Identification of adult stem cells in Schwalbe's line region of the primate eye

Magnetically Steered Cell Therapy For Functional Restoration Of Intraocular Pressure Control In Open-Angle Glaucoma

Trabecular meshwork (TM) cell therapy has been proposed as a next-generation treatment for elevated intraocular pressure (IOP) in glaucoma, the most common cause of irreversible blindness. Using a magnetic cell steering technique with excellent efficiency and tissue-specific targeting, we delivered two types of cells into a mouse model of glaucoma: either human adipose-derived mesenchymal stem cells (hAMSCs) or induced pluripotent cell derivatives (iPSC-TM cells). We observed a 4.5 [3.1, 6.0] mmHg or 27% reduction in intraocular pressure (IOP) for nine months after a single dose of only 1500 magnetically-steered hAMSCs, associated with restoration of function to the conventional outflow pathway, as judged by increased outflow facility and TM cellularity. iPSC-TM cells were also effective, but less so, showing only a 1.9 [0.4, 3.3] mmHg or 13% IOP reduction and increased risk of tumorigenicity. In both cases, injected cells remained detectable in the iridocorneal angle three weeks post-transplantation. Based on the locations of the delivered cells, the mechanism of IOP lowering is most likely paracrine signaling. We conclude that magnetically-steered hAMSC cell therapy has potential for long-term treatment of ocular hypertension in glaucoma.

One Sentence Summary

A novel magnetic cell therapy provided effective intraocular pressure control in a mouse model of glaucoma, motivating future translational studies.

Adult stem cells in the eye: Identification, characterisation, and therapeutic application in ocular regeneration - A review

Adult stem cells, present in various parts of the human body, are undifferentiated cells that can proliferate and differentiate to replace dying cells within tissues. Stem cells have specifically been identified in the cornea, trabecular meshwork, crystalline lens, iris, ciliary body, retina, choroid, sclera, conjunctiva, eyelid, lacrimal gland, and orbital fat. The identification of ocular stem cells broadens the potential therapeutic strategies for untreatable eye diseases. Currently, stem cell transplantation for corneal and conjunctival diseases remains the most common stem cell-based therapy in ocular clinical management. Lens epithelial stem cells have been applied in the treatment of paediatric cataracts. Several early-phase clinical trials for corneal and retinal regeneration using ocular stem cells are also underway. Extensive preclinical studies using ocular stem cells have been conducted, showing encouraging outcomes. Ocular stem cells currently demonstrate great promise in potential treatments of eye diseases. In this review, we focus on the identification, characterisation, and therapeutic application of adult stem cells in the eye.

Posterior corneoscleral limbus: Architecture, stem cells, and clinical implications

The limbus is a transition from the cornea to conjunctiva and sclera. In human eyes, this thin strip has a rich variation of tissue structures and composition, typifying a change from scleral irregularity and opacity to corneal regularity and transparency; a variation from richly vascularized conjunctiva and sclera to avascular cornea; the neural passage and drainage of aqueous humor. The limbal stroma is enriched with circular fibres running parallel to the corneal circumference, giving its unique role in absorbing small pressure changes to maintain corneal curvature and refractivity. It contains specific niches housing different types of stem cells for the corneal epithelium, stromal keratocytes, corneal endothelium, and trabecular meshwork. This truly reflects the important roles of the limbus in ocular physiology, and the limbal functionality is crucial for corneal health and the entire visual system. Since the anterior limbus containing epithelial structures and limbal epithelial stem cells has been extensively reviewed, this article is focused on the posterior limbus. We have discussed the structural organization and cellular components of the region beneath the limbal epithelium, the characteristics of stem cell types: namely corneal stromal stem cells, endothelial progenitors and trabecular meshwork stem cells, and recent advances leading to the emergence of potential cell therapy options to replenish their respective mature cell types and to correct defects causing corneal abnormalities. We have reviewed different clinical disorders associated with defects of the posterior limbus and summarized the available preclinical and clinical evidence about the developing topic of cell-based therapy for corneal disorders.

Application of low-intensity pulsed ultrasound on tissue resident stem cells: Potential for ophthalmic diseases

INTRODUCTION

Tissue-resident stem cells (TRSCs) have the ability to self-renew and differentiate throughout an individual's lifespan, and they utilize both mechanisms to maintain homeostasis and regenerate damaged tissues. Several studies suggest that these stem cells can serve as a potential source for cell-replacement-based therapy by promoting differentiation or expansion. In recent years, low-intensity pulsed ultrasound (LIPUS) has been demonstrated to effectively stimulate stem cell proliferation and differentiation, promote tissue regeneration, and inhibit inflammatory responses.

AIMS

To present a comprehensive overview of current application and mechanism of LIPUS on tissue resident stem cells.

METHODS

We searched PubMed, Web of Science for articles on the effects of LIPUS on tissue resident stem cells and its application.

RESULTS

The LIPUS could modulate cellular activities such as cell viability, proliferation and differentiation of tissue resident stem cells and related cells through various cellular signaling pathways. Currently, LIPUS, as the main therapeutic ultrasound, is being widely used in the treatment of preclinical and clinical diseases.

CONCLUSION

The stem cell research is the hot topic in the biological science, while in recent years, increasing evidence has shown that TRSCs are good targets for LIPUS-regulated regenerative medicine. LIPUS may be a novel and valuable therapeutic approach for the treatment of ophthalmic diseases. How to further improve its efficiency and accuracy, as well as the biological mechanism therein, will be the focus of future research.

