Alterations in mitochondrial structure and function contribute to vascular smooth muscle cell (VSMC) phenotypic switching and are causally linked to pulmonary arterial hypertension (PAH) pathogenesis. The PINK1/Parkin-mediated mitophagy pathway is a key mitochondrial quality control program by which defective mitochondria are targeted for removal. The role of PINK1/ Parkin-mediated mitophagy in VSMC phenotypic switching and PAH pathogenesis is not known. We sought to evaluate if PINK1/Parkin-induced mitophagy modulates VSMC phenotypic switching and contributes to PAH. Mitophagy and PINK1/Parkin expression were evaluated in human PAH lungs and pulmonary artery smooth muscle cells (PASMCs). PINK1 and Parkin were silenced in human and mouse primary PASMCs, and global PINK1 and Parkin knockout mice were used. After silencing of PINK1 and Parkin, PASMC proliferation and apoptosis were measured, and experimental pulmonary hypertension was evaluated after exposure to hypoxia. Parkin and PINK1 levels were reduced in the pulmonary vasculature or PASMCs from PAH lungs, accompanied by decreased mitophagy. PINK1 and Parkin knockout animals had an exaggerated pulmonary hypertension phenotype upon exposure to hypoxia. Genetic silencing of PINK1 and Parkin in human and mouse PASMCs led to increased proliferation and apoptosis resistance. We conclude that reduced PINK1/Parkin-induced mitophagy contributes to PASMC phenotypic switching and exacerbates PAH.

The role of stress granules (SGs) in pulmonary arterial hypertension (PAH) is unknown. We hypothesized that SG formation contributes to abnormal vascular phenotypes, and cardiac and skeletal muscle dysfunction in PAH. Using the rat Sugen/hypoxia (SU/Hx) model of PAH, we demonstrate the formation of SG puncta and increased expression of SG proteins compared to control animals in lungs, right ventricles, and soleus muscles. Acetazolamide (ACTZ) treatment ameliorated the disease and reduced SG formation in all of these tissues. Primary pulmonary artery smooth muscle cells (PASMCs) from diseased animals had increased SG protein expression and SG number after acute oxidative stress and this was ameliorated by ACTZ. Pharmacologic inhibition of SG formation or genetic ablation of the SG assembly protein (G3BP1) altered the SU/Hx-PASMC phenotype by decreasing proliferation, increasing apoptosis and modulating synthetic and contractile marker expression. In human PAH lungs, we found increased SG puncta in pulmonary arteries compared to control lungs and in human PAH-PASMCs we found increased SGs after acute oxidative stress compared to healthy PASMCs. Genetic ablation of G3BP1 in human PAH-PASMCs resulted in a phenotypic switch to a less synthetic and more contractile phenotype. We conclude that increased SG formation in PASMCs and other tissues may contribute to PAH pathogenesis.

AbstractPulmonary arterial hypertension (PAH) causes pulmonary vascular remodeling, increasing pulmonary vascular resistance (PVR) and leading to right heart failure and death. Matrix stiffening early in the disease promotes remodeling in pulmonary artery smooth muscle cells (PASMCs), contributing to PAH pathogenesis. Our research identified YAP and TAZ as key drivers of the mechanobiological feedback loop in PASMCs, suggesting targeting them could mitigate remodeling. However, YAP/TAZ are ubiquitously expressed and carry out diverse functions, necessitating a cell‐specific approach. Our previous work demonstrated that targeting non‐canonical IKB kinase TBK1 reduced YAP/TAZ activation in human lung fibroblasts. Here, we investigate non‐canonical IKB kinases TBK1 and IKKε in pulmonary hypertension (PH) and their potential to modulate PASMC pathogenic remodeling by regulating YAP/TAZ. We show that TBK1 and IKKε are activated in PASMCs in a rat PH model. Inflammatory cytokines, elevated in PAH, activate these kinases in human PASMCs. Inhibiting TBK1/IKKε expression/activity significantly reduces PAH‐associated PASMC remodeling, with longer‐lasting effects on YAP/TAZ than treprostinil, an approved PAH therapy. These results show that non‐canonical IKB kinases regulate YAP/TAZ in PASMCs and may offer a novel approach for reducing vascular remodeling in PAH.

