Role of Natural Antibodies Against Oxidation Specific Epitopes in Bone Homeostasis

脂质过氧化形成高活性的分子，与蛋白质的氨基和 脂类，称为氧化特异性表位(OS)。OS是无处不在的促炎成分，会导致 如果不及时消除，会造成广泛的细胞损伤。先天免疫系统的天然抗体，识别 并阻止它们的不良影响。巨噬细胞和其他细胞表达的清道夫受体 类型识别OS并处理氧化修饰的内源分子。持久性和/或 过量的OS会压倒这些防御机制，并引发炎症反应 通过清道夫受体/Toll受体的激活导致组织损伤和疾病的发展。 含磷胆碱的氧化磷脂(PC-OxPLs)在氧化低密度上形成的磷脂 脂蛋白(OxLDL)和凋亡细胞表面。IgM E06是一种天然抗体，可识别 PC-OxPL。表达E06-IgM抗原结合区单链形式的转基因小鼠 (E06-scFv)可防止动脉粥样硬化，并延长寿命。这种效果是由 防止OSE与巨噬细胞结合以及随后的炎症途径的激活。在……里面 对于人类来说，低水平的天然抗体与心血管疾病的发病率增加有关。 在人类中的流行病学证据以及在老鼠身上的机制研究表明，富含OSE的OxLDL是 也是骨质疏松症的致病因素。值得注意的是，我们发现E06-scFv转基因可以阻止 HFD通过增加骨内成骨细胞数量和骨形成而导致皮质骨丢失。此外, E06-scFv通过增加正常饲料喂养的雄性和雌性C57BL/6J小鼠的松质骨和皮质骨 增加骨形成和成骨细胞数量。机制研究表明，E06免疫球蛋白M可预防 氧化低密度脂蛋白对培养的成骨细胞增殖、分化和存活的负面影响 抗OSE抗体通过阻止OSES对成骨细胞的负面影响来促进骨合成代谢。 在E06-scFv中，巨噬细胞产生的抗骨生成细胞因子始终不受影响 转基因小鼠。PC最丰富的清道夫受体ScrB1的缺失- 在成骨细胞系的细胞中，OxPL可以防止OxLDL对细胞凋亡和分化的不利影响。 此外，在小鼠中，抗PC IgM(包括E06)随着年龄的增长而下降，与骨骼的下降有关 质量。因此，我们假设抗pc-oxpls抗体在骨骼动态平衡中起着有益的作用。 通过保护PC-Oxpls对骨形成的有害影响，ScrB1在 成骨细胞。由于加速的细胞凋亡、氧化应激或慢性疾病，OS的产量增加 炎症，加上抗PC-Oxpls抗体水平随着年龄的下降，导致了 小鼠和人类骨质疏松症的发病机制。在本申请中提出的研究将建立 ScrB1是否通过骨的特性在体内介导PC-OxPLs对成骨细胞的负效应 成骨细胞系细胞中ScrB1基因缺失的小鼠的表型。我们还将 确定E06-scFv是否可以防止老年引起的骨形成减少。此外，我们还将 研究内源性抗PC-IgM水平是否与人体骨密度相关 骨密度(BMD)合格退伍军人中抗PC-IgM水平的测定 采用双X线骨密度仪(DXA)进行评估。这部作品的成功完成可能会让人联想到一部小说 同时处理骨质疏松和动脉粥样硬化的治疗方法。

Lipid peroxidation forms highly reactive molecules that generate adducts with amino groups of proteins and lipids, known as oxidation specific epitopes (OSEs). OSEs are ubiquitous pro-inflammatory moieties that cause extensive cell damage if not promptly eliminated. Natural antibodies of the innate immune system, recognize OSEs and block their adverse effects. Scavenger receptors (SRs) expressed in macrophages and other cell types recognize OSEs and dispose of oxidatively-modified endogenous molecules. Persistence and/or excessive amounts of OSEs overwhelm these defense mechanisms, and the inflammatory response initiated by scavenger receptor/toll-receptor activation causes tissue damage and the development of disease. Phosphocholine-containing oxidized phospholipids (PC-OxPLs) form OSEs on oxidized low density lipoproteins (OxLDLs) and on the surface of apoptotic cells. The IgM E06 is a natural antibody that recognizes PC-OxPL. Transgenic mice expressing a single chain (scFv) form of the antigen-binding domain of E06 IgM (E06-scFv) are protected against atherosclerosis and have increased lifespan. This effect results from the prevention of OSE binding to macrophages and the subsequent activation of inflammatory pathways. In humans, low levels of natural antibodies are associated with increased incidence of cardiovascular disease. Epidemiologic evidence in humans as well as mechanistic studies in mice indicate that the OSE-rich OxLDL is a pathogenic factor for osteoporosis as well. Remarkably, we found that the E06-scFv transgene prevents the cortical bone loss caused by HFD by increasing endosteal osteoblast number and bone formation. In addition, E06-scFv increases cancellous and cortical bone in male and female C57Bl/6J mice fed a normal diet by increasing bone formation and osteoblast number. Mechanistic studies showed that E06 IgM prevents the negative effects of OxLDL on proliferation, differentiation, and survival of cultured osteoblastic cells suggesting that anti-OSE antibodies promote bone anabolism by preventing the negative effects of OSEs on osteoblasts. Consistently, the production of anti-osteogenic cytokines by macrophages was not affected in E06-scFv transgenic mice. Deletion of the scavenger receptor ScrB1, the most abundant scavenger receptor for PC- OxPL in cells of the osteoblast lineage, prevents the adverse effects of OxLDL on apoptosis and differentiation. Moreover, anti-PC IgM (which includes E06) decline with age in mice, in association with a decline in bone mass. Therefore, we hypothesize that anti PC-OxPLs antibodies play a beneficial role in skeletal homeostasis by protecting against deleterious effects of PC-OxPLs on bone formation, that are transmitted by ScrB1 on osteoblasts. Increased production of OSEs due to accelerated apoptosis, oxidative stress, or chronic inflammation, in concert with declining levels of anti PC-OxPLs antibodies with age, contributes to the pathogenesis of osteoporosis in both mice and humans. Studies proposed in this application will establish whether ScrB1 mediates the negative effects of PC-OxPLs on osteoblasts in vivo by characterizing the bone phenotype of mice in which the ScrB1 gene has been deleted in cells of the osteoblast lineage. We will also determine if E06-scFv prevents the reduction in bone formation caused by old age. Additionally, we will investigate whether endogenous anti-PC IgM levels correlate with bone mineral density in humans by measuring the levels of anti-PC IgM in a cohort of eligible Veterans who had a bone mineral density (BMD) assessment by dual X-ray absorptiometry (DXA). Successful completion of this work may may suggest a novel therapeutic approach for the management of osteoporosis and atherosclerosis simultaneously.