Role of inner mitochondrial protein OPA1 in mitochondrial dysfunction by tobacco smoking and in the pathogenesis of COPD

Background Chronic lung diseases, such as chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) are linked to several mitochondrial alterations. Cigarette smoke (CS) alters the structure and function of mitochondria. OPA1 is the main inner mitochondrial GTPase responsible for the fusion events. OPA1 undergoes proteolytic cleavage from long to short forms during acute stress and mitophagy. However, the exact role of OPA1 isoforms and related proteins during CS-induced mitophagy and COPD is not clear. Methods Lung tissues from non-smokers, smokers, COPD and IPF were used to determine the relative expression of OPA1 and related proteins. Additionally, we used mouse lungs from chronic (6 months) CS exposure to evaluate the status of OPA1. Primary lung fibroblasts from normal and COPD patients and naked mole rat (NMR) lung fibroblasts, human fetal lung fibroblast (HFL1), mouse embryonic fibroblast from wild type (WT), OPA1−/−, MFN1 and MFN2−/− were used to determine the effect of CS on OPA1 isoforms. Various mitochondrial fusion promoters/activators (BGP-15, leflunomide, M1) and fission inhibitor (DRP1) were used to determine their effect on OPA1 status and cigarette smoke extract (CSE)-induced lung epithelial (BEAS2B) cell damage, respectively. Seahorse flux analyzer was used to determine the effect of these compounds in BEAS2B cells with and without CSE exposure. Findings Short OPA1 isoforms were predominantly detected and significantly increased in COPD subjects. Acute CSE treatment in various cell lines except NMR was found to increase the conversion of long to short OPA1 isoforms. CSE treatment significantly increased mitochondrial stress-related protein SLP2 in all the cells used. OPA1 interacting partners like prohibitins (PHB1 and 2) were also altered depending on the CS exposure. Finally, BGP-15 and leflunomide treatment were able to preserve the long OPA1 isoform in cells treated with CSE. Interpretation/conclusion The long OPA1 isoform along with SLP2 and prohibitins play a crucial role in CS-induced lung damage, causing mitophagy/mitochondrial dysfunction in COPD, which may be used as a novel therapeutic target in COPD.
Graphical abstract Image 1
Highlights • Smoking is the main causative factor for Chronic Obstructive Pulmonary Disease (COPD) which is associated with mitochondrial dysfunction and altered mitophagy. • Various strategies and models ranging from human samples, mouse models and naked mole rat fibroblasts were used to determine the behavior of the OPA1 forms by cigarette smoke and in COPD. • Cigarette smoke exposure and in patients with COPD the lung cellular levels of S-OPA1 are significantly increased, along with SLP-2 levels with altered prohibitins. • Compounds like BGP-15 and leflunomide promoted/maintained the L-OPA1 levels. • Long OPA1 isoforms along with SLP2 and prohibitins play a crucial role in tobacco smoke-induced lung damage during mitophagy/mitochondrial dysfunction in COPD, which can be a therapeutic target in COPD.