MFN1 and chronic obstructive pulmonary disease: In addition, a permanent low dose-rate of CS exposure in primary bronchial epithelial cells (PBECs) of COPD patients disrupts mitophagy and induces the augmentation of damaged mitochondria and a rise in the fusion proteins mitofusin 1/2 (MFN1/2) and OPA1, resulting in merged mitochondria in PBECs [86,88].