Actions of Parathyroid Hormone (PTH)/PTH related-peptide receptor in Osteocytes i

描述（由申请人提供）：骨细胞占所有骨细胞的90%以上，但对其功能或调节其活性的全身激素的参与知之甚少。这些细胞位于骨矿化基质深处的腔隙中，通过位于长细胞质过程末端的间隙连接相互交流，并与成骨细胞和破骨细胞交流，这些细胞质过程穿过骨隧道（管状管）。最近的研究支持骨细胞发挥主要“机械感觉”作用的理论，即它们受到剪切和拉伸力的刺激，产生局部细胞因子或体液因子（如NO和PGE2），并增加少数基因（如c-fos和IGF-1）的表达。甲状旁腺激素（PTH）是一种由甲状旁腺分泌的84个氨基酸的多肽，是钙、磷和骨骼稳态的主要生理调节剂，在临床上是治疗骨质疏松症唯一可用的合成代谢剂。该激素通过激活g蛋白偶联受体（1型PTH/PTHrP受体（PPR））对靶细胞产生作用，该受体在骨和肾中高度表达。成骨细胞系是骨中甲状旁腺激素作用的关键靶点，最近的证据表明，骨细胞可能在甲状旁腺激素的合成代谢作用中起重要作用。该项目的主要目标是了解PPRs在骨细胞中的作用，并确定这些细胞在介导激素对骨的影响中的作用。为了解决这些问题，将产生在骨细胞中特异性消融PPR表达的小鼠。10Kb-DMP1启动子在骨细胞中具有特异性活性，将在PPR基因两侧有lox-P位点的细胞中驱动他莫昔芬诱导的Cre表达。此外，将使用非诱导型10KbDMP1-Cre和8KbDMP1-Cre模型，并由我们的合作者提供。该动物模型将增强对甲状旁腺激素对骨骼作用的理解，并可指导新型治疗剂的开发。这些结果可能对甲状旁腺功能亢进、骨质疏松症和肾性骨营养不良等骨疾病的治疗具有重要意义。公共卫生相关性：如果成功，这一建议将显著提高我们对骨细胞中甲状旁腺激素和甲状旁腺激素受体作用的认识，并进一步增强我们对这些细胞的理解。这些研究的结果可能对治疗甲状旁腺功能亢进、骨质疏松症和肾性骨营养不良等骨疾病具有重要意义。因此，它与骨骼生物学的相关性很高。

DESCRIPTION (provided by applicant): Osteocytes comprise over 90% of all bone cells, yet little is known of their function(s) or of the involvement of systemic hormones in regulating their activity. These cells reside in the lacunae deep within the mineralized matrix of bone and communicate with one another and with osteoblasts and osteoclasts via gap junctions located at the ends of long cytoplasmic processes that course through tunnels (cannalicula) in the bone. Recent studies support the theory that osteocytes play a major "mechanosensory" role, whereby they are stimulated by shear and stretch forces to produce local cytokines or humoral factors (such as NO and PGE2) and to increase expression of few genes (such as c-fos and IGF-1). Parathyroid hormone (PTH), an 84-amino-acid polypeptide secreted by the parathyroid glands, is a major physiologic regulator of calcium, phosphorous and skeletal homeostasis and, clinically, is the only available anabolic agent to treat osteoporosis. The hormone exerts its effects on target cells via activation of a G-protein coupled receptor, the type-1 PTH/PTHrP receptor (PPR),that is highly expressed in bone and kidney. Cells of the osteoblastic lineage are key targets of PTH action in bone, and recent evidence suggests that osteocytes might be important in the anabolic effects of PTH. The main goal of this project is to understand the role of PPRs in osteocytes and to determine the role(s) of these cells in mediating the effects of the hormone on bone. To address these questions, mice in which PPR expression is specifically ablated in osteocytes will be generated. The 10Kb-DMP1 promoter, active specifically in osteocytes, will drive a Tamoxifen-inducible Cre expression in cells in which the PPR gene is flanked by lox-P sites. In addition a non-inducible 10KbDMP1-Cre and the 8KbDMP1-Cre models will be used and will be provided by our collaborators. This animal models will enable enhanced understanding of PTH action on bone and could direct the development of novel therapeutic agents. These results could have significant implications for therapy of bone disorders such as hyperparathyroidism, osteoporosis and renal osteodystrophy. PUBLIC HEALTH RELEVANCE: If successful this proposal will significantly advance our knowledge of the role of PTH and the PTH receptors in osteocytes and further enhance our understanding of these cells. Results derived from the studies proposed could have significant implications for therapy of bone disorders such as hyperparathyroidism, osteoporosis and renal osteodystrophy. Thus, its relevance is high for skeletal biology.