Rho-associated kinase inhibitors: A novel glaucoma therapy

One-Year Efficacy and Safety Assessment of Ripasudil, a Rho Kinase Inhibitor, in an Addition to or Replacing Existing Treatment Regimens: A Retrospective Study

Purpose: To evaluate efficacy and safety of ripasudil for 1 year in addition to or replacing existing treatment regimens. Methods: We retrospectively reviewed the medical records for 128 eyes of 128 glaucoma patients who were prescribed ripasudil as an addition to or a switch from their preexisting antiglaucoma instillations. We investigated the rate and factors for discontinuation and intraocular pressure (IOP) reduction. Results: Almost half of the patients (60 eyes) discontinued ripasudil treatment before the 1 year mark, while remaining patients completed the treatment. The lack of efficacy and development of adverse effects were significantly correlated with discontinuation (P < 0.001) in the Cox proportional hazards model. In the Kaplan-Meier curve, adverse effects occurred in earlier phase and almost 60% dropped out within 3 months after ripasudil administration. However, adverse effects also occurred randomly throughout the study period. In patients who continued ripasudil, the mean IOPs (mmHg) at baseline, 6 and 12 months after treatment were 17.7 ± 5.1, 14.6 ± 5.0, and 14.8 ± 3.8 in the Addition group, and 17.8 ± 4.1, 15.4 ± 3.2, and 15.4 ± 5.0 in the Switch group, respectively (all P values <0.05). Conclusions: Almost half of the patients discontinued ripasudil owing to the lack of efficacy and the generation of adverse effects within the 1 year. In the remaining half, the addition and switching of ripasudil to the existing glaucoma treatment effectively reduced IOP for 1 year.

Mutations in SPATA13/ASEF2 cause primary angle closure glaucoma

Current estimates suggest 50% of glaucoma blindness worldwide is caused by primary angle-closure glaucoma (PACG) but the causative gene is not known. We used genetic linkage and whole genome sequencing to identify Spermatogenesis Associated Protein 13, SPATA13 (NM_001166271; NP_001159743, SPATA13 isoform I), also known as ASEF2 (Adenomatous polyposis coli-stimulated guanine nucleotide exchange factor 2), as the causal gene for PACG in a large seven-generation white British family showing variable expression and incomplete penetrance. The 9 bp deletion, c.1432_1440del; p.478_480del was present in all affected individuals with angle-closure disease. We show ubiquitous expression of this transcript in cell lines derived from human tissues and in iris, retina, retinal pigment and ciliary epithelia, cornea and lens. We also identified eight additional mutations in SPATA13 in a cohort of 189 unrelated PACS/PAC/PACG samples. This gene encodes a 1277 residue protein which localises to the nucleus with partial co-localisation with nuclear speckles. In cells undergoing mitosis SPATA13 isoform I becomes part of the kinetochore complex co-localising with two kinetochore markers, polo like kinase 1 (PLK-1) and centrosome-associated protein E (CENP-E). The 9 bp deletion reported in this study increases the RAC1-dependent guanine nucleotide exchange factors (GEF) activity. The increase in GEF activity was also observed in three other variants identified in this study. Taken together, our data suggest that SPATA13 is involved in the regulation of mitosis and the mutations dysregulate GEF activity affecting homeostasis in tissues where it is highly expressed, influencing PACG pathogenesis.

Rho-Associated Protein Kinase Inhibitor Treatment Promotes Proliferation and Phagocytosis in Trabecular Meshwork Cells

Purpose

Continuous reductions in trabecular meshwork (TM) cellularity inhibit aqueous humor (AH) outflow, which is the main cause of primary open-angle glaucoma. Rho-associated protein kinase inhibitor (ROCKi) targets the TM to reduce intraocular pressure (IOP) and increase AH outflow facility. However, the underlying mechanisms are not entirely clear. Here, we aimed to investigate the effect of a ROCKi (Y-27632) on TM cell proliferation and phagocytosis.

Methods

Immortalized human TM (iHTM) cells, glaucomatous TM (GTM₃) cells, and primary human TM (pTM) cells were cultured and identified. The effects of various concentrations of Y-27632 on F-actin cytoskeleton were assessed using immunofluorescence. Cell proliferation effects were evaluated using a cell counting kit-8 (CCK8), cell counting, and Ki67 immunostaining. Cell phagocytosis was evaluated using immunofluorescence and flow cytometry in immortalized TM cells. C57BL/6J and Tg-MYOC^Y437H mice were used to investigate the proliferative effects of Y-27632 on TM cells in vivo. The effect of Y-27632 on IOP was monitored for 2 weeks, and the outflow facility was detected 2 weeks after IOP measurement. TM cells in mice were counted using immunohistochemistry.

Results

Y-27632 (100 μM) significantly promoted the proliferation of both immortal TM cells and pTM cells. In GTM₃ cells, phagocytosis was significantly greater in the Y-27632 group than in the control group, nearly reaching the level of phagocytosis in iHTM, as determined using immunofluorescence and flow cytometry. In Tg-MYOC^Y437H mice, treatment with Y-27632 significantly decreased IOP and increased outflow facility, which greatly influenced the long-term IOP-lowering effect. The number of TM cells in Tg-MYOC^Y437H mice was significantly improved after Y-27632 administration.

Conclusion

Y-27632 promoted cell proliferation and phagocytosis of TM cells, and its proliferative effect was demonstrated in a transgenic mouse model. These results revealed a new IOP-lowering mechanism of Y-27632 through effects on TM cells, suggesting the potential for a correlation between TM cellularity and long-term recovery of IOP.

A bioengineering approach to Schlemm's canal-like stem cell differentiation for in vitro glaucoma drug screening

Human Schlemm's canal (HSC) cells are critical for understanding outflow physiology and glaucoma etiology. However, primary donor cells frequently used in research are difficult to isolate. HSC cells exhibit both vascular and lymphatic markers. Human adipose-derived stem cells (ADSCs) represent a potential source of HSC due to their capacity to differentiate into both vascular and lymphatic endothelial cells, via VEGF-A and VEGF-C. Shear stress plays a critical role in maintaining HSC integrity, function, and PROX1 expression. Additionally, the human trabecular meshwork (HTM) microenvironment could provide cues for HSC-like differentiation. We hypothesize that subjecting ADSCs to VEGF-A or VEGF-C, shear stress, and co-culture with HTM cells could provide biological, mechanical, and cellular cues necessary for HSC-like differentiation. To test this hypothesis, effects of VEGF-A, VEGF-C, and shear stress on ADSC differentiation were examined and compared to primary HSC cells in terms of cell morphology, and HSC marker expression using qPCR, immunoblotting, and immunocytochemistry analysis. Furthermore, the effect of co-culture with HTM cells on porous scaffolds on ADSC differentiation was studied. Treatment with VEGF-C under shear stress is effective in differentiating ADSCs into PROX1-expressing HSC-like cells. Co-culture with HTM cells on porous scaffolds leads to HTM/ADSC-derived HSC-like constructs that regulate through-flow and respond as expected to dexamethasone. STATEMENT OF SIGNIFICANCE: We successfully generated human Schlemm's canal (HSC) like cells from adipocyte-derived stem cells induced by biochemical and biomechanical cues as well as bioengineered human trabecular meshwork (HTM) on micropatterned, porous SU8 scaffolds. These stem cell-derived HSC-like cells co-cultured with HTM cells on SU8 scaffolds can regulate through-flow, and in particular, are responsive to steroid treatment as expected. These findings show that ADSC-derived HSC-like cells have the potential to recreate the ocular outflow pathway for in vitro glaucoma drug screening. To the best of our knowledge, it is the very first time to demonstrate derivation of Schlemm's canal-like cells from stem cells. It provides an important alternative source to primary Schlemm's canal cells that are very difficult to be isolated and cultured from human donors.

