Molecular characterization of lymphatic endothelial cells

SCIG: Machine learning uncovers cell identity genes in single cells by genetic sequence codes

Deciphering cell identity genes is pivotal to understanding cell differentiation, development, and cell identity dysregulation involving diseases. Here, we introduce SCIG, a machine-learning method to uncover cell identity genes in single cells. In alignment with recent reports that cell identity genes (CIGs) are regulated with unique epigenetic signatures, we found CIGs exhibit distinctive genetic sequence signatures, e.g. unique enrichment patterns of cis-regulatory elements. Using these genetic sequence signatures, along with gene expression information from single-cell RNA-seq data, SCIG uncovers the identity genes of a cell without a need for comparison to other cells. CIG score defined by SCIG surpassed expression value in network analysis to reveal the master transcription factors (TFs) regulating cell identity. Applying SCIG to the human endothelial cell atlas revealed that the tissue microenvironment is a critical supplement to master TFs for cell identity refinement. SCIG is publicly available at https://doi.org/10.5281/zenodo.14726426  , offering a valuable tool for advancing cell differentiation, development, and regenerative medicine research.

[Anatomy and physiology of the lymph system : What clinicians should know]

The lymphatic vessels are a unidirectional, centripetal system that collects interstitial fluid from tissues and organs, directing it into the venous system. The lymphatic vessels can be categorized into four types: initial lymphatic vessels, precollectors, collectors, and lymphatic trunks. Initial lymphatic vessels comprise interconnected networks characterized by larger mash sizes compared to blood capillaries and are lined with a specialized endothelium. They have interendothelial openings that allow exchange with the surrounding tissue. These vessels also have characteristic markers such as VEGFR‑3, podoplanin, and LYVE‑1. Precollectors have smooth muscle cells that are still arranged irregularly and parietal valves that promote centripetal lymph flow. Collectors have also valves and a continuous layer of spirally arranged muscle fibers that allow the vessels to pulse and contract. This contraction causes the lymph to be transported from one lymphangion to the next. Lymphatic trunks form the next section and often flow into the thoracic duct, which opens into the venous system. Lymph nodes are situated along the course of the collectors and trunks and serve as filter centers to intercept pathogens and increase the colloid osmotic pressure of the lymph. They are organized into groups with a specific structure with cortex, medulla, and embedded B and T lymphocytes. The central lymphatic system transports lymph through segmental connections and anastomoses. The thoracic duct empties into the left venous angle and collects also other lymphatic truncs. The thoracic duct's developmental history and variations occasionally lead to anatomical anomalies.

A vasculature-resident innate lymphoid cell population in mouse lungs

Tissue-resident immune cells such as innate lymphoid cells (ILC) are known to reside in the parenchymal compartments of tissues and modulate local immune protection. Here we use intravascular cell labeling, parabiosis and multiplex 3D imaging to identify a population of group 3 ILCs in mice that are present within the intravascular space of lung blood vessels (vILC3). vILC3s are distributed broadly in alveolar capillary beds from which inhaled pathogens enter the lung parenchyma. By contrast, conventional ILC3s in tissue parenchyma are enriched in lymphoid clusters in proximity to large veins. In a mouse model of pneumonia, Pseudomonas aeruginosa infection results in rapid vILC3 expansion and production of chemokines including CCL4. Blocking CCL4 in vivo attenuates neutrophil recruitment to the lung at the early stage of infection, resulting in prolonged inflammation and delayed bacterial clearance. Our findings thus define the intravascular space as a site of ILC residence in mice, and reveal a unique immune cell population that interfaces with tissue alarmins and the circulating immune system for timely host defense.

Regulatory T cell and endothelial cell crosstalk

Regulatory T (Treg) cells have a central role in the maintenance of immune surveillance and tolerance. They can migrate from lymphoid organs to blood and then into tissues and egress from tissues into draining lymph nodes. Specialized endothelial cells of blood and lymphatic vessels are the key gatekeepers for these processes. Treg cells that transmigrate across single-cell layers of endothelial cells engage in bidirectional crosstalk with these cells and regulate vascular permeability by promoting structural modifications of blood and lymphatic endothelial cells. In turn, blood and lymphatic endothelial cells can modulate Treg cell recirculation and residency. Here, we discuss recent insights into the cellular and molecular mechanisms of the crosstalk between Treg cells and endothelial cells and explore potential therapeutic strategies to target these interactions in autoimmunity, transplantation and cancer.

Multifaceted Role of Notch Signaling in Vascular Health and Diseases

Notch signaling is evolutionarily conserved from Drosophila to mammals and it functions as an essential modulator of vascular growth and development by directing endothelial cell specification, proliferation, migration, arteriovenous differentiation, inflammation, and apoptosis. The interplay between Notch and other signaling pathways plays a homeostatic role by modulating multiple vascular functions, including permeability regulation, angiogenesis, and vascular remodeling. This review explores current knowledge on Notch signaling in vascular development, homeostasis, and disease. It also discusses recent developments in understanding how endothelial Notch signaling affects vascular inflammation via cytokines or aberrant shear stress in endothelial cells while addressing the reciprocal relationship between Notch signaling and inflammation.

Lymphangiomas with the presence of erythrocytes in mesenteric lymph nodes of Wistar Hannover rats

We performed morphological and immunohistochemical analyses of erythrocyte-rich vascular proliferative lesions of mesenteric lymph nodes in six male and one female Wistar Hannover rats. These lesions are conventionally diagnosed as hemangiomas due to abundant erythrocytes. Immunostaining was positive for prospero-related homeobox 1 (Prox-1) and/or vascular endothelial growth factor receptor 3 (VEGFR3) in all lesions, suggesting a lymphangitic origin. In 6 of 7 lesions, von Willebrand factor (vWF) immunostaining was negative, suggesting a non-blood vascular origin. These results demonstrated that almost all hemangiomas in rat mesenteric lymph nodes were lymphangiomas. To the best of our knowledge, this is the first report highlighting the lymphatic origin of vascular proliferative lesions in the mesenteric lymph nodes of rats.

Molecules That Have Rarely Been Studied in Lymphatic Endothelial Cells

A number of standard molecules are used for the molecular and histological characterization of lymphatic endothelial cells (LECs), including lymphatic vessel endothelial hyaluronan receptor 1 (LYVE1), Podoplanin (D2-40), VEGFR3, Prospero homeobox protein 1 (PROX1), and CD31. The number of molecules whose mutations cause lymphatic malformations or primary congenital lymphedema is considerable, but the majority of these diseases have not yet been characterized at the molecular level. Therefore, there is still considerable scope for molecular and functional studies of the lymphatic vasculature. Using RNASeq, we have previously characterized lymphatic endothelial cells (LECs) under normoxic and hypoxic conditions. We used this information to compare it with immunohistochemical data. We carried out some of the immunohistology ourselves, and systematically studied the Human Protein Atlas, a cell and tissue database based in Sweden. Here we describe molecules that are expressed at RNA and protein levels in LECs, hoping to stimulate future functional studies of these molecules.

