VITAMIN D RECEPTOR ABLATION: DIRECT AND INDIRECT CONSEQUENCES

维生素 D 受体消融：直接和间接后果

基本信息

批准号：
7986858
负责人：
Marie Demay
金额：
$ 2.77万
依托单位：
MASSACHUSETTS GENERAL HOSPITAL
依托单位国家：
美国
项目类别：
财政年份：
2010
资助国家：
美国
起止时间：
2010-02-01 至 2010-04-30
项目状态：
已结题

来源：
https://reporter.nih.gov/project-details/7986858
关键词：
Ablation Address Alopecia Apoptosis Attenuated Biological Assay Biological Models Bone Development Cell Lineage Cells Chondrocytes Cutaneous Development Diet Epiphysial cartilage Femoral Fractures Fracture Gene Expression Goals Hair Hair follicle structure Histologic Homeostasis Human Hypophosphatemia Immunoprecipitation In Situ Hybridization Intestines Investigation Ions Knockout Mice Life Ligands Mediating Mediator of activation protein Mesenchymal Stem Cells Metatarsal bone structure Minerals Modeling Molecular Mus Natural regeneration Nuclear Receptors Osteogenesis Osteomalacia Pathway interactions Play Prevention Rickets Role Secondary Hyperparathyroidism Signal Transduction Skeletal Development Skeleton Staging Stem cells Study models System Transgenic Mice Vitamins base bone morphogenetic protein 2 extracellular in vivo inorganic phosphate keratinocyte long bone novel postnatal prevent receptor reconstitution repaired self-renewal skeletal

项目摘要

The investigations in this proposal are focused on identifying the molecularbasis for the direct and indirect consequences ofVitamin D Receptor (VDR) ablation. VDRknockoutmice develophypocalcemia and secondary hyperparathyroidism which, in turn, leads to hypophosphatemia. They also develop rickets and osteomalacia. However,when placed on a special diet that maintains normal mineral ion levels, the VDR null mice have histologically, histomorphometrically and biomechanicallynormal long bones, thus the skeletal effects of VDR ablation are indirect and are a consequence of impaired VDRaction in the intestine which results in abnormal mineral ion homeostasis. This observation led us to focus our investigations on the pathophysiological basis for the development of rickets, which is an indirect consequence ofVDR ablation. We demonstrated that the growth plate abnormalities in the VDRnull mice are a consequenceof hypophosphatemia, which leads to expansion ofthe late hypertrophic chondrocyte layer due to impaired apoptosis ofthese cells. Since hypophosphatemia leads to impaired terminal chondrocytedifferentiation during postnatal life, studies are proposed to address the hypothesis that phosphate restriction also impairs chondrocyte differentiation during endochondral skeletal development and skeletal repair. Investigations will be performed using the ex vivo mouse metatarsal culture system and the in vivo femoral fracture repair models. These studies will identify developmental pathways that are interrupted byhypophosphatemia, an indirect consequence ofVDR ablation. Analogous to humans with VDRmutations, VDRnull mice have hair perinatally,but develop alopecia. Hair reconstitution assays and studies in transgenic mice demonstrate that VDRexpression in keratinocytes is both necessary and sufficient for the prevention of alopecia,thus the effects of the VDRin this cell are direct. We have also demonstrated that the actions ofthe VDRrequired to prevent alopecia are ligand- independent, thus reflect novel molecular actions of this nuclear receptor. Investigations in this proposal will address the hypothesis that the VDRis a key regulator ofthe canonical Wnt signalingpathway in keratinocyte stem cells and that these ligand-independent actions ofthe VDRare required for cutaneous homeostasis. The goal of these studies is not to study keratinocytebiologyper se, but rather to use this model system to characterize the molecularpathway and molecular partners involved in mediating these unique actions ofthe unliganded VDR. Thus, using the keratinocyte as a model,these studies will identify the novel molecular actions of the VDRwhich prevent the development of alopecia, a direct consequence ofVDR ablation.

该提案中的研究重点是确定直接和维生素 D 受体 (VDR) 消融的间接后果。 VDR基因敲除小鼠出现低钙血症继发性甲状旁腺功能亢进症反过来又导致低磷血症。他们还会患佝偻病和骨软化症。然而，当采用维持正常矿物质离子水平的特殊饮食时， VDR 缺失小鼠具有组织学、组织形态测量和生物力学正常的长骨，因此 VDR 消融对骨骼的影响是间接的，是肠道中 VDR 作用受损的结果这导致矿物质离子稳态异常。这一观察结果使我们将调查重点放在佝偻病发生的病理生理学基础，这是 VDR 的间接后果消融。我们证明 VDRnull 小鼠的生长板异常是以下因素的结果低磷血症，由于受损而导致晚期肥大软骨细胞层扩张这些细胞的凋亡。由于低磷血症会导致终末软骨细胞分化受损在出生后的生活中，建议进行研究来解决磷酸盐限制也会损害软骨内骨骼发育和骨骼修复过程中的软骨细胞分化。调查将使用离体小鼠跖骨培养系统和体内股骨骨折修复进行模型。这些研究将确定被低磷血症中断的发育途径，低磷血症是一种 VDR 消融的间接后果。与携带 VDR 突变的人类类似，VDR 缺失小鼠在围产期有毛发，但会出现脱发。转基因小鼠的毛发重建测定和研究表明，角质形成细胞中的 VDR 表达对于预防脱发来说既必要又充分，因此 VDR 在该细胞中的作用是直接的。我们还证明了 VDR 预防脱发所需的作用是配体- 独立，从而反映了该核受体的新分子作用。对此提案的调查将解决了以下假设：VDR 是经典 Wnt 信号通路的关键调节因子角质形成细胞干细胞，并且 VDR 的这些配体独立作用是皮肤皮肤所需的体内平衡。这些研究的目的不是研究角质形成细胞生物学本身，而是使用该模型系统来表征参与介导这些独特的分子途径和分子伙伴未配资的 VDR 的行动。因此，使用角质形成细胞作为模型，这些研究将确定新的 VDR 的分子作用可防止脱发的发生，脱发是 VDR 的直接后果消融。