Background: Pulmonary hypertension (PH) is a life-threatening disease, characterized by excessive pulmonary vascular remodeling, leading to elevated pulmonary arterial pressure and right heart hypertrophy. PH can be caused by chronic hypoxia, leading to hyper-proliferation of pulmonary arterial smooth muscle cells (PASMCs) and apoptosis-resistant pulmonary microvascular endothelial cells (PMVECs). On reexposure to normoxia, chronic hypoxia-induced PH in mice is reversible. In this study, the authors aim to identify novel candidate genes involved in pulmonary vascular remodeling specifically in the pulmonary vasculature. Methods: After microarray analysis, the authors assessed the role of SPARC (secreted protein acidic and rich in cysteine) in PH using lung tissue from idiopathic pulmonary arterial hypertension (IPAH) patients, as well as from chronically hypoxic mice. In vitro studies were conducted in primary human PASMCs and PMVECs. In vivo function of SPARC was proven in chronic hypoxia-induced PH in mice by using an adeno-associated virus–mediated Sparc knockdown approach. Results: C57BL/6J mice were exposed to normoxia, chronic hypoxia, or chronic hypoxia with subsequent reexposure to normoxia for different time points. Microarray analysis of the pulmonary vascular compartment after laser microdissection identified Sparc as one of the genes downregulated at all reoxygenation time points investigated. Intriguingly, SPARC was vice versa upregulated in lungs during development of hypoxia-induced PH in mice as well as in IPAH, although SPARC plasma levels were not elevated in PH. TGF-β1 (transforming growth factor β1) or HIF2A (hypoxia-inducible factor 2A) signaling pathways induced SPARC expression in human PASMCs. In loss of function studies, SPARC silencing enhanced apoptosis and reduced proliferation. In gain of function studies, elevated SPARC levels induced PASMCs, but not PMVECs, proliferation. Coculture and conditioned medium experiments revealed that PMVECs-secreted SPARC acts as a paracrine factor triggering PASMCs proliferation. Contrary to the authors’ expectations, in vivo congenital Sparc knockout mice were not protected from hypoxia-induced PH, most probably because of counter-regulatory proproliferative signaling. However, adeno-associated virus–mediated Sparc knockdown in adult mice significantly improved hemodynamic and cardiac function in PH mice. Conclusions: This study provides evidence for the involvement of SPARC in the pathogenesis of human PH and chronic hypoxia-induced PH in mice, most likely by affecting vascular cell function.

Chronic obstructive pulmonary disease (COPD), which comprises the phenotypes of chronic bronchitis and emphysema, is often associated with pulmonary hypertension (PH). However, currently, no approved therapy exists for PH-COPD. Signalling of the nitric oxide (NO)–cyclic guanosine monophosphate (cGMP) axis plays an important role in PH and COPD.We investigated the treatment effect of riociguat, which promotes the NO–cGMP pathway, in the mouse model of smoke-induced PH and emphysema in a curative approach, and retrospectively analysed the effect of riociguat treatment on PH in single patients with PH-COPD.In mice with established PH and emphysema (after 8 months of cigarette smoke exposure), riociguat treatment for another 3 months fully reversed PH. Moreover, histological hallmarks of emphysema were decreased. Microarray analysis revealed involvement of different signalling pathways,e.g.related to matrix metalloproteinases (MMPs). MMP activity was decreasedin vivoby riociguat. In PH-COPD patients treated with riociguat (n=7), the pulmonary vascular resistance, airway resistance and circulating MMP levels decreased, while oxygenation at rest was not significantly changed.Riociguat may be beneficial for treatment of PH-COPD. Further long-term prospective studies are necessary to investigate the tolerability, efficacy on functional parameters and effect specifically on pulmonary emphysema in COPD patients.

Background: Pulmonary hypertension (PH) is a common complication of COPD, associated with increased mortality and morbidity. Intriguingly, pulmonary vascular alterations have been suggested to drive emphysema development. Previously, we identified inducible nitric oxide synthase (iNOS) as an essential enzyme for development and reversal of smoke-induced PH and emphysema, and showed that iNOS expression in bone-marrow-derived cells drives pulmonary vascular remodelling, but not parenchymal destruction. In this study, we aimed to identify the iNOS-expressing cell type driving smoke-induced PH and to decipher pro-proliferative pathways involved.Methods: To address this question we used 1) myeloid-cell-specific iNOS knockout mice in chronic smoke exposure and 2) co-cultures of macrophages and pulmonary artery smooth muscle cells (PASMCs) to decipher underlying signalling pathways.Results: Myeloid-cell-specific iNOS knockout prevented smoke-induced PH but not emphysema in mice. Moreover, iNOS deletion in myeloid cells ameliorated the increase in expression of CD206, a marker of M2 polarisation, on interstitial macrophages. Importantly, the observed effects on lung macrophages were hypoxia-independent, as these mice developed hypoxia-induced PH.In vitro, smoke-induced PASMC proliferation in co-cultures with M2-polarised macrophages could be abolished by iNOS deletion in phagocytic cells, as well as by extracellular signal-regulated kinase inhibition in PASMCs. Crucially, CD206-positive and iNOS-positive macrophages accumulated in proximity of remodelled vessels in the lungs of COPD patients, as shown by immunohistochemistry.Conclusion: In summary, our results demonstrate that iNOS deletion in myeloid cells confers protection against PH in smoke-exposed mice and provide evidence for an iNOS-dependent communication between M2-like macrophages and PASMCs in underlying pulmonary vascular remodelling.

Background and Purpose: Chronic obstructive pulmonary disease, encompassing chronic airway obstruction and lung emphysema, is a major worldwide health problem and a severe socio‐economic burden. Evidence previously provided by our group has shown that inhibition of inducible NOS (iNOS) prevents development of mild emphysema in a mouse model of chronic tobacco smoke exposure and can even trigger lung regeneration. Moreover, we could demonstrate that pulmonary hypertension is not only abolished in cigarette smoke‐exposed iNOS^−/− mice but also precedes emphysema development. Possible regenerative effects of pharmacological iNOS inhibition in more severe models of emphysema not dependent on tobacco smoke, however, are hitherto unknown.Experimental Approach: We have established a mouse model using a single dose of porcine pancreatic elastase or saline, intratracheally instilled in C57BL/6J mice. Emphysema, as well as pulmonary hypertension development was determined by both structural and functional measurements.Key Results: Our data revealed that (i) emphysema is fully established after 21 days, with the same degree of emphysema after 21 and 28 days post instillation, (ii) emphysema is stable for at least 12 weeks and (iii) pulmonary hypertension is evident, in contrast to smoke models, only after emphysema development. Oral treatment with the iNOS inhibitor N(6)‐(1‐iminoethyl)‐l‐lysine (L‐NIL) was started after emphysema establishment and continued for 12 weeks. This resulted in significant lung regeneration, evident in the improvement of emphysema and reversal of pulmonary hypertension.Conclusion and Implications: Our data indicate that iNOS is a potential new therapeutic target to treat severe emphysema and associated pulmonary hypertension.LINKED ARTICLES: This article is part of a themed issue on Risk factors, comorbidities, and comedications in cardioprotection. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.1/issuetoc