Cystic Fibrosis and Other Respiratory Diseases of Impaired Mucus Clearance

Cystic Fibrosis/Pulmonary Research and Treatment Center, Department of Medicine, The University of North Carolina at Chapel Hill, 27599, USA.
Toxicologic Pathology (Impact Factor: 2.14). 02/2007; 35(1):116-29. DOI: 10.1080/01926230601060025
Source: PubMed


Exposed to a diverse array of potentially noxious agents, the respiratory tract is protected by a highly developed innate defense system. Physiologically regulated epithelial ion and water transport coordinated with mucin secretion, beating cilia, and cough results in continuous flow of fluid and mucus over airway surfaces toward the larynx. This cleansing action is the initial and perhaps most quantitatively important innate defense mechanism. Repeated lung infections and eventual respiratory insufficiency characteristic of human cystic fibrosis (CF) and primary ciliary dyskinesia (PCD) illustrate the consequences of impaired mucus clearance. Altered mucus clearance likely contributes to the initiation, progression, and chronicity of other airway diseases characterized by inflammation and mucous secretory cell hyper/metaplasia that afflict millions worldwide, including chronic obstructive pulmonary disease (COPD). This review concisely discusses the pathophysiology of human diseases characterized by genetic defects that impair mucus clearance. It then explores animal models in which components of the mucus clearance system have been disrupted. These models firmly establish the importance of mucus clearance for respiratory health, and will help elucidate disease mechanisms and therapeutic strategies in CF, PCD and COPD.

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    • "Moreover, the lung microbiome in People living with HIV is similar to that observed in COPD and cystic fibrosis (Huang and Lynch, 2011). Impaired MCC, is primarily responsible for microbial colonization of airways in chronic airway diseases like COPD and cystic fibrosis (Sethi, 2000; Livraghi and Randell, 2007). MCC is a primary innate defense mechanism of the airways and protects the host from airborne pathogens, pollutants, and allergens (Wanner et al., 1996). "
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    ABSTRACT: Impaired mucociliary clearance (MCC) is a hallmark of acquired chronic airway diseases like chronic bronchitis associated with chronic obstructive pulmonary disease (COPD) and asthma. This manifests as microbial colonization of the lung consequently leading to recurrent respiratory infections. People living with HIV demonstrate increased incidence of these chronic airway diseases. Bacterial pneumonia continues to be an important comorbidity in people living with HIV even though anti-retroviral therapy has succeeded in restoring CD4+ cell counts. People living with HIV demonstrate increased microbial colonization of the lower airways. The microbial flora is similar to that observed in diseases like cystic fibrosis and COPD suggesting that mucociliary dysfunction could be a contributing factor to the increased incidence of chronic airway diseases in people living with HIV. The three principal components of the MCC apparatus are, a mucus layer, ciliary beating, and a periciliary airway surface liquid (ASL) layer that facilitates ciliary beating. Cystic fibrosis transmembrane conductance regulator (CFTR) plays a pivotal role in regulating the periciliary ASL. HIV proteins can suppress all the components of the MCC apparatus by increasing mucus secretion and suppressing CFTR function. This can decrease ASL height leading to suppressed ciliary beating. The effects of HIV on MCC are exacerbated when combined with other aggravating factors like smoking or inhaled substance abuse, which by themselves can suppress one or more components of the MCC system. This review discusses the pathophysiological mechanisms that lead to MCC suppression in people living with HIV who also smoke tobacco or abuse illicit drugs.
    Full-text · Article · Nov 2015 · Frontiers in Microbiology
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    • "In cystic fibrosis (CF), chronic injuries of the airways lead to epithelium remodelling that is characterised by mucous secretory hyper/metaplasia and a progressive loss of MCCs, dramatically impairing mucociliary clearance and airway defence (Livraghi and Randell, 2007). Thus, we examined whether BMP pathway inhibition by Noggin treatment was also capable of inducing an increase in the number of MCCs in primary cultures derived from CF patients. "
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    ABSTRACT: Despite the importance of mucociliary epithelia in animal physiology, the mechanisms controlling their establishment are poorly understood. Using the developing Xenopus epidermis and regenerating human upper airways, we reveal the importance of BMP signalling for the construction of vertebrate mucociliary epithelia. In Xenopus, attenuation of BMP activity is necessary for the specification of multiciliated cells (MCCs), ionocytes and small secretory cells (SSCs). Conversely, BMP activity is required for the proper differentiation of goblet cells. Our data suggest that the BMP and Notch pathways interact to control fate choices in the developing epidermis. Unexpectedly, BMP activity is also necessary for the insertion of MCCs, ionocytes and SSCs into the surface epithelium. In human, BMP inhibition also strongly stimulates the formation of MCCs in normal and pathological (cystic fibrosis) airway samples, whereas BMP overactivation has the opposite effect. This work identifies the BMP pathway as a key regulator of vertebrate mucociliary epithelium differentiation and morphogenesis. © 2015. Published by The Company of Biologists Ltd.
    Full-text · Article · Jun 2015 · Development
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    • "The best-known case certainly is mucociliary clearance of the airway epithelia, which constitutes a first-line defense mechanism against pathogens. Patients suffering from impaired mucus production or cilia function show a high prevalence of lung infections (Albee and Dutcher, 2012; Cowan et al., 2001; Livraghi and Randell, 2007; Rubin, 2007). MCEs must be able to adapt to changing environmental conditions. "
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    ABSTRACT: The embryonic skin of Xenopus tadpoles serves as an experimental model system for mucociliary epithelia (MCE) such as the human airway epithelium. MCEs are characterized by the presence of mucus-secreting goblet and multiciliated cells (MCCs). A third cell type, ion-secreting cells (ISCs), is present in the larval skin as well. Synchronized beating of MCC cilia is required for directional transport of mucus. Here we describe a novel cell type in the Xenopus laevis larval epidermis, characterized by serotonin synthesis and secretion. It is termed small secretory cell (SSC). SSCs are detectable at early tadpole stages, unlike MCCs and ISCs, which are specified at early neurulation. Subcellularly, serotonin was found in large, apically localized vesicle-like structures, which were entirely shed into the surrounding medium. Pharmacological inhibition of serotonin synthesis decreased the velocity of cilia-driven fluid flow across the skin epithelium. This effect was mediated by serotonin type 3 receptor (Htr3), which was expressed in ciliated cells. Knockdown of Htr3 compromised flow velocity by reducing the ciliary motility of MCCs. SSCs thus represent a distinct and novel entity of the frog tadpole MCE, required for ciliary beating and mucus transport across the larval skin. The identification and characterization of SSCs consolidates the value of the Xenopus embryonic skin as a model system for human MCEs, which have been known for serotonin-dependent regulation of ciliary beat frequency.
    Full-text · Article · Mar 2014 · Development
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