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（由申请人提供）：骨量的维持需要破骨细胞（OC）和成骨细胞（OB）的综合活性。虽然它们在功能上是不同的，但它们都是极化的，并分别通过调节骨降解和骨合成分子的分泌来执行它们的活动。由于空泡H+ ATP酶插入骨附着的OC质膜和胶原溶解酶组织蛋白酶K的靶向分泌，骨吸收需要细胞外质子转运。类似地，骨骼合成涉及将特定基质蛋白（例如1型胶原蛋白）分泌到现有骨表面上。因此，骨细胞的胞吐能力是骨骼稳态的基础。调节分泌，也称为胞吐作用，需要细胞极性，其中细胞内含有货物的囊泡通过细胞骨架的组织被递送到胞吐质膜结构域，其在OC和OB中与骨并列。在到达胞吐位点后，含货物的囊泡通过许多连接步骤与质膜融合，包括突触结合蛋白（一种囊泡相关衔接子家族）与几种质膜驻留蛋白的高亲和力结合。我们的数据表明，突触结合蛋白VII调节胞吐的OC和OBs在细胞自主的方式。因此，缺乏突触结合蛋白VII的小鼠具有减少的重塑，并且是II型或低转换骨质疏松症的模型。细胞极性是胞吐的先决条件，由保守的信号传导途径调节，其中活化的cdc 42募集非典型蛋白激酶C，其磷酸化必需的下游靶标，包括非典型PKC如PKC;。我们发现RANKL介导的OC细胞骨架组织以及细胞再吸收骨的能力涉及cdc 42/PKC途径的激活。为这种姿势提供额外的支持，OC表达活性cdc 42水平增加的小鼠是骨质疏松症，而缺乏小GTdR的小鼠则患有骨硬化症。类似地，细胞特异性PKC缺失产生不能吸收或再吸收骨的OC。这些观察结果提示了一种模型，其中1）由cdc 42激活的PKC促进OC极化，2）极化后，突触结合蛋白VII控制OC对骨调节分子的胞吐作用。此外，Syt VII调节OB胞吐作用。因此，我们的具体目标是确定1）PKC信号促进OC极化和2）突触结合蛋白VII控制OC和OB的胞吐作用的机制。公共卫生相关性：维持骨量需要调节该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。