Role of Orosomucoid 1-like Protein 3 on Cigarette Smoke-induced Airway Inflammation, Mucus Hypersecretion and Activation of the Unfolded Protein Response in Human Airway Epithelial Cells

Abstract

Introduction: Orosomucoid 1–like protein 3 (ORMDL3), a transmembrane protein localised in endoplasmic reticulum (ER), is strongly linked with childhood-onset asthma. Recent study suggested that ORMDL3 is also associated with chronic obstructive pulmonary disease, in which cigarette smoke (CS) is the major risk factor. We aimed to investigate the effect of ORMDL3 on CS-induced inflammatory responses, mucus hypersecretion, ER stress, and activation of the unfold protein response (UPR). Methods: The expression of ORMDL3 was manipulated in primary normal human bronchial epithelial (NHBE) cells using siRNA technologies. Successful knockdown of ORMDL3 was confirmed at both mRNA and protein level. Cigarette smoke medium (CSM) was directly applied to NHBE cells for 24 hours (n=4). The inflammatory and mucin markers as well as the activation of the UPR were assessed by quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and western blot assay. Results: Cigarette smoke medium caused upregulation of ORMDL3 expression at both mRNA and protein level. ORMDL3 knockdown reduced CSM-induced interleukin 8 release and MUC5AC gene expression. Silencing ORMDL3 also led to reduction of ER stress via inhibition of UPR pathways activating transcription factor 6 (ATF-6) and inositol-requiring enzyme (IRE)1alpha after CSM exposure. Conclusion: The current findings provide evidence of the inducible nature of ORMDL3 in bronchial epithelial cells after CS exposure and suggest UPR pathways of ATF-6 and IRE1alpha through which ORMDL3 may be linked to CS-induced airway injury. Acknowledgemen: This study was supported by YC Chan Scientist Award (Ref 200007691).