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The pulmonary circulation is a low-resistance, low-pressure, and high-compliance system that allows the lungs to receive the entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, and pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis, and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of precapillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels, and intracellular Ca2+ signaling in pulmonary vascular smooth muscle cells in the development and progression of pulmonary hypertension.

Mechanosensitive cation channels and Ca2+ influx through these channels play an important role in the regulation of endothelial cell functions. Transient receptor potential canonical channel 6 (TRPC6) is a diacylglycerol-sensitive nonselective cation channel that forms receptor-operated Ca2+ channels in a variety of cell types. Piezo1 is a mechanosensitive cation channel activated by membrane stretch and shear stress in lung endothelial cells. In this study, we report that TRPC6 and Piezo1 channels both contribute to membrane stretch-mediated cation currents and Ca2+ influx or increase in cytosolic-free Ca2+ concentration ([Ca2+]cyt) in human pulmonary arterial endothelial cells (PAECs). The membrane stretch-mediated cation currents and increase in [Ca2+]cyt in human PAECs were significantly decreased by GsMTX4, a blocker of Piezo1 channels, and by BI-749327, a selective blocker of TRPC6 channels. Extracellular application of 1-oleoyl-2-acetyl- sn-glycerol (OAG), a membrane permeable analog of diacylglycerol, rapidly induced whole cell cation currents and increased [Ca2+]cyt in human PAECs and human embryonic kidney (HEK)-cells transiently transfected with the human TRPC6 gene. Furthermore, membrane stretch with hypo-osmotic or hypotonic solution enhances the cation currents in TRPC6-transfected HEK cells. In HEK cells transfected with the Piezo1 gene, however, OAG had little effect on the cation currents, but membrane stretch significantly enhanced the cation currents. These data indicate that, while both TRPC6 and Piezo1 are involved in generating mechanosensitive cation currents and increases in [Ca2+]cyt in human PAECs undergoing mechanical stimulation, only TRPC6 (but not Piezo1) is sensitive to the second messenger diacylglycerol. Selective blockers of these channels may help develop novel therapies for mechanotransduction-associated pulmonary vascular remodeling in patients with pulmonary arterial hypertension.

Piezo1 is an important mechanosensitive channel implicated in vascular remodeling. However, the role of Piezo1 in different types of vascular cells during the development of pulmonary hypertension (PH) induced by high shear stress is largely unknown.We used a rat PH model established by left pulmonary artery ligation (LPAL, for 2-5 weeks), which mimics the high flow and hemodynamic stress, to study Piezo1 contribution to pulmonary vascular remodeling.Right ventricular systolic pressure (RVSP), a surrogate measure for pulmonary arterial systolic pressure, and right ventricular wall thickness, a measure for right ventricular hypertrophy, were significantly increased in LPAL rats compared with Sham-control (SHAM) rats. Rats in LPAL-5w groups developed remarkable pulmonary vascular remodeling, while phenylephrine-induced contraction and acetylcholine-induced relaxation were both significantly inhibited in these rats. Upregulation of Piezo1, in association with increase in cytosolic Casup2+/supconcentration ([Casup2+/sup]subcyt/sub), was observed in pulmonary arterial smooth muscle cells (PASMCs) from LPAL-2w and LPAL-5w rats in comparison to the SHAM controls. Piezo1 upregulation in PASMCs from LPAL rats was directly related to Yes-associated protein (YAP)/ TEA domain transcription factor 4 (TEAD4). Piezo1 expression was also upregulated in the whole-lung tissue of LPAL rats. The endothelial upregulation of Piezo1 was related to transcriptional regulation by RELA (p65) and lung inflammation.The upregulation of Piezo1 in both PASMCs and ECs coordinates with each other via different cell signaling pathways to cause pulmonary vascular remodeling in LPAL-PH rats, providing novel insights into the cell-type specific pathogenic roles of Piezo1 in shear stress-associated experimental PH.

