The Role of Glycosaminoglycans in Neprilysin Regulation and the Remodelling of Tissues in the Airway

Abstract

Fibroblasts are important resident cells in the airway. They are found in increased numbers in asthmatic airways. They synthesise essential structural components of the extracellular matrix. Abnormal and excessive deposition of these structural components in the lamina reticularis of the basement membrane contributes to the airway wall thickening that is a feature of asthma. Fibroblasts also respond to a variety of pro-inflammatory mediators by secreting their own range of biologically active molecules. These include glycosaminoglycans, polysaccharides that have been shown to influence many inflammatory processes.

In this work organ bath techniques were used with isolated bovine airways to investigate the role of glycosaminoglycans in protecting atrial natriuretic peptide (ANP), which is an important natural bronchodilator, from degradation. This study demonstrated that GAGs such as heterogeneous molecular weight hyaluronic acid, low molecular weight hyaluronic acid, heparin and chondroitin sulphate can protect ANP, possibly by modulating the activity of the enzyme neprilysin (NEP).

Enzyme assays were also employed to investigate the effects of low molecular weight hyaluronic acid and heparin directly on NEP activity. These assays demonstrated that these particular GAGs can modulate the activity of NEP in isolation.

Cell culture techniques were used to investigate the mitogenic effects of numerous pro-inflammatory mediators on a human lung fibroblast cell line. By both cell counting methods and an assay of metabolic activity this was investigated further using endothelin-1, GAGs, and also a combination of both. This investigation demonstrated that the effects of endothelin-1, a potent lung fibroblast mitogen, can be inhibited by heparin. Additionally, this investigation demonstrated that chondroitin sulphate can, on its own, enhance the proliferation of lung fibroblasts.

A protocol has also been developed and established for use in the isolation, detection, separation and quantification of GAGs in the absence of radioisotopes.

The present study has further elucidated the role of GAGs in asthma.

Date of Award	2006
Original language	English
Awarding Institution	Glasgow Caledonian University
Supervisor	Allison Grant (Supervisor) & Jane Nally (Supervisor)