Nickle(II) ions exacerbate bleomycin-induced pulmonary inflammation and fibrosis by activating the ROS/Akt signaling pathway

Nickle (Ni) is a heavy metal found in particulate matter. We previously reported that Ni ions are strongly associated with high apoptosis rates and high expression of IL-1 beta in human bronchial epithelial cells following exposure to PM2.5; however, the effects of Ni ions on pulmonary fibrosis have not been fully elucidated. In the current study, we evaluated whether Ni ions can exacerbate bleomycin (BLM)-induced pulmonary fibrosis in a mouse model and illustrated the potential mechanism. Ni ions inhibited cell proliferation and induced apoptosis in A549 and MRC-5 cells. BLM-induced lung injury and fibrosis in mice were significantly enhanced by nickel treatment, and these findings were also supported by inflammatory cell accumulation in bronchoalveolar lavage fluid and elevated levels of pro-inflammatory cytokines in lung tissues. Ni ions also increased extracellular matrix protein levels, including those of type I collagen and MMP9 in mouse lung tissues and cell lines. Moreover, Ni ions promoted the phosphorylation of AKT in this mouse model. The effect of increased collagen levels and MMP9 expression was inhibited by blocking the AKT phosphorylation. Together, these findings suggest AKT activation as a critical contributor to this Ni-exacerbated pulmonary fibrotic process.