Tm4sf1-marked Endothelial Subpopulation Is Dysregulated in Pulmonary Arterial Hypertension

Lung endothelial cell heterogeneity in health and pulmonary vascular disease

Lung endothelial cells (ECs) are essential for maintaining organ function and homeostasis. Despite sharing some common features with ECs from organ systems, lung ECs exhibit significant heterogeneity in morphology, function, and gene expression. This heterogeneity is increasingly recognized as a key contributor to the development of pulmonary diseases like pulmonary hypertension (PH). In this mini-review, we explore the evolving understanding of lung EC heterogeneity, particularly through the lens of single-cell RNA sequencing (scRNA-seq) technologies. These advances have provided unprecedented insights into the diverse EC subpopulations, their specific roles, and the disturbances in their homeostatic functions that contribute to PH pathogenesis. In particular, these studies identified novel and functionally distinct cell types such as aerocytes and general capillary ECs that are critical for maintaining lung function in health and disease. In addition, multiple novel pathways and mechanisms have been identified that contribute to aberrant pulmonary vascular remodeling in PH. Emerging techniques like single-nucleus RNA sequencing and spatial transcriptomics have further pushed the field forward by discovering novel disease mediators. As research continues to leverage these advanced techniques, the field is poised to uncover novel EC subtypes and disease mechanisms, paving the way for new therapeutic targets in PH and other lung diseases.

Flow Cytometric Determination of Circulating Progenitor Cells in Patients With Pulmonary Arterial Hypertension: A Systematic Review

Pulmonary arterial hypertension (PAH) is characterized by progressive narrowing and obliteration of distal, pre-capillary pulmonary vessels. Yet, noninvasive biomarkers that reflect this disease-defining process are lacking. A systematic review of PAH studies that measured circulating progenitor cells (CPCs) or circulating endothelial cells (CECs) in PAH by flow cytometry was performed to understand how future studies, leveraging state-of-the-art single-cell analyses, can advance the field. The study was conducted in accordance with the Preferred Reporting Items for Systematic Reviews. Of the 2422 studies identified, 20 met inclusion criteria. Nineteen studies measured CPCs by flow cytometry, only one study examined CECs. A total of 647 PAH patients were included across all 19 CPC studies. Marker schemes chosen to define CPCs, and the methods of flow cytometry used, varied significantly across studies. Meta-analysis of a subgroup of CPC studies (n = 8) similarly identified a significant amount of heterogeneity even amongst studies using the same marker scheme. In conclusion, a systematic review of CPC studies in PAH patients reveals the limitations of the current literature. Future studies should include contemporary risk assessments, disease duration, reporting of comorbid conditions, and serial sampling over time. Furthermore, methods that incorporate best practices for detecting rare cell populations by flow cytometry are essential and should be reported in sufficient detail in future publications. With the emergence of single-cell technologies, future studies of circulating progenitor and endothelial cells in PAH remain relevant and may incorporate several insights from the current review to build upon the existing literature.

Endothelial PHD2 deficiency induces apoptosis resistance and inflammation via AKT activation and AIP1 loss independent of HIF2α

In hypoxic and pseudohypoxic rodent models of pulmonary hypertension (PH), hypoxia-inducible factor (HIF) inhibition attenuates disease initiation. However, HIF activation alone, due to genetic alterations or use of inhibitors of prolyl hydroxylase domain (PHD) enzymes, has not been definitively shown to cause PH in humans, indicating the involvement of other mechanisms. Given the association between endothelial cell dysfunction and PH, the effects of pseudohypoxia and its underlying pathways were investigated in primary human lung endothelial cells. PHD2 silencing or inhibition, while activating HIF2α, induced apoptosis-resistance and IFN/STAT activation in endothelial cells, independent of HIF signaling. Mechanistically, PHD2 deficiency activated AKT and ERK, inhibited JNK, and reduced AIP1 (ASK1-interacting protein 1), all independent of HIF2α. Like PHD2, AIP1 silencing affected these same kinase pathways and produced a similar dysfunctional endothelial cell phenotype, which was partially reversed by AKT inhibition. Consistent with these in vitro findings, AIP1 protein levels in lung endothelial cells were decreased in Tie2-Cre/Phd2 knockout mice compared with wild-type controls. Lung vascular endothelial cells from patients with pulmonary arterial hypertension (PAH) showed IFN/STAT activation. Lung tissue from both SU5416/hypoxia PAH rats and patients with PAH all showed AKT activation and dysregulated AIP1 expression. In conclusion, PHD2 deficiency in lung vascular endothelial cells drives an apoptosis-resistant and inflammatory phenotype, mediated by AKT activation and AIP1 loss independent of HIF signaling. Targeting these pathways, including PHD2, AKT, and AIP1, holds the potential for developing new treatments for endothelial dysfunction in PH.NEW & NOTEWORTHY HIF activation alone does not conclusively lead to human PH, suggesting that HIF-independent signaling may also contribute to hypoxia-induced PH. This study demonstrated that PHD2 silencing-induced pseudohypoxia in human lung endothelial cells suppresses apoptosis and activates STAT, effects that persist despite HIF2α inhibition or knockdown and are attributed to AKT and ERK activation, JNK inhibition, and AIP1 loss. These findings align with observations in lung endothelial cells and tissues from PAH rodent models and patients.