Neutrophils with intact multilobulated nuclei show ASC speck formation and high histone H3 citrullination in patients with severe COVID-19. In murine neutrophils, ASC speck forms transiently at the microtubule organizing center, before nuclear rounding, early in NETosis. Abstract Infection by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) engages the inflammasome in monocytes and macrophages and leads to the cytokine storm in COVID-19. Neutrophils, the most abundant leukocytes, release neutrophil extracellular traps (NETs), which have been implicated in the pathogenesis of COVID-19. Our recent study shows that activation of the NLRP3 inflammasome is important for NET release in sterile inflammation. However, the role of neutrophil inflammasome formation in human disease is unknown. We hypothesized that SARS-COV-2 infection may induce inflammasome activation in neutrophils. We also aimed to assess the localization of inflammasome formation, (i.e. ASC speck assembly), and timing relative to NETosis in stimulated neutrophils by real time video microscopy. Neutrophils isolated from severe COVID-19 patients demonstrated that approximately 2% of neutrophils in both the peripheral blood and tracheal aspirates presented ASC speck. ASC speck was observed in neutrophils with an intact poly-lobulated nucleus, suggesting early formation during neutrophil activation. Additionally, 40% of nuclei were positive for citrullinated histone H3, and there was a significant correlation between speck formation and nuclear histone citrullination. Time-lapse microscopy in LPS-stimulated neutrophils from fluorescent ASC reporter mice showed that ASC speck formed transiently and at the microtubule organizing center, long before NET release. Our study shows that ASC speck is present in neutrophils from COVID-19 patients with respiratory failure and that it forms early in NETosis. Our findings suggest that inhibition of neutrophil inflammasomes may be beneficial in COVID-19.

Aging is accompanied by declining lung function and increasing susceptibility to lung diseases. The role of endothelial dysfunction and vascular remodeling in these changes is supported by growing evidence, but underlying mechanisms remain elusive. In this review we summarize functional, structural, and molecular changes in the aging pulmonary vasculature and explore how interacting aging and mechanobiological cues may drive progressive vascular remodeling in the lungs.

Increased proliferation and survival of cells in small pulmonary arteries (PAs) drive pulmonary arterial hypertension (PAH). Because cell growth mediated by the mTOR-containing mTORC1 complex is inhibited by tuberous sclerosis complex 2 (TSC2), we investigated the role of this GTPase-activating protein in PAH pathology. TSC2 abundance was decreased in remodeled small PAs and PA vascular smooth muscle cells (PAVSMCs) from patients with PAH or from rodent pulmonary hypertension (PH) models, as well as PAVSMCs maintained on substrates that reproduced pathology-induced stiffness. Accordingly, mice with smooth muscle–specific reduction in TSC2 developed PH. At the molecular level, decreased TSC2 abundance led to stiffness-induced PAVSMC proliferation, increased abundance of the mechanosensitive transcriptional coactivators YAP/TAZ, and enhanced mTOR kinase activity. Moreover, extracellular matrix (ECM) produced by TSC2-deficient PAVSMCs stimulated the proliferation of nondiseased PA adventitial fibroblasts and PAVSMCs through fibronectin and its receptor, the α 5 β 1 integrin. Reconstituting TSC2 in PAVSMCs from patients with PAH through overexpression or treatment with the SIRT1 activator SRT2104 decreased YAP/TAZ abundance, mTOR activity, and ECM production, as well as inhibited proliferation and induced apoptosis. In two rodent models of PH, SRT2104 treatment restored TSC2 abundance, attenuated pulmonary vascular remodeling, and ameliorated PH. Thus, TSC2 in PAVSMCs integrates ECM composition and stiffness with pro-proliferative and survival signaling, and restoring TSC2 abundance could be an attractive therapeutic option to treat PH.

Vascular stiffening in distal pulmonary arteries plays a key role in the early pathogenesis and progression of pulmonary arterial hypertension (PAH). Pathophysiologic cellular responses to vascular stiffness include upregulation of signaling pathways that promote further vascular remodeling, a process known as mechanobiological feedback. Inflammatory signaling and metabolic shifts, particularly upregulation of aerobic glycolysis and glutaminolysis, have also recently been shown to occur downstream of pulmonary vascular stiffening, and are known to play a critical role in PAH development. In this chapter, we will focus on the specific mechanisms underlying these cellular responses. Vascular cell mechanosensing involves the integration of signals from the cell surface, relayed by molecules such as integrins, small GTPases, membrane-associated kinases, and the actin cytoskeleton, into a downstream transcriptional program via nuclear-cytosolic shuttling proteins. Targeting these mechanosensing pathways offers the potential to disrupt mechanobiological feedback and prevent or reverse pathologic pulmonary vascular remodeling in PAH.

