Lung lymphatic endothelial cells undergo inflammatory and prothrombotic changes in a model of chronic obstructive pulmonary disease.

The lymphatic vasculature regulates lung homeostasis through drainage of fluid and trafficking of immune cells and plays a key role in the response to lung injury in several disease states. We have previously shown that lymphatic dysfunction occurs early in the pathogenesis of chronic obstructive pulmonary disease (COPD) caused by cigarette smoke (CS) and that this is associated with increased thrombin and fibrin clots in lung lymph. However, the direct effects of CS and thrombin on lymphatic endothelial cells (LECs) in COPD are not entirely clear. Studies of the blood vasculature have shown that COPD is associated with increased thrombin after CS exposure that causes endothelial dysfunction characterized by changes in the expression of coagulation factors and leukocyte adhesion proteins. Here, we determined whether similar changes occur in LECs. We used an in vitro cell culture system and treated human lung microvascular lymphatic endothelial cells with cigarette smoke extract (CSE) and/or thrombin. We found that CSE treatment led to decreased fibrinolytic activity in LECs, which was associated with increased expression of plasminogen activator inhibitor 1 (PAI-1). LECs treated with both CSE and thrombin together had a decreased expression of tissue factor pathway inhibitor (TFPI) and increased expression of adhesion molecules. RNA sequencing of lung LECs isolated from mice exposed to CS also showed upregulation of prothrombotic and inflammatory pathways at both acute and chronic exposure time points. Analysis of publicly available single-cell RNA sequencing of LECs as well as immunohistochemical staining of lung tissue from COPD patients supported these data and showed increased expression of inflammatory markers in LECs from COPD patients compared to those from controls. These studies suggest that in parallel with blood vessels, the lymphatic endothelium undergoes inflammatory changes associated with CS exposure and increased thrombin in COPD. Further research is needed to unravel the mechanisms by which these changes affect lymphatic function and drive tissue injury in COPD.

Lymphatic Dysfunction Models an Autoimmune Emphysema Phenotype of Chronic Obstructive Pulmonary Disease.

Chronic Obstructive Pulmonary Disease (COPD) is a heterogeneous disease that is characterized by many clinical phenotypes. One such phenotype of COPD is defined by emphysema, pathogenic lung tertiary lymphoid organs (TLOs), and autoantibody production. We have previously shown that lymphatic dysfunction can cause lung TLO formation and lung injury in mice. We now sought to uncover whether underlying lymphatic dysfunction may be a driver of lung injury in cigarette smoke (CS)-induced COPD. We found that lung TLOs in mice with lymphatic dysfunction produce autoantibodies and are associated with a lymphatic endothelial cell subtype that expresses antigen presentation genes. Mice with underlying lymphatic dysfunction develop increased emphysema after CS exposure, with increased size and activation of TLOs. CS further increased autoantibody production in mice with lymphatic dysfunction. B-cell blockade prevented TLO formation and decreased lung injury after CS in mice with lymphatic dysfunction. Using tissue from human COPD patients, we also found evidence of a lymphatic gene signature that was specific to patients with emphysema and prominent TLOs compared to COPD patients without emphysema. Taken together, these data suggest that lymphatic dysfunction may underlie lung injury in a subset of COPD patients with an autoimmune emphysema phenotype.

Transcriptional Activation of Regenerative Hematopoiesis via Vascular Niche Sensing.

Transition between activation and quiescence programs in hematopoietic stem and progenitor cells (HSC/HSPCs) is perceived to be governed intrinsically and by microenvironmental co-adaptation. However, HSC programs dictating both transition and adaptability, remain poorly defined. Single cell multiome analysis divulging differential transcriptional activity between distinct HSPC states, indicated for the exclusive absence of Fli-1 motif from quiescent HSCs. We reveal that Fli-1 activity is essential for HSCs during regenerative hematopoiesis. Fli-1 directs activation programs while manipulating cellular sensory and output machineries, enabling HSPCs co-adoptability with a stimulated vascular niche. During regenerative conditions, Fli-1 presets and enables propagation of niche-derived Notch1 signaling. Constitutively induced Notch1 signaling is sufficient to recuperate functional HSC impairments in the absence of Fli-1. Applying FLI-1 modified-mRNA transduction into lethargic adult human mobilized HSPCs, enables their vigorous niche-mediated expansion along with superior engraftment capacities. Thus, decryption of stem cell activation programs offers valuable insights for immune regenerative medicine.