A systematic review on the effects of ROCK inhibitors on proliferation and/or differentiation in human somatic stem cells: A hypothesis that ROCK inhibitors support corneal endothelial healing via acting on the limbal stem cell niche

Rho kinase inhibitors (ROCKi) have attracted growing multidisciplinary interest, particularly in Ophthalmology where the question as to how they promote corneal endothelial healing remains unresolved. Concurrently, stem cell biology has rapidly progressed in unravelling drivers of stem cell (SC) proliferation and differentiation, where mechanical niche factors and the actin cytoskeleton are increasingly recognized as key players. There is mounting evidence from the study of the peripheral corneal endothelium that supports the likelihood of an internal limbal stem cell niche. The possibility that ROCKi stimulate the endothelial SC niche has not been addressed. Furthermore, there is currently a paucity of data that directly evaluates whether ROCKi promotes corneal endothelial healing by acting on this limbal SC niche located near the transition zone. Therefore, we performed a systematic review examining the effects ROCKi on the proliferation and differentiation of human somatic SC, to provide insight into its effects on various human SC populations. An appraisal of electronic searches of four databases identified 1 in vivo and 58 in vitro studies (36 evaluated proliferation while 53 examined differentiation). Types of SC studied included mesenchymal (n = 32), epithelial (n = 11), epidermal (n = 8), hematopoietic and other (n = 8). The ROCK 1/2 selective inhibitor Y-27632 was used in almost all studies (n = 58), while several studies evaluated ≥2 ROCKi (n = 4) including fasudil, H-1152, and KD025. ROCKi significantly influenced human somatic SC proliferation in 81% of studies (29/36) and SC differentiation in 94% of studies (50/53). The present systemic review highlights that ROCKi are influential in regulating human SC proliferation and differentiation, and provides evidence to support the hypothesis that ROCKi promotes corneal endothelial division and maintenance via acting on the inner limbal SC niche.

A novel glaucoma approach: Stem cell regeneration of the trabecular meshwork

Glaucoma is the leading cause of global irreversible blindness, necessitating research for new, more efficacious treatment options than currently exist. Trabecular meshwork (TM) cells play an important role in the maintenance and function of the aqueous outflow pathway, and studies have found that there is decreased cellularity of the TM in glaucoma. Regeneration of the TM with stem cells has been proposed as a novel therapeutic option by several reports over the last few decades. Stem cells have the capacity for self-renewal and the potential to differentiate into adult functional cells. Several types of stem cells have been investigated in ocular regenerative medicine: tissue specific stem cells, embryonic stem cells, induced pluripotent stem cells, and adult mesenchymal stem cells. These cells have been used in various glaucoma animal models and ex vivo models and have shown success in IOP homeostasis and TM cellularity restoration. They have also demonstrated stability without serious side effects for a significant period of time. Based on current knowledge of TM pathology in glaucoma and existing literature regarding stem cell regeneration of this tissue, we propose a human clinical study as the next step in understanding this potentially revolutionary treatment paradigm. The ability to protect and replace TM cells in glaucomatous eyes could change the field forever.

Utilization of Modified Induced Pluripotent Stem Cells as the Advance Therapy of Glaucoma: A Systematic Review

Glaucoma is an optic neuropathy disease that causes cupping of the optic disc and decreased visual field. Glaucoma is still the second leading cause of blindness globally, with a worldwide prevalence of more than 76 million people in 2020. However, no therapy can cure glaucoma completely, especially when optic nerve damage has occurred. Available treatments only play a role in keeping the intraocular pressure stable This research aims to determine the potential use of modified stem cell therapy to treat intraocular damage in glaucoma cases. Literature research was conducted by involving seven online databases, namely Pubmed, ScienceDirect^®, Proquest, EBSCOhost^®, SAGE^®, Clinicalkey^®, and Scopus, published between 2010–2020 with the keywords stem cells; therapy; glaucoma; optic nerve. Six articles were selected, and out of the six articles, all writings were experimental research. The entire literature states that modified stem cell therapy has the potential as a therapeutic option in treating intraocular damage in patients with glaucoma. Based on the systematic literature review that has been carried out, it is known that stem cell therapy has the potential to be a therapeutic option in treating glaucoma cases. Much more research is needed to assess the effectiveness of modified stem cell therapy in managing intraocular damage due to glaucoma.

Reduction in trabecular meshwork stem cell content in donor eyes with primary open angle glaucoma

We previously identified and characterized human trabecular meshwork stem cells (TMSCs) based on high expression of ABCG2/p75 positivity and high nucleus to cytoplasmic ratio. These TMSCs expressing high ABCG2 and p75 were located to the insert region of the human TM. Additionally, we demonstrated an age-related reduction in the TMSC content which was significantly associated with TM cell loss. In continuation, this study was aimed to determine the TMSC content in glaucomatous donor eyes wherein a drastic reduction in TM cellularity has already been reported. Anterior segments from known glaucomatous (n = 6) and age-matched normal (n = 8) donors were dissected into four quadrants. A minimum of three sections from each quadrant were used for histopathological analysis as well as immunostaining. Analysis of hematoxylin and eosin-stained sections from glaucomatous tissues revealed a decrease in total TM cellularity, thickening of trabecular beams, fusion of trabeculae, absence of patent Schlemm's canal compared to age-matched controls. In addition, the TM thickness at various positions of the meshwork and the coronal as well as the meridional diameters of the Schlemm's canal were observed to be significantly reduced in glaucomatous eyes. Further, sections from both the groups were immunostained for universal stem cell marker ABCG2 and neural crest derived stem cell marker p75. The images were acquired using Leica SP8 confocal microscope. Quantification of total TM cellularity based on nuclear counterstain (mean ± SD) using ImageJ identified 69.33 ± 12.77 cells/section in control eyes. In glaucomatous donors, the TM cellularity was found to be reduced significantly to 41.83 ± 9.0 (p = 0.0007). In addition, a reduction in the percentage of TMSCs (cells with high ABCG2 expression and p75 positivity) was evident in glaucomatous donors (0.14 ± 0.17%) compared to age-matched controls (4.73 ± 5.46%) (p = 0.064). Thus, the present study confirmed the significant decline in TM cellularity and a reducing trend in the TMSC content, though this reduction was non-significant in glaucomatous donor eyes. Further studies are essential to elucidate the role of TMSCs in the pathogenesis of primary open angle glaucoma.

Cell-Based Therapies for Trabecular Meshwork Regeneration to Treat Glaucoma

Glaucoma is clinically characterized by elevated intraocular pressure (IOP) that leads to retinal ganglion cell (RGC) and optic nerve damage, and eventually blindness if left untreated. Even in normal pressure glaucoma patients, a reduction of IOP is currently the only effective way to prevent blindness, by either increasing aqueous humor outflow or decreasing aqueous humor production. The trabecular meshwork (TM) and the adjacent Schlemm’s canal inner wall play a key role in regulating IOP by providing resistance when aqueous humor drains through the tissue. TM dysfunction seen in glaucoma, through reduced cellularity, abnormal extracellular matrix accumulation, and increased stiffness, contributes to elevated IOP, but current therapies do not target the TM tissue. Stem cell transplantation for regeneration and re-functionalization of damaged TM has shown promise in providing a more direct and effective therapy for glaucoma. In this review, we describe the use of different types of stem cells for TM regeneration in glaucoma models, the mechanisms of regeneration, and the potential for glaucoma treatment using autologous stem cell transplantation.

