Stretch-induced apoptosis in rat alveolar epithelial cells is mediated by the intrinsic mitochondrial pathway

ABSTRACT

Background: Alveolar type II (ATII) cells in the lung are exposed to mechanical stretch during breathing and mechanical ventilation. Increased mechanical stretch contributes to lung injury by induction of apoptosis and necrosis in ATII cells. Aim of the Study: In this study, we investigated the intrinsic and the extrinsic apoptosis pathways, and their involvement in our model of stretch-induced apoptosis. Material and Methods: ATII cells were stretched on elastic membranes for 24 h and apoptosis was determined at different time points. Several factors of the intrinsic and the extrinsic pathway were investigated by FACS, ELISA, and Western blot. We also investigated the inhibition of reactive oxygen species (ROS) expression and cytochrome C release and their influence on induction of apoptosis by stretching. Results: In comparison to static cells, ROS generation and cytochrome C release were increased in stretched cells while at the same time, mitochondrial membrane potential was reduced. Both inhibition of ROS generation by tocopherol and inhibition of cytochrome C release by cyclosporine A led to reduction of stretch-induced apoptosis. An increase of caspase 8 and 9 was observed in stretched cells compared to static cells. In contrast, factors of the extrinsic pathway such as TNF-alpha, TRAIL, TNFRI, Fas, FasL, and FADD were not different to static cells at all time points or where not detectable. Conclusion: Together, these findings suggest predominance of the intrinsic pathway in stretch-induced apoptosis.

KEYWORDS:

• apoptosis pathways
• ATII cells
• cytochrome C
• ROS
• stretch

Acknowledgments

The authors would like to thank Claudia Hänel for their technical assistance.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the article.