Codependence of Bone Morphogenetic Protein Receptor 2 and Transforming Growth Factor-β in Elastic Fiber Assembly and Its Perturbation in Pulmonary Arterial Hypertension

Bioengineered vascular grafts with a pathogenic TGFBR1 variant model aneurysm formation in vivo and reveal underlying collagen defects

Thoracic aortic aneurysm (TAA) is a life-threatening vascular disease frequently associated with underlying genetic causes. An inadequate understanding of human TAA pathogenesis highlights the need for better disease models. Here, we established a functional human TAA model in an animal host by combining human induced pluripotent stem cells (hiPSCs), bioengineered vascular grafts (BVGs), and gene editing. We generated BVGs from isogenic control hiPSC-derived vascular smooth muscle cells (SMCs) and mutant SMCs gene-edited to carry a Loeys-Dietz syndrome (LDS)-associated pathogenic variant (TGFBR1A230T). We also generated hiPSC-derived BVGs using cells from a patient with LDS (PatientA230T/+) and using genetically corrected cells (Patient+/+). Control and experimental BVGs were then implanted into the common carotid arteries of nude rats. The TGFBR1A230T variant led to impaired mechanical properties of BVGs, resulting in lower burst pressure and suture retention strength. BVGs carrying the variant dilated over time in vivo, resembling human TAA formation. Spatial transcriptomics profiling revealed defective expression of extracellular matrix (ECM) formation genes in PatientA230T/+ BVGs compared with Patient+/+ BVGs. Histological analysis and protein assays validated quantitative and qualitative ECM defects in PatientA230T/+ BVGs and patient tissue, including decreased collagen hydroxylation. SMC organization was also impaired in PatientA230T/+ BVGs as confirmed by vascular contraction testing. Silencing of collagen-modifying enzymes with small interfering RNAs reduced collagen proline hydroxylation in SMC-derived tissue constructs. These studies demonstrated the utility of BVGs to model human TAA formation in an animal host and highlighted the role of reduced collagen modifying enzyme activity in human TAA formation.

A computational growth and remodeling framework for adaptive and maladaptive pulmonary arterial hemodynamics

Hemodynamic loading is known to contribute to the development and progression of pulmonary arterial hypertension (PAH). This loading drives changes in mechanobiological stimuli that affect cellular phenotypes and lead to pulmonary vascular remodeling. Computational models have been used to simulate mechanobiological metrics of interest, such as wall shear stress, at single time points for PAH patients. However, there is a need for new approaches that simulate disease evolution to allow for prediction of long-term outcomes. In this work, we develop a framework that models the pulmonary arterial tree through adaptive and maladaptive responses to mechanical and biological perturbations. We coupled a constrained mixture theory-based growth and remodeling framework for the vessel wall with a morphometric tree representation of the pulmonary arterial vasculature. We show that non-uniform mechanical behavior is important to establish the homeostatic state of the pulmonary arterial tree, and that hemodynamic feedback is essential for simulating disease time courses. We also employed a series of maladaptive constitutive models, such as smooth muscle hyperproliferation and stiffening, to identify critical contributors to development of PAH phenotypes. Together, these simulations demonstrate an important step toward predicting changes in metrics of clinical interest for PAH patients and simulating potential treatment approaches.

Elastin stabilization prevents impaired biomechanics in human pulmonary arteries and pulmonary hypertension in rats with left heart disease

Pulmonary hypertension worsens outcome in left heart disease. Stiffening of the pulmonary artery may drive this pathology by increasing right ventricular dysfunction and lung vascular remodeling. Here we show increased stiffness of pulmonary arteries from patients with left heart disease that correlates with impaired pulmonary hemodynamics. Extracellular matrix remodeling in the pulmonary arterial wall, manifested by dysregulated genes implicated in elastin degradation, precedes the onset of pulmonary hypertension. The resulting degradation of elastic fibers is paralleled by an accumulation of fibrillar collagens. Pentagalloyl glucose preserves arterial elastic fibers from elastolysis, reduces inflammation and collagen accumulation, improves pulmonary artery biomechanics, and normalizes right ventricular and pulmonary hemodynamics in a rat model of pulmonary hypertension due to left heart disease. Thus, targeting extracellular matrix remodeling may present a therapeutic approach for pulmonary hypertension due to left heart disease.

BMPR2 Mutation and Metabolic Reprogramming in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension forms the first and most severe of the 5 categories of pulmonary hypertension. Disease pathogenesis is driven by progressive remodeling of peripheral pulmonary arteries, caused by the excessive proliferation of vascular wall cells, including endothelial cells, smooth muscle cells and fibroblasts, and perivascular inflammation. Compelling evidence from animal models suggests endothelial cell dysfunction is a key initial trigger of pulmonary vascular remodeling, which is characterised by hyperproliferation and early apoptosis followed by enrichment of apoptosis-resistant populations. Dysfunctional pulmonary arterial endothelial cells lose their ability to produce vasodilatory mediators, together leading to augmented pulmonary arterial smooth muscle cell responses, increased pulmonary vascular pressures and right ventricular afterload, and progressive right ventricular hypertrophy and heart failure. It is recognized that a range of abnormal cellular molecular signatures underpin the pathophysiology of pulmonary arterial hypertension and are enhanced by loss-of-function mutations in the BMPR2 gene, the most common genetic cause of pulmonary arterial hypertension and associated with worse disease prognosis. Widespread metabolic abnormalities are observed in the heart, pulmonary vasculature, and systemic tissues, and may underpin heterogeneity in responsivity to treatment. Metabolic abnormalities include hyperglycolytic reprogramming, mitochondrial dysfunction, aberrant polyamine and sphingosine metabolism, reduced insulin sensitivity, and defective iron handling. This review critically discusses published mechanisms linking metabolic abnormalities with dysfunctional BMPR2 (bone morphogenetic protein receptor 2) signaling; hypothesized mechanistic links requiring further validation; and their relevance to pulmonary arterial hypertension pathogenesis and the development of potential therapeutic strategies.

