The Schlemm's canal is a VEGF-C/VEGFR-3-responsive lymphatic-like vessel

Transcriptomic profiling of Schlemm's canal cells reveals a lymphatic-biased identity and three major cell states

Schlemm's canal (SC) is central in intraocular pressure regulation but requires much characterization. It has distinct inner and outer walls, each composed of Schlemm's canal endothelial cells (SECs) with different morphologies and functions. Recent transcriptomic studies of the anterior segment added important knowledge, but were limited in power by SEC numbers or did not focus on SC. To gain a more comprehensive understanding of SC biology, we performed bulk RNA sequencing on C57BL/6J SC, blood vessel, and lymphatic endothelial cells from limbal tissue (~4500 SECs). We also analyzed mouse limbal tissues by single-cell and single-nucleus RNA sequencing (C57BL/6J and 129/Sj strains), successfully sequencing 903 individual SECs. Together, these datasets confirm that SC has molecular characteristics of both blood and lymphatic endothelia with a lymphatic phenotype predominating. SECs are enriched in pathways that regulate cell-cell junction formation pointing to the importance of junctions in determining SC fluid permeability. Importantly, and for the first time, our analyses characterize 3 molecular classes of SECs, molecularly distinguishing inner wall from outer wall SECs and discovering two inner wall cell states that likely result from local environmental differences. Further, and based on ligand and receptor expression patterns, we document key interactions between SECs and cells of the adjacent trabecular meshwork (TM) drainage tissue. Also, we present cell type expression for a collection of human glaucoma genes. These data provide a new molecular foundation that will enable the functional dissection of key homeostatic processes mediated by SECs as well as the development of new glaucoma therapeutics.

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.

Healing responses at the angle after micro-invasive glaucoma surgery-an AS-OCT study

PURPOSE

To evaluate structural alterations and healing responses in the trabecular meshwork region with optical coherence tomography (AS-OCT) following after gonioscopy assisted transluminal trabeculotomy (GATT) and microincisional trabeculectomy (MIT).

METHODS

73 eyes of 67 patients (M:F = 45:22) with ≥6 months of follow-up after MIT (n = 41) or GATT (n = 32) with or without combined cataract surgery were included for this prospective study. The angle as seen on AS-OCT at 1, 3, 6 months after surgery were evaluated for structural alterations like peripheral anterior synechiae (PAS), hyphema, and hyperreflective scarring responses. The scarring was graded according to the linear extent measured from the centre of the trabecular meshwork (TM) gutter to the sclera/cornea as mild (<250μ), moderate (250-500μ), and severe(˃500μ), while the pattern of scarring was graded as open saucer/gutter, closed gutter, and trench pattern. The association of the need for medication or surgical outcome and clinical variables and AS-OCT parameters including the pattern and severity of scarring were analysed using multivariate regression.

RESULTS

All eyes achieved significant reduction of IOP and number of medications with a final IOP of 15±3.2mm Hg at a mean follow-up of 8±32. months. While mild scarring was seen more common in MIT, severe scarring was seen in >65% of GATT eyes compared to 31% of MIT eye, p<0.001. An open saucer was equally seen in MIT and GATT while the trench pattern was more commonly seen in GATT eyes (>50%). Severe scarring in a trench pattern seemed to predict the need for medications for IOP control, though they independently did not seem to influence the final IOP or surgical outcome.

CONCLUSION

A severe form of scarring in a trench pattern on AS-OCT predicted the need for glaucoma medications after MIGS surgery. Regular monitoring of the scarring responses by AS-OCT and clinical examination are necessary to identify those at need for medications after MIGS.

Aqueous humor as eye lymph: A crossroad between venous and lymphatic system

Aqueous humor (AQH) is a transparent fluid with characteristics similar to those of the interstitial fluid, which fills the eyeball posterior and anterior chambers and circulates in them from the sites of production to those of drainage. The AQH volume and pressure homeostasis is essential for the trophism of the ocular avascular tissues and their normal structure and function. Different AQH outflow pathways exist, including a main pathway, quite well defined anatomically and referred to as the conventional pathway, and some accessory pathways, more recently described and still not fully morphofunctionally understood, generically referred to as unconventional pathways. The conventional pathway is based on the existence of a series of conduits starting with the trabecular meshwork and Schlemm's Canal and continuing with a system of intrascleral and episcleral venules, which are tributaries to veins of the anterior segment of the eyeball. The unconventional pathways are mainly represented by the uveoscleral pathway, in which AQH flows through clefts, interstitial conduits located in the ciliary body and sclera, and then merges into the aforementioned intrascleral and episcleral venules. A further unconventional pathway, the lymphatic pathway, has been supported by the demonstration of lymphatic microvessels in the limbal sclera and, possibly, in the uvea (ciliary body, choroid) as well as by the ocular glymphatic channels, present in the neural retina and optic nerve. It follows that AQH may be drained from the eyeball through blood vessels (TM-SC pathway, US pathway) or lymphatic vessels (lymphatic pathway), and the different pathways may integrate or compensate for each other, optimizing the AQH drainage. The present review aims to define the state-of-the-art concerning the structural organization and the functional anatomy of all the AQH outflow pathways. Particular attention is paid to examining the regulatory mechanisms active in each of them. The new data on the anatomy and physiology of AQH outflow pathways is the key to understanding the pathophysiology of AQH outflow disorders and could open the way for novel approaches to their treatment.

VEGF-C and 5-Fluorouracil Improve Bleb Survival in a Rabbit Glaucoma Surgery Trabeculectomy Model

Purpose

To evaluate VEGF-C-induced lymphoproliferation in conjunction with 5-fluorouracil (5-FU) antimetabolite treatment in a rabbit glaucoma filtration surgery (GFS) model.

Methods

Thirty-two rabbits underwent GFS and were assigned to four groups (n = 8 each) defined by subconjunctival drug treatment: (a) VEGF-C combined with 5-FU, (b) 5-FU, (c) VEGF-C, (d) and control. Bleb survival, bleb measurements, and IOP were evaluated over 30 days. At the end, histology and anterior segment OCT were performed on some eyes. mRNA was isolated from the remaining eyes for RT-PCR evaluation of vessel-specific markers (lymphatics, podoplanin and LYVE-1; and blood vessels, CD31).

Results

Qualitatively and quantitatively, VEGF-C combined with 5-FU resulted in blebs which were posteriorly longer and wider than the other conditions: vs. 5-FU (P = 0.043 for longer, P = 0.046 for wider), vs. VEGF-C (P < 0.001, P < 0.001) and vs. control (P < 0.001, P < 0.001). After 30 days, the VEGF-C combined with 5-FU condition resulted in longer bleb survival compared with 5-FU (P = 0.025), VEGF-C (P < 0.001), and control (P < 0.001). Only the VEGF-C combined with 5-FU condition showed a negative correlation between IOP and time that was statistically significant (r = -0.533; P = 0.034). Anterior segment OCT and histology demonstrated larger blebs for the VEGF-C combined with 5-FU condition. Only conditions including VEGF-C led to increased expression of lymphatic markers (LYVE-1, P < 0.001-0.008 and podoplanin, P = 0.002-0.011). Expression of CD31 was not different between the groups (P = 0.978).

Conclusions

Adding VEGF-C lymphoproliferation to standard antimetabolite treatment improved rabbit GFS success and may suggest a future strategy to improve human GFSs.

Compartmentalized ocular lymphatic system mediates eye-brain immunity

The eye, an anatomical extension of the central nervous system (CNS), exhibits many molecular and cellular parallels to the brain. Emerging research demonstrates that changes in the brain are often reflected in the eye, particularly in the retina1. Still, the possibility of an immunological nexus between the posterior eye and the rest of the CNS tissues remains unexplored. Here, studying immune responses to herpes simplex virus in the brain, we observed that intravitreal immunization protects mice against intracranial viral challenge. This protection extended to bacteria and even tumours, allowing therapeutic immune responses against glioblastoma through intravitreal immunization. We further show that the anterior and posterior compartments of the eye have distinct lymphatic drainage systems, with the latter draining to the deep cervical lymph nodes through lymphatic vasculature in the optic nerve sheath. This posterior lymphatic drainage, like that of meningeal lymphatics, could be modulated by the lymphatic stimulator VEGFC. Conversely, we show that inhibition of lymphatic signalling on the optic nerve could overcome a major limitation in gene therapy by diminishing the immune response to adeno-associated virus and ensuring continued efficacy after multiple doses. These results reveal a shared lymphatic circuit able to mount a unified immune response between the posterior eye and the brain, highlighting an understudied immunological feature of the eye and opening up the potential for new therapeutic strategies in ocular and CNS diseases.