A multimodal approach identifies lactate as a central feature of right ventricular failure that is detectable in human plasma

Background

In PAH metabolic abnormalities in multiple pathways are well-recognized features of right ventricular dysfunction, however, prior work has focused mainly on the use of a single "omic" modality to describe a single deranged pathway. We integrated metabolomic and epigenomic data using transcriptomics in failing and non-failing RVs from a rodent model to provide novel mechanistic insight and translated these findings to accessible human specimens by correlation with plasma from PAH patients.

Methods

Study was conducted in a doxycycline-inducible BMPR2 mutant mouse model of RV failure. Plasma was collected from controls and PAH patients. Transcriptomic and metabolomic analyses were done on mouse RV tissue and human plasma. For mouse RV, we layered metabolomic and transcriptomic data for multiple metabolic pathways and compared our findings with metabolomic and transcriptomic data obtained for human plasma. We confirmed our key findings in cultured cardiomyocyte cells with BMPR2 mutation.

Results

In failing mouse RVs, (1) in the glycolysis pathway, glucose is converted to lactate via aerobic glycolysis, but may also be utilized for glycogen, fatty acid, and nucleic acid synthesis, (2) in the fatty acid pathway, FAs are accumulated in the cytoplasm because the transfer of FAs to mitochondria is reduced, however, the ß-oxidation pathway is likely to be functional. (3) the TCA cycle is altered at multiple checkpoints and accumulates citrate, and the glutaminolysis pathway is not activated. In PAH patients, plasma metabolic and transcriptomic data indicated that unlike in the failing BMPR2 mutant RV, expression of genes and metabolites measured for the glycolysis pathway, FA pathway, TCA cycle, and glutaminolysis pathway were increased. Lactate was the only metabolite that was increased both in RV and circulation. We confirmed using a stable isotope of lactate that cultured cardiomyocytes with mutant BMPR2 show a modest increase in endogenous lactate, suggesting a possibility of an increase in lactate production by cardiomyocytes in failing BMPR2 mutant RV.

Conclusion

In the failing RV with mutant BMPR2, lactate is produced by RV cardiomyocytes and may be secreted out, thereby increasing lactate in circulation. Lactate can potentially serve as a marker of RV dysfunction in PAH, which warrants investigation.

Novel Role of Endothelial CD45 in Regulating Endothelial-to-Mesenchymal Transition in Atherosclerosis

Background

Protein-tyrosine-phosphatase CD45 is exclusively expressed in all nucleated cells of the hematopoietic system but is rarely expressed in endothelial cells. Interestingly, our recent study indicated that activation of the endogenous CD45 promoter in human endothelial colony forming cells (ECFCs) induced expression of multiple EndoMT marker genes. However, the detailed molecular mechanisms underlying CD45 that drive EndoMT and the therapeutic potential of manipulation of CD45 expression in atherosclerosis are entirely unknown.

Method

We generated a tamoxifen-inducible EC-specific CD45 deficient mouse strain (EC-iCD45KO) in an ApoE-deficient (ApoE-/-) background and fed with a Western diet (C57BL/6) for atherosclerosis and molecular analyses. We isolated and enriched mouse aortic endothelial cells with CD31 beads to perform single-cell RNA sequencing. Biomedical, cellular, and molecular approaches were utilized to investigate the role of endothelial CD45-specific deletion in the prevention of EndoMT in ApoE-/- model of atherosclerosis.

Results

Single-cell RNA sequencing revealed that loss of endothelial CD45 inhibits EndoMT marker expression and transforming growth factor-β signaling in atherosclerotic mice. which is associated with the reductions of lesions in the ApoE-/- mouse model. Mechanistically, the loss of endothelial cell CD45 results in increased KLF2 expression, which inhibits transforming growth factor-β signaling and EndoMT. Consistently, endothelial CD45 deficient mice showed reduced lesion development, plaque macrophages, and expression of cell adhesion molecules when compared to ApoE-/- controls.

