ABSTRACT
Objective: To investigate the role of surfactant associated protein-A (SP-A) in the development and progression of silicosis, and its mechanism. Methods: Homozygous and heterozygous mice of SP-A knockout of specific pathogen free (SPF) grade were selected for mating, and mice with SP-A-/- genotype were selected for subsequent experiments. SP-A wild-type (SP-A+/+) and SP-A-/- mice were divided into SP-A+/+ control group, SP-A-/- control group, SP-A+/+ silicosis group and SP-A-/- silicosis group with six mice in each group by random number table method. Mice in both silicosis groups were given 20.0 μL 250 g/L silica suspension by tracheal exposure, and mice in both control groups were injected with 0.9% sodium chloride solution at the same volume. On the 28th day after modeling, mice were sacrificed. Lung tissues were used for lung histopathology examination. The apoptosis of alveolar type Ⅱ epithelial cells of mice was detected by TUNEL method. The mRNA expression of B-lymphoblastoma 2 (Bcl-2), Bcl-2 associated X protein (Bax), cysteinyl aspartate specific proteinase (Caspase)-3 and Caspase-9 in lung tissues of mice was detected by quantitative real-time polymerase chain reaction. Results: The histopathological result of mice showed that thickened alveolar septum, scattered silicon nodule and collagen fiber formation were observed in the mice lungs of SP-A+/+ silicosis group, and a large number of inflammatory cells were observed in silicosis nodule, after exposure to silica dust. SP-A-/- silicosis group resulted in a more severe pulmonary inflammation and interstitial fibrosis compared to SP-A+/+ silicosis group. The apoptosis of alveolar type Ⅱ epithelial cells and the mRNA relative expression levels of Bax, Caspase-3 and Caspase-9 in lung tissues of mice in each silicosis groups were increased compared with their control groups (all P<0.05). The above four indexes of mice in SP-A-/- silicosis group were higher than those in SP-A+/+ silicosis group (all P<0.05). There was no significant difference in the expression of Bcl-2 mRNA in lung tissues of these four groups (P>0.05). Conclusion: Knockout of SP-A can aggravate inflammation and pulmonary fibrosis in silicosis model mice, and promote apoptosis of alveolar type Ⅱ epithelial cells. The mechanism may be related to the Bcl-2/Bax/Caspase-3 signaling pathway which affects the apoptosis of mitochondrial pathway.