New targets of nascent lymphatic vessels in ocular diseases

Recent advancements in the field of endothelial markers of lymphatic vessels and lymphangiogenic factors have shed light on the association between several ocular diseases and ocular nascent lymphatic vessels. The immune privilege of corneal tissue typically limits the formation of lymphatic vessels in a healthy eye. However, vessels in the eyes can potentially undergo lymphangiogenesis and be conditionally activated. It is evident that nascent lymphatic vessels in the eyes contribute to various ocular pathologies. Conversely, lymphatic vessels are present in the corneal limbus, ciliary body, lacrimal glands, optic nerve sheaths, and extraocular muscles, while a lymphatic vasculature-like system exists in the choroid, that can potentially cause several ocular pathologies. Moreover, numerous studies indicate that many ocular diseases can influence or activate nascent lymphatic vessels, ultimately affecting patient prognosis. By understanding the mechanisms underlying the onset, development, and regression of ocular nascent lymphatic vessels, as well as exploring related research on ocular diseases, this article aims to offer novel perspectives for the treatment of such conditions.

Macrophage-induced integrin signaling promotes Schlemm's canal formation to prevent intraocular hypertension and glaucomatous optic neuropathy

Schlemm's canal (SC) functions to maintain proper intraocular pressure (IOP) by draining aqueous humor and has emerged as a promising therapeutic target for glaucoma, the second-leading cause of irreversible blindness worldwide. However, our current understanding of the mechanisms governing SC development and functionality remains limited. Here, we show that vitronectin (VTN) produced by limbal macrophages promotes SC formation and prevents intraocular hypertension by activating integrin αvβ3 signaling. Genetic inactivation of this signaling system inhibited the phosphorylation of AKT and FOXO1 and reduced β-catenin activity and FOXC2 expression, thereby causing impaired Prox1 expression and deteriorated SC morphogenesis. This ultimately led to increased IOP and glaucomatous optic neuropathy. Intriguingly, we found that aged SC displayed downregulated integrin β3 in association with dampened Prox1 expression. Conversely, FOXO1 inhibition rejuvenated the aged SC by inducing Prox1 expression and SC regrowth, highlighting a possible strategy by targeting VTN/integrin αvβ3 signaling to improve SC functionality.

Cell type evolution reconstruction across species through cell phylogenies of single-cell RNA sequencing data

The origin and evolution of cell types has emerged as a key topic in evolutionary biology. Driven by rapidly accumulating single-cell datasets, recent attempts to infer cell type evolution have largely been limited to pairwise comparisons because we lack approaches to build cell phylogenies using model-based approaches. Here we approach the challenges of applying explicit phylogenetic methods to single-cell data by using principal components as phylogenetic characters. We infer a cell phylogeny from a large, comparative single-cell dataset of eye cells from five distantly related mammals. Robust cell type clades enable us to provide a phylogenetic, rather than phenetic, definition of cell type, allowing us to forgo marker genes and phylogenetically classify cells by topology. We further observe evolutionary relationships between diverse vessel endothelia and identify the myelinating and non-myelinating Schwann cells as sister cell types. Finally, we examine principal component loadings and describe the gene expression dynamics underlying the function and identity of cell type clades that have been conserved across the five species. A cell phylogeny provides a rigorous framework towards investigating the evolutionary history of cells and will be critical to interpret comparative single-cell datasets that aim to ask fundamental evolutionary questions.

Current Advances in Corneal Stromal Stem Cell Biology and Therapeutic Applications

Corneal stromal stem cells (CSSCs) are of particular interest in regenerative ophthalmology, offering a new therapeutic target for corneal injuries and diseases. This review provides a comprehensive examination of CSSCs, exploring their anatomy, functions, and role in maintaining corneal integrity. Molecular markers, wound healing mechanisms, and potential therapeutic applications are discussed. Global corneal blindness, especially in more resource-limited regions, underscores the need for innovative solutions. Challenges posed by corneal defects, emphasizing the urgent need for advanced therapeutic interventions, are discussed. The review places a spotlight on exosome therapy as a potential therapy. CSSC-derived exosomes exhibit significant potential for modulating inflammation, promoting tissue repair, and addressing corneal transparency. Additionally, the rejuvenation potential of CSSCs through epigenetic reprogramming adds to the evolving regenerative landscape. The imperative for clinical trials and human studies to seamlessly integrate these strategies into practice is emphasized. This points towards a future where CSSC-based therapies, particularly leveraging exosomes, play a central role in diversifying ophthalmic regenerative medicine.

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.

Penile cavernous sinusoids are Prox1-positive hybrid vessels

Endothelial cells (ECs) of blood and lymphatic vessels have distinct identity markers that define their specialized functions. Recently, hybrid vasculatures with both blood and lymphatic vessel-specific features have been discovered in multiple tissues. Here, we identify the penile cavernous sinusoidal vessels (pc-Ss) as a new hybrid vascular bed expressing key lymphatic EC identity genes Prox1, Vegfr3,and Lyve1. Using single-cell transcriptome data of human corpus cavernosum tissue, we found heterogeneity within pc-S endothelia and observed distinct transcriptional alterations related to inflammatory processes in hybrid ECs in erectile dysfunction associated with diabetes. Molecular, ultrastructural, and functional studies further established hybrid identity of pc-Ss in mouse, and revealed their morphological adaptations and ability to perform lymphatic-like function in draining high-molecular-weight tracers. Interestingly, we found that inhibition of the key lymphangiogenic growth factor VEGF-C did not block the development of pc-Ss in mice, distinguishing them from other lymphatic and hybrid vessels analyzed so far. Our findings provide a detailed molecular characterization of hybrid pc-Ss and pave the way for the identification of molecular targets for therapies in conditions of dysregulated penile vasculature, including erectile dysfunction.

Effective extracellular vesicles in glioma: Focusing on effective ncRNA exosomes and immunotherapy methods for treatment

This comprehensive article explores the complex field of glioma treatment, with a focus on the important roles of non-coding RNAsRNAs (ncRNAs) and exosomes, as well as the potential synergies of immunotherapy. The investigation begins by examining the various functions of ncRNAs and their involvement in glioma pathogenesis, progression, and as potential diagnostic biomarkers. Special attention is given to exosomes as carriers of ncRNAs and their intricate dynamics within the tumor microenvironment. The exploration extends to immunotherapy methods, analyzing their mechanisms and clinical implications in the treatment of glioma. By synthesizing these components, the article aims to provide a comprehensive understanding of how ncRNAs, exosomes, and immunotherapy interact, offering valuable insights into the evolving landscape of glioma research and therapeutic strategies.

Genomics enabling personalised glaucoma care

Glaucoma is a leading cause of visual impairment and a significant public health concern, but despite ongoing advances in our understanding of the disease, several important clinical challenges remain. With the number of affected people projected to increase substantially over coming decades, novel approaches to screening, risk stratification, therapy and glaucoma research are essential to deal with this expanding burden in an efficient and cost-effective manner. Genomics may hold the key to unlocking further biological insights and enabling precision medicine, in which glaucoma care is tailored to the individual patient, based on their unique profile for disease. Here, we provide an overview of how genomics may enable cost-effective targeted population screening and personalised predictions of risk, response to treatment and effective lifestyle advice. Given rapid advances in genetic testing technology and a move towards population-level genotyping, these early results have several important implications that promise to revolutionise the way in which glaucoma is detected and managed in years to come.