Type-2 diabetes (T2D) increases the risk of cardiovascular diseases 2-4 folds in both sexes compared to non-diabetic individuals. However, more than 50% of female patients who experience chest pain have coronary microvascular disease (CMD) instead of obstructive CAD. On the other hand, 20% of men with chest pain have CMD. CMD is characterized by reduced coronary flow reserve, and coronary flow is regulated by the change in capillary density and vessel diameter. Gap junction protein connexin-40 (Cx40) plays a significant role in coronary microvascular function by controlling endothelium-dependent relaxation (EDR), cardiac endothelial cell (CEC) migration and capillary density. We hypothesized that T2D differentially affects the CX-40 expression and function in male and female coronary artery (CA) and causes CMD. The objective of this study is to identify the molecular mechanisms underlining the development of T2D-induced CMD in male and female mice.T2D mice were generated by a combination of high-fat diet feeding and a low-dose of streptozotocin (75 mg/kg, i.p.). The oral glucose tolerance was conducted at 4-, 8-, 12-, and 16 weeks after diabetes induction. Coronary flow velocity reserve (CFVR) was used to assess coronary microvascular function in mice. Coronary endothelial function was determined by 1) capillary density measurement in the left ventricle and 2) isometric tension experiment in small CAs (3rd order). CECs from male and female mice were isolated to conduct molecular biological experiments.There was no significant difference in CFVR and capillary density between control male and female mice. However, T2D mice of both sexes showed significant differences in the properties of EDR, CFVR and capillary density. T2D male mice exhibited a significant attenuation of EDR accompanied by impaired endothelium-derived nitric oxide(EDNO)-dependent relaxation and endothelium-dependent hyperpolarization (EDH)-mediated relaxation. On the contrary, there is no difference in EDR between control and diabetic female mice. Capillary density was reduced in T2D mice of both sexes compared to the respective controls. Our RNA sequencing data in CECs revealed that Cx40 is one of the genes which contributes to diabetes-mediated CMD. Systemic Cx40-KO male mice showed reduced EDR, EDH-mediated relaxation and capillary density compared to wild type control. T2D reduced the expression of Cx40 and overexpression of Cx40 restored EDR in CAs and increased capillary density in T2D male mice.T2D impaired coronary microvascular function in both sexes. However, the cause of reduced CFVR was different between diabetic male and female mice. In T2D females, capillary rarefaction was a primary cause of reduced CFVR. In contrast, attenuated EDNO- and EDH-mediated relaxation, reduced capillary density and downregulation of Cx40 contributed to decreased CFVR in T2D male mice. Future studies are required to establish the role of Cx40 in the development of CMD in T2D females. Supported by NIH R01HL142214 and DOD W81XWH2110472 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Concentric pulmonary vascular wall thickening due partially to increased pulmonary artery (PA) smooth muscle cell (PASMC) proliferation contributes to elevating pulmonary vascular resistance (PVR) in patients with pulmonary hypertension (PH). Although pulmonary vasoconstriction may be an early contributor to increasing PVR, the transition of contractile PASMCs to proliferative PASMCs may play an important role in the development and progression of pulmonary vascular remodeling in PH. A rise in cytosolic Ca2+ concentration ([Ca2+]cyt) is a trigger for PASMC contraction and proliferation. Here, we report that upregulation of Piezo1, a mechanosensitive cation channel, is involved in the contractile-to-proliferative phenotypic transition of PASMCs and potential development of pulmonary vascular remodeling. By comparing freshly isolated PA (contractile PASMCs) and primary cultured PASMCs (from the same rat) in a growth medium (proliferative PASMCs), we found that Piezo1, Notch2/3, and CaSR protein levels were significantly higher in proliferative PASMCs than in contractile PASMCs. Upregulated Piezo1 was associated with an increase in expression of PCNA, a marker for cell proliferation, whereas downregulation (with siRNA) or inhibition (with GsMTx4) of Piezo1 attenuated PASMC proliferation. Furthermore, Piezo1 in the remodeled PA from rats with experimental PH was upregulated compared with PA from control rats. These data indicate that PASMC contractile-to-proliferative phenotypic transition is associated with the transition or adaptation of membrane channels and receptors. Upregulated Piezo1 may play a critical role in PASMC phenotypic transition and PASMC proliferation. Upregulation of Piezo1 in proliferative PASMCs may likely be required to provide sufficient Ca2+ to assure nuclear/cell division and PASMC proliferation, contributing to the development and progression of pulmonary vascular remodeling in PH.

