T-Cell Mediated Immune Rejection of Beta-2-Microglobulin Knockout Induced Pluripotent Stem Cell-Derived Kidney Organoids.

Immune evasive induced pluripotent stem cell (iPSC)-derived kidney organoids, known as "stealth" organoids, hold promise for clinical transplantation. To address immune rejection, we investigated the impact of genetically modifying human leukocyte antigen (HLA) class I in kidney organoids prior to transplantation. By using CRISPR-Cas9, we successfully knocked out beta-2-microglobulin (B2M), resulting in iPSCs devoid of HLA class I surface expression. In vitro, the B2M knockout protected kidney organoids derived from these iPSCs against T-cell rejection. To assess in vivo protection, unmodified (control) and B2M-/- kidney organoids were transplanted into humanized mice engrafted with human peripheral blood mononuclear cells (PBMCs). Successful engraftment of human PBMCs was confirmed, and after 4 weeks, we observed no discernible difference in the infiltration rate, proliferation, or cytotoxicity of CD4+ and CD8+ T cells between control and B2M-/- organoids. Both groups of organoids showed compromised tissue integrity, displaying tubulitis and loss of tubule integrity. Notably, while B2M-/- organoids failed to express HLA class I on their cell surface, there was preexisting expression of HLA class II in both control and B2M-/- organoids transplanted into mice with human PBMCs. HLA class II expression was not limited to antigen-presenting cells but also evident in epithelial cells of the kidney organoid, posing an additional immunological challenge to its transplantation. Consequently, we conclude that B2M knockout alone is insufficient to protect iPSC-derived kidney organoids from T-cell-mediated immune rejection. Additionally, our findings suggest that modulating HLA class II signaling will be necessary to prevent rejection following transplantation.

Endothelial to mesenchymal transition in kidney fibrosis.

Fibrotic disease are characterized by the uncontrolled accumulation of extracellular matrix (ECM) components leading to disruption of tissue homeostasis. Myofibroblasts as main ECM-producing cells can originate from various differentiated cell types after injury. Particularly, the process of endothelial-to-mesenchymal transition (endMT), describing phenotypic shifts of endothelial cells (ECs) to adopt a fully mesenchymal identity, may contribute to the pool of myofibroblasts in fibrosis, while leading to capillary rarefaction and exacerbation of tissue hypoxia. In renal disease, incomplete recovery from acute kidney injury (AKI) and the ensuing fibrotic reaction stand out as major contributors to chronic kidney disease (CKD) development. While the focus has largely been on impaired tubular epithelial repair as a potential fibrosis-driving mechanism, alterations in the renal microcirculation post-AKI, and in particular endMT as a maladaptive response, could hold equal significance. Dysfunctional interplays among various cell types in the kidney microenvironment can instigate endMT. Transforming growth factor beta (TGF-ß) signaling, with its downstream activation of canonical/Smad-mediated and non-canonical pathways, has been identified as primary driver of this process. However, non-TGF-ß-mediated pathways involving inflammatory agents and metabolic shifts in intercellular communication within the tissue microenvironment can also trigger endMT. These harmful, maladaptive cell-cell interactions and signaling pathways offer potential targets for therapeutic intervention to impede endMT and decelerate fibrogenesis such as in AKI-CKD progression. Presently, partial reduction of TGF-ß signaling using anti-diabetic drugs or statins may hold therapeutic potential in renal context. Nevertheless, further investigation is warranted to validate underlying mechanisms and assess positive effects within a clinical framework.

The pulmonary vasculature in lethal COVID-19 and idiopathic pulmonary fibrosis at single-cell resolution.