Estrogen dysregulation, intraocular pressure, and glaucoma risk

Characterized by optic nerve atrophy due to retinal ganglion cell (RGC) death, glaucoma is the leading cause of irreversible blindness worldwide. Of the major risk factors for glaucoma (age, ocular hypertension, and genetics), only elevated intraocular pressure (IOP) is modifiable, which is largely regulated by aqueous humor outflow through the trabecular meshwork. Glucocorticoids such as dexamethasone have long been known to elevate IOP and lead to glaucoma. However, several recent studies have reported that steroid hormone estrogen levels inversely correlate with glaucoma risk, and that variants in estrogen signaling genes have been associated with glaucoma. As a result, estrogen dysregulation may contribute to glaucoma pathogenesis, and estrogen signaling may protect against glaucoma. The mechanism for estrogen-related protection against glaucoma is not completely understood but likely involves both regulation of IOP homeostasis and neuroprotection of RGCs. Based upon its known activities, estrogen signaling may promote IOP homeostasis by affecting extracellular matrix turnover, focal adhesion assembly, actin stress fiber formation, mechanosensation, and nitric oxide production. In addition, estrogen receptors in the RGCs may mediate neuroprotective functions. As a result, the estrogen signaling pathway may offer a therapeutic target for both IOP control and neuroprotection. This review examines the evidence for a relationship between estrogen and IOP and explores the possible mechanisms by which estrogen maintains IOP homeostasis.

Differential roles of FOXC2 in the trabecular meshwork and Schlemm's canal in glaucomatous pathology

Impaired development and maintenance of Schlemm's canal (SC) are associated with perturbed aqueous humor outflow and intraocular pressure. The angiopoietin (ANGPT)/TIE2 signaling pathway regulates SC development and maintenance, whereas the molecular mechanisms of crosstalk between SC and the neural crest (NC)-derived neighboring tissue, the trabecular meshwork (TM), are poorly understood. Here, we show NC-specific forkhead box (Fox)c2 deletion in mice results in impaired SC morphogenesis, loss of SC identity, and elevated intraocular pressure. Visible-light optical coherence tomography analysis further demonstrated functional impairment of the SC in response to changes in intraocular pressure in NC-Foxc2 -/- mice, suggesting altered TM biomechanics. Single-cell RNA-sequencing analysis identified that this phenotype is predominately characterized by transcriptional changes associated with extracellular matrix organization and stiffness in TM cell clusters, including increased matrix metalloproteinase expression, which can cleave the TIE2 ectodomain to produce soluble TIE2. Moreover, endothelial-specific Foxc2 deletion impaired SC morphogenesis because of reduced TIE2 expression, which was rescued by deleting the TIE2 phosphatase VE-PTP. Thus, Foxc2 is critical in maintaining SC identity and morphogenesis via TM-SC crosstalk.

The novel role of lymphatic vessels in the pathogenesis of ocular diseases

Historically, the eye has been considered as an organ free of lymphatic vessels. In recent years, however, it became evident, that lymphatic vessels or lymphatic-like vessels contribute to several ocular pathologies at various peri- and intraocular locations. The aim of this review is to outline the pathogenetic role of ocular lymphatics, the respective molecular mechanisms and to discuss current and future therapeutic options based thereon. We will give an overview on the vascular anatomy of the healthy ocular surface and the molecular mechanisms contributing to corneal (lymph)angiogenic privilege. In addition, we present (i) current insights into the cellular and molecular mechanisms occurring during pathological neovascularization of the cornea triggered e.g. by inflammation or trauma, (ii) the role of lymphatic vessels in different ocular surface pathologies such as dry eye disease, corneal graft rejection, ocular graft versus host disease, allergy, and pterygium, (iii) the involvement of lymphatic vessels in ocular tumors and metastasis, and (iv) the novel role of the lymphatic-like structure of Schlemm's canal in glaucoma. Identification of the underlying molecular mechanisms and of novel modulators of lymphangiogenesis will contribute to the development of new therapeutic targets for the treatment of ocular diseases associated with pathological lymphangiogenesis in the future. The preclinical data presented here outline novel therapeutic concepts for promoting transplant survival, inhibiting metastasis of ocular tumors, reducing inflammation of the ocular surface, and treating glaucoma. Initial data from clinical trials suggest first success of novel treatment strategies to promote transplant survival based on pretransplant corneal lymphangioregression.

Dual role of Vascular Endothelial Growth Factor-C (VEGF-C) in post-stroke recovery

Using a mouse model of ischemic stroke, this study characterizes stroke-induced lymphangiogenesis at the cribriform plate (CP). While blocking CP lymphangiogenesis with a VEGFR-3 inhibitor improves stroke outcome, administration of VEGF-C induced larger brain infarcts.

Abstract

Cerebrospinal fluid (CSF), antigens, and antigen-presenting cells drain from the central nervous system (CNS) into lymphatic vessels near the cribriform plate and dural meningeal lymphatics. However, the pathological roles of these lymphatic vessels surrounding the CNS during stroke are not well understood. Using a mouse model of ischemic stroke, transient middle cerebral artery occlusion (tMCAO), we show that stroke induces lymphangiogenesis near the cribriform plate. Interestingly, lymphangiogenesis is restricted to lymphatic vessels at the cribriform plate and downstream cervical lymph nodes, without affecting the conserved network of lymphatic vessels in the dura. Cribriform plate lymphangiogenesis peaks at day 7 and regresses by day 14 following tMCAO and is regulated by VEGF-C/VEGFR-3. These newly developed lymphangiogenic vessels transport CSF and immune cells to the cervical lymph nodes. Inhibition of VEGF-C/VEGFR-3 signaling using a blocker of VEGFR-3 prevented lymphangiogenesis and led to improved stroke outcomes at earlier time points but had no effects at later time points following stroke. Administration of VEGF-C after tMCAO did not further increase post-stroke lymphangiogenesis, but instead induced larger brain infarcts. The differential roles for VEGFR-3 inhibition and VEGF-C in regulating stroke pathology call into question recent suggestions to use VEGF-C therapeutically for stroke.

Local Adenoviral Delivery of Vascular Endothelial Growth Factor C Induces Lymphangiogenesis in the Conjunctiva in Rabbits

INTRODUCTION

The purpose of this study was to determine if conjunctival lymphangiogenesis can be induced using adenoviral delivery of vascular endothelial growth factor C (VEGF-C).

METHODS

Seventeen New Zealand white rabbits received a subconjunctival injection containing 3.5 × 107 plaque-forming units of an adenoviral vector containing the gene-encoding VEGF-C (Ad-VEGF-C). The contralateral eye was used for control experiment (the same volume of either saline or an empty vector). After 2 weeks, the animals were examined with trypan blue conjunctival lymphangiography, and the eyes were harvested for histology and immunohistochemistry (podoplanin and CD31).

RESULTS

Trypan blue conjunctival lymphangiography revealed significantly more extensive conjunctival vessel network in the Ad-VEGF-C group compared with control: 1.35 ± 0.67 versus 0.28 ± 0.17 vessel length/analysed area (p = <0.0001). This finding was confirmed with immunohistochemistry, where a significant increase in the number of lymphatic vessels was found compared to control; 34 ± 9 per mm2 versus 13 ± 8 per mm2 (p = 0.0019). Furthermore, there was a significant increase in lymphatic cross-sectional area; 32,500 ± 7,900 µm2 per mm2 versus 17,600 ± 9,700 µm2 per mm2 (p = 0.0149). Quantification of blood vessels revealed no significant difference in blood vessel density between Ad-VEGF-C and control; 19 ± 9 per mm2 versus 14 ± 8 per mm2 (p = 0.1971). There was no significant difference in total blood vessel area; 13,200 ± 7,600 µm2 per mm2 versus 7,100 ± 3,000 µm2 per mm2 (p = 0.0715). Eyes treated with an adenoviral vector (VEGF-C or empty vector) responded with a reactive cellular response, predominantly lymphocytes, towards the vector.

CONCLUSION

The study demonstrates the feasibility of inducing conjunctival lymphangiogenesis with a single subconjunctival injection of Ad-VEGF-C. Future studies will explore how this can be used with a therapeutic purpose.

