2.4 Hydroxyproline assay
To estimate the collagen synthesis in the lungs, we measured the amount of hydroxyproline via ELISA analysis (Shanghai Yubo Biological Technology). Briefly, lung tissues were homogenized in 1 ml phosphate-buffered saline (PBS) and centrifuged at 4000 rpm for 15 min. The supernatant was collected and BCA measurement was performed to examine the total amount of proteins in lung tissues. Hydroxyproline content was measured according to the Manufacturer’s instructions and determined by a colorimetric assay using a spectrophotometer at a wavelength of 450 nm. Data were present as µg hydroxyproline /µg of lung tissue.