Isolation and culture of human trabecular meshwork cells by extracellular matrix digestion

Human trabecular meshwork stem cell-derived small extracellular vesicles enhance trabecular meshwork cell survival and proliferation

Glaucoma is an optic neuropathy, one of the leading causes of irreversible blindness worldwide. Previous studies in animal models have shown that transplantation of trabecular meshwork stem cells (TMSCs-adult tissue-resident stem cells of TM) promotes TM regeneration and restores intraocular pressure through paracrine signaling. One of the major paracrine signal mediators is the extracellular vesicles. Given the advantages of sEV over cell-based therapies, the current work aims to investigate the potential of TMSC-derived small extracellular vesicles (sEV) in promoting TM cell survival and proliferation using in vitro experiments. TM cells were cultured in TM media and stem cell growth media (SCGM). Phenotypic and functional (sphere formation) characterization of cultured cells revealed that the SCGM maintained stemness with greater functional efficacy. sEV from TM cell (TM media) and TMSC (SCGM) conditioned media were isolated using the ultracentrifugation method. Characterization of sEV demonstrated that the sEV were within the size range of 30-200 nm and poly-dispersive spherical in shape. The TM and TMSC sEV express common exosomal marker syntenin, TM specific exosomal markers-emilin and neuropilin. To check the uptake specificity, the labelled sEV were incubated with different cell types. The varying degrees of uptake of the labelled sEV by TM cells, HLEB3 and 3T3 cell lines implied that TM and TMSC sEV might have varied surface components. The regenerative efficacy of the sEV was assessed in vitro by scratch wound assay, immunostaining for proliferation marker Ki67, and 5'-Bromo-2'-deoxyuridine incorporation assay. The TMSC sEV exhibited better wound healing efficacy by inducing TM cell proliferation. Furthermore, evaluation of the antioxidant potential depicted that the TMSC sEV enhanced TM cell viability under chronic oxidative stress by significantly reducing the intracellular reactive oxygen species. Taken together, our study demonstrated for the first time that the TMSC sEV enhanced TM cell proliferation as well as migration in vitro and attenuated oxidative stress-induced cell death by reducing intracellular reactive oxygen species. Further studies in animal models will pave the way for the potential application of TMSC sEV in glaucoma treatment.

Time-Lapse Live-Cell Imaging Using Fluorescent Protein Sensors in Outflow Pathway Cells Under Fluid Flow Conditions

The role of shear stress in regulating aqueous humor (AH) outflow and intraocular pressure (IOP) in the trabecular meshwork (TM) and Schlemm's canal (SC) of the eye is an emerging field. Shear stress has been shown to activate mechanosensitive ion channels in TM cells and induce nitric oxide production in SC cells, which can affect outflow resistance and lower IOP. Live-cell imaging using fluorescent protein sensors has provided real-time data to investigate the physiological relationship between fluid flow and shear stress in the outflow pathway cells. The successful application of time-lapse live-cell imaging in primary cultured cells has led to the identification of key cellular and molecular mechanisms involved in regulating AH outflow and IOP, including the role of autophagy and primary cilia as mechanosensors. This chapter presents a detailed protocol for conducting time-lapse live-cell imaging under fluid flow conditions in the outflow pathway cells.

Evaluation of Cross-Linked Actin Networks (CLANs) in Human Trabecular Meshwork Cells and Tissues

Elevated intraocular pressure (IOP) is a major risk factor for the development and progression of glaucoma, the leading cause of irreversible vision loss and blindness. An overall increase in resistance to aqueous humor outflow causes sustained elevation in IOP. Glaucomatous insults in the aqueous humor outflow pathway, including the trabecular meshwork (TM), precede such chronic physiological changes in IOP. These insults include ultrastructural changes with excessive extracellular matrix deposition and actin cytoskeletal reorganization that leads to pathological stiffening of the ocular tissues. One of the most common cytoskeletal changes associated with TM tissue stiffness in glaucoma is the increased prevalence of cross-linked actin networks (CLANs) in cells of the trabecular meshwork (TM) and lamina cribrosa (LC). In glaucomatous cells, rearrangement of linear actin stress fibers leads to formation of polygonal arrays within the cytoplasm, resembling a geodesic dome-like structure, that we identified as CLANs. In addition to increased amounts of CLANs in POAG TM cells and tissues, we also discovered that glucocorticoid (GC) and TGFβ2 signaling pathways associated with the development of ocular hypertension (OHT) and glaucoma also induced CLANs in the TM. Despite a clear association, we are yet to completely understand the mechanisms involved in CLAN formation and their direct relevance to disease pathology. In this chapter, we will describe methods to identify and characterize CLANs using fluorescent microscopy in primary TM cell cultures, ex vivo perfusion cultured human anterior segments, and in situ in human donor eyes.

Integrated Profiling of Extracellular Vesicle microRNA Impact on Trabecular Meshwork mRNA Expression: Insights From Microarray Analysis

Purpose

Extracellular vesicles (EVs) secreted by non-pigmented ciliary epithelial (NPCE) cells under oxidative stress may contribute to primary open-angle glaucoma (POAG) pathogenesis by altering gene expression in human trabecular meshwork (HTM) cells. This study investigated the impact of microRNAs (miRNAs) carried by NPCE-derived EVs on HTM cell gene expression under oxidative stress conditions.

Methods

NPCE cells were exposed to oxidative stress, and EVs were isolated from control and stressed cells. HTM cells were treated with these EVs, followed by microarray analysis to identify differentially expressed miRNAs in EVs and messenger RNAs (mRNAs) in HTM cells. Bioinformatics analysis was used to explore miRNA-mRNA interactions, enriched Gene Ontology (GO) terms, and miRNA-mRNA-GO networks.

Results

The study identified 54 differentially expressed miRNAs in stressed NPCE EVs. In HTM cells treated with stressed NPCE EVs, 88 genes were upregulated and 58 downregulated. GO analysis of upregulated genes showed enrichment in processes such as extracellular matrix organization, cell proliferation, and adhesion. Downregulated genes were associated with oxidative phosphorylation and adenosine triphosphate (ATP) biosynthesis. Notably, 59 out of 88 upregulated genes are known targets of downregulated miRNAs. Network analysis identified interactions between downregulated miRNAs and upregulated genes involved in key biological processes relevant to POAG pathogenesis.

Conclusions

This study provides new insights into the potential role of NPCE-derived EVs and their miRNA cargo in POAG, suggesting novel mechanisms for disease progression and potential therapeutic targets for further investigation.

TRPV4 overactivation enhances cellular contractility and drives ocular hypertension in TGFβ2 overexpressing eyes

The risk for developing primary open-angle glaucoma (POAG) correlates with the magnitude of ocular hypertension (OHT) and the concentration of transforming growth factor-β2 (TGFβ2) in the aqueous humor. Effective treatment of POAG requires detailed understanding of interaction between pressure sensing mechanisms in the trabecular meshwork (TM) and biochemical risk factors. Here, we employed molecular, optical, electrophysiological and tonometric strategies to establish the role of TGFβ2 in transcription and functional expression of mechanosensitive channel isoforms alongside studies of TM contractility in biomimetic hydrogels, and intraocular pressure (IOP) regulation in a mouse model of TGFβ2 -induced OHT. TGFβ2 upregulated expression of TRPV4 and PIEZO1 transcripts and time-dependently augmented functional TRPV4 activation. TRPV4 activation induced TM contractility whereas pharmacological inhibition suppressed TGFβ2-induced hypercontractility and abrogated OHT in eyes overexpressing TGFβ2. Trpv4-deficient mice resisted TGFβ2-driven increases in IOP. Nocturnal OHT was not additive to TGFβ-evoked OHT. Our study establishes the fundamental role of TGFβ as a modulator of mechanosensing in nonexcitable cells, identifies TRPV4 channel as the final common mechanism for TM contractility and circadian and pathological OHT and offers insights future treatments that can lower IOP in the sizeable cohort of hypertensive glaucoma patients that resist current treatments.

RNA-seq transcriptomic profiling of TGF-β2-exposed human trabecular meshwork explants: Advancing insights beyond conventional cell culture models

Primary open-angle glaucoma (POAG), a leading cause of irreversible vision loss, is closely linked to increased intraocular pressure (IOP), with the trabecular meshwork (TM) playing a critical role in its regulation. The TM, located at the iridocorneal angle, acts as a sieve, filtering the aqueous humor from the eye into the collecting ducts, thus maintaining proper IOP levels. The transforming growth factor-beta 2 (TGF-β2) signaling pathway has been implicated in the pathophysiology of primary open-angle glaucoma POAG particularly, in the dysfunction of the TM. This study utilizes human TM explants to closely mimic in vivo conditions, thereby minimizing transcriptional changes that could arise from cell culture enabling an exploration of the transcriptomic impacts of TGF-β2. Through bulk RNA sequencing and immunohistological analysis, we identified distinct gene expression patterns and morphological changes induced by TGF-β2 exposure (5 ng/ml for 48 h). Bulk RNA sequencing identified significant upregulation in genes linked to extracellular matrix (ECM) regulation and fibrotic signaling. Immunohistological analysis further elucidated the morphological alterations, including cytoskeletal rearrangements and ECM deposition, providing a visual confirmation of the transcriptomic data. Notably, the enrichment analysis unveils TGF-β2's influence on both bone morphogenic protein (BMP) and Wnt signaling pathways, suggesting a complex interplay of molecular mechanisms contributing to TM dysfunction in glaucoma. This characterization of the transcriptomic modifications on an explant model of TM obtained under the effect of this profibrotic cytokine involved in glaucoma is crucial in order to develop and test new molecules that can block their signaling pathways.