Functional characterization of adult human trabecular meshwork stem cells

We earlier identified native human trabecular meshwork stem cells (TMSCs) based on two-parameters- high ABCG2 expression and high nucleus to cytoplasmic ratio. The TMSCs also expressed p75 and AnkyrinG. Based on the high expression of ABCG2 and p75, the TMSCs were identified to be located in the Schwalbe's line region of the TM. In continuation, the current study aimed at elucidating the functional characteristics of human TMSCs. Upon culturing, only a small proportion of TM cells (0.96 ± 0.21% in <30 years) expressing stem cell markers ABCG2 and p75 adhered to the culture dish. This proportion significantly reduced with ageing (0.32 ± 0.23% in 30-60 years and 0.35 ± 0.04% in >60 years). Characterization of the primary TM cultures identified 7.00 ± 1.80% of stem cells with label retaining property. Further, cultured cells had the ability to form TM spheres (0.82 ± 0.23%) which consisted of high ABCG2 and p75 positive cells. Upon dexamethasone induction, 86.00 ± 14.87% and 64.60 ± 7.24% of the cells derived from the TM spheres expressed myocilin and exhibited cross linked actin networks respectively, indicating differentiation of the TMSCs in the sphere to TM cells. In addition, the sphere derived TM cells also possessed phagocytic potential (13.28 ± 3.30%) equivalent to primary TM cells (16.33 ± 4.04%) which was evident upon internalization of zymosan particles. In conclusion, this study has established that a proportion of cultured TM cells had the label retaining property as well as sphere forming ability of adult stem cells. Thus, these results confirm the presence of adult stem cells in the human TM that might be responsible for the maintenance of tissue homeostasis.

A single cell atlas of human cornea that defines its development, limbal progenitor cells and their interactions with the immune cells

Purpose

Single cell (sc) analyses of key embryonic, fetal and adult stages were performed to generate a comprehensive single cell atlas of all the corneal and adjacent conjunctival cell types from development to adulthood.

Methods

Four human adult and seventeen embryonic and fetal corneas from 10 to 21 post conception week (PCW) specimens were dissociated to single cells and subjected to scRNA- and/or ATAC-Seq using the 10x Genomics platform. These were embedded using Uniform Manifold Approximation and Projection (UMAP) and clustered using Seurat graph-based clustering. Cluster identification was performed based on marker gene expression, bioinformatic data mining and immunofluorescence (IF) analysis. RNA interference, IF, colony forming efficiency and clonal assays were performed on cultured limbal epithelial cells (LECs).

Results

scRNA-Seq analysis of 21,343 cells from four adult human corneas and adjacent conjunctivas revealed the presence of 21 cell clusters, representing the progenitor and differentiated cells in all layers of cornea and conjunctiva as well as immune cells, melanocytes, fibroblasts, and blood/lymphatic vessels. A small cell cluster with high expression of limbal progenitor cell (LPC) markers was identified and shown via pseudotime analysis to give rise to five other cell types representing all the subtypes of differentiated limbal and corneal epithelial cells. A novel putative LPCs surface marker, GPHA2, expressed on the surface of 0.41% ± 0.21 of the cultured LECs, was identified, based on predominant expression in the limbal crypts of adult and developing cornea and RNAi validation in cultured LECs. Combining scRNA- and ATAC-Seq analyses, we identified multiple upstream regulators for LPCs and demonstrated a close interaction between the immune cells and limbal progenitor cells. RNA-Seq analysis indicated the loss of GPHA2 expression and acquisition of proliferative limbal basal epithelial cell markers during ex vivo LEC expansion, independently of the culture method used. Extending the single cell analyses to keratoconus, we were able to reveal activation of collagenase in the corneal stroma and a reduced pool of limbal suprabasal cells as two key changes underlying the disease phenotype. Single cell RNA-Seq of 89,897 cells obtained from embryonic and fetal cornea indicated that during development, the conjunctival epithelium is the first to be specified from the ocular surface epithelium, followed by the corneal epithelium and the establishment of LPCs, which predate the formation of limbal niche by a few weeks.

Conclusions

Our scRNA-and ATAC-Seq data of developing and adult cornea in steady state and disease conditions provide a unique resource for defining genes/pathways that can lead to improvement in ex vivo LPCs expansion, stem cell differentiation methods and better understanding and treatment of ocular surface disorders.

Stem cell transplantation rescued a primary open-angle glaucoma mouse model

Glaucoma is a leading cause of irreversible blindness. In this study, we investigated if transplanted stem cells are able to rescue a glaucoma mouse model with transgenic myocilin Y437H mutation and explored the possible mechanisms. Human trabecular meshwork stem cells (TMSCs) were intracamerally transplanted which reduced mouse intraocular pressure, increased outflow facility, protected the retinal ganglion cells and preserved their function. TMSC transplantation also significantly increased the TM cellularity, promoted myocilin secretion from TM cells into the aqueous humor to reduce endoplasmic reticulum stress, repaired the TM tissue with extracellular matrix modulation and ultrastructural restoration. Co-culturing TMSCs with myocilin mutant TM cells in vitro promoted TMSCs differentiating into phagocytic functional TM cells. RNA sequencing revealed that TMSCs had upregulated genes related to TM regeneration and neuroprotection. Our results uncovered therapeutic potential of TMSCs for curing glaucoma and elucidated possible mechanisms by which TMSCs achieve the treatment effect.

Immunology and Pathology in Ocular Drug Development

Clear vision is dependent on features that protect the anatomical integrity of the eye (cornea and sclera) and those that contribute to internal ocular homeostasis by conferring hemangiogenic (avascular tissues and antiangiogenic factors), lymphangiogenic (lack of draining lymphatics), and immunologic (tight junctions that form blood-ocular barriers, immunosuppressive cells, and modulators) privileges. The later examples are necessary components that enable the eye to maintain an immunosuppressive environment that responds to foreign invaders in a deviated manner, minimizing destructive inflammation that would impair vision. These conditions allowed for the observations made by Medawar, in 1948, of delayed rejection of allogenic tissue grafts in the anterior chamber of mouse eye and permit the sequestration of foreign invaders (eg, Toxoplasma gondii) within the retina of healthy individuals. Yet successful development of intraocular drugs (biologics and delivery devices) has been stymied by adverse ocular pathology, much of which is driven by immune pathways. The eye can be intolerant of foreign protein irrespective of delivery route, and endogenous ocular cells have remarkable plasticity when recruited to preserve visual function. This article provides a review of current understanding of ocular immunology and the potential role of immune mechanisms in pathology observed with intraocular drug delivery.

