PM2.5 exposure induces alveolar epithelial cell apoptosis and causes emphysema through p53/Siva-1

This study aims to investigate whether PM2.5 exposure is involved in the induction of alveolar epithelial cell apoptosis and the progression of emphysema in mice, and to further explore its specific molecular mechanism.

A certain number of PM2.5 exposed mice and normal control mice were selected, and a lung resection operation was performed to collect the pulmonary tissue samples, which were then analyzed by hematoxylin and eosin (H&E) staining assay. Subsequently, the total protein in the pulmonary tissues of mice in PM2.5 exposure group and control group was extracted, and the p53 protein level was detected by Western blot. Meanwhile, in A549 cells, after treatment of different doses of PM2.5, the protein levels of p53, caspase3, and clv-caspase3 were examined by Western blot while the mRNA levels of p53, Siva-1, and clv-caspase3 were detected by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR), respectively. In addition, flow cytometry was carried out to measure the incidence of cell apoptosis, while chromatin immunoprecipitation (ChIP) assay was performed to verify whether p53 binds to the Siva-1 promoter region and thus regulates its transcription process.

H&E staining revealed that PM2.5 exposure caused pathological damage in the pulmonary tissues and the expansion of the spatial structure of alveoli, which led to emphysema in mice. Moreover, p53 protein expression in pulmonary tissue of mice in PM2.5 exposure group was remarkably higher than that in the control group. Subsequently, A549 cells were treated with 0, 25, 50, 100 μg/ml PM2.5 for 48 h, and it was found that, with the increase of PM2.5 exposure dose, the p53 protein level, Siva-1 mRNA level and cell apoptosis rate were all found increased in a dose-dependent manner, which could be partially reversed by transfection of si-p53 in A549 cells. In addition, CHIP experiments confirmed that p53 can bind to the Siva-1 promoter region and directly regulate Siva-1 transcription. In A549 cells, PM2.5 exposure increased the expression of the clv-caspase3 protein, which was reversed by the knockdown of p53; however, simultaneous overexpression of Siva-1 could further increase the clv-caspase3 protein level. Additionally, flow cytometry also revealed that PM2.5 exposure induced apoptosis of alveolar epithelial cells, while the knockdown of p53 reduced that, which could be promoted by the overexpression of Siva-1.

PM2.5 exposure can promote the transcription of Siva-1 to induce apoptosis of alveolar epithelial cells and accelerate the progression of emphysema in mice by enhancing p53 protein expression.