Piezo is a mechanosensitive cation channel responsible for stretch-mediated Ca2+ and Na+ influx in multiple types of cells. Little is known about the functional role of Piezo1 in the lung vasculature and its potential pathogenic role in pulmonary arterial hypertension (PAH). Pulmonary arterial endothelial cells (PAECs) are constantly under mechanic stretch and shear stress that are sufficient to activate Piezo channels. Here, we report that Piezo1 is significantly upregulated in PAECs from patients with idiopathic PAH and animals with experimental pulmonary hypertension (PH) compared with normal controls. Membrane stretch by decreasing extracellular osmotic pressure or by cyclic stretch (18% CS) increases Ca2+-dependent phosphorylation (p) of AKT and ERK, and subsequently upregulates expression of Notch ligands, Jagged1/2 (Jag-1 and Jag-2), and Delta like-4 (DLL4) in PAECs. siRNA-mediated downregulation of Piezo1 significantly inhibited the stretch-mediated pAKT increase and Jag-1 upregulation, whereas downregulation of AKT by siRNA markedly attenuated the stretch-mediated Jag-1 upregulation in human PAECs. Furthermore, the mRNA and protein expression level of Piezo1 in the isolated pulmonary artery, which mainly contains pulmonary arterial smooth muscle cells (PASMCs), from animals with severe PH was also significantly higher than that from control animals. Intraperitoneal injection of a Piezo1 channel blocker, GsMTx4, ameliorated experimental PH in mice. Taken together, our study suggests that membrane stretch-mediated Ca2+ influx through Piezo1 is an important trigger for pAKT-mediated upregulation of Jag-1 in PAECs. Upregulation of the mechanosensitive channel Piezo1 and the resultant increase in the Notch ligands (Jag-1/2 and DLL4) in PAECs may play a critical pathogenic role in the development of pulmonary vascular remodeling in PAH and PH.

Pulmonary arterial hypertension is a progressive and fatal disease and rodents with experimental pulmonary hypertension (PH) are often used to study pathogenic mechanisms, identify therapeutic targets, and develop novel drugs for treatment. Here we describe a hands-on set of experimental approaches including ex vivo lung angiography and histology and in vivo right heart catheterization (RHC) to phenotypically characterize pulmonary hemodynamics and lung vascular structure in normal mice and mice with experimental PH. We utilized Microfil polymer as contrast in our ex vivo lung angiogram to quantitatively examine pulmonary vascular remodeling in mice with experimental PH, and lung histology to estimate pulmonary artery wall thickness. The peripheral lung vascular images were selected to determine the total length of lung vascular branches, the number of branches and the number of junctions in a given area (mm −2 ). We found that the three parameters determined by angiogram were not significantly different among the apical, middle, and basal regions of the mouse lung from normal mice, and were not influenced by gender (no significant difference between female and male mice). We conducted RHC in mice to measure right ventricular systolic pressure, a surrogate measure for pulmonary artery systolic pressure and right ventricle (RV) contractility (RV ± dP/dt max ) to estimate RV function. RHC, a short time (4–6 min) procedure, did not alter the lung angiography measurements. In summary, utilizing ex vivo angiogram to determine peripheral vascular structure and density in the mouse lung and utilizing in vivo RHC to measure pulmonary hemodynamics are reliable readouts to phenotype normal mice and mice with experimental PH. Lung angiogram and RHC are also reliable approaches to examine pharmacological effects of new drugs on pulmonary vascular remodeling and hemodynamics.

The pulmonary circulation is a low-resistance, low-pressure and high-compliance system that allows the lungs to receive entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, while pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of pre-capillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels and intracellular Ca

Background: Autophagy plays an important role in the pathogenesis of pulmonary hypertension (PH). ROC-325 is a novel small molecule lysosomal autophagy inhibitor that has more potent anticancer activity than the antimalarial drug hydroxychloroquine, the latter has been prevalently used to inhibit autophagy. Here, we sought to determine the therapeutic benefit and mechanism of action of ROC-325 in experimental PH models. Methods and Results: Hemodynamics, echocardiography, and histology measurement showed that ROC-325 treatment prevented the development of PH, right ventricular hypertrophy, fibrosis, dysfunction, and vascular remodeling after monocrotaline and Sugen5416/hypoxia administration. ROC-325 attenuated high K + or alveolar hypoxia-induced pulmonary vasoconstriction and enhanced endothelial-dependent relaxation in isolated pulmonary artery rings. ROC-325 treatment inhibited autophagy and enhanced endothelial nitric oxide synthase activity in lung tissues of monocrotaline-PH rats. In cultured human and rat pulmonary arterial smooth muscle cell and pulmonary arterial endothelial cell under hypoxia exposure, ROC-325 increased LC3B (light chain 3 beta) and p62 accumulation, endothelial cell nitric oxide production via phosphorylation of endothelial nitric oxide synthase (Ser1177) and dephosphorylation of endothelial nitric oxide synthase (Thr495) as well as decreased HIF (hypoxia-inducible factor)-1α and HIF-2α stabilization. Conclusions: These data indicate that ROC-325 is a promising novel agent for the treatment of PH that inhibits autophagy, downregulates HIF levels, and increases nitric oxide production.