Comprehensive identification, isolation, and culture of human breast cell types

Tissues are formed and shaped by cells of many different types and are orchestrated through countless interactions. Deciphering a tissue's biological complexity thus requires studying it at cell-level resolution, where molecular and biochemical features of different cell types can be explored and thoroughly dissected. Unfortunately, the lack of comprehensive methods to identify, isolate, and culture each cell type from many tissues has impeded progress. Here, we present a method for the breadth of cell types composing the human breast. Our goal has long been to understand the essence of each of these different breast cell types, to reveal the underlying biology explaining their intrinsic features, the consequences of interactions, and their contributions to the tissue. This biological exploration has required cell purification, deep-RNA sequencing, and a thorough dissection of the genes and pathways defining each cell type. While the molecular analysis is presented in an adjoining article, we present here an exhaustive cellular dissection of the human breast and explore its cellular composition and histological organization. Moreover, we introduce a novel FACS antibody panel and rigorous gating strategy capable of isolating each of the 12 major breast cell types to purity. Finally, we describe the creation of primary cell models from nearly every breast cell type-some the first of their kind-and submit these as critical tools for studying the dynamic cellular interactions within breast tissues and tumors. Together, this body of work delivers a unique perspective of the breast, revealing insights into its cellular, molecular, and biochemical composition.

Machine Learning Uncovers Vascular Endothelial Cell Identity Genes by Expression Regulation Features in Single Cells

Deciphering cell identity genes is pivotal to understanding cell differentiation, development, and many diseases involving cell identity dysregulation. Here, we introduce SCIG, a machine-learning method to uncover cell identity genes in single cells. In alignment with recent reports that cell identity genes are regulated with unique epigenetic signatures, we found cell identity genes exhibit distinctive genetic sequence signatures, e.g., unique enrichment patterns of cis-regulatory elements. Using these genetic sequence signatures, along with gene expression information from single-cell RNA-seq data, enables SCIG to uncover the identity genes of a cell without a need for comparison to other cells. Cell identity gene score defined by SCIG surpassed expression value in network analysis to uncover master transcription factors regulating cell identity. Applying SCIG to the human endothelial cell atlas revealed that the tissue microenvironment is a critical supplement to master transcription factors for cell identity refinement. SCIG is publicly available at https://github.com/kaifuchenlab/SCIG , offering a valuable tool for advancing cell differentiation, development, and regenerative medicine research.

Single Cell Analysis of Lung Lymphatic Endothelial Cells and Lymphatic Responses during Influenza Infection

Tissue lymphatic vessels network plays critical roles in immune surveillance and tissue homeostasis in response to pathogen invasion, but how lymphatic system per se is remolded during infection is less understood. Here, we observed that influenza infection induces a significant increase of lymphatic vessel numbers in the lung, accompanied with extensive proliferation of lymphatic endothelial cells (LECs). Single-cell RNA sequencing illustrated the heterogeneity of LECs, identifying a novel PD-L1+ subpopulation that is present during viral infection but not at steady state. Specific deletion of Pd-l1 in LECs elevated the expansion of lymphatic vessel numbers during viral infection. Together these findings elucidate a dramatic expansion of lung lymphatic network in response to viral infection, and reveal a PD-L1+ LEC subpopulation that potentially modulates lymphatic vessel remolding.

Glymphatic and lymphatic communication with systemic responses during physiological and pathological conditions in the central nervous system

Crosstalk between central nervous system (CNS) and systemic responses is important in many pathological conditions, including stroke, neurodegeneration, schizophrenia, epilepsy, etc. Accumulating evidence suggest that signals for central-systemic crosstalk may utilize glymphatic and lymphatic pathways. The glymphatic system is functionally connected to the meningeal lymphatic system, and together these pathways may be involved in the distribution of soluble proteins and clearance of metabolites and waste products from the CNS. Lymphatic vessels in the dura and meninges transport cerebrospinal fluid, in part collected from the glymphatic system, to the cervical lymph nodes, where solutes coming from the brain (i.e., VEGFC, oligomeric α-syn, β-amyloid) might activate a systemic inflammatory response. There is also an element of time since the immune system is strongly regulated by circadian rhythms, and both glymphatic and lymphatic dynamics have been shown to change during the day and night. Understanding the mechanisms regulating the brain-cervical lymph node (CLN) signaling and how it might be affected by diurnal or circadian rhythms is fundamental to find specific targets and timing for therapeutic interventions.

Microbial-Dependent Recruitment of Immature Myeloid Cells Promotes Intestinal Regeneration

BACKGROUND & AIMS

The intestinal epithelium functions both in nutrient absorption and as a barrier, separating the luminal contents from a network of vascular, fibroblastic, and immune cells underneath. After injury to the intestine, multiple cell populations cooperate to drive regeneration of the mucosal barrier, including lymphatic endothelial cells (LECs). A population of granulocytic immature myeloid cells (IMCs), marked by Hdc, participate in regeneration of multiple organs such as the colon and central nervous system, and their contribution to intestinal regeneration was investigated.

METHODS

By using male and female histidine decarboxylase (Hdc) green fluorescent reporter (GFP) mice, we investigated the role of Hdc+ IMCs in intestinal regeneration after exposure to 12 Gy whole-body irradiation. The movement of IMCs was analyzed using flow cytometry and immunostaining. Ablation of Hdc+ cells using the HdcCreERT2 tamoxifen-inducible recombinase Cre system, conditional knockout of Prostaglandin-endoperoxidase synthase 2 (Ptgs2) in Hdc+ cells using HdcCre; Ptgs2 floxed mice, and visualization of LECs using Prox1tdTomato mice also was performed. The role of microbial signals was investigated by knocking down mice gut microbiomes using antibiotic cocktail gavages.

RESULTS

We found that Hdc+ IMCs infiltrate the injured intestine after irradiation injury and promote epithelial regeneration in part by modulating LEC activity. Hdc+ IMCs express Ptgs2 (encoding cyclooxygenase-2/COX-2), and enables them to produce prostaglandin E2. Prostaglandin E2 acts on the prostaglandin E2 receptor 4 receptor (EP4) on LECs to promote lymphangiogenesis and induce the expression of proregenerative factors including R-spondin 3. Depletion of gut microbes leads to reduced intestinal regeneration by impaired recruitment of IMCs.

CONCLUSIONS

Altogether, our results unveil a critical role for IMCs in intestinal repair by modulating LEC activity and implicate gut microbes as mediators of intestinal regeneration.

Tumor Abnormality-Oriented Nanomedicine Design

Anticancer nanomedicines have been proven effective in mitigating the side effects of chemotherapeutic drugs. However, challenges remain in augmenting their therapeutic efficacy. Nanomedicines responsive to the pathological abnormalities in the tumor microenvironment (TME) are expected to overcome the biological limitations of conventional nanomedicines, enhance the therapeutic efficacies, and further reduce the side effects. This Review aims to quantitate the various pathological abnormalities in the TME, which may serve as unique endogenous stimuli for the design of stimuli-responsive nanomedicines, and to provide a broad and objective perspective on the current understanding of stimuli-responsive nanomedicines for cancer treatment. We dissect the typical transport process and barriers of cancer drug delivery, highlight the key design principles of stimuli-responsive nanomedicines designed to tackle the series of barriers in the typical drug delivery process, and discuss the "all-into-one" and "one-for-all" strategies for integrating the needed properties for nanomedicines. Ultimately, we provide insight into the challenges and future perspectives toward the clinical translation of stimuli-responsive nanomedicines.

