BRCC3 Regulation of ALK2 in Vascular Smooth Muscle Cells: Implication in Pulmonary Hypertension

BACKGROUND

An imbalance of antiproliferative BMP (bone morphogenetic protein) signaling and proliferative TGF-β (transforming growth factor-β) signaling is implicated in the development of pulmonary arterial hypertension (PAH). The posttranslational modification (eg, phosphorylation and ubiquitination) of TGF-β family receptors, including BMPR2 (bone morphogenetic protein type 2 receptor)/ALK2 (activin receptor-like kinase-2) and TGF-βR2/R1, and receptor-regulated (R) Smads significantly affects their activity and thus regulates the target cell fate. BRCC3 modifies the activity and stability of its substrate proteins through K63-dependent deubiquitination. By modulating the posttranslational modifications of the BMP/TGF-β-PPARγ pathway, BRCC3 may play a role in pulmonary vascular remodeling, hence the pathogenesis of PAH.

METHODS

Bioinformatic analyses were used to explore the mechanism of BRCC3 deubiquitinates ALK2. Cultured pulmonary artery smooth muscle cells (PASMCs), mouse models, and specimens from patients with idiopathic PAH were used to investigate the rebalance between BMP and TGF-β signaling in regulating ALK2 phosphorylation and ubiquitination in the context of pulmonary hypertension.

RESULTS

BRCC3 was significantly downregulated in PASMCs from patients with PAH and animals with experimental pulmonary hypertension. BRCC3, by de-ubiquitinating ALK2 at Lys-472 and Lys-475, activated receptor-regulated Smad1/5/9 (Smad1/5/9), which resulted in transcriptional activation of BMP-regulated PPARγ, p53, and Id1. Overexpression of BRCC3 also attenuated TGF-β signaling by downregulating TGF-β expression and inhibiting phosphorylation of Smad3. Experiments in vitro indicated that overexpression of BRCC3 or the de-ubiquitin-mimetic ALK2-K472/475R attenuated PASMC proliferation and migration and enhanced PASMC apoptosis. In SM22α-BRCC3-Tg mice, pulmonary hypertension was ameliorated because of activation of the ALK2-Smad1/5-PPARγ axis in PASMCs. In contrast, Brcc3-/- mice showed increased susceptibility of experimental pulmonary hypertension because of inhibition of the ALK2-Smad1/5 signaling.

CONCLUSIONS

These results suggest a pivotal role of BRCC3 in sustaining pulmonary vascular homeostasis by maintaining the integrity of the BMP signaling (ie, the ALK2-Smad1/5-PPARγ axis) while suppressing TGF-β signaling in PASMCs. Such rebalance of BMP/TGF-β pathways is translationally important for PAH alleviation.

Racial and ethnic variation in referral times for thoracic oncologic surgery in a major metropolitan area

OBJECTIVE

The study objective was to understand the impact of race/ethnicity on access to thoracic surgical care for patients undergoing lung resection for cancer.

METHODS

We performed a retrospective analysis on 206 consecutive patients who underwent lung resection for cancer (120 female, 86 male; median age 66 years), with respect to how race and ethnicity impact time to referral for thoracic surgery to a major healthcare center. Time between initial radiographic appearance of a lung nodule/mass 1 cm or greater to surgical referral and time from surgical referral to operation were evaluated for 121 White, 30 Asian, 26 Hispanic, 12 African American, and 17 mixed or other race patients. The impact of age, sex, median income of patient's household, national and state Area Deprivation Indices, insurance type, and distance between the patient's domicile and our hospital was evaluated. The influence of the referring physician's practice (hospital-based, hospital-affiliated, or private), internal or external referral, race/ethnicity, and level of specialization was also studied.

RESULTS

African American, Asian, Hispanic, and mixed/other race patients had significantly longer wait times between initial radiographic finding of a lung nodule/mass 1 cm or greater and surgical referral compared with White individuals (median days: African American, 78; Asian, 95; Hispanic, 92; mixed or other, 65; White, 35). Multiple linear regression analysis demonstrated that race/ethnicity was the only significant predictor of prolonged time to surgical referral when adjusted for age, sex, median household income level, national and state Area Deprivation Indices, insurance type, and distance between patient's home and our hospital. The referring physician's type of practice and internal versus external referral were not significant. However, the physician's race/ethnicity and level of specialization had an impact on referral times, with nonspecialists referring patients sooner to thoracic surgery compared with specialists who ordered more workup tests. For all patient races/ethnicities, there was no difference in time between surgical referral and day of operation.

CONCLUSIONS

Race and ethnicity have a major impact on the time from initial radiographic appearance of a lung nodule/mass 1 cm or greater to referral for surgical resection for cancer. This study suggests the need to develop strategies to reduce minority wait times and improve timely access to surgery for patients with thoracic malignancies.

VIDEO ABSTRACT

Discussion of how race and ethnicity impact referral time to thoracic surgery discussed by Dr Moises Hernandez.

MED1 Regulates BMP/TGF-β in Endothelium: Implication for Pulmonary Hypertension

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.

Mechanosensitive cation currents through TRPC6 and Piezo1 channels in human pulmonary arterial endothelial cells

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.

JAGGED-NOTCH3 signaling in vascular remodeling in pulmonary arterial hypertension

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.

Mechanosensitive channel Piezo1 is required for pulmonary artery smooth muscle cell proliferation

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.

In Vivo and Ex Vivo Experimental Approach for Studying Functional Role of Notch in Pulmonary Vascular Disease

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 Ca²⁺ signaling in pulmonary arterial smooth muscle cells (PASMCs). Pharmacological experiments and genetic approach using animal models of experimental PH (e.g., chronic hypoxia-induced PH) have been routinely utilized to study pathogenic mechanisms of PAH/PH and identify novel therapeutic targets. In this chapter, we describe protocols to investigate the role of Notch by measuring pulmonary hemodynamics in vivo and pulmonary arterial pressure ex vivo in mouse models of experimental PH. Using these experimental protocols, one can study the role of Notch or Notch signaling pathway in the pathogenic mechanisms of pulmonary vascular disease and develop novel therapies by targeting Notch ligands and receptors.

Endothelial upregulation of mechanosensitive channel Piezo1 in pulmonary hypertension

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.