DDX58 variant triggers IFN-β-induced autophagy in trabecular meshwork and influences intraocular pressure

Singleton-Merten syndrome (SMS) is a rare immunogenetic disorder affecting multiple systems, characterized by dental dysplasia, aortic calcification, glaucoma, skeletal abnormalities, and psoriasis. Glaucoma, a key feature of both classical and atypical SMS, remains poorly understood in terms of its molecular mechanism caused by DDX58 mutation. This study presented a novel DDX58 variant (c.1649A>C [p.Asp550Ala]) in a family with childhood glaucoma. Functional analysis showed that DDX58 variant caused an increase in IFN-stimulated gene expression and high IFN-β-based type-I IFN. As the trabecular meshwork (TM) is responsible for controlling intraocular pressure (IOP), we examine the effect of IFN-β on TM cells. Our study is the first to demonstrate that IFN-β significantly reduced TM cell viability and function by activating autophagy. In addition, anterior chamber injection of IFN-β remarkably increased IOP level in mice, which can be attenuated by treatments with autophagy inhibitor chloroquine. To uncover the specific mechanism underlying IFN-β-induced autophagy in TM cells, we performed microarray analysis in IFN-β-treated and DDX58 p.Asp550Ala TM cells. It showed that RSAD2 is necessary for IFN-β-induced autophagy. Knockdown of RSAD2 by siRNA significantly decreased autophagy flux induced by IFN-β. Our findings suggest that DDX58 mutation leads to the overproduction of IFN-β, which elevates IOP by modulating autophagy through RSAD2 in TM cells.

A digoxin derivative that potently reduces intraocular pressure: efficacy and mechanism of action in different animal models

Glaucoma is a blinding disease. Reduction of intraocular pressure (IOP) is the mainstay of treatment, but current drugs show side effects or become progressively ineffective, highlighting the need for novel compounds. We have synthesized a family of perhydro-1,4-oxazepine derivatives of digoxin, the selective inhibitor of Na,K-ATPase. The cyclobutyl derivative (DcB) displays strong selectivity for the human α2 isoform and potently reduces IOP in rabbits. These observations appeared consistent with a hypothesis that in ciliary epithelium DcB inhibits the α2 isoform of Na,K-ATPase, which is expressed strongly in nonpigmented cells, reducing aqueous humor (AH) inflow. This paper extends assessment of efficacy and mechanism of action of DcB using an ocular hypertensive nonhuman primate model (OHT-NHP) (Macaca fascicularis). In OHT-NHP, DcB potently lowers IOP, in both acute (24 h) and extended (7-10 days) settings, accompanied by increased aqueous humor flow rate (AFR). By contrast, ocular normotensive animals (ONT-NHP) are poorly responsive to DcB, if at all. The mechanism of action of DcB has been analyzed using isolated porcine ciliary epithelium and perfused enucleated eyes to study AH inflow and AH outflow facility, respectively. 1) DcB significantly stimulates AH inflow although prior addition of 8-Br-cAMP, which raises AH inflow, precludes additional effects of DcB. 2) DcB significantly increases AH outflow facility via the trabecular meshwork (TM). Taken together, the data indicate that the original hypothesis on the mechanism of action must be revised. In the OHT-NHP, and presumably other species, DcB lowers IOP by increasing AH outflow facility rather than by decreasing AH inflow.NEW & NOTEWORTHY When applied topically, a cyclobutyl derivative of digoxin (DcB) potently reduces intraocular pressure in an ocular hypertensive nonhuman primate model (Macaca fascicularis), associated with increased aqueous humor (AH) flow rate (AFR). The mechanism of action of DcB involves increased AH outflow facility as detected in enucleated perfused porcine eyes and, in parallel, increased (AH) inflow as detected in isolated porcine ciliary epithelium. DcB might have potential as a drug for the treatment of open-angle human glaucoma.

ANGPTL7 and Its Role in IOP and Glaucoma

Purpose

Loss-of-function variants in the ANGPTL7 gene are associated with protection from glaucoma and reduced intraocular pressure (IOP). We investigated the role of ANGPTL7 in IOP homeostasis and its potential as a target for glaucoma therapeutics.

Methods

IOP, outflow facility, and outflow tissue morphology of Angptl7 knockout (KO) mice were assessed with and without dexamethasone (Dex). ANGPTL7 was quantified in conditioned media from human trabecular meshwork cells in response to Dex, in effluent from perfused human donor eyes, and in aqueous humor from human patients treated with steroids. Antibodies to ANGPTL7 were generated and tested in three-dimensional (3D) culture of outflow cells and perfused human donor eyes. Rabbits were injected intravitreally with a neutralizing antibody targeting ANGPTL7, and IOP was measured.

Results

IOP was significantly elevated, but outflow facility and outflow tissue morphology were not different between Angptl7 KO mice and littermates. When challenged with Dex, IOP increased in wild-type but not Angptl7 KO mice. In human samples, increased ANGPTL7 was seen in the aqueous humor of patients treated with steroids, regardless of glaucoma status. Using 3D culture, recombinant ANGPTL7 decreased, and ANGPTL7-blocking antibodies increased hydraulic conductivity. Significantly, outflow facility increased in human eyes treated ex vivo with ANGPTL7-blocking antibodies, and IOP decreased for 21 days in rabbits after a single injection of blocking antibodies.

Conclusions

Using multiple models, we have demonstrated that excess ANGPTL7 increases outflow resistance and IOP and that neutralizing ANGPTL7 has beneficial effects in both naïve and steroid-induced hypertensive eyes, thus motivating the development of ANGPTL7-targeting therapeutics for the treatment of glaucoma.

Small RNA Sequencing Reveals a Distinct MicroRNA Signature between Glucocorticoid Responder and Glucocorticoid Non-Responder Primary Human Trabecular Meshwork Cells after Dexamethasone Treatment

Glucocorticoids (GCs) are known to regulate several physiological processes and are the mainstay in the management of inflammatory eye diseases. The long-term use of GC causes raised intraocular pressure (IOP) or ocular hypertension (OHT) in about 30-50% of the susceptible individuals depending on the route of administration, and can lead to steroid-induced secondary glaucoma. The present study aims to understand the role of microRNAs (miRNAs) in differential glucocorticoid (GC) responsiveness in human trabecular meshwork (HTM) cells using small RNA sequencing. The human organ-cultured anterior segment (HOCAS) model was used to identify whether donor eyes were from GC-responders (GC-R; n = 4) or GC-non-responders (GC-NR; n = 4) following treatment with either 100 nM dexamethasone (DEX) or ethanol (ETH) for 7 days. The total RNA was extracted from cultured HTM cells with known GC responsiveness, and the differentially expressed miRNAs (DEMIRs) were compared among the following five groups: Group #1: ETH vs. DEX-treated GC-R; #2: ETH vs. DEX-treated GC-NR; #3: overlapping DEGs between Group #1 and #2; #4: Unique DEMIRs of GC-R; #5: Unique DEMIRs of GC-NR; and validated by RT-qPCR. There were 13 and 21 DEMIRs identified in Group #1 and Group #2, respectively. Seven miRNAs were common miRNAs dysregulated in both GC-R and GC-NR (Group #3). This analysis allowed the identification of DEMIRs that were unique to GC-R (6 miRNAs) and GC-NR (14 miRNAs) HTM cells, respectively. Ingenuity Pathway Analysis identified enriched pathways and biological processes associated with differential GC responsiveness in HTM cells. This is the first study to reveal a unique miRNA signature between GC-R and GC-NR HTM cells, which raises the possibility of developing new molecular targets for the management of steroid-OHT/glaucoma.