Immunomodulatory properties of the lymphatic endothelium in the tumor microenvironment

The tumor microenvironment (TME) is an intricate complex and dynamic structure composed of various cell types, including tumor, stromal and immune cells. Within this complex network, lymphatic endothelial cells (LECs) play a crucial role in regulating immune responses and influencing tumor progression and metastatic dissemination to lymph node and distant organs. Interestingly, LECs possess unique immunomodulatory properties that can either promote or inhibit anti-tumor immune responses. In fact, tumor-associated lymphangiogenesis can facilitate tumor cell dissemination and metastasis supporting immunoevasion, but also, different molecular mechanisms involved in LEC-mediated anti-tumor immunity have been already described. In this context, the crosstalk between cancer cells, LECs and immune cells and how this communication can shape the immune landscape in the TME is gaining increased interest in recent years. In this review, we present a comprehensive and updated report about the immunomodulatory properties of the lymphatic endothelium within the TME, with special focus on primary tumors and tumor-draining lymph nodes. Furthermore, we outline emerging research investigating the potential therapeutic strategies targeting the lymphatic endothelium to enhance anti-tumor immune responses. Understanding the intricate mechanisms involved in LEC-mediated immune modulation in the TME opens up new possibilities for the development of innovative approaches to fight cancer.

Spontaneous massive fetomaternal hemorrhage: two case reports and a literature review of placental pathology

BACKGROUND

Massive fetomaternal hemorrhage (FMH) is a rare event during pregnancy that may cause severe fetal anemia or death.

CASE PRESENTATION

This paper reports two cases of fetomaternal hemorrhage with unexplained reasons. Both cases required emergency caesarean sections for non-reassuring fetal status and were treated with neonatal blood transfusion. Fetomaternal hemorrhage was confirmed via maternal Kleihauer-Betke test.

CONCLUSION

We found parenchymal pallor, increased nucleated red blood cells (nRBCs), and syncytial knots (SKs) in the placentas, which are compatible with fetal anemia. Immunohistochemical staining indicated VEGF, CD34, and CD31 expression in the endothelial cells of the capillaries, characteristic of massive FMH placenta. This article also reviews the particular histopathological changes in FHM placenta according to the placental lesion classification system.

Reelin through the years: From brain development to inflammation

Reelin was originally identified as a regulator of neuronal migration and synaptic function, but its non-neuronal functions have received far less attention. Reelin participates in organ development and physiological functions in various tissues, but it is also dysregulated in some diseases. In the cardiovascular system, Reelin is abundant in the blood, where it contributes to platelet adhesion and coagulation, as well as vascular adhesion and permeability of leukocytes. It is a pro-inflammatory and pro-thrombotic factor with important implications for autoinflammatory and autoimmune diseases such as multiple sclerosis, Alzheimer's disease, arthritis, atherosclerosis, or cancer. Mechanistically, Reelin is a large secreted glycoprotein that binds to several membrane receptors, including ApoER2, VLDLR, integrins, and ephrins. Reelin signaling depends on the cell type but mostly involves phosphorylation of NF-κB, PI3K, AKT, or JAK/STAT. This review focuses on non-neuronal functions and the therapeutic potential of Reelin, while highlighting secretion, signaling, and functional similarities between cell types.

Sphingosine-1-phosphate and its receptors in vascular endothelial and lymphatic barrier function

The vascular and lymphatic systems both comprise a series of structurally distinct vessels lined with an inner layer of endothelial cells that function to provide a semipermeable barrier to blood and lymph. Regulation of the endothelial barrier is critical for maintaining vascular and lymphatic barrier homeostasis. One of the regulators of endothelial barrier function and integrity is sphingosine-1-phosphate (S1P), a bioactive sphingolipid metabolite secreted into the blood by erythrocytes, platelets, and endothelial cells and into the lymph by lymph endothelial cells. Binding of S1P to its G protein-coupled receptors, known as S1PR1-5, regulates its pleiotropic functions. This review outlines the structural and functional differences between vascular and lymphatic endothelium and describes current understanding of the importance of S1P/S1PR signaling in regulation of barrier functions. Most studies thus far have been primarily focused on the role of the S1P/S1PR1 axis in vasculature and have been summarized in several excellent reviews, and thus, we will only discuss new perspectives on the molecular mechanisms of action of S1P and its receptors. Much less is known about the responses of the lymphatic endothelium to S1P and the functions of S1PRs in lymph endothelial cells, and this is the major focus of this review. We also discuss current knowledge related to signaling pathways and factors regulated by the S1P/S1PR axis that control lymphatic endothelial cell junctional integrity. Gaps and limitations in current knowledge are highlighted together with the need to further understand the role of S1P receptors in the lymphatic system.

Engineering approaches to investigate the roles of lymphatics vessels in rheumatoid arthritis

Rheumatoid arthritis (RA) is one of the most common chronic inflammatory joint disorders. While our understanding of the autoimmune processes that lead to synovial degradation has improved, a majority of patients are still resistant to current treatments and require new therapeutics. An understudied and promising area for therapy involves the roles of lymphatic vessels (LVs) in RA progression, which has been observed to have a significant effect on mediating chronic inflammation. RA disease progression has been shown to correlate with dramatic changes in LV structure and interstitial fluid drainage, manifesting in the retention of distinct immune cell phenotypes within the synovium. Advances in dynamic imaging technologies have demonstrated that LVs in RA undergo an initial expansion phase of increased LVs and abnormal contractions followed by a collapsed phase of reduced lymphatic function and immune cell clearance in vivo. However, current animal models of RA fail to decouple biological and biophysical factors that might be responsible for this lymphatic dysfunction in RA, and a few attempted in vitro models of the synovium in RA have not yet included the contributions from the LVs. Various methods of replicating LVs in vitro have been developed to study lymphatic biology, but these have yet not been integrated into the RA context. This review discusses the roles of LVs in RA and the current engineering approaches to improve our understanding of lymphatic pathophysiology in RA.

Multi-species meta-analysis identifies transcriptional signatures associated with cardiac endothelial responses in the ischaemic heart

AIM

Myocardial infarction remains the leading cause of heart failure. The adult human heart lacks the capacity to undergo endogenous regeneration. New blood vessel growth is integral to regenerative medicine necessitating a comprehensive understanding of the pathways that regulate vascular regeneration. We sought to define the transcriptomic dynamics of coronary endothelial cells following ischaemic injuries in the developing and adult mouse and human heart and to identify new mechanistic insights and targets for cardiovascular regeneration.

METHODS AND RESULTS

We carried out a comprehensive meta-analysis of integrated single-cell RNA-sequencing data of coronary vascular endothelial cells from the developing and adult mouse and human heart spanning healthy and acute and chronic ischaemic cardiac disease. We identified species-conserved gene regulatory pathways aligned to endogenous neovascularization. We annotated injury-associated temporal shifts of the endothelial transcriptome and validated four genes: VEGF-C, KLF4, EGR1, and ZFP36. Moreover, we showed that ZFP36 regulates human coronary endothelial cell proliferation and defined that VEGF-C administration in vivo enhances clonal expansion of the cardiac vasculature post-myocardial infarction. Finally, we constructed a coronary endothelial cell meta-atlas, CrescENDO, to empower future in-depth research to target pathways associated with coronary neovascularization.

CONCLUSION

We present a high-resolution single-cell meta-atlas of healthy and injured coronary endothelial cells in the mouse and human heart, revealing a suite of novel targets with great potential to promote vascular regeneration, and providing a rich resource for therapeutic development.

