The Role of Leptin in Inflammation-Driven Bone Loss

项目总结 瘦素最初被认为是能量代谢的调节剂，是正常骨骼生长和发育所必需的 周转率，使脂肪因子成为结合最佳骨积累和周转率的有吸引力的候选 平衡能源供应。然而，并非所有瘦素的骨骼活动都是有益的；有令人信服的 瘦素通过促进致炎级联反应参与衰老相关骨骼病变的证据 调节炎症导致的骨丢失。调节骨骼活动的分子机制是 定义不明确。我们有强有力的初步数据表明，瘦素影响骨代谢，两者 通过激活细胞(主要是免疫细胞)上的瘦素受体(OB-R)对其有利和不利 来源于造血干细胞(HSCs)。在此基础上，我们假设：(1)瘦素通过 免疫细胞是骨骼正常生长、成熟和更新所必需的，但(2)在 慢性炎症，免疫细胞传递瘦素信号促进净骨质丢失。拟议的研究将 通过实现两个特定的目标，在雄性和雌性小鼠身上测试这些假设。具体目标1： 确定免疫细胞的瘦素信号对骨积累和骨转换平衡的贡献。 我们将用来自OB-R+的HSCs重建生长和成年雄性和雌性小鼠的免疫系统 野生型(WT)或OB-R-db/db小鼠通过过继转移来确定OB-R对 免疫细胞对瘦素对生长期小鼠骨积累和成年小鼠周转平衡的调节， 分别进行了分析。然后我们将确定瘦素的骨骼活动是否主要通过OB-R在细胞上介导 过继将OB-R+和OB-R-单核细胞转移到小鼠的破骨细胞谱系中 形成破骨细胞的能力(CCR2-小鼠)。特定目标2：确定瘦素信号的作用 免疫细胞对炎症导致的骨丢失的保护作用。我们将重建不断增长的免疫系统和 成年雄性和雌性小鼠与来自OB-R+或OB-R-小鼠的HSCs作为特异性靶点1并诱导局部 通过在头盖骨上放置聚乙烯颗粒来模拟无菌假体周围的骨丢失而产生炎症。这些 研究将确定OB-R对免疫细胞在炎症引起的骨丢失中的总体贡献。这个 OB-R对免疫细胞亚群在正常骨转换平衡和颗粒诱导的骨溶解中的作用 然后将OB-R+和OB-R-免疫细胞亚群植入成年小鼠体内进行评估 不能产生/招募单核细胞(CCR2-)、T细胞(TCRA KO)、B细胞(MUMT-)或肥大细胞(KitW-sh)的小鼠。 这项研究的成功完成将通过扩展现有的概念对该领域产生重大影响 瘦素在骨骼健康和疾病中的作用。我们的方法将提供一个强大的工具 揭示瘦素对骨骼和免疫系统的复杂作用机制。这个 拟议的研究有可能为制定干预措施提供新的见解 瘦素介导的炎症级联反应不会影响脂肪因子有益的骨骼活动。

PROJECT SUMMARY Leptin, originally identified as a regulator of energy metabolism, is required for normal bone growth and turnover, making the adipokine an attractive candidate for coupling optimal bone accrual and turnover balance to energy availability. However, not all skeletal actions of leptin are beneficial; there is compelling evidence that leptin contributes to aging-related skeletal pathologies by promoting a proinflammatory cascade mediating inflammation-driven bone loss. The molecular mechanisms mediating the skeletal actions are poorly defined. We have strong preliminary data indicating that leptin influences bone metabolism, both beneficially and detrimentally, by activating leptin receptor (OB-R) on cells (predominately immune cells) derived from hematopoietic stem cells (HSCs). Based on this, we hypothesize that: (1) leptin signaling by immune cells is necessary for normal bone growth, maturation and turnover, but (2) in the presence of chronic inflammation, leptin signaling by immune cells promotes net bone loss. The proposed research will test these hypotheses in male and female mice by accomplishing two Specific Aims. Specific Aim 1: Determine the contribution of leptin signaling by immune cells to bone accrual and turnover balance. We will reconstitute the immune system of growing and adult male and female mice with HSCs from OB-R+ wild type (WT) or OB-R- db/db mice using adoptive transfer to establish the overall contribution of OB-R on immune cells to leptin regulation of bone accrual in growing mice and turnover balance in adult mice, respectively. We will then determine if the skeletal actions of leptin are primarily mediated via OB-R on cells in the osteoclast lineage by adoptively transferring OB-R+ and OB-R- monocytes into mice with reduced ability to form osteoclasts (Ccr2- mice). Specific Aim 2: Determine the contribution of leptin signaling by immune cells to inflammation-driven bone loss. We will reconstitute the immune system of growing and adult male and female mice with HSCs from OB-R+ or OB-R- mice as in Specific Aim 1 and induce local inflammation by placing polyethylene particles over calvaria to model aseptic periprosthetic bone loss. These studies will establish the overall contribution of OB-R on immune cells to inflammation-driven bone loss. The contribution of OB-R on immune cell subsets to normal bone turnover balance and particle-induced osteolysis in adult mice will then be evaluated following engraftment of subsets of OB-R+ and OB-R- immune cells into mice unable to generate/recruit monocytes (Ccr2-), T-cells (Tcra KO), B-cells (muMT-), or mast cells (KitW-sh). Successful completion of this research will have a major impact on the field by expanding existing concepts regarding the role of leptin in skeletal health and disease. Our approach will provide a powerful tool for unraveling mechanisms mediating the complex actions of leptin on the skeleton and immune systems. The proposed research has the potential to provide new insights for the development of interventions to interrupt leptin-mediated inflammatory cascades without compromising the beneficial skeletal actions of the adipokine.