Background: Dysregulated BMP (bone morphogenetic protein) or TGF-β (transforming growth factor beta) signaling pathways are imperative in idiopathic and familial pulmonary arterial hypertension (PAH) as well as experimental pulmonary hypertension (PH) in rodent models. MED1 (mediator complex subunit 1) is a key transcriptional co-activator and KLF4 (Krüppel-like factor 4) is a master transcription factor in endothelium. However, MED1 and KLF4 epigenetic and transcriptional regulations of the BMP/TGF-β axes in pulmonary endothelium and their dysregulations leading to PAH remain elusive. We investigate the MED1/KLF4 co-regulation of the BMP/TGF-β axes in endothelium by studying the epigenetic regulation of BMPR2 (BMP receptor type II), ETS-related gene ( ERG ), and TGFBR2 (TGF-β receptor 2) and their involvement in the PH. Methods: High-throughput screening involving data from RNA-seq, MED1 ChIP-seq, H3K27ac ChIP-seq, ATAC-seq, and high-throughput chromosome conformation capture together with in silico computations were used to explore the epigenetic and transcriptional regulation of BMPR2, ERG, and TGFBR2 by MED1 and KLF4. In vitro experiments with cultured pulmonary arterial endothelial cells (ECs) and bulk assays were used to validate results from these in silico analyses. Lung tissue from patients with idiopathic PAH, animals with experimental PH, and mice with endothelial ablation of MED1 (EC- MED1 −/− ) were used to study the PH-protective effect of MED1. Results: Levels of MED1 were decreased in lung tissue or pulmonary arterial endothelial cells from idiopathic PAH patients and rodent PH models. Mechanistically, MED1 acted synergistically with KLF4 to transactivate BMPR2, ERG, and TGFBR2 via chromatin remodeling and enhancer-promoter interactions. EC- MED1 −/− mice showed PH susceptibility. In contrast, MED1 overexpression mitigated the PH phenotype in rodents. Conclusions: A homeostatic regulation of BMPR2, ERG, and TGFBR2 in ECs by MED1 synergistic with KLF4 is essential for the normal function of the pulmonary endothelium. Dysregulation of MED1 and the resulting impairment of the BMP/TGF-β signaling is implicated in the disease progression of PAH in humans and PH in rodent models.

BACKGROUND AND PURPOSE: Halofuginone is a febrifugine derivative originally isolated from Chinese traditional herb Chang Shan that exhibits anti-hypertrophic, anti-fibrotic and anti-proliferative effects. We sought to investigate whether halofuginone induced pulmonary vasodilation and attenuates chronic hypoxia-induced pulmonary hypertension (HPH). EXPERIMENTAL APPROACH: Patch-clamp experiments were conducted to examine the activity of voltage-dependent Ca(2+) channels (VDCCs) in pulmonary artery smooth muscle cells (PASMCs). Digital fluorescence microscopy was used to measure intracellular Ca(2+) concentration in PASMCs. Isolated perfused and ventilated mouse lungs were used to measure pulmonary artery pressure (PAP). Mice exposed to hypoxia (10% O(2)) for 4 weeks were used as model of HPH for in vivo experiments. KEY RESULTS: Halofuginone increased voltage-gated K(+) (K(v)) currents in PASMCs and K(+) currents through KCNA5 channels in HEK cells transfected with KCNA5 gene. HF (0.03–1 μM) inhibited receptor-operated Ca(2+) entry in HEK cells transfected with calcium-sensing receptor gene and attenuated store-operated Ca(2+) entry in PASMCs. Acute (3–5 min) intrapulmonary application of halofuginone significantly and reversibly inhibited alveolar hypoxia-induced pulmonary vasoconstriction dose-dependently (0.1–10 μM). Intraperitoneal administration of halofuginone (0.3 mg·kg(−1), for 2 weeks) partly reversed established PH in mice. CONCLUSION AND IMPLICATIONS: Halofuginone is a potent pulmonary vasodilator by activating K(v) channels and blocking VDCC and receptor-operated and store-operated Ca(2+) channels in PASMCs. The therapeutic effect of halofuginone on experimental PH is probably due to combination of its vasodilator effects, via inhibition of excitation–contraction coupling and anti-proliferative effects, via inhibition of the PI3K/Akt/mTOR signalling pathway.