AIMS: Severe acute respiratory syndrome coronavirus-2 infection causes COVID-19, which in severe cases evokes life-threatening acute respiratory distress syndrome (ARDS). Transcriptome signatures and the functional relevance of non-vascular cell types (e.g. immune and epithelial cells) in COVID-19 are becoming increasingly evident. However, despite its known contribution to vascular inflammation, recruitment/invasion of immune cells, vascular leakage, and perturbed haemostasis in the lungs of severe COVID-19 patients, an in-depth interrogation of the endothelial cell (EC) compartment in lethal COVID-19 is lacking. Moreover, progressive fibrotic lung disease represents one of the complications of COVID-19 pneumonia and ARDS. Analogous features between idiopathic pulmonary fibrosis (IPF) and COVID-19 suggest partial similarities in their pathophysiology, yet, a head-to-head comparison of pulmonary cell transcriptomes between both conditions has not been implemented to date. METHODS AND RESULTS: We performed single-nucleus RNA-sequencing on frozen lungs from 7 deceased COVID-19 patients, 6 IPF explant lungs, and 12 controls. The vascular fraction, comprising 38 794 nuclei, could be subclustered into 14 distinct EC subtypes. Non-vascular cell types, comprising 137 746 nuclei, were subclustered and used for EC-interactome analyses. Pulmonary ECs of deceased COVID-19 patients showed an enrichment of genes involved in cellular stress, as well as signatures suggestive of dampened immunomodulation and impaired vessel wall integrity. In addition, increased abundance of a population of systemic capillary and venous ECs was identified in COVID-19 and IPF. COVID-19 systemic ECs closely resembled their IPF counterparts, and a set of 30 genes was found congruently enriched in systemic ECs across studies. Receptor-ligand interaction analysis of ECs with non-vascular cell types in the pulmonary micro-environment revealed numerous previously unknown interactions specifically enriched/depleted in COVID-19 and/or IPF. CONCLUSIONS: This study uncovered novel insights into the abundance, expression patterns, and interactomes of EC subtypes in COVID-19 and IPF, relevant for future investigations into the progression and treatment of both lethal conditions.

Spatial dynamic metabolomics identifies metabolic cell fate trajectories in human kidney differentiation.

Accumulating evidence demonstrates important roles for metabolism in cell fate determination. However, it is a challenge to assess metabolism at a spatial resolution that acknowledges both heterogeneity and cellular dynamics in its tissue microenvironment. Using a multi-omics platform to study cell-type-specific dynamics in metabolism in complex tissues, we describe the metabolic trajectories during nephrogenesis in the developing human kidney. Exploiting in situ analysis of isotopic labeling, a shift from glycolysis toward fatty acid ß-oxidation was observed during the differentiation from the renal vesicle toward the S-shaped body and the proximal tubules. In addition, we show that hiPSC-derived kidney organoids are characterized by a metabolic immature phenotype that fails to use mitochondrial long-chain fatty acids for energy metabolism. Furthermore, supplementation of butyrate enhances tubular epithelial differentiation and maturation in cultured kidney organoids. Our findings highlight the relevance of understanding metabolic trajectories to efficiently guide stem cell differentiation.

Analyzing cell-type-specific dynamics of metabolism in kidney repair.

A common drawback of metabolic analyses of complex biological samples is the inability to consider cell-to-cell heterogeneity in the context of an organ or tissue. To overcome this limitation, we present an advanced high-spatial-resolution metabolomics approach using matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) combined with isotope tracing. This method allows mapping of cell-type-specific dynamic changes in central carbon metabolism in the context of a complex heterogeneous tissue architecture, such as the kidney. Combined with multiplexed immunofluorescence staining, this method can detect metabolic changes and nutrient partitioning in targeted cell types, as demonstrated in a bilateral renal ischemia-reperfusion injury (bIRI) experimental model. Our approach enables us to identify region-specific metabolic perturbations associated with the lesion and throughout recovery, including unexpected metabolic anomalies in cells with an apparently normal phenotype in the recovery phase. These findings may be relevant to an understanding of the homeostatic capacity of the kidney microenvironment. In sum, this method allows us to achieve resolution at the single-cell level in situ and hence to interpret cell-type-specific metabolic dynamics in the context of structure and metabolism of neighboring cells.

Vasculogenesis in kidney organoids upon transplantation.

Human induced pluripotent stem cell-derived kidney organoids have potential for disease modeling and to be developed into clinically transplantable auxiliary tissue. However, they lack a functional vasculature, and the sparse endogenous endothelial cells (ECs) are lost upon prolonged culture in vitro, limiting maturation and applicability. Here, we use intracoelomic transplantation in chicken embryos followed by single-cell RNA sequencing and advanced imaging platforms to induce and study vasculogenesis in kidney organoids. We show expansion of human organoid-derived ECs that reorganize into perfused capillaries and form a chimeric vascular network with host-derived blood vessels. Ligand-receptor analysis infers extensive potential interactions of human ECs with perivascular cells upon transplantation, enabling vessel wall stabilization. Perfused glomeruli display maturation and morphogenesis to capillary loop stage. Our findings demonstrate the beneficial effect of vascularization on not only epithelial cell types, but also the mesenchymal compartment, inducing the expansion of ´on target´ perivascular stromal cells, which in turn are required for further maturation and stabilization of the neo-vasculature. The here described vasculogenic capacity of kidney organoids will have to be deployed to achieve meaningful glomerular maturation and kidney morphogenesis in vitro.