Three-Dimensional Human Cell Culture Models to Study the Pathophysiology of the Anterior Eye

In recent decades, the establishment of complex three-dimensional (3D) models of tissues has allowed researchers to perform high-quality studies and to not only advance knowledge of the physiology of these tissues but also mimic pathological conditions to test novel therapeutic strategies. The main advantage of 3D models is that they recapitulate the spatial architecture of tissues and thereby provide more physiologically relevant information. The eye is an extremely complex organ that comprises a large variety of highly heterogeneous tissues that are divided into two asymmetrical portions: the anterior and posterior segments. The anterior segment consists of the cornea, conjunctiva, iris, ciliary body, sclera, aqueous humor, and the lens. Different diseases in these tissues can have devastating effects. To study these pathologies and develop new treatments, the use of cell culture models is instrumental, and the better the model, the more relevant the results. Thus, the development of sophisticated 3D models of ocular tissues is a significant challenge with enormous potential. In this review, we present a comprehensive overview of the latest advances in the development of 3D in vitro models of the anterior segment of the eye, with a special focus on those that use human primary cells.

Deconstructing aqueous humor outflow - The last 50 years

Herein partially summarizes one scientist-clinician's wanderings through the jungles of primate aqueous humor outflow over the past ~45 years. Totally removing the iris has no effect on outflow facility or its response to pilocarpine, whereas disinserting the ciliary muscle (CM) from the scleral spur/trabecular meshwork (TM) completely abolishes pilocarpine's effect. Epinephrine increases facility in CM disinserted eyes. Cytochalasins and latrunculins increase outflow facility, subthreshold doses of cytochalasins and epinephrine given together increase facility, and phalloidin, which has no effect on facility, partially blocks the effect of both cytochalasins and epinephrine. H-7, ML7, Y27632 and nitric oxide - donating compounds all increase facility, consistent with a mechanosensitive TM/SC. Adenosine A1 agonists increase and angiotensin II decrease facility. OCT and optical imaging techniques now permit visualization and digital recording of the distal outflow pathways in real time. Prostaglandin (PG) F2α analogues increase the synthesis and release of matrix metalloproteinases by the CM cells, causing remodeling and thinning of the interbundle extracellular matrix (ECM), thereby increasing uveoscleral outflow and reducing IOP. Combination molecules (one molecule, two or more effects) and fixed combination products (two molecules in one bottle) simplify drug regimens for patients. Gene and stem cell therapies to enhance aqueous outflow have been successful in laboratory models and may fill an unmet need in terms of patient compliance, taking the patient out of the delivery system. Functional transfer of genes inhibiting the rho cascade or decoupling actin from myosin increase facility, while genes preferentially expressed in the glaucomatous TM decrease facility. In live NHP, reporter genes are expressed for 2+ years in the TM after a single intracameral injection, with no adverse reaction. However, except for one recent report, injection of facility-effective genes in monkey organ cultured anterior segments (MOCAS) have no effect in live NHP. While intracameral injection of an FIV. BOVPGFS-myc.GFP PGF synthase vector construct reproducibly induces an ~2 mmHg reduction in IOP, the effect is much less than that of topical PGF2⍺ analogue eyedrops, and dissipates after 5 months. The turnoff mechanism has yet to be defeated, although proteasome inhibition enhances reporter gene expression in MOCAS. Intracanalicular injection might minimize off-target effects that activate turn-off mechanisms. An AD-P21 vector injected sub-tenon is effective in 'right-timing' wound healing after trabeculectomy in live laser-induced glaucomatous monkeys. In human (H)OCAS, depletion of TM cells by saponification eliminates the aqueous flow response to pressure elevation, which can be restored by either cultured TM cells or by IPSC-derived TM cells. There were many other steps along the way, but much was accomplished, biologically and therapeutically over the past half century of research and development focused on one very small but complex ocular apparatus. I am deeply grateful for this award, named for a giant in our field that none of us can live up to.

A Biomimetic, Stem Cell-Derived In Vitro Ocular Outflow Model

Age-related human trabecular meshwork (HTM) cell loss is suggested to affect its ability to regulate aqueous humor outflow in the eye. In addition, disease-related HTM cell loss is suggested to lead to elevated intraocular pressure in glaucoma. Induced pluripotent stem cell (iPSC)-derived trabecular meshwork (TM) cells are promising autologous cell sources that can be used to restore the declining TM cell population and function. Previously, an in vitro HTM model is bioengineered for understanding HTM cell biology and screening of pharmacological or biological agents that affect trabecular outflow facility. In this study, it is demonstrated that human iPSC-derived TM cells cultured on SU-8 scaffolds exhibit HTM-like cell morphology, extracellular matrix deposition, and drug responsiveness to dexamethasone treatment. These findings suggest that iPSC-derived TM cells behave like primary HTM cells and can thus serve as reproducible and scalable cell sources when using this in vitro system for glaucoma drug screening and further understanding of outflow pathway physiology, leading to personalized medicine.

Adipose-derived stem cells integrate into trabecular meshwork with glaucoma treatment potential

The trabecular meshwork (TM) is an ocular tissue that maintains intraocular pressure (IOP) within a physiologic range. Glaucoma patients have reduced TM cellularity and, frequently, elevated IOP. To establish a stem cell-based approach to restoring TM function and normalizing IOP, human adipose-derived stem cells (ADSCs) were induced to differentiate to TM cells in vitro. These ADSC-TM cells displayed a TM cell-like genotypic profile, became phagocytic, and responded to dexamethasone stimulation, characteristic of TM cells. After transplantation into naive mouse eyes, ADSCs and ADSC-TM cells integrated into the TM tissue, expressed TM cell markers, and maintained normal IOP, outflow facility, and extracellular matrix. Cell migration and affinity results indicated that the chemokine pair CXCR4/SDF1 may play an important role in ADSC-TM cell homing. Our study demonstrates the possibility of applying autologous or allogeneic ADSCs and ADSC-TM cells as a potential treatment to restore TM structure and function in glaucoma.

