Effect Of TGF-β On The Expression Of TREM-1in Lung Of Mice And Its Mechanism

Triggering receptors expressed on myeloid cells-1(TREM-1) functions as an inflammatory amplifier through amplifying immune response signal mediated by toll-like receptor (TLR) and nod-like receptor (NLR) and prolonging macrophage survival. TREM-1could increase markedly the expression of TGF-β family, while TGF-β is well known as the most critical profibrogenic cytokine in pulmonary fibrosis. However, whether the TGF-β affects TREM-1expression has not been reported.Objective:This study is to observe the effect of TGF-(3on TREM-1expression in lung of mice and explore its mechanism.Methods:Swiss mice was injected bronchially with bleomycin (BLM) to copy the model of pulmonary fibrosis, and sacrificed on the7th,14th and21th day. The model of pulmonary fibrosis was validated by hematoxylin-eosin (HE) and Masson staining.The transcriptional level of collagen type I and III, TREM-1and the transcription factor c-Jun were detected via Real-time PCR or RT-PCR. TREM-1protein content in the lung tissue of pulmonary fibrosis in mice was measured by Western Blot. The proportion of positive cells containing TREM-1was examined via Flow cytometry to reflect TREM-1protein level on the surface of mouse macrophages. Site-directed mutagenesis technology and Dual-luciferase Reporter Assay validated whether c-Jun involved in TGF-β induced upregulation of TREM-1promoter activity in mouse macrophages. Results:The model of pulmonary fibrosis was successful duplicated in swiss mice. The expression of TGF-β and TREM-1were increased on the7th,14th and21th day after injecting bronchially with BLM (P<0.05), which had a positive correlation (r=0.787, P<0.05). TGF-β upregulated TREM-1mRNA and protein level in mouse macrophages in a time-and dose-dependent manner (P<0.05). The expression of c-Jun was increased on the7th,14th and21th day after injecting bronchially with BLM (P<0.05), which was positively correlated with the expression of TGF-β (r=0.713, P<0.05) and TREM-1(r=0.906, P<0.05), respectively. TGF-β upregulated c-Jun mRNA expression in mouse macrophages in a time-and dose-dependent manner (P<0.05). TGF-β significantly increased relative fluorescence intensity of wild type (WT)-TREM1plasmid (P<0.05), yet had no effect on mutant-TREM1plasmid (the binding site of AP-1site-directed mutagenesis)(P>0.05) in mouse macrophages by site-directed mutagenesis technology and Dual-luciferase Reporter Assay. PKC inhibitor H-7, CaM inhibitor W-7and MAPK inhibitor PD98059dramaticlly reversed the upregulation of TGF-P on the expression of TREM-1and its transcription factor c-Jun in mouse macrophages (P<0.05).Conclusion:1. The expression of TREM-1was expressed highly in the lung tissue of pulmonary fibrosis in mice.2. TGF-β was positively correlated with the expression of TREM-1in the lung tissue of pulmonary fibrosis in mice.3. TGF-β upregulated the expression of TREM-1through PKC, CaM and MAPK signaling pathways increasing the level of transcription factor c-Jun in mouse macrophages.