Emerging studies have reported the mechanosensitive Piezo1 (piezo type mechanosensitive ion channel component 1) plays essential roles in regulating the vascular tone through mechanistic actions on intracellular calcium homeostasis. However, the specific roles of Piezo1 in pulmonary vessels remain incompletely understood. We aim to investigate whether and how Piezo1 regulates the intracellular calcium homeostasis in human pulmonary arterial smooth muscle cells (PASMCs) under normal and pulmonary arterial hypertension (PAH) conditions. Cultured human PASMCs isolated from both control donors and idiopathic PAH patients were used as cell models. Fura-2 based intracellular calcium imaging was performed to measure the intracellular free calcium concentration ([Ca 2+ ] i ). Results showed that activation of Piezo1 by Yoda1 increases [Ca 2+ ] i by inducing both intracellular calcium release from internal calcium stores through the intracellular (intra-) Piezo1 localized at the subcellular organelles, including endoplasmic reticulum/sarcoplasmic reticulum, mitochondria, and nucleus; as well as extracellular calcium influx through the plasma membrane-localized Piezo1 in a mechanism independent of the store-operated calcium entry. Moreover, the Piezo1-mediated increase of [Ca 2+ ] i is linked to increased contraction and proliferation of PASMCs. Yoda1 induces dose-dependent vasocontraction in endothelium-denuded rat intrapulmonary arteries. Significant upregulation and increased activity of Piezo1 were observed in idiopathic PAH-PASMCs versus donor-PASMCs, contributing to the increased [Ca 2+ ] i and excessive proliferation of idiopathic PAH-PASMCs. In summary, Piezo1 mediates the increase of [Ca 2+ ] i by triggering both intracellular calcium release and extracellular influx. The enhanced Piezo1 expression and activity accounts, at least partially, for the abnormally elevated [Ca 2+ ] i and proliferation in idiopathic PAH-PASMCs.

BACKGROUND: PVDOMICS (Pulmonary Vascular Disease Phenomics) is a precision medicine initiative to characterize pulmonary vascular disease (PVD) using deep phenotyping. PVDOMICS tests the hypothesis that integration of clinical metrics with omic measures will enhance understanding of PVD and facilitate an updated PVD classification. OBJECTIVES: The purpose of this study was to describe clinical characteristics and transplant-free survival in the PVDOMICS cohort. METHODS: Subjects with World Symposium Pulmonary Hypertension (WSPH) group 1–5 PH, disease comparators with similar underlying diseases and mild or no PH and healthy control subjects enrolled in a cross-sectional study. PH groups, comparators were compared using standard statistical tests including log-rank tests for comparing time to transplant or death. RESULTS: A total of 1,193 subjects were included. Multiple WSPH groups were identified in 38.9% of PH subjects. Nocturnal desaturation was more frequently observed in groups 1, 3, and 4 PH vs comparators. A total of 50.2% of group 1 PH subjects had ground glass opacities on chest computed tomography. Diffusing capacity for carbon monoxide was significantly lower in groups 1–3 PH than their respective comparators. Right atrial volume index was higher in WSPH groups 1–4 than comparators. A total of 110 participants had a mean pulmonary artery pressure of 21–24 mm Hg. Transplant-free survival was poorest in group 3 PH. CONCLUSIONS: PVDOMICS enrolled subjects across the spectrum of PVD, including mild and mixed etiology PH. Novel findings include low diffusing capacity for carbon monoxide and enlarged right atrial volume index as shared features of groups 1–3 and 1–4 PH, respectively; unexpected, frequent presence of ground glass opacities on computed tomography; and sleep alterations in group 1 PH, and poorest survival in group 3 PH. PVDOMICS will facilitate a new understanding of PVD and refine the current PVD classification. (Pulmonary Vascular Disease Phenomics Program PVDOMICS [PVDOMICS]; NCT02980887)

