MECHANISMS OF POLARIZED SECRETION BY BONE CELLS

骨细胞偏振分泌的机制

• 批准号: 7858352
• 负责人: Steven L Teitelbaum
• 金额: $ 33.86万
• 依托单位: WASHINGTON UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-06-01 至 2014-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7858352
• 关键词: Affinity; Albers-Schonberg disease; Binding; Bone Resorption; Bone Surface; Cell Polarity; Cell membrane; Cell physiology; Cells; Collagen Type I; Cytoskeleton; Data; Disease; Enzymes; Exocytosis; Family; Homeostasis; Link; Maintenance; Mediating; Modeling; Monomeric GTP-Binding Proteins; Mus; Osteoblasts; Osteoclasts; Osteoporosis; Pathway interactions; Pharmaceutical Preparations; Posture; Proteins; Protons; Recruitment Activity; Signal Pathway; Signal Transduction; Site; Vesicle; atypical protein kinase C; bone; bone cell; bone mass; bone turnover; cathepsin K; extracellular; novel; public health relevance; skeletal; synaptotagmin; synaptotagmin VII; vacuolar H+-ATPase

DESCRIPTION (provided by applicant): Maintenance of bone mass requires the integrated activity of osteoclasts (OCs) and osteoblasts (OBs). While they are functionally distinct, both are polarized and execute their activities by regulated secretion of bone-degrading and -synthesizing molecules, respectively. Bone resorption necessitates extracellular proton transport as a result of insertion of the vacuolar H+ATPase into the bone-apposed OC plasma membrane and targeted secretion of the collagenolytic enzyme cathepsin K. Similarly, skeletal synthesis involves secretion of specific matrix proteins such as type 1 collagen onto existing bone surfaces. Thus, the exocytic capacity of bone cells is fundamental to skeletal homeostasis. Regulated secretion, also called exocytosis, requires cell polarity in which intracellular, cargo-containing vesicles are delivered, by organization of the cytoskeleton, to an exocytic plasma membrane domain, which in OCs and OBs is that apposed to bone. Upon arrival at the site of exocytosis, the cargo-containing vesicles fuse with the plasma membrane via a number of linked steps, including high affinity binding of a synaptotagmin, a family of vesicle-associated adaptors, with several plasma membrane-residing proteins. We show data that synaptotagmin VII regulates exocytosis by OCs and OBs in a cell-autonomous manner. In consequence, mice lacking synaptotagmin VII have decreased remodeling and are a model for type II or low turnover osteoporosis. Cell polarity, a pre-requisite for exocytosis, is regulated by a conserved signaling pathway wherein activated cdc42 recruits an atypical protein kinase C, which phosphorylates essential downstream targets, including atypical PKCs such as PKC;. We find that RANKL-mediated organization of the OC cytoskeleton, and the cell's capacity to resorb bone, involve activation of the cdc42/PKC; pathway. Providing additional support for this posture, mice whose OCs express increased levels of active cdc42 are osteoporotic and those lacking the small GTPase have osteopetrosis. Similarly, cell-specific deletion of PKC; generates OCs that fail to polarize or resorb bone. These observations suggest a model in which 1) PKC;, activated by cdc42, promotes OC polarization and 2) following polarization, synaptotagmin VII controls exocytosis of bone- regulating molecules by OCs. Additionally Syt VII regulates OB exocytosis. Hence, our specific aims are to determine the mechanisms by which 1) PKC; signaling promotes OC polarization and 2) synaptotagmin VII controls exocytosis by OCs and OBs. PUBLIC HEALTH RELEVANCE: Maintenance of bone mass requires optimal and coordinated function of the cells regulating this parameter. We have identified novel proteins that individually control bone turnover. We propose to identify the mechanisms by which these two proteins control bone mass, with the view of generating novel drugs to treat diseases such as osteoporosis.

描述(申请人提供)：骨量的维持需要破骨细胞(OCs)和成骨细胞(OBS)的整合活动。虽然它们在功能上是不同的，但它们都是极化的，分别通过调节骨降解和合成分子的分泌来执行它们的活动。骨吸收需要细胞外质子转运，这是由于空泡H+ATPase插入到与骨相关的OC质膜中，并靶向分泌胶原酶组织蛋白酶K。类似地，骨骼合成涉及到分泌特定的基质蛋白，如在现有的骨表面上分泌1型胶原。因此，骨细胞的胞吐能力是骨骼动态平衡的基础。受调节的分泌，也称为胞吐作用，需要细胞的极性，在细胞内，含有货物的囊泡通过细胞骨架的组织被输送到胞外的质膜域，在OCS和OBS中是与骨相对的。当到达胞吐部位时，含货物的囊泡通过一系列相连的步骤与质膜融合，包括与几种质膜驻留蛋白高亲和力结合突触素，一种囊泡相关的适配器家族。我们的数据表明，突触素VII以一种细胞自主的方式调节OCS和OBS的胞吐。因此，缺乏突触素VII的小鼠重塑减少，是II型或低周转率骨质疏松症的模型。细胞极性是胞吐作用的先决条件，由一条保守的信号通路调节，其中激活的CDC42招募非典型蛋白激酶C，该非典型蛋白激酶C可磷酸化重要的下游靶标，包括非典型PKC；我们发现，RANKL介导的OC细胞骨架的组织和细胞吸收骨的能力，涉及到CDC42/PKC途径的激活。为这一姿势提供额外的支持，OCS表达活性CDC42水平增加的小鼠患有骨质疏松症，而那些缺乏小GTP酶的小鼠患有骨石化。同样，PKC的细胞特异性缺失会产生不能极化或吸收骨的OCS。这些观察结果提出了一种模型，在该模型中，1)被Cdc42激活的PKC促进OC极化，2)极化后，synaptopagmin VII控制OCS对骨调节分子的胞吐。此外，SYT VII还调节OB的胞吐作用。因此，我们的具体目标是确定1)PKC信号促进OC极化的机制，2)synaptopagmin VII控制OCS和OBS的胞吐。与公共健康相关：维持骨量需要调节这一参数的细胞的最佳和协调功能。我们已经确定了单独控制骨转换的新蛋白质。我们建议确定这两种蛋白质控制骨量的机制，以期产生治疗骨质疏松症等疾病的新药。