Mechanisms of Polarized Secretion by Bone Cells

骨细胞极化分泌的机制

• 批准号: 8274354
• 负责人: Steven L Teitelbaum
• 金额: $ 32.5万
• 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/8274354
• 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; Health; 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; TNFSF11 gene; Vesicle; atypical protein kinase C; bone; bone cell; bone mass; bone turnover; cathepsin K; extracellular; novel; 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（OCs）和成骨细胞（OBs）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运输，这是由于空泡H+ atp酶插入骨相关的OC质膜和胶原溶解酶组织蛋白酶k的靶向分泌的结果。类似地，骨骼合成涉及将特定基质蛋白（如1型胶原）分泌到现有骨表面。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传递到胞吐质膜结构域，在OCs和OBs中，胞吐质膜结构域与骨相对。到达胞外作用位点后，含有货物的囊泡通过一系列相关步骤与质膜融合，包括突触蛋白（一种囊泡相关接头家族）与几种质膜居住蛋白的高亲和力结合。我们展示了synaptotagmin VII以细胞自主的方式调节OCs和OBs的胞外分泌。因此，缺乏synaptotagmin VII的小鼠重塑减少，是II型或低周转率骨质疏松症的模型。细胞极性是胞外分泌的先决条件，由保守的信号通路调节，其中活化的cdc42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PKCs，如PKC；我们发现rankl介导的OC细胞骨架组织和细胞吸收骨的能力涉及cdc42/PKC的激活；途径。为这种姿势提供额外的支持，OCs表达活性cdc42水平升高的小鼠患有骨质疏松症，而缺乏小GTPase的小鼠患有骨质疏松症。同样，细胞特异性的PKC缺失；产生不能极化或吸收骨的oc。这些观测结果表明，1)PKC；由cdc42激活，促进OC极化和2)极化后，synaptotagmin VII通过OC控制骨调节分子的胞外分泌。此外，Syt VII调节OB胞吐。因此，我们的具体目标是确定以下机制：1)PKC；2) synaptotagmin VII控制OCs和OBs的胞外分泌。公共卫生相关性：骨量的维持需要调节该参数的细胞发挥最佳和协调的功能。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控制骨量的机制，以期产生治疗骨质疏松症等疾病的新药。