Elastic Fibers and F-Box and WD-40 Domain-Containing Protein 2 in Bovine Periosteum and Blood Vessels

Elastic fibers form vessel walls, and elastic fiber calcification causes serious vascular diseases. Elastin is a well-known elastic fiber component; however, the insoluble nature of elastic fibers renders elastic fiber component analysis difficult. A previous study investigated F-box and WD-40 domain-containing protein 2 (FBXW2) in the cambium layer of bovine periosteum and hypothesized that fiber structures of FBXW2 are coated with osteocalcin during explant culture. Here, FBXW2 was expressed around some endothelial cells but not in all microvessels of the bovine periosteum. The author hypothesized that FBXW2 is expressed only in blood vessels with elastic fibers. Immunostaining and Elastica van Gieson staining indicated that FBXW2 was expressed in the same regions as elastic fibers and elastin in the cambium layer of the periosteum. Alpha-smooth muscle actin (αSMA) was expressed in microvessels and periosteum-derived cells. Immunostaining and observation of microvessels with serial sections revealed that osteocalcin was not expressed around blood vessels at 6 and 7 weeks. However, blood vessels and periosteum connoted elastic fibers, FBXW2, and αSMA. These findings are expected to clarify the processes involved in the calcification of elastic fibers in blood vessels.

Single-cell transcriptomics reveals skewed cellular communication and phenotypic shift in pulmonary artery remodeling

A central feature of progressive vascular remodeling is altered smooth muscle cell (SMC) homeostasis; however, the understanding of how different cell populations contribute to this process is limited. Here, we utilized single-cell RNA sequencing to provide insight into cellular composition changes within isolated pulmonary arteries (PAs) from pulmonary arterial hypertension and donor lungs. Our results revealed that remodeling skewed the balanced communication network between immune and structural cells, in particular SMCs. Comparative analysis with murine PAs showed that human PAs harbored heterogeneous SMC populations with an abundant intermediary cluster displaying a gradient transition between SMCs and adventitial fibroblasts. Transcriptionally distinct SMC populations were enriched in specific biological processes and could be differentiated into 4 major clusters: oxygen sensing (enriched in pericytes), contractile, synthetic, and fibroblast-like. End-stage remodeling was associated with phenotypic shift of preexisting SMC populations and accumulation of synthetic SMCs in neointima. Distinctly regulated genes in clusters built nonredundant regulatory hubs encompassing stress response and differentiation regulators. The current study provides a blueprint of cellular and molecular changes on a single-cell level that are defining the pathological vascular remodeling process.

Compromised Cardiopulmonary Function in Fibulin-5 Deficient Mice

Competent elastic fibers are critical to the function of the lung and right circulation. Murine models of elastopathies can aid in understanding the functional roles of the elastin and elastin-associated glycoproteins that constitute elastic fibers. Here, we quantify together lung and pulmonary arterial structure, function, and mechanics with right heart function in a mouse model deficient in the elastin-associated glycoprotein fibulin-5. Differences emerged as a function of genotype, sex, and arterial region. Specifically, functional studies revealed increased lung compliance in fibulin-5 deficiency consistent with a histologically observed increased alveolar disruption. Biaxial mechanical tests revealed that the primary branch pulmonary arteries exhibit decreased elastic energy storage capacity and wall stress despite only modest differences in circumferential and axial material stiffness in the fibulin-5 deficient mice. Histological quantifications confirm a lower elastic fiber content in the fibulin-5 deficient pulmonary arteries, with fragmented elastic laminae in the outer part of the wall - likely the reason for reduced energy storage. Ultrasound measurements confirm sex differences in compromised right ventricular function in the fibulin-5 deficient mice. These results reveal compromised right heart function, but opposite effects of elastic fiber dysfunction on the lung parenchyma (significantly increased compliance) and pulmonary arteries (trend toward decreased distensibility), and call for further probing of ventilation-perfusion relationships in pulmonary pathologies. Amongst many other models, fibulin-5 deficient mice can contribute to our understanding of the complex roles of elastin in pulmonary health and disease.

Development of vascular disease models to explore disease causation and pathomechanisms of rare vascular diseases

As the field of medicine is striving forward heralded by a new era of next-generation sequencing (NGS) and integrated technologies such as bioprinting and biological material development, the utility of rare monogenetic vascular disease modeling in this landscape is starting to emerge. With their genetic simplicity and broader applicability, these patient-specific models are at the forefront of modern personalized medicine. As a collective, rare diseases are a significant burden on global healthcare systems, and rare vascular diseases make up a significant proportion of this. High costs are due to a lengthy diagnostic process, affecting all ages from infants to adults, as well as the severity and chronic nature of the disease. Their complex nature requires sophisticated disease models and integrated approaches involving multidisciplinary teams. Here, we review these emerging vascular disease models, how they contribute to our understanding of the pathomechanisms in rare vascular diseases and provide useful platforms for therapeutic discovery.

The Mechanobiology of Vascular Remodeling in the Aging Lung

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

Lumican deficiency promotes pulmonary arterial remodeling

Pulmonary arterial hypertension (PAH) is caused by progressive extracellular matrix disorganization and increased pulmonary vascular cell proliferation. Lumican is a member of the small leucine-rich proteoglycan family that controls cell proliferation, and is a potential endogenous modulator of TGF-β signaling pathway. We show that the decreased lumican protein levels in pulmonary arterial smooth muscle cells (PASMCs) is related to the vascular remodeling and stiffening observed in PAH. The role of lumican in PASMC accumulation and activation in response to pulmonary vascular remodeling remains unclear and we hypothesized that the loss of lumican in PASMCs promotes the development of PAH. Our aim was to establish that lumican plays a pivotal role in modulating pathological vascular remodeling in humans using a rat model of monocrotaline-induced PAH and chronically hypoxic mice. We found that mice with a homozygous deletion of lumican (Lum-/-) showed severe pulmonary arterial remodeling and right ventricular hypertrophy in response to hypoxia, and these effects in mice with chronic hypoxia-induced pulmonary hypertension were successfully treated by the administration of a lumican C-terminal peptide (LumC13C-A, lumikine). We identified a mechanistic link by which lumican signaling prevents the activation of phosphorylated AKT, resulting in the suppression of PASMC proliferation. Lumican deficiency promotes pulmonary arterial remodeling. Administration of lumikine reverses the PAH pathogenesis caused by hypoxia-induced experimental PAH. Lumican is an antiproliferative target that functions to suppress pAKT activation during pathogenesis.