Delivery of gene therapy through a cerebrospinal fluid conduit to rescue hearing in adult mice

Inner ear gene therapy has recently effectively restored hearing in neonatal mice, but it is complicated in adulthood by the structural inaccessibility of the cochlea, which is embedded within the temporal bone. Alternative delivery routes may advance auditory research and also prove useful when translated to humans with progressive genetic-mediated hearing loss. Cerebrospinal fluid flow via the glymphatic system is emerging as a new approach for brain-wide drug delivery in rodents as well as humans. The cerebrospinal fluid and the fluid of the inner ear are connected via a bony channel called the cochlear aqueduct, but previous studies have not explored the possibility of delivering gene therapy via the cerebrospinal fluid to restore hearing in adult deaf mice. Here, we showed that the cochlear aqueduct in mice exhibits lymphatic-like characteristics. In vivo time-lapse magnetic resonance imaging, computed tomography, and optical fluorescence microscopy showed that large-particle tracers injected into the cerebrospinal fluid reached the inner ear by dispersive transport via the cochlear aqueduct in adult mice. A single intracisternal injection of adeno-associated virus carrying solute carrier family 17, member 8 (Slc17A8), which encodes vesicular glutamate transporter-3 (VGLUT3), rescued hearing in adult deaf Slc17A8^-/- mice by restoring VGLUT3 protein expression in inner hair cells, with minimal ectopic expression in the brain and none in the liver. Our findings demonstrate that cerebrospinal fluid transport comprises an accessible route for gene delivery to the adult inner ear and may represent an important step toward using gene therapy to restore hearing in humans.

Screening of candidate genes at GLC3B and GLC3C loci in Chinese primary congenital glaucoma patients with targeted next generation sequencing

BACKGROUND

Primary congenital glaucoma (PCG) is characterized by developmental abnormalities of the anterior chamber angle. Although several genes have been associated with PCG, pathogenic mutations could only be detected in about 20% of Chinese patients. GLC3B (1p36.2-36.1) and GLC3C (14q24.3) loci were previously identified in PCG pedigrees via linkage analysis. However, no causative genes were reported in these loci. This study was designed to search for novel PCG-related genes in these genetic regions.

MATERIALS AND METHODS

DNA samples from 100 PCG patients and 200 normal controls were pooled and sequenced using a customized panel of 133 positional candidate genes located around GLC3B and GLC3C loci (±1Mb). PCG-related genes were prioritized by the distribution of variants between patients and controls. Confirmation of selected variants and co-segregation analysis were performed using Sanger sequencing.

RESULTS

Patient and control group contained 116 and 147 rare variants respectively after screening. Three genes (ZC2HC1C, VPS13D, and PGF) were prioritized according to the distribution of variants between the two groups. Rare variants of PGF were only identified in PCG patients.

CONCLUSIONS

To the best of our knowledge, this is the first study aiming at exploring novel PCG-related genes at GLC3B and GLC3C loci. Our preliminary results suggest that there are potential associations between ZC2HC1C, VPS13D, PGF, and PCG. However, larger cohort studies and functional assays are required to provide further evidence for the proposed genotype-phenotype association.

Efficacy and Safety of ab Externo Phaco-Canaloplasty versus First-Generation iStent Bypass Implantation Combined with Phacoemulsification in Patients with Primary Open Angle Glaucoma-Early Results

This study evaluated the early outcomes of the hypotensive efficacy and safety profile of ab externo phaco-canaloplasty versus first-generation iStent bypass implantation combined with phacoemulsification in patients with primary open-angle glaucoma (POAG). In total, 82 patients with POAG comprising 92 eyes were divided into phaco-canaloplasty (Group PC, (n = 47) or iStent combined with phacoemulsification (Group PiS, n = 45) groups. Primary outcome measures were intraocular pressure (IOP) reduction and number of glaucoma medications. Secondary outcome measures were best-corrected visual acuity (BCVA), endothelial cell density (EECD), changes in anterior chamber depth (ACD), and complication rate. The follow-up period was approximately 6 months. Preoperative IOPs were 17.30 (15.00; 19.85) mmHg and 17.50 (15.10; 20.90) mmHg in the PC and PiS groups, respectively (p = 0.876). At the end of the follow-up, IOP decreased to 15.00 (13.00; 16.00) mmHg and 15.00 (14.00; 17.00) mmHg in the PC and PiS groups, respectively (p = 0.438). Medication usage decreased from 2.08 to 0.12 and 1.40 to 0.04 in PC and PiS eyes, respectively. Most patients in both groups were medication-free at 6 months follow-up. After 6 months of observation, EECD in PC and PiS groups decreased from 2309.50 (2032.00; 2533.00) to 1966.50 (1262.00; 2353.50) and 2160.00 (1958.50; 2372.50), to1231.00 (1089.00; 2050.00), respectively (p = 0.037). Pre-surgery BCVA was 0.80 (0.50; 1.00) and 0.60 (0.40; 1.00) in PC and PiS eyes, respectively (p = 0.456). Follow-up BCVA was 0.95 (0.60; 1.00) for PC and 1.00 (1.00; 1.00) for PiS. Hyphema and corneal oedema were noted on the first day post-surgery in both groups. Subsequent complications included a transient increase in IOP in the PC group. Phaco-canaloplasty and iStent bypass implantation combined with phacoemulsification significantly lowered IOP and decreased medication burden. All eyes in both groups maintained or exhibited improved BCVA relative to baseline. Both surgeries had low postoperative complication rates and exhibited comparable safety profiles over 6-month follow-up in patients with POAG.

Lymphatic vasculature in the central nervous system

The central nervous system (CNS) is considered as an immune privilege organ, based on experiments in the mid 20th century showing that the brain fails to mount an efficient immune response against an allogeneic graft. This suggests that in addition to the presence of the blood-brain barrier (BBB), the apparent absence of classical lymphatic vasculature in the CNS parenchyma limits the capacity for an immune response. Although this view is partially overturned by the recent discovery of the lymphatic-like hybrid vessels in the Schlemm's canal in the eye and the lymphatic vasculature in the outmost layer of the meninges, the existence of lymphatic vessels in the CNS parenchyma has not been reported. Two potential mechanisms by which lymphatic vasculature may arise in the organs are: 1) sprouting and invasion of lymphatic vessels from the surrounding tissues into the parenchyma and 2) differentiation of blood endothelial cells into lymphatic endothelial cells in the parenchyma. Considering these mechanisms, we here discuss what causes the dearth of lymphatic vessels specifically in the CNS parenchyma.

The Impact of Stem/Progenitor Cells on Lymphangiogenesis in Vascular Disease

Lymphatic vessels, as the main tube network of fluid drainage and leukocyte transfer, are responsible for the maintenance of homeostasis and pathological repairment. Recently, by using genetic lineage tracing and single-cell RNA sequencing techniques, significant cognitive progress has been made about the impact of stem/progenitor cells during lymphangiogenesis. In the embryonic stage, the lymphatic network is primarily formed through self-proliferation and polarized-sprouting from the lymph sacs. However, the assembly of lymphatic stem/progenitor cells also guarantees the sustained growth of lymphvasculogenesis to obtain the entire function. In addition, there are abundant sources of stem/progenitor cells in postnatal tissues, including circulating progenitors, mesenchymal stem cells, and adipose tissue stem cells, which can directly differentiate into lymphatic endothelial cells and participate in lymphangiogenesis. Specifically, recent reports indicated a novel function of lymphangiogenesis in transplant arteriosclerosis and atherosclerosis. In the present review, we summarized the latest evidence about the diversity and incorporation of stem/progenitor cells in lymphatic vasculature during both the embryonic and postnatal stages, with emphasis on the impact of lymphangiogenesis in the development of vascular diseases to provide a rational guidance for future research.

Intracameral Injection of AAV-DJ.COMP-ANG1 Reduces the IOP of Mice by Reshaping the Trabecular Outflow Pathway

Purpose

The angiopoietin-1 (ANG1)-TIE signaling pathway orchestrates the development and maintenance of the Schlemm's canal (SC). In this study, we investigated the impact of adeno-associated virus (AAV)-mediated gene therapy with cartilage oligomeric matrix protein-ANG1 (COMP-ANG1) on trabecular outflow pathway.

Methods

Different serotypes of AAVs were compared for transduction specificity and efficiency in the anterior segment. The selected AAVs encoding COMP-ANG1 or ZsGreen1 (control) were delivered into the anterior chambers of wild-type C57BL/6J mice. The IOP and ocular surface were monitored regularly. Ocular perfusion was performed to measure the outflow facility and label flow patterns of the trabecular drainage pathway. Structural features of SC as well as limbal, retinal, and skin vessels were visualized by immunostaining. Ultrastructural changes in the SC and trabecular meshwork were observed under transmission electron microscopy.

