Finally, RT-qPCR results indicated that metastatic markers, including MMP2, MMP9, TGF-1 and -SMA, were markedly up-regulated by PM2.5 exposure or IL-17a addition. Vimentin. Lung cancer progression was associated with the increased expression of Kras, c-Myc, breast cancer resistance protein BCRP (ABCG2), OCT4, SOX2 and Aldh1a1, but the decreased expression of p53 and PTEN. Importantly, mice with IL-17a knockout (IL-17a-/-) showed significantly alleviated lung injury and CSC properties following PM2.5 exposure. Also, IL-17a-/–attenuated tumor growth was recovered in PM2.5-exposed mice injected with recombinant mouse IL-17a, accompanied with significantly restored lung metastasis. Taken together, these data revealed that PM2.5 could promote the progression of lung cancer by enhancing the proliferation and metastasis through IL-17a signaling. and experiments showed that IL-17 could directly enhance the invasion of NSCLC cells [27, 28]. These findings revealed the potential of IL-17 in the promoting the HDAC3 Gemcabene calcium development of NSCLC. IL-17a is one of six members (A-F) of the IL-17 family [29, 30]. In a recent study, the increased expression of IL-17a in the lung of patients with lung adenocarcinoma was reported. Local suppression of Gemcabene calcium IL-17a in the lung of a model with lung cancer showed improved anti-tumor immunity featured by the enhanced IFN, a reduced number of T-regulatory cell and the inhibited tumor growth [31]. Although previous studies have illustrated the potential of IL-17a during lung cancer progression, its effects on NSCLC induced by PM2.5 have little to be reported. In this present study, we aimed to further explore the effects of PM2.5 on NSCLC progression, as well as its relationship with IL-17a expression change by the and experiments. Here, we showed that long-term PM2.5 exposure led to lung injury and CSC properties. IL-17a expression levels were significantly up-regulated by PM2.5 in pulmonary tissues, peripheral blood lymphocytes and splenic lymphocytes. NSCLC patients exhibited higher IL-17a expression. In NSCLC cells, PM2.5 was discovered to promote the cell proliferation, migration and invasion through up-regulating IL-17a expression levels. Importantly, we for the first time found that IL-17a knockout markedly alleviated PM2. 5-induced lung injury and CSC properties. Of note, the animal studies showed that PM2.5-enhanced tumor growth was clearly abolished by IL-17a knockout in the established tumor xenograft models. Additionally, results by tumor metastasis confirmed that IL-17a knockout inhibited metastasis in PM2.5-challenged mice. Therefore, our results demonstrated that PM2.5 could elevate the proliferation and metastasis via increasing IL-17a expression levels, accelerating NSCLC progression consequently. RESULTS PM2.5 treatments result in pulmonary injury and fibrosis In order to investigate the effects of PM2.5 on NSCLC progression, the pulmonary condition in mice with long-term PM2.5 exposure was firstly calculated. Histopathological analysis of lung sections using H&E and Masson staining demonstrated that PM2.5 treatment for 3 months caused more severe injury and fibrosis than the FA mice (Figure 1A). Compared to the FA group, PM2.5 markedly increased total protein levels in BALF in a time-dependent manner (Figure 1B). Similarly, the number of total cells and neutrophils were significantly increased in mice exposed to PM2.5, indicating the critical inflammation in mice (Figure 1C, ?,1D).1D). EMT is an important process that contributes to fibrogenesis [32]. Then, fibrosis- and/or EMT-associated genes, including MMP2, MMP9, TGF-1, -SMA, Fibronectin and Vimentin [33, 34], in lung samples of mice were highly induced by PM2.5 administration in a time-dependent manner (Figure 1E). Both serum and lung TNF- and IL-6 expression levels were Gemcabene calcium greatly up-regulated in PM2.5-challenged mice (Figure 1F, ?,1G).1G). These results showed that long-term PM2.5 exposure led to severe pulmonary injury in mice. Open in a separate window Figure 1 PM2.5 treatments result in pulmonary injury and fibrosis. (A) H&E staining (up panel) and Masson trichrome staining (down panel) of lung sections from mice challenged with PM2.5 for the indicated time points (n = 6). Scale bar, 100 m. (B) Protein contents in the BALF were measured in mice treated with PM2.5 at the indicated time (n = 8). The number of (C) total cells and (D) neutrophils of BALF were calculated in PM2.5-challenged mice at the indicated time (n =.