Natural Haemozoin Induces Expression and Release of Human Monocyte Tissue Inhibitor of Metalloproteinase-1

Recently matrix metalloproteinase-9 (MMP-9) and its endogenous inhibitor (tissue inhibitor of metalloproteinase-1, TIMP-1) have been implicated in complicated malaria. In vivo, mice with cerebral malaria (CM) display high levels of both MMP-9 and TIMP-1, and in human patients TIMP-1 serum levels directly correlate with disease severity. In vitro, natural haemozoin (nHZ, malarial pigment) enhances monocyte MMP-9 expression and release. The present study analyses the effects of nHZ on TIMP-1 regulation in human adherent monocytes. nHZ induced TIMP-1 mRNA expression and protein release, and promoted TNF-α, IL-1β, and MIP-1α/CCL3 production. Blocking antibodies or recombinant cytokines abrogated or mimicked nHZ effects on TIMP-1, respectively. p38 MAPK and NF-κB inhibitors blocked all nHZ effects on TIMP-1 and pro-inflammatory molecules. Still, total gelatinolytic activity was enhanced by nHZ despite TIMP-1 induction. Collectively, these data indicate that nHZ induces inflammation-mediated expression and release of human monocyte TIMP-1 through p38 MAPK- and NF-κB-dependent mechanisms. However, TIMP-1 induction is not sufficient to counterbalance nHZ-dependent MMP-9 enhancement. Future investigation on proteinase-independent functions of TIMP-1 (i.e. cell survival promotion and growth/differentiation inhibition) is needed to clarify the role of TIMP-1 in malaria pathogenesis.

近年来，基质金属蛋白酶-9（matrix metalloproteinase-9, MMP-9）及其内源性抑制剂金属蛋白酶组织抑制剂-1（tissue inhibitor of metalloproteinase-1, TIMP-1）已被证实与复杂性疟疾相关。在体内实验中，脑型疟疾（cerebral malaria, CM）模型小鼠体内MMP-9与TIMP-1的表达水平均显著升高；而在人类疟疾患者中，血清TIMP-1水平与疾病严重程度直接相关。体外实验显示，天然疟色素（natural haemozoin, nHZ, 又称疟色素）可促进单核细胞MMP-9的表达与分泌。本研究探讨了nHZ对人贴壁单核细胞中TIMP-1表达调控的影响：nHZ可诱导TIMP-1的mRNA表达与蛋白分泌，并促进肿瘤坏死因子-α（TNF-α）、白细胞介素-1β（IL-1β）以及巨噬细胞炎症蛋白-1α/CCL3（MIP-1α/CCL3）的生成。阻断性抗体与重组细胞因子可分别抵消或模拟nHZ对TIMP-1的调控作用。p38丝裂原活化蛋白激酶（p38 MAPK）与核因子-κB（NF-κB）抑制剂可阻断nHZ对TIMP-1及各类促炎分子的所有调控效应。尽管nHZ可诱导TIMP-1的表达，但它仍可提升细胞总明胶酶活性。综上，本研究数据表明，nHZ可通过p38 MAPK与NF-κB依赖的信号通路，诱导人单核细胞TIMP-1的炎症介导型表达与分泌。然而，TIMP-1的诱导表达不足以抵消nHZ介导的MMP-9表达上调。未来需针对TIMP-1不依赖蛋白水解酶的功能（如促进细胞存活、抑制细胞生长与分化）展开研究，以明确其在疟疾发病机制中的具体作用。