TRPC6, a Therapeutic Target for Pulmonary Hypertension

Idiopathic pulmonary arterial hypertension (PAH) is a fatal and progressive disease. Pulmonary vasoconstriction due to pulmonary arterial smooth muscle cell (PASMC) contraction and pulmonary arterial remodeling due to PASMC proliferation are causes for increased pulmonary vascular resistance in patients with PAH. We and others observed upregulation of TRPC6 channels in PASMC from patients with PAH. An increase in cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) in PASMC triggers PASMC contraction and vasoconstriction, while Ca²⁺-dependent activation of PI3K/AKT/mTOR pathway is pivotal for cell proliferation and gene expression. Despite evidence supporting a pathological role of TRPC6, no selective and orally bioavailable TRPC6 blocker has yet been developed and tested for treatment of PAH. We sought to investigate whether block of receptor-operated Ca²⁺ channels or TRPC6 can reverse established PH in mice via inhibiting Ca²⁺-dependent activation of AKT/mTOR signaling. Here we report that intrapulmonary application of 2-aminoethyl diphenyl borniate (2-APB), a non-selective blocker of cation channels or BI-749237, a selective blocker of TRPC6, significantly and reversibly inhibited acute hypoxic pulmonary vasoconstriction. Intraperitoneal injection of 2-APB significantly attenuated the development of PH and partially reversed established PH. Oral gavage of the selective TRPC6 blocker BI-749237 reversed established PH by 50% via regression of pulmonary vascular remodeling. Furthermore, 2-APB and BI-749237 both inhibited PDGF- and serum-mediated phosphorylation of AKT and mTOR in PASMC. These results indicates that the receptor-operated and mechanosensitive TRPC6 channel is a good target for developing novel treatment for PAH. BI-749237, a selective TRPC6 blocker, is potentially a novel and effective drug for treating PAH.

Mouse model of experimental pulmonary hypertension: Lung angiogram and right heart catheterization

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.

Halofuginone, a promising drug for treatment of pulmonary hypertension

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 Ca²⁺ channels (VDCCs) in pulmonary artery smooth muscle cells (PASMCs). Digital fluorescence microscopy was used to measure intracellular Ca²⁺ concentration in PASMCs. Isolated perfused and ventilated mouse lungs were used to measure pulmonary artery pressure (PAP). Mice exposed to hypoxia (10% O₂ ) 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 Ca²⁺ entry in HEK cells transfected with calcium-sensing receptor gene and attenuated store-operated Ca²⁺ 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 Ca²⁺ 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.

Upregulation of Calcium Homeostasis Modulators in Contractile-To-Proliferative Phenotypical Transition of Pulmonary Arterial Smooth Muscle Cells

Excessive pulmonary artery (PA) smooth muscle cell (PASMC) proliferation and migration are implicated in the development of pathogenic pulmonary vascular remodeling characterized by concentric arterial wall thickening and arteriole muscularization in patients with pulmonary arterial hypertension (PAH). Pulmonary artery smooth muscle cell contractile-to-proliferative phenotypical transition is a process that promotes pulmonary vascular remodeling. A rise in cytosolic Ca²⁺ concentration [(Ca²⁺)_cyt] in PASMCs is a trigger for pulmonary vasoconstriction and a stimulus for pulmonary vascular remodeling. Here, we report that the calcium homeostasis modulator (CALHM), a Ca²⁺ (and ATP) channel that is allosterically regulated by voltage and extracellular Ca²⁺, is upregulated during the PASMC contractile-to-proliferative phenotypical transition. Protein expression of CALHM1/2 in primary cultured PASMCs in media containing serum and growth factors (proliferative PASMC) was significantly greater than in freshly isolated PA (contractile PASMC) from the same rat. Upregulated CALHM1/2 in proliferative PASMCs were associated with an increased ratio of pAKT/AKT and pmTOR/mTOR and an increased expression of the cell proliferation marker PCNA, whereas serum starvation and rapamycin significantly downregulated CALHM1/2. Furthermore, CALHM1/2 were upregulated in freshly isolated PA from rats with monocrotaline (MCT)-induced PH and in primary cultured PASMC from patients with PAH in comparison to normal controls. Intraperitoneal injection of CGP 37157 (0.6 mg/kg, q8H), a non-selective blocker of CALHM channels, partially reversed established experimental PH. These data suggest that CALHM upregulation is involved in PASMC contractile-to-proliferative phenotypical transition. Ca²⁺ influx through upregulated CALHM1/2 may play an important role in the transition of sustained vasoconstriction to excessive vascular remodeling in PAH or precapillary PH. Calcium homeostasis modulator could potentially be a target to develop novel therapies for PAH.

Adult stem cell-derived complete lung organoid models emulate lung disease in COVID-19

Background

SARS-CoV-2, the virus responsible for COVID-19, causes widespread damage in the lungs in the setting of an overzealous immune response whose origin remains unclear.

Methods

We present a scalable, propagable, personalized, cost-effective adult stem cell-derived human lung organoid model that is complete with both proximal and distal airway epithelia. Monolayers derived from adult lung organoids (ALOs), primary airway cells, or hiPSC-derived alveolar type II (AT2) pneumocytes were infected with SARS-CoV-2 to create in vitro lung models of COVID-19.

Results

Infected ALO monolayers best recapitulated the transcriptomic signatures in diverse cohorts of COVID-19 patient-derived respiratory samples. The airway (proximal) cells were critical for sustained viral infection, whereas distal alveolar differentiation (AT2→AT1) was critical for mounting the overzealous host immune response in fatal disease; ALO monolayers with well-mixed proximodistal airway components recapitulated both.

Conclusions

Findings validate a human lung model of COVID-19, which can be immediately utilized to investigate COVID-19 pathogenesis and vet new therapies and vaccines.