Severe Pulmonary Arterial Hypertension Is Characterized by Increased Neutrophil Elastase and Relative Elafin Deficiency

BACKGROUND

Preclinical evidence implicates neutrophil elastase (NE) in pulmonary arterial hypertension (PAH) pathogenesis, and the NE inhibitor elafin is under early therapeutic investigation.

RESEARCH QUESTION

Are circulating NE and elafin levels abnormal in PAH and are they associated with clinical severity?

STUDY DESIGN AND METHODS

In an observational Stanford University PAH cohort (n = 249), plasma NE and elafin levels were measured in comparison with those of healthy control participants (n = 106). NE and elafin measurements were then related to PAH clinical features and relevant ancillary biomarkers. Cox regression models were fitted with cubic spline functions to associate NE and elafin levels with survival. To validate prognostic relationships, we analyzed two United Kingdom cohorts (n = 75 and n = 357). Mixed-effects models evaluated NE and elafin changes during disease progression. Finally, we studied effects of NE-elafin balance on pulmonary artery endothelial cells (PAECs) from patients with PAH.

RESULTS

Relative to control participants, patients with PAH were found to have increased NE levels (205.1 ng/mL [interquartile range (IQR), 123.6-387.3 ng/mL] vs 97.6 ng/mL [IQR, 74.4-126.6 ng/mL]; P < .0001) and decreased elafin levels (32.0 ng/mL [IQR, 15.3-59.1 ng/mL] vs 45.5 ng/mL [IQR, 28.1-92.8 ng/mL]; P < .0001) independent of PAH subtype, illness duration, and therapies. Higher NE levels were associated with worse symptom severity, shorter 6-min walk distance, higher N-terminal pro-type brain natriuretic peptide levels, greater right ventricular dysfunction, worse hemodynamics, increased circulating neutrophil levels, elevated cytokine levels, and lower blood BMPR2 expression. In Stanford patients, NE levels of > 168.5 ng/mL portended increased mortality risk after adjustment for known clinical predictors (hazard ratio [HR], 2.52; CI, 1.36-4.65, P = .003) or prognostic cytokines (HR, 2.63; CI, 1.42-4.87; P = .001), and the NE level added incremental value to established PAH risk scores. Similar prognostic thresholds were identified in validation cohorts. Longitudinal NE changes tracked with clinical trends and outcomes. PAH PAECs exhibited increased apoptosis and attenuated angiogenesis when exposed to NE at the level observed in patients' blood. Elafin rescued PAEC homeostasis, yet the required dose exceeded levels found in patients.

INTERPRETATION

Blood levels of NE are increased while elafin levels are deficient across PAH subtypes. Higher NE levels are associated with worse clinical disease severity and outcomes, and this target-specific biomarker could facilitate therapeutic development of elafin.

Whole exome sequencing in patients with Williams-Beuren syndrome followed by disease modeling in mice points to four novel pathways that may modify stenosis risk

Supravalvular aortic stenosis (SVAS) is a narrowing of the aorta caused by elastin (ELN) haploinsufficiency. SVAS severity varies among patients with Williams-Beuren syndrome (WBS), a rare disorder that removes one copy of ELN and 25-27 other genes. Twenty percent of children with WBS require one or more invasive and often risky procedures to correct the defect while 30% have no appreciable stenosis, despite sharing the same basic genetic lesion. There is no known medical therapy. Consequently, identifying genes that modify SVAS offers the potential for novel modifier-based therapeutics. To improve statistical power in our rare-disease cohort (N = 104 exomes), we utilized extreme-phenotype cohorting, functional variant filtration and pathway-based analysis. Gene set enrichment analysis of exome-wide association data identified increased adaptive immune system variant burden among genes associated with SVAS severity. Additional enrichment, using only potentially pathogenic variants known to differ in frequency between the extreme phenotype subsets, identified significant association of SVAS severity with not only immune pathway genes, but also genes involved with the extracellular matrix, G protein-coupled receptor signaling and lipid metabolism using both SKAT-O and RQTest. Complementary studies in Eln+/-; Rag1-/- mice, which lack a functional adaptive immune system, showed improvement in cardiovascular features of ELN insufficiency. Similarly, studies in mixed background Eln+/- mice confirmed that variations in genes that increase elastic fiber deposition also had positive impact on aortic caliber. By using tools to improve statistical power in combination with orthogonal analyses in mice, we detected four main pathways that contribute to SVAS risk.

Reduced neutrophil elastase inhibitor elafin and elevated transforming growth factor-β1 are linked to inflammatory response in sputum of cystic fibrosis patients with Pseudomonas aeruginosa

Research question

Pulmonary disease progression in patients with cystic fibrosis (CF) is characterised by inflammation and fibrosis and aggravated by Pseudomonas aeruginosa (Pa). We investigated the impact of Pa specifically on: 1) protease/antiprotease balance; 2) inflammation; and 3) the link of both parameters to clinical parameters of CF patients.

Methods

Transforming growth factor-β₁ (TGF-β₁), interleukin (IL)-1β, IL-8, neutrophil elastase (NE) and elastase inhibitor elafin were measured (ELISA assays), and gene expression of the NF-κB pathway was assessed (reverse transcriptase PCR) in the sputum of 60 CF patients with a minimum age of 5 years. Spirometry was assessed according to American Thoracic Society guidelines.

Results

Our results demonstrated the following: 1) NE was markedly increased in Pa-positive sputum, whereas elafin was significantly decreased; 2) increased IL-1β/IL-8 levels were associated with both Pa infection and reduced forced expiratory volume in 1 s, and sputum TGF-β₁ was elevated in Pa-infected CF patients and linked to an impaired lung function; and 3) gene expression of NF-κB signalling components was increased in sputum of Pa-infected patients, and these findings were positively correlated with IL-8.

Conclusion

Our study links Pa infection to an imbalance of NE and NE inhibitor elafin and increased inflammatory mediators. Moreover, our data demonstrate an association between high TGF-β₁ sputum levels and a progress in chronic lung inflammation and pulmonary fibrosis in CF. Controlling the excessive airway inflammation by inhibition of NE and TGF-β₁ might be promising therapeutic strategies in future CF therapy and a possible complement to cystic fibrosis transmembrane conductance regulator (CFTR) modulators.

