Studies on the fate of the Osteoclast

描述（由申请人提供）：大多数形式的局部或全身性骨丢失是由于NF-？B介导的骨吸收增加和骨形成不足或减少。尽管最近取得了重大进展，但对所涉及机制的理解仍然不完整，治疗选择有限，药物的潜在不良反应限制了患者的依从性。NF-？B信号传导正调节破骨细胞（OC）形成，但它也抑制成骨细胞（OB）形成，并且需要将TNF受体相关因子（TRAF）募集至细胞因子受体以介导下游信号传导。因此，抑制NF-？B或TRAF功能可减少骨吸收并可能增加骨形成。尽管有这些进步，没有NF-？临床试验中的B抑制剂。我们以前报道过TRAF 3（通常抑制NF-？B信号）限制TNF诱导的OC形成。在当前的资助期内，我们扩展了这些研究，并产生了OC（LysM; traf 3 cKO）和OB（Prx 1; traf 3 cKO）谱系细胞中条件性缺失TRAF 3的小鼠。我们最近发表的和初步的数据表明，TRAF 3的表达不仅需要在OC中，而且需要在OB谱系细胞中随着年龄的增长维持小鼠的正常骨量。具体而言，我们发现RANKL通过自噬促进OC前体（OCP）中的TRAF 3泛素化和降解，自噬抑制剂氯喹（CQ）抑制RANKL诱导的OC形成，并阻止WT中PTH和OVX诱导的骨吸收，但在OC-Traf 3 cKO小鼠中则不然。Prx 1; traf 3 cKO小鼠出现年龄相关性骨丢失，OC数量增加，骨形成减少。来自Prx 1; traf 3 cKO小鼠的骨髓基质细胞（BMSC）表达高水平的RANKL，并具有显著降低的OB分化。转化生长因子这些发现揭示了TRAF 3在OC和OB中的新的和重要的作用，并表明抑制其降解可以防止各种临床情况下的骨丢失。在这种竞争性更新中，我们计划研究TRAF 3调节破骨细胞形成和抑制成骨细胞功能的机制，以及是否抑制自噬降解。 TRAF 3通过靶向OC和OBs防止骨丢失。我们的研究结果应确定TRAF 3作为一个新的和重要的治疗靶点，用于保存骨量，并确定CQ是否可以通过抑制骨细胞中的自噬来防止骨吸收和增加骨形成。

DESCRIPTION (provided by applicant): Most forms of localized or generalized bone loss are due to NF-?B-mediated increased bone resorption and inadequate or decreased bone formation. Despite recent major advances, understanding of the mechanisms involved remains incomplete, therapeutic options are limited, and potential adverse effects of drugs limit patient compliance. NF-?B signaling positively regulates osteoclast (OC) formation, but it also inhibits osteoblast (OB) formation, and requires recruitment of TNF receptor-associated factors (TRAFs) to cytokine receptors to mediate downstream signaling. Thus, strategies to inhibit NF-?B or TRAF functions could reduce bone resorption and potentially increase formation. Despite these advances, there are no NF-?B inhibitors in clinical trials. We reported previously that TRAF3 (which generally works to inhibit NF-?B signaling) limits TNF-induced OC formation. In the current funding period, we extended these studies and generated mice with TRAF3 conditionally deleted in OC (LysM;traf3 cKO) and OB (Prx1;traf3 cKO) lineage cells. Our recently published and preliminary data show that expression of TRAF3 is required not only in OC, but also in OB lineage cells to maintain normal bone mass in mice as they age. Specifically, we have found that RANKL promotes TRAF3 ubiquitylation and degradation in OC precursors (OCPs) via autophagy, and the autophagy inhibitor, chloroquine (CQ), inhibits RANKL-induced OC formation and prevents PTH- and OVX-induced bone resorption in WT, but not in OC-Traf3 cKO mice. Prx1;traf3 cKO mice develop age-related bone loss with increased OC numbers and reduced bone formation. Bone marrow stromal cells (BMSCs) from Prx1;traf3 cKO mice express high levels of RANKL and have markedly decreased OB differentiation. TGF? reduces TRAF3 levels in OBs. These findings reveal novel and important roles for TRAF3 in OCs and OBs and suggest that inhibition of its degradation should prevent bone loss in a variety of clinical settins. In this competitive renewal, we plan to study the mechanisms whereby TRAF3 regulates osteoclast formation and inhibits osteoblast functions, and if inhibition of autophagic degradation of TRAF3 prevents bone loss by targeting both OCs and OBs. Our findings should identify TRAF3 as a new and important therapeutic target for preservation of bone mass and determine if CQ can prevent bone resorption and increase bone formation by inhibiting autophagy in bone cells.