Funding

This work was supported by the National Institutes for Health (NIH) grants 1R01DK107585-01A1, 3R01DK107585-05S1 (to SD); R01-AI141630, CA100768 and CA160911 (to PG) and R01-AI 155696 (to PG, DS and SD); R00-CA151673 and R01-GM138385 (to DS), R01- HL32225 (to PT), UCOP-R00RG2642 (to SD and PG), UCOP-R01RG3780 (to P.G. and D.S) and a pilot award from the Sanford Stem Cell Clinical Center at UC San Diego Health (P.G, S.D, D.S). GDK was supported through The American Association of Immunologists Intersect Fellowship Program for Computational Scientists and Immunologists. L.C.A's salary was supported in part by the VA San Diego Healthcare System. This manuscript includes data generated at the UC San Diego Institute of Genomic Medicine (IGC) using an Illumina NovaSeq 6000 that was purchased with funding from a National Institutes of Health SIG grant (#S10 OD026929).

Adult Stem Cell-derived Complete Lung Organoid Models Emulate Lung Disease in COVID-19

SARS-CoV-2, the virus responsible for COVID-19, causes widespread damage in the lungs in the setting of an overzealous immune response whose origin remains unclear. We present a scalable, propagable, personalized, cost-effective adult stem cell-derived human lung organoid model that is complete with both proximal and distal airway epithelia. Monolayers derived from adult lung organoids (ALOs), primary airway cells, or hiPSC-derived alveolar type-II (AT2) pneumocytes were infected with SARS-CoV-2 to create in vitro lung models of COVID-19. Infected ALO-monolayers best recapitulated the transcriptomic signatures in diverse cohorts of COVID-19 patient-derived respiratory samples. The airway (proximal) cells were critical for sustained viral infection whereas distal alveolar differentiation (AT2→AT1) was critical for mounting the overzealous host immune response in fatal disease; ALO monolayers with well-mixed proximodistal airway components recapitulated both. Findings validate a human lung model of COVID-19 which can be immediately utilized to investigate COVID-19 pathogenesis, and vet new therapies and vaccines.

Revisiting the mechanism of hypoxic pulmonary vasoconstriction using isolated perfused/ventilated mouse lung

Hypoxic Pulmonary Vasoconstriction (HPV) is an important physiological mechanism of the lungs that matches perfusion to ventilation thus maximizing O₂ saturation of the venous blood within the lungs. This study emphasizes on principal pathways in the initiation and modulation of hypoxic pulmonary vasoconstriction with a primary focus on the role of Ca²⁺ signaling and Ca²⁺ influx pathways in hypoxic pulmonary vasoconstriction. We used an ex vivo model, isolated perfused/ventilated mouse lung to evaluate hypoxic pulmonary vasoconstriction. Alveolar hypoxia (utilizing a mini ventilator) rapidly and reversibly increased pulmonary arterial pressure due to hypoxic pulmonary vasoconstriction in the isolated perfused/ventilated lung. By applying specific inhibitors for different membrane receptors and ion channels through intrapulmonary perfusion solution in isolated lung, we were able to define the targeted receptors and channels that regulate hypoxic pulmonary vasoconstriction. We show that extracellular Ca²⁺ or Ca²⁺ influx through various Ca²⁺-permeable channels in the plasma membrane is required for hypoxic pulmonary vasoconstriction. Removal of extracellular Ca²⁺ abolished hypoxic pulmonary vasoconstriction, while blockade of L-type voltage-dependent Ca²⁺ channels (with nifedipine), non-selective cation channels (with 30 µM SKF-96365), and TRPC6/TRPV1 channels (with 1 µM SAR-7334 and 30 µM capsazepine, respectively) significantly and reversibly inhibited hypoxic pulmonary vasoconstriction. Furthermore, blockers of Ca²⁺-sensing receptors (by 30 µM NPS2143, an allosteric Ca²⁺-sensing receptors inhibitor) and Notch (by 30 µM DAPT, a γ-secretase inhibitor) also attenuated hypoxic pulmonary vasoconstriction. These data indicate that Ca²⁺ influx in pulmonary arterial smooth muscle cells through voltage-dependent, receptor-operated, and store-operated Ca²⁺ entry pathways all contribute to initiation of hypoxic pulmonary vasoconstriction. The extracellular Ca²⁺-mediated activation of Ca²⁺-sensing receptors and the cell–cell interaction via Notch ligands and receptors contribute to the regulation of hypoxic pulmonary vasoconstriction.

MDM2-Mediated Ubiquitination of Angiotensin-Converting Enzyme 2 Contributes to the Development of Pulmonary Arterial Hypertension

Supplemental Digital Content is available in the text.

Background:

Angiotensin-converting enzyme 2 (ACE2) converts angiotensin II, a potent vasoconstrictor, to angiotensin-(1–7) and is also a membrane protein that enables coronavirus disease 2019 (COVID-19) infectivity. AMP-activated protein kinase (AMPK) phosphorylation of ACE2 enhances ACE2 stability. This mode of posttranslational modification of ACE2 in vascular endothelial cells is causative of a pulmonary hypertension (PH)–protective phenotype. The oncoprotein MDM2 (murine double minute 2) is an E3 ligase that ubiquitinates its substrates to cause their degradation. In this study, we investigated whether MDM2 is involved in the posttranslational modification of ACE2 through its ubiquitination of ACE2, and whether an AMPK and MDM2 crosstalk regulates the pathogenesis of PH.

Methods:

Bioinformatic analyses were used to explore E3 ligase that ubiquitinates ACE2. Cultured endothelial cells, mouse models, and specimens from patients with idiopathic pulmonary arterial hypertension were used to investigate the crosstalk between AMPK and MDM2 in regulating ACE2 phosphorylation and ubiquitination in the context of PH.

Results:

Levels of MDM2 were increased and those of ACE2 decreased in lung tissues or pulmonary arterial endothelial cells from patients with idiopathic pulmonary arterial hypertension and rodent models of experimental PH. MDM2 inhibition by JNJ-165 reversed the SU5416/hypoxia-induced PH in C57BL/6 mice. ACE2-S680L mice (dephosphorylation at S680) showed PH susceptibility, and ectopic expression of ACE2-S680L/K788R (deubiquitination at K788) reduced experimental PH. Moreover, ACE2-K788R overexpression in mice with endothelial cell–specific AMPKα2 knockout mitigated PH.

Conclusions:

Maladapted posttranslational modification (phosphorylation and ubiquitination) of ACE2 at Ser-680 and Lys-788 is involved in the pathogenesis of pulmonary arterial hypertension and experimental PH. Thus, a combined intervention of AMPK and MDM2 in the pulmonary endothelium might be therapeutically effective in PH treatment.