Significance of BMPR2 mutations in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a debilitating disease that results from progressive remodeling and inflammation of pulmonary arteries. PAH develops gradually, is difficult to diagnose, and has a high mortality rate. Although mutation in the bone morphogenetic protein receptor 2 (BMPR2) gene has been identified as the main genetic cause of PAH, the underlying pathways involving the pathophysiology of PAH are complex and still not fully understood. Endothelial dysfunction has been observed in PAH development that results in a multitude of disturbances in the cellular processes in pulmonary vessels. Changes in the pulmonary vasculature caused by the disruption of BMPR2 signaling are observed in three main vascular components; endothelial cells, smooth muscle cells, and fibroblasts. BMPR2 also has a prominent role in maintenance of the immune system. The disruption of BMPR2 signaling pathway causes an increased degree of inflammation and decreases the ability of the immune system to resolve it. Inflammatory processes and changes in pulmonary vasculature interact with one another, resulting in the progression of chronic PAH. In this review, we highlight the various components of vascular remodeling and immune response that are caused by disruption of BMPR2 signaling, including the clinical evidence and the prospects of these components as a potential target for PAH therapy. Indeed, development of drugs to target the pathogenic pathways involved in PAH may complement existing treatment regimens and improve patient prognosis.

Substrate Stiffness and Stretch Regulate Profibrotic Mechanosignaling in Pulmonary Arterial Adventitial Fibroblasts

Pulmonary arterial adventitial fibroblasts (PAAFs) are important regulators of fibrotic vascular remodeling during the progression of pulmonary arterial hypertension (PAH), a disease that currently has no effective anti-fibrotic treatments. We conducted in-vitro experiments in PAAFs cultured on hydrogels attached to custom-made equibiaxial stretchers at 10% stretch and substrate stiffnesses representing the mechanical conditions of mild and severe stages of PAH. The expression of collagens α(1)I and α(1)III and elastin messenger RNAs (Col1a1, Col3a1, Eln) were upregulated by increased stretch and substrate stiffness, while lysyl oxidase-like 1 and α-smooth muscle actin messenger RNAs (Loxl1, Acta2) were only significantly upregulated when the cells were grown on matrices with an elevated stiffness representative of mild PAH but not on a stiffness representative of severe PAH. Fibronectin messenger RNA (Fn1) levels were significantly induced by increased substrate stiffness and transiently upregulated by stretch at 4 h, but was not significantly altered by stretch at 24 h. We modified our published computational network model of the signaling pathways that regulate profibrotic gene expression in PAAFs to allow for differential regulation of mechanically-sensitive nodes by stretch and stiffness. When the model was modified so that stiffness activated integrin β₃, the Macrophage Stimulating 1 or 2 (MST1\2) kinases, angiotensin II (Ang II), transforming growth factor-β (TGF-β), and syndecan-4, and stretch-regulated integrin β₃, MST1\2, Ang II, and the transient receptor potential (TRP) channel, the model correctly predicted the upregulation of all six genes by increased stiffness and the observed responses to stretch in five out of six genes, although it could not replicate the non-monotonic effects of stiffness on Loxl1 and Acta2 expression. Blocking Ang II Receptor Type 1 (AT₁R) with losartan in-vitro uncovered an interaction between the effects of stretch and stiffness and angiotensin-independent activation of Fn1 expression by stretch in PAAFs grown on 3-kPa matrices. This novel combination of in-vitro and in-silico models of PAAF profibrotic cell signaling in response to altered mechanical conditions may help identify regulators of vascular adventitial remodeling due to changes in stretch and matrix stiffness that occur during the progression of PAH in-vivo.

Xenogeneic-free generation of vascular smooth muscle cells from human induced pluripotent stem cells for vascular tissue engineering

Development of mechanically advanced tissue-engineered vascular grafts (TEVGs) from human induced pluripotent stem cell (hiPSC)-derived vascular smooth muscle cells (hiPSC-VSMCs) offers an innovative approach to replace or bypass diseased blood vessels. To move current hiPSC-TEVGs toward clinical application, it is essential to obtain hiPSC-VSMC-derived tissues under xenogeneic-free conditions, meaning without the use of any animal-derived reagents. Many approaches in VSMC differentiation of hiPSCs have been reported, although a xenogeneic-free method for generating hiPSC-VSMCs suitable for vascular tissue engineering has yet to be established. Based on our previously established standard method of xenogeneic VSMC differentiation, we have replaced all animal-derived reagents with functional counterparts of human origin and successfully derived functional xenogeneic-free hiPSC-VSMCs (XF-hiPSC-VSMCs). Next, our group developed tissue rings via cellular self-assembly from XF-hiPSC-VSMCs, which exhibited comparable mechanical strength to those developed from xenogeneic hiPSC-VSMCs. Moreover, by seeding XF-hiPSC-VSMCs onto biodegradable polyglycolic acid (PGA) scaffolds, we generated engineered vascular tissues presenting effective collagen deposition which were suitable for implantation into an immunodeficient mice model. In conclusion, our xenogeneic-free conditions for generating hiPSC-VSMCs produce cells with the comparable capacity for vascular tissue engineering as standard xenogeneic protocols, thereby moving the hiPSC-TEVG technology one step closer to safe and efficacious clinical translation.

Phenotypic diversity and metabolic specialization of renal endothelial cells

Complex multicellular life in mammals relies on functional cooperation of different organs for the survival of the whole organism. The kidneys play a critical part in this process through the maintenance of fluid volume and composition homeostasis, which enables other organs to fulfil their tasks. The renal endothelium exhibits phenotypic and molecular traits that distinguish it from endothelia of other organs. Moreover, the adult kidney vasculature comprises diverse populations of mostly quiescent, but not metabolically inactive, endothelial cells (ECs) that reside within the kidney glomeruli, cortex and medulla. Each of these populations supports specific functions, for example, in the filtration of blood plasma, the reabsorption and secretion of water and solutes, and the concentration of urine. Transcriptional profiling of these diverse EC populations suggests they have adapted to local microenvironmental conditions (hypoxia, shear stress, hyperosmolarity), enabling them to support kidney functions. Exposure of ECs to microenvironment-derived angiogenic factors affects their metabolism, and sustains kidney development and homeostasis, whereas EC-derived angiocrine factors preserve distinct microenvironment niches. In the context of kidney disease, renal ECs show alteration in their metabolism and phenotype in response to pathological changes in the local microenvironment, further promoting kidney dysfunction. Understanding the diversity and specialization of kidney ECs could provide new avenues for the treatment of kidney diseases and kidney regeneration.