Implanted Tissue-Engineered Vascular Graft Cell Isolation with Single-Cell RNA Sequencing Analysis

The advent of single-cell RNA sequencing (scRNA-Seq) has brought with it the ability to gain greater insights into the cellular composition of tissues and heterogeneity in gene expression within specific cell types. For tissue-engineered blood vessels, this is particularly impactful to better understand how neotissue forms and remodels into tissue resembling a native vessel. A notable challenge, however, is the ability to separate cells from synthetic biomaterials to generate high-quality single-cell suspensions to interrogate the cellular composition of our tissue-engineered vascular grafts (TEVGs) during active remodeling in situ. We present here a simple, commercially available approach to separate cells within our TEVG from the residual scaffold for downstream use in a scRNA-Seq workflow. Utilizing this method, we identified the cell populations comprising explanted TEVGs and compared these with results from immunohistochemical analysis. The process began with explanted TEVGs undergoing traditional mechanical and enzymatic dissociation to separate cells from scaffold and extracellular matrix proteins. Magnetically labeled antibodies targeting murine origin cells were incubated with enzymatic digests of TEVGs containing cells and scaffold debris in suspension allowing for separation by utilizing a magnetic separator column. Single-cell suspensions were processed through 10 × Genomics and data were analyzed utilizing R to generate cell clusters. Expression data provided new insights into a diverse composition of phenotypically unique subclusters within the fibroblast, macrophage, smooth muscle cell, and endothelial cell populations contributing to the early neotissue remodeling stages of TEVGs. These populations were correlated qualitatively and quantitatively with immunohistochemistry highlighting for the first time the potential of scRNA-Seq to provide exquisite detail into the host cellular response to an implanted TEVG. These results additionally demonstrate magnetic cell isolation is an effective method for generating high-quality cell suspensions for scRNA-Seq. While this method was utilized for our group's TEVGs, it has broader applications to other implantable materials that use biodegradable synthetic materials as part of scaffold composition. Impact statement Single-cell RNA sequencing is an evolving technology with the ability to provide detailed information on the cellular composition of remodeling biomaterials in vivo. This present work details an effective approach for separating nondegraded biomaterials from cells for downstream RNA-sequencing analysis. We applied this method to implanted tissue-engineered vascular grafts and for the first time describe the cellular composition of the remodeling graft at a single-cell gene expression level. While this method was effective in our scaffold, it has broad applicability to other implanted biomaterials that necessitate separation of cell from residual scaffold materials for single-cell RNA sequencing.

CD146 expression profile in human skin and pre-vascularized dermo-epidermal skin substitutes in vivo

BACKGROUND

CD146 is a cell adhesion molecule whose expression profile in human skin has not yet been elucidated. Here, we characterize CD146 expression pattern in human skin, in particular in blood endothelial cells (BECs) and lymphatic endothelial cells (LECs), which constitute human dermal microvascular endothelial cells (HDMECs), as well as in perivascular cells.

RESULTS

We demonstrated that CD146 is a specific marker of BECs, but not of LECs. Moreover, we found CD146 expression also in human pericytes surrounding blood capillaries in human skin. In addition, we demonstrated that CD146 expression is up-regulated by the TNFα-IL-1β/NF-kB axis in both BECs and pericytes. Finally, we engineered 3D collagen hydrogels composed of HDMECs, CD146⁺ pericytes, and fibroblasts which developed, in vitro and in vivo, a complete microvasculature network composed of blood and lymphatic capillaries with pericytes investing blood capillaries.

CONCLUSIONS

Overall, our results proved that CD146 is a specific marker of BECs and pericytes, but not LECs in human skin. Further, the combination of CD146⁺ pericytes with HDMECs in skin substitutes allowed to bioengineer a comprehensive 3D in vitro and in vivo model of the human dermal microvasculature.

Platelets and (Lymph)angiogenesis

The formation of new blood and lymphatic vessels is essential for both the development of multicellular organisms and (patho)physiological processes like wound repair and tumor growth. In the 1990s, circulating blood platelets were first postulated to regulate tumor angiogenesis by interacting with the endothelium and releasing angiogenic regulators from specialized α granules. Since then, many studies have validated the contributions of platelets to tumor angiogenesis, while uncovering novel roles for platelets in other angiogenic processes like wound resolution and retinal vascular disease. Although the majority of (lymph)angiogenesis occurs during development, platelets appear necessary for lymphatic but not vascular growth, implying their particular importance in pathological cases of adult angiogenesis. Future work is required to determine whether drugs targeting platelet production or function offer a clinically relevant tool to limit detrimental angiogenesis.

Lymphatic/blood vessel plasticity: motivation for a future research area based on present and past observations

The lymphatic system plays a significant role in homeostasis and drainage of excess fluid back into venous circulation. Lymphatics are also associated with a number of diseases including lymphedema, tumor metastasis, and various lymphatic malformations. Emerging evidence suggests that lymphatics might have a bigger connection to the blood vascular system than originally presumed. As these two systems are often studied in isolation, several knowledge gaps exist surrounding what constitutes lymphatic vascular plasticity, under what conditions it arises, and where structures characteristic of plasticity can form. The objective of this review is to overview current structural, cell lineage-based, and cell identity-based evidence for lymphatic plasticity. These examples of plasticity will then be considered in the context of potential clinical and surgical implications of this evolving research area. This review details our current understanding of lymphatic plasticity, highlights key unanswered questions in the field, and motivates future research aimed at clarifying the role and therapeutic potential of lymphatic plasticity in disease.

Integrative single-cell analysis of cardiogenesis identifies developmental trajectories and non-coding mutations in congenital heart disease

To define the multi-cellular epigenomic and transcriptional landscape of cardiac cellular development, we generated single-cell chromatin accessibility maps of human fetal heart tissues. We identified eight major differentiation trajectories involving primary cardiac cell types, each associated with dynamic transcription factor (TF) activity signatures. We contrasted regulatory landscapes of iPSC-derived cardiac cell types and their in vivo counterparts, which enabled optimization of in vitro differentiation of epicardial cells. Further, we interpreted sequence based deep learning models of cell-type-resolved chromatin accessibility profiles to decipher underlying TF motif lexicons. De novo mutations predicted to affect chromatin accessibility in arterial endothelium were enriched in congenital heart disease (CHD) cases vs. controls. In vitro studies in iPSCs validated the functional impact of identified variation on the predicted developmental cell types. This work thus defines the cell-type-resolved cis-regulatory sequence determinants of heart development and identifies disruption of cell type-specific regulatory elements in CHD.

Pathophysiology, Diagnosis, and Management of Canine Intestinal Lymphangiectasia: A Comparative Review

Intestinal lymphangiectasia was first described in the dog over 50 years ago. Despite this, canine IL remains poorly understood and challenging to manage. Intestinal lymphangiectasia is characterized by variable intestinal lymphatic dilation, lymphatic obstruction, and/or lymphangitis, and is a common cause of protein-losing enteropathy in the dog. Breed predispositions are suggestive of a genetic cause, but IL can also occur as a secondary process. Similarly, both primary and secondary IL have been described in humans. Intestinal lymphangiectasia is definitively diagnosed via intestinal histopathology, but other diagnostic results can be suggestive of IL. Advanced imaging techniques are frequently utilized to aid in the diagnosis of IL in humans but have not been thoroughly investigated in the dog. Management strategies differ between humans and dogs. Dietary modification is the mainstay of therapy in humans with additional pharmacological therapies occasionally employed, and immunosuppressives are rarely used due to the lack of a recognized immune pathogenesis. In contrast, corticosteroid and immunosuppressive therapies are more commonly utilized in canine IL. This review aims toward a better understanding of canine IL with an emphasis on recent discoveries, comparative aspects, and necessary future investigations.