Lysyl oxidase-like 1-antisense 1 (LOXL1-AS1) lncRNA differentially regulates gene and protein expression, signaling and morphology of human ocular cells

Pseudoexfoliation glaucoma (PEXG) is characterized by dysregulated extracellular matrix (ECM) homeostasis that disrupts conventional outflow function and increases intraocular pressure (IOP). Prolonged IOP elevation results in optic nerve head damage and vision loss. Uniquely, PEXG is a form of open angle glaucoma that has variable penetrance, is difficult to treat and does not respond well to common IOP-lowering pharmaceuticals. Therefore, understanding modulators of disease severity will aid in targeted therapies for PEXG. Genome-wide association studies have identified polymorphisms in the long non-coding RNA lysyl oxidase-like 1-antisense 1 (LOXL1-AS1) as a risk factor for PEXG. Risk alleles, oxidative stress and mechanical stretch all alter LOXL1-AS1 expression. As a long non-coding RNA, LOXL1-AS1 binds hnRNPL and regulates global gene expression. In this study, we focus on the role of LOXL1-AS1 in the ocular cells (trabecular meshwork and Schlemm's canal) that regulate IOP. We show that selective knockdown of LOXL1-AS1 leads to cell-type-specific changes in gene expression, ECM homeostasis, signaling and morphology. These results implicate LOXL1-AS1 as a modulator of cellular homeostasis, altering cell contractility and ECM turnover, both of which are well-known contributors to PEXG. These findings support LOXL1-AS1 as a key target for modifying the disease.

Comparison of the extracellular vesicle proteome between glaucoma and non-glaucoma trabecular meshwork cells

Introduction

Extracellular matrix (ECM) materials accumulate in the trabecular meshwork (TM) tissue of patients with glaucoma, which is associated with a decrease in aqueous humor outflow and therefore an increase in intraocular pressure. To explore a potential mechanism for ECM regulation in the TM, we purified extracellular vesicles (EVs) from conditioned media of differentiated TM cells in culture isolated from non-glaucomatous and glaucomatous human donor eyes.

Methods

EVs were purified using the double cushion ultracentrifugation gradient method. Fractions containing EV markers CD9 and TSG101 were analyzed using nanoparticle tracking analysis to determine their size and concentration. We then determined their proteomic cargo by mass spectrometry and compared protein profiles of EVs between normal and glaucomatous TM cells using PANTHER. Key protein components from EV preparations were validated with Western blotting.

Results

Results showed changes in the percentage of ECM proteins associated with EVs from glaucomatous TM cells compared to non-glaucomatous TM cells (5.7% vs 13.1% respectively). Correspondingly, we found that two ECM-related cargo proteins found across all samples, fibronectin and EDIL3 were significantly less abundant in glaucomatous EVs (<0.3 fold change across all groups) compared to non-glaucomatous EVs.

Discussion

Overall, these data establish that ECM materials are prominent proteomic cargo in EVs from TM cells, and their binding to EVs is diminished in glaucoma.

Simvastatin Attenuates Glucocorticoid-Induced Human Trabecular Meshwork Cell Dysfunction via YAP/TAZ Inactivation

PURPOSE

Impairment of the trabecular meshwork (TM) is the principal cause of increased outflow resistance in the glaucomatous eye. Yes-associated protein (YAP) and transcriptional coactivator with PDZ binding motif (TAZ) are emerging as potential mediators of TM cell/tissue dysfunction. Furthermore, YAP/TAZ activity was recently found to be controlled by the mevalonate pathway in non-ocular cells. Clinically used statins block the mevalonate cascade and were shown to improve TM cell pathobiology; yet, the link to YAP/TAZ signaling was not investigated. In this study, we hypothesized that simvastatin attenuates glucocorticoid-induced human TM (HTM) cell dysfunction via YAP/TAZ inactivation.

METHODS

Primary HTM cells were seeded atop or encapsulated within bioengineered extracellular matrix (ECM) hydrogels. Dexamethasone was used to induce a pathologic phenotype in HTM cells in the absence or presence of simvastatin. Changes in YAP/TAZ activity, actin cytoskeletal organization, phospho-myosin light chain levels, hydrogel contraction/stiffness, and fibronectin deposition were assessed.

RESULTS

Simvastatin potently blocked pathologic YAP/TAZ nuclear localization/activity, actin stress fiber formation, and myosin light chain phosphorylation in HTM cells. Importantly, simvastatin co-treatment significantly attenuated dexamethasone-induced ECM contraction/stiffening and fibronectin mRNA and protein levels. Sequential treatment was similarly effective but did not match clinically-used Rho kinase inhibition.

CONCLUSIONS

YAP/TAZ inactivation with simvastatin attenuates HTM cell pathobiology in a tissue-mimetic ECM microenvironment. Our data may help explain the association of statin use with a reduced risk of developing glaucoma via indirect YAP/TAZ inhibition as a proposed regulatory mechanism.

Rare protective variants and glaucoma-relevant cell stressors modulate Angiopoietin-like 7 expression

Rare missense and nonsense variants in the Angiopoietin-like 7 (ANGPTL7) gene confer protection from primary open-angle glaucoma (POAG), though the functional mechanism remains uncharacterized. Interestingly, a larger variant effect size strongly correlates with in silico predictions of increased protein instability (r = -0.98), suggesting that protective variants lower ANGPTL7 protein levels. Here, we show that missense and nonsense variants cause aggregation of mutant ANGPTL7 protein in the endoplasmic reticulum (ER) and decreased levels of secreted protein in human trabecular meshwork (TM) cells; a lower secreted:intracellular protein ratio strongly correlates with variant effects on intraocular pressure (r = 0.81). Importantly, accumulation of mutant protein in the ER does not increase expression of ER stress proteins in TM cells (P > 0.05 for all variants tested). Cyclic mechanical stress, a glaucoma-relevant physiologic stressor, also significantly lowers ANGPTL7 expression in primary cultures of human Schlemm's canal (SC) cells (-2.4-fold-change, P = 0.01). Collectively, these data suggest that the protective effects of ANGPTL7 variants in POAG stem from lower levels of secreted protein, which may modulate responses to physiologic and pathologic ocular cell stressors. Downregulation of ANGPTL7 expression may therefore serve as a viable preventative and therapeutic strategy for this common, blinding disease.

Dexamethasone Modulates the Dynamics of Wnt Signaling in Human Trabecular Meshwork Cells

Trabecular meshwork (TM) tissue is highly specialized, and its structural integrity is crucial for maintaining homeostatic intraocular pressure (IOP). The administration of glucocorticoids, such as dexamethasone (DEX), can perturb the TM structure and significantly increase IOP in susceptible individuals, resulting in ocular diseases such as steroid-induced glaucoma, a form of open-angle glaucoma. Although the exact mechanism involved in steroid-induced glaucoma remains elusive, increasing evidence suggests that DEX may act through various signaling cascades in TM cells. Despite uncertainty surrounding the specific process by which steroid-induced glaucoma occurs, there is growing evidence to indicate that DEX can impact multiple signaling pathways within TM cells. In this study, we examined the impact of DEX treatment on the Wnt signaling pathway in TM cells, given that Wnt signaling has been reported to play a crucial role in regulating extracellular matrix (ECM) levels in the TM. To further elucidate the role of Wnt signaling in the glaucomatous phenotype, we examined mRNA expression patterns between Wnt signaling markers AXIN2 and sFRP1 and DEX-mediated induction of myocilin (MYOC) mRNA and protein levels over 10 days in DEX-treated primary TM cells. We observed a sequential pattern of peak expression between AXIN2, sFRP1, and MYOC. Based on the study, we propose that sFRP1 upregulation could be a result of a negative feedback mechanism generated by stressed TM cells to suppress abnormal Wnt signaling activities.

Proposed Mechanism of Long-Term Intraocular Pressure Lowering With the Bimatoprost Implant

Purpose

The purpose of this study was to evaluate the effects of pharmacologically relevant bimatoprost and bimatoprost free acid (BFA) concentrations on matrix metalloproteinase (MMP) gene expression in cells from human aqueous outflow tissues.

Methods

MMP gene expression by human trabecular meshwork (TM), scleral fibroblast (SF), and ciliary muscle (CM) cells exposed to 10 to 1000 µM bimatoprost or 0.1 to 10 µM BFA (intraocular concentrations after intracameral bimatoprost implant and topical bimatoprost dosing, respectively) was measured by polymerase chain reaction array.

Results

Bimatoprost dose-dependently upregulated MMP1 and MMP14 mRNA in all cell types and MMP10 and MMP11 mRNA in TM and CM cells; in TM cells from normal eyes, mean MMP1 mRNA levels were 62.9-fold control levels at 1000 µM bimatoprost. BFA upregulated MMP1 mRNA only in TM and SF cells, to two- to three-fold control levels. The largest changes in extracellular matrix (ECM)-related gene expression by TM cells derived from normal (n = 6) or primary open-angle glaucoma (n = 3) eyes occurred with 1000 µM bimatoprost (statistically significant, ≥50% change for 9-11 of 84 genes on the array, versus 1 gene with 10 µM BFA).