Results

AAV-DJ could effectively infect the anterior segment. Intracameral injection of AAV-DJ.COMP-ANG1 lowered IOP in wild-type C57BL/6J mice. No signs of inflammation or angiogenesis were noticed. Four weeks after AAV injection, the conventional outflow facility and effective filtration area were increased significantly (P = 0.005 and P = 0.04, respectively). Consistently, the area of the SC was enlarged (P < 0.001) with increased density of giant vacuoles in the inner wall (P = 0.006). In addition, the SC endothelia lay on a more discontinuous basement membrane (P = 0.046) and a more porous juxtacanalicular tissue (P = 0.005) in the COMP-ANG1 group.

Conclusions

Intracamerally injected AAV-DJ.COMP-ANG1 offers a significant IOP-lowering effect by remodeling the trabecular outflow pathway of mouse eyes.

High-Resolution Imaging of the Ocular Vasculature of Conjunctivitis in Mice Using Highly Bright Polymer Dots

Ocular diseases are mainly caused by vascular aberrations in the eye, and accurate imaging and analysis of the ocular vascular structure is crucial. In this study, poly(9,9-dioctylfluorene-alt-benzothiadiazole) (PFBT) polymer dots (Pdots), with the advantages of easy synthesis, high brightness, and low toxicity, are used as nanoprobes to perform high-resolution imaging of the vasculature of the eyeball and optic nerve. Moreover, rapid imaging of the choroidal microvessels is carried out by stereoscopic fluorescence microscopy with a resolution of up to 1.6 µm. The comprehensive 3D vascular information of retinal aorta and optic nerve microvessels is obtained by combining tissue clearing and multiphoton microscopy. In addition, the vascular density of Schlemm's canal and iris blood vessels is compared between the conjunctivitis mice and the normal mice. These results suggest that PFBT Pdots have great application potential in the fast and accurate imaging of ocular diseases.

Genetic association of ANGPT2 with primary open-angle glaucoma

BACKGROUND

To determine the association of the ANGPT2 gene with primary open-angle glaucoma (POAG) in Chinese.

METHODS

Six single-nucleotide polymorphisms (SNPs) in ANGPT2 (rs2515487, rs2922869, rs13255574, rs4455855, rs13269021, and rs11775442) were genotyped in a total of 2601 study subjects from two cohorts. One is a Hong Kong Chinese cohort of 484 high tension glaucoma (HTG) and 537 normal tension glaucoma (NTG) patients, and 496 non-glaucoma control subjects. Another cohort is a Shantou Chinese cohort of 403 HTG and 135 NTG patients, and 543 non-glaucoma control subjects. Subgroup analysis by sex was conducted. Outcomes from different cohorts were combined for meta-analysis.

RESULTS

The association of SNP rs11775442 with NTG in the Hong Kong cohort [P = 0.0498, OR = 1.24, 95% confidence interval (CI) 1.00-1.55] after adjusting for age and sex did not reach statistical significance after Bonferroni correction. Other SNPs were not significantly associated with NTG, HTG and POAG in individual cohort or in the combined analyses (P > 0.05). In the subgroup analysis by sex, SNP rs13269021 in the Shantou cohort, but not in the Hong Kong cohort, was significantly associated with NTG in males (P = 0.0081, OR = 1.67, 95% CI: 1.14-2.43) but not in females (P = 0.874). In the combined analyses by sex, no SNPs were significantly associated with NTG, HTG and POAG.

CONCLUSIONS

In the subgroup analysis by sex, a significant association was shown in SNP rs13269021 with NTG in Shantou males, but not in Hong Kong males. Further studies are needed to verify the association between ANGPT2 locus (rs13269021) and NTG in Chinese males.

Cooperation of Angiopoietin-2 and Angiopoietin-4 in Schlemm's Canal Maintenance

Purpose

Defects in the iridocorneal angle tissues, including the trabecular meshwork (TM) and Schlemm's canal (SC), impair aqueous humor flow and increase the intraocular pressure (IOP), eventually resulting in glaucoma. Activation of endothelial tyrosine kinase receptor Tie2 by angiopoietin-1 (Angpt1) has been demonstrated to be essential for SC formation, but roles of the other two Tie2 ligands, Angpt2 and Angpt4, have been controversial or not yet characterized, respectively.

Methods

Angpt4 expression was investigated using genetic cell fate mapping and reporter mice. Congenital deletion of Angpt2 and Angpt4 and tamoxifen-inducible deletion of Angpt1 in mice were used to study the effects of Angpt4 deletion alone and in combination with the other angiopoietins. SC morphology was examined with immunofluorescent staining. IOP measurements, electron microscopy, and histologic evaluation were used to study glaucomatous changes.

Results

Angpt4 was postnatally expressed in the TM. While Angpt4 deletion alone did not affect SC and Angpt4 deletion did not aggravate Angpt1 deletion phenotype, absence of Angpt4 combined with Angpt2 deletion had detrimental effects on SC morphology in adult mice. Consequently, Angpt2^−/−;Angpt4^−/− mice displayed glaucomatous changes in the eye. Mice with Angpt2 deletion alone showed only moderate SC defects, but Angpt2 was necessary for proper limbal vasculature development. Mechanistically, analysis of Tie2 phosphorylation suggested that Angpt2 and Angpt4 cooperate as agonistic Tie2 ligands in maintaining SC integrity.

Conclusions

Our results indicated an additive effect of Angpt4 in SC maintenance and Tie2 activation and a spatiotemporally regulated interplay between the angiopoietins in the mouse iridocorneal angle.

Ocular Lymphatic and Glymphatic Systems: Implications for Retinal Health and Disease

Clearance of ocular fluid and metabolic waste is a critical function of the eye in health and disease. The eye has distinct fluid outflow pathways in both the anterior and posterior segments. Although the anterior outflow pathway is well characterized, little is known about posterior outflow routes. Recent studies suggest that lymphatic and glymphatic systems play an important role in the clearance of fluid and waste products from the posterior segment of the eye. The lymphatic system is a vascular network that runs parallel to the blood circulatory system. It plays an essential role in maintenance of fluid homeostasis and immune surveillance in the body. Recent studies have reported lymphatics in the cornea (under pathological conditions), ciliary body, choroid, and optic nerve meninges. The evidence of lymphatics in optic nerve meninges is, however, limited. An alternative lymphatic system termed the glymphatic system was recently discovered in the rodent eye and brain. This system is a glial cell-based perivascular network responsible for the clearance of interstitial fluid and metabolic waste. In this review, we will discuss our current knowledge of ocular lymphatic and glymphatic systems and their role in retinal degenerative diseases.

Schlemm's canal: the outflow 'vessel'

In a healthy eye, the aqueous humour (AH) flows via the ciliary body and trabecular meshwork into the collector channels, which carry it to the episcleral veins. In glaucoma, a heterogeneous group of eye disorders affecting approximately 60 million individuals worldwide, the juxtacanalicular meshwork offers greater resistance to the outflow of the AH, leading to an increase in outflow resistance that gradually results in elevated intraocular pressure (IOP). The present review comprehensively covers the morphology of Schlemm’s canal (SC) and AH pathways. The path of the AH from the anterior chamber through the trabeculum into suprascleral and conjunctival veins via collector channels is described, and the role of SC in the development of glaucoma and outflow resistance is discussed. Finally, channelography is presented as a precise method of assessing the conventional drainage pathway and facilitating localization of an uncollapsed collector and aqueous veins. Attention is also given to the relationship between aqueous and episcleral veins and heartbeat. Possible directions of future research are proposed.