Endothelial platelet-derived growth factor-mediated activation of smooth muscle platelet-derived growth factor receptors in pulmonary arterial hypertension

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.

Notch enhances Ca2+ entry by activating calcium-sensing receptors and inhibiting voltage-gated K+ channels

The increase in cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) and upregulation of calcium-sensing receptor (CaSR) and stromal interaction molecule 2 (STIM2) along with inhibition of voltage-gated K⁺ (K_V) channels in pulmonary arterial smooth muscle cells (PASMC) have been implicated in the development of pulmonary arterial hypertension; however, the precise upstream mechanisms remain elusive. Activation of CaSR, a G protein-coupled receptor (GPCR), results in Ca²⁺ release from the endoplasmic/sarcoplasmic reticulum (ER/SR) and Ca²⁺ influx through receptor-operated and store-operated Ca²⁺ channels (SOC). Upon Ca²⁺ depletion from the SR, STIM forms clusters to mediate store-operated Ca²⁺ entry. Activity of K_V channels, like KCNA5/K_V1.5 and KCNA2/K_V1.2, contributes to regulating membrane potential, and inhibition of K_V channels results in membrane depolarization that increases [Ca²⁺]_cyt by opening voltage-dependent Ca²⁺ channels. In this study, we show that activation of Notch by its ligand Jag-1 promotes the clustering of STIM2, and clustered STIM2 subsequently enhances the CaSR-induced Ca²⁺ influx through SOC channels. Extracellular Ca²⁺-mediated activation of CaSR increases [Ca²⁺]_cyt in CASR-transfected HEK293 cells. Treatment of CASR-transfected cells with Jag-1 further enhances CaSR-mediated increase in [Ca²⁺]_cyt. Moreover, CaSR-mediated increase in [Ca²⁺]_cyt was significantly augmented in cells co-transfected with CASR and STIM2. CaSR activation results in STIM2 clustering in CASR/STIM2-cotransfected cells. Notch activation also induces significant clustering of STIM2. Furthermore, activation of Notch attenuates whole cell K⁺ currents in KCNA5- and KCNA2-transfected cells. Together, these results suggest that Notch activation enhances CaSR-mediated increases in [Ca²⁺]_cyt by enhancing store-operated Ca²⁺ entry and inhibits KCNA5/K_V1.5 and KCNA2/K_V1.2, ultimately leading to voltage-activated Ca²⁺ entry.

MicroRNA-mediated downregulation of K+ channels in pulmonary arterial hypertension

Downregulated expression of K+ channels and decreased K+ currents in pulmonary artery smooth muscle cells (PASMC) have been implicated in the development of sustained pulmonary vasoconstriction and vascular remodeling in patients with idiopathic pulmonary arterial hypertension (IPAH). However, it is unclear exactly how K+ channels are downregulated in IPAH-PASMC. MicroRNAs (miRNAs) are small non-coding RNAs that are capable of posttranscriptionally regulating gene expression by binding to the 3'-untranslated regions of their targeted mRNAs. Here, we report that specific miRNAs are responsible for the decreased K+ channel expression and function in IPAH-PASMC. We identified 3 miRNAs (miR-29b, miR-138, and miR-222) that were highly expressed in IPAH-PASMC in comparison to normal PASMC (>2.5-fold difference). Selectively upregulated miRNAs are correlated with the decreased expression and attenuated activity of K+ channels. Overexpression of miR-29b, miR-138, or miR-222 in normal PASMC significantly decreased whole cell K+ currents and downregulated voltage-gated K+ channel 1.5 (KV1.5/KCNA5) in normal PASMC. Inhibition of miR-29b in IPAH-PASMC completely recovered K+ channel function and KV1.5 expression, while miR-138 and miR-222 had a partial or no effect. Luciferase assays further revealed that KV1.5 is a direct target of miR-29b. Additionally, overexpression of miR-29b in normal PASMC decreased large-conductance Ca2+-activated K+ (BKCa) channel currents and downregulated BKCa channel β1 subunit (BKCaβ1 or KCNMB1) expression, while inhibition of miR-29b in IPAH-PASMC increased BKCa channel activity and BKCaβ1 levels. These data indicate upregulated miR-29b contributes at least partially to the attenuated function and expression of KV and BKCa channels in PASMC from patients with IPAH.

AMP-activated Protein Kinase Phosphorylation of Angiotensin-Converting Enzyme 2 in Endothelium Mitigates Pulmonary Hypertension

RATIONALE

Endothelial dysfunction plays an integral role in pulmonary hypertension (PH). AMPK (AMP-activated protein kinase) and ACE2 (angiotensin-converting enzyme 2) are crucial in endothelial homeostasis. The mechanism by which AMPK regulates ACE2 in the pulmonary endothelium and its protective role in PH remain elusive.

OBJECTIVES

We investigated the role of AMPK phosphorylation of ACE2 Ser680 in ACE2 stability and deciphered the functional consequences of this post-translational modification of ACE2 in endothelial homeostasis and PH.

METHODS

Bioinformatics prediction, kinase assay, and antibody against phospho-ACE2 Ser680 (p-ACE2 S680) were used to investigate AMPK phosphorylation of ACE2 Ser680 in endothelial cells. Using CRISPR-Cas9 genomic editing, we created gain-of-function ACE2 S680D knock-in and loss-of-function ACE2 knockout (ACE2^-/-) mouse lines to address the involvement of p-ACE2 S680 and ACE2 in PH. The AMPK-p-ACE2 S680 axis was also validated in lung tissue from humans with idiopathic pulmonary arterial hypertension.

MEASUREMENTS AND MAIN RESULTS

Phosphorylation of ACE2 by AMPK enhanced the stability of ACE2, which increased Ang (angiotensin) 1-7 and endothelial nitric oxide synthase-derived NO bioavailability. ACE2 S680D knock-in mice were resistant to PH as compared with wild-type littermates. In contrast, ACE2-knockout mice exacerbated PH, a similar phenotype found in mice with endothelial cell-specific deletion of AMPKα2. Consistently, the concentrations of phosphorylated AMPK, p-ACE2 S680, and ACE2 were decreased in human lungs with idiopathic pulmonary arterial hypertension.

