Discussion
This study describes an apparent lung phenotype during experimental HF
characterized by vascular remodelling and tissue inflammation. For the
first time, we show that pharmacological correction of CFTR mitigates
the HF-induced downregulation of pulmonary CFTR expression and increases
the proportion of CFTR+ cells in the lung, normalises
vessel wall thickness, and diminishes the HF-associated elevation of
classically-activated non-alveolar macrophages within the lungs. Our
data suggest pharmacological CFTR correction as promising approach to
alleviate HF-induced inflammation in the lung.
The manifestation of HF in the lung is well-established. However,
difficulties in the treatment of HF patients with chronic lung
phenotypes remain, as standard therapies are often complicated by
contraindications. Here, we verify a HF-mediated CFTR downregulation in
the lung [5], a concept that may provide new mechanism-based
treatment options for HF patients with pulmonary complications. Given
the increasing evidence for an acquired CFTR dysfunction not only during
HF but also in classic chronic lung diseases such as COPD and asthma
[33], the indication that CFTR modulators may be useful therapeutics
in the treatment of acquired CFTR abnormalities is certainly of interest
to the field. First trials verified efficacy of the CFTR potentiator
ivacaftor in COPD patients with chronic bronchitis [34]. Here, we
describe beneficial effects of CFTR correction with Lum on lung
inflammation and associated structural alterations during experimental
HF. Specifically, Lum therapy attenuated the HF-associated increase in
small vessel wall thickness, indicating beneficial effects on pulmonary
arteriopathy, which often accompanies HF in patients with chronic left
ventricular dysfunction [35], generally associating with increased
risk of pulmonary complications and hence, overall poor disease outcome.
Despite thickened pulmonary vessel walls, we did not observe higher
collagen accumulation within HF lungs or around the pulmonary
vasculature. In our experiments, we aim at obtaining physiological
values for animal ventilation during surgery to avoid ventilator-induced
lung injury [36], which cannot be excluded from other studies that
reported additional structural alterations and higher collagen content
in HF lungs in mice with comparable EF [37, 38].
Inflammation is a key player in both chronic heart and lung diseases and
critically contributes to vasculopathies. Here, we find increased
numbers of pro-inflammatory monocytes/macrophages infiltrating the HF
lung and an accumulation of monocytes/macrophages around the pulmonary
vasculature, suggesting inflammation-associated vascular remodelling.
Monocytes/macrophages have been shown to be among the primary effectors
of inflammation in pulmonary lesions, and lung interstitial macrophages
play a major role in lung inflammation and dysfunction in several
diseases. Monocytes expressing certain chemokine receptors have been
shown to differentiate into interstitial perivascular macrophages, which
secrete pro-inflammatory cytokines and contribute to vascular
remodelling [39]. Whether changes in CFTR surface expression on
circulating monocytes/macrophages mediates similar effects is an
interesting question especially, considering their relatively high CFTR
positivity compared to other immune cells, reported increased secretion
of pro-inflammatory cytokines after pharmacological CFTR inhibition in
macrophages [17], and the herein observed activation-induced CFTR
surface reduction on macrophages.
HF leads to systemic TNF-α elevation in mice and men [5, 24, 40],
which negatively affects target organs, including the lung [40]. We
previously showed that TNF-α sequestration with Etanercept attenuated
the HF-associated reduction of pulmonary CFTR protein expression
[5]. TNF-α was shown to mediate reduction of CFTR expression on the
surface of different cell types [5, 29], suggesting that the herein
detected HF-associated augmentation of pulmonary TNF-α might be directly
linked to the observed overall CFTR downregulation in the HF lung.
TNF-α, amongst other pro-inflammatory cytokines, induces M1-like
macrophage phenotypes [41] and is secreted by classically-polarized
CD80+ macrophages [42], which accumulate in the HF
lung in our model. TNF-α sequestration using Etanercept was shown to
reduce M1-type markers supported by decreases of CD40 and CD80 surface
markers and increased expression of M2-type markers in human
monocyte-derived macrophages [43]. Here, we find a similar lowering
of CD80+ non-alveolar macrophages in the HF lung after
Lum therapy, suggesting an intimate link between CFTR signalling and
inflammation. Although direct Lum application to the lung resulted in
higher CFTR expression on pulmonary CFTR+ cells,
supporting higher corrector efficacy, increased CD80+alveolar macrophage numbers that were observed with this treatment
regimen may limit long-term benefits of lung-specific Lum application.
CFTR corrector-induced increases of IL-10 in combination with the
elevation of CD206+ cells in our model are suggestive
of an involvement of CFTR in macrophage phenotype switching that promote
a more restorative environment [42]. An alternative activation of
human monocytes from CF patients after CFTR correction as evidenced by
increased IL-10 secretion [44] corroborate our findings. Since CFTR
alterations in pulmonary macrophages and monocyte-derived macrophages
present with an exaggerated cytokine response to bacterial
lipopolysaccharide [19] altered bactericidal activity [45], and
adhesion [46], a direct role of CFTR in lung inflammation during HF
is likely.