Skeletal Anabolism by Simultaneously Targeting the PTH1R and CaSR

描述(申请人提供)：骨质疏松症是一种以加速骨丢失和骨组织结构完整性恶化为特征的疾病，导致骨折易感性。当破骨细胞(OCL)的骨吸收速率大于成骨细胞(OBS)的骨形成速率时，就会导致这种衰弱的疾病。目前的证据表明，附件骨和椎骨以及颅面和口腔的骨结构都会受到影响，导致颌骨质量减少和牙周骨丢失，从而使牙科治疗复杂化。间歇性甲状旁腺激素(PTH)是FDA批准的唯一一种产生骨合成代谢并增强骨损伤修复的治疗方法。然而，甲状旁腺素的剂量仅限于短期使用，剂量相对较低，因为它具有不良的高钙素效应和在骨骼中的致癌潜力。因此，需要更好地了解甲状旁腺素的骨合成代谢作用和不良反应的分子和细胞机制，以制定加强甲状旁腺激素治疗的策略。我们假设OB系中细胞外钙敏感受体(CaSR)的激活是在附件和颅面部位对间歇性PTH产生骨合成代谢反应的重要步骤，与仿钙剂联合治疗将通过同时增强正常和骨折骨OB中的CaSR活性来增强间歇性PTH的骨合成代谢效应。为了验证这一假说，将采取一种药理学方法来确定通过共同注射类钙素NPS-R568来激活OBS中的CASR是否在不产生高钙血症的情况下增强衰老和雌激素缺乏小鼠模型中甲状旁腺素的骨合成代谢。这项应用旨在确定仿钙剂是否通过延长间歇性甲状旁腺激素的合成代谢窗口和/或增加其成骨能力来增强间歇性甲状旁腺激素的合成代谢。这将通过评估结构性骨参数、骨形成和骨吸收速率、组织形态计量学、骨中干细胞数量和血清骨转换标志物的时间变化来实现。使用OB特异的CaSR-KO小鼠模型，结合生化和骨骼分析，将采用功能丧失的方法来确定CaSR的表达是否对于(I)早期Ob的生长、存活和成熟以及(Ii)成熟Ob在PTH和PTH/拟钙化联合处理的细胞反应中的矿化功能是必需的。使用类似的方法，将确定在成年小鼠中，联合应用NPS-R568和PTH是否比单独使用PTH更能产生更强劲的胫骨和下颌骨骨折愈合。这项工作将揭示间歇性甲状旁腺激素和钙离子在骨骼合成代谢中的新的协同作用，并建立临床前治疗方案以恢复骨质疏松的骨骼和加速骨折的修复。

DESCRIPTION (provided by applicant): Osteoporosis is a disease characterized by accelerated bone loss and deterioration of structural integrity of bone tissue, which lead to bone fracture susceptibility. This debilitating disease results when the rate of bone resorption by osteoclasts (OCLs) is greater than the rate of bone formation by osteoblasts (OBs). Current evidence shows that appendicular and vertebral bone as well as the craniofacial and oral bone structures are affected, resulting in reduced jawbone mass and periodontal bone loss, which complicates dental treatments. Intermittent parathyroid hormone (PTH) administration is the only FDA-approved therapy that produces bone anabolism and enhances bone injury repair. However, PTH dosing is limited to a short-term use with a relatively low dose due to its adverse hypercalcemic effects and oncogenic potential in bone. Therefore, a better understanding of the molecular and cellular mechanisms underlying the osteoanabolic actions and adverse effects of PTH is required to devise strategies to enhance PTH therapy. We hypothesize that the activation of the extracellular calcium-sensing receptors (CaSR) in the OB lineages are essential steps in producing osteoanabolic responses to intermittent PTH at appendicular and craniofacial sites and that combined treatment with a calcimimetic will enhance the osteoanabolic effects of intermittent PTH by simultaneously potentiating CaSR activities in OBs in normal and fracture bones. To test this hypothesis, a pharmacological approach will be taken to determine whether activating CaSRs in OBs by co-injecting the calcimimetic NPS-R568 enhances osteoanabolism of PTH in mouse models of aging and estrogen deficiency without producing hypercalcemia. This application aims to establish whether calcimimetics enhance anabolism of intermittent PTH by extending its anabolic window and/or by increasing its capacity to build bone. This will be achieved by assessing temporal changes in structural bone parameters, bone-forming and bone-resorbing rates histomorphometrically, numbers of stem cells in bone, and serum bone turnover markers. A loss-of- function approach using an OB-specific CaSR-KO mouse model with the combined regimens followed by biochemical and skeletal analysis will be taken to ascertain whether CaSR expression is required for (i) the growth, survival, and maturation of early OBs, and (ii) the mineralizing functions of mature OBs in the response of the cells to PTH and combined PTH/calcimimetic treatments. Using similar methods, it will be determined whether co-administration of NPS-R568 and PTH produces more robust healing of tibial and mandibular fractures than administration of PTH alone in adult mice. This work will reveal novel synergistic actions of intermittent PTH and Ca2+ in producing skeletal anabolism and establish preclinical regimens to restore osteoporotic skeleton and accelerate bone fracture repair.