Safety and Efficacy of Long-Term Ripasudil 0.4% Instillation for the Reduction of Intraocular Pressure in Japanese Open-Angle Glaucoma Patients

Purpose: Rho-associated kinase-inhibitor ripasudil 0.4% eye drops are reportedly effective for the reduction of intraocular pressure (IOP) in glaucoma patients. However, the previous studies investigated the efficacy of IOP reduction for only about 1 year. Here, we evaluated the safety and efficacy of long-term ripasudil instillation in Japanese open-angle glaucoma (OAG) patients. Methods: This study involved 312 eyes of 312 Japanese OAG patients newly initiated with ripasudil treatment at Kyoto Prefectural University of Medicine and Oike-Ikeda Eye Clinic, Kyoto, Japan. In all patients, adverse events leading to discontinuation of ripasudil treatment were investigated. Of the 312 patients, 129 patients able to continue ripasudil administration for over 12-months post-treatment initiation were enrolled to investigate the long-term efficacy. IOP data at 0-, 1-, 3-, 6-, 12-, 18-, and 24-months post initiation of continuous ripasudil use were obtained, and the IOP values at each time point were then compared. The first period (from 1-6 months) and second period (from 12-24 months) IOP data were also compared based on the mixed model. Results: IOP at each time-point post-treatment initiation was significantly reduced compared with that at pre initiation (P < 0.05). Differences in IOP between the first and second periods of the study were not statistically significant (P = 0.058). Adverse events leading to discontinuation of treatment included blepharitis (15.7%) and conjunctival hyperemia (9.0%). Conclusions: We found that in Japanese OAG patients, 24-month ripasudil eye drop instillation is both safe and effective for lowering IOP and that blepharitis is the primary adverse event for discontinuation of use.

Comprehensive bioinformatics analysis of trabecular meshwork gene expression data to unravel the molecular pathogenesis of primary open-angle glaucoma

PURPOSE

Performing bioinformatics analyses using trabecular meshwork (TM) gene expression data in order to further elucidate the molecular pathogenesis of primary open-angle glaucoma (POAG), and to identify candidate target genes.

METHODS

A systematic search in Gene Expression Omnibus and ArrayExpress was conducted, and quality control and preprocessing of the data was performed with ArrayAnalysis.org. Molecular pathway overrepresentation analysis was performed with PathVisio using pathway content from three pathway databases: WikiPathways, KEGG and Reactome. In addition, Gene Ontology (GO) analysis was performed on the gene expression data. The significantly changed pathways were clustered into functional categories which were combined into a network of connected genes.

RESULTS

Ninety-two significantly changed pathways were clustered into five functional categories: extracellular matrix (ECM), inflammation, complement activation, senescence and Rho GTPase signalling. ECM included pathways involved in collagen, actin and cell-matrix interactions. Inflammation included pathways entailing NF-κB and arachidonic acid. The network analysis showed that several genes overlap between the inflammation cluster on the one hand, and the ECM, complement activation and senescence clusters on the other hand. GO analysis, identified additional clusters, related to development and corticosteroids.

CONCLUSION

This study provides an overview of the processes involved in the molecular pathogenesis of POAG in the TM. The results show good face validity and confirm findings from histological, biochemical, genome-wide association and transcriptomics studies. The identification of known points of action for drugs, such as Rho GTPase, arachidonic acid, NF-κB, prostaglandins and corticosteroid clusters, supports the value of this approach to identify potential drug targets.

Phenotypic and Functional Alterations in Tunneling Nanotubes Formed by Glaucomatous Trabecular Meshwork Cells

Purpose

Trabecular meshwork (TM) cells detect and coordinate responses to intraocular pressure (IOP) in the eye. TM cells become dysfunctional in glaucoma where IOP is often elevated. Recently, we showed that normal TM (NTM) cells communicate by forming tubular connections called tunneling nanotubes (TNTs). Here, we investigated TNTs in glaucomatous TM (GTM) cells.

Methods

Primary GTM and NTM cells were established from cadaver eyes. Transfer of Vybrant DiO and DiD-labeled vesicles via TNT connections was measured. Imaris software measured the number and length of cell protrusions from immunofluorescent confocal images. Live-cell imaging of the actin cytoskeleton was performed. The distribution of myosin-X, a regulator of TNTs/filopodia, was investigated in TM cells and tissue.

Results

GTM cells contained significantly more transferred fluorescent vesicles than NTM cells (49.6% vs. 35%). Although NTM cells had more protrusions at the cell surface than GTM cells (7.61 vs. 4.65 protrusions/cell), GTM protrusions were significantly longer (12.1 μm vs. 9.76 μm). Live-cell imaging demonstrated that the GTM actin cytoskeleton was less dynamic, and vesicle transfer between cells was significantly slower than NTM cells. Furthermore, rearrangement of the actin cortex adjacent to the TNT may influence TNT formation. Myosin-X immunostaining was punctate and disorganized in GTM cells and tissue compared to age-matched NTM controls.

Conclusions

Together, our data demonstrate that GTM cells have phenotypic and functional differences in their TNTs. Significantly slower vesicle transfer via TNTs in GTM cells may delay the timely propagation of cellular signals when pressures become elevated in glaucoma.

Myosin-X Silencing in the Trabecular Meshwork Suggests a Role for Tunneling Nanotubes in Outflow Regulation

Purpose

The actin cytoskeleton plays a key role in outflow regulation through the trabecular meshwork (TM). Although actin stress fibers are a target of glaucoma therapies, the role of other actin cellular structures is unclear. Myosin-X (Myo10) is an actin-binding protein that is involved in tunneling nanotube (TNT) and filopodia formation. Here, we inhibited Myo10 pharmacologically or by gene silencing to investigate the role of filopodia/TNTs in the TM.