Inflammatory responses in the placenta upon SARS-CoV-2 infection late in pregnancy.

The effect of SARS-CoV-2 infection on placental function is not well understood. Analysis of placentas from women who tested positive at delivery showed SARS-CoV-2 genomic and subgenomic RNA in 22 out of 52 placentas. Placentas from two mothers with symptomatic COVID-19 whose pregnancies resulted in adverse outcomes for the fetuses contained high levels of viral Alpha variant RNA. The RNA was localized to the trophoblasts that cover the fetal chorionic villi in direct contact with maternal blood. The intervillous spaces and villi were infiltrated with maternal macrophages and T cells. Transcriptome analysis showed an increased expression of chemokines and pathways associated with viral infection and inflammation. Infection of placental cultures with live SARS-CoV-2 and spike protein-pseudotyped lentivirus showed infection of syncytiotrophoblast and, in rare cases, endothelial cells mediated by ACE2 and Neuropilin-1. Viruses with Alpha, Beta, and Delta variant spikes infected the placental cultures at significantly greater levels.

Specification of fetal liver endothelial progenitors to functional zonated adult sinusoids requires c-Maf induction.

The liver vascular network is patterned by sinusoidal and hepatocyte co-zonation. How intra-liver vessels acquire their hierarchical specialized functions is unknown. We study heterogeneity of hepatic vascular cells during mouse development through functional and single-cell RNA-sequencing. The acquisition of sinusoidal endothelial cell identity is initiated during early development and completed postnatally, originating from a pool of undifferentiated vascular progenitors at E12. The peri-natal induction of the transcription factor c-Maf is a critical switch for the sinusoidal identity determination. Endothelium-restricted deletion of c-Maf disrupts liver sinusoidal development, aberrantly expands postnatal liver hematopoiesis, promotes excessive postnatal sinusoidal proliferation, and aggravates liver pro-fibrotic sensitivity to chemical insult. Enforced c-Maf overexpression in generic human endothelial cells switches on a liver sinusoidal transcriptional program that maintains hepatocyte function. c-Maf represents an inducible intra-organotypic and niche-responsive molecular determinant of hepatic sinusoidal cell identity and lays the foundation for the strategies for vasculature-driven liver repair.

Disulfiram inhibits neutrophil extracellular trap formation and protects rodents from acute lung injury and SARS-CoV-2 infection.

Severe acute lung injury has few treatment options and a high mortality rate. Upon injury, neutrophils infiltrate the lungs and form neutrophil extracellular traps (NETs), damaging the lungs and driving an exacerbated immune response. Unfortunately, no drug preventing NET formation has completed clinical development. Here, we report that disulfiram - an FDA-approved drug for alcohol use disorder - dramatically reduced NETs, increased survival, improved blood oxygenation, and reduced lung edema in a transfusion-related acute lung injury (TRALI) mouse model. We then tested whether disulfiram could confer protection in the context of SARS-CoV-2 infection, as NETs are elevated in patients with severe COVID-19. In SARS-CoV-2-infected golden hamsters, disulfiram reduced NETs and perivascular fibrosis in the lungs, and it downregulated innate immune and complement/coagulation pathways, suggesting that it could be beneficial for patients with COVID-19. In conclusion, an existing FDA-approved drug can block NET formation and improve disease course in 2 rodent models of lung injury for which treatment options are limited.

SATB2 preserves colon stem cell identity and mediates ileum-colon conversion via enhancer remodeling.

Adult stem cells maintain regenerative tissue structure and function by producing tissue-specific progeny, but the factors that preserve their tissue identities are not well understood. The small and large intestines differ markedly in cell composition and function, reflecting their distinct stem cell populations. Here we show that SATB2, a colon-restricted chromatin factor, singularly preserves LGR5+ adult colonic stem cell and epithelial identity in mice and humans. Satb2 loss in adult mice leads to stable conversion of colonic stem cells into small intestine ileal-like stem cells and replacement of the colonic mucosa with one that resembles the ileum. Conversely, SATB2 confers colonic properties on the mouse ileum. Human colonic organoids also adopt ileal characteristics upon SATB2 loss. SATB2 regulates colonic identity in part by modulating enhancer binding of the intestinal transcription factors CDX2 and HNF4A. Our study uncovers a conserved core regulator of colonic stem cells able to mediate cross-tissue plasticity in mature intestines.

