Ccbe1 regulates Vegfc-mediated induction of Vegfr3 signaling during embryonic lymphangiogenesis

Epidermal growth factor-like domain 7 drives brain lymphatic endothelial cell development through integrin αvβ3

In zebrafish, brain lymphatic endothelial cells (BLECs) are essential for meningeal angiogenesis and cerebrovascular regeneration. Although epidermal growth factor-like domain 7 (Egfl7) has been reported to act as a pro-angiogenic factor, its roles in lymphangiogenesis remain unclear. Here, we show that Egfl7 is expressed in both blood and lymphatic endothelial cells. We generate an egfl7 cq180 mutant with a 13-bp-deletion in exon 3 leading to reduced expression of Egfl7. The egfl7 cq180 mutant zebrafish exhibit defective formation of BLEC bilateral loop-like structures, although trunk and facial lymphatic development remains unaffected. Moreover, while the egfl7 cq180 mutant displays normal BLEC lineage specification, the migration and proliferation of these cells are impaired. Additionally, we identify integrin αvβ3 as the receptor for Egfl7. αvβ3 is expressed in the CVP and sprouting BLECs, and blocking this integrin inhibits the formation of BLEC bilateral loop-like structures. Thus, this study identifies a role for Egfl7 in BLEC development that is mediated through the integrin αvβ3.

The relationship between the secondary vascular system and the lymphatic vascular system in fish

New technologies have resulted in a better understanding of blood and lymphatic vascular heterogeneity at the cellular and molecular levels. However, we still need to learn more about the heterogeneity of the cardiovascular and lymphatic systems among different species at the anatomical and functional levels. Even the deceptively simple question of the functions of fish lymphatic vessels has yet to be conclusively answered. The most common interpretation assumes a similar dual setup of the vasculature in zebrafish and mammals: a cardiovascular circulatory system, and a lymphatic vascular system (LVS), in which the unidirectional flow is derived from surplus interstitial fluid and returned into the cardiovascular system. A competing interpretation questions the identity of the lymphatic vessels in fish as at least some of them receive their flow from arteries via specialised anastomoses, neither requiring an interstitial source for the lymphatic flow nor stipulating unidirectionality. In this alternative view, the 'fish lymphatics' are a specialised subcompartment of the cardiovascular system, called the secondary vascular system (SVS). Many of the contradictions found in the literature appear to stem from the fact that the SVS develops in part or completely from an embryonic LVS by transdifferentiation. Future research needs to establish the extent of embryonic transdifferentiation of lymphatics into SVS blood vessels. Similarly, more insight is needed into the molecular regulation of vascular development in fish. Most fish possess more than the five vascular endothelial growth factor (VEGF) genes and three VEGF receptor genes that we know from mice or humans, and the relative tolerance of fish to whole-genome and gene duplications could underlie the evolutionary diversification of the vasculature. This review discusses the key elements of the fish lymphatics versus the SVS and attempts to draw a picture coherent with the existing data, including phylogenetic knowledge.

Angpt1 binding to Tie1 regulates the signaling required for lymphatic vessel development in zebrafish

Development of the vascular system is regulated by multiple signaling pathways mediated by receptor tyrosine kinases. Among them, angiopoietin (Ang)/Tie signaling regulates lymphatic and blood vessel development in mammals. Of the two Tie receptors, Tie2 is well known as a key mediator of Ang/Tie signaling, but, unexpectedly, recent studies have revealed that the Tie2 locus has been lost in many vertebrate species, whereas the Tie1 gene is more commonly present. However, Tie1-driven signaling pathways, including ligands and cellular functions, are not well understood. Here, we performed comprehensive mutant analyses of angiopoietins and Tie receptors in zebrafish and found that only angpt1 and tie1 mutants show defects in trunk lymphatic vessel development. Among zebrafish angiopoietins, only Angpt1 binds to Tie1 as a ligand. We indirectly monitored Ang1/Tie1 signaling and detected Tie1 activation in sprouting endothelial cells, where Tie1 inhibits nuclear import of EGFP-Foxo1a. Angpt1/Tie1 signaling functions in endothelial cell migration and proliferation, and in lymphatic specification during early lymphangiogenesis, at least in part by modulating Vegfc/Vegfr3 signaling. Thus, we show that Angpt1/Tie1 signaling constitutes an essential signaling pathway for lymphatic development in zebrafish.

Multiple cis-regulatory elements control prox1a expression in distinct lymphatic vascular beds

During embryonic development, lymphatic endothelial cell (LEC) precursors are distinguished from blood endothelial cells by the expression of Prospero-related homeobox 1 (Prox1), which is essential for lymphatic vasculature formation in mouse and zebrafish. Prox1 expression initiation precedes LEC sprouting and migration, serving as the marker of specified LECs. Despite its crucial role in lymphatic development, Prox1 upstream regulation in LECs remains to be uncovered. SOX18 and COUP-TFII are thought to regulate Prox1 in mice by binding its promoter region. However, the specific regulation of Prox1 expression in LECs remains to be studied in detail. Here, we used evolutionary conservation and chromatin accessibility to identify enhancers located in the proximity of zebrafish prox1a active in developing LECs. We confirmed the functional role of the identified sequences through CRISPR/Cas9 mutagenesis of a lymphatic valve enhancer. The deletion of this region results in impaired valve morphology and function. Overall, our results reveal an intricate control of prox1a expression through a collection of enhancers. Ray-finned fish-specific distal enhancers drive pan-lymphatic expression, whereas vertebrate-conserved proximal enhancers refine expression in functionally distinct subsets of lymphatic endothelium.

Central conducting lymphatic anomaly: from bench to bedside

Central conducting lymphatic anomaly (CCLA) is a complex lymphatic anomaly characterized by abnormalities of the central lymphatics and may present with nonimmune fetal hydrops, chylothorax, chylous ascites, or lymphedema. CCLA has historically been difficult to diagnose and treat; however, recent advances in imaging, such as dynamic contrast magnetic resonance lymphangiography, and in genomics, such as deep sequencing and utilization of cell-free DNA, have improved diagnosis and refined both genotype and phenotype. Furthermore, in vitro and in vivo models have confirmed genetic causes of CCLA, defined the underlying pathogenesis, and facilitated personalized medicine to improve outcomes. Basic, translational, and clinical science are essential for a bedside-to-bench and back approach for CCLA.

The cytoskeleton adaptor protein Sorbs1 controls the development of lymphatic and venous vessels in zebrafish

BACKGROUND

Lymphangiogenesis, the formation of lymphatic vessels, is tightly linked to the development of the venous vasculature, both at the cellular and molecular levels. Here, we identify a novel role for Sorbs1, the founding member of the SoHo family of cytoskeleton adaptor proteins, in vascular and lymphatic development in the zebrafish.

RESULTS

We show that Sorbs1 is required for secondary sprouting and emergence of several vascular structures specifically derived from the axial vein. Most notably, formation of the precursor parachordal lymphatic structures is affected in sorbs1 mutant embryos, severely impacting the establishment of the trunk lymphatic vessel network. Interestingly, we show that Sorbs1 interacts with the BMP pathway and could function outside of Vegfc signaling. Mechanistically, Sorbs1 controls FAK/Src signaling and subsequently impacts on the cytoskeleton processes regulated by Rac1 and RhoA GTPases. Inactivation of Sorbs1 altered cell-extracellular matrix (ECM) contacts rearrangement and cytoskeleton dynamics, leading to specific defects in endothelial cell migratory and adhesive properties.

CONCLUSIONS

Overall, using in vitro and in vivo assays, we identify Sorbs1 as an important regulator of venous and lymphatic angiogenesis independently of the Vegfc signaling axis. These results provide a better understanding of the complexity found within context-specific vascular and lymphatic development.