Methods

Short hairpin RNA interference (RNAi) silencing lentivirus targeting myosin-X (shMyo10) was generated. Human anterior segments were perfused with shMyo10 or CK-666, an Arp2/3 inhibitor. Confocal microscopy investigated the colocalization of Myo10 with matrix metalloproteinase (MMPs). Western immunoblotting investigated the protein levels of MMPs and extracellular matrix (ECM) proteins. MMP activity and phagocytosis assays were performed.

Results

CK-666 and shMyo10-silencing lentivirus caused a significant reduction in outflow rates in anterior segment perfusion culture, an ex vivo method to study intraocular pressure regulation. In human TM cells, Myo10 colocalized with MMP2, MMP14, and cortactin in podosome-like structures, which function as regions of focal ECM degradation. Furthermore, MMP activity, thrombospondin-1 and SPARC protein levels were significantly reduced in the media of CK-666-treated and shMyo10-silenced TM cells. However, neither Myo10 silencing or CK-666 treatment significantly affected phagocytic uptake.

Conclusions

Inhibiting filopodia/TNTs caused opposite effects on outflow compared with inhibiting stress fibers. Moreover, Myo10 may also play a role in focal ECM degradation in TM cells. Our results provide additional insight into the function of actin supramolecular assemblies and actin-binding proteins in outflow regulation.

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.

Impact of pigment dispersion on trabecular meshwork cells

PURPOSE

Dysfunction of the trabecular meshwork (TM) in pigmentary glaucoma contributes to increased aqueous humor outflow resistance and intraocular pressure. In this study, we investigated the effect of pigment dispersion on trabecular meshwork cells.

METHODS

Porcine TM cells from ab interno trabeculectomy specimens were exposed to pigment dispersion, then, analyzed for changes in morphology, immunostaining, and ultrastructure. Their abilities to phagocytose migrate, and contraction was quantified. An expression microarray, using 23,937 probes, and a pathway analysis were performed.

RESULTS

Stress fiber formation was increased in the pigment dispersion group (P) (60.1 ± 0.3%, n = 10) compared to control (C) (38.4 ± 2.5%, n = 11, p < 0.001). Phagocytosis declined (number of cells with microspheres in P = 37.0 ± 1.1% and in C = 68.7 ± 1.3%, n = 3, p < 0.001) and migration was reduced after 6 h (cells within the visual field over 6 h in P = 28.0.1 ± 2.3 (n = 12) and in C = 40.6 ± 3.3 (n = 13), p < 0.01). Pigment induced contraction at 24 h onwards (p < 0.01). Microarray analysis revealed that Rho signaling was central to these responses.

CONCLUSION

Exposure of TM cells to pigment dispersion resulted in reduced phagocytosis and migration, as well as increased stress fiber formation and cell contraction. The Rho signaling pathway played a central and early role, suggesting that its inhibitors could be used as a specific intervention in treatment of pigmentary glaucoma.

Rho kinase inhibitors-a review on the physiology and clinical use in Ophthalmology

The Rho kinase (ROCK) signaling pathway is involved in several cellular events that include cell proliferation and cytoskeleton modulation leading to cell adhesion. The ROCK pathway in the human eye has been hypothesized to play important roles in corneal endothelial cell physiology and pathologic states. In addition, ROCK signaling has been identified as an important regulator of trabecular meshwork (TM) outflow, which is altered in glaucomatous eyes. These roles in corneal and glaucomatous disease states have led to the growing interest in the development of drugs selectively targeting this pathway (ROCK inhibitors). The authors provide a review of the literature on the pathobiology of the ROCK signaling in corneal endothelial disease, glaucoma, and vitreoretinal disease, as well as the clinical usefulness of ROCK inhibitors in Ophthalmology.

Evaluation of offset of conjunctival hyperemia induced by a Rho-kinase inhibitor; 0.4% Ripasudil ophthalmic solution clinical trial

Glaucoma leads to irreversible blindness. Numerous anti-glaucoma eye drops have been developed. Unfortunately, many patients with glaucoma still suffer from progressive visual disorders. Recently, ripasudil hydrochloride hydrate, a selective Rho-associated protein kinase inhibitor, was launched for the treatment of glaucoma. However, adverse events, such as conjunctival hyperemia, are often noted in clinical trials using healthy subjects. Therefore, we investigated the onset, offset, and kinetic changes of conjunctival hyperemia induced by ripasudil ophthalmic solution in patients with open-angle glaucoma or ocular hypertension who had already been treated with anti-glaucoma eye drops other than ripasudil. Conjunctival hyperemia was evaluated by both clinical grading by 3 ophthalmic physicians and pixel coverage of conjunctival blood vessels determined by conjunctival hyperemia-analyzing software. Conjunctival hyperemia appeared within 10 min post-instillation in most of the participants. Clinical grade and pixel coverage increased significantly 10 min post-instillation and then decreased. In most of the participants, hyperemia resolved within 2 h. Median conjunctival hyperemia offset was 90 min. A tendency of monotonic increase was observed between clinical grade and pixel coverage. Taken altogether, hyperemia induced by ripasudil was transient in glaucoma patients who had already been treated with anti-glaucoma eye drops other than ripasudil.

An in vitro study of scarring formation mediated by human Tenon fibroblasts: Effect of Y-27632, a Rho kinase inhibitor

Scar formation is the most common cause for failure of glaucoma filtration surgery because of increased fibroblast proliferation and activation. We have now examined the effect of Y‐27632, a Rho‐associated protein kinase (ROCK) inhibitor, on postsurgical scarring formation in human Tenon fibroblasts (HTFs). Collagen gel contraction assay was used to compare contractility activity of Y‐27632 with several antiglaucoma drugs. Immunofluorescence and western blotting were used to examine expression of scar formation–related factors. We found that Y‐27632 inhibited collagen gel contraction, as well as α‐smooth muscle actin and vimentin expression; these were promoted by treatment with latanoprost, timolol, or transforming growth factor (TGF)–β. To investigate the effect of Y‐27632 in postsurgical scarring, we mimicked TGF‐β secretion by stimulating HTFs with TGF‐β prior to Y‐27632 treatment. HTFs cultured in the presence of TGF‐β significantly increased gel contraction. In contrast, when HTFs were treated with 10μM Y‐27632, contraction was significantly inhibited. Furthermore, Y‐27632 reduced TGF‐β–induced phosphorylation of mitogen‐activated protein kinase signalling. These results suggest that ROCK inhibitors may inhibit fibrosis by inhibiting transdifferentiation of Tenon fibroblasts into myofibroblasts and by inhibiting TGF‐β signalling after surgery through mitogen‐activated protein kinase pathway suppression. These results implicate that ROCK inhibitors may improve outcomes after filtering surgery with a potential antiscarring effect, while latanoprost and timolol may induce fibrosis.

