Mechanisms of Rankl Mediated Osteoclast Activation

描述（由申请人提供）：与骨接触后，rankl诱导的破骨细胞（OC）中的基质来源信号促使细胞极化其细胞骨架，最终在多核细胞和骨骼表面之间形成孤立的微环境。矿化基质的最终降解是由褶皱边界介导的，褶皱边界是oc独特的结构，是细胞的吸收细胞器，包含在这个有限的空间内。因此，介导皱边形成的细胞内分子和它们传递到吸收微环境中的骨降解产物是当前或潜在的治疗靶点。皱褶边界是由溶酶体衍生的液泡插入骨相关的质膜形成的，我们已经建立了在突触蛋白VII （Syt VII）的庇护下发生。这些囊泡含有空泡H+ atp酶和组织蛋白酶K，它们分别调动骨的矿物质和有机相。不能将分泌囊泡运送到与骨相对的质膜，会阻碍吸收。自噬是一种保守的途径，蛋白质和细胞器被隔离到自噬体中并被降解。像皱边一样，自噬体与溶酶体融合。因此，在骨吸收和自噬机制之间存在理论上的共性。在这方面，我们发现像SytVII缺乏一样，自噬蛋白Atg5的缺乏通过阻止组织蛋白酶K转运到吸收微环境中来抑制骨降解。这一观察结果反映了小鼠、缺乏atg5的肠Paneth细胞和克罗恩病患者的囊泡极化失败。因此，我们假设自噬蛋白Atg5通过抑制分泌囊泡极化来介导rankl诱导的骨吸收。因此，我们补充的具体目标是确定自噬蛋白Atg5介导rankl诱导的骨吸收的机制。

DESCRIPTION (provided by applicant): Upon contact with bone, matrix-derived signals in the RANKL-induced osteoclast (OC) prompt the cell to polarize its cytoskeleton, eventuating in formation of an isolated microenvironment between the polykaryon and skeletal surface. Ultimate degradation of mineralized matrix is mediated by the ruffled border, an OC-unique structure which is the cell's resorptive organelle, contained within this confined space. Thus, the intracellular molecules mediating ruffled border formation and the bone-degrading products they deliver into the resorptive microenvironment are current or potential therapeutic targets. The ruffled border is formed by insertion of lysosome-derived vacuoles into the bone- apposed plasma membrane which we have established occurs under the aegis of synaptotagmin VII (Syt VII). These vesicles contain the vacuolar H+ATPase and cathepsin K which mobilize the mineral and organic phases of bone, respectively. Failure to deliver secretory vesicles to the bone-apposed plasmalemma arrests resorption. Autophagy is a conserved pathway by which proteins and organelles are sequested into autophagosomes and degraded. Like the ruffled border, autophagosomes fuse with lysosomes. Thus, a theoretical commonality exits between the mechanisms of bone resorption and autophagy. In this regard, we find that like SytVII deficiency, absence of the autophagy protein, Atg5, dampens bone degradation by preventing transport of cathepsin K into the resorptive microenvironment. This observation mirrors the failure of vesicle polarization in murine, Atg5-deficient intestinal Paneth cells and those of patients with Crohn's disease. We therefore hypothesize that the autophagy protein, Atg5, mediates RANKL-induced bone resorption by inhibiting secretory vesicle polarization. Thus, our supplemental specific aim is to determine the mechanism by which the autophagy protein, Atg5, mediates RANKL-induced bone resorption. PUBLIC HEALTH RELEVANCE: Inhibition of bone resorption remains our major venue for treating osteoporotic diseases. Information garnered from the supplemental Specific Aim may add to our armamentarium of potential anti-bone resorption therapeutic targets.