Transplantation of iPSC-TM stimulates division of trabecular meshwork cells in human eyes

The trabecular meshwork’s (TM) physiological role is to maintain normal intraocular pressure by regulating aqueous humor outflow. With age, and particularly in eyes with primary open angle glaucoma, the number of cells residing within the TM is markedly decreased and the function of the tissue is compromised. Here we evaluate if transplantation of induced pluripotent stem cell derived TM like cells (iPSC-TM) restores TM cellularity and function in human eyes obtained from older human donors. Human iPSC were differentiated into iPSC-TM and compared to primary TM cells by RNAseq. iPSC-TM were then injected into the anterior segments of human eyes maintained in perfusion culture. Seven and 14 days eyes after injection eyes that received iPSC-TM contained significantly more cells in the TM. Fewer than 1% of all cells appeared to be iPSC-TM, but significantly more cells in these eyes were immunopositive for Ki 67 and incorporated BrdU. Our study demonstrates that transplantation iPSC-TM stimulates proliferation of endogenous TM cells in perfusion cultured human eyes from aged donors. These data, in concert with our previous findings in animal models, suggest that functional regeneration of the TM may be possible in human eyes with primary open angle glaucoma.

α5β1 Integrin Promotes Anchoring and Integration of Transplanted Stem Cells to the Trabecular Meshwork in the Eye for Regeneration

Stem cell-based therapy to restore the function of abnormal trabecular meshwork (TM) and decrease intraocular pressure (IOP) provides a novel approach to treat open-angle glaucoma. However, molecular mechanism for stem cells homing and anchoring to the TM remains unclear. This study aimed to discover the function of integrins in homing and integration of exogenous TM stem cells (TMSCs) to the TM. Integrin expression in TMSCs and fibroblasts was evaluated by quantitative real-time PCR (qPCR), flow cytometry, immunofluorescent staining, and western blotting. Expression of integrin ligand fibronectin was detected in cultured TM cells and murine TM tissue by immunostaining. Cell affinity to TM cells or fibronectin matrix was examined to compare TMSCs with TMSCs functionally blocked with an α5β1 integrin antibody. TMSCs and TMSCs with α5β1 integrin-blocking were intracamerally injected into wild-type mice. Wholemounts and cryosections were analyzed to discover cell distribution and integration at 3 days and 1 month. IOP was measured to detect possible changes. We discovered that human TMSCs expressed a higher level of α5β1 integrin than fibroblasts, but similar levels of αvβ3 and αvβ5 integrin. Upregulation of fibronectin was found in both TM cells treated with dexamethasone for 14 days and murine TM tissues damaged by laser photocoagulation. TMSCs were able to attach to the TM cells and fibronectin matrix in vitro. When the surface α5β1 integrin was blocked, the attached cell numbers were significantly reduced. Both TMSCs and TMSCs incubated with an α5β1 integrin-blocking antibody could home to the mouse TM after injection. TMSCs blocked with the α5β1 integrin-blocking antibody were not retained in the TM tissue at 1 month. The injected cells did not affect mouse IOP. In conclusion, highly expressed α5β1 integrin participates in maintaining TMSCs anchored and integrated to the TM, which would be crucial for stem cell-based therapy for glaucoma.

Stem cells from trabecular meshwork cells can secrete extracellular matrix

Isolation of trabecular meshwork stem cells in vitro provides the foundation of a novel treatment for glaucoma. Trabecular meshwork stem cells (TMSCs) of the fetal calve were extracted and cultured for this experiment. TMSCs were isolated through side population cell sorting. TMSCs were then identified using immunofluorescent staining. Extracellular matrix (ECM) expression in TM cells derived from TMSCs was evaluated with Western blot. Our results showed a positive expression of stem cell markers Notch1 and OCT-3/4 in TMSCs, but no TM cells markers TIMP3 or AQP1. In contrast, primary TM cells expressed these TM cell markers but no stem cell markers. Our result confirmed that there are expression of ECM components, such as fibronectin, laminin, collagen I and collagen IV in TM cells differentiated from TMSCs. CONCLUSION: TM cells derived from TMSCs can secrete ECM components which is important for sustain the physiological function.

Stem Cells from Human Trabecular Meshwork Hold the Potential to Develop into Ocular and Non-Ocular Lineages After Long-Term Storage

Stem cells from the eye hold a great potential for vision restoration and can also be used for regeneration in other tissues. In this study, we characterized the stem cell properties of Trabecular meshwork stem cells (TMSCs) after long-term cryopreservation (∼8 years). TMSCs derived from four donors were examined for their viability and proliferation, as well as stem cell marker expression. Spheroid formation, colony formation, and multipotency were investigated. We observed that TMSCs were fully viable with variable proliferation ability. They expressed the stem cell markers CD90, CD166, CD105, CD73, OCT4, SSEA4, Notch1, KLF4, ABCG2, Nestin, and HNK1 detected by flow cytometry, quantitative polymerase chain reaction, or immunofluorescent staining. They could form spheroids and colonies after thawing. All TMSCs were able to differentiate into osteocytes, neural cells, and trabecular meshwork (TM) cells, but not adipocytes. Differentiated TM cells responded to dexamethasone treatment with increased expression of myocilin and angiopoietin-like 7 (ANGPTL7). In a nutshell, our study demonstrated that TMSCs retain their stem cell properties after long-term cryopreservation and hence can be an effective cell therapy source for various clinical applications.

The Rapid Transformation of Transplantation for Corneal Endothelial Diseases: An Evolution From Penetrating to Lamellar to Cellular Transplants

The cornea is the major focusing structure of the human eye and the corneal endothelium maintains the relatively dehydrated state of the cornea required for clarity. The endothelial cells respond to disease or injury by migration and cellular enlargement. Our current understanding is that there is a very limited degree of proliferative or regenerative capacity in the human corneal endothelium. Thus, corneal endothelial diseases may result in corneal edema, significantly impact vision and quality of life. Contemporary surgical transplantation options for treating moderate to advanced endothelial dysfunction include penetrating keratoplasty (PK), Descemet stripping endothelial keratoplasty (DSEK), and Descemet membrane endothelial keratoplasty. Advances in surgical techniques aim to bring faster visual recovery and improve visual outcomes; however, there is still a significant donor cornea shortage worldwide and alternative methods for treatment for corneal endothelial disease are rapidly evolving. Indeed, we are at a pivotal point in corneal transplantation for endothelial disease and novel surgical strategies include using 1 donor for multiple recipients, a minimally attached endothelial graft, and Descemet membrane stripping only. Crucially, forthcoming approaches include the use of Rho-Kinase (ROCK) inhibitors, endothelial cell therapy, tissue engineered grafts, and consideration of stem cell techniques. Ultimately, the choice of technique will be dependent on recipient factors such as age, type of endothelial disease, extent of the disease, and associated ocular disorders. The safety and efficacy of these rapidly developing treatments warrant further investigations. In time, some or all of these alternatives for corneal transplantation will alleviate the reliance on limited corneal donor tissue.