Neovascularization directed by CAVIN1/CCBE1/VEGFC confers TMZ-resistance in glioblastoma

Acquisition of resistance to temozolomide (TMZ) poses a significant challenge in glioblastoma (GBM) therapy. Neovascularization, a pivotal process in tumorigenesis and development, remains poorly understood in its contribution to chemoresistance in GBMs. This study unveils aberrant vascular networks within TMZ-resistant (TMZ-R) GBM tissues and identifies the extracellular matrix (ECM) protein CCBE1 as a potential mediator. Through in vivo and in vitro experiments involving gain and loss of function assessments, we demonstrate that high expression of CCBE1 promotes hyper-angiogenesis and orchestrates partial endothelial-to-mesenchymal transition (EndMT) in human microvascular endothelial cells (HCMEC/d3) within GBM. This is likely driven by VEGFC/Rho signaling. Intriguingly, CCBE1 overexpression substantially fails to promote tumor growth, but endows resistance to GBM cells in a vascular endothelial cell-dependent manner. Mechanically, the constitutive phosphorylation of SP1 at Ser101 drives the upregulation of CCBE1 transcription in TMZ resistant tumors, and the excretion of CCBE1 depends on caveolae associated protein 1 (CAVIN1) binding and assembling. Tumor cells derived CCBE1 promotes VEGFC maturation, activates VEGFR2/VEGFR3/Rho signaling in vascular endothelial cells, and ultimately results in hyper-angiogenesis in TMZ-R tumors. Collectively, the current study uncovers the cellular and molecular basis of abnormal angiogenesis in a chemo resistant microenvironment, implying that curbing CCBE1 is key to reversing TMZ resistance.

Copper nanoparticles and silver nanoparticles impair lymphangiogenesis in zebrafish

Lymphatic system distributes in almost all vertebrate tissues and organs, and plays important roles in the regulation of body fluid balance, lipid absorption and immune monitoring. Although CuNPs or AgNPs accumulation has been reported to be closely associated with delayed hatching and motor dysfunction in zebrafish embryos, their biological effects on lymphangiogenesis remain unknown. In this study, thoracic duct was observed to be partially absent in both CuNPs and AgNPs stressed zebrafish larvae. Specifically, CuNPs stress induced hypermethylation of E2F7/8 binding sites on CCBE1 promoters via their producing ROS, thereby leading to the reduction of binding enrichment of E2F7/8 on CCBE1 promoter and its subsequently reduced expression, then resulting in defective lymphatic vessel formation. Differently, AgNPs stress induced down-regulated CCBE1 expression via down-regulating mRNA and protein levels of E2F7/8 transcription factors, thereby resulting in defective lymphatic vessel formation. This study may be the first to demonstrate that CuNPs and AgNPs damaged lymphangiogenesis during zebrafish embryogenesis, mechanistically, CuNPs epigenetically regulated the expression of lymphangiogenesis regulator CCBE1 via hypermethylating its promoter binding sites of E2F7/8, while AgNPs via regulating E2F7/8 expression. Meanwhile, overexpression of ccbe1 mRNA effectively rescued the lymphangiogenesis defects in both AgNPs and CuNPs stressed larvae, while overexpression of e2f7/8 mRNA effectively rescued the lymphangiogenesis defects in AgNPs rather than CuNPs stressed larvae. The results in this study will shed some light on the safety assessment of nanomaterials applied in medicine and on the ecological security assessments of nanomaterials. Video Abstract.

Lymphatic vessel: origin, heterogeneity, biological functions, and therapeutic targets

Lymphatic vessels, comprising the secondary circulatory system in human body, play a multifaceted role in maintaining homeostasis among various tissues and organs. They are tasked with a serious of responsibilities, including the regulation of lymph absorption and transport, the orchestration of immune surveillance and responses. Lymphatic vessel development undergoes a series of sophisticated regulatory signaling pathways governing heterogeneous-origin cell populations stepwise to assemble into the highly specialized lymphatic vessel networks. Lymphangiogenesis, as defined by new lymphatic vessels sprouting from preexisting lymphatic vessels/embryonic veins, is the main developmental mechanism underlying the formation and expansion of lymphatic vessel networks in an embryo. However, abnormal lymphangiogenesis could be observed in many pathological conditions and has a close relationship with the development and progression of various diseases. Mechanistic studies have revealed a set of lymphangiogenic factors and cascades that may serve as the potential targets for regulating abnormal lymphangiogenesis, to further modulate the progression of diseases. Actually, an increasing number of clinical trials have demonstrated the promising interventions and showed the feasibility of currently available treatments for future clinical translation. Targeting lymphangiogenic promoters or inhibitors not only directly regulates abnormal lymphangiogenesis, but improves the efficacy of diverse treatments. In conclusion, we present a comprehensive overview of lymphatic vessel development and physiological functions, and describe the critical involvement of abnormal lymphangiogenesis in multiple diseases. Moreover, we summarize the targeting therapeutic values of abnormal lymphangiogenesis, providing novel perspectives for treatment strategy of multiple human diseases.

CCBE1 regulates the development and prevents the age-dependent regression of meningeal lymphatics

Recent studies have described the importance of lymphatics in numerous organ-specific physiological and pathological processes. The role of meningeal lymphatics in various neurological and cerebrovascular diseases has been suggested. It has also been shown that these structures develop postnatally and are altered by aging and that the vascular endothelial growth factor C (VEGFC)/ vascular endothelial growth factor receptor 3 (VEGFR3) signaling plays an essential role in the development and maintenance of them. However, the molecular mechanisms governing the development and maintenance of meningeal lymphatics are still poorly characterized. Recent in vitro cell culture-based experiments, and in vivo studies in zebrafish and mouse skin suggest that collagen and calcium binding EGF domains 1 (CCBE1) is involved in the processing of VEGFC. However, the organ-specific role of CCBE1 in developmental lymphangiogenesis and maintenance of lymphatics remains unclear. Here, we aimed to investigate the organ-specific functions of CCBE1 in developmental lymphangiogenesis and maintenance of meningeal lymphatics during aging. We demonstrate that inducible deletion of CCBE1 leads to impaired postnatal development of the meningeal lymphatics and decreased macromolecule drainage to deep cervical lymph nodes. The structural integrity and density of meningeal lymphatics are gradually altered during aging. Furthermore, the meningeal lymphatic structures in adults showed regression after inducible CCBE1 deletion. Collectively, our results indicate the importance of CCBE1-dependent mechanisms not only in the development, but also in the prevention of the age-related regression of meningeal lymphatics. Therefore, targeting CCBE1 may be a good therapeutic strategy to prevent age-related degeneration of meningeal lymphatics.

Dysregulation of Lymphatic Endothelial VEGFR3 Signaling in Disease

Vascular endothelial growth factor (VEGF) receptor 3 (VEGFR3), a receptor tyrosine kinase encoded by the FLT4 gene, plays a significant role in the morphogenesis and maintenance of lymphatic vessels. Under both normal and pathologic conditions, VEGF-C and VEGF-D bind VEGFR3 on the surface of lymphatic endothelial cells (LECs) and induce lymphatic proliferation, migration, and survival by activating intracellular PI3K-Akt and MAPK-ERK signaling pathways. Impaired lymphatic function and VEGFR3 signaling has been linked with a myriad of commonly encountered clinical conditions. This review provides a brief overview of intracellular VEGFR3 signaling in LECs and explores examples of dysregulated VEGFR3 signaling in various disease states, including (1) lymphedema, (2) tumor growth and metastasis, (3) obesity and metabolic syndrome, (4) organ transplant rejection, and (5) autoimmune disorders. A more complete understanding of the molecular mechanisms underlying the lymphatic pathology of each disease will allow for the development of novel strategies to treat these chronic and often debilitating illnesses.

Lymphatic Defects in Zebrafish sox18 Mutants Are Exacerbated by Perturbed VEGFC Signaling, While Masked by Elevated sox7 Expression

Mutations in the transcription factor-coding gene SOX18, the growth factor-coding gene VEGFC and its receptor-coding gene VEGFR3/FLT4 cause primary lymphedema in humans. In mammals, SOX18, together with COUP-TFII/NR2F2, activates the expression of Prox1, a master regulator in lymphatic identity and development. Knockdown studies have also suggested an involvement of Sox18, Coup-tfII/Nr2f2, and Prox1 in zebrafish lymphatic development. Mutants in the corresponding genes initially failed to recapitulate the lymphatic defects observed in morphants. In this paper, we describe a novel zebrafish sox18 mutant allele, sa12315, which behaves as a null. The formation of the lymphatic thoracic duct is affected in sox18 homozygous mutants, but defects are milder in both zygotic and maternal-zygotic sox18 mutants than in sox18 morphants. Remarkably, in sox18 mutants, the expression of the closely related sox7 gene is elevated where lymphatic precursors arise. Sox7 could thus mask the absence of a functional Sox18 protein and account for the mild lymphatic phenotype in sox18 mutants, as shown in mice. Partial knockdown of vegfc exacerbates lymphatic defects in sox18 mutants, making them visible in heterozygotes. Our data thus reinforce the genetic interaction between Sox18 and Vegfc in lymphatic development, previously suggested by knockdown studies, and highlight the ability of Sox7 to compensate for Sox18 lymphatic dysfunction.

