism

描述(由申请人提供)：项目摘要：目前，55%的50岁以上的美国人有或正在面临骨质疏松的风险。这项建议的长期目标是表征在饮食或合成配体激活该核受体的过程中，PPARG基因等位基因变异对骨骼代谢的影响。B6.C3H6T(6T)小鼠是一种人类年龄相关性骨丢失的模型，携带来自C3H/HeJ品系的PPARG等位基因，背景为C57BL/6J(B6)，并具有低骨密度(BMD)。膳食脂肪是PPARG蛋白的激活剂，已被发现与PPARG的等位基因变异相互作用，从而影响BMD。更具体地说，喂食高脂肪饮食会导致6T小鼠的骨密度降低，但不会导致B6小鼠的骨密度降低。在人类身上也发现了类似的相互作用。这项建议的第一个具体目标是识别和表征饮食脂肪影响骨获取的分子途径。影响PPARG或作为PPARG靶点的关键基因的基因表达将通过高通量定量实时聚合酶链式反应(QPCR)在B6和6T小鼠的肝脏和股骨中进行检测，这些小鼠喂食高脂肪或低脂肪食物。目前，60岁以上的美国人中约有21%患有糖尿病。噻唑烷二酮(TZD)是治疗II型糖尿病的常用药物，是PPARG的配体，已被证明对BMD有负面影响。在第二个具体目标中，罗格列酮(一种TZD)激活PPARG的体内后果将被表征，以确定对骨骼维持的影响。雌性B6和6T小鼠给予罗格列酮(20 mg/kg/d)治疗8周。将收集股骨，并对其进行骨密度、骨结构和骨髓肥胖症的表型鉴定。在另一组单独但相同处理的小鼠中，将收集骨骼和肝脏，并将通过QPCR检测在Aim One中确定的关键基因的表达。这一目标的目的是确定饮食脂肪和ROSI激活PPARG之间的区别和相似之处。胰岛素样生长因子-1是一种关键的骨生长因子，在体外受PPARG负调控。罗格列酮的治疗将扩大到包括5个近交系菌株，以确定血清IGF-1是否是罗格列酮引起的骨丢失的一个方便的替代标记物。与公共健康相关：这项研究将确定为什么在携带某些PPARG基因的人中，高脂肪饮食会导致低骨密度。此外，罗格列酮是一种常见的作用于PPARG的2型糖尿病药物，但该药物的治疗也可能降低骨密度。这项研究将确定罗格列酮是否会影响骨骼，以及在什么情况下。

DESCRIPTION (provided by applicant): Project summary: Currently 55% of American over the age of 50 have or are at risk for osteoporosis. The long term objective of this proposal is to characterize the impact of allelic variation in the Peroxisome Proliferator Activated Receptor Gamma (Pparg) gene on skeletal metabolism during activation of this nuclear receptor by dietary or synthetic ligand. The B6.C3H-6T (6T) mouse, a model of human age related bone loss, carries alleles from the C3H/HeJ strain for Pparg, on an otherwise C57BL/6J (B6) background, and has low Bone Mineral Density (BMD). Dietary fat is an activator of PPARG protein and has been found to interact with allelic variation in Pparg to influence BMD. More specifically, feeding a high fat diet results in low BMD in 6T but not B6 mice. A similar interaction has been found in humans. The first specific aim of this proposal is to identify and characterize the molecular pathways by which dietary fat impacts bone acquisition. Gene expression of key genes that affect or are targets of PPARG will be examined by high throughput Quantitative Real Time PCR (QPCR), in liver and femur from B6 and 6T mice fed a high or a low fat diet. Approximately 21 % of Americans over the age of 60 currently have diabetes. Thiazolidinediones (TZDs) are popular drugs for the treatment of Type II diabetes, are ligands for PPARG, and have been shown to negatively affect BMD. In the second specific aim, the in vivo consequences of PPARG activation by, Rosiglitazone (a TZD), will be characterized to determined the impact on skeletal maintenance. Groups of female B6 and 6T mice will be treated with Rosiglitazone (20 mg/kg/day) for 8 wks. Femurs will be collected and phenotyped for BMD, bone architecture and marrow adiposity. In a separate, but identically treated group of mice, bones and livers will be collected and the expression of key genes identified in Aim One will be examined by QPCR. The goal of this aim is to to ascertain differences and similarities between activation of PPARG by either dietary fat or Rosi. Insulin-like Growth factor-1 is a key growth factor for bone and in vitro is negatively regulated by PPARG. Treatment with Rosiglitazone will be expanded to include 5 inbred strains to determine if serum IGF-1 is a convenient surrogate marker for bone loss induced by Rosiglitazone. Relevance to Public Health: This research will determine why a high fat diet results in low bone density, in people carrying certain versions of the PPARG gene. In addition, Rosiglitazone is a common Type 2 Diabetes drug which acts on PPARG, but treatment with this drug may also decrease bone density. This research will determine if Rosiglitazone affects bone and under what circumstances.