Proprotein convertase 5/6a is associated with bone morphogenetic protein-2-induced squamous cell differentiation

Mechanisms of Bone Morphogenetic Protein 2 in Respiratory Diseases

PURPOSE OF REVIEW

Bone morphogenetic protein 2 (BMP2) belongs to the transforming growth factor-β (TGF-β) superfamily and plays an important role in regulating embryonic development, angiogenesis, osteogenic differentiation, tissue homeostasis, and cancer invasion. Increasing studies suggest BMP2 is involved in several respiratory diseases. This study aimed to review the role and mechanisms of BMP2 in respiratory diseases.

RECENT FINDINGS

BMP2 signaling pathway includes the canonical and non-canonical signaling pathway. The canonical signaling pathway is the BMP2-SMAD pathway, and the non-canonical signaling pathway includes mitogen-activated protein kinase (MAPK) pathway and phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway. The BMP2 is related to pulmonary hypertension (PH), lung cancer, pulmonary fibrosis (PF), asthma, and chronic obstructive pulmonary disease (COPD). BMP2 inhibits the proliferation of pulmonary artery smooth muscle cells (PASMCs), promotes the apoptosis of PASMCs to reduce pulmonary vascular remodeling in PH, which is closely related to the canonical and non-canonical pathway. In addition, BMP2 stimulates the proliferation and migration of cells to promote the occurrence, colonization, and metastasis of lung cancer through the canonical and the non-canonical pathway. Meanwhile, BMP2 exert anti-fibrotic function in PF through canonical signaling pathway. Moreover, BMP2 inhibits airway inflammation to maintain airway homeostasis in asthma. However, the signaling pathways involved in asthma are poorly understood. BMP2 inhibits the expression of ciliary protein and promotes squamous metaplasia of airway epithelial cells to accelerate the development of COPD. In conclusion, BMP2 may be a therapeutic target for several respiratory diseases.

The Role of Proprotein Convertases in Upper Airway Remodeling

Chronic rhinosinusitis (CRS) is a multifactorial, heterogeneous disease characterized by persistent inflammation of the sinonasal mucosa and tissue remodeling, which can include basal/progenitor cell hyperplasia, goblet cell hyperplasia, squamous cell metaplasia, loss or dysfunction of ciliated cells, and increased matrix deposition. Repeated injuries can stimulate airway epithelial cells to produce inflammatory mediators that activate epithelial cells, immune cells, or the epithelial-mesenchymal trophic unit. This persistent inflammation can consequently induce aberrant tissue remodeling. However, the molecular mechanisms driving disease within the different molecular CRS subtypes remain inadequately characterized. Numerous secreted and cell surface proteins relevant to airway inflammation and remodeling are initially synthesized as inactive precursor proteins, including growth/differentiation factors and their associated receptors, enzymes, adhesion molecules, neuropeptides, and peptide hormones. Therefore, these precursor proteins require post-translational cleavage by proprotein convertases (PCs) to become fully functional. In this review, we summarize the roles of PCs in CRS-associated tissue remodeling and discuss the therapeutic potential of targeting PCs for CRS treatment.

Malfunction of airway basal stem cells plays a crucial role in pathophysiology of tracheobronchopathia osteoplastica

Understanding disease-associated stem cell abnormality has major clinical implications for prevention and treatment of human disorders, as well as for regenerative medicine. Here we report a multifaceted study on airway epithelial stem cells in Tracheobronchopathia Osteochondroplastica (TO), an under-detected tracheobronchial disorder of unknown etiology and lack of specific treatment. Epithelial squamous metaplasia and heterotopic bone formation with abnormal cartilage proliferation and calcium deposits are key pathological hallmarks of this disorder, but it is unknown whether they are coincident or share certain pathogenic mechanisms in common. By functional evaluation and genome-wide profiling at both transcriptional and epigenetic levels, we reveal a role of airway basal cells in TO progression by acting as a repository of inflammatory and TGFβ-BMP signals, which contributes to both epithelial metaplasia and mesenchymal osteo-chondrogenesis via extracellular signaling and matrix remodeling. Restoration of microenvironment by cell correction or local pathway intervention may provide therapeutic benefits.

