5 research outputs found
RNA-Seq quantification of the human small airway epithelium transcriptome
<p>Abstract</p> <p>Background</p> <p>The small airway epithelium (SAE), the cell population that covers the human airway surface from the 6<sup>th </sup>generation of airway branching to the alveoli, is the major site of lung disease caused by smoking. The focus of this study is to provide quantitative assessment of the SAE transcriptome in the resting state and in response to chronic cigarette smoking using massive parallel mRNA sequencing (RNA-Seq).</p> <p>Results</p> <p>The data demonstrate that 48% of SAE expressed genes are ubiquitous, shared with many tissues, with 52% enriched in this cell population. The most highly expressed gene, SCGB1A1, is characteristic of Clara cells, the cell type unique to the human SAE. Among other genes expressed by the SAE are those related to Clara cell differentiation, secretory mucosal defense, and mucociliary differentiation. The high sensitivity of RNA-Seq permitted quantification of gene expression related to infrequent cell populations such as neuroendocrine cells and epithelial stem/progenitor cells. Quantification of the absolute smoking-induced changes in SAE gene expression revealed that, compared to ubiquitous genes, more SAE-enriched genes responded to smoking with up-regulation, and those with the highest basal expression levels showed most dramatic changes. Smoking had no effect on SAE gene splicing, but was associated with a shift in molecular pattern from Clara cell-associated towards the mucus-secreting cell differentiation pathway with multiple features of cancer-associated molecular phenotype.</p> <p>Conclusions</p> <p>These observations provide insights into the unique biology of human SAE by providing quantit-ative assessment of the global transcriptome under physiological conditions and in response to the stress of chronic cigarette smoking.</p
Intracellular signaling in the lung : A role for C/EBP transcription factors in chronic obstructive pulmonary disease, glucocorticoid signaling and lung development
Over the last decade, a previously unknown role has been established for
members of the C/EBP transcription factor family in lung gene expression.
In other organs, C/EBPs are well known regulators of cell differentiation
and linked processes such as proliferation, apoptosis, gene expression as
well as central regulators of inflammatory responses and infectious
defenses. The scope of this thesis is to investigate the role of C/EBP
transcription factors in the human and mouse lung as well as a putative
role in the pathogenesis of chronic obstructive pulmonary disease (COPD).
As a first approach, DNA-binding activity of C/EBPs was studied in the
airway epithelium of humans and in adult mice. We found that C/EBPbeta is
the dominant DNA-binding C/EBP transcription factor. Interestingly, we
also found that C/EBPbeta-activity is increased in the airways of
asymptomatic smokers, whereas smokers that develop COPD lack this
increase. We hypothesize that altered activity of C/EBPbeta in airway
epithelial cells has a previously unknown role in the pathogenesis of
COPD. Here it could affect the production of inflammatory mediators and
genes involved in anti-oxidative and infectious defenses in addition to
affecting epithelial cell proliferation, thereby making the lungs more
susceptible to destruction and inflammation which augment the progression
of the disease. Inflammation in COPD typically exhibits partial
resistance to the anti-inflammatory action of glucocorticoids. When
studying glucocorticoid signaling in the lung epithelium, we found that
the glucocorticoid receptor, at least partially, mediates the effects of
glucocorticoids in lung epithelium by inducing phosphorylation of
C/EBPbeta, thereby augmenting its DNA-binding activity. This raises the
possibility that the decrease in C/EBP-binding activity in the airway
epithelium of patients with COPD may have a causative role for the
relative resistance to glucocorticoids seen in this disease.
As a means to deepen our understanding of the C/EBP family s role in the
lung, as well as to critically address whether C/EBPs have a role in COPD
pathogenesis and related pathological processes, an animal model was used
due to the limitations in sampling the human lung. As a first approach to
evaluate whether the mouse is a suitable model to study C/EBP functions
in the lung, we investigated the expression of C/EBPs in the human and
mouse lung epithelium in addition to the lung epithelium of COPD
patients. By using immunohistochemistry we found that the adult
expression pattern of C/EBPs in the mouse lung is highly similar to the
expression pattern of C/EBPalpha and C/EBPbeta in the human lung,
suggesting the mouse as a suitable model to study the C/EBP family s role
in lung. In addition, we found that C/EBPalpha displays dynamic
expression during lung development that together with the respiratory
distress of neonatal C/EBPalpha knockout mice, suggest a crucial role for
C/EBPalpha in the development of the lung. We generated a gain-offunction
mouse model ectopically expressing C/EBPalpha in the lung epithelium
(SFTPC-Cebpa mice), and a lossof-function mouse model using the Cre-LoxP
technique, with lung epithelial disruption of the C/EBPalpha gene
(CebpadeltaLE mice) to address this hypothesis. Both CebpadeltaLE mice
and FTPC-Cebpa mice display strikingly similar impaired lung phenotypes
during development characterized by a decreased number of growing
epithelial tubules which are larger in size as well as a thickened
interstitsium, indicating that the tempo-spatial expression of C/EBPalpha
is important for correct lung development. Further, adult CebpadeltaLE
mice, that survive the perinatal lethality, demonstrate a severe
pathological picture with 1) goblet cell hyperplasia, bronchiolar
metaplasia, fibrosis and mucus plugging, together pathologically defined
as bronchiolitis, 2) emphysema and 3) extensive macrophage and lymphocyte
infiltrations. C/EBPalpha has a vital role in lung development and lung
epithelial differentiation. Repair processes generally descend from
mechanisms and signaling pathways used during organ or tissue
development. Therefore, C/EBPalpha could have a potential role also in
remodeling processes, which in COPD patients either is impaired or
inadequate. The diagnosis of COPD is based on clinical, radiological and
functional features but there are well-recognized histopathological
correlates including all the histopathological findings in the
CebpadeltaLE mice. In line with this, it is tempting to speculate that
the pathological processes in COPD and CebpadeltaLE mice share at least
some underlying mechanisms, with a linkage between the epithelial
differentiation-repair process inherent in COPD and the epithelial
differentiation during lung development. In summary, the findings
presented in this thesis suggest that investigations of the role of
C/EBPs in the pathogenesis of COPD could provide important knowledge,
that may potentially serve as a base for the development of new
treatments for this devastating disease