CONCLUSIONS

Impaired phosphorylation of ACE2 Ser680 by AMPK in pulmonary endothelium leads to a labile ACE2 and hence is associated with the pathogenesis of PH. Thus, AMPK regulation of the vasoprotective ACE2 is a potential target for PH treatment.

Multifocal Endobronchial Fibromas Presenting as Unilobar Emphysema

Tracheobronchial fibromas are very rare, locally-invasive tumors of the airways. Fewer than 30 cases have been reported within the English-speaking literature. Historically, these neoplasms have been diagnosed as isolated endobronchial masses, with affected patients presenting with wheezing, cough, stridor, hemoptysis, dyspnea, or pneumonia. We report the case of 39-year-old man with multiple, synchronous endobronchial fibromas causing unilobar emphysema. A computed tomographic scan and bronchoscopy with biopsy were performed preoperatively to diagnose these lesions in the orifices of the anterior segment and the lingula within the left upper lobe. The patient underwent successful video-assisted left upper lobectomy, without recurrence at 3 years. This is the first report of a synchronous presentation of multiple pulmonary endobronchial fibromas within the same patient and the first report of endobronchial fibroma presenting as unilobar air trapping. Recognition of the unusual presentation of this uncommon pathology can lead to timely intervention.

Notch Activation of Ca(2+) Signaling in the Development of Hypoxic Pulmonary Vasoconstriction and Pulmonary Hypertension

Hypoxic pulmonary vasoconstriction (HPV) is an important physiological response that optimizes the ventilation/perfusion ratio. Chronic hypoxia causes vascular remodeling, which is central to the pathogenesis of hypoxia-induced pulmonary hypertension (HPH). We have previously shown that Notch3 is up-regulated in HPH and that activation of Notch signaling enhances store-operated Ca(2+) entry (SOCE), an important mechanism that contributes to pulmonary arterial smooth muscle cell (PASMC) proliferation and contraction. Here, we investigate the role of Notch signaling in HPV and hypoxia-induced enhancement of SOCE. We examined SOCE in human PASMCs exposed to hypoxia and pulmonary arterial pressure in mice using the isolated perfused/ventilated lung method. Wild-type and canonical transient receptor potential (TRPC) 6(-/-) mice were exposed to chronic hypoxia to induce HPH. Inhibition of Notch signaling with a γ-secretase inhibitor attenuates hypoxia-enhanced SOCE in PASMCs and hypoxia-induced increase in pulmonary arterial pressure. Our results demonstrate that hypoxia activates Notch signaling and up-regulates TRPC6 channels. Additionally, treatment with a Notch ligand can mimic hypoxic responses. Finally, inhibition of TRPC6, either pharmacologically or genetically, attenuates HPV, hypoxia-enhanced SOCE, and the development of HPH. These results demonstrate that hypoxia-induced activation of Notch signaling mediates HPV and the development of HPH via functional activation and up-regulation of TRPC6 channels. Understanding the molecular mechanisms that regulate cytosolic free Ca(2+) concentration and PASMC proliferation is critical to elucidation of the pathogenesis of HPH. Targeting Notch regulation of TRPC6 will be beneficial in the development of novel therapies for pulmonary hypertension associated with hypoxia.

ERG-APLNR axis controls pulmonary venule endothelial proliferation in pulmonary veno-occlusive disease

BACKGROUND

Pulmonary veno-occlusive disease is caused by excessive cell proliferation and fibrosis, which obliterate the lumen of pulmonary venules, leading to pulmonary hypertension, right ventricular failure, and death. This condition has no effective treatment and a 5-year survival of <5%. Understanding the mechanism of this disease and designing effective therapies are urgently needed.

METHODS AND RESULTS

We show that mice with homozygous deletion of the Ets transcription factor Erg die between embryonic day 16.5 and 3 months of age as a result of pulmonary veno-occlusive disease, capillary hemorrhage, and pancytopenia. We demonstrate that Erg binds to and serves as a transcriptional activator of the G-protein-coupled receptor gene Aplnr, the expression of which is uniquely specific for venous endothelium and that knockout of either Erg or Aplnr results in pulmonary venule-specific endothelial proliferation in vitro. We show that mice with either homozygous-global or endothelium-directed deletion of Aplnr manifest pulmonary veno-occlusive disease and right heart failure, detectable at 8 months of age. Levels of pulmonary ERG and APLNR in patients with pulmonary veno-occlusive disease undergoing lung transplantation were significantly lower than those of control subjects.

CONCLUSIONS

Our results suggest that ERG and APLNR are essential for endothelial homeostasis in venules in the lung and that perturbation in ERG-APLNR signaling is crucial for the development of pulmonary veno-occlusive disease. We identify this pathway as a potential therapeutic target for the treatment of this incurable disease.

Activation of Notch signaling by short-term treatment with Jagged-1 enhances store-operated Ca(2+) entry in human pulmonary arterial smooth muscle cells

Notch signaling plays a critical role in controlling proliferation and differentiation of pulmonary arterial smooth muscle cells (PASMC). Upregulated Notch ligands and Notch3 receptors in PASMC have been reported to promote the development of pulmonary vascular remodeling in patients with pulmonary arterial hypertension (PAH) and in animals with experimental pulmonary hypertension. Activation of Notch receptors by their ligands leads to the cleavage of the Notch intracellular domain (NICD) to the cytosol by γ-secretase; NICD then translocates into the nucleus to regulate gene transcription. In this study, we examined whether short-term activation of Notch functionally regulates store-operated Ca(2+) entry (SOCE) in human PASMC. Treatment of PASMC with the active fragment of human Jagged-1 protein (Jag-1) for 15-60 min significantly increased the amplitude of SOCE induced by passive deletion of Ca(2+) from the intracellular stores, the sarcoplasmic reticulum (SR). The Jag-1-induced enhancement of SOCE was time dependent: the amplitude was maximized at 30 min of treatment with Jag-1, which was closely correlated with the time course of Jag-1-mediated increase in NICD protein level. The scrambled peptide of Jag-1 active fragment had no effect on SOCE. Inhibition of γ-secretase by N-[N-(3,5-difluorophenacetyl-L-alanyl)]-S-phenylglycine t-butyl ester (DAPT) significantly attenuated the Jag-1-induced augmentation of SOCE. In addition to the short-term effect, prolonged treatment of PASMC with Jag-1 for 48 h also markedly enhanced the amplitude of SOCE. These data demonstrate that short-term activation of Notch signaling enhances SOCE in PASMC; the NICD-mediated functional interaction with store-operated Ca(2+) channels (SOC) may be involved in the Jag-1-mediated enhancement of SOCE in human PASMC.