Svep1 is a binding ligand of Tie1 and affects specific aspects of facial lymphatic development in a Vegfc-independent manner

Multiple factors are required to form functional lymphatic vessels. Here, we uncover an essential role for the secreted protein Svep1 and the transmembrane receptor Tie1 during the development of subpopulations of the zebrafish facial lymphatic network. This specific aspect of the facial network forms independently of Vascular endothelial growth factor C (Vegfc) signalling, which otherwise is the most prominent signalling axis in all other lymphatic beds. Additionally, we find that multiple specific and newly uncovered phenotypic hallmarks of svep1 mutants are also present in tie1, but not in tie2 or vegfc mutants. These phenotypes are observed in the lymphatic vasculature of both head and trunk, as well as in the development of the dorsal longitudinal anastomotic vessel under reduced flow conditions. Therefore, our study demonstrates an important function for Tie1 signalling during lymphangiogenesis as well as blood vessel development in zebrafish. Furthermore, we show genetic interaction between svep1 and tie1 in vivo, during early steps of lymphangiogenesis, and demonstrate that zebrafish as well as human Svep1/SVEP1 protein bind to the respective Tie1/TIE1 receptors in vitro. Since compound heterozygous mutations for SVEP1 and TIE2 have recently been reported in human glaucoma patients, our data have clinical relevance in demonstrating a role for SVEP1 in TIE signalling in an in vivo setting.

Turning gray selenium and sublimed sulfur into a nanocomposite to accelerate tissue regeneration by isothermal recrystallization

BACKGROUND

Globally, millions of patients suffer from regenerative deficiencies, such as refractory wound healing, which is characterized by excessive inflammation and abnormal angiogenesis. Growth factors and stem cells are currently employed to accelerate tissue repair and regeneration; however, they are complex and costly. Thus, the exploration of new regeneration accelerators is of considerable medical interest. This study developed a plain nanoparticle that accelerates tissue regeneration with the involvement of angiogenesis and inflammatory regulation.

METHODS

Grey selenium and sublimed sulphur were thermalized in PEG-200 and isothermally recrystallised to composite nanoparticles (Nano-Se@S). The tissue regeneration accelerating activities of Nano-Se@S were evaluated in mice, zebrafish, chick embryos, and human cells. Transcriptomic analysis was performed to investigate the potential mechanisms involved during tissue regeneration.

RESULTS

Through the cooperation of sulphur, which is inert to tissue regeneration, Nano-Se@S demonstrated improved tissue regeneration acceleration activity compared to Nano-Se. Transcriptome analysis revealed that Nano-Se@S improved biosynthesis and ROS scavenging but suppressed inflammation. The ROS scavenging and angiogenesis-promoting activities of Nano-Se@S were further confirmed in transgenic zebrafish and chick embryos. Interestingly, we found that Nano-Se@S recruits leukocytes to the wound surface at the early stage of regeneration, which contributes to sterilization during regeneration.

CONCLUSION

Our study highlights Nano-Se@S as a tissue regeneration accelerator, and Nano-Se@S may provide new inspiration for therapeutics for regenerative-deficient diseases.

Vascular and Neuronal Network Formation Regulated by Growth Factors and Guidance Cues

Blood vessels and nerves are distributed throughout the body and show a high degree of anatomical parallelism and functional crosstalk. These networks transport oxygen, nutrients, and information to maintain homeostasis. Thus, disruption of network formation can cause diseases. Nervous system development requires the navigation of the axons of neurons to their correct destination. Blood vessel formation occurs via vasculogenesis and angiogenesis. Vasculogenesis is the process of de novo blood vessel formation, and angiogenesis is the process whereby endothelial cells sprout from pre-existing vessels. Both developmental processes require guidance molecules to establish precise branching patterns of these systems in the vertebrate body. These network formations are regulated by growth factors, such as vascular endothelial growth factor; and guidance cues, such as ephrin, netrin, semaphorin, and slit. Neuronal and vascular structures extend lamellipodia and filopodia, which sense guidance cues that are mediated by the Rho family and actin cytosol rearrangement, to migrate to the goal during development. Furthermore, endothelial cells regulate neuronal development and vice versa. In this review, we describe the guidance molecules that regulate neuronal and vascular network formation.

Sinusoidal and lymphatic vessel growth is controlled by reciprocal VEGF-C-CDH5 inhibition

Sinusoids are specialized, low pressure blood vessels in the liver, bone marrow, and spleen required for definitive hematopoiesis. Unlike other blood endothelial cells (ECs), sinusoidal ECs express high levels of VEGFR3. VEGFR3 and its ligand VEGF-C are known to support lymphatic growth, but their function in sinusoidal vessels is unknown. In this study, we define a reciprocal VEGF-C/VEGFR3-CDH5 (VE-cadherin) signaling axis that controls growth of both sinusoidal and lymphatic vessels. Loss of VEGF-C or VEGFR3 resulted in cutaneous edema, reduced fetal liver size, and bloodless bone marrow due to impaired lymphatic and sinusoidal vessel growth. Mice with membrane-retained VE-cadherin conferred identical lymphatic and sinusoidal defects, suggesting that VE-cadherin opposes VEGF-C/VEGFR3 signaling. In developing mice, loss of VE-cadherin rescued defects in sinusoidal and lymphatic growth caused by loss of VEGFR3 but not loss of VEGF-C, findings explained by potentiated VEGF-C/VEGFR2 signaling in VEGFR3-deficient lymphatic ECs. Mechanistically, VEGF-C/VEGFR3 signaling induces VE-cadherin endocytosis and loss of function via SRC-mediated phosphorylation, while VE-cadherin prevents VEGFR3 endocytosis required for optimal receptor signaling. These findings establish an essential role for VEGF-C/VEGFR3 signaling during sinusoidal vascular growth, identify VE-cadherin as a powerful negative regulator of VEGF-C signaling that acts through both VEGFR3 and VEGFR2 receptors, and suggest that negative regulation of VE-cadherin is required for effective VEGF-C/VEGFR3 signaling during growth of sinusoidal and lymphatic vessels. Manipulation of this reciprocal negative regulatory mechanism, e.g. by reducing VE-cadherin function, may be used to stimulate therapeutic sinusoidal or lymphatic vessel growth.

Low Efficacy of Genetic Tests for the Diagnosis of Primary Lymphedema Prompts Novel Insights into the Underlying Molecular Pathways

Lymphedema is a chronic inflammatory disorder caused by ineffective fluid uptake by the lymphatic system, with effects mainly on the lower limbs. Lymphedema is either primary, when caused by genetic mutations, or secondary, when it follows injury, infection, or surgery. In this study, we aim to assess to what extent the current genetic tests detect genetic variants of lymphedema, and to identify the major molecular pathways that underlie this rather unknown disease. We recruited 147 individuals with a clinical diagnosis of primary lymphedema and used established genetic tests on their blood or saliva specimens. Only 11 of these were positive, while other probands were either negative (63) or inconclusive (73). The low efficacy of such tests calls for greater insight into the underlying mechanisms to increase accuracy. For this purpose, we built a molecular pathways diagram based on a literature analysis (OMIM, Kegg, PubMed, Scopus) of candidate and diagnostic genes. The PI3K/AKT and the RAS/MAPK pathways emerged as primary candidates responsible for lymphedema diagnosis, while the Rho/ROCK pathway appeared less critical. The results of this study suggest the most important pathways involved in the pathogenesis of lymphedema, and outline the most promising diagnostic and candidate genes to diagnose this disease.

Drainage of senescent astrocytes from brain via meningeal lymphatic routes

Recent progress on the central lymphatic system has greatly increased our understanding of how the brain maintains its own waste homeostasis. Here, we showed that perivascular spaces and meningeal lymphatic vessels form a functional route for clearance of senescent astrocytes from the aging brain. Blocking meningeal lymphatic drainage by ligation of the deep cervical lymph nodes impaired clearance of senescent astrocytes from brain parenchyma, subsequently increasing neuroinflammation in aged mice. By contrast, enhancing meningeal lymphatic vessel diameter by a recombinant adeno-associated virus encoding mouse vascular endothelial growth factor-C (VEGF-C) improved clearance of senescent astrocytes and mitigated neuroinflammation. Mechanistically, VEGF-C was highly expressed in senescent astrocytes, contributing themselves to migrate across lymphatic vessels along C-C motif chemokine ligand 21 (CCL21) gradient by interacting with VEGF receptor 3. Moreover, intra-cisternal injection of antibody against CCL21 hampered senescent astrocytes into the lymphatic vessels and exacerbated short memory defects of aged mice. Together, these findings reveal a new perspective for the meningeal lymphatics in the removal of senescent astrocytes, thus offering a valuable target for therapeutic intervention.