Macrophages Inhibit Ciliary Protein Levels by Secreting BMP-2 Leading to Airway Epithelial Remodeling Under Cigarette Smoke Exposure

Chronic obstructive pulmonary disease (COPD) is a chronic respiratory disease with high morbidity and mortality worldwide. So far, smoking is still its leading cause. The characteristics of COPD are emphysema and airway remodeling, as well as chronic inflammation, which were predominated by macrophages. Some studies have reported that macrophages were involved in emphysema and chronic inflammation, but whether there is a link between airway remodeling and macrophages remains unclear. In this study, we found that both acute and chronic cigarette smoke exposure led to an increase of macrophages in the lung and a decrease of ciliated cells in the airway epithelium of a mouse model. The results of in vitro experiments showed that the ciliary protein (β-tubulin-IV) levels of BEAS-2B cells could be inhibited when co-cultured with human macrophage line THP-1, and the inhibitory effect was augmented with the stimulation of cigarette smoke extract (CSE). Based on the results of transcriptome sequencing, we focused on the protein, bone morphogenetic protein-2 (BMP-2), secreted by the macrophage, which might mediate this inhibitory effect. Further studies confirmed that BMP-2 protein inhibited β-tubulin-IV protein levels of BEAS-2B cells under the stimulation of CSE. Coincidentally, this inhibitory effect could be nearly blocked by the BMP receptor inhibitor, LDN, or could be interfered with BMP-2 siRNA. This study suggests that activation and infiltration of macrophages in the lung induced by smoke exposure lead to a high expression of BMP-2, which in turn inhibits the ciliary protein levels of the bronchial epithelial cells, contributing to the remodeling of airway epithelium, and aggravates the development of COPD.

Bone morphogenetic protein-2 as a novel biomarker for refractory chronic rhinosinusitis with nasal polyps

BACKGROUND

Bone morphogenetic proteins (BMPs), which are members of the TGF-β superfamily, regulate bone remodeling by stimulating osteoblasts and osteoclasts. Although the association between osteitis and poor surgical outcomes is well known in patients with chronic rhinosinusitis (CRS), BMPs have not been fully investigated as potential biomarkers for the prognosis of CRS.

OBJECTIVE

Our aim was to investigate the role of BMPs in osteitis in patients with CRS with nasal polyps (NPs) (CRSwNPs), as well as associations between BMPs and inflammatory markers in sinonasal tissues from patients with CRSwNP.

METHODS

We investigated the expression of 6 BMPs (BMP-2, BMP-4, BMP-6, BMP-7, BMP-9, and BMP-10) and their cellular origins in NPs of human subjects by using immunohistochemistry and ELISA of NP tissues. Exploratory factor analysis was performed to identify associations between BMPs and inflammatory markers. Air-liquid interface cell culture of human nasal epithelial cells was performed to evaluate the induction of the epithelial-mesenchymal transition by BMPs.

RESULTS

Of the 6 BMPs studied, BMP-2 and BMP-7 were associated with refractoriness. Only BMP-2 concentrations were higher in patients with severe osteitis and advanced disease extent according to the computed tomography findings. Eosinophils and some macrophages were identified as cellular sources of BMP-2 in immunofluorescence analysis. An in vitro experiment revealed that BMP-2 induced epithelial-mesenchymal transition in air-liquid interface-cultured human nasal epithelial cells, particularly in a T_H2 milieu.

CONCLUSION

BMP-2 could reflect the pathophysiology of mucosa and bone remodeling and may be a novel biomarker for refractory CRSwNP.

Interleukin (IL)-13 and IL-17A contribute to neo-osteogenesis in chronic rhinosinusitis by inducing RUNX2

Background

There is increasing evidence supporting the impact of neoosteogenesis in the pathophysiology of chronic rhinosinusitis (CRS), especially in the recalcitrant group of patients. Runt-related transcription factor 2 (RUNX2), a member of the RUNX family, controls osteoblast differentiation and bone formation. However, the role and regulation of RUNX2 in CRS patients with neoosteogenesis remain unclear. The aim of the study is to determine the role of RUNX2 in neoosteogenesis of CRS patients.

Methods

Sinonasal bone and overlying mucosa samples were obtained from CRS patients with or without neoosteogenesis (n = 67) and healthy controls (n = 11). Double immunofluorescence, immunohistochemistry, and immunoblotting were used to evaluate RUNX2 expression in CRS patients with and without neoosteogenesis. In addition, the osteogenic activity of pro-inflammatory cytokines was examined by measuring alkaline phosphatase (ALP) activity and bone mineralisation in vitro.