Transcriptome sequencing of tumor subpopulations reveals a spectrum of therapeutic options for squamous cell lung cancer

Background

The only therapeutic options that exist for squamous cell lung carcinoma (SCC) are standard radiation and cytotoxic chemotherapy. Cancer stem cells (CSCs) are hypothesized to account for therapeutic resistance, suggesting that CSCs must be specifically targeted. Here, we analyze the transcriptome of CSC and non-CSC subpopulations by RNA-seq to identify new potential therapeutic strategies for SCC.

Methods

We sorted a SCC into CD133− and CD133+ subpopulations and then examined both by copy number analysis (CNA) and whole genome and transcriptome sequencing. We analyzed The Cancer Genome Atlas (TCGA) transcriptome data of 221 SCCs to determine the generality of our observations.

Results

Both subpopulations highly expressed numerous mRNA isoforms whose protein products are active drug targets for other cancers; 31 (25%) correspond to 18 genes under active investigation as mAb targets and an additional 4 (3%) are of therapeutic interest. Moreover, we found evidence that both subpopulations were proliferatively driven by very high levels of c-Myc and the TRAIL long isoform (TRAIL_L) and that normal apoptotic responses to high expression of these genes was prevented through high levels of Mcl-1_L and Bcl-x_L and c-Flip_L—isoforms for which drugs are now in clinical development. SCC RNA-seq data (n = 221) from TCGA supported our findings. Our analysis is inconsistent with the CSC concept that most cells in a cancer have lost their proliferative potential. Furthermore, our study suggests how to target both the CSC and non-CSC subpopulations with one treatment strategy.

Conclusions

Our study is relevant to SCC in particular for it presents numerous potential options to standard therapy that target the entire tumor. In so doing, it demonstrates how transcriptome sequencing provides insights into the molecular underpinnings of cancer propagating cells that, importantly, can be leveraged to identify new potential therapeutic options for cancers beyond what is possible with DNA sequencing.

Surgical management of endobronchial inflammatory myofibroblastic tumors

BACKGROUND

Endobronchial myofibroblastic tumors are neoplasms composed of clonal populations of smooth muscle cells and a variable lymphocytic inflammatory component. They represent a challenge with respect to diagnosis, classification, and surgical resection due to their infrequent occurrence.

METHODS

We retrospectively reviewed our experience with patients who had myofibroblastic tumors in the major airways over a 15-year period, in order to understand the incidence, natural biology, treatment, and long-term outcome of individuals with this type of neoplasm in an endobronchial location.

RESULTS

Between 1995 and 2010, 11 patients (9 female, 2 male) underwent surgical resection of a myofibroblastic tumor arising within the tracheobronchial tree. The mean age was 39.6 years (range, 22.3 to 53.6 years). All patients were symptomatic, with cough and dyspnea as the most common presenting complaints. Rigid bronchoscopy with endobronchial biopsy was utilized to establish the diagnosis in 9 of 11 patients. Laser-mechanical debulking was performed to relieve airway obstruction prior to operation in 10 of 11 patients. Because of wide submucosal infiltration of the neoplasms, surgical resection for complete removal was required for all individuals. Tracheal resection was performed in 3 patients, carinal resection in 1 patient, mainstem bronchial resection in 2 patients, sleeve resection in 3 patients, bilobectomy in 1 patient, and right lower lobectomy in 1 patient. Resection with tumor-free margins was accomplished in all patients. Mean tumor size was 2.3 cm (range, 1.5 to 3.5 cm). There were no operative deaths, with all patients alive and disease-free at a mean of 6.1 ± 3.7 years.

CONCLUSIONS

Complete surgical resection of inflammatory myofibroblastic tumors presenting in a major airway is safe and leads to excellent survival for patients with this uncommon disease.

Somatic chromosome abnormalities in the lungs of patients with pulmonary arterial hypertension

RATIONALE

Vascular remodeling in pulmonary arterial hypertension (PAH) involves proliferation and migration of endothelial and smooth muscle cells, leading to obliterative vascular lesions. Previous studies have indicated that the endothelial cell proliferation is quasineoplastic, with evidence of monoclonality and instability of short DNA microsatellite sequences.

OBJECTIVES

To assess whether there is larger-scale genomic instability.

METHODS

We performed genome-wide microarray copy number analysis on pulmonary artery endothelial cells and smooth muscle cells isolated from the lungs of patients with PAH.

MEASUREMENTS AND MAIN RESULTS

Mosaic chromosomal abnormalities were detected in PAEC cultures from five of nine PAH lungs but not in normal (n = 8) or disease control subjects (n = 5). Fluorescent in situ hybridization analysis confirmed the presence of these abnormalities in vivo in two of three cases. One patient harbored a germline mutation of BMPR2, the primary genetic cause of PAH, and somatic loss of chromosome-13, which constitutes a second hit in the same pathway by deleting Smad-8. In two female subjects with mosaic loss of the X chromosome, methylation analysis showed that the active X was deleted. One subject also showed completely skewed X-inactivation in the nondeleted cells, suggesting the pulmonary artery endothelial cell population was clonal before the acquisition of the chromosome abnormality.

CONCLUSIONS

Our data indicate a high frequency of genetically abnormal subclones within PAH lung vessels and provide the first definitive evidence of a second genetic hit in a patient with a germline BMPR2 mutation. We propose that these chromosome abnormalities may confer a growth advantage and thus contribute to the progression of PAH.

Juvenile exposure to anthracyclines impairs cardiac progenitor cell function and vascularization resulting in greater susceptibility to stress-induced myocardial injury in adult mice

BACKGROUND

The anthracycline doxorubicin is an effective chemotherapeutic agent used to treat pediatric cancers but is associated with cardiotoxicity that can manifest many years after the initial exposure. To date, very little is known about the mechanism of this late-onset cardiotoxicity.

