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

描述(申请人提供)：骨细胞占所有骨细胞的90%以上，但对其功能或系统激素参与调节其活动知之甚少(S)。这些细胞驻留在骨矿化基质深处的腔隙中，彼此交流，并通过位于长细胞质突起末端的缝隙连接与成骨细胞和破骨细胞沟通，这些缝隙突起穿过骨骼中的隧道(小管)。最近的研究支持这样的理论，即骨细胞在剪切力和牵伸力的刺激下，发挥着主要的“机械感觉”作用，产生局部细胞因子或体液因子(如NO和PGE2)，并增加少数基因的表达(如c-fos和IGF-1)。甲状旁腺激素(PTH)是由甲状旁腺分泌的一种由84个氨基酸组成的多肽，是钙、磷和骨骼动态平衡的主要生理调节剂，临床上是治疗骨质疏松症的唯一有效的合成代谢药物。这种激素通过激活一种G蛋白偶联受体-1型PTH/PTHrP受体(PPR)来作用于靶细胞，该受体在骨骼和肾脏中高度表达。成骨细胞系的细胞是甲状旁腺激素在骨中作用的关键靶点，最近的证据表明骨细胞可能在甲状旁腺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PPR在骨细胞中的作用，并确定这些细胞在调节激素对骨的影响中的作用(S)。为了解决这些问题，将产生PPR在骨细胞中特异表达的小鼠。10kb-DMP1启动子在骨细胞中特异激活，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，还将使用非感应式10KbDMP1-CRE和8KbDMP1-CRE型号，并由我们的合作者提供。该动物模型将有助于加深对甲状旁腺激素对骨骼作用的了解，并可能指导新型治疗药物的开发。这些结果可能对甲状旁腺功能亢进症、骨质疏松症和肾性骨营养不良等骨病的治疗具有重要意义。公共卫生相关性：如果成功，这项建议将极大地提高我们对甲状旁腺素及其受体在骨细胞中的作用的了解，并进一步增强我们对这些细胞的理解。所提出的研究结果可能对甲状旁腺功能亢进症、骨质疏松症和肾性骨营养不良等骨骼疾病的治疗具有重要意义。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.