by Charité – Universitätsmedizin Berlin

CT images and tissue sections show how healthy, air-filled tissue is
replaced by thickened, stiff connective tissue. Credit: Leitz/Charité

Working alongside research groups from Heidelberg, researchers from
Charité – Universitätsmedizin Berlin have elucidated the novel disease
processes involved in the development of pulmonary fibrosis. They were
able to show that the protein known as NEDD4-2 plays a key role in
lung health and that loss of this crucial regulatory molecule has a
significant impact on various mechanisms involved in the development
of chronic progressive lung disease. These new insights make it easier
to further investigate the precise mechanisms involved in the
development and progression of pulmonary fibrosis. The researchers’
findings, which have been published in Nature Communications, will
enable researchers to develop new therapeutic approaches.

Pulmonary fibrosis is a serious lung disease which mainly affects
older people; there are virtually no effective treatments. The disease
is characterized by progressive tissue changes which lead to scarring
of the lung. However, its causes are largely unknown, and the cellular
mechanisms involved in its development remain poorly understood. The
term ‘mucociliary clearance’ refers to a self-cleaning mechanism which
relies on ciliated cells in the lung epithelium propelling inhaled
pathogens and other particles trapped in mucus out of the airways. We
know that changes in the epithelium are associated with the production
of excess mucus. They are also associated with the impaired clearance
of this mucus and its primary structural components (known as
‘mucins’). NEDD4-2 is involved in the degradation of a range of other
proteins which in turn are responsible for using these processes to
regulate lung epithelial function. This means NEDD4-2 is a key protein
with a central role in the pathogenesis of pulmonary fibrosis.

Working alongside colleagues from the German Center for Lung Research
(DZL), Heidelberg University Hospital and the German Cancer Research
Center, the team of researchers led by Prof. Dr. Marcus Mall (Director
of Charité’s Department of Pediatric Pulmonology, Immunology and
Critical Medicine and Professor at the Berlin Institute of Health
[BIH]) succeeded in developing a novel animal model of idiopathic
pulmonary fibrosis (IPF). As NEDD4-2 is crucial for early development,
the researchers only deleted the relevant encoding gene in lung
epithelial cells once the animals had reached adulthood. The
researchers examined the animals once they had reached a stage roughly
comparable to the point at which the disease would be diagnosed in a
human patient. Oxygen saturation measurements taken at that stage
revealed a level of lung function impairment which is characteristic
of the disease. Using tissue sections and CT imaging to examine the
lungs, the researchers also found evidence of patchy scarring, a type
of structural abnormality which is indicative of fibrosis. The
researchers found further evidence of the significance of NEDD4-2 in
the pathogenesis of IPF: lung tissue biopsy samples of patients with
IPF contained significantly reduced levels of both transcripts and
proteins. Using mass spectrometry, the researchers then performed what
is known as ‘protein profiling’, an analysis of the complete set of
proteins produced in the lungs. This revealed a high degree of overlap
between the proteins found to be expressed differently in the lungs of
patients with IPF and in the animals used in this study. “Our findings
can help researchers to further investigate the pathogenesis and
progression of this lung disease and develop new treatments. This
model could prove useful for the preclinical testing of compounds with
therapeutic potential, or to develop markers for the early detection
of the disease,” says Prof. Mall.

When studying the underlying disease mechanisms, the researchers
discovered that reduced levels of NEDD4-2 in epithelial cells result
in epithelial remodeling in the airways. Not only are the different
cell types present in different proportions, the cells also produce
increased amounts of certain mucins. When combined with changes in
epithelial sodium transport and the resultant reduction in the volume
of airway surface liquid, this will lead to impaired mucociliary
clearance. Lack of NEDD4-2 also causes increased activity of the TGFβ
signaling pathway, which promotes the formation of fibrosis. Summing
up the findings of the study, the study’s first author, Dr. Julia
Dürr, says: “This means we were able to establish that a lack of
NEDD4-2 is directly linked with mucociliary clearance dysfunction and
the dysregulation of the TGFβ signaling pathway. According to current
state of knowledge, both of these play a role in the pathogenesis of
IPF.”

Anti-fibrotic drugs have been used to treat pulmonary fibrosis for
some years. While these drugs usually succeed in slowing the
development of scarring, they cannot wholly replace lungtransplants as
a last resort treatment option. “Using our model and an already
licensed anti-fibrotic agent, we were able to confirm that this type
of treatment can slow disease progression but does not constitute a
curative treatment.” By way of explanation, Prof. Mall adds: “We hope
that, by providing an improved preclinical testing model, we can help
speed up the development of new therapeutic options.” As a next step,
the researchers plan to test predictive biomarkers which might aid in
early diagnosis. They also plan to test the effectiveness of potential
new drugs which could be used to treat pulmonary fibrosis.

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A new target for the treatment of idiopathic pulmonary fibrosis

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More information: Duerr J et al. Conditional deletion of Nedd4-2 in
lung epithelial cells causes progressive pulmonary fibrosis in adult
mice. Nat Commun (2020), DOI: 10.1038/s41467-020-15743-6.
Journal information: Nature Communications

Provided by Charité – Universitätsmedizin Berlin