NLRP3 inflammasome Regulation of Bone Resorption

描述（由申请人提供）：Nod富含亮氨酸的重复与Pyrin结构域3（NLRP 3）炎性体是一种细胞内蛋白复合物，负责白细胞介素（IL）-1和IL-18的成熟。NLRP 3的功能获得性突变导致脑源性多系统炎性疾病（NOMID）。NOMID患者产生过量的IL-1，并表现出骨骼畸形和骨质减少，这表明组成性激活的NLRP 3（NOMID NLRP 3）显著影响骨重建。这些患者的关节病性病变对IL-1靶向治疗无效，这一发现表明IL-1的产生可能不是NOMID NLRP 3在骨骼中作用的唯一机制。事实上，这种炎性小体也参与裂解的聚（ADP-核糖）聚合酶1（PARP 1），一种新的机制NF-？B共活化和破骨细胞（OC）发育。然而，NOMID患者的骨质减少本身是否对IL-1抑制剂无效仍不清楚。我们发现 全面表达NOMID NLRP 3的小鼠模仿人类NOMID综合征，因为它们过度产生IL-1并减少骨量。进一步的初步数据表明，这种炎性小体在骨重建中具有更广泛的作用。首先，表达NOMID NLRP 3的小鼠，特别是在骨髓细胞或OC中表达的小鼠也具有低骨量，表明这种炎性小体的OC谱系作用。第二，NLRP 3炎性体促进PARP 1切割和OC形成，而PARP 1敲低抑制OC形成。这表明炎性小体促进PARP 1裂解可能是骨吸收超过IL-1产生的另一种机制。最后，骨基质降解产物激活NLRP 3，并刺激OC形成，这意味着这种炎性小体可能在所有高骨转换状态下都是活跃的。因此，我们的初步数据表明，NLRP 3炎性体激活不限于炎症条件，并可能代表一个基本的正反馈回路，放大骨吸收。该提议的中心假设是NLRP 3炎性体是以高骨转换为特征的炎性和非炎性病症中骨吸收的多功能调节剂。为了验证这一假设，我们将使用小鼠遗传模型和人类细胞系统：1）确定PARP 1和IL-1在NOMID NLRP 3炎性小体引起的骨吸收中的作用; 2）研究这种炎性小体在高骨转换的非炎性条件下的作用和激活机制。完成后，该项目将确定这种炎性小体在炎性和非炎性骨丢失中起着重要作用，从而将其定位为骨丢失疾病的潜在治疗靶点。

DESCRIPTION (provided by applicant): The Nod Leucine rich Repeat with a Pyrin domain 3 (NLRP3) inflammasome is an intracellular protein complex responsible for the maturation of interleukin (IL)-1¿ and IL-18. Gain-of-function mutations of NLRP3 cause neonatal-onset multisystem inflammatory disease (NOMID). NOMID patients produce excessive amounts of IL-1¿, and exhibit skeletal deformities and osteopenia, suggesting that constitutively activated NLRP3 (NOMID NLRP3) significantly impacts bone remodeling. The finding that arthropathic lesions in these patients are refractory to IL-1 targeted therapy suggests that IL-1 production may not be the only mechanism of NOMID NLRP3 action in the skeleton. Indeed, this inflammasome is also involved in the cleavage of poly(ADP-ribose) polymerase 1 (PARP1), a novel mechanism of NF-?B co- activation, and osteoclast (OC) development. However, whether osteopenia per se in NOMID patients is refractory to IL-1 inhibitors is still unclear. We find that mice globally expressing NOMID NLRP3 mimic the human NOMID syndrome as they over-produce IL-1¿ and diminished bone mass. Further preliminary data suggest a broader role of this inflammasome in bone remodeling. First, mice expressing NOMID NLRP3, specifically in myeloid cells or in OC also have low bone mass, suggesting an OC lineage action of this inflammasome. Second, NLRP3 inflammasome promotes PARP1 cleavage and OC formation, while PARP1 knockdown inhibits OC formation. This suggests that inflammasome promotion of PARP1 cleavage may be an alternative mechanism of bone resorption over IL-1¿ production. Finally, bone matrix degradation products activate NLRP3, and stimulate OC formation, implying that this inflammasome may be active in all states of high bone turnover. Thus, our preliminary data suggest that NLRP3 inflammasome activation is not restricted to inflammatory conditions, and may represent a fundamental positive feedback loop that amplifies bone resorption. The central hypothesis of this proposal is that the NLRP3 inflammasome is a multifunctional regulator of bone resorption in inflammatory and non-inflammatory conditions characterized by high bone turnover. To test this hypothesis, we will use mouse genetic models and human cell systems to: 1) Define the role of PARP1 and IL-1¿ in bone resorption caused by NOMID NLRP3 inflammasome; 2) Investigate the role and the mechanisms of activation of this inflammasome in non-inflammatory conditions of high bone turnover. Upon completion, this project will establish that this inflammasome plays a significant role in inflammatory and non-inflammatory bone loss, thus positioning it as a potential therapeutic target for diseases of bone loss.