Protocols for endothelial cell isolation from mouse tissues: brain, choroid, lung, and muscle.

Endothelial cells (ECs) harbor distinct phenotypical and functional characteristics depending on their tissue localization and contribute to brain, eye, lung, and muscle diseases such as dementia, macular degeneration, pulmonary hypertension, and sarcopenia. To study their function, isolation of pure ECs in high quantities is crucial. Here, we describe protocols for rapid and reproducible blood vessel EC purification established for scRNA sequencing from murine tissues using mechanical and enzymatic digestion followed by magnetic and fluorescence-activated cell sorting. For complete details on the use and execution of these protocol, please refer to Kalucka et al. (2020), Rohlenova et al. (2020), and Goveia et al. (2020).

Protocols for endothelial cell isolation from mouse tissues: kidney, spleen, and testis.

Endothelial cells (ECs) exhibit phenotypic and functional tissue specificities, critical for studies in the vascular field and beyond. Thus, tissue-specific methods for isolation of highly purified ECs are necessary. Kidney, spleen, and testis ECs are relevant players in health and diseases such as chronic kidney disease, acute kidney injury, myelofibrosis, and cancer. Here, we provide tailored protocols for rapid and reproducible EC purification established for scRNA sequencing from these adult murine tissues using the combination of magnetic- and fluorescence-activated cell sorting. For complete details on the use and execution of these protocols, please refer to Kalucka et al. (2020) and Dumas et al. (2020).

Tumor vessel co-option probed by single-cell analysis.

Tumor vessel co-option is poorly understood, yet it is a resistance mechanism against anti-angiogenic therapy (AAT). The heterogeneity of co-opted endothelial cells (ECs) and pericytes, co-opting cancer and myeloid cells in tumors growing via vessel co-option, has not been investigated at the single-cell level. Here, we use a murine AAT-resistant lung tumor model, in which VEGF-targeting induces vessel co-option for continued growth. Single-cell RNA sequencing (scRNA-seq) of 31,964 cells reveals, unexpectedly, a largely similar transcriptome of co-opted tumor ECs (TECs) and pericytes as their healthy counterparts. Notably, we identify cell types that might contribute to vessel co-option, i.e., an invasive cancer-cell subtype, possibly assisted by a matrix-remodeling macrophage population, and another M1-like macrophage subtype, possibly involved in keeping or rendering vascular cells quiescent.

Protocols for endothelial cell isolation from mouse tissues: small intestine, colon, heart, and liver.

Endothelial cells (ECs) from the small intestine, colon, liver, and heart have distinct phenotypes and functional adaptations that are dependent on their physiological environment. Gut ECs adapt to low oxygen, heart ECs to contractile forces, and liver ECs to low flow rates. Isolating high-purity ECs in sufficient quantities is crucial to study their functions. Here, we describe protocols combining magnetic and fluorescent activated cell sorting for rapid and reproducible EC purification from four adult murine tissues. For complete details on the use and execution of these protocols, please refer to Kalucka et al. (2020).

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.

Metabolic Signatures of Distinct Endothelial Phenotypes.

Angiogenesis is crucial for the development of the blood vasculature during embryogenesis, but also contributes to cancer and other diseases. While therapeutic targeting of endothelial cells (ECs) through growth factor inhibition is limited by insufficient efficacy and resistance, a new paradigm for modulating angiogenesis by targeting EC metabolism has emerged. Findings from the past decade highlight how ECs adapt their metabolism to proliferate or migrate during vessel sprouting, or to maintain the vascular barrier and protect themselves against oxidative stress in the high-oxygen environment they are exposed to in healthy conditions. We overview key endothelial metabolic pathways underlying the different EC phenotypes, as well as potential opportunities for targeting EC metabolism in therapeutic settings.

Comparison of Human and Experimental Pulmonary Veno-Occlusive Disease.

