Vitamin D Receptor Coactivators in Osteoblasts

描述（由申请人提供）：1，25-二羟基维生素D3（1，25（OH）2D 3）是维生素D内分泌系统的生物活性激素。它通过维生素D受体（VDR）发挥作用，通过增加肠道钙吸收和直接影响成骨细胞/破骨细胞活性来影响骨骼。本研究的总体目标是研究1，25（OH）2D 3和VDR在成骨细胞中的直接转录作用。为了实现这一目标，表达阵列鉴定了成骨细胞中由1，25（OH）2D 3诱导的几个新基因。该提案的重点是一个1，25（OH）2D 3诱导的基因，影响成骨细胞生物学，即脑膜瘤-1或MN 1。MN 1是一种转录因子，在核受体介导的转录中充当共激活因子。小鼠MN 1基因的缺失显著损害膜内骨化，导致颅骨骨骼发育缺陷。这些数据证明了MN 1在骨骼稳态中的重要生物学作用。我们的初步数据表明，MN 1在许多成骨细胞系中表达，并且其表达在成骨细胞中受1，25（OH）2D 3的调节。MN 1在成骨细胞中的异位表达抑制成骨细胞增殖，并且shRNA介导的MN 1表达的敲低减少体外成骨细胞分化标记物。这些研究是第一个解决MN 1在骨骼稳态中的功能。在这个提议中测试的一个主要假设是，VDR和1，25（OH）2D 3是MN 1基因表达和维持正常骨骼稳态所需的其他基因的有效调节剂。我们建议通过关注MN 1在成骨细胞功能中的持续表征来研究维生素D内分泌系统在骨骼稳态中的意义。具体而言，我们建议：1）确定MN 1在无骨和中轴骨的发育和维持中的重要性，2）确定在成骨细胞中通过1，25（OH）2D 3参与MN 1基因转录调节的分子机制，3）建立MN 1在成骨细胞中1，25（OH）2D 3激活的转录中的功能重要性，（4）确定MN 1在控制成骨细胞增殖和分化中的作用。这些研究将为维生素D内分泌系统在骨骼稳态中的直接作用提供新的见解，并提高对维持骨骼完整性所需关键因素的理解。公共卫生相关性：维生素D在骨和成骨细胞中作用的分子细节在很大程度上是未知的。我们的工作假设表明，维生素D控制MN 1辅激活蛋白的表达，并影响成骨细胞的功能。该提案的主要目标是确定成骨细胞中VDR-RXR异源二聚体的新靶基因。

DESCRIPTION (provided by applicant): 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) is the bioactive hormone of the vitamin D endocrine system. It functions via the vitamin D receptor (VDR) to impact bone by increasing intestinal calcium absorption and by directly affecting osteoblast/osteoclast activity. The overall goal of this research proposal is to examine direct transcriptional effects of 1,25(OH)2D3 and VDR in osteoblasts. Toward this goal, expression arrays identified several novel genes that are induced by 1,25(OH)2D3 in osteoblastic cells. This proposal focuses on one 1,25(OH)2D3-induced gene that impact osteoblast biology, namely Meningioma-1 or MN1. MN1 is a transcription factor that serves as a coactivator in nuclear receptor- mediated transcription. Deletion of the MN1 gene in mice markedly impairs intramembranous ossification leading to defects in cranial skeletal development. These data demonstrate an important biological role for MN1 in skeletal homeostasis. Our preliminary data show that MN1 is expressed in numerous osteoblastic cell lines and its expression is regulated by 1,25(OH)2D3 in osteoblastic cells in vitro and in vivo. Ectopic expression of MN1 in osteoblasts inhibits osteoblast proliferation and shRNA- mediated knock-down of MN1 expression reduces osteoblast differentiation markers in vitro. These studies are the first to address MN1 function in skeletal homeostasis. A major hypothesis tested in this proposal is that VDR and 1,25(OH)2D3 are potent regulators of MN1 gene expression and of other genes that are required to maintain normal skeletal homeostasis. We propose to examine the significance of the vitamin D endocrine system in skeletal homeostasis by focusing on the continued characterization of MN1 in osteoblast function. Specifically, we propose to: 1) determine the significance of MN1 in development and maintenance of the appendicular and axial skeletons, 2) determine the molecular mechanisms involved in the transcriptional regulation of the MN1 gene by 1,25(OH)2D3 in osteoblastic cells, 3) establish the functional significance of MN1 in 1,25(OH)2D3-activated transcription in osteoblastic cells, and 4) determine the role of MN1 in controlling osteoblast proliferation and differentiation. These studies will provide new insight into the direct actions of the vitamin D endocrine system in skeletal homeostasis and an improved understanding of key factors that are needed to maintain skeletal integrity. PUBLIC HEALTH RELEVANCE: The molecular details involved in vitamin D effects in bone and osteoblasts are largely unknown. Our working hypothesis states that vitamin D controls the expression of the MN1 coactivator protein and impacts osteoblast function. The main goal of this proposal is to define novel target genes for VDR-RXR heterodimers in osteoblasts.