High-mobility group box 1 protein induces epithelialmesenchymal transition in upper airway epithelial cells

Downregulation of TET2 Contributes to Nasal Polypogenesis Through Hypoxia-Inducible Factor 1α-Mediated Epithelial-to-Mesenchymal Transition

OBJECTIVES

Hypoxia-inducible factor 1α (HIF1α) and Tet methylcytosine dioxygenase 2 (TET2) have been reported to mediate nasal polypogenesis through the epithelial-to-mesenchymal transition (EMT). Additionally, HIF1α can regulate the expression and function of TET2. However, the precise mechanism of how TET2 regulates the EMT through HIF1α mediation in nasal epithelial cells is still poorly understood.

METHODS

Nasal tissue samples were collected from patients with chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP), CRS without nasal polyps (CRSsNP), and controls. The expression of HIF1α and TET2 was detected using Western blotting and immunohistochemistry. EMT markers (E-cadherin and vimentin) were also evaluated by immunohistochemistry. Primary human nasal epithelial cells (hNECs) were stimulated with CoCl2 to mimic hypoxia. Vitamin C (VC), a TET2 non-specific activator, and small interfering RNA (siRNA) transfection of TET2 were used to further determine the role of TET2 in hypoxia-induced EMT. Finally, reactive oxygen species (ROS) and Nrf2 were measured to explore the downstream consequences of TET2 in hypoxic hNECs.

RESULTS

TET2 levels were lower in the nasal epithelium of CRSwNP patients and were positively correlated with E-cadherin but negatively correlated with vimentin in CRS. However, HIF1α exhibited the opposite pattern and was negatively correlated with TET2 expression. CoCl2-simulated hypoxia led to EMT and increased HIF1α in hNECs in vitro, with simultaneous downregulation of TET2 expression. Addition of VC activated TET2 expression in hNECs, but inhibited EMT and HIF1α expression. Furthermore, siRNA knockdown of TET2 contributed to the EMT in CoCl2-simulated hNECs despite the addition of VC. Finally, TET2 regulated the EMT in hypoxic hNECs through Nrf2 expression and ROS generation.

CONCLUSION

TET2 was negatively correlated with HIF1α and EMT in vivo. TET2 was downregulated by HIF1α, resulting in the EMT in CoCl2-hypoxic hNECs via regulation of oxidative stress in vitro. Hence, TET2 might provide a new therapeutic approach for CRSwNP.

The role of hypoxia in the pathophysiology of chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is a chronic inflammatory disease of the nasal cavity characterized by excessive nasal mucus secretion and nasal congestion. The development of CRS is related to pathological mechanisms induced by hypoxia. Under hypoxic conditions, the stable expression of both Hypoxia inducible factor-1 (HIF-1) α and HIF-2α are involved in the immune response and inflammatory pathways of CRS. The imbalance in the composition of nasal microbiota may affect the hypoxic state of CRS and perpetuate existing inflammation. Hypoxia affects the differentiation of nasal epithelial cells such as ciliated cells and goblet cells, induces fibroblast proliferation, and leads to epithelial-mesenchymal transition (EMT) and tissue remodeling. Hypoxia also affects the proliferation and differentiation of macrophages, eosinophils, basophils, and mast cells in sinonasal mucosa, and thus influences the inflammatory state of CRS by regulating T cells and B cells. Given the multifactorial nature in which HIF is linked to CRS, this study aims to elucidate the effect of hypoxia on the pathogenic mechanisms of CRS.

Immunological Aspects of Chronic Rhinosinusitis

Chronic rhinosinusitis (CRS) is related to persistent inflammation with a dysfunctional relationship between environmental agents and the host immune system. Disturbances in the functioning of the sinus mucosa lead to common clinical symptoms. The major processes involved in the pathogenesis of CRS include airway epithelial dysfunctions that are influenced by external and host-derived factors which activate multiple immunological mechanisms. The molecular bases for CRS remain unclear, although some factors commonly correspond to the disease: bacterial, fungal and viral infections, comorbidity diseases, genetic dysfunctions, and immunodeficiency. Additionally, air pollution leads increased severity of symptoms. CRS is a heterogeneous group of sinus diseases with different clinical courses and response to treatment. Immunological pathways vary depending on the endotype or genotype of the patient. The recent knowledge expansion into mechanisms underlying the pathogenesis of CRS is leading to a steadily increasing significance of precision medicine in the treatment of CRS. The purpose of this review is to summarize the current state of knowledge regarding the immunological aspects of CRS, which are essential for ensuring more effective treatment strategies.

Effects of HMGB1 on Tricellular Tight Junctions via TGF-β Signaling in Human Nasal Epithelial Cells

The airway epithelium of the human nasal mucosa acts as a physical barrier that protects against inhaled substances and pathogens via bicellular and tricellular tight junctions (bTJs and tTJs) including claudins, angulin-1/LSR and tricellulin. High mobility group box-1 (HMGB1) increased by TGF-β1 is involved in the induction of nasal inflammation and injury in patients with allergic rhinitis, chronic rhinosinusitis, and eosinophilic chronic rhinosinusitis. However, the detailed mechanisms by which this occurs remain unknown. In the present study, to investigate how HMGB1 affects the barrier of normal human nasal epithelial cells, 2D and 2.5D Matrigel culture of primary cultured human nasal epithelial cells were pretreated with TGF-β type I receptor kinase inhibitor EW-7197 before treatment with HMGB1. Knockdown of angulin-1/LSR downregulated the epithelial barrier. Treatment with EW-7197 decreased angulin-1/LSR and concentrated the expression at tTJs from bTJs and increased the epithelial barrier. Treatment with a binder to angulin-1/LSR angubindin-1 decreased angulin-1/LSR and the epithelial barrier. Treatment with HMGB1 decreased angulin-1/LSR and the epithelial barrier. In 2.5D Matrigel culture, treatment with HMGB1 induced permeability of FITC-dextran (FD-4) into the lumen. Pretreatment with EW-7197 prevented the effects of HMGB1. HMGB1 disrupted the angulin-1/LSR-dependent epithelial permeability barriers of HNECs via TGF-β signaling in HNECs.