Airway Exposure to E-Cigarette Vapors Impairs Autophagy and Induces Aggresome Formation.

Aims: Electronic cigarettes (e-cigarettes) are proposed to be a safer alternative to tobacco cigarettes. Hence, we evaluated if e-cigarette vapors (eCV) impair cellular proteostasis similar to cigarette smoke exposure.

Results: First, we evaluated the impact of eCV exposure (2.5 or 7.5 mg) on Beas2b cells that showed significant increase in accumulation of total polyubiquitinated proteins (Ub, insoluble fractions) with time-dependent decrease in proteasomal activities from 1 h (p < 0.05), 3 h (p < 0.001) to 6 h (p < 0.001) of eCV exposure compared to room air control. We verified that even minimal eCV exposure (1 h) induces valosin-containing protein (VCP; p < 0.001), sequestosome-1/p62 (aberrant autophagy marker; p < 0.05), and aggresome formation (total poly-Ub-accumulation; p < 0.001) using immunoblotting (IB), fluorescence microscopy, and immunoprecipitation (IP). The inhibition of protein synthesis by 6 h of cycloheximide (50 μg/ml) treatment significantly (p < 0.01) alleviates eCV-induced (1 h) aggresome bodies. We also observed that eCV (1 h)-induced protein aggregation can activate oxidative stress, apoptosis (caspase-3/7), and senescence (p < 0.01) compared to room air controls. We verified using an autophagy inducer carbamazepine (20 μM, 6 h) or cysteamine (250 μM; 6 h, antioxidant) that eCV-induced changes in oxidative stress, poly-ub-accumulation, proteasomal activity, autophagy, apoptosis, and/or senescence could be controlled by autophagy induction. We further confirmed the role of acute eCV exposure on autophagy impairment in murine lungs (C57BL/6 and CD1) by IB (Ub, p62, VCP) and IP (VCP, p62), similar to in-vitro experiments.

Innovation: In this study, we report for the first time that eCV exposure induces proteostasis/autophagy impairment leading to oxidative stress, apoptosis, and senescence that can be ameliorated by an autophagy inducer.

Conclusion: eCV-induced autophagy impairment and aggresome formation suggest their potential role in chronic obstructive pulmonary disease-emphysema pathogenesis. Antioxid. Redox Signal. 00, 000-000.