BACKGROUND: Patients with coronavirus disease 2019 (COVID-19) can present with severe respiratory distress requiring intensive care unit (ICU)–level care. Such care often requires placement of an arterial line for monitoring of pulmonary disease progression, hemodynamics, and laboratory tests. During the first wave of the COVID-19 pandemic in March 2020, experienced physicians anecdotally reported multiple attempts, decreased insertion durations, and greater need for replacement of arterial lines in patients with COVID-19 due to persistent thrombosis. Because invasive procedures in patients with COVID-19 may increase the risk for caregiver infection, better defining difficulties in maintaining arterial lines in COVID-19 patients is important. We sought to explore the association between COVID-19 infection and arterial line thrombosis in critically ill patients. METHODS: In this primary exploratory analysis, a multivariable Fine-Gray subdistribution hazard model was used to retrospectively estimate the association between critically ill COVID-19 (versus sepsis/acute respiratory distress syndrome [ARDS]) patients and the risk of arterial line removal for thrombosis (with arterial line removal for any other reason treated as a competing risk). As a sensitivity analysis, we compared the number of arterial line clots per 1000 arterial line days between critically ill COVID-19 and sepsis/ARDS patients using multivariable negative binomial regression. RESULTS: We retrospectively identified 119 patients and 200 arterial line insertions in patients with COVID-19 and 54 patients and 68 arterial line insertions with non-COVID ARDS. Using a Fine-Gray subdistribution hazard model, we found the adjusted subdistribution hazard ratio (95% confidence interval [CI]) for arterial line clot to be 2.18 (1.06–4.46) for arterial lines placed in COVID-19 patients versus non–COVID-19 sepsis/ARDS patients (P = .034). Patients with COVID-19 had 36.3 arterial line clots per 1000 arterial line days compared to 19.1 arterial line clots per 1000 arterial line days in patients without COVID-19 (adjusted incidence rate ratio [IRR] [95% CI], 1.78 [0.94–3.39]; P = .078). CONCLUSIONS: Our study suggests that arterial line complications due to thrombosis are more likely in COVID-19 patients and supports the need for further research on the association between COVID-19 and arterial line dysfunction requiring replacement.

Background Cell stress promotes degradation of mitochondria which release danger-associated molecular patterns that are catabolized to N -formylmethionine. We hypothesized that in critically ill adults, the response to N -formylmethionine is associated with increases in metabolomic shift-related metabolites and increases in 28-day mortality. Methods We performed metabolomics analyses on plasma from the 428-subject Correction of Vitamin D Deficiency in Critically Ill Patients trial (VITdAL-ICU) cohort and the 90-subject Brigham and Women’s Hospital Registry of Critical Illness (RoCI) cohort. In the VITdAL-ICU cohort, we analyzed 983 metabolites at Intensive Care Unit (ICU) admission, day 3, and 7. In the RoCI cohort, we analyzed 411 metabolites at ICU admission. The association between N -formylmethionine and mortality was determined by adjusted logistic regression. The relationship between individual metabolites and N -formylmethionine abundance was assessed with false discovery rate correction via linear regression, linear mixed-effects, and Gaussian graphical models. Results Patients with the top quartile of N -formylmethionine abundance at ICU admission had a significantly higher adjusted odds of 28-day mortality in the VITdAL-ICU (OR, 2.4; 95%CI 1.5–4.0; P = 0.001) and RoCI cohorts (OR, 5.1; 95%CI 1.4–18.7; P = 0.015). Adjusted linear regression shows that with increases in N -formylmethionine abundance at ICU admission, 55 metabolites have significant differences common to both the VITdAL-ICU and RoCI cohorts. With increased N -formylmethionine abundance, both cohorts had elevations in individual short-chain acylcarnitine, branched chain amino acid, kynurenine pathway, and pentose phosphate pathway metabolites. Conclusions The results indicate that circulating N -formylmethionine promotes a metabolic shift with heightened mortality that involves incomplete mitochondrial fatty acid oxidation, increased branched chain amino acid metabolism, and activation of the pentose phosphate pathway. Graphic Abstract

