Chaperone-mediated autophagy modulates epithelial cell apoptosis in COPD pathogenesis

Introduction: Cigarette smoke (CS) induces oxidative modifications, enhancing unfold protein response (UPR) and autophagy. UPR has an ability to induce apoptosis during excessive endoplasmic reticulum (ER) stress. Among three types of autophagic pathways, chaperone-mediated autophagy (CMA) is responsible for selective degradation of proteins with KFERQ peptide motif. Although the participation of CS extract (CSE)-induced epithelial cell apoptosis has been reported, mechanistic involvement of CMA in COPD pathogenesis, especially in terms of UPR remains obscure. Methods: We used normal and COPD lung tissues, and cultured their primary human bronchial epithelial cells (HBECs). CMA activity was evaluated by the expression levels of lysosomal associated membrane protein type 2a (LAMP2A). Cell death and viability were assessed by LDH assay, MTT assay, and flow cytometry. ER stress-related signaling pathway was evaluated by western blotting and real-time PCR. Results: Immunohistochemical staining of COPD HBECs showed low LAMP2A expression compared to normal HBECs. Furthermore, we found that CSE treatment in HBECs attenuated LAMP2A expression level dependent of NRF2, which mediates anti-oxidant responses. SiRNA-mediated LAMP2A knock down in CSE-treated HBECs significantly increased epithelial cell apoptosis in caspase-dependent manner. Consistently, the LAMP2A knock down increased ATF4 and CHOP expressions, which induce apoptosis via ER stress-related signaling pathway in CSE-treated HBECs. Conclusion: These findings suggest that reduced CMA activity may be involved in the mechanism for epithelial cell apoptosis by enhancing CS-induced UPR in COPD pathogenesis.