Significance of the study

Scar formation is the primary cause of failure after glaucoma filtration surgery. A ROCK inhibitor, Y‐27632, has been introduced as a novel potential antiglaucoma treatment to reduce intraocular pressure. The aim of our study was to elucidate the effect of Y‐27632 on scarring formation after glaucoma filtration surgery, in direct comparison with other antiglaucoma drugs. Our findings thus suggested that Y‐27632 may inhibit fibrosis and improve outcome after glaucoma filtration surgery through inhibition of transdifferentiation of Tenon fibroblasts into myofibroblasts, and the TGF‐β and MAPK signalling after surgery, while latanoprost and timolol may induce fibrosis.

Topical Rho-Associated Kinase Inhibitor, Y27632, Accelerates Corneal Endothelial Regeneration in a Canine Cryoinjury Model

PURPOSE

Corneal endothelial cell regeneration varies by species, with nonhuman primates (NHPs) and rabbits displaying low and high proliferative capacities, respectively. Recent studies report that topical application of rho-associated kinase (ROCK) inhibitors accelerates corneal endothelial wound healing in animal models and human patients with endothelial dysfunction. This study determines the regenerative capacity of canine corneal endothelial cells in vivo and their response to a topical ROCK inhibitor, Y27632, after transcorneal freezing.

METHODS

Right eyes of 6 beagles underwent transcorneal freezing; 10 mM ROCK inhibitor Y27632 or vehicle control was applied topically to both eyes at least 4 times daily for 56 days. Endothelial cell density was evaluated by in vivo confocal microscopy, and corneal thickness was measured by Fourier-domain optical coherence tomography (FD-OCT) and ultrasound pachymetry.

RESULTS

Transcorneal freezing induced severe central corneal edema in dogs, with restoration of transparency occurring within 4 weeks. Y27632 significantly decreased corneal thickness by FD-OCT and ultrasound pachymetry in the acute phase and significantly increased endothelial cell density at days 28 and 42 post-cryoinjury, suggesting faster restoration of endothelial cell recovery.

CONCLUSIONS

Canine corneal endothelial function recovers at a similar rate as NHPs but more slowly than rabbits after cryoinjury. Faster corneal endothelial wound healing was observed by in vivo confocal microscopy and FD-OCT in dogs treated with Y27632 versus vehicle controls. Thus, a canine cryoinjury model may be a useful alternative to NHPs in detecting a response to therapies directed at endothelial regeneration.

Probe Sensitivity to Cortical versus Intracellular Cytoskeletal Network Stiffness

In development, wound healing, and pathology, cell biomechanical properties are increasingly recognized as being of central importance. To measure these properties, experimental probes of various types have been developed, but how each probe reflects the properties of heterogeneous cell regions has remained obscure. To better understand differences attributable to the probe technology, as well as to define the relative sensitivity of each probe to different cellular structures, here we took a comprehensive approach. We studied two cell types-Schlemm's canal endothelial cells and mouse embryonic fibroblasts (MEFs)-using four different probe technologies: 1) atomic force microscopy (AFM) with sharp tip, 2) AFM with round tip, 3) optical magnetic twisting cytometry (OMTC), and 4) traction microscopy (TM). Perturbation of Schlemm's canal cells with dexamethasone treatment, α-actinin overexpression, or RhoA overexpression caused increases in traction reported by TM and stiffness reported by sharp-tip AFM as compared to corresponding controls. By contrast, under these same experimental conditions, stiffness reported by round-tip AFM and by OMTC indicated little change. Knockout (KO) of vimentin in MEFs caused a diminution of traction reported by TM, as well as stiffness reported by sharp-tip and round-tip AFM. However, stiffness reported by OMTC in vimentin-KO MEFs was greater than in wild type. Finite-element analysis demonstrated that this paradoxical OMTC result in vimentin-KO MEFs could be attributed to reduced cell thickness. Our results also suggest that vimentin contributes not only to intracellular network stiffness but also cortex stiffness. Taken together, this evidence suggests that AFM sharp tip and TM emphasize properties of the actin-rich shell of the cell, whereas round-tip AFM and OMTC emphasize those of the noncortical intracellular network.

Rho Kinase Inhibitors as a Novel Treatment for Glaucoma and Ocular Hypertension

In an elegant example of bench-to-bedside research, a hypothesis that cells in the outflow pathway actively regulate conventional outflow resistance was proposed in the 1990s and systematically pursued, exposing novel cellular and molecular mechanisms of intraocular pressure (IOP) regulation. The critical discovery that pharmacologic manipulation of the cytoskeleton of outflow pathway cells decreased outflow resistance placed a spotlight on the Rho kinase pathway that was known to regulate the cytoskeleton. Ultimately, a search for Rho kinase inhibitors led to the discovery of several molecules of therapeutic interest, leaving us today with 2 new ocular hypotensive agents approved for clinical use: ripasudil in Japan and netarsudil in the United States. These represent members of the first new class of clinically useful ocular hypotensive agents since the US Food and Drug Administration approval of latanoprost in 1996. The development of Rho kinase inhibitors as a class of medications to lower IOP in patients with glaucoma and ocular hypertension represents a triumph in translational research. Rho kinase inhibitors are effective alone or when combined with other known ocular hypotensive medications. They also offer the possibility of neuroprotective activity, a favorable impact on ocular blood flow, and even an antifibrotic effect that may prove useful in conventional glaucoma surgery. Local adverse effects, however, including conjunctival hyperemia, subconjunctival hemorrhages, and cornea verticillata, are common. Development of Rho kinase inhibitors targeted to the cells of the outflow pathway and the retina may allow these agents to have even greater clinical impact. The objectives of this review are to describe the basic science underlying the development of Rho kinase inhibitors as a therapy to lower IOP and to summarize the results of the clinical studies reported to date. The neuroprotective and vasoactive properties of Rho kinase inhibitors, as well as the antifibrotic properties, of these agents are reviewed in the context of their possible role in the medical and surgical treatment of glaucoma.

Mutual regulation of the Hippo/Wnt/LPA/TGF‑β signaling pathways and their roles in glaucoma (Review)

Glaucoma is the leading cause of irreversible blindness worldwide and there is no effective treatment thus far. The trabecular meshwork has been identified as the major pathological area involved. Certain signaling pathways in the trabecular meshwork, including the Wnt, lysophosphatidic acid and transforming growth factor-β pathways, have been identified as novel therapeutic targets in glaucoma treatment. Meanwhile, it has been reported that key proteins in these pathways, particularly the primary transcription regulator Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), exhibit interactions with the Hippo pathway. The Hippo pathway, which was first identified in Drosophila, has drawn great focus with regard to various aspects of studies in recent years. One role of the Hippo pathway in the regulation of organ size was indicated by more recent evidence. Defining the relevant physiological function of the Hippo pathway has proven to be extremely complicated. Studies have ascribed a role for the Hippo pathway in an overwhelming number of processes, including cell proliferation, cell death and cell differentiation. Therefore, the present review aimed to unravel the roles of YAP and TAZ in the Hippo pathway and the pathogenesis of glaucoma. Furthermore, a new and creative study for the treatment of glaucoma is provided.