Conclusions

Bimatoprost and BFA had differential effects on MMP/ECM gene expression. Dramatic upregulation in MMP1 and downregulation of fibronectin, which occurred only with bimatoprost at high concentrations observed in bimatoprost implant-treated eyes, may promote sustained outflow tissue remodeling and long-term intraocular pressure reduction beyond the duration of intraocular drug bioavailability. Variability in bimatoprost-stimulated MMP upregulation among cell strains from different donors may help explain differential long-term responses of patients to bimatoprost implant.

TGFβ2 Regulates Human Trabecular Meshwork Cell Contractility via ERK and ROCK Pathways with Distinct Signaling Crosstalk Dependent on the Culture Substrate

PURPOSE

Transforming growth factor-beta 2 (TGFβ2) is a major contributor to the pathologic changes occurring in human trabecular meshwork (HTM) cells in primary open-angle glaucoma (POAG). TGFβ2 activates extracellular-signal-regulated kinase (ERK) and Rho-associated kinase (ROCK) signaling pathways, both affecting HTM cell behavior. However, exactly how these signaling pathways converge to regulate HTM cell contractility is unclear. Here, we investigated the molecular mechanism underlying TGFβ2-induced pathologic HTM cell contractility, and the crosstalk between ERK and ROCK signaling pathways with different culture substrates.

METHODS

Hydrogels were engineered by mixing collagen type I, elastin-like polypeptide, and hyaluronic acid, each containing photoactive functional groups, followed by UV crosslinking. Primary HTM cells were seeded atop pre-formed hydrogels for comparisons with glass, or encapsulated within the hydrogels. Changes in actin cytoskeleton, extracellular matrix (ECM) production, phospho-myosin light chain (p-MLC) levels, and hydrogel contraction were assessed.

RESULTS

HTM cell morphology and filamentous (F)-actin organization were affected by the underlying culture substrates. TGFβ2 increased HTM cell contractility via ERK and ROCK signaling pathways by differentially regulating F-actin, α-smooth muscle actin (αSMA), fibronectin (FN), and p-MLC in HTM cells. ERK inhibition, even as short as 4 h, further increased TGFβ2-induced p-MLC in HTM cells on hydrogels, but not on glass. This translated into hypercontractility of HTM cell-laden hydrogels. ROCK inhibition had precisely the opposite effects and potently relaxed the TGFβ2-induced hydrogels.

CONCLUSIONS

Our data suggest that ERK signaling negatively regulates ROCK-mediated HTM cell contractility. These findings emphasize the critical importance of using tissue-mimetic ECM substrates for investigating HTM cell physiology and glaucomatous pathophysiology in vitro.

Isolation and Culture of Vascular Distal Outflow Pathway (VDOP) Cells From Human Donor Eyes

Glaucoma, a progressive neurodegenerative ocular disease, is the leading cause of irreversible blindness worldwide. Elevated intraocular pressure (IOP) is the most common-and the only treatable-risk factor for glaucoma. IOP is generated by the balance between production and removal of aqueous humor in the anterior part of the eye, and the latter happens either through the uveoscleral or the conventional pathway. Although both pathways are important for aqueous humor removal, dysfunction within the conventional pathway is more commonly associated with increased resistance leading to elevated IOP and glaucoma. The conventional pathway can be separated into proximal (trabecular meshwork and inner wall of Schlemm's canal) and distal (outer wall of Schlemm's canal, collector channels, and episcleral vasculature) regions. Both regions contribute resistance to aqueous humor removal, but the proximal region has been studied more extensively due to the availability of model systems. In contrast, little is known about the role of the distal region in outflow resistance, largely due to the lack of suitable in vitro models. To address this, we have developed a novel method of isolating and culturing vascular distal outflow pathway (VDOP) cells from the distal outflow region of human eyes. VDOP cells can be used to study the physiological and molecular functions of cells in the distal outflow region and can help in the development of ocular hypotensive drugs that specifically target this area. We also provide a protocol describing immunohistochemical methods to validate the molecular profile of these cells, utilizing cell surface markers that distinguish them from adjacent cells. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Isolation and culture of VDOP cells Basic Protocol 2: Analysis of cell surface markers.

Effects of Netarsudil-Family Rho Kinase Inhibitors on Human Trabecular Meshwork Cell Contractility and Actin Remodeling Using a Bioengineered ECM Hydrogel

Interactions between trabecular meshwork (TM) cells and their extracellular matrix (ECM) are critical for normal outflow function in the healthy eye. Multifactorial dysregulation of the TM is the principal cause of elevated intraocular pressure that is strongly associated with glaucomatous vision loss. Key characteristics of the diseased TM are pathologic contraction and actin stress fiber assembly, contributing to overall tissue stiffening. Among first-line glaucoma medications, the Rho-associated kinase inhibitor (ROCKi) netarsudil is known to directly target the stiffened TM to improve outflow function via tissue relaxation involving focal adhesion and actin stress fiber disassembly. Yet, no in vitro studies have explored the effect of netarsudil on human TM (HTM) cell contractility and actin remodeling in a 3D ECM environment. Here, we use our bioengineered HTM cell-encapsulated ECM hydrogel to investigate the efficacy of different netarsudil-family ROCKi compounds on reversing pathologic contraction and actin stress fibers. Netarsudil and all related experimental ROCKi compounds exhibited significant ROCK1/2 inhibitory and focal adhesion disruption activities. Furthermore, all ROCKi compounds displayed potent contraction-reversing effects on HTM hydrogels upon glaucomatous induction in a dose-dependent manner, relatively consistent with their biochemical/cellular inhibitory activities. At their tailored EC50 levels, netarsudil-family ROCKi compounds exhibited distinct effect signatures of reversing pathologic HTM hydrogel contraction and actin stress fibers, independent of the cell strain used. Netarsudil outperformed the experimental ROCKi compounds in support of its clinical status. In contrast, at uniform EC50-levels using netarsudil as reference, all ROCKi compounds performed similarly. Collectively, our data suggest that netarsudil exhibits high potency to rescue HTM cell pathobiology in a tissue-mimetic 3D ECM microenvironment, solidifying the utility of our bioengineered hydrogel model as a viable screening platform to further our understanding of TM pathophysiology in glaucoma.

Mechanistic Effects of Baicalein on Aqueous Humor Drainage and Intraocular Pressure

Elevated intraocular pressure (IOP) is a major risk factor for glaucoma that results from impeded fluid drainage. The increase in outflow resistance is caused by trabecular meshwork (TM) cell dysfunction and excessive extracellular matrix (ECM) deposition. Baicalein (Ba) is a natural flavonoid and has been shown to regulate cell contraction, fluid secretion, and ECM remodeling in various cell types, suggesting the potential significance of regulating outflow resistance and IOP. We demonstrated that Ba significantly lowered the IOP by about 5 mmHg in living mice. Consistent with that, Ba increased the outflow facility by up to 90% in enucleated mouse eyes. The effects of Ba on cell volume regulation and contractility were examined in primary human TM (hTM) cells. We found that Ba (1–100 µM) had no effect on cell volume under iso-osmotic conditions but inhibited the regulatory volume decrease (RVD) by up to 70% under hypotonic challenge. In addition, Ba relaxed hTM cells via reduced myosin light chain (MLC) phosphorylation. Using iTRAQ-based quantitative proteomics, 47 proteins were significantly regulated in hTM cells after a 3-h Ba treatment. Ba significantly increased the expression of cathepsin B by 1.51-fold and downregulated the expression of D-dopachrome decarboxylase and pre-B-cell leukemia transcription factor-interacting protein 1 with a fold-change of 0.58 and 0.40, respectively. We suggest that a Ba-mediated increase in outflow facility is triggered by cell relaxation via MLC phosphorylation along with inhibiting RVD in hTM cells. The Ba-mediated changes in protein expression support the notion of altered ECM homeostasis, potentially contributing to a reduction of outflow resistance and thereby IOP.

Short and long-term effect of dexamethasone on the transcriptome profile of primary human trabecular meshwork cells in vitro

In the quest of identifying newer molecular targets for the management of glucocorticoid-induced ocular hypertension (GC-OHT) and glaucoma (GCG), several microarray studies have attempted to investigate the genome-wide transcriptome profiling of primary human trabecular meshwork (TM) cells in response to dexamethasone (DEX). However, no studies are reported so far to demonstrate the temporal changes in the expression of genes in the cultured human TM cells in response to DEX treatment. Therefore, in the present study, the time-dependent changes in the genome-wide expression of genes in primary human TM cells after short (16 hours: 16 h) and long exposure (7 days: 7 d) of DEX was investigated using RNA sequencing. There were 199 (118 up-regulated; 81 down-regulated) and 525 (119 up-regulated; 406 down-regulated) DEGs in 16 h and 7 d treatment groups respectively. The unique genes identified in 16 h and 7 d treatment groups were 152 and 478 respectively. This study found a distinct gene signature and pathways between two treatment regimes. Longer exposure of DEX treatment showed a dys-regulation of Wnt and Rap1 signaling and so highlighted potential therapeutic targets for pharmacological management of GC-OHT/glaucoma.

