The Role of MMP13 in Multiple Myeloma Bone Disease

描述（由申请人提供）：多发性骨髓瘤（MM）的特征是破骨细胞（OCL）活性增加，导致约80%的患者发生骨破坏和单纯溶解性病变。过度的骨吸收由OCL介导，OCL由MM细胞分泌的因子及其微环境激活。这一发现支持MM细胞总是位于与活性骨吸收部位密切相关的位置。 基质金属蛋白酶13（MMP 13）属于能够降解和重塑所有细胞外基质（ECM）组分的内肽酶家族。我们最近发现MM细胞分泌的MMP 13比其他MMPs高400倍。组织芯片分析显示MMP 13在MM细胞中高表达，而在正常浆细胞中不表达。MM患者血清的ELISA显示MMP 13蛋白的检测与骨疾病之间100%相关，而MMP 13在健康供体中检测不到。在体外，MMP 13增加骨吸收，其增强作用与OCL大小和核数/OCL显著增加相关，表明MMP 13诱导OCL前体融合。此外，与WT小鼠相比，Mmp 13-/-小鼠产生的OCL显示出显著减少的细胞核数量和平均OCL细胞大小以及骨吸收能力。MMP 13的加入逆转了Mmp 13-/- MNCs的融合缺陷。此外，MMP 13在MM细胞中响应于IL-6而强烈上调，并且EMSA揭示IL-6介导的AP-1活化促进MMP 13转录。树突状细胞特异性跨膜蛋白（DC-STAMP），破骨细胞前体细胞的细胞-细胞融合所必需的，上调外源性MMP 13。 综上所述，我们推测骨髓瘤细胞来源的MMP 13在MM诱导的骨破坏中起着关键作用。我们认为MM微环境上调IL-6触发MM细胞分泌MMP 13。反过来，MMP 13诱导DC-STAMP，导致OCL活性增加，骨吸收和ECM降解。因此，靶向MMP 13可能代表治疗骨髓瘤骨病（MMBD）的有效和新方法。为了验证这些假设，我们将1）研究MM细胞中MMP 13诱导的自分泌和旁分泌机制，2）研究MMP 13增强OCL形成和活性的机制，3）在体内证实MMP 13在骨髓瘤诱导的溶骨性骨病变发展中的作用。这项工作的成功完成对于我们实现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.