Role of Transcriptional and Epigenetic Regulation in Lymphatic Endothelial Cell Development

The lymphatic system is critical for maintaining the homeostasis of lipids and interstitial fluid and regulating the immune cell development and functions. Developmental anomaly-induced lymphatic dysfunction is associated with various pathological conditions, including lymphedema, inflammation, and cancer. Most lymphatic endothelial cells (LECs) are derived from a subset of endothelial cells in the cardinal vein. However, recent studies have reported that the developmental origin of LECs is heterogeneous. Multiple regulatory mechanisms, including those mediated by signaling pathways, transcription factors, and epigenetic pathways, are involved in lymphatic development and functions. Recent studies have demonstrated that the epigenetic regulation of transcription is critical for embryonic LEC development and functions. In addition to the chromatin structures, epigenetic modifications may modulate transcriptional signatures during the development or differentiation of LECs. Therefore, the understanding of the epigenetic mechanisms involved in the development and function of the lymphatic system can aid in the management of various congenital or acquired lymphatic disorders. Future studies must determine the role of other epigenetic factors and changes in mammalian lymphatic development and function. Here, the recent findings on key factors involved in the development of the lymphatic system and their epigenetic regulation, LEC origins from different organs, and lymphatic diseases are reviewed.

Lymph Leakage Promotes Immunosuppression by Enhancing Anti-Inflammatory Macrophage Polarization

Lymphatic vasculature is a network of capillaries and vessels capable of draining extracellular fluid back to blood circulation and to facilitate immune cell migration. Although the role of the lymphatic vasculature as coordinator of fluid homeostasis has been extensively studied, the consequences of abnormal lymphatic vasculature function and impaired lymph drainage have been mostly unexplored. Here, by using the Prox1+/- mice with defective lymphatic vasculature and lymphatic leakage, we provide evidence showing that lymph leakage induces an immunosuppressive environment by promoting anti-inflammatory M2 macrophage polarization in different inflammatory conditions. In fact, by using a mouse model of tail lymphedema where lymphatic vessels are thermal ablated leading to lymph accumulation, an increasing number of anti-inflammatory M2 macrophages are found in the lymphedematous tissue. Moreover, RNA-seq analysis from different human tumors shows that reduced lymphatic signature, a hallmark of lymphatic dysfunction, is associated with increased M2 and reduced M1 macrophage signatures, impacting the survival of the patients. In summary, we show that lymphatic vascular leakage promotes an immunosuppressive environment by enhancing anti-inflammatory macrophage differentiation, with relevance in clinical conditions such as inflammatory bowel diseases or cancer.

The genetic basis for adult onset glaucoma: Recent advances and future directions

Glaucoma, a diverse group of eye disorders that results in the degeneration of retinal ganglion cells, is the world's leading cause of irreversible blindness. Apart from age and ancestry, the major risk factor for glaucoma is increased intraocular pressure (IOP). In primary open-angle glaucoma (POAG), the anterior chamber angle is open but there is resistance to aqueous outflow. In primary angle-closure glaucoma (PACG), crowding of the anterior chamber angle due to anatomical alterations impede aqueous drainage through the angle. In exfoliation syndrome and exfoliation glaucoma, deposition of white flaky material throughout the anterior chamber directly interfere with aqueous outflow. Observational studies have established that there is a strong hereditable component for glaucoma onset and progression. Indeed, a succession of genome wide association studies (GWAS) that were centered upon single nucleotide polymorphisms (SNP) have yielded more than a hundred genetic markers associated with glaucoma risk. However, a shortcoming of GWAS studies is the difficulty in identifying the actual effector genes responsible for disease pathogenesis. Building on the foundation laid by GWAS studies, research groups have recently begun to perform whole exome-sequencing to evaluate the contribution of protein-changing, coding sequence genetic variants to glaucoma risk. The adoption of this technology in both large population-based studies as well as family studies are revealing the presence of novel, protein-changing genetic variants that could enrich our understanding of the pathogenesis of glaucoma. This review will cover recent advances in the genetics of primary open-angle glaucoma, primary angle-closure glaucoma and exfoliation glaucoma, which collectively make up the vast majority of all glaucoma cases in the world today. We will discuss how recent advances in research methodology have uncovered new risk genes, and how follow up biological investigations could be undertaken in order to define how the risk encoded by a genetic sequence variant comes into play in patients. We will also hypothesise how data arising from characterising these genetic variants could be utilized to predict glaucoma risk and the manner in which new therapeutic strategies might be informed.

The meningeal lymphatic vasculature in neuroinflammation

The lymphatic vasculature is a unidirectional network of lymphatic endothelial cells, whose main role is to maintain fluid homeostasis along with the absorption of dietary fat in the gastrointestinal organs and management and coordination of immune cell trafficking into lymph nodes during homeostasis and under inflammatory conditions. In homeostatic conditions, immune cells, such as dendritic cells, macrophages, or T cells can enter into the lymphatic vasculature and move easily through the lymph reaching secondary lymph nodes where immune cell activation or peripheral tolerance can be modulated. However, under inflammatory conditions such as pathogen infection, increased permeabilization of lymphatic vessels allows faster immune cell migration into inflamed tissues following a chemokine gradient, facilitating pathogen clearance and the resolution of inflammation. Interestingly, since the re-discovery of lymphatic vasculature in the central nervous system, known as the meningeal lymphatic vasculature, the role of these lymphatics as a key player in several neurological disorders has been described, with emphasis on the neurodegenerative process. Alternatively, less has been discussed about meningeal lymphatics and its role in neuroinflammation. In this review, we discuss current knowledge about the anatomy and function of the meningeal lymphatic vasculature and specifically analyze its contribution to different neuroinflammatory processes, highlighting the potential therapeutic target of meningeal lymphatic vasculature in these pathological conditions.

Lymphatic Tissue and Organ Engineering for In Vitro Modeling and In Vivo Regeneration

The lymphatic system has an important role in maintaining fluid homeostasis and transporting immune cells and biomolecules, such as dietary fat, metabolic products, and antigens in different organs and tissues. Therefore, impaired lymphatic vessel function and/or lymphatic vessel deficiency can lead to numerous human diseases. The discovery of lymphatic endothelial markers and prolymphangiogenic growth factors, along with a growing number of in vitro and in vivo models and technologies has expedited research in lymphatic tissue and organ engineering, advancing therapeutic strategies. In this article, we describe lymphatic tissue and organ engineering in two- and three-dimensional culture systems and recently developed microfluidics and organ-on-a-chip systems in vitro. Next, we discuss advances in lymphatic tissue and organ engineering in vivo, focusing on biomaterial and scaffold engineering and their applications for lymphatic vessels and lymphoid organ regeneration. Last, we provide expert perspective and prospects in the field of lymphatic tissue engineering.

Emerging roles of inflammation-mediated endothelial–mesenchymal transition in health and disease

Endothelial–mesenchymal transition (EndoMT), a cellular differentiation process in which endothelial cells (ECs) lose their properties and differentiate into mesenchymal cells, has been observed not only during development but also in various pathological states in adults, including cancer progression and organ/tissue fibrosis. Transforming growth factor-β (TGF-β), an inflammation-related cytokine, has been shown to play central roles in the induction of EndoMT. TGF-β induces EndoMT by regulating the expression of various transcription factors, signaling molecules, and cellular components that confer ECs with mesenchymal characteristics. However, TGF-β by itself is not necessarily sufficient to induce EndoMT to promote the progression of EndoMT-related diseases to a refractory extent. In addition to TGF-β, additional activation by other inflammatory factors is often required to stabilize the progression of EndoMT. Since recent lines of evidence indicate that inflammatory signaling molecules act as enhancers of EndoMT, we summarize the roles of inflammatory factors in the induction of EndoMT and related diseases. We hope that this review will help to develop therapeutic strategies for EndoMT-related diseases by targeting inflammation-mediated EndoMT.

Screening and Functional Analysis of TEK Mutations in Chinese Children With Primary Congenital Glaucoma

Purposes: Recent studies have suggested that loss-of-function mutations of the tunica intima endothelial receptor tyrosine kinase (TEK) are responsible for approximately 5% of primary congenital glaucoma (PCG) cases in diverse populations. However, the causative role of TEK mutations has not been studied in Chinese PCG patients. Here, we report the mutation spectrum of TEK after screening a large cohort of PCG patients of Chinese Han origin and analyze the identified variants in functional assays.

Methods: TEK-targeted next-generation sequencing (NGS) was performed in 200 PCG patients. Candidate variants were prioritized by mutation type and allele frequency in public datasets. Plasmids containing wild type and identified variants of TEK were constructed and used to assess protein expression, solubility, receptor auto-phosphorylation, and response to ligand stimulation in cell-based assays.