Hepatic lymphatic vascular system in health and disease

In recent years, significant advances have been made in the study of lymphatic vessels with the identification of their specific markers and the development of research tools that have accelerated our understanding of their role in tissue homeostasis and disease pathogenesis in many organs. Compared to other organs, the lymphatic system in the liver is understudied despite its obvious importance for hepatic physiology and pathophysiology. In this review, we describe fundamental aspects of the hepatic lymphatic system and its role in a range of liver-related pathological conditions such as portal hypertension, ascites formation, malignant tumours, liver transplantation, congenital liver diseases, non-alcoholic fatty liver disease, and hepatic encephalopathy. The article concludes with a discussion regarding the modulation of lymphangiogenesis as a potential therapeutic strategy for liver diseases.

mafba and mafbb differentially regulate lymphatic endothelial cell migration in topographically distinct manners

Lymphangiogenesis, formation of lymphatic vessels from pre-existing vessels, is a dynamic process that requires cell migration. Regardless of location, migrating lymphatic endothelial cell (LEC) progenitors probe their surroundings to form the lymphatic network. Lymphatic-development regulation requires the transcription factor MAFB in different species. Zebrafish Mafba, expressed in LEC progenitors, is essential for their migration in the trunk. However, the transcriptional mechanism that orchestrates LEC migration in different lymphatic endothelial beds remains elusive. Here, we uncover topographically different requirements of the two paralogs, Mafba and Mafbb, for LEC migration. Both mafba and mafbb are necessary for facial lymphatic development, but mafbb is dispensable for trunk lymphatic development. On the molecular level, we demonstrate a regulatory network where Vegfc-Vegfd-SoxF-Mafba-Mafbb is essential in facial lymphangiogenesis. We identify that mafba and mafbb tune the directionality of LEC migration and vessel morphogenesis that is ultimately necessary for lymphatic function.

A narrative review on the biology of piezo1 with platelet-rich plasma in cardiac cell regeneration

Cardiomyocyte regeneration following cardiac damage is challenging to study because of the inflammatory process, the multiplication of cells in the stroma, and the creation of scar tissue. In addition to the initial damage, the subsequent decrease in cardiac myocytes adds to heart failure. Piezo1 is remarkably understudied in the heart, which may be related to its recent discovery. Despite this, Piezo1 is expressed in a variety of cardiovascular cell populations, notably epithelial cells (EC), cardiac fibroblasts (CF), and cardiac myocytes (CM), in both animal and human samples, with fibroblasts expressing more than myocytes. Researchers have recently shown that disrupting Piezo1 signaling causes defects in zebrafish developing the outflow tract (OFT) and aortic valves. Platelet plasma membranes may provide lipid substrates, such as phosphatidylinositol bisphosphate, that aid in activating the piezo 1 ion channel in the cardiovascular system. In addition, CXC chemokine ligand 8/CXC chemokine receptor 1/2 (CXCL8-CXCR1/2) signaling was identified to establish the proliferation of coronary endothelial cells during cardiac regeneration. Notably, all these pathways are calcium-dependent, and cell proliferation and angiogenesis were necessary to recover myocardial cells. This review will examine the most current findings to understand further how platelet-rich plasma (PRP) and the piezo 1 channel might aid in cardiomyocyte regeneration.

Real-time evaluation of glioblastoma growth in patient-specific zebrafish xenografts

BACKGROUND

Patient-derived xenograft (PDX) models of glioblastoma (GBM) are a central tool for neuro-oncology research and drug development, enabling the detection of patient-specific differences in growth, and in vivo drug response. However, existing PDX models are not well suited for large-scale or automated studies. Thus, here, we investigate if a fast zebrafish-based PDX model, supported by longitudinal, AI-driven image analysis, can recapitulate key aspects of glioblastoma growth and enable case-comparative drug testing.

METHODS

We engrafted 11 GFP-tagged patient-derived GBM IDH wild-type cell cultures (PDCs) into 1-day-old zebrafish embryos, and monitored fish with 96-well live microscopy and convolutional neural network analysis. Using light-sheet imaging of whole embryos, we analyzed further the invasive growth of tumor cells.

RESULTS

Our pipeline enables automatic and robust longitudinal observation of tumor growth and survival of individual fish. The 11 PDCs expressed growth, invasion and survival heterogeneity, and tumor initiation correlated strongly with matched mouse PDX counterparts (Spearman R = 0.89, p < 0.001). Three PDCs showed a high degree of association between grafted tumor cells and host blood vessels, suggesting a perivascular invasion phenotype. In vivo evaluation of the drug marizomib, currently in clinical trials for GBM, showed an effect on fish survival corresponding to PDC in vitro and in vivo marizomib sensitivity.

CONCLUSIONS

Zebrafish xenografts of GBM, monitored by AI methods in an automated process, present a scalable alternative to mouse xenograft models for the study of glioblastoma tumor initiation, growth, and invasion, applicable to patient-specific drug evaluation.

A Vegfc-Emilin2a-Cxcl8a Signaling Axis Required for Zebrafish Cardiac Regeneration

BACKGROUND

Ischemic heart disease following the obstruction of coronary vessels leads to the death of cardiac tissue and the formation of a fibrotic scar. In contrast to adult mammals, zebrafish can regenerate their heart after injury, enabling the study of the underlying mechanisms. One of the earliest responses following cardiac injury in adult zebrafish is coronary revascularization. Defects in this process lead to impaired cardiomyocyte repopulation and scarring. Hence, identifying and investigating factors that promote coronary revascularization holds great therapeutic potential.

METHODS

We used wholemount imaging, immunohistochemistry and histology to assess various aspects of zebrafish cardiac regeneration. Deep transcriptomic analysis allowed us to identify targets and potential effectors of Vegfc (vascular endothelial growth factor C) signaling. We used newly generated loss- and gain-of-function genetic tools to investigate the role of Emilin2a (elastin microfibril interfacer 2a) and Cxcl8a (chemokine (C-X-C) motif ligand 8a)-Cxcr1 (chemokine (C-X-C) motif receptor 1) signaling in cardiac regeneration.

RESULTS

We first show that regenerating coronary endothelial cells upregulate vegfc upon cardiac injury in adult zebrafish and that Vegfc signaling is required for their proliferation during regeneration. Notably, blocking Vegfc signaling also significantly reduces cardiomyocyte dedifferentiation and proliferation. Using transcriptomic analyses, we identified emilin2a as a target of Vegfc signaling and found that manipulation of emilin2a expression can modulate coronary revascularization as well as cardiomyocyte proliferation. Mechanistically, Emilin2a induces the expression of the chemokine gene cxcl8a in epicardium-derived cells, while cxcr1, the Cxcl8a receptor gene, is expressed in coronary endothelial cells. We further show that Cxcl8a-Cxcr1 signaling is also required for coronary endothelial cell proliferation during cardiac regeneration.

CONCLUSIONS

These data show that after cardiac injury, coronary endothelial cells upregulate vegfc to promote coronary network reestablishment and cardiac regeneration. Mechanistically, Vegfc signaling upregulates epicardial emilin2a and cxcl8a expression to promote cardiac regeneration. These studies aid in understanding the mechanisms underlying coronary revascularization in zebrafish, with potential therapeutic implications to enhance revascularization and regeneration in injured human hearts.

Proper migration of lymphatic endothelial cells requires survival and guidance cues from arterial mural cells

The migration of lymphatic endothelial cells (LECs) is key for the development of the complex and vast lymphatic vascular network that pervades most tissues in an organism. In zebrafish, arterial intersegmental vessels together with chemokines have been shown to promote lymphatic cell migration from the horizontal myoseptum (HM). We observed that emergence of mural cells around the intersegmental arteries coincides with lymphatic departure from HM which raised the possibility that arterial mural cells promote LEC migration. Our live imaging and cell ablation experiments revealed that LECs migrate slower and fail to establish the lymphatic vascular network in the absence of arterial mural cells. We determined that mural cells are a source for the C-X-C motif chemokine 12 (Cxcl12a and Cxcl12b), vascular endothelial growth factor C (Vegfc) and collagen and calcium-binding EGF domain-containing protein 1 (Ccbe1). We showed that chemokine and growth factor signalling function cooperatively to induce robust LEC migration. Specifically, Vegfc-Vegfr3 signalling, but not chemokines, induces extracellular signal-regulated kinase (ERK) activation in LECs, and has an additional pro-survival role in LECs during the migration. Together, the identification of mural cells as a source for signals that guide LEC migration and survival will be important in the future design for rebuilding lymphatic vessels in disease contexts.