Pulmonary veno-occlusive disease (PVOD) occurs in humans either as a heritable form (hPVOD) due to biallelic inactivating mutations of EIF2AK4 (encoding GCN2) or as a sporadic form in older age (sPVOD). The chemotherapeutic agent mitomycin C (MMC) is a potent inducer of PVOD in humans and in rats (MMC-PVOD). Here, we compared human hPVOD and sPVOD, and MMC-PVOD pathophysiology at the histological, cellular, and molecular levels to unravel common altered pathomechanisms. MMC exposure in rats was associated primarily with arterial and microvessel remodeling, and secondarily by venous remodeling, when PVOD became symptomatic. In all forms of PVOD tested, there was convergent GCN2-dependent but eIF2α-independent pulmonary protein overexpression of HO-1 (heme oxygenase 1) and CHOP (CCAAT-enhancer-binding protein [C/EBP] homologous protein), two downstream effectors of GCN2 signaling and endoplasmic reticulum stress. In human PVOD samples, CHOP immunohistochemical staining mainly labeled endothelial cells in remodeled veins and arteries. Strong HO-1 staining was observed only within capillary hemangiomatosis foci, where intense microvascular proliferation occurs. HO-1 and CHOP stainings were not observed in control and pulmonary arterial hypertension lung tissues, supporting the specificity for CHOP and HO-1 involvement in PVOD pathobiology. In vivo loss of GCN2 (EIF2AK4 mutations carriers and Eif2ak4-/- rats) or in vitro GCN2 inhibition in cultured pulmonary artery endothelial cells using pharmacological and siRNA approaches demonstrated that GCN2 loss of function negatively regulates BMP (bone morphogenetic protein)-dependent SMAD1/5/9 signaling. Exogenous BMP9 was still able to reverse GCN2 inhibition-induced proliferation of pulmonary artery endothelial cells. In conclusion, we identified CHOP and HO-1 inhibition, and BMP9, as potential therapeutic options for PVOD.

Lowering the increased intracellular pH of human-induced pluripotent stem cell-derived endothelial cells induces formation of mature Weibel-Palade bodies.

Differentiation of human-induced pluripotent stem cells (hiPSCs) into vascular endothelium is of great importance to tissue engineering, disease modeling, and use in regenerative medicine. Although differentiation of hiPSCs into endothelial-like cells (hiPSC-derived endothelial cells [hiPSC-ECs]) has been demonstrated before, controversy exists as to what extent these cells faithfully reflect mature endothelium. To address this issue, we investigate hiPSC-ECs maturation by their ability to express von Willebrand factor (VWF) and formation of Weibel-Palade bodies (WPBs). Using multiple hiPSCs lines, hiPSC-ECs failed to form proper VWF and WPBs, essential for angiogenesis, primary and secondary homeostasis. Lowering the increased intracellular pH (pHi) of hiPSC-ECs with acetic acid did result in the formation of elongated WPBs. Nuclear magnetic resonance data showed that the higher pHi in hiPSC-ECs occurred in association with decreased intracellular lactate concentrations. This was explained by decreased glycolytic flux toward pyruvate and lactate in hiPSC-ECs. In addition, decreased expression of monocarboxylate transporter member 1, a member of the solute carrier family (SLC16A1), which regulates lactate and H+ uptake, contributed to the high pHi of hiPSC-EC. Mechanistically, pro-VWF dimers require the lower pH environment of the trans-Golgi network for maturation and tubulation. These data show that while hiPSC-ECs may share many features with mature EC, they are characterized by metabolic immaturity hampering proper EC function.

Single-Cell Transcriptome Atlas of Murine Endothelial Cells.

The heterogeneity of endothelial cells (ECs) across tissues remains incompletely inventoried. We constructed an atlas of >32,000 single-EC transcriptomes from 11 mouse tissues and identified 78 EC subclusters, including Aqp7+ intestinal capillaries and angiogenic ECs in healthy tissues. ECs from brain/testis, liver/spleen, small intestine/colon, and skeletal muscle/heart pairwise expressed partially overlapping marker genes. Arterial, venous, and lymphatic ECs shared more markers in more tissues than did heterogeneous capillary ECs. ECs from different vascular beds (arteries, capillaries, veins, lymphatics) exhibited transcriptome similarity across tissues, but the tissue (rather than the vessel) type contributed to the EC heterogeneity. Metabolic transcriptome analysis revealed a similar tissue-grouping phenomenon of ECs and heterogeneous metabolic gene signatures in ECs between tissues and between vascular beds within a single tissue in a tissue-type-dependent pattern. The EC atlas taxonomy enabled identification of EC subclusters in public scRNA-seq datasets and provides a powerful discovery tool and resource value.

Single-Cell RNA Sequencing Reveals Renal Endothelium Heterogeneity and Metabolic Adaptation to Water Deprivation.