METHODS AND RESULTS

To understand this problem, we developed a pediatric model of late-onset doxorubicin-induced cardiotoxicity in which juvenile mice were exposed to doxorubicin, using a cumulative dose that did not induce acute cardiotoxicity. These mice developed normally and had no obvious cardiac abnormalities as adults. However, evaluation of the vasculature revealed that juvenile doxorubicin exposure impaired vascular development, resulting in abnormal vascular architecture in the hearts with less branching and decreased capillary density. Both physiological and pathological stress induced late-onset cardiotoxicity in the adult doxorubicin-treated mice. Moreover, adult mice subjected to myocardial infarction developed rapid heart failure, which correlated with a failure to increase capillary density in the injured area. Progenitor cells participate in regeneration and blood vessel formation after a myocardial infarction, but doxorubicin-treated mice had fewer progenitor cells in the infarct border zone. Interestingly, doxorubicin treatment reduced proliferation and differentiation of the progenitor cells into cells of cardiac lineages.

CONCLUSIONS

Our data suggest that anthracycline treatment impairs vascular development as well as progenitor cell function in the young heart, resulting in an adult heart that is more susceptible to stress.

Notch3 signaling promotes the development of pulmonary arterial hypertension

Notch receptor signaling is implicated in controlling smooth muscle cell proliferation and in maintaining smooth muscle cells in an undifferentiated state. Pulmonary arterial hypertension is characterized by excessive vascular resistance, smooth muscle cell proliferation in small pulmonary arteries, leading to elevation of pulmonary vascular resistance, right ventricular failure and death. Here we show that human pulmonary hypertension is characterized by overexpression of NOTCH3 in small pulmonary artery smooth muscle cells and that the severity of disease in humans and rodents correlates with the amount of NOTCH3 protein in the lung. We further show that mice with homozygous deletion of Notch3 do not develop pulmonary hypertension in response to hypoxic stimulation and that pulmonary hypertension can be successfully treated in mice by administration of N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), a gamma-secretase inhibitor that blocks activation of Notch3 in smooth muscle cells. We show a mechanistic link from NOTCH3 receptor signaling through the Hairy and enhancer of Split-5 (HES-5) protein to smooth muscle cell proliferation and a shift to an undifferentiated smooth muscle cell phenotype. These results suggest that the NOTCH3-HES-5 signaling pathway is crucial for the development of pulmonary arterial hypertension and provide a target pathway for therapeutic intervention.

Inhibition of mTOR attenuates store-operated Ca2+ entry in cells from endarterectomized tissues of patients with chronic thromboembolic pulmonary hypertension

Pulmonary vascular remodeling occurs in patients with chronic thromboembolic pulmonary hypertension (CTEPH). One factor contributing to this vascular wall thickening is the proliferation of pulmonary artery smooth muscle cells (PASMC). Store-operated Ca(2+) entry (SOCE) and cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) in PASMC are known to be important in cell proliferation and vascular remodeling in pulmonary hypertension. Rapamycin is widely known for its antiproliferative effects in injured coronary arteries. Although several reports have suggested favorable effects of rapamycin in animal models of pulmonary hypertension, no reports have been published to date in human tissues. Here we report that rapamycin has an inhibitory effect on SOCE and an antiproliferative effect on PASMC derived from endarterectomized tissues of CTEPH patients. Cells were isolated from endarterectomized tissues obtained from patients undergoing pulmonary thromboendarterectomy (PTE). Immunohistochemical analysis indicated high deposition of platelet-derived growth factor (PDGF) in tissue sections from PTE tissues and increased PDGF receptor expression. PDGF transiently phosphorylated Akt, mammalian target of rapamycin (mTOR), and p70S6 kinase in CTEPH cells from CTEPH patients. Acute treatment (30 min) with rapamycin (10 nM) slightly increased cyclopiazonic acid (10 microM)-induced Ca(2+) mobilization and significantly reduced SOCE. Chronic treatment (24 h) with rapamycin reduced Ca(2+) mobilization and markedly inhibited SOCE. The inhibitory effects of rapamycin on SOCE were less prominent in control cells. Rapamycin also significantly reduced PDGF-stimulated cell proliferation. In conclusion, the data from this study indicate the importance of the mTOR pathway in the development of pulmonary vascular remodeling in CTEPH and suggest a potential therapeutic benefit of rapamycin (or inhibition of mTOR) in these patients.

Cellular and molecular basis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is caused by functional and structural changes in the pulmonary vasculature, leading to increased pulmonary vascular resistance. The process of pulmonary vascular remodeling is accompanied by endothelial dysfunction, activation of fibroblasts and smooth muscle cells, crosstalk between cells within the vascular wall, and recruitment of circulating progenitor cells. Recent findings have reestablished the role of chronic vasoconstriction in the remodeling process. Although the pathology of PAH in the lung is well known, this article is concerned with the cellular and molecular processes involved. In particular, we focus on the role of the Rho family guanosine triphosphatases in endothelial function and vasoconstriction. The crosstalk between endothelium and vascular smooth muscle is explored in the context of mutations in the bone morphogenetic protein type II receptor, alterations in angiopoietin-1/TIE2 signaling, and the serotonin pathway. We also review the role of voltage-gated K(+) channels and transient receptor potential channels in the regulation of cytosolic [Ca(2+)] and [K(+)], vasoconstriction, proliferation, and cell survival. We highlight the importance of the extracellular matrix as an active regulator of cell behavior and phenotype and evaluate the contribution of the glycoprotein tenascin-c as a key mediator of smooth muscle cell growth and survival. Finally, we discuss the origins of a cell type critical to the process of pulmonary vascular remodeling, the myofibroblast, and review the evidence supporting a contribution for the involvement of endothelial-mesenchymal transition and recruitment of circulating mesenchymal progenitor cells.

A functional single-nucleotide polymorphism in the TRPC6 gene promoter associated with idiopathic pulmonary arterial hypertension

BACKGROUND

Excessive proliferation of pulmonary artery smooth muscle cells (PASMCs) plays an important role in the development of idiopathic pulmonary arterial hypertension (IPAH), whereas a rise in cytosolic Ca2+ concentration triggers PASMC contraction and stimulates PASMC proliferation. Recently, we demonstrated that upregulation of the TRPC6 channel contributes to proliferation of PASMCs isolated from IPAH patients. This study sought to identify single-nucleotide polymorphisms (SNPs) in the TRPC6 gene promoter that are associated with IPAH and have functional significance in regulating TRPC6 activity in PASMCs.