Effects of BMP-2 compound with fibrin on osteoporotic vertebral fracture healing in rats

OBJECTIVES

To investigate the effects of bone morphogenetic protein-2 (BMP-2) compound with fibrin on osteoporotic vertebral fracture healing in rats.

METHODS

For the present study 160 Specific-Pathogen Free 32-week-old female Sprague-Dawley rats were used. 120 rats were randomly divided in three groups (experimental, model and sham operation group- n=40 per group) and were ovariectomized to establish the osteoporosis model. 40 rats served as a control group without treatment. The expression of BMP-2 in the fracture zone at the 4th, 6th, 8th, and 12th weeks was detected by qRT-PCR. The expression of BALP and CTX-I in serum at the 12th week was detected by Elisa.

RESULTS

At week 8, the morphology of the sham operation group was the same and the fracture healing occurred more slowly than in the other groups. At week 12, the expression of BMP-2 in the model group was significantly higher than that in the other three groups (p<0.05). At week 12, the maximum load, maximum strain, and elastic modulus of model group were significantly lower than those of the other three groups.

CONCLUSIONS

BMP-2 compound with fibrin can enhance the timing and quality of bone fracture healing in rats.

Mendelian randomization and experimental IUGR reveal the adverse effect of low birth weight on lung structure and function

Intrauterine growth restriction (IUGR) and low birth weigth (LBW) are risk factors for neonatal chronic lung disease. However, maternal and fetal genetic factors and the molecular mechanisms remain unclear. We investigated the relationship between LBW and lung function with Mendelian randomisation analyses and studied angiogenesis in a low protein diet rat model of IUGR. Our data indicate a possible association between LBW and reduced FEV1 (p = 5.69E−18, MR-PRESSO) and FVC (6.02E-22, MR-PRESSO). Complimentary, we demonstrated two-phased perinatal programming after IUGR. The intrauterine phase (embryonic day 21) is earmarked by a reduction of endothelial cell markers (e.g. CD31) as well as mRNA expression of angiogenic factors (e.g., Vegfa, Flt1, Klf4). Protein analysis identified an activation of anti-angiogenic mTOR effectors. In the postnatal phase, lung capillaries (< 20 µm) were significantly reduced, expression of CD31 and VE-Cadherin were unaffected, whereas SMAD1/5/8 signaling and Klf4 protein were increased (p < 0.01). Moreover, elevated proteolytic activity of MMP2 and MMP9 was linked to a 50% reduction of lung elastic fibres. In conclusion, we show a possible link of LBW in humans and reduced lung function in adulthood. Experimental IUGR identifies an intrauterine phase with inhibition of angiogenic signaling, and a postnatal phase with proteolytic activity and reduced elastic fibres.

Human iPS Cell-derived Tissue Engineered Vascular Graft: Recent Advances and Future Directions

Tissue engineered vascular grafts (TEVGs) generated from human primary cells represent a promising vascular interventional therapy. However, generation and application of these TEVGs may be significantly hindered by the limited accessibility, finite expandability, donor-donor functional variation and immune-incompatibility of primary seed cells from donors. Alternatively, human induced pluripotent stem cells (hiPSCs) offer an infinite source to obtain functional vascular cells in large quantity and comparable quality for TEVG construction. To date, TEVGs (hiPSC-TEVGs) with significant mechanical strength and implantability have been generated using hiPSC-derived seed cells. Despite being in its incipient stage, this emerging field of hiPSC-TEVG research has achieved significant progress and presented promising future potential. Meanwhile, a series of challenges pertaining hiPSC differentiation, vascular tissue engineering technologies and future production and application await to be addressed. Herein, we have composed this review to introduce progress in TEVG generation using hiPSCs, summarize the current major challenges, and encapsulate the future directions of research on hiPSC-based TEVGs. Graphical abstract.

Endothelin-1 induces lysyl oxidase expression in pulmonary artery smooth muscle cells

The increase in thickening of the arterial wall of pulmonary arterial hypertension (PAH) includes cellular proliferation as well as matrix deposition and interrupted internal elastic lamina (IEL) consisting of a thick homogeneous sheet of elastin. Little is, although, known about the detail of IEL formation in PAH. Endothelin-1 is overexpressed in pulmonary arterioles of PAH. We aimed to examine the expression of genes contributing to IEL formation in pulmonary artery smooth muscle cells (PASMCs) especially focused on lysyl oxidase (LOx), an exreacellular matrix enzyme that catalyzes the cross-linking of collagens or elastin. We quantified mRNA expressions of genes contributing to IEL formation including LOx in PASMCs using real-time quantitative polymerase chain reaction. We stimulated human PASMCs with endothelin-1 with prostacyclin or trapidil. Endothelin-1 significantly increased LOx expression. Prostacyclin and trapidil restored endothelin-1-induced LOx expression to the basal level. Endothelin-1 increased LOx expression strongly in PASMCs from PAH patients compared to those from controls. Trapidil reduced LOx expression only in PASMCs from PAH patients. Overexpressed endothelin-1 in PAH patients can increase expression of LOx and agitate cross-linking of elastin and collagen, resulting in ectopic deposition of these in the vascular media.

Remodeling Matrix Synthesis in a Rat Model of Aortocaval Fistula and the Cyclic Stretch: Impaction in Pulmonary Arterial Hypertension-Congenital Heart Disease

Pulmonary arterial hypertension-congenital heart disease (PAH-CHD) is characterized by systemic to pulmonary arterial shunts and sensitively responds to volume overload and stretch of the vascular wall leading to pulmonary vascular remodeling. We hypothesized that the responses of pulmonary artery smooth muscle cells (PASMCs) to mechanical stress-associated volume overload may promote vascular remodeling in PAH-CHD. Here, we show that significantly increased collagen was in the PA adventitial layer by trichrome staining in PAH-CHD patients and an aortocaval fistula (ACF) rat model in which chronic vascular volume overload induced-PAH. We assessed the gene expression profiles of SMC markers, extracellular matrix, and collagen in isolated SMCs from pulmonary and thoracic vessels with cyclic stretch-triggered responses by real-time PCR analysis. The data corresponded to collagen deposition, which modulated pulmonary vascular remodeling in clinical and experimental PAH-ACF cases as well as in cyclic stretch-triggered SMCs in an in vitro model. We observe that collagen I A2 (COLIA2) is expressed in the control rat, but collagen I A1 (COLIA1) and Notchs remarkably increase in the lungs of ACF rats. Interestingly, closing the left-to-right shunt that leads to a reduced blood volume in the PA system of ACF rats (ACFRs) decreased the expression of COLIA1 and increased that of collagen I A2(COLIA2). This study contributes to the stretch-induced responses of SMCs and provides important future directions for therapies aimed at preventing abnormal matrix protein synthesis in volume overload-induced pulmonary hypertension (PH).