A Comparative Genome-Wide Transcriptome Analysis of Glucocorticoid Responder and Non-Responder Primary Human Trabecular Meshwork Cells

Aim: To investigate genes and pathways involved in differential glucocorticoid (GC) responsiveness in human trabecular meshwork (HTM) cells using RNA sequencing. Methods: Using paired human donor eyes, human organ-cultured anterior segment (HOCAS) was established in one eye to characterize GC responsiveness based on intra ocular pressure (IOP) change and, in the other eye, primary HTM cell culture was established. For RNA sequencing, total RNA extracted from GC-responder (GC-R) and non-responder (GC-NR) cells after dexamethasone (DEX) or ethanol (ETH) treatment for 7d was used. Differentially expressed genes (DEGs) were compared among five groups and validated. Results: In total, 616 and 216 genes were identified as significantly dysregulated in Group #1 and #2 (#1: ETH vs. DEX-treated GC-R; #2: ETH vs. DEX-treated GC-NR), respectively. Around 80 genes were commonly dysregulated in Group #3 (overlapping DEGs between #1 and #2), whereas 536 and 136 genes were uniquely expressed in GC-R (#4) and GC-NR HTM (#5) cells, respectively. Pathway analysis revealed that WNT signaling, drug metabolism cytochrome p450, cell adhesion, TGF-β signaling, and MAPK signaling were associated with GC responsiveness. Conclusion: This is the first study reporting distinct gene signatures and their associated pathways for GC-R and GC-NR HTM cells. WNT and MAPK signaling are potential therapeutic targets for the management of GC-induced glaucoma.

A Role of Caveolae in Trabecular Meshwork Mechanosensing and Contractile Tone

Polymorphisms in the CAV1/2 gene loci impart increased risk for primary open-angle glaucoma (POAG). CAV1 encodes caveolin-1 (Cav1), which is required for biosynthesis of plasma membrane invaginations called caveolae. Cav1 knockout mice exhibit elevated intraocular pressure (IOP) and decreased outflow facility, but the mechanistic role of Cav1 in IOP homeostasis is unknown. We hypothesized that caveolae sequester/inhibit RhoA, to regulate trabecular meshwork (TM) mechanosensing and contractile tone. Using phosphorylated myosin light chain (pMLC) as a surrogate indicator for Rho/ROCK activity and contractile tone, we found that pMLC was elevated in Cav1-deficient TM cells compared to control (131 ± 10%, n = 10, p = 0.016). Elevation of pMLC levels following Cav1 knockdown occurred in cells on a soft surface (137 ± 7%, n = 24, p < 0.0001), but not on a hard surface (122 ± 17%, n = 12, p = 0.22). In Cav1-deficient TM cells where pMLC was elevated, Rho activity was also increased (123 ± 7%, n = 6, p = 0.017), suggesting activation of the Rho/ROCK pathway. Cyclic stretch reduced pMLC/MLC levels in TM cells (69 ± 7% n = 9, p = 0.002) and in Cav1-deficient TM cells, although not significantly (77 ± 11% n = 10, p = 0.059). Treatment with the Cav1 scaffolding domain mimetic, cavtratin (1 μM) caused a reduction in pMLC (70 ± 5% n = 7, p = 0.001), as did treatment with the scaffolding domain mutant cavnoxin (1 μM) (82 ± 7% n = 7, p = 0.04). Data suggest that caveolae differentially regulate RhoA signaling, and that caveolae participate in TM mechanotransduction. Cav1 regulation of these key TM functions provide evidence for underlying mechanisms linking polymorphisms in the Cav1/2 gene loci with increased POAG risk.

Extracellular Matrix Stiffness and TGFβ2 Regulate YAP/TAZ Activity in Human Trabecular Meshwork Cells

Primary open-angle glaucoma progression is associated with increased human trabecular meshwork (HTM) stiffness and elevated transforming growth factor beta 2 (TGFβ2) levels in the aqueous humor. Increased transcriptional activity of Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ), central players in mechanotransduction, are implicated in glaucomatous HTM cell dysfunction. Yet, the detailed mechanisms underlying YAP/TAZ modulation in HTM cells in response to alterations in extracellular matrix (ECM) stiffness and TGFβ2 levels are not well understood. Using biomimetic ECM hydrogels with tunable stiffness, here we show that increased ECM stiffness elevates YAP/TAZ nuclear localization potentially through modulating focal adhesions and cytoskeletal rearrangement. Furthermore, TGFβ2 increased nuclear YAP/TAZ in both normal and glaucomatous HTM cells, which was prevented by inhibiting extracellular-signal-regulated kinase and Rho-associated kinase signaling pathways. Filamentous (F)-actin depolymerization reversed TGFβ2-induced YAP/TAZ nuclear localization. YAP/TAZ depletion using siRNA or verteporfin decreased focal adhesions, ECM remodeling and cell contractile properties. Similarly, YAP/TAZ inactivation with verteporfin partially blocked TGFβ2-induced hydrogel contraction and stiffening. Collectively, our data provide evidence for a pathologic role of aberrant YAP/TAZ signaling in glaucomatous HTM cell dysfunction, and may help inform strategies for the development of novel multifactorial approaches to prevent progressive ocular hypertension in glaucoma.

Identification of Estrogen Signaling in a Prioritization Study of Intraocular Pressure-Associated Genes

Elevated intraocular pressure (IOP) is the only modifiable risk factor for primary open-angle glaucoma (POAG). Herein we sought to prioritize a set of previously identified IOP-associated genes using novel and previously published datasets. We identified several genes for future study, including several involved in cytoskeletal/extracellular matrix reorganization, cell adhesion, angiogenesis, and TGF-β signaling. Our differential correlation analysis of IOP-associated genes identified 295 pairs of 201 genes with differential correlation. Pathway analysis identified β-estradiol as the top upstream regulator of these genes with ESR1 mediating 25 interactions. Several genes (i.e., EFEMP1, FOXC1, and SPTBN1) regulated by β-estradiol/ESR1 were highly expressed in non-glaucomatous human trabecular meshwork (TM) or Schlemm’s canal (SC) cells and specifically expressed in TM/SC cell clusters defined by single-cell RNA-sequencing. We confirmed ESR1 gene and protein expression in human TM cells and TM/SC tissue with quantitative real-time PCR and immunofluorescence, respectively. 17β-estradiol was identified in bovine, porcine, and human aqueous humor (AH) using ELISA. In conclusion, we have identified estrogen receptor signaling as a key modulator of several IOP-associated genes. The expression of ESR1 and these IOP-associated genes in TM/SC tissue and the presence of 17β-estradiol in AH supports a role for estrogen signaling in IOP regulation.

Replacement of the Trabecular Meshwork Cells-A Way Ahead in IOP Control?

Glaucoma is one of the leading causes of vision loss worldwide, characterised with irreversible optic nerve damage and progressive vision loss. Primary open-angle glaucoma (POAG) is a subset of glaucoma, characterised by normal anterior chamber angle and raised intraocular pressure (IOP). Reducing IOP is the main modifiable factor in the treatment of POAG, and the trabecular meshwork (TM) is the primary site of aqueous humour outflow (AH) and the resistance to outflow. The structure and the composition of the TM are key to its function in regulating AH outflow. Dysfunction and loss of the TM cells found in the natural ageing process and more so in POAG can cause abnormal extracellular matrix (ECM) accumulation, increased TM stiffness, and increased IOP. Therefore, repair or regeneration of TM's structure and function is considered as a potential treatment for POAG. Cell transplantation is an attractive option to repopulate the TM cells in POAG, but to develop a cell replacement approach, various challenges are still to be addressed. The choice of cell replacement covers autologous or allogenic approaches, which led to investigations into TM progenitor cells, induced pluripotent stem cells (iPSCs), and mesenchymal stem cells (MSCs) as potential stem cell source candidates. However, the potential plasticity and the lack of definitive cell markers for the progenitor and the TM cell population compound the biological challenge. Morphological and differential gene expression of TM cells located within different regions of the TM may give rise to different cell replacement or regenerative approaches. As such, this review describes the different approaches taken to date investigating different cell sources and their differing cell isolation and differentiation methodologies. In addition, we highlighted how these approaches were evaluated in different animal and ex vivo model systems and the potential of these methods in future POAG treatment.

