Overexpression of MMP12 activated the IL-6/Stat3 pathway in alveolar type II epithelial cells of c-fms-rtTA/(TetO)7-CMV-MMP12 bitransgenic mice. (A) MMP12-specific enzymatic activity was analyzed in BALF from 3-month doxycycline-treated wild-type (WT) mice, doxycycline-treated (+DOX), or untreated (−DOX) bitransgenic mice. Results are the mean ± SD, n = 5; **P < .01. (B) The concentration of IL-6 was measured in BALF at 1, 3, 6, and 9 months of doxycycline treatment (1, 3, 6, and 9 months) by ELISA. Results are the mean ± SD, n > 4. (C) The purified lung alveolar type II epithelial cells were stained with SP-C (specific marker for alveolar type II epithelial cells) and phospho-Stat3. Phospho-Stat3 positive cells were analyzed by flow cytometry in gated SP-C–positive cells. The shaded area shows isotype controls. (D) Real-time PCR analysis of Stat3 mRNA expression in the whole lung, alveolar macrophages, and alveolar type II epithelial cells from 3-month wild-type (WT), doxycycline-treated (+DOX), or untreated (−DOX) bitransgenic mice. Results are the mean ± SD, n > 4. (E) Real-time PCR analysis of Stat3 downstream cytokine and chemokine mRNA expression was assessed in the whole lung, alveolar macrophages, and alveolar type II epithelial cells in the same groups of mice as outlined in panel D. Results are the mean ± SD, n > 4.