Introduction: Phenotypic switching of vascular cells is a complex process associated with vascular disorders, including thoracic aortic aneurysm (TAA). Vascular smooth muscle cells (VSMCs) appear to switch from a contractile to synthetic phenotype in TAA. Single nuclear RNA-seq (snRNA-seq) of normal human and TAA aortas may be used to characterize cell heterogeneity of normal aortas, population shifts in disease, and the transcriptional profile of VSMC phenotypic switching. Hypothesis: snRNA-seq of normal and TAA aortas will identify the cell heterogeneity and transcriptional profiles of TAA. Methods: We performed snRNA-seq of 5 aortas from 2 normal and 3 TAA patients. We used a 10X-CellBender pipeline for profiling and analysis. Results: snRNA-seq identified 6 major cell types. The majority were VSMCs, exhibiting 4 sub-populations in all specimens (a). Cell distribution comparisons showed VSMC1 (ELN, PKD1, FLNA high) and VSMC2 (PRKG1, PDE3A, PCDH7 high) to be differentially-enriched in controls and TAA samples, respectively (b,c). Gene set and trajectory analyses confirmed prior observations of phenotypic switching (d,e). Genes associated with switching in VSMCs included TAA genes (PRKG1, PKD1, FLNA) with concordance of expression and putative function of Mendelian variants (i-k). Cell junction and regulation of muscle contraction pathways drove trajectory. We further assessed cell-type heritability of vascular GWAS variants (h). These gene sets were differentially-regulated between control and TAA. The strongest association was between VSMC2 and ascending aortic size (h). Conclusions: In this study, we demonstrated a dissociation bias-free method for snRNA-Seq of human vasculature. We confirmed enrichment of synthetic VSMCs in TAA and implicate phenotypic switching as a pathologic mechanism. Our study identifies a cell type-specific transcriptional profile of aortopathy genes, which may drive TAA and represent therapeutic targets.

YouTube’s algorithm is often accused of putting users in filter bubbles and generating rabbit holes of radicalization. However, evidence on these issues is inconclusive. We conduct a systematic audit of the platform using 100,000 sock puppets ... Algorithms of social media platforms are often criticized for recommending ideologically congenial and radical content to their users. Despite these concerns, evidence on such filter bubbles and rabbit holes of radicalization is inconclusive. We conduct ...

Elevated VTE rates have been reported in COVID-19 patients [1,2]. Although ICU patients in general have an elevated VTE risk [3] we recently reported a higher incidence of VTE in ICU compared to ward patients with COVID-19 [4]. As the optimal approach for thromboprophylaxis is unknown, we implemented intermediate dose anticoagulation in COVID-19 ICU patients. We hypothesized that intermediate dose heparin prophylaxis would be associated with lower incidences of symptomatic VTE, death, or a composite outcome of both in COVID-19 ICU patients.

Background Although acute respiratory distress syndrome (ARDS) is associated with high mortality, its direct causal link with death is unclear. Clarifying this link is important to justify costly research on prevention of ARDS. Objective To estimate the attributable mortality, if any, of ARDS. Design First, we performed a systematic review and meta-analysis of observational studies reporting mortality of critically ill patients with and without ARDS matched for underlying risk factor. Next, we conducted a survival analysis of prospectively collected patient-level data from subjects enrolled in three intensive care unit (ICU) cohorts to estimate the attributable mortality of critically ill septic patients with and without ARDS using a novel causal inference method. Results In the meta-analysis, 44 studies (47 cohorts) involving 56 081 critically ill patients were included. Mortality was higher in patients with versus without ARDS (risk ratio 2.48, 95% CI 1.86 to 3.30; p<0.001) with a numerically stronger association between ARDS and mortality in trauma than sepsis. In the survival analysis of three ICU cohorts enrolling 1203 critically ill patients, 658 septic patients were included. After controlling for confounders, ARDS was found to increase the mortality rate by 15% (95% CI 3% to 26%; p=0.015). Significant increases in mortality were seen for severe (23%, 95% CI 3% to 44%; p=0.028) and moderate (16%, 95% CI 2% to 31%; p=0.031), but not for mild ARDS. Conclusions ARDS has a direct causal link with mortality. Our findings provide information about the extent to which continued funding of ARDS prevention trials has potential to impart survival benefit. PROSPERO Registration Number CRD42017078313