Conclusions

These findings demonstrate that the loss of endothelial CD45 protects against EndoMT-driven atherosclerosis, promoting KLF2 expression while inhibiting TGFβ signaling and EndoMT markers. Thus, targeting endothelial CD45 may be a novel therapeutic strategy for EndoMT and atherosclerosis.

Charting the cellular landscape of pulmonary arterial hypertension through single-cell omics

This review examines how single-cell omics technologies, particularly single-cell RNA sequencing (scRNAseq), enhance our understanding of pulmonary arterial hypertension (PAH). PAH is a multifaceted disorder marked by pulmonary vascular remodeling, leading to high morbidity and mortality. The cellular pathobiology of this heterogeneous disease, involving various vascular and non-vascular cell types, is not fully understood. Traditional PAH studies have struggled to resolve the complexity of pathogenic cell populations. scRNAseq offers a refined perspective by detailing cellular diversity within PAH, identifying unique cell subsets, gene networks, and molecular pathways that drive the disease. We discuss significant findings from recent literature, summarizing how scRNAseq has shifted our understanding of PAH in human, rat, and mouse models. This review highlights the insights gained into cellular phenotypes, gene expression patterns, and novel molecular targets, and contemplates the challenges and prospective paths for research. We propose ways in which single-cell omics could inform future research and translational efforts to combat PAH.

Ddx5 Targeted Epigenetic Modification of Pericytes in Pulmonary Hypertension After Intrauterine Growth Restriction

Newborns with intrauterine growth restriction (IUGR) have a higher likelihood of developing pulmonary arterial hypertension (PAH) in adulthood. Although there is increasing evidence suggesting that pericytes play a role in regulating myofibroblast transdifferentiation and angiogenesis in malignant and cardiovascular diseases, their involvement in the pathogenesis of IUGR-related pulmonary hypertension and the underlying mechanisms remain incompletely understood. To address this issue, a study was conducted using a Sprague-Dawley rat model of IUGR-related pulmonary hypertension. Our investigation revealed increased proliferation and migration of pulmonary microvascular pericytes in IUGR-related pulmonary hypertension, accompanied by weakened endothelial-pericyte interactions. Through whole-transcriptome sequencing, Ddx5 (DEAD-box protein 5) was identified as one of the hub genes in pericytes. DDX5, a member of the RNA helicase family, plays a role in the regulation of ATP-dependent RNA helicase activities and cellular function. MicroRNAs have been implicated in the pathogenesis of PAH, and microRNA-205 (miR-205) regulates cell proliferation, migration, and angiogenesis. The results of dual-luciferase reporter assays confirmed the specific binding of miR-205 to Ddx5. Mechanistically, miR-205 negatively regulates Ddx5, leading to the degradation of β-catenin by inhibiting the phosphorylation of Gsk3β at serine 9. In vitro experiments showed the addition of miR-205 effectively ameliorated pericyte dysfunction. Furthermore, in vivo experiments demonstrated that miR-205 agomir could ameliorate pulmonary hypertension. Our findings indicated that the downregulation of miR-205 expression mediates pericyte dysfunction through the activation of Ddx5. Therefore, targeting the miR-205/Ddx5/p-Gsk3β/β-catenin axis could be a promising therapeutic approach for IUGR-related pulmonary hypertension.

Single-cell RNA sequencing reveals cancer stem-like cells and dynamics in tumor microenvironment during cholangiocarcinoma progression

Cholangiocarcinoma is a malignancy of the bile ducts that is driven by activities of cancer stem-like cells and characterized by a heterogeneous tumor microenvironment. To better understand the transcriptional profiles of cancer stem-like cells and dynamics in the tumor microenvironment during the progression of cholangiocarcinoma, we performed single-cell RNA analysis on cells collected from three different timepoints of tumorigenesis in a YAP/AKT mouse model. Bulk RNA sequencing data from TCGA (The Cancer Genome Atlas program) and ICGC cohorts were used to verify and support the finding. In vitro and in vivo experiments were performed to assess the stemness of cancer stem-like cells. We identified Tm4sf1high malignant cells as cancer stem-like cells. Across timepoints of cholangiocarcinoma formation in YAP/AKT mice, we found dynamic change in cancer stem-like cell/stromal/immune cell composition. Nevertheless, the dynamic interaction among cancer stem-like cells, immune cells, and stromal cells at different timepoints was elaborated. Collectively, these data serve as a useful resource for better understanding cancer stem-like cell and malignant cell heterogeneity, stromal cell remodeling, and immune cell reprogramming. It also sheds new light on transcriptomic dynamics during cholangiocarcinoma progression at single-cell resolution.