Effect of Cromakalim Prodrug 1 (CKLP1) on Aqueous Humor Dynamics and Feasibility of Combination Therapy With Existing Ocular Hypotensive Agents

Purpose

Cromakalim prodrug 1 (CKLP1) is a water-soluble ATP-sensitive potassium channel opener that has shown ocular hypotensive properties in ex vivo and in vivo experimental models. To determine its mechanism of action, we assessed the effect of CKLP1 on aqueous humor dynamics and in combination therapy with existing ocular hypotensive agents.

Methods

Outflow facility was assessed in C57BL/6 mice by ex vivo eye perfusions and by in vivo constant flow infusion following CKLP1 treatment. Human anterior segments with no trabecular meshwork were evaluated for effect on pressure following CKLP1 treatment. CKLP1 alone and in combination with latanoprost, timolol, and Rho kinase inhibitor Y27632 were evaluated for effect on intraocular pressure in C57BL/6 mice and Dutch-belted pigmented rabbits.

Results

CKLP1 lowered episcleral venous pressure (control: 8.9 ± 0.1 mm Hg versus treated: 6.2 ± 0.1 mm Hg, P < 0.0001) but had no detectable effect on outflow facility, aqueous humor flow rate, or uveoscleral outflow. Treatment with CKLP1 in human anterior segments without the trabecular meshwork resulted in a 50% ± 9% decrease in pressure, suggesting an effect on the distal portion of the conventional outflow pathway. CKLP1 worked additively with latanoprost, timolol, and Y27632 to lower IOP, presumably owing to combined effects on different aspects of aqueous humor dynamics.

Conclusions

CKLP1 lowered intraocular pressure by reducing episcleral venous pressure and lowering distal outflow resistance in the conventional outflow pathway. Owing to this unique mechanism of action, CKLP1 works in an additive manner to lower intraocular pressure with latanoprost, timolol, and Rho kinase inhibitor Y27632.

Efficacy of Topically Administered Rho-Kinase Inhibitor AR-12286 in Patients With Exfoliation Syndrome and Ocular Hypertension or Glaucoma

PURPOSE

To evaluate the efficacy of rho-associated protein kinase inhibitor, AR-12286 topical solution, for its effect in eyes with exfoliation syndrome (XFS) and ocular hypertension (OHT) or exfoliative glaucoma (XFG) and examine any lasting effect on intraocular pressure (IOP) after discontinuation.

METHODS

Prospective, double-masked, randomized, interventional study. Patients with XFS and OHT or XFG were enrolled. The study eyes were treated once daily with AR-12286, randomized to 0.5% or 0.7% for 24 weeks. Visits included baseline, 1, 4, and 12 weeks after drug initiation; at 12 weeks AR-12286 was discontinued for 1 week and was resumed at week 13. At the week 24 visit, AR-12286 was discontinued, and a final reexamination was performed at week 25.

RESULTS

Ten patients were treated. Mean baseline IOP was 25±2.4 mm Hg, mean IOP was reduced to 19.1±2.3 mm Hg at 1 week (P<0.001), 17.5±3.6 mm Hg at 4 weeks (P<0.001), and 17.4±3.6 mm Hg at 12 weeks (P<0.001), yielding an average IOP reduction of 23.6%, 30%, and 30.4%, respectively. At the week 13 visit, 1 week after the drug was discontinued, mean IOP increased to 21.6±5.4 mm Hg (P=0.06 compared with baseline visit). At week 24, the mean IOP was 21.8±7.8 mm Hg (P=0.2, and AR-12286 was discontinued). At week 25, the mean IOP was 21.3±5.3 mm Hg (P=0.06).

CONCLUSIONS

AR-12286 was well tolerated and provided statistically significant reduction in IOP in patients with XFS and OHT or XFG. This drug may represent an additional therapeutic paradigm for the treatment of XFG.

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.

Topical treatment of glaucoma: established and emerging pharmacology

INTRODUCTION

Glaucoma is a collection of optic neuropathies consisting of retinal ganglion cell death and corresponding visual field loss. Glaucoma is the leading cause of irreversible vision loss worldwide and is forecasted to precipitously increase in prevalence in the coming decades. Current treatment options aim to lower intraocular pressure (IOP) via topical or oral therapy, laser treatment to the trabecular meshwork or ciliary body, and incisional surgery. Despite increasing use of trabecular laser therapy, topical therapy remains first-line in the treatment of most forms of glaucoma. Areas covered: Novel glaucoma therapies are a long-standing focus of investigational study. More than two decades have passed since the last United States Food and Drug Administration (FDA) approval of a topical glaucoma drug. Here, the authors review established topical glaucoma drops as well as those currently in FDA phase 2 and 3 clinical trial, nearing clinical use. Expert opinion: Current investigational glaucoma drugs lower IOP, mainly through enhanced trabecular meshwork outflow. Although few emerging therapies show evidence of retinal ganglion cell and optic nerve neuroprotection in animal models, emerging drugs are focused on lowering IOP, similar to established medicines.

Comparative Study of the Effects of Trabecular Meshwork Outflow Drugs on the Permeability and Nitric Oxide Production in Trabecular Meshwork Cells

PURPOSE

To compare the effects of the barrier function in human trabecular meshwork (TM) cells monolayer and the production of nitric oxide (NO) between trabecular outflow drugs, Rho-associated kinase (ROCK) inhibitors, adenosine, and statin.

METHODS

Primary cultured TM cells were exposed to 10 or 25 μM Y-27632, 0.1 or 1 μM N6-cyclohexyladenosine (CHA), or 15 or 30 μM simvastatin for 24 hours. NO production and expression of endothelial nitric oxide synthase mRNA were measured by Griess assay and reverse transcription polymerase chain reaction, respectively. Barrier functions of the TM cell monolayer were measured by carboxyfluorescein and trans-endothelial electrical resistance. The expression of matrix metalloproteinase-2 mRNA was assessed with reverse transcription polymerase chain reaction.

RESULTS

In TM cells, treatment with each drug increased endothelial nitric oxide synthase mRNA expression. Treatment with 25 μM Y-27632 and 1.0 μM CHA increased NO production significantly (p = 0.035 and p = 0.043, respectively). Treatment with each drug increased the permeability (all p = 0.001) and decreased the trans-endothelial electron resistance of the TM cell monolayer. Treatment with 0.1 μM and 1.0 μM CHA significantly increased matrix metalloproteinase-2 mRNA expression, but simvastatin inhibited its expression.

