CXCL17 Exerts A Role In Diesel Exhaust Emissions Exposure-induced Lung Damage By Regulating Macrophage Function

Objective:As a common important air pollution source in production and living environment,diesel exhaust(DE)is strongly linked to several respiratory diseases,including chronic obstructive pulmonary disease(COPD),asthma and lung cancer.Previous studies showed that DE exposure can impair the phagocytic activity of macrophages.Macrophage chemokine C-X-C motif ligand 17(CXCL17),a potent chemoattractant for macrophages,has recently been found to be abundantly and specifically expressed in mucosal sites.However,the role of CXCL17 in the lung damage caused by DE exposure in mice remains unclear.This study aimed to determine the CXCL17 expression in airway epithelium after DE exposure and explore its role and possible mechanism in DE-exposed lung injury,to provide a theoretical rationale for prevention and control of DE-exposed health hazard.Methods:1.In vivo,a mice model of DE-exposure was constructed,and adeno-associated virus vector type 5(AAV5)was instilled into the airways to overexpressing CXCL17.Pulmonary function of mice was determined using whole-body plethysmography.The leucocytes in alveolar lavage fluid(BALF)were classified and the carbon content in airway macrophages(CCAM)was calculated.The pathological changes of lung tissues were detected by HE staining;masson’s trichrome staining was used to evaluate the lung collagen deosition;α-smooth muscle actin(α-SMA)immunohistochemistry was performed to evaluate the airway smooth muscle hyperplasia.CXCL17 levels in the BALF and serum were determined by ELISA;the mRNA and protein level of CXCL17 was determined with q RTPCR and immunohistochemistry;the expression of fibronectin,collagen Ⅰ,Bax and cleaved caspase3 were detected by Western blot.2.In vitro,human bronchial epithelial cells(16HBE)were stimulated with diesel exhaust particles(DEP).Phorbol 12-myristate 13-acetate is used to stimulate the transformation of human monocytic leukemia cells(THP-1)into macrophages.A macrophage(THP-1)and 16 HBE co-culture system was constructed.The Transwell assay was carried out to evaluate the effect of rh-CXCL17 on DEP-induced THP-1 cell migration;q RT-PCR was conducted to determine the mRNA level of CXCL17 and inflammation/remodeling indicator(IL-6,IL8,TGF-β and PDGFB);flow cytometry was conducted to assess the apoptosis of 16 HBE.Results:1.The mice exposed to DE showed attenuated pulmonary function,increased neutrophil in BALF,increased CCAM but not the number of macrophages in BALF,ciliary injury in airway epithelium,airway smooth muscle hyperplasia,increased collagen deosition;DE exposure down-regulated CXCL17 expression in the airways and BALF of mice.This suggests that DE exposure can cause airway injury and remodeling,attenuate pulmonary function,and down-regulate expression of CXCL17 in mice.In vitro,DEP stimulation increased the cell apoptosis,elevated the expression of IL-6,IL-8,TGF-β and PDGFB,and reduced CXCL17 expression in 16 HBE cells.This suggests that DEP can induce apoptosis,inflammation /remodeling,accompanied by a reduced expression of CXCL17 in 16 HBE cells.2.AAV5-CXCL17 improved pulmonary function,increased CCAM and the number of macrophages,mitigated airway smooth muscle and hyperplasia collagen DEPosition,accompanied by a reduced expression of fibronectin,collagen Ⅰ,Bax and cleaved caspase3.This suggests that AAV5-CXCL17 can enhance macrophage recruitment and clearance of DE in the lungs of mice and partially improve pulmonary function,airway injury,and airway remodeling in mice.In vitro,the result of Transwell assay showed that CXCL17 recruited more macrophages to migrate,swallowed more DEP particles,improved the apoptosis of 16 HBE cells in the lower ventricle,and reduced the expression of inflammatory remodeling indicators(IL-6,TGF-β and PDGFB).Conclusion:CXCL17 might recruit pulmonary macrophages,enhance the phagocytic function and attenuate lung damage triggered by DE exposure,which is,therefore,expected to be a novel therapeutic target for DE-associated lung damage.