NLRP3 inflammasome Regulation of Bone Resorption

描述(申请人提供)：富含亮氨酸重复序列的NLRP3炎症体是一种细胞内蛋白质复合体，负责白介素1和白介素18的成熟。NLRP3功能获得突变导致新生儿发病的多系统炎症性疾病(NOMID)。NOMID患者产生过多的IL-1，并表现出骨骼畸形和骨量减少，这表明结构性激活的NLRP3(NOMID NLRP3)显著影响骨重建。这些患者的关节病变对IL-1靶向治疗无效的发现表明，IL-1的产生可能不是NOMID NLRP3在骨骼中作用的唯一机制。事实上，这个炎性小体也参与了聚(ADP-核糖)聚合酶1(PARP1)的裂解，这是一种新的核因子-B共激活机制，并参与了破骨细胞(OC)的发育。然而，NOMID患者的骨量减少本身是否对IL-1抑制剂无效仍不清楚。我们发现 全球表达NOMID NLRP3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发挥着更广泛的作用。首先，表达NOMID NLRP3的小鼠，特别是在髓系细胞或OC中表达的小鼠也有较低的骨量，这表明这种炎症体具有OC谱系作用。第二，NLRP3炎性小体促进PARP1的裂解和OC的形成，而PARP1基因敲除则抑制OC的形成。这提示炎性小体促进PARP1裂解可能是骨吸收的另一种机制，而不是IL-1的产生。最后，骨基质降解产物激活NLRP3，并刺激OC的形成，这意味着这个炎症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，NLRP3炎症小体的激活并不局限于炎症条件，可能代表了一个放大骨吸收的基本正反馈回路。这一建议的中心假设是，NLRP3炎症小体是一种多功能的骨吸收调节因子，在炎症性和非炎症性条件下以高骨转换为特征。为了验证这一假说，我们将使用小鼠遗传模型和人类细胞系统：1)确定PARP1和IL-1β在NOMID NLRP3炎症性小体引起的骨吸收中的作用；2)研究这种炎症性小体在高骨转换的非炎性条件下的激活作用和机制。该项目完成后，将确定该炎症性小体在炎症性和非炎症性骨丢失中发挥重要作用，从而将其定位为治疗骨丢失疾病的潜在靶点。

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.