The Peripheral Lymphatic System Is Impaired by the Loss of Neuronal Control Associated with Chronic Spinal Cord Injury

Spinal cord injury (SCI) is associated with venous vascular dysfunction below the level of injury, resulting in dysregulation of tissue fluid homeostasis in afflicted skin. The purpose of this study was to determine whether loss of neuronal control in chronic SCI also affects the skin lymphatic system. Morphology of lymphatics was characterized by immunohistochemistry and lymphatic gene expression profiles determined by DNA microarray analysis. In SCI, skin lymphatic function appeared to be impaired, because the ratio of functionally dilated versus collapsed lymphatic vessels was decreased 10-fold compared with control. Consequently, the average lumen area of lymphatic vessels was almost halved, possibly due to the known impaired connective tissue integrity of SCI skin. In fact, collagenases were found to be overexpressed in SCI skin, and dermal collagen structure was impaired. Molecular profiling also suggested an SCI-specific phenotype of increased connective tissue turnover and decreased lymphatic contractility. The total number of lymphatic vessels in SCI skin, however, was doubled, pointing to enhanced lymphangiogenesis. In conclusion, these data show, for the first time, that lymphatic function and development in human skin are under neuronal control. Because peripheral venous and lymphatic vascular defects are associated with disturbed fluid homeostasis, inappropriate wound healing reactions, and impaired skin immunity, they might contribute to the predisposition of afflicted individuals to pressure ulcer formation and wound healing disorders.

Blood-Lymphatic Integrated System with Heterogeneous Melanoma Spheroids via In-Bath Three-Dimensional Bioprinting for Modelling of Combinational Targeted Therapy

Although metastatic melanoma can be managed with chemotherapy, its heterogeneity and resistance to therapy remain poorly understood. In addition to the spread of melanoma in the bloodstream, melanoma-stroma interaction and the lymphatic system play active roles in said heterogeneity and resistance, leading to its progression and metastasis. Reproducing the complexities of the melanoma microenvironment in vitro will help understanding its progression and enhance the translatability of potential cancer therapeutics. A blood-lymphatic integrated system with heterogeneous melanoma spheroids (BLISH) using the in-bath bioprinting process is developed. The process uniformly prints size-controllable metastatic melanoma spheroids along with biomimetic blood and lymphatic vessels (LVs). The system reproduces hallmark events of metastatic melanoma, such as tumor stroma interaction, melanoma invasion, and intravasation. The application of the system to investigate the anticancer effect of combinational targeted therapy suggests that it can be used to study the pathophysiology of melanoma and improve the accuracy of drug response monitoring in skin cancer.

The lymphatic vascular system: much more than just a sewer

Almost 400 years after the (re)discovery of the lymphatic vascular system (LVS) by Gaspare Aselli (Asellius G. De lactibus, sive lacteis venis, quarto vasorum mesaraicorum genere, novo invento Gasparis Asellii Cremo. Dissertatio. (MDCXXIIX), Milan; 1628.), structure, function, development and evolution of this so-called 'second' vascular system are still enigmatic. Interest in the LVS was low because it was (and is) hardly visible, and its diseases are not as life-threatening as those of the blood vascular system. It is not uncommon for patients with lymphedema to be told that yes, they can live with it. Usually, the functions of the LVS are discussed in terms of fluid homeostasis, uptake of chylomicrons from the gut, and immune cell circulation. However, the broad molecular equipment of lymphatic endothelial cells suggests that they possess many more functions, which are also reflected in the pathophysiology of the system. With some specific exceptions, lymphatics develop in all organs. Although basic structure and function are the same regardless their position in the body wall or the internal organs, there are important site-specific characteristics. We discuss common structure and function of lymphatics; and point to important functions for hyaluronan turn-over, salt balance, coagulation, extracellular matrix production, adipose tissue development and potential appetite regulation, and the influence of hypoxia on the regulation of these functions. Differences with respect to the embryonic origin and molecular equipment between somatic and splanchnic lymphatics are discussed with a side-view on the phylogeny of the LVS. The functions of the lymphatic vasculature are much broader than generally thought, and lymphatic research will have many interesting and surprising aspects to offer in the future.

Enhancement of Lymphangiogenesis by Human Mesenchymal Stem Cell Sheet

Preparation of human mesenchymal stem cell (hMSC) suspension for lymphedema treatment relies on conventional enzymatic digestion methods, which severely disrupts cell-cell and cell-extracellular matrix (ECM) connections, and drastically impairs cell retention and engraftment after transplantation. The objective of the present study is to evaluate the ability of hMSC-secreted ECM to augment lymphangiogenesis by using an in vitro coculturing model of hMSC sheets with lymphatic endothelial cells (LECs) and an in vivo mouse tail lymphedema model. Results demonstrate that the hMSC-secreted ECM augments the formation of lymphatic capillary-like structure by a factor of 1.2-3.6 relative to the hMSC control group, by serving as a prolymphangiogenic growth factor reservoir and facilitating cell regenerative activities. hMSC-derived ECM enhances MMP-2 mediated matrix remodeling, increases the synthesis of collagen IV and laminin, and promotes lymphatic microvessel-like structure formation. The injection of rat MSC sheet fragments into a mouse tail lymphedema model confirms the benefits of the hMSC-derived ECM by stimulating lymphangiogenesis and wound closure.

Functional Expression of Multidrug-Resistance (MDR) Transporters in Developing Human Fetal Brain Endothelial Cells

There is little information about the functional expression of the multidrug resistance (MDR) transporters P-glycoprotein (P-gp, encoded by ABCB1) and breast cancer resistance protein (BCRP/ABCG2) in the developing blood−brain barrier (BBB). We isolated and cultured primary human fetal brain endothelial cells (hfBECs) from early and mid-gestation brains and assessed P-gp/ABCB1 and BCRP/ABCG2 expression and function, as well as tube formation capability. Immunolocalization of the von Willebrand factor (marker of endothelial cells), zonula occludens-1 and claudin-5 (tight junctions) was detected in early and mid-gestation-derived hfBECs, which also formed capillary-like tube structures, confirming their BEC phenotype. P-gp and BCRP immunostaining was detected in capillary-like tubes and in the cytoplasm and nucleus of hfBECs. P-gp protein levels in the plasma membrane and nuclear protein fractions, as well as P-gp protein/ABCB1 mRNA and BCRP protein levels decreased (p < 0.05) in hfBECs, from early to mid-gestation. No differences in P-gp or BCRP activity in hfBECs were observed between the two age groups. The hfBECs from early and mid-gestation express functionally competent P-gp and BCRP drug transporters and may thus contribute to the BBB protective phenotype in the conceptus from early stages of pregnancy.

Effect of Human Synovial Fluid From Osteoarthritis Patients and Healthy Individuals on Lymphatic Contractile Activity

The lymphatic system has been proposed to play a crucial role in preventing the development and progression of osteoarthritis (OA). As OA develops and progresses, inflammatory cytokines and degradation by-products of joint tissues build up in the synovial fluid (SF) providing a feedback system to exacerbate disease. The lymphatic system plays a critical role in resolving inflammation and maintaining overall joint homeostasis; however, there is some evidence that the lymphatics can become dysfunctional during OA. We hypothesized that the functional mechanics of lymphatic vessels (LVs) draining the joint could be directly compromised due to factors within SF derived from osteoarthritis patients (OASF). Here, we utilized OASF and SF derived from healthy (non-OA) individuals (healthy SF (HSF)) to investigate potential effects of SF entering the draining lymph on migration of lymphatic endothelial cells (LECs) in vitro, and lymphatic contractile activity of rat femoral LVs (RFLVs) ex vivo. Dilutions of both OASF and HSF containing serum resulted in a similar LEC migratory response to the physiologically endothelial basal medium-treated LECs (endothelial basal medium containing serum) in vitro. Ex vivo, OASF and HSF treatments were administered within the lumen of isolated LVs under controlled pressures. OASF treatment transiently enhanced the RFLVs tonic contractions while phasic contractions were significantly reduced after 1 h of treatment and complete ceased after overnight treatment. HSF treatment on the other hand displayed a gradual decrease in lymphatic contractile activity (both tonic and phasic contractions). The observed variations after SF treatments suggest that the pump function of lymphatic vessel draining the joint could be directly compromised in OA and thus might present a new therapeutic target.