BACKGROUND: Renal endothelial cells from glomerular, cortical, and medullary kidney compartments are exposed to different microenvironmental conditions and support specific kidney processes. However, the heterogeneous phenotypes of these cells remain incompletely inventoried. Osmotic homeostasis is vitally important for regulating cell volume and function, and in mammals, osmotic equilibrium is regulated through the countercurrent system in the renal medulla, where water exchange through endothelium occurs against an osmotic pressure gradient. Dehydration exposes medullary renal endothelial cells to extreme hyperosmolarity, and how these cells adapt to and survive in this hypertonic milieu is unknown. METHODS: We inventoried renal endothelial cell heterogeneity by single-cell RNA sequencing >40,000 mouse renal endothelial cells, and studied transcriptome changes during osmotic adaptation upon water deprivation. We validated our findings by immunostaining and functionally by targeting oxidative phosphorylation in a hyperosmolarity model in vitro and in dehydrated mice in vivo. RESULTS: We identified 24 renal endothelial cell phenotypes (of which eight were novel), highlighting extensive heterogeneity of these cells between and within the cortex, glomeruli, and medulla. In response to dehydration and hypertonicity, medullary renal endothelial cells upregulated the expression of genes involved in the hypoxia response, glycolysis, and-surprisingly-oxidative phosphorylation. Endothelial cells increased oxygen consumption when exposed to hyperosmolarity, whereas blocking oxidative phosphorylation compromised endothelial cell viability during hyperosmotic stress and impaired urine concentration during dehydration. CONCLUSIONS: This study provides a high-resolution atlas of the renal endothelium and highlights extensive renal endothelial cell phenotypic heterogeneity, as well as a previously unrecognized role of oxidative phosphorylation in the metabolic adaptation of medullary renal endothelial cells to water deprivation.

Closing the Mitochondrial Permeability Transition Pore in hiPSC-Derived Endothelial Cells Induces Glycocalyx Formation and Functional Maturation.

Human induced pluripotent stem cells (hiPSCs) are used to study organogenesis and model disease as well as being developed for regenerative medicine. Endothelial cells are among the many cell types differentiated from hiPSCs, but their maturation and stabilization fall short of that in adult endothelium. We examined whether shear stress alone or in combination with pericyte co-culture would induce flow alignment and maturation of hiPSC-derived endothelial cells (hiPSC-ECs) but found no effects comparable with those in primary microvascular ECs. In addition, hiPSC-ECs lacked a luminal glycocalyx, critical for vasculature homeostasis, shear stress sensing, and signaling. We noted, however, that hiPSC-ECs have dysfunctional mitochondrial permeability transition pores, resulting in reduced mitochondrial function and increased reactive oxygen species. Closure of these pores by cyclosporine A improved EC mitochondrial function but also restored the glycocalyx such that alignment to flow took place. These results indicated that mitochondrial maturation is required for proper hiPSC-EC functionality.

Functional interaction between PDGFß and GluN2B-containing NMDA receptors in smooth muscle cell proliferation and migration in pulmonary arterial hypertension.

In this study, we explored the complex interactions between platelet-derived growth factor (PDGF) and N-methyl-d-aspartate receptor (NMDAR) and their effect on the excessive proliferation and migration of smooth muscle cells leading to obstructed arteries in pulmonary arterial hypertension (PAH). We report lower expression of glutamate receptor NMDA-type subunit 2B (GluN2B), a subunit composing NMDARs expected to affect cell survival/proliferation of pulmonary artery smooth muscle cells (PASMCs), in PAH patient lungs. PASMC exposure to PDGF-BB stimulated immediate increased levels of phosphorylated Src family kinases (SFKs) together with increased phosphorylated GluN2B (its active form) and cell surface relocalization, suggesting a cross talk between PDGFR-recruited SFKs and NMDAR. Selective inhibition of PDGFR-ß or SFKs with imatinib or A-419259, respectively, on one hand, or with specific small-interfering RNAs (siRNAs) on the other hand, aborted PDGF-induced phosphorylation of GluN2B, thus validating the pathway. Selective inhibition of GluN2B using Rö25-6981 and silencing with specific siRNA, in the presence of PDGF-BB, significantly increased both migration and proliferation of PASMCs, thus strengthening the functional importance of the pathway. Together, these results indicate that GluN2B-type NMDAR activation may confer to PASMCs antiproliferative and antimigratory properties. The decreased levels of GluN2B observed in PAH pulmonary arteries could mediate the excessive proliferation of PASMCs, thus contributing to medial hyperplasia and PAH development.

NMDA-Type Glutamate Receptor Activation Promotes Vascular Remodeling and Pulmonary Arterial Hypertension.

