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.