CCBE1 in Cardiac Development and Disease

The collagen- and calcium-binding EGF-like domains 1 (CCBE1) is a secreted protein extensively described as indispensable for lymphangiogenesis during development enhancing VEGF-C signaling. In human patients, mutations in CCBE1 have been found to cause Hennekam syndrome, an inherited disease characterized by malformation of the lymphatic system that presents a wide variety of symptoms such as primary lymphedema, lymphangiectasia, and heart defects. Importantly, over the last decade, an essential role for CCBE1 during heart development is being uncovered. In mice, Ccbe1 expression was initially detected in distinct cardiac progenitors such as first and second heart field, and the proepicardium. More recently, Ccbe1 expression was identified in the epicardium and sinus venosus (SV) myocardium at E11.5–E13.5, the stage when SV endocardium–derived (VEGF-C dependent) coronary vessels start to form. Concordantly, CCBE1 is required for the correct formation of the coronary vessels and the coronary artery stem in the mouse. Additionally, Ccbe1 was found to be enriched in mouse embryonic stem cells (ESC) and revealed as a new essential gene for the differentiation of ESC-derived early cardiac precursor cell lineages. Here, we bring an up-to-date review on the role of CCBE1 in cardiac development, function, and human disease implications. Finally, we envisage the potential of this molecule’s functions from a regenerative medicine perspective, particularly novel therapeutic strategies for heart disease.

Zebrafish vascular quantification: a tool for quantification of three-dimensional zebrafish cerebrovascular architecture by automated image analysis

Zebrafish transgenic lines and light sheet fluorescence microscopy allow in-depth insights into three-dimensional vascular development in vivo. However, quantification of the zebrafish cerebral vasculature in 3D remains highly challenging. Here, we describe and test an image analysis workflow for 3D quantification of the total or regional zebrafish brain vasculature, called zebrafish vasculature quantification (ZVQ). It provides the first landmark- or object-based vascular inter-sample registration of the zebrafish cerebral vasculature, producing population average maps allowing rapid assessment of intra- and inter-group vascular anatomy. ZVQ also extracts a range of quantitative vascular parameters from a user-specified region of interest, including volume, surface area, density, branching points, length, radius and complexity. Application of ZVQ to 13 experimental conditions, including embryonic development, pharmacological manipulations and morpholino-induced gene knockdown, shows that ZVQ is robust, allows extraction of biologically relevant information and quantification of vascular alteration, and can provide novel insights into vascular biology. To allow dissemination, the code for quantification, a graphical user interface and workflow documentation are provided. Together, ZVQ provides the first open-source quantitative approach to assess the 3D cerebrovascular architecture in zebrafish.

Summary: An image analysis workflow pipeline for 3D quantification of the total or regional zebrafish brain vasculature, called zebrafish vasculature quantification or ZVQ.

Hsa_circ_0076931 suppresses malignant biological properties, down-regulates miR-6760-3p through direct binding, and up-regulates CCBE1 in glioma

The function of circular RNAs (circRNAs) in gliomas is as yet unknown. The present study explored role of hsa_circ_0076931 in glioma. circRNA expression profiles were identified via RNA-seq followed by qRT-PCR validation in three pairs of glioma and normal brain tissues (NBT). The function of hsa_circ_0076931 was investigated in vitro using cell lines as well as in vivo using a xenograft tumor. Hsa_circ_0076931 was up-regulated by overexpression and an mRNA profile compared with wild-type was identified by RNA-seq. The relationship between miR-6760-3p and hsa_circ_0076931 or CCBE1 was confirmed via luciferase reporter or AGO2-RIP assays. A total of 507 circRNAs were identified in glioma tissues that were differentially expressed compared with that in NBT, and the sequencing data were deposited in BioProject (ID: PRJNA746438). Hsa_circ_0007694 and hsa_circ_0008016 were memorably increased whereas hsa_circ_0076931 and hsa_circ_0076948 decreased in glioma compared with those in NBT. Additionally, hsa_circ_0076931 expression was negatively correlated with histological grade. Overexpression of hsa_circ_0076931 inhibited proliferation, migration, and invasion while promoting apoptosis of glioma cells. A total of 4383 and 537 aberrantly expressed genes were identified between the hsa_circ_0076931-overexpressed and control groups in H4 and U118-MG cells, respectively; the sequencing data were deposited in BioProject (ID: PRJNA746438). These differentially expressed genes were mainly enriched in cancer-related pathways. In addition, elevated hsa_circ_0076931 levels induced the expression of CCBE1 while suppressing miR-6760-3p expression. miR-6760-3p can bind to hsa_circ_0076931. The experimental evidence supports using hsa_circ_0076931 as a marker for glioma and to help prevent malignant progression. The mechanism might be relevant to miR-6760-3p and CCBE1.

Copper stress impairs angiogenesis and lymphangiogenesis during zebrafish embryogenesis by down-regulating pERK1/2-foxm1-MMP2/9 axis and epigenetically regulating ccbe1 expression

Molecular transport and cell circulation between tissues and organs through blood and lymphatic vessels are essential for physiological homeostasis in vertebrates. Despite the report of its association with vessel formation in solid tumors, the biological effects of Copper (Cu) accumulation on angiogenesis and lymphangiogenesis during embryogenesis are still unknown. In this study, we unveiled that intersegmental blood circulation was partially blocked in Cu²⁺-stressed zebrafish embryos and cell migration and tube formation were impaired in Cu²⁺-stressed mammalian HUVECs. Specifically, Cu²⁺-stressed embryos showed down-regulation in the expression of amotl2 and its downstream pERK1/2-foxm1-MMP2/9 regulatory axis, and knockdown/knockout of foxm1 in zebrafish embryos phenocopied angiogenesis defects, while FOXM1 knockdown HUVECs phenocopied cell migration and tube formation defects, indicating that excessive Cu²⁺-induced angiogenesis defects and blocked cell migration via down-regulating amotl2-pERK1/2-foxm1-MMP2/9 regulatory axis in both embryos and mammalian cells. Additionally, thoracic duct was revealed to be partially absent in Cu²⁺-stressed zebrafish embryos. Specifically, Cu²⁺-stressed embryos showed down-regulation in the expression of ccbe1 (a gene with pivotal function in lymphangiogenesis) due to the hypermethylation of the E2F7/8 binding sites on ccbe1 promoter to reduce their binding enrichment on the promoter, contributing to the potential mechanisms for down-regulation of ccbe1 and the formation of lymphangiogenesis defects in Cu²⁺-stressed embryos and mammalian cells. These integrated data demonstrate that Cu²⁺ stress impairs angiogenesis and lymphangiogenesis via down-regulation of pERK1/2-foxm1-MMP2/9 axis and epigenetic regulation of E2F7/8 transcriptional activity on ccbe1 expression, respectively.

Vascular endothelial growth factor c regulates hematopoietic stem cell fate in the dorsal aorta

Hematopoietic stem and progenitor cells (HSPCs) are multipotent cells that self-renew or differentiate to establish the entire blood hierarchy. HSPCs arise from the hemogenic endothelium of the dorsal aorta (DA) during development in a process called endothelial-to-hematopoietic transition. The factors and signals that control HSPC fate decisions from the hemogenic endothelium are not fully understood. We found that Vegfc has a role in HSPC emergence from the zebrafish DA. Using time-lapse live imaging, we show that some HSPCs in the DA of vegfc loss-of-function embryos display altered cellular behavior. Instead of typical budding from the DA, emergent HSPCs exhibit crawling behavior similar to myeloid cells. This was confirmed by increased myeloid cell marker expression in the ventral wall of the DA and the caudal hematopoietic tissue. This increase in myeloid cells corresponded with a decrease in HSPCs that persisted into larval stages. Together, our data suggest that Vegfc regulates HSPC emergence in the hemogenic endothelium, in part by suppressing a myeloid cell fate. Our study provides a potential signal for modulation of HSPC fate in stem cell differentiation protocols.

