The role of orosomucoid 1-like protein 3 (ORMDL3) in cigarette smoke-induced airway injury

Abstract

Chronic obstructive pulmonary disease (COPD), as the third leading cause of mortality globally, is characterized by progressively persistent airflow limitation and chronic airway inflammation. Cigarette smoke (CS) is the major risk factor for COPD. Currently, no effective medications could reverse long-term decline in lung function of patients with COPD. Orosomucoid 1-like protein 3 (ORMDL3), an endoplasmic reticulum (ER) transmembrane protein, is genetically associated with COPD, in addition to childhood-onset asthma. However, the impact of ORMDL3 in CS-induced injury of airway structural cells, including airway epithelial cells and airway smooth muscle cells, is still limited. In vivo CS-exposed animal study suggested that ORMDL3 was a CS-inducible protein with wide expression in rat lungs, including alveolar macrophages, airway epithelium and lesser extent in airway smooth muscle. To investigate the role of ORMDL3 on ER stress in specific airway cell types in CS-induced airway injury, silencing ORMDL3 by using siRNA was performed in human bronchial epithelial cells (HBECs) and human airway smooth muscle cells (HASMCs) respectively. Differential regulations of ORMDL3 in CS-induced ER stress via unfolded protein response (UPR) pathways activation were found between HBECs and HASMCs in this study. In HBECs, ORMDL3 regulated cigarette smoke medium (CSM)-induced ER stress via inositol-requiring enzyme 1 (IRE1) and activating transcription factor 6 (ATF6) of UPR signalling pathways. ORMDL3 mediated CSM-induced activation of IRE1α, resulting in the generation of spliced X-box binding protein (XBP-1s) that indirectly induced inflammation via nuclear factor-κB (NF-κB) signalling pathway to activate the expression of inflammatory cytokine genes. On the other hand, the activation of ATF6 regulated downstream target sarco-endoplasmic reticulum Ca2+ ATPase 2 (SERCA2) and subsequent protein folding and ER-associated degradation (ERAD) process. Furthermore, ATF6 caused activation of NF-κB signalling pathway through phosphorylation of Akt leading to airway inflammation and mucus hypersecretion. However, the study in HASMCs suggested that ORMDL3 regulated CSM-induced ER stress via protein kinase RNA-like ER kinase (PERK) and ATF6 arms of UPR signalling pathways. Activation of PERK induced transcription of CCAAT/enhancer-binding protein-homologous protein (CHOP) leading to airway smooth muscle proliferation. PERK activation also caused activation of NF-κB signalling pathway leading to airway inflammation. Similar to HBECs, ORMDL3 also regulated CSM-induced ER stress via activation of UPR-ATF6 pathway in HASMCs. I have also established an effective three-dimensional co-culture model of well-differentiated HBECs and HASMCs to study the direct interaction. The findings showed greater responses in CSM-induced airway inflammation and mucus hypersecretion in co-culture model via regulation of ORMDL3-meditaed UPR-ATF6 pathway. In summary, this study demonstrated for the first insight on the role of ORMDL3 in CS-induced airway injury, including airway inflammation, cell proliferation, mucus hypersecretion, ER stress, and mitochondrial dysfunction in HBECs and HASMCs respectively as well as in the novel co-culture model. The present findings provide evidence to suggest that ORMDL3 might be a novel therapeutic target for CS-mediated disease such as COPD.