TWIK-2 ( KCNK6 ) is a member of the 2-pore domain (K _2P ) family of potassium channels, which are highly expressed in the vascular system. We tested the hypothesis that TWIK-2 deficiency leads to pulmonary hypertension. TWIK-2 knockout mice and their wildtype littermates at 8 weeks of age had similar mean right ventricular systolic pressures (24±3 and 21±3 mm Hg, respectively.) Significantly, by 20 weeks of age, the mean right ventricular systolic pressures in TWIK-2 knockout mice increased to 35±3 mm Hg ( P ≤0.036), whereas mean right ventricular systolic pressures in wildtype littermates remained at 22±3 mm Hg. Elevated mean right ventricular systolic pressures in the TWIK-2 knockout mice was accompanied by pulmonary vascular remodeling as determined by a 25% increase in the cross-sectional area of the vessels occupied by the vessel wall. Additionally, secondary branches of the pulmonary artery from 20-week-old TWIK-2 knockout mice showed an enhanced contractile response to U46619 (10 ^–6 moles/L), a thromboxane A2 mimetic, which was completely abolished with the Rho-kinase inhibitor, Y27632 (10 ^–6 and 10 ^–5 moles/L). Treatment of TWIK-2 knockout mice with the Rho-kinase inhibitor, fasudil, in the drinking water for 12 weeks, abolished the development of pulmonary hypertension and attenuated the vessel remodeling. We concluded that mice deficient in the TWIK-2 channel develop pulmonary hypertension between 8 and 20 weeks of age through a mechanism involving Rho-kinase. Our results suggest that downregulation of TWIK-2 in the pulmonary vasculature may be an underlying mechanism in the development of pulmonary hypertension.

The 1918 influenza killed approximately 50 million people in a few short years, and now, the world is facing another pandemic. In December 2019, a novel coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused an international outbreak of a respiratory illness termed coronavirus disease 2019 (COVID-19) and rapidly spread to cause the worst pandemic since 1918. Recent clinical reports highlight an atypical presentation of acute respiratory distress syndrome (ARDS) in COVID-19 patients characterized by severe hypoxemia, an imbalance of the renin–angiotensin system, an increase in thrombogenic processes, and a cytokine release storm. These processes not only exacerbate lung injury but can also promote pulmonary vascular remodeling and vasoconstriction, which are hallmarks of pulmonary hypertension (PH). PH is a complication of ARDS that has received little attention; thus, we hypothesize that PH in COVID-19-induced ARDS represents an important target for disease amelioration. The mechanisms that can promote PH following SARS-CoV-2 infection are described. In this review article, we outline emerging mechanisms of pulmonary vascular dysfunction and outline potential treatment options that have been clinically tested.

Pulmonary hypertension (PH) carries significant associated morbidity and mortality and the underlying molecular mechanisms of PH are not well understood. Loss-of-function mutations in TASK-1 potassium channels are associated with PH in humans. Although TASK-1 has been considered in the development of PH for over a decade, characterization of TASK-1 knockout mice has been limited to in vitro studies or in vivo studies in room air at isolated time points. The purpose of this study was two-fold. First, we sought to determine if TASK -/- male and female mice developed PH over the span of one year. Second, we sought to determine the effect of chronic hypoxia, a stimulus for PH, and its recovery on PH in TASK-1 -/- mice. We measured right ventricular systolic pressure (RVSP) and vascular remodeling in male and female C57BL/6 WT and TASK-1 -/- mice at separate time points:20 to 24 weeks and 1 year of age. Additionally, we measured RVSP and vascular remodeling in TASK-1 -/- and wildtype mice between 13 to 16 weeks of age exposed to 10% hypoxia for three weeks followed by recovery to room air conditions for an additional six weeks. Results: RVSP was similar between WT and TASK-/- mice. Male and female WT and TASK-1 -/- mice all demonstrated age-related increases in RVSP, which correlated to age-related vascular remodeling in male mice but not in female mice. Male TASK-1 -/- and WT mice exposed to chronic hypoxia demonstrated increased RVSP which decreased following room air recovery. WT and TASK-1 -/- male mice demonstrated vascular remodeling upon exposure to hypoxia that persisted in room air recovery. Conclusions: Female and male TASK-1 -/- mice do not develop hemodynamic or vascular evidence for PH, but RVSP rises in an age dependent manner independent of genotype. TASK-1-/- and WT male mice develop hypoxia-induced elevations in RVSP that decrease to baseline after recovery in room air. TASK-1-/- and WT male mice demonstrate vascular remodeling after exposure to hypoxia that persists despite recovery to room air conditions, and does not correlate with RVSP normalization.