Lymphatic endothelial cell fate specification in the mammalian embryo: An historical perspective

Development of the mammalian lymphatic vasculature is a stepwise process requiring the specification of lymphatic endothelial cell progenitors in the embryonic veins, and their subsequent budding to give rise to most of the mature lymphatic vasculature. In mice, formation of the lymphatic vascular network starts inside the cardinal vein at around E9.5 when a subpopulation of venous endothelial cells gets committed into the lymphatic lineage by their acquisition of Prox1 expression. Identification of critical genes regulating lymphatic development facilitated the detailed cellular and molecular characterization of some of the cellular and molecular mechanisms regulating the early steps leading to the formation of the mammalian lymphatic vasculature. A better understanding of basic aspects of early lymphatic development, and the availability of novel tools and animal models has been instrumental in the identification of important novel functional roles of this vasculature network.

The lymphangiogenic factor CCBE1 promotes angiogenesis and tumor growth in colorectal cancer

BACKGROUND

Collagen and calcium-binding EGF domain-1 (CCBE1) is essential for the development of the lymphatic vasculature and colorectal cancer (CRC) lymphangiogenesis as it enhances the proteolytic process of vascular endothelial growth factor C (VEGFC) activating VEGFR3. The fully processed mature VEGFC could also activate VEGFR2, the important endothelial-specific receptor tyrosine kinase, involved in blood vascular development and tumor angiogenesis. However, the role of CCBE1 in cancer angiogenesis remains undefined.

METHODS

In this paper, we find that the protein expression of CCBE1 is higher in the primary CRC tissue with distant metastasis and positively correlated with blood vessel density.

RESULTS

The mRNA expression of CCBE1 is closely positively correlated with the vascular endothelial marker CD31 and VEGFR2 in CRC from TCGA datasets. The supernatant of the colorectal cancer cell line HCT116 with CCBE1 overexpression significantly promotes the tube formation ability of the human umbilical vein endothelial cells (HUVECs) in vitro and enhances angiogenesis and tumor growth in vivo. Knockdown of CCBE1 decreases the angiogenic ability of CRC.

CONCLUSION

Our results demonstrate the angiogenic role of CCBE1 in CRC.

The RNA helicase Ddx21 controls Vegfc-driven developmental lymphangiogenesis by balancing endothelial cell ribosome biogenesis and p53 function

The development of a functional vasculature requires the coordinated control of cell fate, lineage differentiation and network growth. Cellular proliferation is spatiotemporally regulated in developing vessels, but how this is orchestrated in different lineages is unknown. Here, using a zebrafish genetic screen for lymphatic-deficient mutants, we uncover a mutant for the RNA helicase Ddx21. Ddx21 cell-autonomously regulates lymphatic vessel development. An established regulator of ribosomal RNA synthesis and ribosome biogenesis, Ddx21 is enriched in sprouting venous endothelial cells in response to Vegfc-Flt4 signalling. Ddx21 function is essential for Vegfc-Flt4-driven endothelial cell proliferation. In the absence of Ddx21, endothelial cells show reduced ribosome biogenesis, p53 and p21 upregulation and cell cycle arrest that blocks lymphangiogenesis. Thus, Ddx21 coordinates the lymphatic endothelial cell response to Vegfc-Flt4 signalling by balancing ribosome biogenesis and p53 function. This mechanism may be targetable in diseases of excessive lymphangiogenesis such as cancer metastasis or lymphatic malformation.

Development and physiological functions of the lymphatic system: insights from human genetic studies of primary lymphedema

Primary lymphedema is a long-term (chronic) condition characterized by tissue lymph retention and swelling that can affect any part of the body, although it usually develops in the arms or legs. Due to the relevant contribution of the lymphatic system to human physiology, while this review mainly focuses on the clinical and physiological aspects related to the regulation of fluid homeostasis and edema, clinicians need to know that the impact of lymphatic dysfunction with a genetic origin can be wide ranging. Lymphatic dysfunction can affect immune function so leading to infection; it can influence cancer development and spread, and it can determine fat transport so impacting on nutrition and obesity. Genetic studies and the development of imaging techniques for the assessment of lymphatic function have enabled the recognition of primary lymphedema as a heterogenic condition in terms of genetic causes and disease mechanisms. In this review, the known biological functions of several genes crucial to the development and function of the lymphatic system are used as a basis for understanding normal lymphatic biology. The disease conditions originating from mutations in these genes are discussed together with a detailed clinical description of the phenotype and the up-to-date knowledge in terms of disease mechanisms acquired from in vitro and in vivo research models.

Regulation of VEGFR Signalling in Lymphatic Vascular Development and Disease: An Update

The importance of lymphatic vessels in a myriad of human diseases is rapidly gaining recognition; lymphatic vessel dysfunction is a feature of disorders including congenital lymphatic anomalies, primary lymphoedema and obesity, while improved lymphatic vessel function increases the efficacy of immunotherapy for cancer and neurological disease and promotes cardiac repair following myocardial infarction. Understanding how the growth and function of lymphatic vessels is precisely regulated therefore stands to inform the development of novel therapeutics applicable to a wide range of human diseases. Lymphatic vascular development is initiated during embryogenesis following establishment of the major blood vessels and the onset of blood flow. Lymphatic endothelial progenitor cells arise from a combination of venous and non-venous sources to generate the initial lymphatic vascular structures in the vertebrate embryo, which are then further ramified and remodelled to elaborate an extensive lymphatic vascular network. Signalling mediated via vascular endothelial growth factor (VEGF) family members and vascular endothelial growth factor receptor (VEGFR) tyrosine kinases is crucial for development of both the blood and lymphatic vascular networks, though distinct components are utilised to different degrees in each vascular compartment. Although much is known about the regulation of VEGFA/VEGFR2 signalling in the blood vasculature, less is understood regarding the mechanisms by which VEGFC/VEGFD/VEGFR3 signalling is regulated during lymphatic vascular development. This review will focus on recent advances in our understanding of the cellular and molecular mechanisms regulating VEGFA-, VEGFC- and VEGFD-mediated signalling via VEGFRs which are important for driving the construction of lymphatic vessels during development and disease.

The physiological and pathological functions of VEGFR3 in cardiac and lymphatic development and related diseases

Vascular endothelial growth factor receptors (VEGFRs) are part of the evolutionarily conserved VEGF signalling pathways that regulate the development and maintenance of the body's cardiovascular and lymphovascular systems. VEGFR3, encoded by the FLT4 gene, has an indispensable and well-characterized function in development and establishment of the lymphatic system. Autosomal dominant VEGFR3 mutations, that prevent the receptor functioning as a homodimer, cause one of the major forms of hereditary primary lymphoedema; Milroy disease. Recently, we and others have shown that FLT4 variants, distinct to those observed in Milroy disease cases, predispose individuals to Tetralogy of Fallot, the most common cyanotic congenital heart disease, demonstrating a novel function for VEGFR3 in early cardiac development. Here, we examine the familiar and emerging roles of VEGFR3 in the development of both lymphovascular and cardiovascular systems, respectively, compare how distinct genetic variants in FLT4 lead to two disparate human conditions, and highlight the research still required to fully understand this multifaceted receptor.

3,4-Difluorobenzocurcumin Inhibits Vegfc-Vegfr3-Erk Signalling to Block Developmental Lymphangiogenesis in Zebrafish

Lymphangiogenesis, the formation of new lymphatic vessels from pre-existing vasculature, plays critical roles in disease, including in cancer metastasis and chronic inflammation. Preclinical and recent clinical studies have now demonstrated therapeutic utility for several anti-lymphangiogenic agents, but optimal agents and efficacy in different settings remain to be determined. We tested the anti-lymphangiogenic property of 3,4-Difluorobenzocurcumin (CDF), which has previously been implicated as an anti-cancer agent, using zebrafish embryos and cultured vascular endothelial cells. We used transgenic zebrafish labelling the lymphatic system and found that CDF potently inhibits lymphangiogenesis during embryonic development. We also found that the parent compound, Curcumin, does not inhibit lymphangiogenesis. CDF blocked lymphatic and venous sprouting, and lymphatic migration in the head and trunk of the embryo. Mechanistically, CDF impaired VEGFC-VEGFR3-ERK signalling in vitro and in vivo. In an in vivo pathological model of Vegfc-overexpression, treatment with CDF rescued endothelial cell hyperplasia. CDF did not inhibit the kinase activity of VEGFR3 yet displayed more prolonged activity in vivo than previously reported kinase inhibitors. These findings warrant further assessment of CDF and its mode of action as a candidate for use in metastasis and diseases of aberrant lymphangiogenesis.

