The role of miR-21 in nickel nanoparticle-induced MMP-2 and MMP-9 production in mouse primary monocytes: In vitro and in vivo studies.

Exposure to metal nanoparticles causes both pulmonary and systemic effects. Nanoparticles can enter the circulation and act directly or indirectly on blood cells, such as monocytes. Monocytes/macrophages are among the first cells to home to inflammatory sites and play a key role in the immune response. Here we investigated the effects of nickel nanoparticles (Nano-Ni), partially [O]-passivated Nano-Ni (Nano-Ni-P), and carbon-coated Nano-Ni (Nano-Ni-C) on MMP-2 and MMP-9 production in mouse primary monocytes both in vitro and in vivo and explored the potential mechanisms involved. The dose- and time-response studies showed that exposure of primary monocytes from wild-type (WT) mice to 30 μg/mL of Nano-Ni for 24 h caused significant MMP-2 and MMP-9 production; therefore, these dose and time point were chosen for the following in vitro studies. Nano-Ni and Nano-Ni-P caused miR-21 upregulation, as well as MMP-2, MMP-9, TIMP-1 and TIMP-2 upregulation in monocytes from WT, but not miR-21 knock-out (KO), mice, indicating the important role of miR-21 in Nano-Ni-induced MMPs and TIMPs upregulation. However, Nano-Ni-C did not cause these effects, suggesting surface modification of Nano-Ni, such as carbon coating, alleviates Nano-Ni-induced miR-21 and MMPs upregulation. These results were further confirmed by in vivo studies by intratracheal instillation of nickel nanoparticles into WT and miR-21 KO mice. Finally, our results demonstrated that exposure of primary monocytes from WT mice to Nano-Ni and Nano-Ni-P caused downregulation of RECK, a direct miR-21 target, suggesting the involvement of miR-21/RECK pathway in Nano-Ni-induced MMP-2 and MMP-9 production.