Pulmonary arterial hypertension (PAH) is a severe disease characterized by sustained vasoconstriction, concentric wall thickening and vascular remodeling leading to increased pulmonary vascular resistance, causing right heart failure and death. Acute alveolar hypoxia causes pulmonary vasoconstriction, while sustained hypoxia causes pulmonary hypertension (PH). Activation of Notch signaling is implicated in the development of PAH and chronic hypoxia induced PH via partially its enhancing effect on Ca

Within the pulmonary arterial tree, the NOTCH3 pathway is crucial in controlling vascular smooth muscle cell proliferation and maintaining smooth muscle cells in an undifferentiated state. Pulmonary arterial hypertension (PAH) is a fatal disease without cure, characterized by elevated pulmonary vascular resistance due to vascular smooth muscle cell proliferation in precapillary arteries, perivascular inflammation, and asymmetric neointimal hyperplasia. Here, we show that human PAH is characterized by overexpression of the NOTCH ligand JAGGED-1 (JAG-1) in small pulmonary artery smooth muscle cells and that JAG-1 selectively controls NOTCH3 signaling and cellular proliferation in an autocrine fashion. In contrast, the NOTCH ligand DELTA-LIKE 4 is minimally expressed in small pulmonary artery smooth muscle cells from individuals with PAH, inhibits NOTCH3 cleavage and signaling, and retards vascular smooth muscle cell proliferation. A new monoclonal antibody for the treatment of PAH, which blocks JAG-1 cis- and trans-induced cleavage of the NOTCH3 receptor in the pulmonary vasculature, was developed. Inhibition of JAG-1–induced NOTCH3 signaling in the lung reverses clinical and pathologic pulmonary hypertension in two rodent models of disease, without toxic side effects associated with nonspecific NOTCH inhibitors. Our data suggest opposing roles of NOTCH ligands in the pulmonary vasculature in pulmonary hypertension. We propose that selectively targeting JAG-1 activation of NOTCH3 may be an effective, safe strategy to treat PAH.

Rationale: Dysregulated bone morphogenetic protein (BMP) or transforming growth factor β (TGF-β) signaling pathways are imperative in idiopathic and familial pulmonary arterial hypertension (PAH) as well as experimental pulmonary hypertension (PH) in rodent models. Mediator 1 (MED1) is a key transcriptional coactivator and Krüppel-like factor 4 (KLF4) is a master transcription factor in endothelium. However, MED1 and KLF4 epigenetic and transcriptional regulations of the BMP/TGF-β axes in pulmonary endothelium and their dysregulations leading to PAH remain elusive. Objectives: We investigate the MED1/KLF4 co-regulation of the BMP/TGF-β axes in endothelium by studying the epigenetic regulation of BMP receptor type II (BMPR2), ETS-related gene (ERG), and TGF-β receptor 2 (TGFBR2) and their involvement in the PH. Methods: High throughput screening involving data from RNA-seq, MED1 ChIP-seq, H3K27ac ChIP-seq, KLF4 ATAC-seq, and high-throughput chromosome conformation capture (HiC) together with in silico computations were used to explore the epigenetic and transcriptional regulation of BMPR2, ERG, and TGFBR2 by MED1 and KLF4. In vitro experiments with cultured pulmonary arterial endothelial cells (PAECs) and bulk assays were used to validate results from these in silico analyses. Lung tissue from patients with idiopathic pulmonary arterial hypertension (IPAH), animals with experimental PH, and mice with endothelial ablation of MED1 (EC-MED1 -/- ) were used to study the PH-protective effect of MED1. Results: Levels of MED1 were decreased in lung tissue or PAECs from IPAH patients and rodent PH models. Mechanistically, MED1 acted synergistically with KLF4 to transactivate BMPR2, ERG, and TGFBR2 via chromatin remodeling and enhancer-promoter interactions. EC-MED1 -/- mice showed PH susceptibility. In contrast, MED1 overexpression mitigated the PH phenotype in rodents. Conclusions: A homeostatic regulation of BMPR2, ERG, and TGFBR2 in ECs by MED1 synergistic with KLF4 is essential for normal function of the pulmonary endothelium. Dysregulation of MED1 and the resulting impairment of the BMP/TGF-β signaling can lead to the development of PAH/PH.