Recombinant antibodies recognize conformation-dependent epitopes of the leucine zipper of misfolding-prone myocilin

Recombinant antibodies with well-characterized epitopes and known conformational specificities are critical reagents to support robust interpretation and reproducibility of immunoassays across biomedical research. For myocilin, a protein prone to misfolding that is associated with glaucoma and an emerging player in other human diseases, currently available antibodies are unable to differentiate among the numerous disease-associated protein states. This fundamentally constrains efforts to understand the connection between myocilin structure, function, and disease. To address this concern, we used protein engineering methods to develop new recombinant antibodies that detect the N-terminal leucine zipper structural domain of myocilin and that are cross-reactive for human and mouse myocilin. After harvesting spleens from immunized mice and in vitro library panning, we identified two antibodies, 2A4 and 1G12. 2A4 specifically recognizes a folded epitope while 1G12 recognizes a range of conformations. We matured antibody 2A4 for improved biophysical properties, resulting in variant 2H2. In a human IgG1 format, 2A4, 1G12, and 2H2 immunoprecipitate full-length folded myocilin present in the spent media of human trabecular meshwork (TM) cells, and 2H2 can visualize myocilin in fixed human TM cells using fluorescence microscopy. These new antibodies should find broad application in glaucoma and other research across multiple species platforms.

Thrombospondin-1 mediates Rho-kinase inhibitor-induced increase in outflow-facility

Rho‐kinase (ROCK) inhibitors, a novel class of anti‐glaucoma agents, act by increasing the aqueous humor outflow through the conventional trabecular meshwork pathway. However, the downstream signaling consequences of the ROCK inhibitor are not completely understood. Our data show that Y39983, a selective ROCK inhibitor, could induce filamentous actin remodeling, reduced cell motility (as measured by cell migration), and transepithelial resistance in primary human TM (hTM) cells. After 2 days Y39983 treatment of hTM cells, a proteomic study identified 20 proteins whose expression was significantly altered. Pathway analysis of those proteins revealed the involvement of the p53 pathway, integrin signaling pathway, and cytoskeletal pathway regulation by Rho GTPase. Thrombospondin‐1 (TSP1), a matricellular protein that is increased in glaucoma patients, was downregulated fivefold following Y39983 treatment. More importantly, both TSP1 antagonist leucine–serine–lysine–leucine (LSKL) and small interfering RNA (siRNA) reduced TSP1 gene and protein expressions as well as hTM cell migration. In the presence of Y39983, no further inhibition of cell migration resulted after LSKL and TSP1 siRNA knockdown. Likewise, LSKL triggered a dose‐dependent increase in outflow facility in ex vivo mouse eyes, to a similar extent as Y39983 (83.8% increase by Y39983 vs. 71.2% increase by LSKL at 50 µM). There were no additive effects with simultaneous treatment with LSKL and Y39983, supporting the notion that the effects of ROCK inhibition were mediated by TSP1.

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 tissue-engineered human trabecular meshwork hydrogel for advanced glaucoma disease modeling

Abnormal human trabecular meshwork (HTM) cell function and extracellular matrix (ECM) remodeling contribute to HTM stiffening in primary open-angle glaucoma (POAG). Most current cellular HTM model systems do not sufficiently replicate the complex native three dimensional (3D) cell-ECM interface, limiting their use for investigating POAG pathology. Tissue-engineered hydrogels are ideally positioned to overcome shortcomings of current models. Here, we report a novel biomimetic HTM hydrogel and test its utility as a POAG disease model. HTM hydrogels were engineered by mixing normal donor-derived HTM cells with collagen type I, elastin-like polypeptide and hyaluronic acid, each containing photoactive functional groups, followed by UV crosslinking. Glaucomatous conditions were induced with dexamethasone (DEX), and effects of the Rho-associated kinase (ROCK) inhibitor Y27632 on cytoskeletal organization and tissue-level function, contingent on HTM cell-ECM interactions, were assessed. DEX exposure increased HTM hydrogel contractility, f-actin and alpha smooth muscle actin abundance and rearrangement, ECM remodeling, and fibronectin deposition - all contributing to HTM hydrogel condensation and stiffening consistent with glaucomatous HTM tissue behavior. Y27632 treatment produced precisely the opposite effects and attenuated the DEX-induced pathologic changes, resulting in HTM hydrogel relaxation and softening. For model validation, confirmed glaucomatous HTM (GTM) cells were encapsulated; GTM hydrogels showed increased contractility, fibronectin deposition, and stiffening vs. normal HTM hydrogels despite reduced GTM cell proliferation. We have developed a biomimetic HTM hydrogel model for detailed investigation of 3D cell-ECM interactions under normal and simulated glaucomatous conditions. Its bidirectional responsiveness to pharmacological challenge and rescue suggests promising potential to serve as screening platform for new POAG treatments with focus on HTM biomechanics.

A Porcine Organ-Culture Glaucoma Model Mimicking Trabecular Meshwork Damage Using Oxidative Stress

Purpose

Re-cellularization of the trabecular meshwork (TM) using stem cells is a potential novel treatment for ocular hypertension associated with glaucoma. To assess the therapeutic efficacy of this approach, improved in vivo and ex vivo models of TM pathophysiology are needed. Here, we investigate whether oxidative stress, induced by hydrogen peroxide (H2O2), can model glaucomatous ocular hypertension in the readily available porcine anterior segment organ culture model.

Methods

The impact of H2O2 on TM cell viability and function was first evaluated in vitro using primary porcine TM cells. Oxidative stress was then induced by H2O2 infusion into perfused porcine anterior segments. Trabecular meshwork function was assessed by tracking matrix metalloproteinase (MMP) activity and the ability of the preparation to maintain intraocular pressure (IOP) homeostasis after a flow challenge (doubled fluid infusion rate). Finally, the TM was evaluated histologically.

Results

H2O2 treatment resulted in a titratable reduction in cellularity across multiple primary TM cell donor strains. In organ culture preparations, H2O2-treated eyes showed impaired IOP homeostasis (i.e., IOPs stabilized at higher levels after a flow challenge vs. control eyes). This result was consistent with reduced MMP activity and TM cellularity; however, damage to the TM microstructure was not histologically evident in anterior segments receiving H2O2.

Conclusions

Titrated H2O2 infusion resulted in TM cellular dysfunction without destruction of TM structure. Thus, this porcine organ culture model offers a useful platform for assessing trabecular meshwork therapies to treat ocular hypertension associated with glaucoma.

Isolation and characterization of novel primary cells from the human distal outflow pathway

Ocular hypertension occurs due to increased resistance to aqueous humor removal through the conventional outflow pathway. Unlike the proximal region of the conventional outflow pathway, the distal region has not been well studied, mostly due to lack of model systems. Here we describe isolation and characterization of human primary vascular distal outflow pathway (VDOP) cells from the distal region of the conventional outflow pathway. Tissue from the distal region was isolated from human corneo-scleral rims, digested with collagenase type I (100 U/ml) and placed on gelatin coated plates to allow cellular growth in Dulbecco's Modified Eagle's Medium (low glucose) containing fetal bovine serum and antibiotic/antimycotic. VDOP cells showed consistent proliferation for up to 7 passages, retained endothelial-like nature of the parent tissues and showed a unique marker phenotype of Lectin+VEGFR2-CD34-NG2- that was distinct from neighboring trabecular meshwork (Lectin+VEGFR2-CD34-NG2+) and Schlemm's canal (Lectin+VEGFR2+CD34+NG2+) cells. Dexamethasone treated VDOP cells did not express myocilin and did not form cross-linked actin networks, in contrast to trabecular meshwork cells. These data show that VDOP cells are unique to the distal outflow region and can be used as a viable in vitro model system to understand the biology of the distal outflow pathway and intraocular pressure regulation.

The β4-Subunit of the Large-Conductance Potassium Ion Channel KCa1.1 Regulates Outflow Facility in Mice

Purpose

The large-conductance calcium-activated potassium channel K_Ca1.1 (BK_Ca, maxi-K) influences aqueous humor outflow facility, but the contribution of auxiliary β-subunits to K_Ca1.1 activity in the outflow pathway is unknown.

Methods

Using quantitative polymerase chain reaction, we measured expression of β-subunit genes in anterior segments of C57BL/6J mice (Kcnmb1-4) and in cultured human trabecular meshwork (TM) and Schlemm's canal (SC) cells (KCNMB1-4). We also measured expression of Kcnma1/KCNMA1 that encodes the pore-forming α-subunit. Using confocal immunofluorescence, we visualized the distribution of β₄ in the conventional outflow pathway of mice. Using iPerfusion, we measured outflow facility in enucleated mouse eyes in response to 100 or 500 nM iberiotoxin (IbTX; N = 9) or 100 nM martentoxin (MarTX; N = 12). MarTX selectively blocks β₄-containing K_Ca1.1 channels, whereas IbTX blocks K_Ca1.1 channels that lack β₄.

Results

Kcnmb4 was the most highly expressed β-subunit in mouse conventional outflow tissues, expressed at a level comparable to Kcnma1. β₄ was present within the juxtacanalicular TM, appearing to label cellular processes connecting to SC cells. Accordingly, KCNMB4 was the most highly expressed β-subunit in human TM cells, and the sole β-subunit in human SC cells. To dissect functional contribution, MarTX decreased outflow facility by 35% (27%, 42%; mean, 95% confidence interval) relative to vehicle-treated contralateral eyes, whereas IbTX reduced outflow facility by 16% (6%, 25%).