Results: Ten missense and one nonsense heterozygous variants were detected by NGS in 11 families. The clinical features of TEK variants carriers were comparable to that of TEK-mutated patients identified in other populations and CYP1B1-mutated individuals from in-house database. Functional analysis confirmed four variants involving evolutionarily conserved residues to be loss-of-function, while one variant (p.R1003H) located in tyrosine kinase domain seemed to be an activating mutation. However, our results did not support the pathogenicity of the other five variants (p.H52R, p.M131I, p.M228V, p.H494Y, and p.L888P).

Conclusion: We provide evidence for TEK variants to be causative in Chinese PCG patients for the first time. Attention needs to be paid to TEK mutations in future genetic testing.

Cellular crosstalk regulates the aqueous humor outflow pathway and provides new targets for glaucoma therapies

Primary congenital glaucoma (PCG) is a severe disease characterized by developmental defects in the trabecular meshwork (TM) and Schlemm's canal (SC), comprising the conventional aqueous humor outflow pathway of the eye. Recently, heterozygous loss of function variants in TEK and ANGPT1 or compound variants in TEK/SVEP1 were identified in children with PCG. Moreover, common variants in ANGPT1and SVEP1 have been identified as risk alleles for primary open angle glaucoma (POAG) in GWAS studies. Here, we show tissue-specific deletion of Angpt1 or Svep1 from the TM causes PCG in mice with severe defects in the adjacent SC. Single-cell transcriptomic analysis of normal and glaucomatous Angpt1 deficient eyes allowed us to identify distinct TM and SC cell populations and discover additional TM-SC signaling pathways. Furthermore, confirming the importance of angiopoietin signaling in SC, delivery of a recombinant ANGPT1-mimetic promotes developmental SC expansion in healthy and Angpt1 deficient eyes, blunts intraocular pressure (IOP) elevation and RGC loss in a mouse model of PCG and lowers IOP in healthy adult mice. Our data highlight the central role of ANGPT1-TEK signaling and TM-SC crosstalk in IOP homeostasis and provide new candidates for SC-targeted glaucoma therapy.

Aqueous outflow channels and its lymphatic association: A review

The human eye has a unique immune architecture and behavior. While the conjunctiva is known to have a well-defined lymphatic drainage system, the cornea, sclera, and uveal tissues were historically considered "alymphatic" and thought to be immune privileged. The very fact that the aqueous outflow channels carry a clear fluid (aqueous humor) along the outflow pathway makes it hard to ignore its lymphatic-like characteristics. The development of novel lymphatic lineage markers and expression of these markers in aqueous outflow channels and improved imaging capabilities has sparked a renewed interest in the study of ocular lymphatics. Ophthalmic lymphatic research has had a directional shift over the last decade, offering an exciting new physiological platform that needs further in-depth understanding. The evidence of a presence of distinct lymphatic channels in the human ciliary body is gaining significant traction. The uveolymphatic pathway is an alternative new route for aqueous outflow and adds a new dimension to pathophysiology and management of glaucoma. Developing novel animal models, markers, and non-invasive imaging tools to delineate the core anatomical structure and physiological functions may help pave some crucial pathways to understand disease pathophysiology and help develop novel targeted therapeutic approaches for glaucoma.

The lymphatics in kidney health and disease

The mammalian vascular system consists of two networks: the blood vascular system and the lymphatic vascular system. Throughout the body, the lymphatic system contributes to homeostatic mechanisms by draining extravasated interstitial fluid and facilitating the trafficking and activation of immune cells. In the kidney, lymphatic vessels exist mainly in the kidney cortex. In the medulla, the ascending vasa recta represent a hybrid lymphatic-like vessel that performs lymphatic-like roles in interstitial fluid reabsorption. Although the lymphatic network is mainly derived from the venous system, evidence supports the existence of lymphatic beds that are of non-venous origin. Following their development and maturation, lymphatic vessel density remains relatively stable; however, these vessels undergo dynamic functional changes to meet tissue demands. Additionally, new lymphatic growth, or lymphangiogenesis, can be induced by pathological conditions such as tissue injury, interstitial fluid overload, hyperglycaemia and inflammation. Lymphangiogenesis is also associated with conditions such as polycystic kidney disease, hypertension, ultrafiltration failure and transplant rejection. Although lymphangiogenesis has protective functions in clearing accumulated fluid and immune cells, the kidney lymphatics may also propagate an inflammatory feedback loop, exacerbating inflammation and fibrosis. Greater understanding of lymphatic biology, including the developmental origin and function of the lymphatics and their response to pathogenic stimuli, may aid the development of new therapeutic agents that target the lymphatic system.

Immune responses to injury and their links to eye disease

The eye is regarded as an immune privileged site. Since the presence of a vasculature would impair vision, the vasculature of the eye is located outside of the central light path. As a result, many regions of the eye evolved mechanisms to deliver immune cells to sites of dysgenesis, injury, or in response to the many age-related pathologies. While the purpose of these immune responses is reparative or protective, cytokines released by immune cells compromise visual acuity by inducing inflammation and fibrosis. The response to traumatic or pathological injury is distinct in different regions of the eye. Age-related diseases impact both the anterior and posterior segment and lead to reduced quality of life and blindness. Here we focus attention on the role that inflammation and fibrosis play in the progression of age-related pathologies of the cornea and the lens as well as in glaucoma, the formation of epiretinal membranes, and in proliferative vitreoretinopathy.

Targeting the Angiopoietin/Tie Pathway: Prospects for Treatment of Retinal and Respiratory Disorders

Anti-angiogenic approaches have significantly advanced the treatment of vascular-related pathologies. The ephemeral outcome and known side effects of the current vascular endothelial growth factor (VEGF)-based anti-angiogenic treatments have intensified research on other growth factors. The angiopoietin/Tie (Ang/Tie) family has an established role in vascular physiology and regulates angiogenesis, vascular permeability, and inflammatory responses. The Ang/Tie family consists of angiopoietins 1-4, their receptors, tie1 and 2 and the vascular endothelial-protein tyrosine phosphatase (VE-PTP). Modulation of Tie2 activation has provided a promising outcome in preclinical models and has led to clinical trials of Ang/Tie-targeting drug candidates for retinal disorders. Although less is known about the role of Ang/Tie in pulmonary disorders, several studies have revealed great potential of the Ang/Tie family members as drug targets for pulmonary vascular disorders as well. In this review, we summarize the functions of the Ang/Tie pathway in retinal and pulmonary vascular physiology and relevant disorders and highlight promising drug candidates targeting this pathway currently being or expected to be under clinical evaluation for retinal and pulmonary vascular disorders.

Comorbidity and Lymphatic Disease: The Lymphatic Continuum Re-Examined

It has now been ∼20 years since the original Lymphatic Continuum conference was convened, and this continuum has transitioned from a compelling concept to a reality. The explosive growth in our comprehension of lymphatic genetics, development, and function has expanded and modified our traditional views regarding what is, and is not, lymphatic disease. Groundbreaking investigations over the past decade have now defined a large and growing list of pathological conditions in which morphological or function lymphatic alterations can be identified. This list includes atherosclerosis and dyslipidemia, hypertension and other cardiovascular diseases, inflammation and inflammatory bowel disease, obesity, narrow angle glaucoma, and, most recently and compellingly, neurodegenerative disease. The sometimes overlapping but largely disparate nature of these various aforementioned disease categories suggests that the presence, or absence, of structural or functional lymphatic derangements may represent a previously unrecognized unifying influence in the maintenance of health and the promotion of disease. Future investigation of lymphatic mechanisms in disease will likely continue to elucidate the influences of lymphatic dysfunction, perhaps subtle, that can invest other, seemingly unrelated, diseases. In future, such discoveries will provide mechanistic insights and may potentiate the development of a new lymphatic-based approach to human disease diagnosis and therapeutics.

