Cigarette smoke impact on the pulmonary artery: implications on COPD-related pulmonary hypertension

Abstract

Cigarette smoke (CS) stands out as a fundamental environmental risk factor for chronic obstructive pulmonary disease (COPD). Low O2 levels, resulting from COPD pathognomonic airflow obstruction and/or emphysema, have been conceived as a main agent causing pulmonary artery (PA) thickening and sustained vasoconstriction, and therefore triggering pulmonary hypertension (PH). However, direct CS impact on the PA has also been proposed as another key pathogenic mechanism of COPDrelated PH. Although CS effects on lung inflammation and endothelial dysfunction have been more widely described, the damage on resident PA fibroblasts (PAFib) and smooth muscle cells (PASMC) is largely unknown. Thus, we focused on characterizing the consequences of direct CS exposure on these cells, regarding both PA remodeling and vascular tone dysregulation. Our results showed that CS directly made human PAFib and PASMC themselves senescent, but their secretomes were able to stimulate proliferation onto non CS-exposed cells, which could contribute to in vivo PA remodeling. Additionally, we observed that CS diminished human PASMC contractility, and caused murine PA stiffening with decreased vasoconstriction and vasodilation responses. This was accompanied by diminished voltage-gated K+ (Kv) currents, membrane depolarization and Kv7.4 channel downregulation. Importantly, COPD patients and healthy smokers showed diminished Kv7.4 levels compared to non-smokers, so its dysregulation might indeed occur independently of hypoxia. Oxidative stress might behave as a unifying cause for these alterations, since it could induce cell senescence and indicate a mitochondrial dysfunction with to insufficient ATP production. This could indeed explain the reduced contractility even in a contradictory scenario of reduced Kv currents. Oxidative stress might also make guanylyl cyclase insensitive to nitric oxide and reduce the vasodilation capacity of CS-treated PA. After CS exposure, our data proved increased total and mitochondrial superoxide (O2 ·–) levels, which did not parallel a counterbalancing antioxidant enzymes upregulation in human PA cells. Antioxidant N-acetylcysteine prevented CS-driven senescence development, and mitochondrial O2 ·– chelator mitoTEMPO partially reverted mitochondrial fission and membrane potential depolarization caused by CS. MitoTEMPO, however, did not prevent PA vasoconstriction loss, so CS might cause additional dysfunctions in PASMC contractile machinery, besides mitochondrial damage. Finally, we observed a CS-driven downregulation of Cyb5R3, the enzyme which prevents guanylyl cyclase oxidation in PASMC. Together with decreased Kv currents, this might explain the CS-mediated loss in PA vasodilation we observed. Most importantly, PA vasodilation was recovered after mitoTEMPO treatment. Thus, oxidative stress reduction might protect against PA senescence and insensitivity to vasodilators, and be considered as a novel therapeutic approach in the managing of COPD-related PH