Biomedical Engineering Reference
In-Depth Information
Figure 4
Respiratory tract mucins. Top panel: Schematic representation of gene
products of MUC2, MUC5AC, and MUC5B. These gene products comprise the
mucins in airway secretions from patients with COPD. Lower panels: Schematic
representation of a gel-forming mucin molecule. The mucin subunit (~500 nm in
length) comprises an amino acid backbone with highly glycosylated areas and folded
regions, stabilized via disulphide bonds, with little or no glycosylation. Glycosylation
is via O-linkages and is highly diverse. In the mature secreted molecule, the subunits
arejoinedend-to-endbydisulphidebonds(S-S)intolongthread-likemolecules.
and 16-20 (13-18). Although a number of these genes are expressed in the
airways (9), it is the MUC5AC and MUC5B gene products that are the
major gel forming mucins in 'normal' respiratory tract secretions (9),
although MUC2 may be upregulated in COPD (see below) (Fig. 4).
III. MUCUS HYPERSECRETORY PHENOTYPE IN COPD
Airway mucus hypersecretion in COPD has characteristic pathophysiologi-
cal features. Many of these features, for example sputum production and
goblet cell hyperplasia, are common to other hypersecretory respiratory
diseases, for example asthma and cystic fibrosis. Other features appear to
be specifically associated with COPD (see below). Differences in mucus
pathophysiology between COPD and asthma have been discussed previously
(19), and are summarized in Figure 5. Presumably, differences in the pul-
monary inflammatory 'profile' of COPD and asthma (the former essentially
a macrophage-driven neutrophilia and latter a Th2 lymphocyte-driven
