Steroid-Induced Ocular Hypertension in Mice Is Differentially Reduced by Selective EP2, EP3, EP4, and IP Prostanoid Receptor Agonists.

We tested five chemically and metabolically stable prostaglandin (PG) receptor agonists in a mouse model of dexamethasone-induced ocular hypertension (OHT). Whilst all compounds significantly (p < 0.05, ANOVA) lowered intraocular pressure (IOP) after twice-daily bilateral topical ocular dosing (5 µg/dose) over three weeks, the time course and magnitude of the responses varied. The onset of action of NS-304 (IP-PG receptor agonist) and rivenprost (EP4-PG receptor agonist) was slower than that of misoprostol (mixed EP2/EP3/EP4-PG receptor agonist), PF-04217329 (EP2-PG receptor agonist), and butaprost (EP2-PG receptor agonist). The rank order of IOP-lowering efficacies aligned with the onset of actions of these compounds. Peak IOP reductions relative to vehicle controls were as follows: misoprostol (74.52%) = PF-04217329 (74.32%) > butaprost (65.2%) > rivenprost (58.4%) > NS-304 (55.3%). A literature survey indicated that few previously evaluated compounds (e.g., latanoprost, timolol, pilocarpine, brimonidine, dorzolamide, cromakalim analog (CKLP1), losartan, tissue plasminogen activator, trans-resveratrol, sodium 4-phenyl acetic acid, etc.) in various animal models of steroid-induced OHT were able to match the effectiveness of misoprostol, PF-04217329 or butaprost. Since a common feature of the latter compounds is their relatively high affinity and potency at the EP2-PG receptor sub-type, which activates the production of intracellular cAMP in target cells, our studies suggest that drugs selective for the EP2-PG receptor may be suited to treat corticosteroid-induced OHT.

Lentiviral mediated delivery of CRISPR/Cas9 reduces intraocular pressure in a mouse model of myocilin glaucoma.

Mutations in myocilin (MYOC) are the leading known genetic cause of primary open-angle glaucoma, responsible for about 4% of all cases. Mutations in MYOC cause a gain-of-function phenotype in which mutant myocilin accumulates in the endoplasmic reticulum (ER) leading to ER stress and trabecular meshwork (TM) cell death. Therefore, knocking out myocilin at the genome level is an ideal strategy to permanently cure the disease. We have previously utilized CRISPR/Cas9 genome editing successfully to target MYOC using adenovirus 5 (Ad5). However, Ad5 is not a suitable vector for clinical use. Here, we sought to determine the efficacy of adeno-associated viruses (AAVs) and lentiviruses (LVs) to target the TM. First, we examined the TM tropism of single-stranded (ss) and self-complimentary (sc) AAV serotypes as well as LV expressing GFP via intravitreal (IVT) and intracameral (IC) injections. We observed that LV_GFP expression was more specific to the TM injected via the IVT route. IC injections of Trp-mutant scAAV2 showed a prominent expression of GFP in the TM. However, robust GFP expression was also observed in the ciliary body and retina. We next constructed lentiviral particles expressing Cas9 and guide RNA (gRNA) targeting MYOC (crMYOC) and transduction of TM cells stably expressing mutant myocilin with LV_crMYOC significantly reduced myocilin accumulation and its associated chronic ER stress. A single IVT injection of LV_crMYOC in Tg-MYOCY437H mice decreased myocilin accumulation in TM and reduced elevated IOP significantly. Together, our data indicates, LV_crMYOC targets MYOC gene editing in TM and rescues a mouse model of myocilin-associated glaucoma.

Viral Vector-Induced Ocular Hypertension in Mice.

Viral transduction of the mouse trabecular meshwork using a variety of transgenes associated with glaucoma generates an inducible and reproducible method for generating ocular hypertension due to increased aqueous humor outflow resistance of the conventional outflow pathway. Both adenovirus serotype 5 (Ad5) and lentiviruses have selective tropism for the mouse trabecular meshwork with intraocular injections. Accurate intraocular pressures are easily measured using a rebound tonometer, and aqueous humor outflow facilities can be measured in anesthetized live mice.

Lentiviral mediated delivery of CRISPR/Cas9 reduces intraocular pressure in a mouse model of myocilin glaucoma.

