Mechanisms of Rankl Mediated Osteoclast Activation

描述(申请人提供)：RANKL诱导的破骨细胞(OC)与骨接触时，基质来源的信号会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一个孤立的微环境。矿化基质的最终降解是由褶皱的边界介导的，褶皱的边界是细胞的吸收细胞器，包含在这个有限的空间内。因此，介导褶皱边缘形成的细胞内分子及其输送到吸收微环境中的骨降解产物是当前或潜在的治疗靶点。褶皱边缘是通过将溶酶体衍生的空泡插入到与骨相对的质膜中而形成的，我们已经确定这种质膜是在突触素VII(SYT VII)的保护下发生的。这些囊泡含有空泡H+ATPase和组织蛋白酶K，它们分别动员骨骼的矿物相和有机相。不能将分泌囊泡输送到与骨相对的质膜上会阻止吸收。自噬是蛋白质和细胞器被隔离成自噬小体并被降解的一种保守途径。就像褶皱的边界一样，自噬小体与溶酶体融合。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，就像SytVII缺乏一样，缺乏自噬蛋白ATG5，通过阻止组织蛋白酶K进入吸收微环境来抑制骨降解。这一观察反映了ATG5缺乏的小鼠肠道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通过抑制分泌性囊泡极化来介导RANKL诱导的骨吸收。因此，我们补充的特定目的是确定自噬蛋白ATG5介导RANKL诱导的骨吸收的机制。 公共卫生相关性：抑制骨吸收仍然是我们治疗骨质疏松症的主要场所。从补充的特定靶点获得的信息可能会增加我们潜在的抗骨吸收治疗靶点。

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.