Cadmium mediates pyroptosis of human dermal lymphatic endothelial cells in a NLRP3 inflammasome-dependent manner

Pyroptosis is a form of inflammasome-trigged programmed cell death in response to a variety of stimulators, including environmental cytotoxic pollutant Cadmium (Cd). Vascular endothelial cell is one of the first-line cell types of Cd cell toxicity. Studies report that Cd exposure causes pyroptosis in vascular endothelial cells. Vascular and lymphatic endothelial cells have many common properties, but these two cell types are distinguished in gene expression profile and the responsive behaviors to chemokine or physical stimulations. Whether Cd exposure also causes pyroptosis in lymphatic endothelial cells has not been investigated. Here, we found that Cd treatment significantly decreased the viability of human dermal lymphatic endothelial cells (HDLECs). Cd treatment induced inflammasome activation indicated by elevated cleavage of pro-caspase-1 into active form Casp1p20, elevated secretion of pro-inflammatory cytokines and production of reactive oxygen species (ROS). Flow cytometry showed that caspase-1 activity was significantly increased in Cd-treated cells. Moreover, knockdown of NLRP3 effectively rescued Cd-induced inflammasome activation and pyroptosis in HDLECs. Collectively, our results indicated that Cd induced pyroptosis in a NLRP3 inflammasome-dependent manner in lymphatic endothelial cells.

Sprouting Angiogenesis in Human Pituitary Adenomas

Introduction

Angiogenesis in pituitary tumors is not fully understood, and a better understanding could help inform new pharmacologic therapies, particularly for aggressive pituitary tumors.

Materials and Methods

219 human pituitary tumors and 12 normal pituitary glands were studied. Angiogenic genes were quantified by an angiogenesis qPCR array and a TaqMan probe-based absolute qPCR. Angiogenesis inhibition in pituitary tumors was evaluated in vitro with the endothelial tube formation assay and in vivo in RbΔ19 mice.

Results

71 angiogenic genes, 40 of which are known to be involved in sprouting angiogenesis, were differentially expressed in pituitary tumors. Expression of endothelial markers CD31, CD34, and ENG was significantly higher in pituitary tumors, by 5.6, 22.3, and 8.2-fold, respectively, compared to in normal pituitary tissue. There was no significant difference in levels of the lymphatic endothelial marker LYVE1 in pituitary tumors compared with normal pituitary gland tissue. Pituitary tumors also expressed significantly higher levels of angiogenesis growth factors, including VEGFA (4.2-fold), VEGFB (2.2), VEGFC (19.3), PGF (13.4), ANGPT2 (9.2), PDGFA (2.7), PDGFB (10.5) and TGFB1 (3.8) compared to normal pituitary tissue. Expression of VEGFC and PGF was highly correlated with the expression of endothelial markers in tumor samples, including CD31, CD34, and ENG (endoglin, a co-receptor for TGFβ). Furthermore, VEGFR inhibitors inhibited angiogenesis induced by human pituitary tumors and prolonged survival of RbΔ19 mice.

Conclusion

Human pituitary tumors are characterized by more active angiogenesis than normal pituitary gland tissue in a manner consistent with sprouting angiogenesis. Angiogenesis in pituitary tumors is regulated mainly by PGF and VEGFC, not VEGFA and VEGFB. Angiogenesis inhibitors, such as the VEGFR2 inhibitor cabozantinib, may merit further investigation as therapies for aggressive human pituitary tumors.

Molecular mechanisms of cyclic phosphatidic acid-induced lymphangiogenic actions in vitro

The lymphatic system plays important roles in various physiological and pathological phenomena. As a bioactive phospholipid, lysophosphatidic acid (LPA) has been reported to function as a lymphangiogenic factor as well as some growth factors, yet the involvement of phospholipids including LPA and its derivatives in lymphangiogenesis is not fully understood. In the present study, we have developed an in-vitro lymphangiogenesis model (termed a collagen sandwich model) by utilizing type-I collagen, which exists around the lymphatic endothelial cells of lymphatic capillaries in vivo. The collagen sandwich model has revealed that cyclic phosphatidic acid (cPA), and not LPA, augmented the tube formation of human dermal lymphatic endothelial cells (HDLECs). Both cPA and LPA increased the migration of HDLECs cultured on the collagen. As the gene expression of LPA receptor 6 (LPA₆) was predominantly expressed in HDLECs, a siRNA experiment against LPA₆ attenuated the cPA-mediated tube formation. A synthetic LPA_1/3 inhibitor, Ki16425, suppressed the cPA-augmented tube formation and migration of the HDLECs, and the LPA-induced migration. The activity of Rho-associated protein kinase (ROCK) located at the downstream of the LPA receptors was augmented in both the cPA- and LPA-treated cells. A potent ROCK inhibitor, Y-27632, suppressed the cPA-dependent tube formation but not the migration of the HDLECs. Furthermore, cPA, but not LPA, augmented the gene expression of VE-cadherin and β-catenin in the HDLECs. These results provide novel evidence that cPA facilitates the capillary-like morphogenesis and the migration of HDLECs through LPA₆/ROCK and LPA_1/3 signaling pathways in concomitance with the augmentation of VE-cadherin and β-catenin expression. Thus, cPA is likely to be a potent lymphangiogenic factor for the initial lymphatics adjacent to type I collagen under physiological conditions.

Targeting the Gut Mucosal Immune System Using Nanomaterials

The gastrointestinal (GI) tract is one the biggest mucosal surface in the body and one of the primary targets for the delivery of therapeutics, including immunotherapies. GI diseases, including, e.g., inflammatory bowel disease and intestinal infections such as cholera, pose a significant public health burden and are on the rise. Many of these diseases involve inflammatory processes that can be targeted by immune modulatory therapeutics. However, nonspecific targeting of inflammation systemically can lead to significant side effects. This can be avoided by locally targeting therapeutics to the GI tract and its mucosal immune system. In this review, we discuss nanomaterial-based strategies targeting the GI mucosal immune system, including gut-associated lymphoid tissues, tissue resident immune cells, as well as GI lymph nodes, to modulate GI inflammation and disease outcomes, as well as take advantage of some of the primary mechanisms of GI immunity such as oral tolerance.

