Macrophages are related to goblet cell hyperplasia and induce MUC5B but not MUC5AC in human bronchus epithelial cells

Abstract

Airway goblet cell hyperplasia (GCH)-detectable by mucin staining-and abnormal macrophage infiltrate are pathological features present in many chronic respiratory disorders. However, it is unknown if both factors are associated. Using in-vivo and in-vitro models, we investigated whether macrophages are related with GCH and changes in mucin immunophenotypes. Lung sections from Sprague-Dawley rats treated for 48 h with one intra-tracheal dose of PBS or LPS (n ¼ 4-6 per group) were immunophenotyped for rat-goblet cells, immune, and proliferation markers. Human monocytederived macrophages (MDM) were pre-treated with or without LPS, immunophenotyped, and their supernatant, as well as cytokines at levels equivalent to supernatant were used to challenge primary culture of normal human bronchus epithelial cells (HBEC) in air-liquid interface, followed by MUC5B and MUC5AC mucin immunostaining. An association between increased bronchiolar goblet cells and terminal-bronchiolar proliferative epithelial cells confirmed the presence of GCH in our LPS rat model, which was related with augmented bronchiolar CD68 macrophage infiltration. The in-vitro experiments have shown that MUC5AC phenotype was inhibited when HBEC were challenged with supernatant from MDM pre-treated with or without LPS. In contrast, TNF-a and interleukin-1b at levels equivalent to supernatant from LPS-treated MDM increased MUC5AC. MUC5B was induced by LPS, supernatant from LPS-treated MDM, a mix of cytokines including TNF-a and TNF-a alone at levels present in supernatant from LPS-treated MDM. We demonstrated that macrophages are related with bronchiolar GCH, and that they induced MUC5B and inhibited MUC5AC in HBEC, suggesting a role for them in the pathogenesis of airway MUC5B-related GCH. KEYWORDS: airways; cytokines; LPS; lung inflammation; TNF-alphaMucus is a gel that covers the airway epithelium and is constituted by different glycoproteins called mucins, which are secreted by goblet cells from submucosal glands and the airway epithelium. 1 Mucus dissolves noxious gases and entraps foreign particles and pathogens, facilitating their clearance by mucociliary transport as a mechanism of innate defense. 2 However, in chronic inflammatory respiratory diseases, such as asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF), there is a pathological goblet cell hyperplasia (GCH) and mucus hypersecretion that can generate airway occlusion, associated with morbidity and death. 1 The main gel-forming mucins found in human airways are MUC5B and MUC5AC. 1 In healthy individuals, low levels of MUC5B and MUC5AC can be detected in mucus; although MUC5B is mainly present in the submucosal glands and MUC5AC is predominantly distributed in the airway epithelium. 3 In baseline conditions of chronic inflammatory respiratory disorders, MUC5B and/or MUC5AC are increased in different compartments of the respiratory tract. [3][4][5][6] For example, MUC5B and MUC5AC are augmented in small airway lumen and epithelium from patients with advanced CF; 4 GC...

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“…In addition, the presence of other cell types besides neutrophils, such as macrophages, seem important for goblet cell hyperplasia. This has been suggested in the literature [26][27][28][29]. Furthermore, several studies suggest that various other factors that are involved in COPD pathogenesis, including bacterial and viral infections, might have an important role in promoting goblet cell hyperplasia [30,31].…”

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“…One possible explanation for the increased mucus metaplasia in the airways of OVA-treated Adam8 −/− vs. WT mice in the presence of similar lung levels of Il-13 is that OVA-treated Adam8 −/− mice have higher airway macrophages and eosinophil counts (Fig. 1C) and these cells and their products (including TNF-α) increase mucin gene expression by airway epithelium (69,70). It is noteworthy that we detected higher lung levels of TNF-α in OVA-treated Adam8 −/− mice (Fig.…”

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“…The available evidence is indirect or correlative. 41,46,49,50,74,75 It also is not in agreement with other studies, which show that ciliated cells do not give rise to goblet cells during airway remodeling in rodents and humans, and with studies that provide evidence for increased goblet cell proliferation. 48,56,[76][77][78] Therefore, we consider biological plausibility for this KER (KE2/KE3) to be moderate.…”

“…Alternatively, classical downstream activation of the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway, also known as Raf/ Ras/MAPK/ERK pathway, increases airway epithelial cell proliferation 30,43,44 (KE4: Increased Proliferation of Epithelial Cells) and facilitates epithelial wound repair. 12,20,45 While there is evidence that increased goblet cell proliferation may be the underlying cause of goblet cell hyperplasia (KE7: Goblet cell hyperplasia (GCH)), 46 the key players mediating an increase in airway goblet cell numbers following EGFR activation are still largely unexplored. Basal epithelial cells which exhibit stem cell-like properties have been postulated to function as a source of goblet cells in injured airways, utilizing cell fate pathways that favor secretory cells over other cell populations.…”