Squamous Metaplasia Is Increased in the Bronchial Epithelium of Smokers with Chronic Obstructive Pulmonary Disease
May
Squamous Metaplasia Is Increased in the Bronchial Epithelium of Smokers with Chronic Obstructive Pulmonary Disease
Helen M. Rigden 0 1
Ahmad Alias 0 1
Thomas Havelock 0 1
Rory O'Donnell 0 1
Ratko Djukanovic 0 1
Donna E. Davies 0 1
Susan J. Wilson 0 1
0 Academic Unit of Clinical and Experimental Sciences, Faculty of Medicine, University of Southampton , Southampton , United Kingdom , 2 NIHR Southampton Respiratory Biomedical Research Unit, University Hospital Southampton , Tremona Road, Southampton , United Kingdom
1 Editor: Srikumar Chellappan, H. Lee Moffitt Cancer Center & Research Institute , UNITED STATES
Data Availability Statement; All relevant data are within the paper
-
OPEN ACCESS
Competing Interests: The authors have declared
that no competing interests exist.
Aims
Methods
To quantify the extent of squamous metaplasia in bronchial biopsies and relate it to the
presence of chronic obstructive pulmonary disease (COPD), a smoking-related pathology.
Bronchial biopsies (n = 15 in each group) from smokers with COPD GOLD stage1 and
GOLD stage2, smokers without COPD and healthy non-smokers were stained
immunohistochemically with a panel of antibodies that facilitated the identification of pseudostratified
epithelium and distinction of squamous metaplasia and squamous epithelium from
tangentially cut epithelium. The percentage length of each of these epithelial phenotypes was
measured as a percent of total epithelial length using computerised image analysis. Sections
were also stained for carcinoembryonic antigen and p53, early markers of carcinogenesis,
and Ki67, and the percentage epithelial expression measured.
Results
The extent of squamous metaplasia was significantly increased in both COPD1 and
COPD2 compared to healthy smokers and healthy non-smokers. The amount of fully differentiated squamous epithelium was also increased in COPD1 and COPD2 compared to healthy non-smokers, as was the expression of carcinoembryonic antigen. These features correlated with one other.
Conclusion
In subjects with COPD there is a loss of pseudostratified epithelium accompanied by an increase in squamous metaplasia with transition into a fully squamous epithelium and expression of early markers of carcinogenesis.
Introduction
Squamous metaplasia (SQM) is a pre-neoplastic change of the bronchial epithelium observed
in the lungs in response to toxic injury induced by cigarette smoke [
1–4
]. It is part of a
multistage process [
5–7
] which may eventually lead to full neoplastic transformation, i.e. bronchial
carcinoma. Not all SQM lesions progress to a neoplasia, particularly if low grade and some
may regress to a normal epithelium [
8–10
], especially after smoking cessation [11].
Initially, during SQM quiescent basal cells within the pseudostratified epithelium re-enter
the cell cycle and become hyperproliferative. During the next stage of the process, the
epithelium begins to express markers of a squamous phenotype rather than those of the normal
pseudostratified epithelium. These include squamous epithelial cytokeratins (CK) [
5,6,12–14
] and
the cell adhesion molecule SQM1 [
15
]. Finally, when fully differentiated, having a squamous
cell morphology, cells will express involucrin, a marker of terminal differentiation [
16
].
A history of cigarette smoking is associated with 90% of lung cancers with 15% of lifetime
smokers developing lung cancer [
17–20
]. Chronic obstructive pulmonary disease (COPD) is
also associated with smoking and is an independent risk factor for developing lung cancer, the
risk being increased by up to 4.5 fold [
21–26
]. Between 50 and 70% of subjects with lung cancer
also have COPD [
18,27
]. The cause of this increased susceptibility in subjects with COPD is
unknown. Several possibilities have been suggested, including common molecular pathways
[
28,29
], impaired ability to clear carcinogens due to obstructive airways [
30
] and ongoing
chronic inflammation within the airways [
27,31
].
SQM is observed in the bronchial epithelium of smokers [
11
], but to date there have been,
to our knowledge, no studies to quantify it and relate it to the coexistence and severity of
COPD. We have previously identified a panel of antibodies, CK7, CK13 and involucrin, that
are suitable for identification and distinction of SQM and squamous epithelium in
endobronchial biopsies, from tangentially cut epithelium [
32
], which is difficult based on morphology
alone in small biopsies. CK7 is seen in luminal cells of the pseudostratified epithelium and its
expression is lost during SQM and absent in squamous epithelium. CK13 expression is
restricted to the basal cells of pseudostratified epithelium but is observed throughout the
epithelium with SQM or a squamous phenotype. Involucrin is restricted to cells with a fully
differentiated squamous morphology. This staining pattern is summarised in Fig 1 in the results.
The aim of the current study was to quantitate (...truncated)