Lymphatic Malformations: Genetics, Mechanisms and Therapeutic Strategies

Lymphatic vessels maintain tissue fluid homeostasis by returning to blood circulation interstitial fluid that has extravasated from the blood capillaries. They provide a trafficking route for cells of the immune system, thus critically contributing to immune surveillance. Developmental or functional defects in the lymphatic vessels, their obstruction or damage, lead to accumulation of fluid in tissues, resulting in lymphedema. Here we discuss developmental lymphatic anomalies called lymphatic malformations and complex lymphatic anomalies that manifest as localized or multifocal lesions of the lymphatic vasculature, respectively. They are rare diseases that are caused mostly by somatic mutations and can present with variable symptoms based upon the size and location of the lesions composed of fluid-filled cisterns or channels. Substantial progress has been made recently in understanding the molecular basis of their pathogenesis through the identification of their genetic causes, combined with the elucidation of the underlying mechanisms in animal disease models and patient-derived lymphatic endothelial cells. Most of the solitary somatic mutations that cause lymphatic malformations and complex lymphatic anomalies occur in genes that encode components of oncogenic growth factor signal transduction pathways. This has led to successful repurposing of some targeted cancer therapeutics to the treatment of lymphatic malformations and complex lymphatic anomalies. Apart from the mutations that act as lymphatic endothelial cell-autonomous drivers of these anomalies, current evidence points to superimposed paracrine mechanisms that critically contribute to disease pathogenesis and thus provide additional targets for therapeutic intervention. Here, we review these advances and discuss new treatment strategies that are based on the recently identified molecular pathways.

When form meets function: the cells and signals that shape the lymphatic vasculature during development

The lymphatic vasculature is an integral component of the cardiovascular system. It is essential to maintain tissue fluid homeostasis, direct immune cell trafficking and absorb dietary lipids from the digestive tract. Major advances in our understanding of the genetic and cellular events important for constructing the lymphatic vasculature during development have recently been made. These include the identification of novel sources of lymphatic endothelial progenitor cells, the recognition of lymphatic endothelial cell specialisation and heterogeneity, and discovery of novel genes and signalling pathways underpinning developmental lymphangiogenesis. Here, we review these advances and discuss how they inform our understanding of lymphatic network formation, function and dysfunction.

miR-942-5p Inhibits Proliferation, Metastasis, and Epithelial-Mesenchymal Transition in Colorectal Cancer by Targeting CCBE1

Although colorectal cancer (CRC) is common, there is a paucity of information regarding its molecular pathogenesis. Studies have shown that miRNAs play pivotal roles in the development and progression of CRC. There is a need to further investigate the biological functions of miRNAs in CRC. In particular, it has been reported that miR-942-5p exhibits tumor-suppressive properties. Thus, we analyzed the functional significance of miR-942-5p in CRC and the underlying molecular mechanisms. We found that miR-942-5p was downregulated in CRC tissues and cells. Cell Counting Kit-8, EdU, and colony formation assays revealed that the overexpression of miR-942-5p by mimics inhibited the proliferation of CRC cells. Use of the miR-942-5p inhibitor effectively enhanced the proliferative potential of CRC cells. Further, in vivo xenograft experiments confirmed these results. Increased expression of miR-942-5p suppressed the invasion, migration, and epithelial-mesenchymal transition of CRC cell lines, while decreased miR-942-5p expression had the opposite effect. CCBE1, a secretory molecule for lymphangiogenesis, was established as a downstream target of miR-942-5p, and its expression was inversely correlated with the expression of miR-942-5p in CRC cells. Additionally, cotransfection of the miR-942-5p inhibitor with si-CCBE1 into CRC cells reversed the effects induced by miR-942-5p overexpression. In conclusion, we confirmed that miR-942-5p exerts oncogenic actions in CRC by targeting CCBE1 and identified miR-942-5p as a potential clinical biomarker for CRC diagnosis and therapy.

The adaptor protein Grb2b is an essential modulator for lympho-venous sprout formation in the zebrafish trunk

Vegfc/Vegfr3 signaling is critical for lymphangiogenesis, the sprouting of lymphatic vessels. In zebrafish, cells sprouting from the posterior cardinal vein can either form lymphatic precursor cells or contribute to intersegmental vein formation. Both, the Vegfc-dependent differential induction of Prox1a in sprouting cells as well as a Notch-mediated pre-pattern within intersegmental vessels have been associated with the regulation of secondary sprout behavior. However, how exactly a differential lymphatic versus venous sprout cell behavior is achieved is not fully understood. Here, we characterize a zebrafish mutant in the adaptor protein Grb2b, and demonstrate through genetic interaction studies that Grb2b acts within the Vegfr3 pathway. Mutant embryos exhibit phenotypes that are consistent with reduced Vegfr3 signaling outputs prior to the sprouting of endothelial cells from the vein. During secondary sprouting stages, loss of grb2b leads to defective cell behaviors resulting in a loss of parachordal lymphangioblasts, while only partially affecting the number of intersegmental veins. A second GRB2 zebrafish ortholog, grb2a, contributes to the development of lymphatic structures in the meninges and in the head, but not in the trunk. Our results illustrate an essential role of Grb2b in vivo for cell migration to the horizontal myoseptum and for the correct formation of the lymphatic vasculature, while being less critically required in intersegmental vein formation. Thus, there appear to be higher requirements for Grb2b and therefore Vegfr3 downstream signaling levels in lymphatic versus vein precursor-generating sprouts.

Proteolytic Cleavages in the VEGF Family: Generating Diversity among Angiogenic VEGFs, Essential for the Activation of Lymphangiogenic VEGFs

Specific proteolytic cleavages turn on, modify, or turn off the activity of vascular endothelial growth factors (VEGFs). Proteolysis is most prominent among the lymph-angiogenic VEGF-C and VEGF-D, which are synthesized as precursors that need to undergo enzymatic removal of their C- and N-terminal propeptides before they can activate their receptors. At least five different proteases mediate the activating cleavage of VEGF-C: plasmin, ADAMTS3, prostate-specific antigen, cathepsin D, and thrombin. All of these proteases except for ADAMTS3 can also activate VEGF-D. Processing by different proteases results in distinct forms of the "mature" growth factors, which differ in affinity and receptor activation potential. The "default" VEGF-C-activating enzyme ADAMTS3 does not activate VEGF-D, and therefore, VEGF-C and VEGF-D do function in different contexts. VEGF-C itself is also regulated in different contexts by distinct proteases. During embryonic development, ADAMTS3 activates VEGF-C. The other activating proteases are likely important for non-developmental lymphangiogenesis during, e.g., tissue regeneration, inflammation, immune response, and pathological tumor-associated lymphangiogenesis. The better we understand these events at the molecular level, the greater our chances of developing successful therapies targeting VEGF-C and VEGF-D for diseases involving the lymphatics such as lymphedema or cancer.

Atypical cadherin FAT4 orchestrates lymphatic endothelial cell polarity in response to flow

The atypical cadherin FAT4 has established roles in the regulation of planar cell polarity and Hippo pathway signaling that are cell context dependent. The recent identification of FAT4 mutations in Hennekam syndrome, features of which include lymphedema, lymphangiectasia, and mental retardation, uncovered an important role for FAT4 in the lymphatic vasculature. Hennekam syndrome is also caused by mutations in collagen and calcium binding EGF domains 1 (CCBE1) and ADAM metallopeptidase with thrombospondin type 1 motif 3 (ADAMTS3), encoding a matrix protein and protease, respectively, that regulate activity of the key prolymphangiogenic VEGF-C/VEGFR3 signaling axis by facilitating the proteolytic cleavage and activation of VEGF-C. The fact that FAT4, CCBE1, and ADAMTS3 mutations underlie Hennekam syndrome suggested that all 3 genes might function in a common pathway. We identified FAT4 as a target gene of GATA-binding protein 2 (GATA2), a key transcriptional regulator of lymphatic vascular development and, in particular, lymphatic vessel valve development. Here, we demonstrate that FAT4 functions in a lymphatic endothelial cell-autonomous manner to control cell polarity in response to flow and is required for lymphatic vessel morphogenesis throughout development. Our data reveal a crucial role for FAT4 in lymphangiogenesis and shed light on the mechanistic basis by which FAT4 mutations underlie a human lymphedema syndrome.

