Autophagy mechanisms in sputum and peripheral blood cells of patients with severe asthma: a new therapeutic target

Summary Background Autophagy and genetic predisposition have been suggested to potentially play roles in the development of asthma. However, little is known about the role of autophagy in the pathogenesis of severe asthma. Objective We compared autophagy in the sputum granulocytes, peripheral blood cells ( PBC s) and peripheral blood eosinophils ( PBE s) between patients with severe asthma and those with non‐severe asthma and investigated the functional effects of autophagy. Methods We enrolled 36 patients with severe asthma, 14 with non‐severe asthma and 23 normal healthy controls in this study. Sputum granulocytes, PBC s and PBE s were isolated from each subject. Autophagy was evaluated based on the expression of microtubule‐associated protein light chain 3 ( LC 3) by Western blot, confocal microscopy, transmission electron microscopy and flow cytometry. IL ‐8 levels were measured by ELISA . To induce autophagy, HL ‐60 cells, human primary small airway epithelial cells (SAECs) and A549 cells were treated with IL ‐5, IL ‐1β and TNF ‐α. To inhibit autophagy, PI 3K inhibitors ( LY 29400 and 3‐methyladenine [3‐ MA ]) and hydroxychloroquine ( HCQ ) were used. Knockdown of ATG 5 and Beclin‐1 was performed in A549 cells, and the therapeutic effects of dexamethasone were evaluated. Results Higher autophagy levels were noted in sputum granulocytes, PBC s and PBE s from patients with severe asthma than from patients with non‐severe asthma and healthy controls ( P < 0.05 for all). IL ‐5 increased autophagy levels in both PBC s and PBE s ( P < 0.05). 3‐ MA attenuated the increased expression of LC 3‐ II and eosinophil cationic protein in HL ‐60 cells induced by IL ‐5 ( P = 0.034 for both). Dexamethasone did not affect autophagy levels in PBE s. IL ‐1β increased LC 3‐ II expression and IL ‐8 production ( P < 0.01) in SAEC s, and this was attenuated by LY 294002, 3‐ MA , HCQ and knockdown of ATG 5 and Beclin‐1 (in A549 cells) ( P < 0.01). Conclusions and Clinical Relevance Autophagy could play a role in the pathogenesis of severe asthma. Autophagy modulation may be a novel therapeutic target for conventional therapy‐resistant severe asthma.