Vascular Endothelial Cells: Heterogeneity and Targeting Approaches

Forming the inner layer of the vascular system, endothelial cells (ECs) facilitate a multitude of crucial physiological processes throughout the body. Vascular ECs enable the vessel wall passage of nutrients and diffusion of oxygen from the blood into adjacent cellular structures. ECs regulate vascular tone and blood coagulation as well as adhesion and transmigration of circulating cells. The multitude of EC functions is reflected by tremendous cellular diversity. Vascular ECs can form extremely tight barriers, thereby restricting the passage of xenobiotics or immune cell invasion, whereas, in other organ systems, the endothelial layer is fenestrated (e.g., glomeruli in the kidney), or discontinuous (e.g., liver sinusoids) and less dense to allow for rapid molecular exchange. ECs not only differ between organs or vascular systems, they also change along the vascular tree and specialized subpopulations of ECs can be found within the capillaries of a single organ. Molecular tools that enable selective vascular targeting are helpful to experimentally dissect the role of distinct EC populations, to improve molecular imaging and pave the way for novel treatment options for vascular diseases. This review provides an overview of endothelial diversity and highlights the most successful methods for selective targeting of distinct EC subpopulations.

APOE4-mediated Alzheimer disease and "Vascular"-"Meningeal Lymphatic" components: towards a novel therapeutic era?

A three-dimensional graphic design representation of the potential role of meningeal vessels in Alzheimer disease. Although there are major differences between APOE4(+) and APOE4(−) Alzheimer disease cases (described in detail in the Comment article by Mentis and colleagues), the figure depicts the clearance of macromolecules and other solutes from meningeal lymphatic vessels. Cover image: Ella Maru Studio.

Endothelial Reprogramming Stimulated by Oncostatin M Promotes Inflammation and Tumorigenesis in VHL-Deficient Kidney Tissue

Clear-cell renal cell carcinoma (ccRCC) is the most prevalent subtype of renal cell carcinoma (RCC), and its progression has been linked to chronic inflammation. About 70% of the ccRCC cases are associated with inactivation of the von Hippel-Lindau (VHL) tumor-suppressor gene. However, it is still not clear how mutations in VHL, encoding the substrate-recognition subunit of an E3 ubiquitin ligase that targets the alpha subunit of hypoxia-inducible factor-α (HIFα), can coordinate tissue inflammation and tumorigenesis. We previously generated mice with conditional Vhlh knockout in kidney tubules, which resulted in severe inflammation and fibrosis in addition to hyperplasia and the appearance of transformed clear cells. Interestingly, the endothelial cells (EC), although not subject to genetic manipulation, nonetheless showed profound changes in gene expression that suggest a role in promoting inflammation and tumorigenesis. Oncostatin M (OSM) mediated the interaction between VHL-deficient renal tubule cells and the ECs, and the activated ECs in turn induced macrophage recruitment and polarization. The OSM-dependent microenvironment also promoted metastasis of exogenous tumors. Thus, OSM signaling initiates reconstitution of an inflammatory and tumorigenic microenvironment by VHL-deficient renal tubule cells, which plays a critical role in ccRCC initiation and progression. SIGNIFICANCE: A novel mechanism of cross-talk between ECs and VHL-deficient kidney tubules that stimulates inflammation and tumorigenesis is discovered, suggesting OSM could be a potential target for ccRCC intervention.

Neuroinflammation-Driven Lymphangiogenesis in CNS Diseases

The central nervous system (CNS) undergoes immunosurveillance despite the lack of conventional antigen presenting cells and lymphatic vessels in the CNS parenchyma. Additionally, the CNS is bathed in a cerebrospinal fluid (CSF). CSF is continuously produced, and consequently must continuously clear to maintain fluid homeostasis despite the lack of conventional lymphatics. During neuroinflammation, there is often an accumulation of fluid, antigens, and immune cells to affected areas of the brain parenchyma. Failure to effectively drain these factors may result in edema, prolonged immune response, and adverse clinical outcome as observed in conditions including traumatic brain injury, ischemic and hypoxic brain injury, CNS infection, multiple sclerosis (MS), and brain cancer. Consequently, there has been renewed interest surrounding the expansion of lymphatic vessels adjacent to the CNS which are now thought to be central in regulating the drainage of fluid, cells, and waste out of the CNS. These lymphatic vessels, found at the cribriform plate, dorsal dural meninges, base of the brain, and around the spinal cord have each been implicated to have important roles in various CNS diseases. In this review, we discuss the contribution of meningeal lymphatics to these processes during both steady-state conditions and neuroinflammation, as well as discuss some of the many still unknown aspects regarding the role of meningeal lymphatics in neuroinflammation. Specifically, we focus on the observed phenomenon of lymphangiogenesis by a subset of meningeal lymphatics near the cribriform plate during neuroinflammation, and discuss their potential roles in immunosurveillance, fluid clearance, and access to the CSF and CNS compartments. We propose that manipulating CNS lymphatics may be a new therapeutic way to treat CNS infections, stroke, and autoimmunity.

Cancer-associated fibroblasts in renal cell carcinoma: implication in prognosis and resistance to anti-angiogenic therapy

OBJECTIVES

To investigate the role of cancer-associated fibroblasts (CAFs) in clear cell renal cell carcinoma (ccRCC) with respect to tumour aggressiveness, metastasis development, and resistance to anti-angiogenic therapy (vascular endothelial growth factor receptor-tyrosine kinase inhibitors [VEGFR-TKI]).

PATIENTS AND METHODS

Our study involved tissue samples from three distinct and independent cohorts of patients with ccRCC. The presence of CAFs and tumour lymphangiogenesis was investigated, respectively, by transcriptional signatures and then correlated with tumour development and prognosis. The effect of these CAFs on tumour cell migration and VEGFR-TKI resistance was analysed on co-cultures of ccRCC cells with CAFs.

RESULTS

Results from our cohorts and from in silico investigations showed that VEGFR-TKI significantly increase the number of CAFs in tumours. In the same populations of patients with ccRCC, the proportion of intra-tumoral CAFs correlated to shorter disease-free and overall survival. The presence of CAFs was also correlated with lymphangiogenesis and lymph node metastasis. CAFs increased the migration and decreased the VEGFR-TKI-dependent cytotoxic effect of tumour cells.

CONCLUSIONS

Our results show that VEGFR-TKI promote the development of CAFs, and CAFs favour tumour aggressiveness, metastatic dissemination, and resistance to treatment in ccRCC. CAFs could represent a new therapeutic target to fight resistance to treatment of ccRCC. Targeting CAF and immunotherapies combination are emerging as efficient treatments in many types of solid tumours. Our results highlight their relevance in ccRCC.

FOXC2 Autoregulates Its Expression in the Pulmonary Endothelium After Endotoxin Stimulation in a Histone Acetylation-Dependent Manner

The innate immune response of pulmonary endothelial cells (EC) to lipopolysaccharide (LPS) induces Forkhead box protein C2 (FOXC2) activation through Toll Like Receptor 4 (TLR4). The mechanisms by which FOXC2 expression is regulated in lung EC under LPS stimulation remain unclear. We postulated that FOXC2 regulates its own expression in sepsis, and its transcriptional autoregulation directs lymphatic EC cell-fate decision. Bioinformatic analysis identified potential FOXC2 binding sites in the FOXC2 promoter. In human lung EC, we verified using chromatin immunoprecipitation (ChIP) and luciferase assays that FOXC2 bound to its own promoter and stimulated its expression after LPS stimulation. Chemical inhibition of histone acetylation by garcinol repressed LPS-induced histone acetylation in the FOXC2 promoter region, and disrupted LPS-mediated FOXC2 binding and transcriptional activation. CRISPR/dCas9/gRNA directed against FOXC2-binding-element (FBE) suppressed LPS-stimulated FOXC2 binding and autoregulation by blocking FBEs in the FOXC2 promoter, and repressed expression of lymphatic EC markers. In a neonatal mouse model of sterile sepsis, LPS-induced FOXC2 binding to FBE and FOXC2 expression in lung EC was attenuated with garcinol treatment. These data reveal a new mechanism of LPS-induced histone acetylation-dependent FOXC2 autoregulation.