CONCLUSIONS

Since treatment with ROCK inhibitor more greatly increased NO production and permeability than did adenosine or statin, ROCK inhibitor seems to be more effective for lowering intraocular pressure.

Epigenetics and Signaling Pathways in Glaucoma

Glaucoma is the most common cause of irreversible blindness worldwide. This neurodegenerative disease becomes more prevalent with aging, but predisposing genetic and environmental factors also contribute to increased risk. Emerging evidence now suggests that epigenetics may also be involved, which provides potential new therapeutic targets. These three factors work through several pathways, including TGF-β, MAP kinase, Rho kinase, BDNF, JNK, PI-3/Akt, PTEN, Bcl-2, Caspase, and Calcium-Calpain signaling. Together, these pathways result in the upregulation of proapoptotic gene expression, the downregulation of neuroprotective and prosurvival factors, and the generation of fibrosis at the trabecular meshwork, which may block aqueous humor drainage. Novel therapeutic agents targeting these pathway members have shown preliminary success in animal models and even human trials, demonstrating that they may eventually be used to preserve retinal neurons and vision.

Neuropathy optic glaucomatosa induced by systemic hypertension through activation endothelin-1 signaling pathway in central retinal artery in rats

AIM

To evaluate effect of hypertension on retinal ganglion cell (RGC) apoptosis, intraocular pressure (IOP), and the activation of endothelin-1 (ET-1) signaling pathway in central retinal artery (CRA) in rats.

METHODS

The experimental study was performed on 20 male Sprague Dawley rats that were divided into control group, and hypertension groups. The hypertension was induced by subcutaneous deoxycorticoacetate (DOCA) 10 mg/kg twice a week and administered 0.9% NaCl solution daily for 2, 6, and 10wk. Blood pressure (BP) was measured using animal BP analyzer. IOP was measured by handheld tonometry. Retinal tissue preparations by paraffin blocks were made after enucleation. The expression of ET-1, eNOS, ET-1 receptor A (ETR_A), ET-1 receptor B (ETR_B), and phosphorylated myosin light chain kinase (MLCK), and caldesmon (CaD) in CRA and RGC apoptosis were evaluated through immunofluorescent staining method then observed using laser scanning confocal microscopy.

RESULTS

BP significantly increased in all of the hypertension groups compared to control (P=0.001). Peak IOP elevation (7.78±4.14 mm Hg) and RGC apoptosis (576.15±33.28 Au) occurred on 2wk of hypertension. ET-1 expression (1238.6±55.1 Au) and eNOS expression (2814.2±70.7 Au) were found highest in 2wk of hypertension, although the ratio of ET-1/eNOS decreased since 2wk. ETR_A reached peak expression in 10wk of hypertension (1219.4±6.3 Au), while ETR_B significantly increased only in 2 weeks group (1069.2±9.6 Au). The highest MLCK expression (1190.09±58.32 Au), CaD (1670.28±18.36 Au) were also found in 2wk of hypertension.

CONCLUSION

Hypertension effects to activation of ET-1 signaling pathway significantly in CRA, elevation of IOP, and RGC apoptosis. The highest value was achieved at 2wk, which is the development phase of hypertension.

Rho-Mancing to Sensitize Calcium Signaling for Contraction in the Vasculature: Role of Rho Kinase

Vascular smooth muscle contraction is an important physiological process contributing to cardiovascular homeostasis. The principal determinant of smooth muscle contraction is the intracellular free Ca²⁺ concentration, and phosphorylation of myosin light chain (MLC) by activated myosin light chain kinase (MLCK) in response to increased Ca²⁺ is the main pathway by which vasoconstrictor stimuli induce crossbridge cycling of myosin and actin filaments. A secondary pathway for vascular smooth muscle contraction that is not directly dependent on Ca²⁺ concentration, but rather mediating Ca²⁺ sensitization, is the RhoA/Rho kinase pathway. In response to contractile stimuli, the small GTPase RhoA activates its downstream effector Rho kinase which, in turn, promotes contraction via myosin light chain phosphatase (MLCP) inhibition. RhoA/Rho kinase-mediated MLCP inhibition occurs mainly by phosphorylation and inhibition of MYPT1, the regulatory subunit of MLCP, or by CPI-17-mediated inhibition of the catalytic subunit of MLCP. In this review, we describe the molecular mechanisms underlying the pivotal role exerted by Rho kinase on vascular smooth muscle contraction and discuss the main regulatory pathways for its activity.

Role of the Rho GTPase/Rho kinase signaling pathway in pathogenesis and treatment of glaucoma: Bench to bedside research

Glaucoma is a leading cause of irreversible blindness worldwide. Elevated intraocular pressure (IOP) is considered to be a predominant risk factor for primary open angle glaucoma, the most prevalent form of glaucoma. Although the etiological mechanisms responsible for increased IOP are not completely clear, impairment in aqueous humor (AH) drainage through the conventional or trabecular pathway is recognized to be a primary cause in glaucoma patients. Importantly, lowering of IOP has been demonstrated to reduce progression of vision loss and is a mainstay of treatment for all types of glaucoma. Currently however, there are limited therapeutic options available for lowering IOP especially as it relates to enhancement of AH outflow through the trabecular pathway. Towards addressing this challenge, bench and bedside research conducted over the course of the last decade and a half has identified the significance of inhibiting Rho kinase for lowering IOP. Rho kinase is a downstream effector of Rho GTPase signaling that regulates actomyosin dynamics in numerous cell types. Studies from several laboratories have demonstrated that inhibition of Rho kinase lowers IOP via relaxation of the trabecular meshwork which enhances AH outflow. By contrast, activation of Rho GTPase/Rho kinase signaling in the trabecular outflow pathway increases IOP by altering the contractile, cell adhesive and permeability barrier characteristics of the trabecular meshwork and Schlemm's canal tissues, and by influencing extracellular matrix production and fibrotic activity. This article, written in honor of the late David Epstein, MD, summarizes findings from both basic and clinical studies that have been instrumental for recognition of the importance of the Rho/Rho kinase signaling pathway in regulation of AH outflow, and in the development of Rho kinase inhibitors as promising IOP- lowering agents for glaucoma treatment.

