Utility of Abbreviated Exposure Time in Mice ‐ Contribution to Understanding Pathogenesis of Cigarette Smoke Induced Lung Disease

Background The utility of the mouse to understand the pathogenesis of cigarette smoke (CS) induced lung disease in humans is challenged as much by the diversity of the human disease phenotype as it is by the diversity of pre‐clinical protocols (ie. strain, duration/intensity of CS exposure, co‐stimuli, and measurement profiles). Given the limitations of translating rodent findings to humans, comprehensive characterization of a CS exposed mouse is a necessary starting point. Here we describe our CS exposed mouse preparation, reproduce a model of acute exacerbation, and present representative data of the physiologic, inflammatory, and structural phenotype generated from our tissue biobank to provide further insight regarding the pathogenesis of CS‐induced lung disease. Methods Female C57BL/6J mice (17–21 g) were randomly assigned to whole body exposure to either filtered room air (RA: n=14) or cigarette smoke (CS; n =14, SciReq; In‐Expose; 3R4F University of Kentucky reference cigarettes; ISO 1991 standard exposure; 1 hr/2× daily, 5 days/week; total particulate matter was 100 mg/m 3 for the first 3 days then 300 mg/m 3 for a total of 4 weeks). In the last 2 weeks, half of each RA and CS group received intratracheal saline (50 uL) or poly I:C (50 uL; 1 ug/uL) twice/week. We evaluated demographics, lung mechanics (flexiVent), bronchoalveolar fluid (BALF) cell population, lung morphometry (histology, mean linear intercept‐MLI), lung surfactant protein /inflammatory/oxidative/apotosis/goblet cell profile using qPCR (CXCL1, IL‐6, Type I IFN β, TLR3, MUC 1 gene expression), Western blot (SP‐C, CC10, NFkβ), staining of 5 um serial paraffin embedded sections by immunohistochemistry/fluorescence (4‐HNE, TUNEL, active caspase 3, macrophage phenotyping: M1 [CCR7], M2 [CD206] and progenitor macrophages [S100A9], PAS/Alcian Blue). Results In comparison to the RA alone, mice treated with CS +/− poly IC demonstrated significantly (all parameters: p <0.05) less weight gain, greater pulmonary compliance and resistance, greater #s of monocytes, neutrophils, and lymphocytes in BALF, lower lung SP‐C and CC10, greater lung CXCL‐1, IL‐6, TLR 3, and MUC‐1 gene expression, increased M1>M2 with decrease in %M2 and comparable S100A9 macrophages, increased goblet cells and MLI, greater apoptosis as detected by TUNEL and active caspase 3 expression, and greater oxidative stress by 4‐HNE staining. A similar response profile was found to poly IC in RA exposed animals, whereas, CS attenuated the effect of poly IC on CXCL‐1, IL‐6, Type I IFN β, MUC‐1, NFkβ and macrophage phenotype responses. Conclusions These data demonstrate the ability to produce robust physiologic, immunologic/oxidative/cell death and lung structural responses in 4 weeks of CS exposure in a mouse model. In addition, the finding of attenuated responses to poly I:C in CS mice support the notion that CS induced lung pathology may be due in part due to altered innate immunity, in favor of proinflammatory as opposed to a repair/remodeling process. Support or Funding Information NIH: 400969 (MRW); 361185 (BK)