The Role of MMP13 in Multiple Myeloma Bone Disease

描述(申请人提供)：多发性骨髓瘤(MM)的特征是破骨细胞(OCL)活性增加，导致约80%的患者骨质破坏和纯粹的溶骨性病变。骨肉瘤的过度骨吸收是由骨肉瘤细胞及其微环境分泌的因子激活的骨肉瘤细胞介导的。MM细胞总是与活跃的骨吸收部位密切相关，这一发现支持了这一点。 基质金属蛋白酶13(MMP13)属于内肽酶家族，能够降解和重塑细胞外基质(ECM)的所有成分。我们最近发现MM细胞分泌MMP13的能力是其他MMPs的400倍。原代组织芯片分析显示，MMP13在MM细胞中高表达，而在正常浆细胞中不表达。检测MM患者血清MMP13蛋白与骨病的相关性为100%，而在健康献血员中检测不到MMP13蛋白。在体外，MMP13促进骨吸收，其促进作用与OCL大小和核数目/OCL显著增加有关，提示MMP13诱导OCL前体融合。此外，与WT小鼠相比，Mmp13-/-小鼠产生的OCL的核数量、平均OCL细胞大小和骨吸收能力显著减少。MMP13的加入逆转了MMP13-/-MNC的融合缺陷。IL-6诱导的MM细胞MMP13表达上调，EMSA显示IL-6介导的AP-1激活促进了MMP13的转录。树突状细胞特异性跨膜蛋白(DC-STAMP)是破骨前细胞细胞-细胞融合所必需的，受外源MMP13上调。 综上所述，我们假设骨髓瘤细胞来源的MMP13在MM诱导的骨破坏中起关键作用。我们认为，多发性骨髓瘤微环境上调IL-6可触发多发性骨髓瘤细胞分泌MMP13。反过来，MMP13诱导DC-STAMP，导致OCL活性增加，骨吸收和ECM降解。因此，靶向MMP13可能是治疗骨髓瘤骨病(MMBD)的一种有效的新方法。为了验证这些假说，我们将1)研究MMP13诱导MM细胞的自分泌和旁分泌机制，2)研究MMP13促进OCL形成和活性的机制，3)在体内证实MMP13在骨髓瘤诱导的溶骨性骨损伤中的作用。这项工作的成功完成将对实现我们确定骨髓瘤骨病新疗法的总体目标至关重要。

DESCRIPTION (provided by applicant): Multiple myeloma (MM) is characterized by increased osteoclast (OCL) activity that results in bone destruction and purely lytic lesions in ~80% patients. The excessive bone resorption is mediated by OCLs, which are activated by factors secreted by MM cells and their microenvironment. This is supported by the finding that MM cells are always located in close association with sites of active bone resorption. Matrix metalloproteinase 13 (MMP13) belongs to a family of endopeptidases capable of degrading and remodeling all extracellular matrix (ECM) components. We recently found that secretion of MMP13 by MM cells is up to 400-fold higher than other MMPs. Primary tissue array analysis showed that MMP13 is highly expressed in MM cells, but not in normal plasma cells. ELISA of MM patient sera revealed a 100% correlation between detection of MMP13 protein and bone disease while MMP13 was undetectable in healthy donors. In vitro MMP13 increased bone resorption, where its enhancing effects were associated with dramatically increased OCL size and nuclear number/OCL, suggesting that MMP13 induces fusion of OCL precursors. Further, OCL generated from Mmp13-/- mice showed a significantly decreased number of nuclei and average OCL cell size and bone resorption capacity compared to WT mice. Addition of MMP13 reversed the fusion defect of Mmp13-/- MNCs. Further, MMP13 was strongly upregulated in MM cells in response to IL-6 and EMSA revealed that IL-6-mediated AP-1 activation promoted MMP13 transcription. Dendritic cell-specific transmembrane protein (DC-STAMP), essential for cell-cell fusion of preosteoclasts, was upregulated by exogenous MMP13. Taken together, we hypothesize that myeloma cell-derived MMP13 plays a pivotal role in MM-induced bone destruction. We contend that the upregulation of IL-6 by the MM microenvironment triggers the secretion of MMP13 in MM cells. In turn, MMP13 induces DC-STAMP, resulting in increased OCL activity, bone resorption and ECM degradation. As such, targeting MMP13 may represent an effective and new approach to treat myeloma bone disease (MMBD). To test these hypotheses, we will 1) investigate the autocrine and paracrine mechanisms of MMP13 induction in MM cells, 2) investigate the mechanisms of enhancing of OCL formation and activity by MMP13 and 3) confirm in vivo the role of MMP13 in the development of myeloma-induced osteolytic bone lesions. A successful completion of this work will be crucial for the achievement of our overall goal to identify novel therapies for myeloma bone disease.