Cooperative ETS Transcription Factors Enforce Adult Endothelial Cell Fate and Cardiovascular Homeostasis.

Current dogma dictates that during adulthood, endothelial cells (ECs) are locked in an immutable stable homeostatic state. By contrast, herein we show that maintenance of EC fate and function are linked and active processes, which depend on the constitutive cooperativity of only two ETS-transcription factors (TFs) ERG and Fli1. While deletion of either Fli1 or ERG manifest subtle vascular dysfunction, their combined genetic deletion in adult EC results in acute vasculopathy and multiorgan failure, due to loss of EC fate and integrity, hyperinflammation, and spontaneous thrombosis, leading to death. ERG and Fli1 co-deficiency cause rapid transcriptional silencing of pan- and organotypic vascular core genes, with dysregulation of inflammation and coagulation pathways. Vascular hyperinflammation leads to impaired hematopoiesis with myeloid skewing. Accordingly, enforced ERG and FLI1 expression in adult human mesenchymal stromal cells activates vascular programs and functionality enabling engraftment of perfusable vascular network. GWAS-analysis identified vascular diseases are associated with FLI1/Erg mutations. Constitutive expression of ERG and Fli1 uphold EC fate, physiological function, and resilience in adult vasculature; while their functional loss can contribute to systemic human diseases.

Cardiomyocytes recruit monocytes upon SARS-CoV-2 infection by secreting CCL2.

Heart injury has been reported in up to 20% of COVID-19 patients, yet the cause of myocardial histopathology remains unknown. Here, using an established in vivo hamster model, we demonstrate that SARS-CoV-2 can be detected in cardiomyocytes of infected animals. Furthermore, we found damaged cardiomyocytes in hamsters and COVID-19 autopsy samples. To explore the mechanism, we show that both human pluripotent stem cell-derived cardiomyocytes (hPSC-derived CMs) and adult cardiomyocytes (CMs) can be productively infected by SARS-CoV-2, leading to secretion of the monocyte chemoattractant cytokine CCL2 and subsequent monocyte recruitment. Increased CCL2 expression and monocyte infiltration was also observed in the hearts of infected hamsters. Although infected CMs suffer damage, we find that the presence of macrophages significantly reduces SARS-CoV-2-infected CMs. Overall, our study provides direct evidence that SARS-CoV-2 infects CMs in vivo and suggests a mechanism of immune cell infiltration and histopathology in heart tissues of COVID-19 patients.

Reversal of emphysema by restoration of pulmonary endothelial cells.

Chronic obstructive pulmonary disease (COPD) is marked by airway inflammation and airspace enlargement (emphysema) leading to airflow obstruction and eventual respiratory failure. Microvasculature dysfunction is associated with COPD/emphysema. However, it is not known if abnormal endothelium drives COPD/emphysema pathology and/or if correcting endothelial dysfunction has therapeutic potential. Here, we show the centrality of endothelial cells to the pathogenesis of COPD/emphysema in human tissue and using an elastase-induced murine model of emphysema. Airspace disease showed significant endothelial cell loss, and transcriptional profiling suggested an apoptotic, angiogenic, and inflammatory state. This alveolar destruction was rescued by intravenous delivery of healthy lung endothelial cells. Leucine-rich α-2-glycoprotein-1 (LRG1) was a driver of emphysema, and deletion of Lrg1 from endothelial cells rescued vascular rarefaction and alveolar regression. Hence, targeting endothelial cell biology through regenerative methods and/or inhibition of the LRG1 pathway may represent strategies of immense potential for the treatment of COPD/emphysema.

Human Induced Pluripotent Stem Cell-Derived Brain Endothelial Cells: Current Controversies.