Progression on canaloplasty for primary open angle glaucoma

As a non-penetrating glaucoma surgery (NPGS), canaloplasty aims to reconstruct the physiological outflow of aqueous humor by dilating the Schlemm's canal. Ab interno canaloplasty (ABiC), which can reconstruct the natural outflow pathways of aqueous humor in mild-to-moderate primary open angle glaucoma (POAG) patients, is a new minimally invasive glaucoma surgery (MIGS) procedure improving from traditional canaloplasty. Canaloplasty can reduce intraocular pressure (IOP) with high efficiency and security. There are no complications such as scar formation and encapsulation for this no-bleb canaloplasty.

Identification, quantification and age-related changes of human trabecular meshwork stem cells

Background

Loss of cells in the human trabecular meshwork (TM) has been reported with ageing and in glaucoma. This study aims to identify, quantify and determine the age-related changes of human TM stem cells (TMSCs).

Methods

Isolation of TM cells/ paraffin sectioning was carried out using human corneoscleral rings and whole globes. The TM cells/ sections were immunostained for the stem cell markers ATP-binding cassette protein G2 (ABCG2), nerve growth factor receptor p75 and AnkyrinG (AnkG). Images were acquired using Leica SP8 confocal microscope. The isolated cells were analyzed for two parameters- ABCG2 expression and nucleus to cytoplasmic ratio (N/C ratio). The total number of TM cells and those positive for ABCG2 and p75 in each section were quantified. Spearman rank order correlation was used to determine the association between age and the cell counts.

Results

The TMSCs were identified based on two parameters- high ABCG2 expression and high N/C ratio > 0.7. These stem cells were also positive for p75 and AnkG. The TMSC content based on the two parameters was 21.0 ± 1.4% in < 30 years age group, 12.6 ± 6.6% in 30-60 years and 4.0 ± 3.5% in > 60 years. The stem cells with high ABCG2 and p75 expression were restricted to the Schwalbe's line region of the TM. A significant correlation was observed between the reduction in TMSC content and TM cell count during ageing.

Conclusion

The human TMSCs were identified and quantified based on two parameter analysis. This study established a significant association between age-related reduction in TMSC content and TM cell loss.

Trabecular Meshwork Regeneration - A Potential Treatment for Glaucoma

Purpose

In this review, we overview the pathophysiology of primary open-angle glaucoma as it relates to the trabecular meshwork (TM), exploring modes of TM dysfunction and regeneration via stem cell therapies.

Recent Findings

Stem cells from a variety of sources, including trabecular meshwork, mesenchymal, adipose and induced pluripotent stem cells, have shown the potential to differentiate into TM cells in vitro or in vivo and to regenerate the TM in vivo, lowering intraocular pressure (IOP) and reducing glaucomatous retinal ganglion cell damage.

Summary

Stem cell therapies for TM regeneration provide a robust and promising suite of treatments for eventual lowering of IOP and prevention of glaucomatous vision loss in humans in the future. Further investigation into stem cell homing mechanisms and the safety of introducing these cells into human anterior chamber, for instance, are required before clinical applications in treating glaucoma patients.

Trabecular meshwork cells are a valuable resource for cellular therapy of glaucoma

Trabecular meshwork (TM) contains a subset of adult stem cells or progenitors that can be differentiated into corneal endothelial cells, adipocytes and chondrocytes, but not osteocytes or keratocytes. Accordingly, these progenitors can be utilized as a cell‐based therapy to prevent blindness caused by glaucoma, corneal endothelial dysfunction and other diseases in general. In this review, we review in vitro expansion techniques for TM progenitors, discuss their phenotypic properties, and highlight their potential clinical applications in various ophthalmic diseases.

Human stem cells home to and repair laser-damaged trabecular meshwork in a mouse model

Glaucoma is the leading cause of irreversible vision loss, and reducing elevated intraocular pressure is currently the only effective clinical treatment. The trabecular meshwork is the main resistance site for aqueous outflow that maintains intraocular pressure. In this study, we transplanted human trabecular meshwork stem cells (TMSCs) intracamerally into mice that received laser photocoagulation over a 180° arc of the trabecular meshwork. TMSCs preferentially homed and integrated to the laser-damaged trabecular meshwork region and expressed differentiated cell markers at 2 and 4 weeks. Laser-induced inflammatory and fibrotic responses were prevented by TMSC transplantation with simultaneous ultrastructure and function restoration. Cell affinity and migration assays and elevated expression of CXCR4 and SDF1 in laser-treated mouse trabecular meshwork suggest that the CXCR4/SDF1 chemokine axis plays an important role in TMSC homing. Our results suggest that TMSCs may be a viable candidate for trabecular meshwork refunctionalization as a novel treatment for glaucoma.

Hongmin Yun et al. show that implanted human stem cells can accurately home to and repair damaged trabecular meshwork tissue in the mouse eye via a chemokine axis defined by CXCR4 and SDF1. The study suggests that stem cells from the trabecular meshwork could be used to refunctionalize the outflow pathway as a treatment for glaucoma.

Consensus recommendations for trabecular meshwork cell isolation, characterization and culture

Cultured trabecular meshwork (TM) cells are a valuable model system to study the cellular mechanisms involved in the regulation of conventional outflow resistance and thus intraocular pressure; and their dysfunction resulting in ocular hypertension. In this review, we describe the standard procedures used for the isolation of TM cells from several animal species including humans, and the methods used to validate their identity. Having a set of standard practices for TM cells will increase the scientific rigor when used as a model, and enable other researchers to replicate and build upon previous findings.