Conclusions

The β₄-subunit regulates K_Ca1.1 activity in the conventional outflow pathway, significantly influencing outflow function. Targeting β₄-containing K_Ca1.1 channels may be a promising approach to lower intraocular pressure to treat glaucoma.

Data on differentially expressed proteins in rock inhibitor-treated human trabecular meshwork cells using SWATH-based proteomics

Rho-associated coiled coil-forming protein kinase (ROCK) inhibitors represent a novel class of anti-glaucoma drugs because of their ocular hypotensive effects. However, the underlying mechanisms responsible for lowering intraocular pressure (IOP) are not completely clear. The protein profile changes in primary human trabecular meshwork (TM) cells after two days treatment with a ROCK inhibitor were studied using label-free SWATH acquisition. These results provided significant data of key protein candidates underlying the effect of ROCK inhibitor. Using the sensitive label-free mass spectrometry approach with data-independent acquisition (SWATH-MS), we established a comprehensive TM proteome library. All raw data generated from IDA and SWATH acquisitions were uploaded and published in the Peptide Atlas public repository (http://www.peptideatlas.org/) for general release (Data ID PASS01254).

Isolation and characterization of human optic nerve head astrocytes and lamina cribrosa cells

The lamina cribrosa is the initial site of glaucomatous injury. Pathological changes to the lamina cribrosa include posterior displacement of the lamina cribrosa, loss of trophic support, and remodeling of the extracellular matrix. Optic nerve head (ONH) astrocytes and lamina cribrosa cells synthesize extracellular matrix proteins to support and maintain the lamina cribrosa under physiological conditions. During glaucoma, these cells respond to mechanical strain and other stimuli, which leads to pathological remodeling of the ONH. Although ONH astrocytes and lamina cribrosa cells have been previously cultured, there is no well-accepted, straightforward technique to isolate both cell types from a single dissected human ONH. To better understand the pathophysiology of glaucoma, we obtained and cultured lamina cribrosa explants from human donor eyes. Initially, cells that grew out from the explant were ONH astrocytes and lamina cribrosa cells. Using a specialized medium, we isolated pure populations of lamina cribrosa cells and ONH astrocytes. ONH astrocytes expressed glial fibrillary acidic protein (GFAP). Lamina cribrosa cells expressed alpha-smooth muscle actin (α-SMA), but were negative for GFAP. This method of ONH cell isolation and cell-culture will provide a technique to better understand the molecular and cell-specific changes in glaucomatous damage to the ONH.

Expression of mRNAs, miRNAs, and lncRNAs in Human Trabecular Meshwork Cells Upon Mechanical Stretch

Purpose

Intraocular pressure (IOP), the primary risk factor for primary open-angle glaucoma, is determined by resistance to aqueous outflow through the trabecular meshwork (TM). IOP homeostasis relies on TM responses to mechanical stretch. To model the effects of elevated IOP on the TM, this study sought to identify coding and non-coding RNAs differentially expressed in response to mechanical stretch.

Methods

Monolayers of TM cells from non-glaucomatous donors (n = 5) were cultured in the presence or absence of 15% mechanical stretch, 1 cycle/second, for 24 hours using a computer-controlled Flexcell unit. We profiled mRNAs and lncRNAs with stranded total RNA sequencing and microRNA (miRNA) expression with NanoString-based miRNA assays. We used two-tailed paired t-tests for mRNAs and long non-coding RNAs (lncRNAs) and the Bioconductor limma package for miRNAs. Gene ontology and pathway analyses were performed with WebGestalt. miRNA-mRNA interactions were identified using Ingenuity Pathway Analysis Integrative miRNA Target Finder software. Validation of differential expression was conducted using droplet digital PCR.

Results

We identified 219 mRNAs, 42 miRNAs, and 387 lncRNAs with differential expression in TM cells upon cyclic mechanical stretch. Pathway analysis indicated significant enrichment of genes involved in steroid biosynthesis, glycerolipid metabolism, and extracellular matrix-receptor interaction. We also identified several miRNA master regulators (miR-125a-5p, miR-30a-5p, and miR-1275) that regulate several mechanoresponsive genes.

Conclusions

To our knowledge, this is the first demonstration of the differential expression of coding and non-coding RNAs in a single set of cells subjected to cyclic mechanical stretch. Our results validate previously identified, as well as novel, genes and pathways.

Endogenous ocular lipids as potential modulators of intraocular pressure

Elevated intraocular pressure (IOP) is a risk factor in glaucoma, a group of irreversible blinding diseases. Endogenous lipids may be involved in regulation of IOP homeostasis. We present comparative fold analysis of phospholipids and sphingolipids of aqueous humour and trabecular meshwork from human control vs primary open-angle glaucoma and mouse control (normotensive) vs ocular hypertensive state. The fold analysis in control vs disease state was based on ratiometric mass spectrometric data for above classes of lipids. We standardized in vitro assays for rapid characterization of lipids undergoing significant diminishment in disease state. Evaluation of lipids using in vitro assays helped select a finite number of lipids that may potentially expand cellular interstitial space embedded in an artificial matrix or increase fluid flow across a layer of cells. These assays reduced a number of lipids for initial evaluation using a mouse model, DBA/2J with spontaneous IOP elevation. These lipids were then used in other mouse models for confirmation of IOP lowering potential of a few lipids that were found promising in previous assessments. Our results provide selected lipid molecules that can be pursued for further evaluation and studies that may provide insight into their function.

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.

Establishment of human trabecular meshwork cell cultures using nontransplantable corneoscleral rims

Human trabecular meshwork (hTM) cell isolation in academic settings utilizes the motile nature of these cells, allowing them to migrate away from the explant and proliferate on distal regions of the culture substrate. Corneoscleral rims used for transplantation are a potential source of explants for the establishment of hTM cell cultures. However, cell isolation and the initiation of primary cell cultures from ocular tissues stored in Optisol-GS medium for an extended period of time (>6 days) has proven difficult, since Optisol-GS remarkably reduces cell viability and cellularity. Therefore, explants obtained from ocular tissues stored in Optisol-GS do not often provide adequate cell yield to initiate primary cell cultures if conventional culture techniques are used. Therefore, the majority of the research on primary hTM cell isolation has been accomplished using donor tissue obtained within 72 h postmortem. The goal of this study was to develop an hTM cell isolation procedure from nontransplantable ocular materials, utilizing the anchorage dependency of TM cells. This procedure yielded functionally viable cells, eficiently dissociated from the trabecular meshwork. Isolated cells demonstrated typical hTM cell characteristics including monolayer formation, contact inhibition, phagocytosis, and responses to glucocorticoid exposure. To the best of our knowledge, this is the first time an expired explant has been utilized in the successful isolation of hTM cells. Our results clearly demonstrate the advantage of increasing the anchor points of hTM cells for enhanced cell migration out from the explants, which have limited cell proliferative capacity.

The effects of losartan on cytomegalovirus infection in human trabecular meshwork cells

Background

Human cytomegalovirus (CMV) has been emerged as one of the causes of acute recurrent or chronic hypertensive anterior uveitis in immunocompetent. In hypertensive anterior uveitis, human trabecular meshwork (TM) cells are considered a focus of inflammation. We investigated the effects of losartan, a selective angiotensin II receptor antagonist, on CMV infection in human TM cells.

Methods

Human TM cells were infected with CMV AD169. Virus infected and mock-infected cells were treated with losartan or dexamethasone or ganciclovir with or without transforming growth factor (TGF)-β1. Viral DNA accumulation and host cell response were analyzed using real-time PCR. Levels of secreted TGF-β1 were measured by determining its concentration in conditioned medium using a commercially available sandwich enzyme-linked immunosorbent assay (ELISA) kits.

Results

CMV infection significantly increased the concentrations of the secreted TGF-β1 at 3, 5, and 7 day post infection in TM cells. Treatment with dexamethasone or losartan significantly decreased the levels of TGF-β1, whereas treatment with ganciclovir did not affect TGF-β1 levels. TM cells treated with TGF-β1 along with the presence of losartan for 48 hours showed marked decrease in the expression of α-smooth muscle actin (SMA), lysyl oxidase (LOX), connective tissue growth factor (CTGF), fibronectin and collagen-1A, compared with cells treated with TGF-β1 alone. CMV-infected TM cells stimulated by TGF-β1 significantly increased the expression of α-SMA and CTGF, which were attenuated by additional treatment with losartan.

Conclusion

Losartan inhibited the expression of TGF-β1 and fibrogenic molecules in human TM cells. Thus, losartan has the potential to decrease TM fibrosis in patients with CMV-induced hypertensive anterior uveitis.