Mutations in myocilin (MYOC) are the leading known genetic cause of primary open-angle glaucoma, responsible for about 4% of all cases. Mutations in MYOC cause a gain-of-function phenotype in which mutant myocilin accumulates in the endoplasmic reticulum (ER) leading to ER stress and trabecular meshwork (TM) cell death. Therefore, knocking out myocilin at the genome level is an ideal strategy to permanently cure the disease. We have previously utilized CRISPR/Cas9 genome editing successfully to target MYOC using adenovirus 5 (Ad5). However, Ad5 is not a suitable vector for clinical use. Here, we sought to determine the efficacy of adeno-associated viruses (AAVs) and lentiviruses (LVs) to target the TM. First, we examined the TM tropism of single-stranded (ss) and self-complimentary (sc) AAV serotypes as well as LV expressing GFP via intravitreal (IVT) and intracameral (IC) injections. We observed that LV_GFP expression was more specific to the TM injected via the IVT route. IC injections of Trp-mutant scAAV2 showed a prominent expression of GFP in the TM. However, robust GFP expression was also observed in the ciliary body and retina. We next constructed lentiviral particles expressing Cas9 and guide RNA (gRNA) targeting MYOC (crMYOC) and transduction of TM cells stably expressing mutant myocilin with LV_crMYOC significantly reduced myocilin accumulation and its associated chronic ER stress. A single IVT injection of LV_crMYOC in Tg-MYOCY437H mice decreased myocilin accumulation in TM and reduced elevated IOP significantly. Together, our data indicates, LV_crMYOC targets MYOC gene editing in TM and rescues a mouse model of myocilin-associated glaucoma.

A Novel Mouse Model of TGFß2-Induced Ocular Hypertension Using Lentiviral Gene Delivery.

Glaucoma is a multifactorial disease leading to irreversible blindness. Primary open-angle glaucoma (POAG) is the most common form and is associated with the elevation of intraocular pressure (IOP). Reduced aqueous humor (AH) outflow due to trabecular meshwork (TM) dysfunction is responsible for IOP elevation in POAG. Extracellular matrix (ECM) accumulation, actin cytoskeletal reorganization, and stiffening of the TM are associated with increased outflow resistance. Transforming growth factor (TGF) ß2, a profibrotic cytokine, is known to play an important role in the development of ocular hypertension (OHT) in POAG. An appropriate mouse model is critical in understanding the underlying molecular mechanism of TGFß2-induced OHT. To achieve this, TM can be targeted with recombinant viral vectors to express a gene of interest. Lentiviruses (LV) are known for their tropism towards TM with stable transgene expression and low immunogenicity. We, therefore, developed a novel mouse model of IOP elevation using LV gene transfer of active human TGFß2 in the TM. We developed an LV vector-encoding active hTGFß2C226,228S under the control of a cytomegalovirus (CMV) promoter. Adult C57BL/6J mice were injected intravitreally with LV expressing null or hTGFß2C226,228S. We observed a significant increase in IOP 3 weeks post-injection compared to control eyes with an average delta change of 3.3 mmHg. IOP stayed elevated up to 7 weeks post-injection, which correlated with a significant drop in the AH outflow facility (40.36%). Increased expression of active TGFß2 was observed in both AH and anterior segment samples of injected mice. The morphological assessment of the mouse TM region via hematoxylin and eosin (H&E) staining and direct ophthalmoscopy examination revealed no visible signs of inflammation or other ocular abnormalities in the injected eyes. Furthermore, transduction of primary human TM cells with LV_hTGFß2C226,228S exhibited alterations in actin cytoskeleton structures, including the formation of F-actin stress fibers and crossed-linked actin networks (CLANs), which are signature arrangements of actin cytoskeleton observed in the stiffer fibrotic-like TM. Our study demonstrated a mouse model of sustained IOP elevation via lentiviral gene delivery of active hTGFß2C226,228S that induces TM dysfunction and outflow resistance.

Early-Onset Glaucoma in egl1 Mice Homozygous for Pitx2 Mutation.