Anaemia, iron homeostasis and pulmonary hypertension: a review

Anaemia is a highly prevalent condition, which negatively impacts on patients' cardiovascular performance and quality of life. Anaemia is mainly caused by disturbances of iron homeostasis. While absolute iron deficiency mostly as a consequence of chronic blood loss or insufficient dietary iron absorption results in the emergence of iron deficiency anaemia, inflammation-driven iron retention in innate immune cells and blockade of iron absorption leads to the development of anaemia of chronic disease. Both, iron deficiency and anaemia have been linked to the clinical course of pulmonary hypertension. Various mechanistic links between iron homeostasis, anaemia, and pulmonary hypertension have been described and current treatment guidelines suggest regular iron status assessment and the implementation of iron supplementation strategies in these patients. The pathophysiology, diagnostic assessment as well as current and future treatment options concerning iron deficiency with or without anaemia in individuals suffering from pulmonary hypertension are discussed within this review.

Tissue-Engineered Vascular Grafts with Advanced Mechanical Strength from Human iPSCs

Vascular smooth muscle cells (VSMCs) can be derived in large numbers from human induced pluripotent stem cells (hiPSCs) for producing tissue-engineered vascular grafts (TEVGs). However, hiPSC-derived TEVGs are hampered by low mechanical strength and significant radial dilation after implantation. Here, we report generation of hiPSC-derived TEVGs with mechanical strength comparable to native vessels used in arterial bypass grafts by utilizing biodegradable scaffolds, incremental pulsatile stretching, and optimal culture conditions. Following implantation into a rat aortic model, hiPSC-derived TEVGs show excellent patency without luminal dilation and effectively maintain mechanical and contractile function. This study provides a foundation for future production of non-immunogenic, cellularized hiPSC-derived TEVGs composed of allogenic vascular cells, potentially serving needs to a considerable number of patients whose dysfunctional vascular cells preclude TEVG generation via other methods.

BMPR2 acts as a gatekeeper to protect endothelial cells from increased TGFβ responses and altered cell mechanics

Balanced transforming growth factor-beta (TGFβ)/bone morphogenetic protein (BMP)-signaling is essential for tissue formation and homeostasis. While gain in TGFβ signaling is often found in diseases, the underlying cellular mechanisms remain poorly defined. Here we show that the receptor BMP type 2 (BMPR2) serves as a central gatekeeper of this balance, highlighted by its deregulation in diseases such as pulmonary arterial hypertension (PAH). We show that BMPR2 deficiency in endothelial cells (ECs) does not abolish pan-BMP-SMAD1/5 responses but instead favors the formation of mixed-heteromeric receptor complexes comprising BMPR1/TGFβR1/TGFβR2 that enable enhanced cellular responses toward TGFβ. These include canonical TGFβ-SMAD2/3 and lateral TGFβ-SMAD1/5 signaling as well as formation of mixed SMAD complexes. Moreover, BMPR2-deficient cells express genes indicative of altered biophysical properties, including up-regulation of extracellular matrix (ECM) proteins such as fibrillin-1 (FBN1) and of integrins. As such, we identified accumulation of ectopic FBN1 fibers remodeled with fibronectin (FN) in junctions of BMPR2-deficient ECs. Ectopic FBN1 deposits were also found in proximity to contractile intimal cells in pulmonary artery lesions of BMPR2-deficient heritable PAH (HPAH) patients. In BMPR2-deficient cells, we show that ectopic FBN1 is accompanied by active β1-integrin highly abundant in integrin-linked kinase (ILK) mechano-complexes at cell junctions. Increased integrin-dependent adhesion, spreading, and actomyosin-dependent contractility facilitates the retrieval of active TGFβ from its latent fibrillin-bound depots. We propose that loss of BMPR2 favors endothelial-to-mesenchymal transition (EndMT) allowing cells of myo-fibroblastic character to create a vicious feed-forward process leading to hyperactivated TGFβ signaling. In summary, our findings highlight a crucial role for BMPR2 as a gatekeeper of endothelial homeostasis protecting cells from increased TGFβ responses and integrin-mediated mechano-transduction.

Application of Human Induced Pluripotent Stem Cells in Generating Tissue-Engineered Blood Vessels as Vascular Grafts

In pace with the advancement of tissue engineering during recent decades, tissue-engineered blood vessels (TEBVs) have been generated using primary seed cells, and their impressive success in clinical trials have demonstrated the great potential of these TEBVs as implantable vascular grafts in human regenerative medicine. However, the production, therapeutic efficacy, and readiness in emergencies of current TEBVs could be hindered by the accessibility, expandability, and donor-donor variation of patient-specific primary seed cells. Alternatively, using human induced pluripotent stem cells (hiPSCs) to derive seed vascular cells for vascular tissue engineering could fundamentally address this current dilemma in TEBV production. As an emerging research field with a promising future, the generation of hiPSC-based TEBVs has been reported recently with significant progress. Simultaneously, to further promote hiPSC-based TEBVs into vascular grafts for clinical use, several challenges related to the safety, readiness, and structural integrity of vascular tissue need to be addressed. Herein, this review will focus on the evolution and role of hiPSCs in vascular tissue engineering technology and summarize the current progress, challenges, and future directions of research on hiPSC-based TEBVs.