Rho Kinases in Health and Disease: From Basic Science to Translational Research

Rho-associated kinases ROCK1 and ROCK2 are key regulators of actin cytoskeleton dynamics downstream of Rho GTPases that participate in the control of important physiologic functions, S including cell contraction, migration, proliferation, adhesion, and inflammation. Several excellent review articles dealing with ROCK function and regulation have been published over the past few years. Although a brief overview of general molecular, biochemical, and functional properties of ROCKs is included, an effort has been made to produce an original work by collecting and synthesizing recent studies aimed at translating basic discoveries from cell and experimental models into knowledge of human physiology, pathophysiological mechanisms, and medical therapeutics. This review points out the specificity and distinct roles of ROCK1 and ROCK2 isoforms highlighted in the last few years. Results obtained from genetically modified mice and genetic analysis in humans are discussed. This review also addresses the involvement of ROCKs in human diseases and the potential use of ROCK activity as a biomarker or a pharmacological target for specific inhibitors.

Conjunctival fibrosis following filtering glaucoma surgery

Despite advances in surgical technique and postoperative care, fibrosis remains the major impediment to a marked reduction of intraocular pressure without the need of additional medication (complete success) following filtering glaucoma surgery. Several aspects specific to filtering surgery may contribute to enhanced fibrosis. Changes in conjunctival tissue structure and composition due to preceding treatments as well as alterations in interstitial fluid flow and content due to aqueous humor efflux may act as important drivers of fibrosis. In light of these pathophysiological considerations, current and possible future strategies to control fibrosis following filtering glaucoma surgery are discussed.

Live cell imaging of actin dynamics in dexamethasone-treated porcine trabecular meshwork cells

The regulation of the actin cytoskeleton in trabecular meshwork (TM) cells is important for controlling outflow of the aqueous humor. In some reports, dexamethasone (DEX) increased the aqueous humor outflow resistance and induced unusual actin structures, such as cross-linked actin networks (CLAN), in TM cells. However, the functions and dynamics of CLAN in TM cells are not completely known, partly because actin stress fibers have been observed only in fixed cells. We conducted live-cell imaging of the actin dynamics in TM cells with or without DEX treatment. An actin-green fluorescent protein (GFP) fusion construct with a modified insect virus was transfected into porcine TM cells. Time-lapse imaging of live TM cells treated with 25 μM Y-27632 and 100 nM DEX was performed using an inverted fluorescence microscope. Fluorescent images were recorded every 15 s for 30 min after Y-27632 treatment or every 30 min for 72 h after DEX treatment. The GFP-actin was expressed in 22.7 ± 10.9% of the transfected TM cells. In live TM cells, many actin stress fibers were observed before the Y-27632 treatment. Y-27632 changed the cell shape and decreased stress fibers in a time-dependent manner. In fixed cells, CLAN-like structures were seen in 26.5 ± 1.7% of the actin-GFP expressed PTM cells treated with DEX for 72 h. In live imaging, there was 28% CLAN-like structure formation at 72 h after DEX treatment, and the lifetime of CLAN-like structures increased after DEX treatment. The DEX-treated cells with CLAN-like structures showed less migration than DEX-treated cells without CLAN-like structures. Furthermore, the control cells (without DEX treatment) with CLAN-like structures also showed less migration than the control cells without CLAN-like structures. These results suggested that CLAN-like structure formation was correlated with cell migration in TM cells. Live cell imaging of the actin cytoskeleton provides valuable information on the actin dynamics in TM cells.

Rho Kinase (ROCK) Inhibitors and Their Therapeutic Potential

Rho kinases (ROCKs) belong to the serine-threonine family, the inhibition of which affects the function of many downstream substrates. As such, ROCK inhibitors have potential therapeutic applicability in a wide variety of pathological conditions including asthma, cancer, erectile dysfunction, glaucoma, insulin resistance, kidney failure, neuronal degeneration, and osteoporosis. To date, two ROCK inhibitors have been approved for clinical use in Japan (fasudil and ripasudil) and one in China (fasudil). In 1995 fasudil was approved for the treatment of cerebral vasospasm, and more recently, ripasudil was approved for the treatment of glaucoma in 2014. In this Perspective, we present a comprehensive review of the physiological and biological functions for ROCK, the properties and development of over 170 ROCK inhibitors as well as their therapeutic potential, the current status, and future considerations.

Effect of Rho-kinase Inhibitor, Y27632, on Porcine Corneal Endothelial Cell Culture, Inflammation and Immune Regulation

PURPOSE

To investigate the effect of the Rho-kinase inhibitor, Y27632, on pig corneal endothelial cell (pCEC) culture, and on inflammation and immune regulation of the responses of human cells to pCECs.

METHODS

pCECs were cultured with/without Y27632 to assess cell proliferation and in vitro wound healing assay. The level of MCP-1 and VEGF in pCECs stimulated with human TNF-α were measured. Proliferation of human PBMCs stimulated with pCECs, and cytokine production in human T cells, and monocyte migration after stimulation were investigated.

RESULTS

Y27632 promoted pCEC proliferation, prevented pCEC death, and enhanced in vitro wound healing. After stimulation, there were significantly lower levels of MCP-1 and VEGF measured in pCECs cultured with Y27632, and significantly reduced human PBMC proliferation, cytokine production, and monocyte migration.

CONCLUSIONS

The application of the Rho-kinase inhibitor will be beneficial when culturing pCECs, and may provide a novel therapy to reduce inflammation after corneal xenotransplantation.

Genes, pathways, and animal models in primary open-angle glaucoma

Glaucoma is an optic neuropathy characterized by loss of retinal ganglion cells (RGCs) and consequently visual field loss. It is a complex and heterogeneous disease in which both environmental and genetic factors play a role. With the advent of genome-wide association studies (GWASs), the number of loci associated with primary open-angle glaucoma (POAG) have increased greatly. There has also been major progress in understanding the genes determining the vertical cup-disc ratio (VCDR), disc area (DA), cup area (CA), intraocular pressure (IOP), and central corneal thickness (CCT). In this review, we will update and summarize the genetic loci associated so far with POAG, VCDR, DA, CA, IOP, and CCT. We will describe the pathways revealed and supported by genetic association studies, integrating current knowledge from human and experimental data. Finally, we will discuss approaches for functional genomics and clinical translation.

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.

Elevated intraocular pressure induces Rho GTPase mediated contractile signaling in the trabecular meshwork

Rho GTPase regulated contractile signaling in the trabecular meshwork (TM) has been shown to modulate aqueous humor (AH) outflow and intraocular pressure (IOP). To explore whether elevated IOP, a major risk factor for primary open angle glaucoma (POAG) influences Rho GTPase signaling in the TM, we recorded AH outflow in enucleated contralateral porcine eyes perfused for 4-5 h at either 15 mm or 50 mm Hg pressure. After perfusion, TM tissue extracted from perfused eyes was evaluated for the activation status of Rho GTPase, myosin light chain (MLC), myosin phosphatase target substrate 1 (MYPT1), myristoylated alanine-rich C-kinase substrate (MARCKS) and paxillin. Eyes perfused at 50 mm Hg exhibited a significant decrease in AH outflow facility compared with those perfused at 15 mm Hg. Additionally, TM tissue from eyes perfused at 50 mm Hg revealed significantly increased levels of activated RhoA and phosphorylated MLC, MYPT1, MARCKS and paxillin compared to TM tissue derived from eyes perfused at 15 mm Hg. Taken together, these observations indicate that elevated IOP-induced activation of Rho GTPase-dependent contractile signaling in the TM is associated with increased resistance to AH outflow through the trabecular pathway, and demonstrate the sensitivity of Rho GTPase signaling to mechanical force in the AH outflow pathway.