Mutations in PITX2 cause Axenfeld-Rieger syndrome, with congenital glaucoma as an ocular feature. The egl1 mouse strain carries a chemically induced Pitx2 mutation and develops early-onset glaucoma. In this study, we characterized the glaucomatous features in egl1 mice. The eyes of egl1 and C57BL/6J control mice were assessed by slit lamp examination, total aqueous humor outflow facility, intraocular pressure (IOP) measurement, pattern electroretinography (PERG) recording, and histologic and immunohistochemistry assessment beginning at 3 weeks and up to 12 months of age. The egl1 mice developed elevated IOP as early as 4 weeks old. The IOP elevation was variable and asymmetric within and between the animals. The aqueous humor outflow facility was significantly reduced in 12-month-old animals. PERG detected a decreased response at 2 weeks after the development of IOP elevation. Retinal ganglion cell (RGC) loss was detected after 8 weeks of IOP elevation. Slit lamp and histologic evaluation revealed corneal opacity, iridocorneal adhesions (anterior synechiae), and ciliary body atrophy in egl1 mice. Immunohistochemistry assessment demonstrated glial cell activation and RGC axonal injury in response to IOP elevation. These results show that the eyes of egl1 mice exhibit anterior segment dysgenesis and early-onset glaucoma. The egl1 mouse strain may represent a useful model for the study of congenital glaucoma.

Effect of ATP-sensitive Potassium Channel Openers on Intraocular Pressure in Ocular Hypertensive Animal Models.

Purpose: To evaluate the effect of ATP-sensitive potassium channel openers cromakalim prodrug 1 (CKLP1) and diazoxide on IOP in three independent mouse models of ocular hypertension. Methods: Baseline IOP was measured in TGFß2 overexpression, steroid-induced, and iris dispersion (DBA/2J) ocular hypertension mouse models, followed by once daily eyedrop administration with CKLP1 (5 mM) or diazoxide (5 mM). The IOP was measured in conscious animals with a handheld rebound tonometer. Aqueous humor dynamics were assessed by a constant perfusion method. Effect of treatment on ocular tissues was evaluated by transmission electron microscopy. Results: CKLP1 decreased the IOP by 20% in TGFß2 overexpressing mice (n = 6; P < 0.0001), 24% in steroid-induced ocular hypertensive mice (n = 8; P < 0.0001), and 43% in DBA/2J mice (n = 15; P < 0.0001). Diazoxide decreased the IOP by 32% in mice with steroid-induced ocular hypertension (n = 13; P < 0.0001) and by 41% in DBA/2J mice (n = 4; P = 0.005). An analysis of the aqueous humor dynamics revealed that CKLP1 decreased the episcleral venous pressure by 29% in TGFß2 overexpressing mice (n = 13; P < 0.0001) and by 72% in DBA/2J mice (n = 4 control, 3 treated; P = 0.0002). Diazoxide lowered episcleral venous pressure by 35% in steroid-induced ocular hypertensive mice (n = 3; P = 0.03). Tissue histology and cell morphology appeared normal when compared with controls. Accumulation of extracellular matrix was reduced in CKLP1- and diazoxide-treated eyes in the steroid-induced ocular hypertension model. Conclusions: ATP-sensitive potassium channel openers CKLP1 and diazoxide effectively decreased the IOP in ocular hypertensive animal models by decreasing the episcleral venous pressure, supporting a potential therapeutic application of these agents in ocular hypertension and glaucoma.

Consensus Recommendation for Mouse Models of Ocular Hypertension to Study Aqueous Humor Outflow and Its Mechanisms.

Due to their similarities in anatomy, physiology, and pharmacology to humans, mice are a valuable model system to study the generation and mechanisms modulating conventional outflow resistance and thus intraocular pressure. In addition, mouse models are critical for understanding the complex nature of conventional outflow homeostasis and dysfunction that results in ocular hypertension. In this review, we describe a set of minimum acceptable standards for developing, characterizing, and utilizing mouse models of open-angle ocular hypertension. We expect that this set of standard practices will increase scientific rigor when using mouse models and will better enable researchers to replicate and build upon previous findings.

ID1 and ID3 are Negative Regulators of TGFß2-Induced Ocular Hypertension and Compromised Aqueous Humor Outflow Facility in Mice.