The LRRC8-mediated volume-regulated anion channel is altered in glaucoma

Regulation of cellular volume is an essential process to balance volume changes during cell proliferation and migration or when intracellular osmolality increases due to transepithelial transport. We previously characterized the key role of volume-regulated anion channels (VRAC) in the modulation of the volume of trabecular meshwork (TM) cells and, in turn, the aqueous humour (AH) outflow from the eye. The balance between the secretion and the drainage of AH determines the intraocular pressure (IOP) that is the major casual risk factor for glaucoma. Glaucoma is an ocular disease that causes irreversible blindness due to the degeneration of retinal ganglion cells. The recent identification of Leucine-Rich Repeat-Containing 8 (LRRC8A-E) proteins as the molecular components of VRAC opens the field to elucidate their function in the physiology of TM and glaucoma. Human TM cells derived from non-glaucomatous donors and from open-angle glaucoma patients were used to determine the expression and the functional activity of LRRC8-mediated channels. Expression levels of LRRC8A-E subunits were decreased in HTM glaucomatous cells compared to normotensive HTM cells. Consequently, the activity of VRAC currents and volume regulation of TM cells were significantly affected. Impaired cell volume regulation will likely contribute to altered aqueous outflow and intraocular pressure.

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.

A porcine ex vivo model of pigmentary glaucoma

Pigment dispersion can lead to pigmentary glaucoma, a poorly understood condition of younger myopic eyes with fluctuating high intraocular pressure. It has been difficult to investigate its pathogenesis without a model similar to human eyes in size and behavior. Here we present a porcine ex vivo model that recreates several features of pigmentary glaucoma, including intraocular hypertension, accumulation of pigment in the trabecular meshwork, and declining phagocytosis. We found that trabecular meshwork cells regulate outflow, form actin stress fibers, and have a decreased phagocytic activity. Gene expression microarrays and a pathway analysis of TM monolayers as well as ex vivo anterior segment perfusion cultures indicated that RhoA plays a central role in regulating the cytoskeleton, motility, and phagocytosis in the trabecular meshwork, providing new insights and targets to investigate in pigmentary 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.

Physical exosome:exosome interactions

Exosomes are extracellular nanovesicles that mediate a number of cellular processes, including intracellular signalling. There are many published examples of exosome-exosome dimers; however, their relevance has not been explored. Here, we propose that cells release exosomes to physically interact with incoming exosomes, forming dimers that we hypothesize attenuate incoming exosome-mediated signalling. We discuss experiments to test this hypothesis and potential relevance in health and disease.

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.

Experimental research on the relationship between the stiffness and the expressions of fibronectin proteins and adaptor proteins of rat trabecular meshwork cells

Background

Trabecular meshwork (TM) plays an important role in maintaining normal intraocular pressure (IOP). Studies have shown that glaucomatous TM tissues are stiffer than those of normal tissue. The high expression of fibronectin protein (FN) and adaptor protein (LNK) may be related to high resistance to aqueous humor outflow as well as high IOP. Our concern is what factors lead to the variation of the stiffness of trabecular tissue/cells.

Methods

Atomic force microscope (AFM) and Western blot (WB) analysis were applied to test TM cells of rats cultured with different concentrations of dexamethasone (DEX) and mifepristone (MIF). Rat TM cells were randomly divided into 7 groups, marked as D1, D2, D3 and M1, M2 M3 for different concentrations of DEX and MIF, respectively, and C for blank control.

Results

The elastic modulus of the treated cells were 2.67 ± 0.914 KPa, 2.92 ± 0.986 KPa, 4.52 ± 1.22 KPa for D1, D2, D3, 2.06 ± 0.745 KPa, 1.23 ± 0.462 KPa, 0.467 ± 0.275 KPa for M1, M2, M3, and 2.43 ± 0.713 KPa for C group, respectively. Expressions of FN and LNK increase (decrease) with the increase of the concentrations of DEX (MIF).

Discussion

We focus on the relationship between the stiffness and the expressions of FN and LNK of rat TM cells. We analyzed the correlation between cell stiffness and FN, LNK expression, discussed the relationship between cell stiffness and aqueous humor outflow resistance.

Conclusions

The changes of TM cell stiffness and the expressions of FN and LNK are positively correlated.

Tunneling Nanotubes are Novel Cellular Structures That Communicate Signals Between Trabecular Meshwork Cells

Purpose

The actin cytoskeleton of trabecular meshwork (TM) cells plays a role in regulating aqueous humor outflow. Many studies have investigated stress fibers, but F-actin also assembles into other supramolecular structures including filopodia. Recently, specialized filopodia called tunneling nanotubes (TNTs) have been described, which communicate molecular signals and organelles directly between cells. Here, we investigate TNT formation by TM cells.

Methods

Human TM cells were labeled separately with the fluorescent dyes, DiO and DiD, or with mitochondrial dye. Fixed or live TM cells were imaged using confocal microscopy. Image analysis software was used to track fluorescent vesicles and count the number and length of filopodia. The number of fluorescently labeled vesicles transferred between cells was counted in response to specific inhibitors of the actin cytoskeleton. Human TM tissue was stained with phalloidin.

Results

Live-cell confocal imaging of cultured TM cells showed transfer of fluorescently labeled vesicles and mitochondria via TNTs. In TM tissue, a long (160 μm) actin-rich cell process bridged an intertrabecular space and did not adhere to the substratum. Treatment of TM cells with CK-666, an Arp2/3 inhibitor, significantly decreased the number and length of filopodia, decreased transfer of fluorescently labeled vesicles and induced thick stress fibers compared to vehicle control. Conversely, inhibiting stress fibers using Y27632 increased transfer of vesicles and induced long cell processes.

Conclusions

Identification of TNTs provides a means by which TM cells can directly communicate with each other over long distances. This may be particularly important to overcome limitations of diffusion-based signaling in the aqueous humor fluid environment.

New Insight of Common Regulatory Pathways in Human Trabecular Meshwork Cells in Response to Dexamethasone and Prednisolone Using an Integrated Quantitative Proteomics: SWATH and MRM-HR Mass Spectrometry

The molecular pathophysiology of corticosteroid-induced ocular hypertension (CIH) is not well understood. To determine the biological mechanisms of CIH, this study investigated protein expression profiles of human trabecular meshwork (hTM) cells in response to dexamethasone and prednisolone treatment. Both discovery-based sequential windowed data independent acquisition of the total high-resolution mass spectra (SWATH-MS) and targeted based high resolution multiple reaction monitoring (MRM-HR) confirmation were applied using a hybrid quadrupole-time-of-flight mass spectrometer. A comprehensive list of 1759 proteins (1% FDR) was generated from the hTM. Quantitative proteomics revealed 20 differentially expressed proteins (p-value ≤ 0.05 and fold-change ≥ 1.5 or ≤ 0.67) commonly induced by prednisolone and dexamethasone, both at 300 nM. These included connective tissue growth factor (CTGF) and thrombospondin-1 (THBS1), two proteins previously implicated in ocular hypertension, glaucoma, and the transforming growth factor-β pathway. Their gene expressions in response to corticosteroids were further confirmed using reverse-transcription polymerase chain reaction. Together with other novel proteins identified in the data sets, additional pathways implicated by these regulated proteins were the phosphatidylinositol 3-kinase (PI3K)-protein kinase B (Akt) signaling pathway, integrin cell surface interaction, extracellular matrix (ECM) proteoglycans, and ECM-receptor interaction. Our results indicated that an integrated platform of SWATH-MS and MRM-HR allows high throughput identification and confirmation of novel and known corticosteroid-regulated proteins in trabecular meshwork cells, demonstrating the power of this technique in extending the current understanding of the pathogenesis of CIH.

Characterizing differences between MSCs and TM cells: Toward autologous stem cell therapies for the glaucomatous trabecular meshwork

Glaucoma, a leading cause of blindness, is characterized by an increase in intraocular pressure, which is largely determined by resistance to aqueous humour outflow through the trabecular meshwork (TM). In glaucoma, the cellularity of the TM is decreased, and, as a result, stem cell therapies for the TM represent a potential therapeutic option for restoring TM function and treating glaucoma patients. We here focus on adipose derived mesenchymal stem cells (MSCs) as a potential autologous cell source for TM regenerative medicine applications and describe characterization techniques at the messenger (reverse transcription-quantitative polymerase chain reaction), protein (western blotting, flow cytometry), and functional (contractility, phagocytosis) levels to distinguish MSCs from TM cells. We present a panel of 12 transcripts to allow: (a) suitable normalization of reverse transcription-quantitative polymerase chain reaction results across cell types and after exposure to potential differentiation stimuli; (b) distinguishing MSCs from TM cells; (c) distinguishing subtypes of TM cells; and (d) distinguishing TM cells from those in neighbouring tissue. At the protein level, dexamethasone induction of myocilin was a robust discriminating factor between MSCs and TM cells and was complemented by other protein markers. Finally, we show that contractility and phagocytosis differ between MSCs and TM cells. These methods are recommended for use in future differentiation studies to fully define if a functional TM-like phenotype is being achieved.