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，但对相关机制的了解仍然不完整，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信号传导积极调节破骨细胞（OC）的形成，但它也抑制成骨细胞（OB）的形成，并且需要TNF受体相关因子（TRAFs）向细胞因子受体募集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。尽管取得了这些进展，但没有NF-？B抑制剂的临床试验。我们之前报道过TRAF3(通常可以抑制NF-？B信号)限制了tnf诱导的OC形成。在目前的资助期内，我们扩展了这些研究，并在OC （LysM; TRAF3 cKO）和OB （Prx1; TRAF3 cKO）谱系细胞中产生了TRAF3条件缺失的小鼠。我们最近发表的初步数据表明，TRAF3的表达不仅在OC中是必需的，而且在OB谱系细胞中也是必需的，以维持小鼠正常的骨量。具体来说，我们发现RANKL通过自噬促进OC前体（ocp）中TRAF3的泛素化和降解，自噬抑制剂氯喹（CQ）抑制RANKL诱导的OC形成，并阻止PTH-和ovx诱导的骨吸收，但在OC- TRAF3 cKO小鼠中没有。这种破坏;traf3 cKO小鼠出现与年龄相关的骨质流失，OC数量增加，骨形成减少。骨髓基质细胞（BMSCs）来自Prx1；traf3 cKO小鼠表达高水平的RANKL，并显著降低OB分化。TGF吗?降低OBs的TRAF3水平这些发现揭示了TRAF3在OCs和OBs中新的重要作用，并表明抑制其降解可以防止各种临床情况下的骨质流失。在这个竞争性更新中，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，以及它对自噬降解的抑制

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.