Prevention of nocturnal elevation of intraocular pressure by gene transfer of dominant-negative RhoA in rats

IMPORTANCE

We developed a gene transfer tool for the control of nocturnal elevated intraocular pressure (IOP).

OBJECTIVE

To demonstrate that inhibiting the trabecular meshwork RhoA pathway by delivering a mutated, dominant-negative RhoA gene (dnRhoA) carried inside a long-expressing recombinant virus would reduce nocturnal elevated IOP in a living animal.

DESIGN AND SETTING

We generated an optimized recombinant viral molecule by inserting a mutated RhoA complementary DNA with a translation enhancer-promoter into a specially designed plasmid containing mutated viral terminal repeats. We then generated the virus particle, self-complementary adeno-associated virus serotype 2 carrying the mutated gene (scAAV2.dnRhoA) and assessed its function in vitro by infecting primary human trabecular meshwork cells and in vivo by injecting living rats intracamerally with therapeutic and control viruses. Three different models of 12-hour light and dark cycles were used. Viruses were injected when animals showed the circadian dark IOP elevation. The IOP measurements were conducted with a tonometer at 2 to 4 hours after onset of the nocturnal and diurnal cycles. Values at preinjection time were used as baselines. Animals were euthanized at 4 to 8 weeks after injection.

EXPOSURES

Intraocular injection of rodent eyes with the recombinant viral vector scAAV2.dnRhoA.

MAIN OUTCOMES AND MEASURES

Nocturnal elevation of IOP blocked for prolonged periods by transferred RhoA gene.

RESULTS

By visual inspection, human trabecular meshwork cells infected with scAAV2.dnRhoA showed diminished stress fiber formation. Living rats exhibited a circadian IOP cycle that could be reset by adjusting light conditions to facilitate light and dark nocturnal IOP studies. A single-dose injection of scAAV2.dnRhoA into the rat eyes prevented elevation of IOP during the nocturnal cycle for at least 4 weeks (mean [SE], 9.2 [0.2] mm Hg light IOP and 9.6 [0.4] mm Hg dark IOP), while control eyes showed a significantly higher IOP over baseline (9.5 [0.4] mm Hg light IOP and 13.5 [0.3] mm Hg dark IOP).

CONCLUSIONS AND RELEVANCE

To our knowledge, this is the first example of a gene transfer strategy that prevents nocturnal IOP elevation in living animals for prolonged periods. Inhibiting the RhoA pathway upstream of Rho kinase with a safe gene drug could provide a new enhanced treatment for long-term management of elevated nocturnal IOP.

Mechanical interactions and crosstalk between corneal keratocytes and the extracellular matrix

The generation of cellular forces and the application of these physical forces to the ECM play a central role in mediating matrix patterning and remodeling during fundamental processes such as developmental morphogenesis and wound healing. In addition to growth factors and other biochemical factors that can modulate the keratocyte mechanical phenotype, another key player in the regulation of cell-induced ECM patterning is the mechanical state of the ECM itself. In this review we provide an overview of the biochemical and biophysical factors regulating the mechanical interactions between corneal keratocytes and the stromal ECM at the cellular level. We first provide an overview of how Rho GTPases regulate the sub-cellular pattern of force generation by corneal keratocytes, and the impact these forces have on the surrounding ECM. We next review how feedback from local matrix structural and mechanical properties can modulate keratocyte phenotype and mechanical activity. Throughout this review, we provide examples of how these biophysical interactions may contribute to clinical outcomes, with a focus on corneal wound healing.

Effect of AR-13324 on episcleral venous pressure in Dutch belted rabbits

PURPOSE

AR-13324 is a potential new drug for the treatment of patients with glaucoma that has been shown to lower intraocular pressure (IOP) by increasing trabecular outflow facility and decreasing aqueous production. The present study tested the hypothesis that AR-13324 also lowers IOP by reducing episcleral venous pressure (EVP).

METHODS

In Dutch Belted (DB) rabbits (n=11), arterial pressure (AP), IOP, carotid blood flow (BFcar), heart rate (HR), and EVP were measured invasively. Animals were dosed with AR-13324 (0.04%, topical, n=6) once daily for 3 days. On day 3, the animals were anesthetized, and then, measurements were obtained before dosing with AR-13324 or vehicle (n=5) and for 3 h after dosing. The data (mean±standard error of the mean) were analyzed by repeated measures ANOVA with post hoc testing. Retrospective baseline data from prior similar studies in New Zealand White rabbits were also compiled.

RESULTS

Baseline values were as follows: AP, 101±3 mmHg; IOP; 33±3 mmHg; EVP, 16±1 mmHg; BFcar, 41±4 mL/min; and HR, 330±6 bpm. Three hours after AR-13324 dosing, IOP was reduced by 39%±7% (P<0.001) and EVP decreased by 35%±4% (P<0.05); after vehicle dosing, IOP was reduced by 24%±4% (P<0.05) and EVP increased by 25%±5% (P<0.05). AP, BFcar, and HR were unchanged.

CONCLUSIONS

AR-13324 produces statistically significant lowering of EVP in DB rabbits. In addition, the baseline values for AP, IOP, EVP, BFcar, and HR in the DB rabbit are higher than those previously reported in the New Zealand rabbit.

Pharmacotherapy of glaucoma

Glaucoma is a group of diseases involving the optic nerve and associated structures, which is characterized by progressive visual field loss and typical changes of the optic nerve head (ONH). The only known treatment of the disease is reduction of intraocular pressure (IOP), which has been shown to reduce glaucoma progression in a variety of large-scale clinical trials. Nowadays, a relatively wide array of topical antiglaucoma drugs is available, including prostaglandin analogues, carbonic anhydrase inhibitors, beta-receptor antagonists, adrenergic agonists, and parasympathomimetics. In clinical routine, this allows for individualized treatment taking risk factors, efficacy, and safety into account. A major challenge is related to adherence to therapy. Sustained release devices may help minimize this problem but are not yet available for clinical routine use. Another hope arises from non-IOP-related treatment concepts. In recent years, much knowledge has been gained regarding the molecular mechanisms that underlie the disease process in glaucoma. This also strengthens the hope that glaucoma therapy beyond IOP lowering will become available. Implementing this concept with clinical trials remains, however, a challenge.