Development and aging of the lymphatic vascular system

The lymphatic vasculature has a pivotal role in regulating body fluid homeostasis, immune surveillance and dietary fat absorption. The increasing number of in vitro and in vivo studies in the last decades has shed light on the processes of lymphatic vascular development and function. Here, we will discuss the current progress in lymphatic vascular biology such as the mechanisms of lymphangiogenesis, lymphatic vascular maturation and maintenance and the emerging mechanisms of lymphatic vascular aging.

Lymphatic Vasculature: An Emerging Therapeutic Target and Drug Delivery Route

The lymphatic system has received increasing scientific and clinical attention because a wide variety of diseases are linked to lymphatic pathologies and because the lymphatic system serves as an ideal conduit for drug delivery. Lymphatic vessels exert heterogeneous roles in different organs and vascular beds, and consequently, their dysfunction leads to distinct organ-specific outcomes. Although studies in animal model systems have led to the identification of crucial lymphatic genes with potential therapeutic benefit, effective lymphatic-targeted therapeutics are currently lacking for human lymphatic pathological conditions. Here, we focus on the therapeutic roles of lymphatic vessels in diseases and summarize the promising therapeutic targets for modulating lymphangiogenesis or lymphatic function in preclinical or clinical settings. We also discuss considerations for drug delivery or targeting of lymphatic vessels for treatment of lymphatic-related diseases. The lymphatic vasculature is rapidly emerging as a critical system for targeted modulation of its function and as a vehicle for innovative drug delivery.

Lymphangiogenesis in renal fibrosis arises from macrophages via VEGF-C/VEGFR3-dependent autophagy and polarization

Inflammation plays a crucial role in the occurrence and development of renal fibrosis, which ultimately results in end-stage renal disease (ESRD). There is new focus on lymphangiogenesis in the field of inflammation. Recent studies have revealed the association between lymphangiogenesis and renal fibrosis, but the source of lymphatic endothelial cells (LECs) is not clear. It has also been reported that macrophages are involved in lymphangiogenesis through direct and indirect mechanisms in other tissues. We hypothesized that there was a close relationship between macrophages and lymphatic endothelial progenitor cells in renal fibrosis. In this study, we demonstrated that lymphangiogenesis occurred in a renal fibrosis model and was positively correlated with the degree of fibrosis and macrophage infiltration. Compared to resting (M0) macrophages and alternatively activated (M2) macrophages, classically activated (M1) macrophages predominantly transdifferentiated into LECs in vivo and in vitro. VEGF-C further increased M1 macrophage polarization and transdifferentiation into LECs by activating VEGFR3. It was suggested that VEGF-C/VEGFR3 pathway activation downregulated macrophage autophagy and subsequently regulated macrophage phenotype. The induction of autophagy in macrophages by rapamycin decreased M1 macrophage polarization and differentiation into LECs. These results suggested that M1 macrophages promoted lymphangiogenesis and contributed to newly formed lymphatic vessels in the renal fibrosis microenvironment, and VEGF-C/VEGFR3 signaling promoted macrophage M1 polarization by suppressing macrophage autophagy and then increased the transdifferentiation of M1 macrophages into LECs.

Endothelial cell-type-specific molecular requirements for angiogenesis drive fenestrated vessel development in the brain

Vascular endothelial cells (vECs) in the brain exhibit structural and functional heterogeneity. Fenestrated, permeable brain vasculature mediates neuroendocrine function, body-fluid regulation, and neural immune responses; however, its vascular formation remains poorly understood. Here, we show that specific combinations of vascular endothelial growth factors (Vegfs) are required to selectively drive fenestrated vessel formation in the zebrafish myelencephalic choroid plexus (mCP). We found that the combined, but not individual, loss of Vegfab, Vegfc, and Vegfd causes severely impaired mCP vascularization with little effect on neighboring non-fenestrated brain vessel formation, demonstrating fenestrated-vEC-specific angiogenic requirements. This Vegfs-mediated vessel-selective patterning also involves Ccbe1. Expression analyses, cell-type-specific ablation, and paracrine activity-deficient vegfc mutant characterization suggest that vEC-autonomous Vegfc and meningeal fibroblast-derived Vegfab and Vegfd are critical for mCP vascularization. These results define molecular cues and cell types critical for directing fenestrated CP vascularization and indicate that vECs’ distinct molecular requirements for angiogenesis underlie brain vessel heterogeneity.

The Bruton's Tyrosine Kinase Inhibitor Ibrutinib Impairs the Vascular Development of Zebrafish Larvae

Ibrutinib is an orally bioavailable, irreversible selective Bruton’s tyrosine kinase inhibitor that has demonstrated impressive therapeutic effects in patients with B cell malignancies. However, adverse effects, such as bleeding and hypertension, are also reported, implying that studies on the toxicological effect of ibrutinib on living organisms are needed. Here, we have used zebrafish, a successful model organism for studying toxicology, to investigate the influence of ibrutinib during embryogenesis. We found that ibrutinib had potent toxicity on embryonic development, especially vascular development in zebrafish embryos. We also revealed that ibrutinib perturbed vascular formation by suppressing angiogenesis, rather than vasculogenesis. In addition, ibrutinib exposure led to the collapse of the vascular lumen, as well as reduced proliferation and enhanced apoptosis of vascular endothelial cells. Moreover, the expression of vascular development-related genes was also altered in ibrutinib-treated embryos. To our knowledge, this is the first study to describe the vascular toxicity of ibrutinib in an animal model, providing a theoretical basis for clinical safety guidelines in ibrutinib treatment.

Transcriptome profiling of different developmental stages of corpus luteum during the estrous cycle in pigs

To better understand the molecular basis of corpus luteum (CL) development and function RNA-Seq was utilized to identify differentially expressed genes (DEGs) in porcine CL during different physiological stages of the estrous cycle viz. early (EL), mid (ML), late (LL) and regressed (R) luteal. Stage wise comparisons obtained 717 (EL vs. ML), 568 (EL vs. LL), 527 (EL vs. R), 786 (ML vs. LL), 474 (ML vs. R) and 534 (LL vs. R) DEGs with log₂(FC) ≥1 and p < 0.05. The process of angiogenesis, steroidogenesis, signal transduction, translation, cell proliferation and tissue remodelling were significantly (p < 0.05) enriched in EL, ML and LL stages, where as apoptosis was most active in regressed stage. Pathway analysis revealed that most annotated genes were associated with lipid metabolism, translation, immune and endocrine system pathways depicting intra-luteal control of diverse CL function. The network analysis identified genes AR, FOS, CDKN1A, which were likely the novel hub genes regulating CL physiology.

Network patterning, morphogenesis and growth in lymphatic vascular development

The lymphatic vasculature is a vital component of the vertebrate vascular system that mediates tissue fluid homeostasis, lipid uptake and immune surveillance. The development of the lymphatic vasculature starts in the early vertebrate embryo, when a subset of blood vascular endothelial cells of the cardinal veins acquires lymphatic endothelial cell fate. These cells sprout from the veins, migrate, proliferate and organize to give rise to a highly structured and unique vascular network. Cellular cross-talk, cell-cell communication and the interpretation of signals from surrounding tissues are all essential for coordinating these processes. In this chapter, we highlight new findings and review research progress with a particular focus on LEC migration and guidance, expansion of the LEC lineage, network remodeling and morphogenesis of the lymphatic vasculature.

Cellular Origins of the Lymphatic Endothelium: Implications for Cancer Lymphangiogenesis

The lymphatic system plays important roles in physiological and pathological conditions. During cancer progression in particular, lymphangiogenesis can exert both positive and negative effects. While the formation of tumor associated lymphatic vessels correlates with metastatic dissemination, increased severity and poor patient prognosis, the presence of functional lymphatics is regarded as beneficial for anti-tumor immunity and cancer immunotherapy delivery. Therefore, a profound understanding of the cellular origins of tumor lymphatics and the molecular mechanisms controlling their formation is required in order to improve current strategies to control malignant spread. Data accumulated over the last decades have led to a controversy regarding the cellular sources of tumor-associated lymphatic vessels and the putative contribution of non-endothelial cells to this process. Although it is widely accepted that lymphatic endothelial cells (LECs) arise mainly from pre-existing lymphatic vessels, additional contribution from bone marrow-derived cells, myeloid precursors and terminally differentiated macrophages, has also been claimed. Here, we review recent findings describing new origins of LECs during embryonic development and discuss their relevance to cancer lymphangiogenesis.