Studies on the fate of the Osteoclast

描述(申请人提供)：大多数形式的局限性或全身性骨丢失是由于核因子-κB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，但对所涉及的机制的了解仍然不完全，治疗选择有限，药物的潜在不良反应限制了患者的依从性。核因子-肿瘤坏死因子B信号对破骨细胞(OC)的形成有正向调节作用，但也抑制成骨细胞(OB)的形成，需要κ受体相关因子(TRAF)与细胞因子受体结合，介导下游信号传导。因此，抑制NF-κB或TRAF功能的策略可以减少骨吸收，并潜在地促进骨形成。尽管取得了这些进展，但临床试验中还没有出现核因子-κB抑制剂。我们之前报道过TRAF3(它通常作用于抑制 核因子-肿瘤坏死因子B信号转导)限制肿瘤坏死因子诱导的OC的形成。在目前的资助期间，我们延长了这些研究，并在OC(LysM；TRAF3 CKO)和OB(PRX1；TRAF3 CKO)系细胞中产生了TRAF3有条件缺失的小鼠。我们最近发表的初步数据表明，TRAF3不仅在OC中表达，而且在OB系细胞中也需要表达，以维持小鼠随年龄增长的正常骨量。具体地说，我们发现RANKL通过自噬促进了TRAF3泛素化和OC前体(OCP)的降解，自噬抑制剂氯喹(CQ)抑制了RANKL诱导的OC的形成，并阻止了PTH和OVX诱导的WT小鼠的骨吸收，但在OC-Traf3 CKO小鼠中没有。PRX1；TRAF3 CKO小鼠发生与年龄相关的骨丢失，OC数量增加，骨形成减少。来自PRX1和TRAF3 CKO小鼠的骨髓基质细胞(BMSCs)表达高水平的RANKL，并显著降低OB分化。转化生长因子降低OBS中TRAF3的水平。这些发现揭示了TRAF3在OCS和OBS中的新的和重要的作用，并表明抑制其降解应该防止在各种临床环境中的骨丢失。在这一竞争性更新中，我们计划研究TRAF3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 TRAF3通过靶向OCS和OBS来预防骨丢失。我们的发现将确认TRAF3是一种新的重要的骨量保护治疗靶点，并确定CQ是否可以通过抑制骨细胞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-κB-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-κB 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-κB or TRAF functions could reduce bone resorption and potentially increase formation. Despite these advances, there are no NF-κB inhibitors in clinical trials. We reported previously that TRAF3 (which generally works to inhibit NF-κB 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. TGFß 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.