Analysis of the proteome of human airway epithelial secretions
52
Citation
51
Reference
10
Related Paper
Citation Trend
Abstract:
Abstract Background Airway surface liquid, often referred to as mucus, is a thin layer of fluid covering the luminal surface that plays an important defensive role against foreign particles and chemicals entering the lungs. Airway mucus contains various macromolecules, the most abundant being mucin glycoproteins, which contribute to its defensive function. Airway epithelial cells cultured in vitro secrete mucins and nonmucin proteins from their apical surface that mimics mucus production in vivo . The current study was undertaken to identify the polypeptide constituents of human airway epithelial cell secretions to gain a better understanding of the protein composition of respiratory mucus. Results Fifty-five proteins were identified in the high molecular weight fraction of apical secretions collected from in vitro cultures of well-differentiated primary human airway epithelial cells and isolated under physiological conditions. Among these were MUC1, MUC4, MUC5B, and MUC16 mucins. By proteomic analysis, the nonmucin proteins could be classified as inflammatory, anti-inflammatory, anti-oxidative, and/or anti-microbial. Conclusions Because the majority of the nonmucin proteins possess molecular weights less than that selected for analysis, it is theoretically possible that they may associate with the high molecular weight and negatively charged mucins to form a highly ordered structural organization that is likely to be important for maintaining the proper defensive function of airway mucus.Keywords:
Proteome
Mucostasis and small airway plugging lead to chronic infection, hyperinflammation, and a spiral of progressive lung damage in cystic fibrosis (CF), ultimately causing bronchiectasis and pulmonary function decline [1]. Even in the absence of bacterial infection, mucus accumulation can lead to inflammatory upregulation, resulting in lung damage despite bacterial eradication [2]. Airway mucus has been postulated to be overproduced and inefficiently transported in CF [3, 4]. In human epithelial cells as well as multiple animal models of CF, mucus is hyperviscous and abnormally elastic [5–9]. In CF pigs, mucus is also aberrantly tethered to the gland duct openings, a factor which may underlie the propensity for CF mucus to spend less time in motion than in the normal condition [10]. While the mucus layer of the airway surface liquid (ASL) contains numerous proteins, surfactants, antibacterial proteases and anti-proteases [11], its major components are mucins [12]. Mucins are large glycopolymers that can either be tethered to the epithelium or secreted into the lumen as gel-forming polymers, as is the case with MUC5B and MUC5AC [13]. While the roles of individual mucins, namely MUC5B and MUC5AC, have been well identified in other disease states, such as asthma and bacterial infections, it is less well delineated how they are overproduced or dysregulated in CF [13]. Furthermore, in CF, in the absence of adequate bicarbonate concentrations, mucins may not exist in the appropriate conformation, a potential cause of many of these abnormalities [14, 15]. Yet, despite all that is known about mucins and mucus in CF and other muco-obstructive diseases, a means to correcting these abnormalities and restoring normal mucus clearance has yet to be identified. Mucus bundles are important for airway clearance and are regulated by cholinergic stimulus
Mucin 2
Submucosal glands
Cite
Citations (0)
The sections in this article are: 1 Adherent Mucus Gel 1.1 In Vivo Continuity and Thickness 1.2 Physical and Permeability Properties 2 Isolated Mucin Glycoprotein 2.1 Technology 2.2 Mucin Carbohydrate Chain Structure 2.3 Protein Core of Mucins and Macromolecular Polymeric Structure 2.4 Gel-Formation and Physical Properties of Mucins 2.5 Lipid and Protein Components of Mucus Secretions 3 Biosynthesis and Secretion of Mucus: Cellular Aspects 3.1 Mucus-Secreting Cells 3.2 Mucin Biosynthesis 3.3 Secretion of Mucus 4 Secretion of Mucus: Measurement and Control 4.1 Measurement 4.2 Control of Secretion of Gastric Mucus 4.3 Control of Secretion of Intestinal and Colonic Mucus 5 Degradation of Mucus 6 Function of Mucus
Cite
Citations (49)
The transport of mucus on a ciliated epithelium, and the penetration of sperm through cervical mucus, have been shown to be functions of the rheological, principally viscoelastic, properties of the secretion. These physicochemical properties, in turn, are largely determined by the composition and concentration of mucin glycoproteins, which are the principal macromolecular components of the secretion. These functions and properties of various types of mucous secretions are discussed, emphasizing both similarities and differences. Background and data are presented supporting these concepts, based on studies of human cervical and middle ear mucus, as well as bovine cervical and canine tracheal mucus. A major determinant of differences in function between mucus samples appears to be the carbohydrate composition of the mucin, after corrections are made for environmental factors such as pH, ionic strength and mucin concentration Mucin behaviour also depends on specific solutes in the secretion, such as Ca2+. Although significant differences in mucus properties and function exist, it is hypothesized that these developed as variations of the major function common to all mucous secretions, which is to maintain and control the water balance of epithelial mucosa.
Cervical mucus
Cite
Citations (15)
Mucociliary clearance
Respiratory tract
Cite
Citations (165)
Mucus is essential for protection of the airways; however, in chronic airway disease mucus hypersecretion is an important factor in morbidity and mortality. The properties of the mucus gel are dictated in large part by the oligomeric mucins and, over the past decade, we have gained a better understanding of the molecular nature of these complex O-linked glycoproteins. We know now that MUC5AC mucins, as well as different glycoforms of the MUC5B mucin, are the predominant gel-forming glycoproteins in airways mucus. Furthermore, the amount, molecular size, and morphology of these glycoproteins can be altered in disease. From more recent data, it has become clear that oligomeric mucins alone do not constitute mucus, and other mucin and nonmucin components must be important contributors to mucus organization and hence airways defense. Therefore, the challenge over the coming decade will be to investigate how the oligomeric mucins are organized to yield “functional” mucus. Such studies will provide a clearer pe...
Cite
Citations (16)
Large intestine
Mucin 2
Cite
Citations (491)
Hexose
Cite
Citations (16)
Functional food
Cite
Citations (24)
Mucociliary clearance
Submucosal glands
Cite
Citations (110)
Mucus accumulation is a feature of inflammatory airway disease in the horse and has been associated with reduced performance in racehorses. In this study, we have analysed the two major airways gel-forming mucins Muc5b and Muc5ac in respect of their site of synthesis, their biochemical properties, and their amounts in mucus from healthy horses and from horses with signs of airway mucus accumulation. Polyclonal antisera directed against equine Muc5b and Muc5ac were raised and characterised. Immunohistochemical staining of normal equine trachea showed that Muc5ac and Muc5b are produced by cells in the submucosal glands, as well as surface epithelial goblet cells. Western blotting after agarose gel electrophoresis of airway mucus from healthy horses, and horses with mucus accumulation, was used to determine the amounts of these two mucins in tracheal wash samples. The results showed that in healthy horses Muc5b was the predominant mucin with small amounts of Muc5ac. The amounts of Muc5b and Muc5ac were both dramatically increased in samples collected from horses with high mucus scores as determined visually at the time of endoscopy and that this increase also correlated with increase number of bacteria present in the sample. The change in amount of Muc5b and Muc5ac indicates that Muc5b remains the most abundant mucin in mucus. In summary, we have developed mucin specific polyclonal antibodies, which have allowed us to show that there is a significant increase in Muc5b and Muc5ac in mucus accumulated in equine airways and these increases correlated with the numbers of bacteria.
Polyclonal antibodies
Cite
Citations (8)