Brain microvascular endothelial cells (BMECs) possess unique properties that are crucial for many functions of the blood-brain-barrier (BBB) including maintenance of brain homeostasis and regulation of interactions between the brain and immune system. The generation of a pure population of putative brain microvascular endothelial cells from human pluripotent stem cell sources (iBMECs) has been described to meet the need for reliable and reproducible brain endothelial cells in vitro. Human pluripotent stem cells (hPSCs), embryonic or induced, can be differentiated into large quantities of specialized cells in order to study development and model disease. These hPSC-derived iBMECs display endothelial-like properties, such as tube formation and low-density lipoprotein uptake, high transendothelial electrical resistance (TEER), and barrier-like efflux transporter activities. Over time, the de novo generation of an organotypic endothelial cell from hPSCs has aroused controversies. This perspective article highlights the developments made in the field of hPSC derived brain endothelial cells as well as where experimental data are lacking, and what concerns have emerged since their initial description.

An Immuno-Cardiac Model for Macrophage-Mediated Inflammation in COVID-19 Hearts.

[Figure: see text].

Endothelial Jak3 expression enhances pro-hematopoietic angiocrine function in mice.

Jak3 is the only non-promiscuous member of the Jak family of secondary messengers. Studies to date have focused on understanding and targeting the cell-autonomous role of Jak3 in immunity, while functional Jak3 expression outside the hematopoietic system remains largely unreported. We show that Jak3 is expressed in endothelial cells across hematopoietic and non-hematopoietic organs, with heightened expression in the bone marrow. The bone marrow niche is understood as a network of different cell types that regulate hematopoietic function. We show that the Jak3-/- bone marrow niche is deleterious for the maintenance of long-term repopulating hematopoietic stem cells (LT-HSCs) and that JAK3-overexpressing endothelial cells have increased potential to expand LT-HSCs in vitro. This work may serve to identify a novel function for a highly specific tyrosine kinase in the bone marrow vascular niche and to further characterize the LT-HSC function of sinusoidal endothelium.

Pluripotent stem cell-derived epithelium misidentified as brain microvascular endothelium requires ETS factors to acquire vascular fate.

Cells derived from pluripotent sources in vitro must resemble those found in vivo as closely as possible at both transcriptional and functional levels in order to be a useful tool for studying diseases and developing therapeutics. Recently, differentiation of human pluripotent stem cells (hPSCs) into brain microvascular endothelial cells (ECs) with blood-brain barrier (BBB)-like properties has been reported. These cells have since been used as a robust in vitro BBB model for drug delivery and mechanistic understanding of neurological diseases. However, the precise cellular identity of these induced brain microvascular endothelial cells (iBMECs) has not been well described. Employing a comprehensive transcriptomic metaanalysis of previously published hPSC-derived cells validated by physiological assays, we demonstrate that iBMECs lack functional attributes of ECs since they are deficient in vascular lineage genes while expressing clusters of genes related to the neuroectodermal epithelial lineage (Epi-iBMEC). Overexpression of key endothelial ETS transcription factors (ETV2, ERG, and FLI1) reprograms Epi-iBMECs into authentic endothelial cells that are congruent with bona fide endothelium at both transcriptomic as well as some functional levels. This approach could eventually be used to develop a robust human BBB model in vitro that resembles the human brain EC in vivo for functional studies and drug discovery.

Identification of SARS-CoV-2 inhibitors using lung and colonic organoids.

There is an urgent need to create novel models using human disease-relevant cells to study severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) biology and to facilitate drug screening. Here, as SARS-CoV-2 primarily infects the respiratory tract, we developed a lung organoid model using human pluripotent stem cells (hPSC-LOs). The hPSC-LOs (particularly alveolar type-II-like cells) are permissive to SARS-CoV-2 infection, and showed robust induction of chemokines following SARS-CoV-2 infection, similar to what is seen in patients with COVID-19. Nearly 25% of these patients also have gastrointestinal manifestations, which are associated with worse COVID-19 outcomes1. We therefore also generated complementary hPSC-derived colonic organoids (hPSC-COs) to explore the response of colonic cells to SARS-CoV-2 infection. We found that multiple colonic cell types, especially enterocytes, express ACE2 and are permissive to SARS-CoV-2 infection. Using hPSC-LOs, we performed a high-throughput screen of drugs approved by the FDA (US Food and Drug Administration) and identified entry inhibitors of SARS-CoV-2, including imatinib, mycophenolic acid and quinacrine dihydrochloride. Treatment at physiologically relevant levels of these drugs significantly inhibited SARS-CoV-2 infection of both hPSC-LOs and hPSC-COs. Together, these data demonstrate that hPSC-LOs and hPSC-COs infected by SARS-CoV-2 can serve as disease models to study SARS-CoV-2 infection and provide a valuable resource for drug screening to identify candidate COVID-19 therapeutics.