Isolation and Expansion of Multipotent Progenitors from Human Trabecular Meshwork

To expand multi-potent progenitors from human trabecular meshwork (TM), we have created a new optimized method on two-dimensional (2D) followed by three-dimensional (3D) Matrigel in modified embryonic stem cell medium supplemented with 5% fetal bovine serum (MESCM + 5% FBS). The expanded TM cells were small cuboidal cells expressing TM markers such as AQP1, MGP, CHI3L1, and AnkG, embryonic stem cell (ESC) markers such as Oct4, Sox2, Nanog, and ABCG2, and neural crest (NC) markers such as p75NTR, FOXD3, Sox9, Sox10, and MSX1. Although expanded cells lost expression of these markers after passage, the cells regained the markers when Passage 2 cells were seeded on 3D Matrigel through activation of canonical BMP signaling. Such restored progenitors could differentiate into corneal endothelial cells, adipocytes, and chondrocytes but not keratocytes or osteocytes. Therefore, we have concluded that human TM harbors multipotent progenitors that can be effectively isolated and expanded using 2D Matrigel in MESCM + 5% FBS. This unique in vitro model system can be used to understand how TM is altered in glaucoma and whether such TM progenitor cells might one day be used for treating glaucoma or corneal endothelial dysfunction.

Mechanism of the reconstruction of aqueous outflow drainage

Glaucoma is the leading cause of irreversible blindness worldwide. The reconstruction of aqueous outflow drainage (RAOD) has recently been proposed to aid in restoring aqueous outflow drainage in primary open-angle glaucoma. However, the mechanism of RAOD remains to be fully understood. Based on literature review and research studies, the potential mechanisms of RAOD are the following: (i) Circumferential dilation of the Schlemm's canal (SC) and surrounding collector channels. (ii) Instant formation of microcracks through RAOD procedures. (iii) Formation of more pores, and local detachment between the SC endothelium (SCE) and basement membrane. (iv) Activation of stem cells by constant mechanical stress caused by the tensional suture placed at the anterior part of the SC. (v) Reversal of trabecular meshwork (TM) herniation. (vi) Mobilization of the reserve of the aqueous drainage. (vii) Change of SCE phenotype. (viii) Mechanosensing and mechanotransducing of TM.

Deletion of Endothelial Transforming Growth Factor-β Signaling Leads to Choroidal Neovascularization

The molecular pathogenesis of choroidal neovascularization (CNV), an angiogenic process that critically contributes to vision loss in age-related macular degeneration, is unclear. Herein, we analyzed the role of transforming growth factor (TGF)-β signaling for CNV formation by generating a series of mutant mouse models with induced conditional deletion of TGF-β signaling in the entire eye, the retinal pigment epithelium (RPE), or the vascular endothelium. Deletion of TGF-β signaling in the eye caused CNV, irrespectively if it was ablated in newborn or 3-week-old mice. Areas of CNV showed photoreceptor degeneration, multilayered RPE, basal lamina deposits, and accumulations of monocytes/macrophages. The changes progressed, leading to marked structural and functional alterations of the retina. Although the specific deletion of TGF-β signaling in the RPE caused no obvious changes, specific deletion in vascular endothelial cells caused CNV and a phenotype similar to that observed after the deletion in the entire eye. We conclude that impairment of TGF-β signaling in the vascular endothelium of the eye is sufficient to trigger CNV formation. Our findings highlight the importance of TGF-β signaling as a key player in the development of ocular neovascularization and indicate a fundamental role of TGF-β signaling in the pathogenesis of age-related macular degeneration.

SMAD7 deficiency stimulates Müller progenitor cell proliferation during the development of the mammalian retina

The transforming growth factor-β (TGF-β) pathway contributes to maintain the quiescence of adult neural stem and progenitor cells in the brain. In the retina, Müller cells are discussed to represent a glial cell population with progenitor-like characteristics. Here, we aimed to investigate if elevated TGF-β signaling modulates the proliferation of Müller cells during retinal development. We generated mutant mice with a systemic, heterozygous up-regulation of TGF-β signaling by deleting its inhibitor SMAD7. We investigated apoptosis, proliferation, and differentiation of Müller cells in the developing retina. We show that a heterozygous deletion of SMAD7 results in an increased proliferation of Müller cell progenitors in the central retina at postnatal day 4, the time window when Müller cells differentiate in the mouse retina. This in turn results in a thickened retina and inner nuclear layer and a higher number of differentiated Müller cells in the more developed retina. Müller cells in mutant mice contain higher amounts of nestin than those of control animals which indicates that the increase in TGF-β signaling activity during retinal development contribute to maintain some progenitor-like characteristics in Müller cells even after their differentiation period. We conclude that TGF-β signaling influences Müller cell proliferation and differentiation during retinal development.

Transplantation of iPSC-derived TM cells rescues glaucoma phenotypes in vivo

Glaucoma is a common cause of vision loss or blindness and reduction of intraocular pressure (IOP) has been proven beneficial in a large fraction of glaucoma patients. The IOP is maintained by the trabecular meshwork (TM) and the elevation of IOP in open-angle glaucoma is associated with dysfunction and loss of the postmitotic cells residing within this tissue. To determine if IOP control can be maintained by replacing lost TM cells, we transplanted TM-like cells derived from induced pluripotent stem cells into the anterior chamber of a transgenic mouse model of glaucoma. Transplantation led to significantly reduced IOP and improved aqueous humor outflow facility, which was sustained for at least 9 wk. The ability to maintain normal IOP engendered survival of retinal ganglion cells, whose loss is ultimately the cause for reduced vision in glaucoma. In vivo and in vitro analyses demonstrated higher TM cellularity in treated mice compared with littermate controls and indicated that this increase is primarily because of a proliferative response of endogenous TM cells. Thus, our study provides in vivo demonstration that regeneration of the glaucomatous TM is possible and points toward novel approaches in the treatment of this disease.

Stem Cells in the Trabecular Meshwork for Regulating Intraocular Pressure

Intraocular pressure (IOP) is still the main treatment target for glaucoma. Outflow resistance mainly exists at the trabecular meshwork (TM) outflow pathway, which is responsible for IOP regulation. Changes of TM cellularity and TM extracellular matrix turnover may play important roles in IOP regulation. In this article, we review basic anatomy and physiology of the outflow pathway and TM stem cell characteristics regarding the location, isolation, identification and function. TM stem cells are localized at the insert region of the TM and are label-retaining in vivo. They can be isolated by side-population cell sorting, cloning culture, or sphere culture. TM stem cells are multipotent with the ability to home to the TM region and differentiate into TM cells in vivo. Other stem cell types, such as adipose-derived stem cells, mesenchymal stem cells and induced pluripotent stem cells have been discovered for TM cell differentiation and TM regeneration. We also review glaucomatous animal models, which are suitable to study stem cell-based therapies for TM regeneration.

