Role of the gut microbiome in the bone loss induced by hyperparathyroidism in mice and humans

摘要 原发性甲状旁腺功能亢进症(PHPT)是由甲状旁腺激素过度分泌引起的一种疾病 甲状旁腺激素(PTH)会导致侵袭性骨丢失、骨质疏松和增加骨折风险。耐人寻味的是，PHPT 一种异质性疾病，一些患者继续发生骨丢失，而另一些患者则没有，而且很少。 生物标志物可以用来预测疾病的进程。我们最近在NAT上报道了这一点。通讯。那就是 肠道微生物群是控制甲状旁腺素诱导骨丢失能力的一个重要因素。具体来说，我们 在小鼠身上显示，甲状旁腺素水平的升高与微生物释放的产品相结合，可以增强 肠道组织中产生炎症性肿瘤坏死因子的T细胞的激活，然后这些T细胞从肠道迁移到骨骼 骨髓(BM)。在一个只有在微生物群中存在特定种类的细菌的过程中才会发生， 肠道产生肿瘤坏死因子的T细胞可诱导肠道内Th17细胞的扩张。骨髓中升高的肿瘤坏死因子诱导 趋化因子配体的表达可吸引Th17细胞进入骨髓。一旦进入骨髓，Th17细胞就会释放 导致RANKL介导的骨丢失的破骨因子IL-17。在人类群体中，有 肠道微生物组多样性的显著异质性，包括肠道微生物组多样性频率的显著差异 激活Th17细胞成熟的特定细菌的存在。我们假设这种异质性直接 解释了人群中PHPT相关性骨丢失的异质性，那里只有患者 那些被Th17细胞诱导细菌定植的人会经历PHPT诱导的骨丢失。为了支持这一点 假设，我们展示了令人信服的新数据，即特定菌株的Th17细胞的相对频率- PHPT患者长双歧杆菌诱导菌与骨密度呈负相关。在目标1中，我们 将测试人类PHPT患者发生骨丢失的倾向是否可以通过 肠道微生物群的组成。此外，为了证明因果关系，我们将无菌小鼠 用PHTP患者的微生物组或长双歧杆菌来确定PHPT是否诱导， 肠道细菌依赖性骨丢失表型可在微生物体内转移。这些研究将 证明粪便微生物组测序可作为预测PHPT患者的一种新的筛查方法 导致骨质流失。此外，对使甲状旁腺激素具有成骨能力的细菌进行了鉴定 损失将为未来的研究提供理由，在这些研究中，有针对性的抗菌素方法旨在根除 Th17细胞诱导菌可用于预防PHPT患者的骨丢失。在目标2中，我们将使用 强大的新型光敏小鼠模型，我们可以在其中可视化运输细胞，以测量其影响 甲状旁腺激素对产生肿瘤坏死因子的T细胞和Th17细胞从肠道到骨髓的迁移。身份的鉴定 人类微生物群诱导的T细胞从肠道向骨髓迁移的机制将产生必要的 根据使用情况，为预防PHPT相关骨骼并发症的新策略提供数据 FDA批准的阻止T细胞从肠道流出和/或流入骨髓的药物。

SUMMARY Primary hyperparathyroidism (PHPT) is a condition caused by the excessive secretion of parathyroid hormone (PTH) that can lead to aggressive bone loss, osteoporosis and increased risk of fractures. Intriguingly, PHPT is a heterogeneous disease where some patients go on to develop bone loss while others do not, and few biomarkers are available to predict the course of the disease. We recently reported in Nat. Comm. that the intestinal microbiome is a potent factor governing the capacity of PTH to induce bone loss. Specifically, we showed in mice that elevated levels of PTH in combination with microbial-released products potentiates the activation of pro-inflammatory TNF producing T cells in gut tissue, which then migrate from the gut to the bone marrow (BM). In a process that only occur if specific species of bacteria are present in the microbiome, intestinal TNF producing T cells induce the expansion of Th17 cells in the gut. Elevated TNF in the BM induce the expression of chemokine ligands that attract Th17 cells to the BM. Once in the BM, Th17 cells release the osteoclastogenic factor IL-17 which causes RANKL-mediated bone loss. In human populations, there is significant heterogeneity in gut microbiome diversity, including considerable variation in the frequency of presence of specific bacteria that activate Th17 cell maturation. We hypothesize that this heterogeneity directly accounts for the heterogeneous nature of PHPT-associated bone loss within populations, where only patients that are colonized with Th17 cell-inducing bacteria experience PHPT-induced bone loss. In support of this hypothesis, we show compelling new data that the relative frequency of a specific strain of the Th17 cell- inducing bacteria Bifidobacterium longum correlates inversely with bone density in PHPT patients. In Aim 1, we will test if the propensity of human patients with PHPT to develop bone loss can be predicted by the composition of the gut microbiome. Furthermore, to demonstrate causality, we will colonize germ-free mice with either the microbiome of PHTP patients, or Bifidobacterium longum and determine if the PHPT-induced, and gut bacterial-dependent bone loss phenotype is transferable within the microbiome. These studies will demonstrate that stool microbiome sequencing may be used as a novel screen to predict which PHPT patients develop bone loss. In addition, identification of the bacteria that endow PTH with the capacity to induce bone loss will provide a rationale for future studies where targeted antimicrobial approaches aimed at eradicating Th17 cell-inducing bacteria may be used to prevent bone loss in PHPT patients. In Aim 2, we will use a powerful new photosensitive murine model where we can visualize the trafficking cells, to measure the effects of PTH on the migration of TNF producing T cells, and Th17 cells from the gut to the BM. The identification of the mechanisms of human microbiome-induced T cells migration from the gut to the BM will yield essential data to inform novel strategies for preventing skeletal complications associated with PHPT, based on the use of FDA approved agents that block the egress of T cells from the gut and/or their influx into the BM.