Cathepsin S promotes the development of pulmonary arterial hypertension

Cysteine cathepsin proteases play critical roles in cardiovascular disease progression and are implicated in extracellular matrix (ECM) degradation. Patients with pulmonary arterial hypertension (PAH) exhibit increased elastase production by pulmonary arterial smooth muscle cells (PASMCs), which is related to the degradation of elastic fibers and pulmonary vascular remodeling. However, the mechanism by which cathepsins regulate the ECM and PASMC proliferation in PAH remains unclear. We hypothesized that cathepsin proteases in PASMCs promote the development of PAH. Here, we show overexpression of cathepsin S (Cat S) and degradation of elastic laminae in the lungs of patients with idiopathic PAH and in the PASMCs of monocrotaline-induced PAH model (MCT-PAH) rats. In addition, pulmonary hypertension can be treated in MCT-PAH rats by administering a selective Cat S inhibitor, Millipore-219393, which stimulates peroxisome proliferator-activated receptor-γ (PPARγ) to inhibit the expression of Cat S, thus suppressing the proliferation and migration of MCT-PAH PASMCs. We then reduced Cat S or PPARγ expression by using small interfering RNA in human PASMCs to demonstrate a mechanistic link between Cat S signaling and PPARγ protein, and the results suggest that PPARγ is upstream of Cat S signaling. In conclusion, the activity of Cat S in pulmonary vascular remodeling and degradation of elastin fibers through the disruption of PPARγ is pathophysiologically significant in PAH.

Modeling elastin-associated vasculopathy with patient induced pluripotent stem cells and tissue engineering

Elastin-associated vasculopathies are life-threatening conditions of blood vessel dysfunction. The extracellular matrix protein elastin endows the recoil and compliance required for physiologic arterial function, while disruption of function can lead to aberrant vascular smooth muscle cell proliferation manifesting through stenosis, aneurysm, or vessel dissection. Although research efforts have been informative, they remain incomplete as no viable therapies exist outside of a heart transplant. Induced pluripotent stem cell technology may be uniquely suited to address current obstacles as these present a replenishable supply of patient-specific material with which to study disease. The following review will cover the cutting edge in vascular smooth muscle cell modeling of elastin-associated vasculopathy, and aid in the development of human disease modeling and drug screening approaches to identify potential treatments. Vascular proliferative disease can affect up to 50% of the population throughout the world, making this a relevant and critical area of research for therapeutic development.

Biomechanical characterization of murine pulmonary arteries

The biomechanical properties of the major pulmonary arteries play critical roles in normal physiology as well as in diverse pathophysiologies and clinical interventions. Importantly, advances in medical imaging enable simulations of pulmonary hemodynamics, but such models cannot reach their full potential until they are informed with region-specific material properties. In this paper, we present passive and active biaxial biomechanical data for the right and left main pulmonary arteries from wild-type mice. We also evaluate the suitability of a four-fiber family constitutive model as a descriptor of the passive behavior. Despite regional differences in size, the biaxial mechanical properties, including passive stiffness and elastic energy storage, the biaxial wall stresses at in vivo pressures, and the overall contractile capacity in response to smooth muscle cell stimulation under in vivo conditions are remarkably similar between the right and left branches. The proposed methods and results can serve as baseline protocols and measurements for future biaxial experiments on murine models of pulmonary pathologies, and the constitutive model can inform computational models of normal pulmonary growth and remodeling. Our use of consistent experimental protocols and data analyses can also facilitate comparative studies in health and disease across the systemic and pulmonary circulations as well as studies seeking to understand remodeling in surgeries such as the Fontan procedure, which involves different types of vessels.

Pathology and pathobiology of pulmonary hypertension: state of the art and research perspectives

Clinical and translational research has played a major role in advancing our understanding of pulmonary hypertension (PH), including pulmonary arterial hypertension and other forms of PH with severe vascular remodelling (e.g. chronic thromboembolic PH and pulmonary veno-occlusive disease). However, PH remains an incurable condition with a high mortality rate, underscoring the need for a better transfer of novel scientific knowledge into healthcare interventions. Herein, we review recent findings in pathology (with the questioning of the strict morphological categorisation of various forms of PH into pre- or post-capillary involvement of pulmonary vessels) and cellular mechanisms contributing to the onset and progression of pulmonary vascular remodelling associated with various forms of PH. We also discuss ways to improve management and to support and optimise drug development in this research field.

Vascular Development

The vascular system forms as a branching network of endothelial cells that acquire identity as arterial, venous, hemogenic, or lymphatic. Endothelial specification depends on gene targets transcribed by Ets domain-containing factors, including Ets variant gene 2 (Etv2), together with the activity of chromatin-remodeling complexes containing Brahma-related gene-1 (Brg1). Once specified and assembled into vessels, mechanisms regulating lumen diameter and axial growth ensure that the structure of the branching vascular network matches the need for perfusion of target tissues. In addition, blood vessels provide important morphogenic cues that guide or direct the development of organs forming around them. As the embryo grows and lumen diameters increase, smooth muscle cells wrap around the nascent vessel walls to provide mechanical strength and vasomotor control of the circulation. Increasing mechanical stretch and wall strain promote smooth muscle cell differentiation via coupling of actin cytoskeletal remodeling to myocardin and serum response factor-dependent transcription. Remodeling of artery walls by developmental signaling pathways reappears in postnatal blood vessels during physiological and pathological adaptation to vessel wall injury, inflammation, or chronic hypoxia. Recent reports providing insights into major steps in vascular development are reviewed here with a particular emphasis on studies that have been recently published in Arteriosclerosis, Thrombosis, and Vascular Biology.

Consequences of BMPR2 Deficiency in the Pulmonary Vasculature and Beyond: Contributions to Pulmonary Arterial Hypertension

Since its association with familial pulmonary arterial hypertension (PAH) in 2000, Bone Morphogenetic Protein Receptor II (BMPR2) and its related signaling pathway have become recognized as a key regulator of pulmonary vascular homeostasis. Herein, we define BMPR2 deficiency as either an inactivation of the receptor, decreased receptor expression, or an impairment of the receptor’s downstream signaling pathway. Although traditionally the phenotypic consequences of BMPR2 deficiency in PAH have been thought to be limited to the pulmonary vasculature, there is evidence that abnormalities in BMPR2 signaling may have consequences in many other organ systems and cellular compartments. Revisiting how BMPR2 functions throughout health and disease in cells and organs beyond the lung vasculature may provide insight into the contribution of these organ systems to PAH pathogenesis as well as the potential systemic manifestation of PAH. Here we review our knowledge of the consequences of BMPR2 deficiency across multiple organ systems.

