Mononuclear Phagocytes and Airway Epithelial Cells: Novel Sources of Matrix Metalloproteinase-8 (MMP-8) in Patients with Idiopathic Pulmonary Fibrosis

ObjectivesMatrix metalloproteinase-8 (MMP-8) promotes lung fibrotic responses to bleomycin in mice. Although prior studies reported that MMP-8 levels are increased in plasma and bronchoalveolar lavage fluid (BALF) samples from IPF patients, neither the bioactive forms nor the cellular sources of MMP-8 in idiopathic pulmonary fibrosis (IPF) patients have been identified. It is not known whether MMP-8 expression is dys-regulated in IPF leukocytes or whether MMP-8 plasma levels correlate with IPF outcomes. Our goal was to address these knowledge gaps.MethodsWe measured MMP-8 levels and forms in blood and lung samples from IPF patients versus controls using ELISAs, western blotting, and qPCR, and assessed whether MMP-8 plasma levels in 73 IPF patients correlate with rate of lung function decline and mortality. We used immunostaining to localize MMP-8 expression in IPF lungs. We quantified MMP-8 levels and forms in blood leukocytes from IPF patients versus controls.ResultsIPF patients have increased BALF, whole lung, and plasma levels of soluble MMP-8 protein. Active MMP-8 is the main form elevated in IPF lungs. MMP-8 mRNA levels are increased in monocytes from IPF patients, but IPF patients and controls have similar levels of MMP-8 in PMNs. Surprisingly, macrophages and airway epithelial cells are the main cells expressing MMP-8 in IPF lungs. Plasma and BALF MMP-8 levels do not correlate with decline in lung function and/or mortality in IPF patients.ConclusionBlood and lung MMP-8 levels are increased in IPF patients. Active MMP-8 is the main form elevated in IPF lungs. Surprisingly, blood monocytes, lung macrophages, and airway epithelial cells are the main cells in which MMP-8 is upregulated in IPF patients. Plasma and BALF MMP-8 levels are unlikely to serve as a prognostic biomarker for IPF patients. These results provide new information about the expression patterns of MMP-8 in IPF patients.研究目的 基质金属蛋白酶-8（Matrix metalloproteinase-8, MMP-8）可促进小鼠博莱霉素诱导的肺纤维化反应。既往研究虽已证实特发性肺纤维化（idiopathic pulmonary fibrosis, IPF）患者的血浆及支气管肺泡灌洗液（bronchoalveolar lavage fluid, BALF）样本中MMP-8水平升高，但目前尚未明确IPF患者体内MMP-8的生物活性形式及其细胞来源。尚不明确IPF患者白细胞中MMP-8的表达是否存在失调，也不清楚MMP-8血浆水平是否与IPF患者的临床预后相关。本研究旨在填补上述认知空白。 研究方法 本研究采用酶联免疫吸附试验（enzyme-linked immunosorbent assay, ELISA）、蛋白质印迹法（western blotting）及实时定量聚合酶链反应（quantitative polymerase chain reaction, qPCR），检测并对比IPF患者与对照组的血液及肺组织样本中MMP-8的水平与存在形式；纳入73例IPF患者，分析其血浆MMP-8水平与肺功能下降速率及死亡率的相关性。通过免疫染色法定位IPF肺组织中MMP-8的表达位点，并定量检测IPF患者与对照组外周血白细胞中MMP-8的水平与存在形式。 研究结果 IPF患者的BALF、全肺组织及血浆中可溶性MMP-8蛋白水平均显著升高。活化型MMP-8是IPF肺组织中升高的主要MMP-8形式。IPF患者单核细胞中MMP-8 mRNA水平升高，但IPF患者与对照组的中性粒细胞（polymorphonuclear neutrophils, PMNs）中MMP-8水平无显著差异。令人意外的是，IPF肺组织中表达MMP-8的主要细胞为巨噬细胞及气道上皮细胞。IPF患者的血浆及BALF中MMP-8水平与肺功能下降速率及/或死亡率无显著相关性。 研究结论 IPF患者的血液及肺组织中MMP-8水平均升高。活化型MMP-8是IPF肺组织中升高的主要MMP-8形式。值得注意的是，IPF患者体内MMP-8表达上调的主要细胞来源为外周血单核细胞、肺巨噬细胞及气道上皮细胞。血浆及BALF中的MMP-8水平不太可能作为IPF患者的预后生物标志物。本研究结果为IPF患者体内MMP-8的表达模式提供了新的科学认知。