Macroautophagy in lymphatic endothelial cells inhibits T cell-mediated autoimmunity

Lymphatic endothelial cells (LECs) present peripheral tissue antigens to induce T cell tolerance. In addition, LECs are the main source of sphingosine-1-phosphate (S1P), promoting naive T cell survival and effector T cell exit from lymph nodes (LNs). Autophagy is a physiological process essential for cellular homeostasis. We investigated whether autophagy in LECs modulates T cell activation in experimental arthritis. Whereas genetic abrogation of autophagy in LECs does not alter immune homeostasis, it induces alterations of the regulatory T cell (T reg cell) population in LNs from arthritic mice, which might be linked to MHCII-mediated antigen presentation by LECs. Furthermore, inflammation-induced autophagy in LECs promotes the degradation of Sphingosine kinase 1 (SphK1), resulting in decreased S1P production. Consequently, in arthritic mice lacking autophagy in LECs, pathogenic Th17 cell migration toward LEC-derived S1P gradients and egress from LNs are enhanced, as well as infiltration of inflamed joints, resulting in exacerbated arthritis. Our results highlight the autophagy pathway as an important regulator of LEC immunomodulatory functions in inflammatory conditions.

Multiple combinations of melanocytic and vascular endothelial markers enhance the detection rate of lymphovascular invasion in cutaneous melanoma

BACKGROUND

Lymphovascular invasion (LVI) is believed to be the mechanism by which melanoma cells can disseminate to regional lymph nodes and distant sites and may be predictive of adverse outcome. Lymphovascular invasion often difficult to detect on hematoxylin-eosin (HE) stained sections, are readily identified with dual immunohistochemistry (IHC) for melanocytic and vascular markers.

METHODS

A total of 100 primary cutaneous malignant melanoma cases that had a Breslow thickness of 1-4 mm and lacked LVI by conventional HE assessment were included. We compared the LVI detection rates of double staining for CD31/S100 and CD34/S100, and D2-40/S100, and examined the association of LVI with clinical outcomes.

RESULTS

The dual immunohistochemical positivity for CD31/S100, CD34/S100, and D2-40/S100 were 40(40%), 17(17%) and 35(35%), respectively. On multivariate analysis, LVI was an independent predictor of SLN status. Multivariate analysis revealed that LVI and male gender were independent risk factors for overall survival.

CONCLUSIONS

The recognition of LVI is improved by dual IHC and predicts SLN metastasis. The detection of LVI using dual IHC, especially by a combination of CD31/S100 and D2-40/S100 is a useful step that inclusion should be recommended in basic evaluation parameters for cutaneous melanoma.

CD31 and D2-40 Contribute to Peritoneal Metastasis of Colorectal Cancer by Promoting Epithelial-Mesenchymal Transition

Background/Aims

Colorectal cancer (CRC) patients often exhibit peritoneal metastasis, which negatively impacts their prognosis. CD31 and D2-40 have recently been suggested to be predictors of breast cancer prognosis, but their role in colorectal peritoneal metastasis (CRPM) remains unknown.

Methods

The expression profiles of CD31 and D2-40 were analyzed in CRC patients with or without CRPM and in CRC cell lines with increasing metastatic potential. Overexpression and short hairpin RNA knockdown assays were performed in CRC cells, and the effects of these alterations on epithelial-mesenchymal transition (EMT) in vitro, growth of xenograft tumors in vivo, and peritoneal metastasis potential in a mouse model of CRPM were examined.

Results

The expressions of CD31 and D2-40 were upregulated in CRC tumor tissues and was elevated further in tumor tissues from patients with CRPM. CD31 and D2-40 expression levels exhibited increasing trends parallel to the EMT potential of CRC cells. CD31 and D2-40 are essential for CRC cell EMT in vitro as well as for xenograft tumor growth and peritoneal metastasis in vivo.

Conclusions

CD31 and D2-40 contribute to CRPM by promoting EMT and may serve as prognostic markers and therapeutic targets for CRC, particularly in patients with peritoneal metastasis.

Machine-perfused donor kidneys as a source of human renal endothelial cells

Renal endothelial cells (ECs) play crucial roles in vasorelaxation, ultrafiltration, and selective transport of electrolytes and water, but also in leakage of the glomerular filtration barrier and inflammatory processes like complement activation and leukocyte recruitment. In addition, they are target cells for both cellular and antibody-mediated rejection in the transplanted kidney. To study the molecular and cellular processes underlying EC behavior in renal disease, well-characterized primary renal ECs are indispensible. In this report, we describe a straightforward procedure to isolate ECs from the perfusion fluid of human donor kidneys by a combination of negative selection of monocytes/macrophages, positive selection by CD31 Dynabeads, and propagation in endothelium-specific culture medium. Thus, we isolated and propagated renal ECs from 102 donor kidneys, representative of all blood groups and major human leukocyte antigen (HLA) class I and II antigens. The obtained ECs were positive for CD31 and von Willebrand factor, expressed other endothelial markers such as CD34, VEGF receptor-2, TIE2, and plasmalemmal vesicle associated protein-1 to a variable extent, and were negative for the monocyte marker CD14 and lymphatic endothelial marker podoplanin. HLA class II was either constitutively expressed or could be induced by interferon-γ. Furthermore, as a proof of principle, we showed the diagnostic value of this renal endothelial biobank in renal endothelium-specific cross-matching tests for HLA antibodies.NEW & NOTEWORTHY We describe a new and widely accessible approach to obtain human primary renal endothelial cells in a standardized fashion, by isolating from the perfusate of machine-perfused donor kidneys. Characterization of the cells showed a mixed population originating from different compartments of the kidney. As a proof of principle, we demonstrated a possible diagnostic application in an endothelium-specific cross-match. Next to transplantation, we foresee further applications in the field renal endothelial research.

Lymphatic Tissue Engineering: A Further Step for Successful Lymphedema Treatment

BACKGROUND

 Secondary lymphedema, caused by oncologic surgery, radiation, and chemotherapy, is one of the most relevant, nononcological complications affecting cancer survivors. Severe functional deficits can result in impairing quality of life and a societal burden related to increased treatment costs. Often, conservative treatments are not sufficient to alleviate lymphedema or to prevent stage progression of the disease, as they do not address the underlying etiology that is the disruption of lymphatic pathways. In recent years, lymphatic surgery approaches were revolutionized by advances in microsurgical technique. Currently, lymphedema can effectively be treated by procedures such as lymphovenous anastomosis (LVA) and lymph node transfer (LNT). However, not all patients have suitable lymphatic vessels, and lymph node harvesting is associated with risks. In addition, some data have revealed nonresponders to the microsurgical techniques.

METHODS

 A literature review was performed to evaluate the value of lymphatic tissue engineering for plastic surgeons and to give an overview of the achievements, challenges, and goals of the field.

RESULTS

 While certain challenges exist, including cell harvesting, nutrient supply, biocompatibility, and hydrostatic properties, it is possible and desirable to engineer lymph nodes and lymphatic vessels. The path toward clinical translation is considered more complex for LNTs secondary to the complex microarchitecture and pending final mechanistic clarification, while LVA is more straight forward.

CONCLUSION

 Lymphatic tissue engineering has the potential to be the next step for microsurgical treatment of secondary lymphedema. Current and future researches are necessary to optimize this clinical paradigm shift for improved surgical treatment of lymphedema.