Biochemical and mechanical signals in the lymphatic vasculature

Lymphatic vasculature is an integral part of the cardiovascular system where it maintains interstitial fluid balance. Additionally, lymphatic vasculature regulates lipid assimilation and inflammatory response. Lymphatic vasculature is composed of lymphatic capillaries, collecting lymphatic vessels and valves that function in synergy to absorb and transport fluid against gravitational and pressure gradients. Defects in lymphatic vessels or valves leads to fluid accumulation in tissues (lymphedema), chylous ascites, chylothorax, metabolic disorders and inflammation. The past three decades of research has identified numerous molecules that are necessary for the stepwise development of lymphatic vasculature. However, approaches to treat lymphatic disorders are still limited to massages and compression bandages. Hence, better understanding of the mechanisms that regulate lymphatic vascular development and function is urgently needed to develop efficient therapies. Recent research has linked mechanical signals such as shear stress and matrix stiffness with biochemical pathways that regulate lymphatic vessel growth, patterning and maturation and valve formation. The goal of this review article is to highlight these innovative developments and speculate on unanswered questions.

Surface Engineering of FLT4-Targeted Nanocarriers Enhances Cell-Softening Glaucoma Therapy

Primary open-angle glaucoma is associated with elevated intraocular pressure (IOP) that damages the optic nerve and leads to gradual vision loss. Several agents that reduce the stiffness of pressure-regulating Schlemm's canal (SC) endothelial cells, in the conventional outflow pathway of the eye, lower IOP in glaucoma patients and are approved for clinical use. However, poor drug penetration and uncontrolled biodistribution limit their efficacy and produce local adverse effects. Compared to other ocular endothelia, FLT4/VEGFR3 is expressed at elevated levels by SC endothelial cells and can be exploited for targeted drug delivery. Here, we validate FLT4 receptors as clinically relevant targets on SC cells from glaucomatous human donors and engineer polymeric self-assembled nanocarriers displaying lipid-anchored targeting ligands that optimally engage this receptor. Targeting constructs were synthesized as lipid-PEGx-peptide, differing in the number of PEG spacer units (x), and were embedded in micelles. We present a novel proteolysis assay for quantifying ligand accessibility that we employ to design and optimize our FLT4-targeting strategy for glaucoma nanotherapy. Peptide accessibility to proteases correlated with receptor-mediated targeting enhancements. Increasing the accessibility of FLT4-binding peptides enhanced nanocarrier uptake by SC cells while simultaneously decreasing the uptake by off-target vascular endothelial cells. Using a paired longitudinal IOP study in vivo, we show that this enhanced targeting of SC cells translates to IOP reductions that are sustained for a significantly longer time as compared to controls. Confocal microscopy of murine anterior segment tissue confirmed nanocarrier localization to SC within 1 h after intracameral administration. This work demonstrates that steric effects between surface-displayed ligands and PEG coronas significantly impact the targeting performance of synthetic nanocarriers across multiple biological scales. Minimizing the obstruction of modular targeting ligands by PEG measurably improved the efficacy of glaucoma nanotherapy and is an important consideration for engineering PEGylated nanocarriers for targeted drug delivery.

Immune Checkpoint Inhibitors in Human Glioma Microenvironment

Gliomas are the most common primary brain tumors in adults. Despite the fact that they are relatively rare, they cause significant morbidity and mortality. High-grade gliomas or glioblastomas are rapidly progressing tumors with a very poor prognosis. The presence of an intrinsic immune system in the central nervous system is now more accepted. During the last decade, there has been no major progress in glioma therapy. The lack of effective treatment for gliomas can be explained by the strategies that cancer cells use to escape the immune system. This being said, immunotherapy, which involves blockade of immune checkpoint inhibitors, has improved patients' survival in different cancer types. This novel cancer therapy appears to be one of the most promising approaches. In the present study, we will start with a review of the general concept of immune response within the brain and glioma microenvironment. Then, we will try to decipher the role of various immune checkpoint inhibitors within the glioma microenvironment. Finally, we will discuss some promising therapeutic pathways, including immune checkpoint blockade and the body's effective anti-glioma immune response.

Expression of Vascular Endothelial Growth Factor-C in the Trabecular Meshwork of Patients with Neovascular Glaucoma and Primary Open-Angle Glaucoma

To investigate the expression of vascular endothelial growth factor (VEGF)-C and vascular endothelial growth factor receptor (VEGFR)3 in the trabecular meshwork (TM) of patients with glaucoma and cultured TM cells. Methods: The expressions of VEGF-C in angle tissues collected by trabeculectomy from patients with glaucoma and non-glaucomatous choroidal malignant melanoma were analyzed by immunohistochemistry. Additionally, VEGF-C concentrations were determined in the aqueous humor of patients with glaucoma by ELISA. The expressions of VEGFR3, which is a receptor of VEGF-C in cultured TM cells, were analyzed by Western blot analysis and immunocytochemistry. Cultured TM cells were stimulated by oxidative stress, hypoxia, or high glucose conditions, and VEGF-C concentrations in supernatants and cell lysates were determined by ELISA. Results: VEGF-C immunoreactivity was positive in TM tissues of glaucoma patients, but not in those of non-glaucomatous controls. VEGF-C concentrations in the aqueous humor of patients with neovascular glaucoma and primary open-angle glaucoma were lower than those with non-glaucoma patients. VEGFR3 was expressed in cultured TM cells. VEGF-C concentrations in supernatants or cell lysates of TM cells cultured under oxidative stress and hypoxia were significantly elevated compared with those under steady conditions (p < 0.05). VEGF-C concentrations in supernatants and cell lysates of TM cells cultured in high glucose were significantly higher than those in low glucose (p < 0.01). Conclusions: VEGF-C was expressed in TM tissues of patients with glaucoma, which was secreted from cultured TM cells under various pathological conditions. These results suggest that VEGF-C may be involved in the pathology of glaucoma.

Aqueous outflow regulation - 21st century concepts

We propose an integrated model of aqueous outflow control that employs a pump-conduit system in this article. Our model exploits accepted physiologic regulatory mechanisms such as those of the arterial, venous, and lymphatic systems. Here, we also provide a framework for developing novel diagnostic and therapeutic strategies to improve glaucoma patient care. In the model, the trabecular meshwork distends and recoils in response to continuous physiologic IOP transients like the ocular pulse, blinking, and eye movement. The elasticity of the trabecular meshwork determines cyclic volume changes in Schlemm's canal (SC). Tube-like SC inlet valves provide aqueous entry into the canal, and outlet valve leaflets at collector channels control aqueous exit from SC. Connections between the pressure-sensing trabecular meshwork and the outlet valve leaflets dynamically control flow from SC. Normal function requires regulation of the trabecular meshwork properties that determine distention and recoil. The aqueous pump-conduit provides short-term pressure control by varying stroke volume in response to pressure changes. Modulating TM constituents that regulate stroke volume provides long-term control. The aqueous outflow pump fails in glaucoma due to the loss of trabecular tissue elastance, as well as alterations in ciliary body tension. These processes lead to SC wall apposition and loss of motion. Visible evidence of pump failure includes a lack of pulsatile aqueous discharge into aqueous veins and reduced ability to reflux blood into SC. These alterations in the functional properties are challenging to monitor clinically. Phase-sensitive OCT now permits noninvasive, quantitative measurement of pulse-dependent TM motion in humans. This proposed conceptual model and related techniques offer a novel framework for understanding mechanisms, improving management, and development of therapeutic options for glaucoma.

Lymphatics in Eye Fluid Homeostasis: Minor Contributors or Significant Actors?

Lymphatic vessels exert major effects on the maintenance of interstitial fluid homeostasis, immune cell trafficking, lipid absorption, tumor progression and metastasis. Recently, novel functional roles for the lymphatic vasculature have emerged, which can be associated with pathological situations. Among them, lymphatics have been proposed to participate in eye aqueous humor drainage, with potential consequences on intraocular pressure, a main risk factor for progression of glaucoma disease. In this review, after the description of eye fluid dynamics, we provide an update on the data concerning the distribution of ocular lymphatics. Particular attention is given to the results of investigations allowing the three dimensional visualization of the ocular surface vasculature, and to the molecular mechanisms that have been characterized to regulate ocular lymphatic vessel development. The studies concerning the potential role of lymphatics in aqueous humor outflow are reported and discussed. We also considered the novel studies mentioning the existence of an ocular glymphatic system which may have, in connection with lymphatics, important repercussions in retinal clearance and in diseases affecting the eye posterior segment. Some remaining unsolved questions and new directions to explore are proposed to improve the knowledge about both lymphatic and glymphatic system interactions with eye fluid homeostasis.