Binding of MMP13 to Immune Checkpoint Receptor PD-1H links Bone Disease with Immune Suppression in Multiple Myeloma

多发性骨髓瘤(MM)骨病仍然是这种无法治愈的最可怕的并发症之一 癌症。MM细胞产生的破骨细胞激活因子诱导破骨细胞，导致骨量过多 约80%的患者即使在病情缓解后愈合不良，也会出现骨吸收和溶骨性病变。 为了筛选激活破骨细胞的潜在骨髓瘤衍生因子，我们鉴定了基质。 基质金属蛋白酶13(MMP13)由原代MM细胞高分泌并在骨肉瘤患者中升高 疾病。基质金属蛋白酶-13在体外和体内均能剂量依赖性地诱导骨吸收。多发性骨髓瘤中的骨病 在小鼠模型中，下调MM细胞中的基质金属蛋白酶-13可显著抑制溶骨性病变的发展， 证实基质金属蛋白酶-13在多发性骨髓瘤骨病的发生发展中起关键作用。它是特别的 依赖于基质金属蛋白酶-13的破骨细胞活化独立于其酶活性发生的重要性，因此 建立骨吸收调控的新范式。综上所述，我们已经证明了基质金属蛋白酶-13 在多发性骨髓瘤所致的骨破坏中起着关键作用。 我们现在有令人信服的证据表明免疫检查点蛋白程序性死亡-1同源物(PD-1H)，a 广泛表达于各种造血细胞谱系的跨膜蛋白，是一种 此前未被认识的基质金属蛋白酶-13信号受体。我们发现PD-1H基因在破骨细胞块中被敲除 基质金属蛋白酶-13诱导破骨细胞活化和骨吸收，提示基质金属蛋白酶-13与PD-1H结合在骨吸收中起重要作用 在多发性骨髓瘤引起的骨病中起关键作用。此外，我们还发现，基质金属蛋白酶-13具有PD-1H介导的抑制作用 对T细胞增殖的影响。基质金属蛋白酶-13-/-抗原提呈细胞对 同种异体反应性T细胞体外培养。在同种异体反应的体内模型中，供体T细胞在基质金属蛋白酶中的扩增明显更多。 13-/-受体，证实宿主基质金属蛋白酶-13的表达缓解了T细胞的扩张。 这项研究的中心假设是PD-1H是基质金属蛋白酶-13信号转导的关键受体 对破骨细胞、抗原提呈细胞和T细胞的影响，导致骨吸收和 MM中的免疫抑制我们提出了以下4个目标：1)将PD-1H的作用定义为基质金属蛋白酶-13 破骨细胞中的受体；2)研究基质金属蛋白酶-13/PD-1H轴在骨骼改建和多发性骨髓瘤中的作用 3)研究基质金属蛋白酶-13/PD-1H轴作为免疫检查点在多发性骨髓瘤中的作用；以及4)证实 基质金属蛋白酶-13/PD-1H轴在多发性骨髓瘤骨病及免疫抑制中的作用总而言之，我们的发现 突出一条先前未知的破骨细胞激活的新途径，涉及基质金属蛋白酶-13/PD-1H轴 这将骨病与MM的免疫抑制联系在一起。我们提出，我们的工作将形成新的 免疫反应受抑相关的MM骨病的治疗策略。此外，这一点 研究将有助于更好地了解MM骨病与骨髓瘤免疫之间的相互作用 环境。

Multiple Myeloma (MM) bone disease remains one of the most dreaded complications of this still incurable cancer. Osteoclast-activating factors produced by MM cells induce osteoclasts, cause excessive bone resorption, and lytic bone lesions in ~80% of patients with poor healing even after achieving disease remission. In an effort to screen for potential myeloma-derived factors that activate osteoclasts, we identified matrix metalloproteinase 13 (MMP-13) to be highly secreted by primary MM cells and elevated in patients with bone disease. MMP-13 dose-dependently induces extensive bone resorption in vitro and in vivo. In MM bone disease mouse models, MMP-13 knockdown in MM cells significantly inhibits the development of lytic bone lesions, confirming that MMP-13 is critical for the development of multiple myeloma bone disease. It is of particular importance that MMP-13-dependent osteoclast activation occurs independently of its enzymatic activity, thereby establishing a new paradigm in the regulation of bone resorption. In overview, we have shown that MMP-13 plays a pivotal role in MM-induced bone destruction. We now have compelling evidence that immune checkpoint protein programmed death-1 homolog (PD-1H), a transmembrane protein broadly expressed on various hematopoietic cell lineages, serves as a previously unrecognized signaling receptor for MMP-13. We found that Pd-1h knockout in osteoclast blocks MMP-13-induced osteoclast activation and bone resorption, suggesting that MMP-13 binding to PD-1H plays a critical role in MM induced bone disease. Furthermore, we show that MMP-13 has a PD-1H mediated inhibitory effect on T cell expansion. Mmp-13-/- antigen presenting cells have increased stimulatory capacity on alloreactive T cells in vitro. In an in vivo model of alloreactivity, donor T cells expand significantly more in Mmp- 13-/- recipients, confirming that host MMP-13 expression mitigates the expansion of T cells. It is the central hypothesis of this grant that PD-1H is the key receptor for MMP-13 signaling and mediates its effects on osteoclasts, antigen presenting cells and T cells, resulting in bone resorption and immunosuppression in MM. We propose the following 4 Aims: 1) Define the role of PD-1H as the MMP-13 receptor in osteoclasts; 2) Characterize the role of the MMP-13/PD-1H axis in skeletal remodeling and MM bone disease; 3) Investigate the role of the MMP-13/PD-1H axis as an immune checkpoint in MM; and 4) Confirm the role of MMP-13/PD-1H axis in MM bone disease and immunosuppression in MM patients. Together, our findings highlight a previously unrecognized and new pathway of osteoclasts activation involving MMP-13/PD-1H axis that links the bone disease with immunosuppression in MM. We propose that our work will form the basis for novel treatment strategies in MM bone disease associated with suppressed immune response. Furthermore, this research will help to better understand the interaction between MM bone disease and the myeloma immune environment.