Overexpression of MMP12 caused MDSC expansion, emphysema, and bronchoalveolar adenocarcinoma in the lung of c-fms-rtTA/(TetO)7-CMV-MMP12 the bitransgenic mice. (A) A representative flow cytometric analysis of Gr-1+ and CD11b+ cells from the lung of 3-month doxycycline-treated wild-type (WT) mice, doxycycline-treated (+DOX) bitransgenic mice, and doxycycline-untreated (−DOX) bitransgenic mice. (B) Absolute numbers of Gr-1+CD11b+ cells, Gr-1−CD11b+ cells, and Gr-1+CD11b− cells in the lung of 3-, 6-, and 9-month (3, 6, 9 months) doxycycline-treated (Tg +DOX), untreated (Tg −DOX) bitransgenic mice, and age-matched doxycycline-treated wild-type mice (WT +DOX). Results are the mean ± SD, n > 4. (C) Histologic analysis of doxycycline-treated (+DOX) and untreated (−DOX) bitransgenic mice by H&E staining. After 6 weeks of doxycycline treatment (+DOX 6W), emphysema was observed (original magnification, ×100). Bronchoalveolar adenocarcinomas were found in 4-month (4M) doxycycline-treated lungs, not in age-matched untreated lungs (original magnification, −40). After 9 months (9M) of doxycycline treatment, tumor size became grossly identifiable (pointed by green arrow). (D) Quantitative measurements of alveolar numbers, average mean cord length (Lm), average alveolar surface area, and average alveolar volume for emphysema were determined by MetaMorph imaging software. Results are the mean ± SD, n = 10. (E) The lung adenocarcinoma incidence in 4- to 12-month doxycycline-treated (+DOX) and untreated bitransgenic mice (-DOX). Thirteen of 40 doxycycline-treated mice showed bronchoalveolar adenocarcinoma, and 2 of 40 untreated mice showed tumor; n = 40/group.
