Studies of the Fate of the Osteoclast

描述(申请人提供)：破骨细胞是常见骨病(包括类风湿性关节炎和绝经后骨质疏松症)的骨骼建模和重塑以及介导骨丢失所必需的，在这些疾病中，促炎症细胞因子(如肿瘤坏死因子)水平增加，并通过RANKL和三组转录因子：核因子-？B、c-Fos和NFATc1直接或间接推动破骨细胞的形成。这些基因的表达对于破骨细胞的形成是必不可少的。RANKL/RANK信号通路通过典型的核因子-β1/p65和另一条核因子-β2/RelB途径。到目前为止，对破骨细胞中的核因子-βB的研究大多集中在经典途径上，而对核因子-β2和RelB在调节破骨细胞和其他骨细胞中的功能作用知之甚少。最近，我们发现，肿瘤坏死因子诱导了核因子-β2的表达，并且核因子-β2的缺失增加了肿瘤坏死因子诱导的破骨细胞的形成。肿瘤坏死因子转基因/核因子B2-/-小鼠的关节侵蚀、炎症和全身性骨丢失比肿瘤坏死基因转基因小鼠更早、更严重。此外，我们发现RelB基因缺失的小鼠有轻微的骨石化。这些发现强调了替代途径在骨骼中的重要性，并表明除了刺激破骨细胞形成的已知作用外，肿瘤坏死因子还具有限制RANKL诱导的骨丢失的新作用。根据我们的初步数据，我们假设，肿瘤坏死因子可以诱导核因子-β2的表达，以限制RANKL刺激的破骨细胞的形成，而对核因子-β2/受体B表达的调控将直接影响破骨细胞的功能。这一假设将在以下三个具体目标中得到检验。在目标1中，我们将确定核因子-β2是否通过控制典型的和替代的核因子-βB通路中的信号来限制OC的形成。在目标2中，我们将确定核因子-β2和RelB在破骨细胞形成和活性中的作用。在目标3中，我们将确定过表达的核因子-βB2p100在肿瘤坏死因子诱导的骨丢失中的作用。我们建议的研究应该确定核因子-β2和RelB在破骨细胞形成和活性中的作用，并提供概念证据，证明它们是限制细胞因子刺激的骨丢失的新的治疗干预措施的有力候选者。与公共健康相关的破骨细胞是降解骨骼的细胞，在常见疾病中，如类风湿性关节炎，破骨细胞的过度活动会导致骨丢失。我们建议的研究，使用这些疾病的动物模型，应该会导致更好地理解破骨细胞活动是如何被调节的，并最终开发出一种新的治疗方法来限制这些骨骼疾病的这种活动。

DESCRIPTION (provided by applicant): Osteoclasts are essential for bone modeling and remodeling and mediate bone loss in common bone diseases, including rheumatoid arthritis and postmenopausal osteoporosis, in which levels of proinflammatory cytokines, such as TNF, are increased and drive osteoclast formation both directly and indirectly through RANKL and three sets of transcription factors: NF-?B; c-Fos; and NFATc1. Expression of these is essential for osteoclast formation. RANKL/RANK signals through a canonical NF-?B1/p65 and an alternative NF-?B2/RelB pathway. To-date, most studies of NF-?B in osteoclasts have focused on the canonical pathway, and much less is known about the functional roles of NF-?B2 and RelB in regulating osteoclasts and other bone cells. Recently, we found that TNF induces NF-?B2 expression and that deletion of NF-?B2 increases TNF-induced osteoclast formation. TNF transgenic/NF-?B2-/- mice develop earlier and more severe joint erosion and inflammation and systemic bone loss than TNF-Tg mice. Furthermore, we found that RelB null mice have mild osteopetrosis. These findings highlight the importance of the alternative pathway in bone and suggest a new role for TNF to limit RANKL-induced bone loss in addition to its known role to stimulate osteoclast formation. Based on our preliminary data, we hypothesize that TNF can induce NF-?B2 expression to limit osteoclast formation stimulated by RANKL and that manipulation of NF-?B2/RelB expression will directly affect osteoclast functions. This hypothesis will be tested in the following 3 Specific Aims. In Aim 1, we will determine if NF-?B2 limits OC formation by controlling signaling in both the canonical and alternative NF-?B pathways. In Aim 2, we will determine the roles of NF-?B2 and RelB in osteoclast formation and activity. In Aim 3, we will determine the effects of over-expression of NF-?B2p100 on TNF-induced bone loss. Our proposed studies should define the roles of NF-?B2 and RelB in osteoclast formation and activity and provide proof of concept that they are strong candidates for novel therapeutic intervention to limit cytokine-stimulated bone loss. PUBLIC HEALTH RELEVANCE Osteoclasts are the cells that degrade bone and over-activity of them causes bone loss in common diseases, such as rheumatoid arthritis. Our proposed studies, using animal models of these diseases, should lead to a better understanding of how osteoclast activity is regulated and eventually to the development of a novel therapy to limit this activity in these bone disorders.