BACKGROUND: Excessive proliferation and apoptosis resistance in pulmonary vascular cells underlie vascular remodeling in pulmonary arterial hypertension (PAH). Specific treatments for PAH exist, mostly targeting endothelial dysfunction, but high pulmonary arterial pressure still causes heart failure and death. Pulmonary vascular remodeling may be driven by metabolic reprogramming of vascular cells to increase glutaminolysis and glutamate production. The N-methyl-d-aspartate receptor (NMDAR), a major neuronal glutamate receptor, is also expressed on vascular cells, but its role in PAH is unknown. METHODS: We assessed the status of the glutamate-NMDAR axis in the pulmonary arteries of patients with PAH and controls through mass spectrometry imaging, Western blotting, and immunohistochemistry. We measured the glutamate release from cultured pulmonary vascular cells using enzymatic assays and analyzed NMDAR regulation/phosphorylation through Western blot experiments. The effect of NMDAR blockade on human pulmonary arterial smooth muscle cell proliferation was determined using a BrdU incorporation assay. We assessed the role of NMDARs in vascular remodeling associated to pulmonary hypertension, in both smooth muscle-specific NMDAR knockout mice exposed to chronic hypoxia and the monocrotaline rat model of pulmonary hypertension using NMDAR blockers. RESULTS: We report glutamate accumulation, upregulation of the NMDAR, and NMDAR engagement reflected by increases in GluN1-subunit phosphorylation in the pulmonary arteries of human patients with PAH. Kv channel inhibition and type A-selective endothelin receptor activation amplified calcium-dependent glutamate release from human pulmonary arterial smooth muscle cell, and type A-selective endothelin receptor and platelet-derived growth factor receptor activation led to NMDAR engagement, highlighting crosstalk between the glutamate-NMDAR axis and major PAH-associated pathways. The platelet-derived growth factor-BB-induced proliferation of human pulmonary arterial smooth muscle cells involved NMDAR activation and phosphorylated GluN1 subunit localization to cell-cell contacts, consistent with glutamatergic communication between proliferating human pulmonary arterial smooth muscle cells via NMDARs. Smooth-muscle NMDAR deficiency in mice attenuated the vascular remodeling triggered by chronic hypoxia, highlighting the role of vascular NMDARs in pulmonary hypertension. Pharmacological NMDAR blockade in the monocrotaline rat model of pulmonary hypertension had beneficial effects on cardiac and vascular remodeling, decreasing endothelial dysfunction, cell proliferation, and apoptosis resistance while disrupting the glutamate-NMDAR pathway in pulmonary arteries. CONCLUSIONS: These results reveal a dysregulation of the glutamate-NMDAR axis in the pulmonary arteries of patients with PAH and identify vascular NMDARs as targets for antiremodeling treatments in PAH.

[The cancer paradigm in pulmonary arterial hypertension: towards anti-remodeling therapies targeting metabolic dysfunction?] / Le paradigme du cancer dans l'hypertension artérielle pulmonaire : vers une thérapie anti-remodelage ciblant la dysfonction métabolique ?

Pulmonary arterial hypertension (PAH) is a rare, complex and multifactorial disease in which pulmonary vascular remodeling plays a major role ending in right heart failure and death. Current specific therapies of PAH that mainly target the vasoconstriction/vasodilatation imbalance are not curative. Bi-pulmonary transplantation remains the only option in patients resistant to current therapies. It is thus crucial to identify novel vascular anti-remodeling therapeutic targets. This remodeling displays several properties of cancer cells, especially overproliferation and apoptosis resistance of pulmonary vascular cells, hallmarks of cancer related to the metabolic shift known as the "Warburg effect". The latter is characterized by a shift of ATP production, from oxidative phosphorylation to low rate aerobic glycolysis. In compensation, the cancer cells exhibit exacerbated glutaminolysis thus resulting in glutamine addiction, necessary to their overproliferation. Glutamine intake results in glutamate production, a molecule at the crossroads of energy metabolism and cancer cell communication, thus contributing to cell proliferation. Accordingly, therapeutic strategies targeting glutamate production, its release into the extracellular space and its membrane receptors have been suggested to treat different types of cancers, not only in the central nervous system but also in the periphery. We propose that similar strategies targeting glutamatergic signaling may be considered in PAH, especially as they could affect not only the vascular remodeling but also the right heart hypertrophy known to involve the glutaminolysis pathway. Ongoing studies aim to characterize the involvement of the glutamate pathway and its receptors in vascular remodeling, and the therapeutic potential of specific molecules targeting this pathway.