The prognosis and therapeutic responses are worse for pulmonary arterial hypertension associated with systemic sclerosis (SSc-PAH) compared with idiopathic pulmonary arterial hypertension (IPAH). This discrepancy could be driven by divergence in underlying metabolic determinants of disease.Are circulating bioactive metabolites differentially altered in SSc-PAH vs IPAH, and can this alteration explain clinical disparity between these PAH subgroups?Plasma biosamples from 400 patients with SSc-PAH and 1,082 patients with IPAH were included in the study. Another cohort of 100 patients with scleroderma with no PH and 44 patients with scleroderma with PH was included for external validation. More than 700 bioactive lipid metabolites, representing a range of vasoactive and immune-inflammatory pathways, were assayed in plasma samples from independent discovery and validation cohorts using liquid chromatography/high-resolution mass spectrometry-based approaches. Regression analyses were used to identify metabolites that exhibited differential levels between SSc-PAH and IPAH and associated with disease severity.From hundreds of circulating bioactive lipid molecules, five metabolites were found to distinguish between SSc-PAH and IPAH, as well as associate with markers of disease severity. Relative to IPAH, patients with SSc-PAH carried increased levels of fatty acid metabolites, including lignoceric acid and nervonic acid, as well as eicosanoids/oxylipins and sex hormone metabolites.Patients with SSc-PAH are characterized by an unfavorable bioactive metabolic profile that may explain the poor and limited response to therapy. These data provide important metabolic insights into the molecular heterogeneity underlying differences between subgroups of PAH.

The molecular mechanisms leading to high-altitude pulmonary hypertension (HAPH) remains poorly understood. We previously analyzed the whole genome sequence of Kyrgyz highland population and identified eight genomic intervals having a potential role in HAPH. Tropomodulin 3 gene (TMOD3), which encodes a protein that binds and caps the pointed ends of actin filaments and inhibits cell migration, was one of the top candidates. Here we systematically sought additional evidence to validate the functional role of TMOD3. In-silico analysis reveals that some of the SNPs in HAPH associated genomic intervals were positioned in a regulatory region that could result in alternative splicing of TMOD3. In order to functionally validate the role of TMOD3 in HAPH, we exposed Tmod3−/+ mice to 4 weeks of constant hypoxia, i.e. 10% O2 and analyzed both functional (hemodynamic measurements) and structural (angiography) parameters related to HAPH. The hemodynamic measurements, such as right ventricular systolic pressure, a surrogate measure for pulmonary arterial systolic pressure, and right ventricular contractility (RV- ± dP/dt), increases with hypoxia did not separate between Tmod3−/+ and control mice. Remarkably, there was a significant increase in the number of lung vascular branches and total length of pulmonary vascular branches (P

Objective: Although type 2 diabetes mellitus (T2DM) has been reported as a risk factor for coronavirus disease 2019 (COVID-19), the effect of pharmacologic agents used to treat T2DM, such as metformin, on COVID-19 outcomes remains unclear. Metformin increases the expression of angiotensin converting enzyme 2, a known receptor for severe acute respiratory syndrome coronavirus 2. Data from people with T2DM hospitalized for COVID-19 were used to test the hypothesis that metformin use is associated with improved survival in this population. Methods: Retrospective analyses were performed on de-identified clinical data from a major hospital in Wuhan, China, that included patients with T2DM hospitalized for COVID-19 during the recent epidemic. One hundred and thirty-one patients diagnosed with COVID-19 and T2DM were used in this study. The primary outcome was mortality. Demographic, clinical characteristics, laboratory data, diabetes medications, and respiratory therapy data were also included in the analysis. Results: Of these 131 patients, 37 used metformin with or without other antidiabetes medications. Among the 37 metformin-taking patients, 35 (94.6%) survived and 2 (5.4%) did not survive. The mortality rates in the metformin-taking group versus the non-metformin group were 5.4% (2/37) versus 22.3% (21/94). Using multivariate analysis, metformin was found to be an independent predictor of survival in this cohort (P = .02). Conclusion: This study reveals a significant association between metformin use and survival in people with T2DM diagnosed with COVID-19. These clinical data are consistent with potential benefits of the use of metformin for COVID-19 patients with T2DM.