Purpose: In POAG, elevated IOP remains the major risk factor in irreversible vision loss. Increased TGFß2 expression in POAG aqueous humor and in the trabecular meshwork (TM) amplifies extracellular matrix (ECM) deposition and reduces ECM turnover in the TM, leading to a decreased aqueous humor (AH) outflow facility and increased IOP. Inhibitor of DNA binding proteins (ID1 and ID3) inhibit TGFß2-induced fibronectin and PAI-1 production in TM cells. We examined the effects of ID1 and ID3 gene expression on TGFß2-induced ocular hypertension and decreased AH outflow facility in living mouse eyes. Methods: IOP and AH outflow facility changes were determined using a mouse model of Ad5-hTGFß2C226S/C288S-induced ocular hypertension. The physiological function of ID1 and ID3 genes were evaluated using Ad5 viral vectors to enhance or knockdown ID1/ID3 gene expression in the TM of BALB/cJ mice. IOP was measured in conscious mice using a Tonolab impact tonometer. AH outflow facilities were determined by constant flow infusion in live mice. Results: Over-expressing ID1 and ID3 significantly blocked TGFß2-induced ocular hypertension (P < 0.0001). Although AH outflow facility was significantly decreased in TGFß2-transduced eyes (P < 0.04), normal outflow facility was preserved in eyes injected concurrently with ID1 or ID3 along with TGFß2. Knockdown of ID1 or ID3 expression exacerbated TGFß2-induced ocular hypertension. Conclusions: Increased expression of ID1 and ID3 suppressed both TGFß2-elevated IOP and decreased AH outflow facility. ID1 and/or ID3 proteins thus may show promise as future candidates as IOP-lowering targets in POAG.

Impaired TRPV4-eNOS signaling in trabecular meshwork elevates intraocular pressure in glaucoma.

Primary Open Angle Glaucoma (POAG) is the most common form of glaucoma that leads to irreversible vision loss. Dysfunction of trabecular meshwork (TM) tissue, a major regulator of aqueous humor (AH) outflow resistance, is associated with intraocular pressure (IOP) elevation in POAG. However, the underlying pathological mechanisms of TM dysfunction in POAG remain elusive. In this regard, transient receptor potential vanilloid 4 (TRPV4) cation channels are known to be important Ca2+ entry pathways in multiple cell types. Here, we provide direct evidence supporting Ca2+ entry through TRPV4 channels in human TM cells and show that TRPV4 channels in TM cells can be activated by increased fluid flow/shear stress. TM-specific TRPV4 channel knockout in mice elevated IOP, supporting a crucial role for TRPV4 channels in IOP regulation. Pharmacological activation of TRPV4 channels in mouse eyes also improved AH outflow facility and lowered IOP. Importantly, TRPV4 channels activated endothelial nitric oxide synthase (eNOS) in TM cells, and loss of eNOS abrogated TRPV4-induced lowering of IOP. Remarkably, TRPV4-eNOS signaling was significantly more pronounced in TM cells compared to Schlemm's canal cells. Furthermore, glaucomatous human TM cells show impaired activity of TRPV4 channels and disrupted TRPV4-eNOS signaling. Flow/shear stress activation of TRPV4 channels and subsequent NO release were also impaired in glaucomatous primary human TM cells. Together, our studies demonstrate a central role for TRPV4-eNOS signaling in IOP regulation. Our results also provide evidence that impaired TRPV4 channel activity in TM cells contributes to TM dysfunction and elevated IOP in glaucoma.

Nanoencapsulated hybrid compound SA-2 with long-lasting intraocular pressure-lowering activity in rodent eyes.