The Role of Neutrophils and Neutrophil Elastase in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a severe vasculopathy characterized by the presence of fibrotic lesions in the arterial wall and the loss of small distal pulmonary arteries. The vasculopathy is accompanied by perivascular inflammation and increased protease levels, with neutrophil elastase notably implicated in aberrant vascular remodeling. However, the source of elevated elastase levels in PAH remains unclear. A major source of neutrophil elastase is the neutrophil, an understudied cell population in PAH. The principal function of neutrophils is to destroy invading pathogens by means of phagocytosis and NET formation, but proteases, chemokines, and cytokines implicated in PAH can be released by and/or prime and activate neutrophils. This review focuses on the contribution of inflammation to the development and progression of the disease, highlighting studies implicating neutrophils, neutrophil elastase, and other neutrophil proteases in PAH. The roles of cytokines, chemokines, and neutrophil elastase in the disease are discussed and we describe new insight into the role neutrophils potentially play in the pathogenesis of PAH.

Perivascular Adipose Tissue-Derived PDGF-D Contributes to Aortic Aneurysm Formation During Obesity

Obesity increases the risk of vascular diseases, including aortic aneurysm (AA). Perivascular adipose tissue (PVAT) surrounding arteries are altered during obesity. However, the underlying mechanism of adipose tissue, especially PVAT, in the pathogenesis of AA is still unclear. Here we showed that angiotensin II (AngII) infusion increases the incidence of AA in leptin-deficient obese mice (ob/ob) and high-fat diet-induced obese mice with adventitial inflammation. Furthermore, transcriptome analysis revealed that platelet-derived growth factor-D (PDGF-D) was highly expressed in the PVAT of ob/ob mice. Therefore, we hypothesized that PDGF-D mediates adventitial inflammation, which provides a direct link between PVAT dysfunction and AA formation in AngII-infused obese mice. We found that PDGF-D promotes the proliferation, migration, and inflammatory factors expression in cultured adventitial fibroblasts. In addition, the inhibition of PDGF-D function significantly reduced the incidence of AA in AngII-infused obese mice. More importantly, adipocyte-specific PDGF-D transgenic mice are more susceptible to AA formation after AngII infusion accompanied by exaggerated adventitial inflammatory and fibrotic responses. Collectively, our findings reveal a notable role of PDGF-D in the AA formation during obesity, and modulation of this cytokine might be an exploitable treatment strategy for the condition.

Circulating bone morphogenetic protein-9 levels are associated with hypertension and insulin resistance in humans

It has been demonstrated that bone morphogenetic protein-9 (BMP-9) may have an important role in vascular development and stability. However, the association of circulating BMP-9 with essential hypertension (HTN) has not been established in humans. The objective of this study is to observe the changes of circulating BMP-9 levels in patients with HTN and to investigate the association of circulation BMP-9 and insulin resistance (IR) in a cross-sectional study. Two hundred twenty-five individuals, including 132 patients with hypertension, and 93 healthy controls, were included in the present study. Circulating BMP-9 concentrations were measured with an ELISA kit. The association of circulating BMP-9 with other parameters was analyzed. When compared with healthy subjects, circulating BMP-9 concentrations were markedly lower in HTN patients (46.20 [31.85-62.80] vs. 77.21 [39.33-189.15], P < .01) and correlated negatively with blood pressure and the homeostasis model assessment of insulin resistance (P < .05 or P < .01). Decreasing levels of BMP-9 were independently and markedly related to HTN. In a multiple linear regression analysis, only systolic blood pressure and free fatty acid concentrations were independently associated with circulating BMP-9. Our findings suggest that BMP-9 may be a serum biomarker for HTN and IR.

Upregulation of Human Endogenous Retrovirus-K Is Linked to Immunity and Inflammation in Pulmonary Arterial Hypertension

BACKGROUND

Immune dysregulation has been linked to occlusive vascular remodeling in pulmonary arterial hypertension (PAH) that is hereditary, idiopathic, or associated with other conditions. Circulating autoantibodies, lung perivascular lymphoid tissue, and elevated cytokines have been related to PAH pathogenesis but without a clear understanding of how these abnormalities are initiated, perpetuated, and connected in the progression of disease. We therefore set out to identify specific target antigens in PAH lung immune complexes as a starting point toward resolving these issues to better inform future application of immunomodulatory therapies.

METHODS

Lung immune complexes were isolated and PAH target antigens were identified by liquid chromatography tandem mass spectrometry, confirmed by enzyme-linked immunosorbent assay, and localized by confocal microscopy. One PAH antigen linked to immunity and inflammation was pursued and a link to PAH pathophysiology was investigated by next-generation sequencing, functional studies in cultured monocytes and endothelial cells, and hemodynamic and lung studies in a rat.

RESULTS

SAM domain and HD domain-containing protein 1 (SAMHD1), an innate immune factor that suppresses HIV replication, was identified and confirmed as highly expressed in immune complexes from 16 hereditary and idiopathic PAH versus 12 control lungs. Elevated SAMHD1 was localized to endothelial cells, perivascular dendritic cells, and macrophages, and SAMHD1 antibodies were prevalent in tertiary lymphoid tissue. An unbiased screen using metagenomic sequencing related SAMHD1 to increased expression of human endogenous retrovirus K (HERV-K) in PAH versus control lungs (n=4). HERV-K envelope and deoxyuridine triphosphate nucleotidohydrolase mRNAs were elevated in PAH versus control lungs (n=10), and proteins were localized to macrophages. HERV-K deoxyuridine triphosphate nucleotidohydrolase induced SAMHD1 and proinflammatory cytokines (eg, interleukin 6, interleukin 1β, and tumor necrosis factor α) in circulating monocytes, pulmonary arterial endothelial cells, and also activated B cells. Vulnerability of pulmonary arterial endothelial cells (PAEC) to apoptosis was increased by HERV-K deoxyuridine triphosphate nucleotidohydrolase in an interleukin 6-independent manner. Furthermore, 3 weekly injections of HERV-K deoxyuridine triphosphate nucleotidohydrolase induced hemodynamic and vascular changes of pulmonary hypertension in rats (n=8) and elevated interleukin 6.

CONCLUSIONS

Our study reveals that upregulation of the endogenous retrovirus HERV-K could both initiate and sustain activation of the immune system and cause vascular changes associated with PAH.