METHODS AND RESULTS

Genomic DNA was isolated from blood samples of 237 normal subjects and 268 IPAH patients. Three biallelic SNPs, -361 (A/T), -254(C/G), and -218 (C/T), were identified in the 2000-bp sequence upstream of the transcriptional start site of TRPC6. Although the allele frequencies of the -361 and -218 SNPs were not different between the groups, the allele frequency of the -254(C-->G) SNP in IPAH patients (12%) was significantly higher than in normal subjects (6%; P<0.01). Genotype data showed that the percentage of -254G/G homozygotes in IPAH patients was 2.85 times that of normal subjects. Moreover, the -254(C-->G) SNP creates a binding sequence for nuclear factor-kappaB. Functional analyses revealed that the -254(C-->G) SNP enhanced nuclear factor-kappaB-mediated promoter activity and stimulated TRPC6 expression in PASMCs. Inhibition of nuclear factor-kappaB activity attenuated TRPC6 expression and decreased agonist-activated Ca2+ influx in PASMCs of IPAH patients harboring the -254G allele.

CONCLUSIONS

These results suggest that the -254(C-->G) SNP may predispose individuals to an increased risk of IPAH by linking abnormal TRPC6 transcription to nuclear factor-kappaB, an inflammatory transcription factor.

Identification of putative endothelial progenitor cells (CD34+CD133+Flk-1+) in endarterectomized tissue of patients with chronic thromboembolic pulmonary hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is characterized by a fibrotic thrombus persisting and obliterating the lumen of pulmonary arteries; its pathogenesis remains poorly defined. This study investigates a potential contribution for progenitor cell types in the development of vascular obliteration and remodeling in CTEPH patients. Endarterectomized tissue from patients undergoing pulmonary thromboendarterectomy was collected and examined for the structure and cellular composition. Our data show an organized fibrin network structure in unresolved thromboemboli and intimal remodeling in vascular wall tissues, characterized by smooth muscle alpha-actin (SM-alphaA)-positive cell proliferation in proximal regions (adjacent to thromboemboli) and neoangiogenesis/recanalization in distal regions (downstream from thromboemboli). Cells that are positively stained with CD34 and fetal liver kinase-1 (Flk-1) (CD34(+)Flk-1(+)) were identified in both the proximal and distal vascular tissues; a subpopulation of CD34(+)Flk-1(+)CD133(+) cells were further identified by immunostaining. Triple-positive cells are indicative of a population of putative endothelial progenitor cells or potential colony-forming units of endothelial cells. In addition, inflammatory cells (CD45(+)) and collagen-secreting cells (procollagen-1(+)) were detected in the proximal vascular wall. Some of the CD34(+) cells in CTEPH cells isolated from proximal regions were also positive for SM-alphaA. Our data indicate that putative progenitor cell types are present in the neointima of occluded vessels of CTEPH patients. It is possible that the microenvironment provided by thromboemboli may promote these putative progenitor cells to differentiate and enhance intimal remodeling.

Technique and outcomes of pulmonary endarterectomy surgery

Pulmonary endarterectomy (PTE) is the definitive treatment for chronic pulmonary hypertension resulting from thromboembolic disease. Chronic thromboembolic pulmonary hypertension is estimated to occur in approximately 4% of patients who have developed an acute pulmonary embolism, though the true prevalence is suspected to be much higher. Chronic thromboembolic pulmonary hypertension is characterized by intraluminal thrombus organization, fibrous stenosis, and vascular remodeling of pulmonary vessels. PTE is an operation considered to be a curative for this affliction and is therefore superior to transplantation. The procedure involves the removal of organized and incorporated fibrous obstructive tissue from the pulmonary arterial tree and is a true endarterectomy, not an embolectomy. Surgical outcomes with respect to functional status, quality of life, hemodynamics, right ventricular function, and gas exchange are favorable. Preoperative hemodynamic severity and site of anatomical obstruction are key predictors of postoperative outcome. This article focuses on the surgical techniques and outcomes of patients undergoing PTE for chronic thromboembolic pulmonary hypertension and discusses the currently known factors that affect survival after this operation.

Endothelial expression of bone morphogenetic protein receptor type 1a is required for atrioventricular valve formation

BACKGROUND

Atrioventricular canal defects account for 4% of all congenital heart anomalies. They arise from failure of endocardial cushion formation, a process dependent on transition of endothelial cells into clustered mesenchymal cells in the mid-atrioventricular septum. To date, the genetic signals necessary for atrioventricular canal defects are poorly understood. We hypothesized that bone morphogenetic protein signaling in cardiac endothelial cells may be crucial to this process.

METHODS

To study the role of bone morphogenetic protein receptors (Bmpr) in the developing heart, we created knockout mice with inactivation of Bmpr1a selectively in endocardium. Two strains of null mice were created: one with constitutive endothelial-specific knockout of Bmpr1a and one with time-inducible, endothelial-specific knockout of Bmpr1a. Embryos and animals were analyzed by microscopy, RNA in situ hybridization, and microangiography.

RESULTS

Animals with null mutation of Bmpr1a in endothelium were embryonic lethal at E11.5 to 12.0 and demonstrated absence of endocardial cushion formation. Embryos failed to form atrioventricular valves and adjacent septa. Endocardial knockout of Bmpr1a did not affect development of the outflow tract or aortic arches. Using time-inducible, cell-specific knockout mice, we show that Bmpr1a has two functions in the developing atrioventricular canal: to induce endocardial endothelial-mesenchymal transition, and to pattern the septal mesenchyme into endocardial cushions. We demonstrate that these processes are temporally linked to expression of the transcription factors Id1 and Id3.

CONCLUSIONS

Endocardial cushion formation is dependent on cell-specific expression of Bmpr1a. Our results suggest that Bmpr1a-mediated signaling is a crucial pathway involved in pathogenesis of atrioventricular septal and valve malformations, which are among the most common congenital heart defects in humans.