SARS-CoV-2 Infected Cardiomyocytes Recruit Monocytes by Secreting CCL2.

Heart injury has been reported in up to 20% of COVID-19 patients, yet the cause of myocardial histopathology remains unknown. In order to study the cause of myocardial pathology in COVID-19 patients, we used a hamster model to determine whether following infection SARS-CoV-2, the causative agent of COVID-19, can be detected in heart tissues. Here, we clearly demonstrate that viral RNA and nucleocapsid protein is present in cardiomyocytes in the hearts of infected hamsters. Interestingly, functional cardiomyocyte associated gene expression was decreased in infected hamster hearts, corresponding to an increase in reactive oxygen species (ROS). This data using an animal model was further validated using autopsy heart samples of COVID-19 patients. Moreover, we show that both human pluripotent stem cell-derived cardiomyocytes (hPSC-derived CMs) and adult cardiomyocytes (CMs) can be infected by SARS-CoV-2 and that CCL2 is secreted upon SARS-CoV-2 infection, leading to monocyte recruitment. Increased CCL2 expression and macrophage infiltration was also observed in the hearts of infected hamsters. Using single cell RNA-seq, we also show that macrophages are able to decrease SARS-CoV-2 infection of CMs. Overall, our study provides direct evidence that SARS-CoV-2 infects CMs in vivo and proposes a mechanism of immune-cell infiltration and pathology in heart tissue of COVID-19 patients.

Identification of Candidate COVID-19 Therapeutics using hPSC-derived Lung Organoids.

The SARS-CoV-2 virus has caused already over 3.5 million COVID-19 cases and 250,000 deaths globally. There is an urgent need to create novel models to study SARS-CoV-2 using human disease-relevant cells to understand key features of virus biology and facilitate drug screening. As primary SARS-CoV-2 infection is respiratory-based, we developed a lung organoid model using human pluripotent stem cells (hPSCs) that could be adapted for drug screens. The lung organoids, particularly aveolar type II cells, express ACE2 and are permissive to SARS-CoV-2 infection. Transcriptomic analysis following SARS-CoV-2 infection revealed a robust induction of chemokines and cytokines with little type I/III interferon signaling, similar to that observed amongst human COVID-19 pulmonary infections. We performed a high throughput screen using hPSC-derived lung organoids and identified FDA-approved drug candidates, including imatinib and mycophenolic acid, as inhibitors of SARS-CoV-2 entry. Pre- or post-treatment with these drugs at physiologically relevant levels decreased SARS-CoV-2 infection of hPSC-derived lung organoids. Together, these data demonstrate that hPSC-derived lung cells infected by SARS-CoV-2 can model human COVID-19 disease and provide a valuable resource to screen for FDA-approved drugs that might be repurposed and should be considered for COVID-19 clinical trials.

A Human Pluripotent Stem Cell-based Platform to Study SARS-CoV-2 Tropism and Model Virus Infection in Human Cells and Organoids.

SARS-CoV-2 has caused the COVID-19 pandemic. There is an urgent need for physiological models to study SARS-CoV-2 infection using human disease-relevant cells. COVID-19 pathophysiology includes respiratory failure but involves other organ systems including gut, liver, heart, and pancreas. We present an experimental platform comprised of cell and organoid derivatives from human pluripotent stem cells (hPSCs). A Spike-enabled pseudo-entry virus infects pancreatic endocrine cells, liver organoids, cardiomyocytes, and dopaminergic neurons. Recent clinical studies show a strong association with COVID-19 and diabetes. We find that human pancreatic beta cells and liver organoids are highly permissive to SARS-CoV-2 infection, further validated using adult primary human islets and adult hepatocyte and cholangiocyte organoids. SARS-CoV-2 infection caused striking expression of chemokines, as also seen in primary human COVID-19 pulmonary autopsy samples. hPSC-derived cells/organoids provide valuable models for understanding the cellular responses of human tissues to SARS-CoV-2 infection and for disease modeling of COVID-19.