Findings

RUNX2 was highly expressed in osteoblasts of CRS patients with neoosteogenesis compared with tissues from control subjects and those with CRS without neoosteogenesis. Mucosal extracts from CRS patients with neoosteogenesis showed increased RUNX2 expression and ALP activity in C2C12 cells, whereas those from patients without neoosteogenesis did not. Expression of interleukin (IL)-13 and IL-17A was upregulated in CRS patients with neoosteogenesis. ALP activity and Alizarin Red staining showed IL-13 and IL-17A dose-dependent osteoblast differentiation and mineralisation in vitro.

Interpretation

These findings suggested that IL-13- or IL-17A-induced RUNX2 contributed to new bone formation in CRS patients through its effect on the activity of osteoblasts. RUNX2 may be a novel target for preventing neoosteogenesis in CRS patients.

ROS-dependent HMGB1 secretion upregulates IL-8 in upper airway epithelial cells under hypoxic condition

High-mobility group box 1 (HMGB1) mediates various functions according to the location. We tried to investigate the role of HMGB1 in upper airway under hypoxic conditions. We cultured primary normal human nasal epithelium (NHNE) cells under hypoxic conditions and evaluated the movement of HMGB1 by western blotting, immunofluorescence, and enzyme-linked immunosorbent assay (ELISA). Reactive oxygen species (ROS) level was evaluated to estimate the translocation mechanism of HMGB1. The role of secreted HMGB1 was evaluated by ELISA assay. Furthermore, we collected human nasal mucosa samples and nasal lavage fluids from patients conditioned under hypoxic and non-hypoxic environment, and compared the expression of HMGB1 in human nasal mucosa samples by immunohistochemistry and the levels of HMGB1 in lavage fluids using ELISA assay. Hypoxia induced translocation of HMGB1 into the extracellular area and it was dependent on ROS produced by dual oxidase 2. Secreted HMGB1 was involved in the upregulation of interleukin (IL)-8. In human samples, HMGB1 was translocated from nucleus to the cytoplasm in hypoxic-conditioned nasal mucosa. HMGB1 was increased in nasal lavage samples of chronic rhinosinusitis patients, whose sinus mucosa was supposed to be hypoxic as compared with controls. We suggest that HMGB1 is secreted in hypoxic condition via ROS-dependent mechanism and secreted HMGB1 participates in IL-8 upregulation mediating inflammatory response.

Proprotein convertase inhibition promotes ciliated cell differentiation - a potential mechanism for the inhibition of Notch1 signalling by decanoyl-RVKR-chloromethylketone

Chronic repetitive rounds of injury and repair in the airway lead to airway remodelling, including ciliated cell loss and mucous cell hyperplasia. Airway remodelling is mediated by many growth and differentiation factors including Notch1, which are proteolytically processed by proprotein convertases (PCs). The present study evaluated a novel approach for controlling basal cell‐type determination based on the inhibition of PCs. It was found that decanoyl‐RVKR‐chloromethylketone (CMK), a PC inhibitor, promotes ciliated cell differentiation and has no effect on the ciliary beat frequency in air–liquid interface (ALI) cultures of human nasal epithelial cells (HNECs). Comparative microarray analysis revealed that CMK considerably increases ciliogenesis‐related gene expression. Use of cell‐permeable and cell‐impermeable PC inhibitors suggests that intracellular PCs regulate basal cell‐type determination in ALI culture. Furthermore, CMK effect on ciliated cell differentiation was reversed by a Notch inhibitor N‐[N‐(3,5‐difluorophenacetyl)‐l‐alanyl]‐S‐phenylglycine t‐butyl ester (DAPT). CMK inhibited the processing of Notch1, a key regulator of basal cell differentiation toward secretory cell lineages in the airway epithelium, and down‐regulated the expression of Notch1 target genes together with furin, a PC. Specific lentiviral shRNA‐mediated knockdown of furin resulted in reduced Notch1 processing and increased numbers of ciliated cells in HNECs. Moreover, CMK inhibited Notch1 processing and promoted regeneration and ciliogenesis of the mouse nasal respiratory epithelium after ZnSO₄ injury. These observations suggest that PC inhibition promotes airway ciliated cell differentiation, possibly through suppression of furin‐mediated Notch1 processing. © 2016 The Authors Journal of Tissue Engineering and Regenerative Medicine Published by John Wiley & Sons Ltd