Sox2/Oct4: A delicately balanced partnership in pluripotent stem cells and embryogenesis

Considerable progress has been made in understanding the roles of Sox2 and Oct4 in embryonic stem cells and mammalian embryogenesis. Specifically, significant progress has been made in answering three questions about the functions of Sox2 and Oct4, which are the focus of this review. 1) Are the first or second cell lineage decisions during embryogenesis controlled by Oct4 and/or Sox2? 2) Do the levels of Oct4 and Sox2 need to be maintained within narrow limits to promote normal development and to sustain the self-renewal of pluripotent stem cells? 3) Do Oct4 and Sox2 work closely together or is the primary role of Sox2 in pluripotent cells to ensure the expression of Oct4? Although significant progress has been made in answering these questions, additional studies are needed to resolve several important remaining issues. Nonetheless, the preponderance of the evidence suggests there is considerable crosstalk between Sox2 and Oct4, and further suggests Sox2 and Oct4 function as molecular rheostats and utilize negative feedback loops to carefully balance their expression and other critical genes during embryogenesis. This article is part of a Special Issue entitled: The Oct transcription factor family, edited by Dr. Dean Tantin.

The Outflow Pathway: A Tissue With Morphological and Functional Unity

The trabecular meshwork (TM) plays an important role in high-tension glaucomas. Indeed, the TM is a true organ, through which the aqueous humor flows from the anterior chamber to Schlemm's canal (SC). Until recently, the TM, which is constituted by endothelial-like cells, was described as a kind of passive filter. In reality, it is much more. The cells delineating the structures of the collagen framework of the TM are endowed with a cytoskeleton, and are thus able to change their shape. These cells also have the ability to secrete the extracellular matrix, which expresses proteins and cytokines, and are capable of phagocytosis and autophagy. The cytoskeleton is attached to the nuclear membrane and can, in millionths of a second, send signals to the nucleus in order to alter the expression of genes in an attempt to adapt to biomechanical insult. Oxidative stress, as happens in aging, has a deleterious effect on the TM, leading eventually to cell decay, tissue malfunction, subclinical inflammation, changes in the extracellular matrix and cytoskeleton, altered motility, reduced outflow facility, and (ultimately) increased IOP. TM failure is the most relevant factor in the cascade of events triggering apoptosis in the inner retinal layers, including ganglion cells. J. Cell. Physiol. 231: 1876-1893, 2016. © 2016 Wiley Periodicals, Inc.

Stem cell approaches to glaucoma: from aqueous outflow modulation to retinal neuroprotection

Long-term pharmacological management of glaucoma currently relies on self-administered drugs to regulate intraocular pressure (IOP). A number of approaches using stem cells have recently shown promise as potential future treatment strategies complementary to IOP lowering. Several sources of endogenous stem cells have been identified in the eye, some of which may be able to repair the damaged trabecular meshwork and restore functional regulation of aqueous outflow. Neural and mesenchymal stem cells secrete growth factors which provide neuroprotective effects, reducing loss of retinal ganglion cells (RGCs) in animal models. In the future, stem cells may even replace RGCs to reform functional connections between the eye and the brain, although the complexity of such a repair task is formidable. With advances in biomaterial cell scaffolds and concurrent efforts in other neural systems, stem cell therapies are becoming a realistic option for treating multiple eye diseases, and despite ongoing challenges, there are reasons for optimism that stem cells may play a role in the treatment of human glaucoma in the future.

The aqueous humor outflow pathways in glaucoma: A unifying concept of disease mechanisms and causative treatment

Intraocular pressure (IOP) is the critical risk factor for glaucoma, a neurodegenerative disease and frequent cause of blindness worldwide. As of today, all effective strategies to treat glaucoma aim at lowering IOP. IOP is generated and maintained via the aqueous humor circulation system in the anterior eye. Aqueous humor is secreted by the ciliary processes and exits the eye through the trabecular meshwork (TM) or the uveoscleral outflow pathways. The TM outflow pathways provide resistance to aqueous humor outflow and IOP builds up in response to it. In the normal eye, the resistance is localized in the inner wall region, which comprises the juxtacanalicular connective tissue (JCT) and the inner wall endothelium of Schlemm's canal (SC). Outflow resistance in the inner wall region is lowered through the contraction of the ciliary muscle or the relaxation of contractile myofibroblasts in the posterior part of the TM and the adjacent scleral spur. Patients with primary open-angle glaucoma (POAG), the most frequent form of glaucoma, typically suffer from an abnormally high outflow resistance of the inner wall region. There is increasing evidence that the increase in TM outflow resistance in POAG is the result of a characteristic change in the biological properties of the resident cells in the JCT, which increasingly acquire the phenotype of contractile myofibroblasts. This scenario strengthens simultaneously both their actin cytoskeleton and their directly associated extracellular matrix fibrils, leads to overall stiffening of the tissue, and is modulated by transforming growth factor-β (TGF-β)/connective tissue growth factor (CTGF) signaling. Essentially comparable changes appear to occur in SC endothelial cells in glaucoma. Causative therapy concepts targeting the aqueous outflow pathways in glaucoma should aim at interfering with this process either by attenuating TM or SC stiffness, and/or by modulating TGF-β/CTGF signaling.

Recent Developments in Understanding the Role of Aqueous Humor Outflow in Normal and Primary Open Angle Glaucoma

Primary open angle glaucoma (POAG) is the second leading cause of blindness in the world's rapidly aging population. POAG is characterized by progressive degeneration of neural structures in the posterior segment, often associated with a concomitant elevation of intraocular pressure. Changes in IOP are believed to be caused by a disruption in the normal outflow of aqueous humor. This article reviews recent research associated with normal and POAG aqueous humor outflow. Novel findings elucidating biochemical and pathological changes in the ocular tissues affected in POAG are presented. Stem cell research, identification of lymphatic markers, and increased use of mouse models give researchers exciting new tools to understand aqueous humor outflow, changes associated with POAG and identify underlying causes of the disease.