Congenital diaphragmatic hernia (CDH) leads to pathophysiologic pulmonary vasoreactivity. Previous studies show that mesenchymal stromal cell-derived extracellular vesicles (MSCEv) inhibit lung inflammation and vascular remodeling. We characterize MSCEv and human pulmonary artery endothelial cell (HPAEC) interaction, as well as the pulmonary artery (PA) response to MSCEv treatment. HPAECs were cultured with and without exposure to nitrofen (2,4-dichloro-phenyl-p-nitrophenylether) and treated with MSCEv. HPAEC viability, architecture, production of reactive oxygen species (ROS), endothelial dysfunction-associated protein levels (PPARγ, LOX-1, LOX-2, nuclear factor-κB [NF-κB], endothelial NO synthase [eNOS], ET-1 [endothelin 1]), and the nature of MSCEv-cellular interaction were assessed. Newborn rodents with and without CDH (nitrofen model and Sprague-Dawley) were treated with intravascular MSCEv or vehicle control, and their PAs were isolated. Contractility was assessed by wire myography. The contractile (KCL and ET-1) and relaxation (fasudil) responses were evaluated. HPAEC viability correlated inversely with nitrofen dose, while architectural compromise was directly proportional. There was a 2.1 × increase in ROS levels in nitrofen HPAECs ( P < 0.001), and MSCEv treatment attenuated ROS levels by 1.5 × versus nitrofen HPAECs ( P < 0.01). Nitrofen-induced alterations in endothelial dysfunction-associated proteins are shown, and exposure to MSCEv restored more physiologic expression. Nitrofen HPAEC displayed greater MSCEv uptake (80% increase, P < 0.05). Adenosine, a clathrin-mediated endocytosis inhibitor, decreased uptake by 46% ( P < 0.05). CDH PA contraction was impaired with KCL (108.6% ± 1.4% vs. 112.0% ± 1.4%, P = 0.092) and ET-1 (121.7% ± 3.0% vs. 131.2% ± 1.8%, P < 0.01). CDH PA relaxation was impaired with fasudil (32.2% ± 1.9% vs. 42.1% ± 2.2%, P < 0.001). After MSCEv treatment, CDH PA contraction improved (125.9% ± 3.4% vs. 116.4 ± 3.5, P = 0.06), and relaxation was unchanged (32.5% ± 3.2% vs. 29.4% ± 3.1%, P = 0.496). HPAEC exposure to nitrofen led to changes consistent with vasculopathy in CDH, and MSCEv treatment led to a more physiologic cellular response. MSCEv were preferentially taken up by nitrofen-treated cells by clathrin-dependent endocytosis. In vivo, MSCEv exposure improved PA contractile response. These data reveal mechanisms of cellular and signaling alterations that characterize MSCEv-mediated attenuation of pulmonary vascular dysfunction in CDH-associated pulmonary hypertension.

SARS-CoV-2 has devastated the global community with almost 6 million deaths and expected ongoing deaths with the rise of new variants.^1,2 One challenging aspect of treating COVID-19 is understanding why certain infected individuals experience severe, life-threatening complications, while others remain minimally symptomatic. Severity risks associated with SARS-CoV-2 infection are purported to be related to variable factors including patient ancestry, socioeconomic status, health care utilization, and comorbid conditions.^3-5 Although socioeconomic status and social determinants of health have been discussed as possible causes for the higher burden of increased morbidity and mortality in minoritized racial and ethnic communities in the US, the contribution of biology toward disease severity has been minimally explored.⁶ As a result, despite almost 3 years of observational data, the biologic bases of susceptibility to SARS-CoV-2 infection and risks of severe outcomes after infection are largely unknown.

We have previously shown Twik‐2^−/− mice develop pulmonary hypertension and vascular remodeling. We hypothesized that distal pulmonary arteries (D‐PAs) of the Twik‐2^−/− mice are hypercontractile under physiological venous conditions due to altered electrophysiologic properties between the conduit and resistance vessels in the pulmonary vascular bed. We measured resting membrane potential and intracellular calcium through Fura‐2 in freshly digested pulmonary artery smooth muscles (PASMCs) from both the right main (RM‐PA) and D‐PA (distal) regions of pulmonary artery from WT and Twik‐2^−/− mice. Whole segments of RM‐PAs and D‐PAs from 20 to 24‐week‐old wildtype (WT) and Twik‐2^−/− mice were also pressurized between two glass micropipettes and bathed in buffer with either arterial or venous conditions. Abluminally‐applied phenylephrine (PE) and U46619 were added to the buffer at log increments and vessel diameter was measured. All values were expressed as averages with ±SEM. Vasoconstrictor responses did not differ between WT and Twik‐2^−/− RM‐PAs under arterial conditions. Under venous conditions, Twik‐2^−/− RM‐PAs showed an increased sensitivity to PE with a lower EC50 (P = 0.02). Under venous conditions, Twik‐2^−/− D‐PAs showed an increase maximal vasoconstrictor response to both phenylephrine and U46619 compared to the WT mice (P < 0.05). Isolated PASMCs from Twik‐2 ^−/− D‐PA were depolarized and had higher intracellular calcium levels compared to PASMCs from RM‐PA of both WT and Twik‐2^−/− mice. These studies suggest that hypercontractile responses and electrophysiologic properties unique to the anatomic location of the D‐PAs may contribute to pulmonary hypertensive vasculopathy.