Platelet-derived growth factor is one of the major growth factors found in human and mammalian serum and tissues. Abnormal activation of platelet-derived growth factor signaling pathway through platelet-derived growth factor receptors may contribute to the development and progression of pulmonary vascular remodeling and obliterative vascular lesions in patients with pulmonary arterial hypertension. In this study, we examined the expression of platelet-derived growth factor receptor isoforms in pulmonary arterial smooth muscle and pulmonary arterial endothelial cells and investigated whether platelet-derived growth factor secreted from pulmonary arterial smooth muscle cell or pulmonary arterial endothelial cell promotes pulmonary arterial smooth muscle cell proliferation. Our results showed that the protein expression of platelet-derived growth factor receptor α and platelet-derived growth factor receptor β in pulmonary arterial smooth muscle cell was upregulated in patients with idiopathic pulmonary arterial hypertension compared to normal subjects. Platelet-derived growth factor activated platelet-derived growth factor receptor α and platelet-derived growth factor receptor β in pulmonary arterial smooth muscle cell, as determined by phosphorylation of platelet-derived growth factor receptor α and platelet-derived growth factor receptor β. The platelet-derived growth factor-mediated activation of platelet-derived growth factor receptor α/platelet-derived growth factor receptor β was enhanced in idiopathic pulmonary arterial hypertension-pulmonary arterial smooth muscle cell compared to normal cells. Expression level of platelet-derived growth factor-AA and platelet-derived growth factor-BB was greater in the conditioned media collected from idiopathic pulmonary arterial hypertension-pulmonary arterial endothelial cell than from normal pulmonary arterial endothelial cell. Furthermore, incubation of idiopathic pulmonary arterial hypertension-pulmonary arterial smooth muscle cell with conditioned culture media from normal pulmonary arterial endothelial cell induced more platelet-derived growth factor receptor α activation than in normal pulmonary arterial smooth muscle cell. Accordingly, the conditioned media from idiopathic pulmonary arterial hypertension-pulmonary arterial endothelial cell resulted in more pulmonary arterial smooth muscle cell proliferation than the media from normal pulmonary arterial endothelial cell. These data indicate that (a) the expression and activity of platelet-derived growth factor receptor are increased in idiopathic pulmonary arterial hypertension-pulmonary arterial smooth muscle cell compared to normal pulmonary arterial smooth muscle cell, and (b) pulmonary arterial endothelial cell from idiopathic pulmonary arterial hypertension patients secretes higher level of platelet-derived growth factor than pulmonary arterial endothelial cell from normal subjects. The enhanced secretion (and production) of platelet-derived growth factor from idiopathic pulmonary arterial hypertension-pulmonary arterial endothelial cell and upregulated platelet-derived growth factor receptor expression (and function) in idiopathic pulmonary arterial hypertension-pulmonary arterial smooth muscle cell may contribute to enhancing platelet-derived growth factor/platelet-derived growth factor receptor-associated pulmonary vascular remodeling in pulmonary arterial hypertension.

We previously demonstrated involvement of NAMPT (nicotinamide phosphoribosyltransferase) in pulmonary arterial hypertension (PAH) and now examine NAMPT regulation and extracellular NAMPT’s (eNAMPT’s) role in PAH vascular remodeling. NAMPT transcription and protein expression in human lung endothelial cells were assessed in response to PAH-relevant stimuli (PDGF [platelet-derived growth factor], VEGF [vascular endothelial growth factor], TGF-β1 [transforming growth factor-β1], and hypoxia). Endothelial-to-mesenchymal transition was detected by SNAI1 (snail family transcriptional repressor 1) and PECAM1 (platelet endothelial cell adhesion molecule 1) immunofluorescence. An eNAMPT-neutralizing polyclonal antibody was tested in a PAH model of monocrotaline challenge in rats. Plasma eNAMPT concentrations, significantly increased in patients with idiopathic pulmonary arterial hypertension, were highly correlated with indices of PAH severity. eNAMPT increased endothelial-to-mesenchymal transition, and each PAH stimulus significantly increased endothelial cell NAMPT promoter activity involving transcription factors STAT5 (signal transducer and activator of transcription 5), SOX18 (SRY-box transcription factor 18), and SOX17 (SRY-box transcription factor 17), a PAH candidate gene newly defined by genome-wide association study. The hypoxia-induced transcription factor HIF-2α (hypoxia-inducible factor-2α) also potently regulated NAMPT promoter activity, and HIF-2α binding sites were identified between −628 bp and −328 bp. The PHD2 (prolyl hydroxylase domain-containing protein 2) inhibitor FG-4592 significantly increased NAMPT promoter activity and protein expression in an HIF-2α–dependent manner. Finally, the eNAMPT-neutralizing polyclonal antibody significantly reduced monocrotaline-induced vascular remodeling, PAH hemodynamic alterations, and NF-κB activation. eNAMPT is a novel and attractive therapeutic target essential to PAH vascular remodeling.