Introduction: Mitophagy is the key mitochondrial quality control process of selective removal of damaged mitochondria which is necessary for maintaining cellular homeostasis. While studies have demonstrated that abnormalities in mitochondrial metabolism drive a hyperproliferative phenotype of pulmonary vasculature in PAH, there is limited understanding of mitophagy dysregulation in PAH. Recent studies have shown that hypoxia induced Parkin/Pink1-mediated mitophagy promotes vascular remodeling, however another report suggests that loss of Pink1 and reduced mitophagy in hypoxia promotes PASMC proliferation. The role and mechanisms of altered mitochondrial dynamics/mitophagy dysregulation in driving pulmonary vascular remodeling in PAH remain incompletely understood. Hypothesis: We hypothesized that impaired mitophagy and reduced Parkin expression may drive the apoptosis-resistant, hyperproliferative phenotype in PAH PASMCs. Methods: Mitophagy was assessed in human PASMCs from control donors and PAH patients stably expressing mtKeima protein and in lungs from hypoxia-exposed mtKeima transgenic mice. Parkin expression was assessed by Western blotting and immunocytochemistry. Immunofluorescence staining for Parkin was performed in lungs from mice exposed to chronic hypoxia. Human PASMCs from control donors were transfected with siControl and siParkin and assessed for proliferation and apoptosis by Ki67 and Annexin V/PI flow cytometry and PCNA expression. Results: PASMCs from PAH patients showed reduced KeimaRed vs. KeimaGreen ratio compared to control donors indicating reduced mitophagy i.e. further confirmed by decreased Parkin in PAH PASMCs. Parkin deficient PASMCs demonstrated more Ki67 and less Annexin V/PI positive cells and increased PCNA. Interestingly, lungs from hypoxia-exposed mtKeima transgenic mice showed increased KeimaRed vs. KeimaGreen ratio and increased Parkin in lungs of hypoxia-exposed mice. Conclusions: PAH PASMCs demonstrate impaired mitophagy and reduced Parkin expression; Parkin deficiency promotes proliferation and inhibits apoptosis in PASMCs. Our findings suggest that Parkin may regulate remodeling phenotypes in PASMCs and thus may represent a potential therapeutic target in PAH.

Rationale: Mechanical signaling through cell-matrix interactions plays a major role in progressive vascular remodeling in pulmonary arterial hypertension (PAH). MMP-8 (matrix metalloproteinase-8) is an interstitial collagenase involved in regulating inflammation and fibrosis of the lung and systemic vasculature, but its role in PAH pathogenesis remains unexplored. Objectives: To evaluate MMP-8 as a modulator of pathogenic mechanical signaling in PAH. Methods: MMP-8 levels were measured in plasma from patients with pulmonary hypertension (PH) and controls by ELISA. MMP-8 vascular expression was examined in lung tissue from patients with PAH and rodent models of PH. MMP-8(-/-) and MMP-8(+/+) mice were exposed to normobaric hypoxia or normoxia for 4-8 weeks. PH severity was evaluated by right ventricular systolic pressure, echocardiography, pulmonary artery morphometry, and immunostaining. Proliferation, migration, matrix component expression, and mechanical signaling were assessed in MMP-8(-/-) and MMP-8(+/+) pulmonary artery smooth muscle cells (PASMCs). Measurements and Main Results: MMP-8 expression was significantly increased in plasma and pulmonary arteries of patients with PH compared with controls and induced in the pulmonary vasculature in rodent PH models. Hypoxia-exposed MMP-8(-/-) mice had significant mortality, increased right ventricular systolic pressure, severe right ventricular dysfunction, and exaggerated vascular remodeling compared with MMP-8(+/+) mice. MMP-8(-/-) PASMCs demonstrated exaggerated proliferation and migration mediated by altered matrix protein expression, elevated integrin-beta 3 levels, and induction of FAK (focal adhesion kinase) and downstream YAP (Yes-associated protein)/TAZ (transcriptional coactivator with PDZ-binding motif) activity. Conclusions: MMP-8 is a novel protective factor upregulated in the pulmonary vasculature during PAH pathogenesis. MMP-8 opposes pathologic mechanobiological feedback by altering matrix composition and disrupting integrin-beta 3/FAK and YAP/TAZ-dependent mechanical signaling in PASMCs.