Purpose: Glaucoma is a neurodegenerative disease of the eye with an estimated prevalence of more than 111.8 million patients worldwide by 2040, with at least 6 to 8 million projected to become bilaterally blind. Clinically, the current method of slowing glaucomatous vision loss is to reduce intraocular pressure (IOP). In this manuscript, we describe the in vitro cytoprotective and in vivo long lasting IOP-lowering activity of the poly D, L-lactic-co-glycolic acid (PLGA) nanoparticle-encapsulated hybrid compound SA-2, possessing nitric oxide (NO) donating and superoxide radical scavenging functionalities. Methods: Previously characterized primary human trabecular meshwork (hTM) cells were used for the study. hTM cells were treated with SA-2 (100 µM, 200 µM, and 1,000 µM), SA-2 PLGA-loaded nanosuspension (SA-2 NPs, 0.1%), or vehicle for 30 min. Cyclic guanosine monophosphate (cGMP) and super oxide dismutase (SOD) levels were analyzed using commercial kits. In another experiment, hTM cells were pretreated with tert-butyl hydrogen peroxide (TBHP, 300 µM) for 30 min followed by treatment with escalating doses of SA-2 for 24 h, and CellTiter 96 cell proliferation assay was performed. For the biodistribution study, the cornea, aqueous humor, vitreous humor, retina, choroid, and sclera were collected after 1 h of administration of a single eye drop (30 µl) of SA-2 NPs (1% w/v) formulated in PBS to rat (n = 6) eyes. Compound SA-2 was quantified using high performance liquid chromatography /mass spectrometry (HPLC/MS). For the IOP-lowering activity study, a single SA-2 NPs (1%) eye drop was instilled in normotensive rats eyes and in the IOP-elevated rat eyes (n = 3/group, in the Morrison model of glaucoma), or Ad5TGFß2-induced ocular hypertensive (OHT) mouse eyes (n = 5/group). IOP was measured at various time points up to 72 h, and the experiment was repeated in triplicate. Mouse aqueous humor outflow facility was determined with multiple flow-rate infusion and episcleral venous pressure estimated with manometry. Results: SA-2 upregulated cGMP levels (six- to ten-fold) with an half maximal effective concentration (EC50) of 20.3 µM in the hTM cells and simultaneously upregulated (40-fold) the SOD enzyme when compared with the vehicle-treated hTM cells. SA-2 also protected hTM cells from TBHP-induced decrease in cell survival with an EC50 of 0.38 µM. A single dose of slow-release SA-2 NPs (1% w/v) delivered as an eye drop significantly lowered IOP (by 30%) in normotensive and OHT rodent eyes after 3 h post-dose, with the effect lasting up to 72 h. A statistically significant increase in aqueous outflow facility and a decrease in episcleral venous pressure was observed in rodents at this dose at 54 h. Conclusions: Hybrid compound SA-2 upregulated cGMP in hTM cells, increased outflow facility and decreased IOP in rodent models of OHT. Compound SA-2 possessing an antioxidant moiety provided additive cytoprotective activity to oxidatively stressed hTM cells by scavenging reactive oxygen species (ROS) and increasing SOD enzyme activity. Additionally, the PLGA nanosuspension formulation (SA-2 NPs) provided longer duration of IOP-lowering activity (up to 3 days) in comparison with the free non-encapsulated SA-2 drug. The data have implications for developing novel, non-prostaglandin therapeutics for IOP-lowering and cytoprotective effects with the possibility of an eye drop dosing regimen of once every 3 days for patients with glaucoma.

Secreted protein acidic and rich in cysteine (SPARC) knockout mice have greater outflow facility.

PURPOSE: Secreted protein acidic and rich in cysteine (SPARC) is a matricellular protein that regulates intraocular pressure (IOP) by altering extracellular matrix (ECM) homeostasis within the trabecular meshwork (TM). We hypothesized that the lower IOP previously observed in SPARC -/- mice is due to a greater outflow facility. METHODS: Mouse outflow facility (Clive) was determined by multiple flow rate infusion, and episcleral venous pressure (Pe) was estimated by manometry. The animals were then euthanized, eliminating aqueous formation rate (Fin) and Pe. The C value was determined again (Cdead) while Fin was reduced to zero. Additional mice were euthanized for immunohistochemistry to analyze ECM components of the TM. RESULTS: The Clive and Cdead of SPARC -/- mice were 0.014 ± 0.002 µL/min/mmHg and 0.015 ± 0.002 µL/min/mmHg, respectively (p = 0.376, N/S). Compared to the Clive = 0.010 ± 0.002 µL/min/mmHg and Cdead = 0.011 ± 0.002 µL/min/mmHg in the WT mice (p = 0.548, N/S), the Clive and Cdead values for the SPARC -/- mice were higher. Pe values were estimated to be 8.0 ± 0.2 mmHg and 8.3 ± 0.7 mmHg in SPARC -/- and WT mice, respectively (p = 0.304, N/S). Uveoscleral outflow (Fu) was 0.019 ± 0.007 µL/min and 0.022 ± 0.006 µL/min for SPARC -/- and WT mice, respectively (p = 0.561, N/S). Fin was 0.114 ± 0.002 µL/min and 0.120 ± 0.016 µL/min for SPARC -/- and WT mice (p = 0.591, N/S). Immunohistochemistry demonstrated decreases of collagen types IV and VI, fibronectin, laminin, PAI-1, and tenascin-C within the TM of SPARC -/- mice (p < 0.05). CONCLUSIONS: The lower IOP of SPARC -/- mice is due to greater aqueous humor outflow facility through the conventional pathway. Corresponding changes in several matricellular proteins and ECM structural components were noted in the TM of SPARC -/- mice.

ATF4 leads to glaucoma by promoting protein synthesis and ER client protein load.

The underlying pathological mechanisms of glaucomatous trabecular meshwork (TM) damage and elevation of intraocular pressure (IOP) are poorly understood. Here, we report that the chronic endoplasmic reticulum (ER) stress-induced ATF4-CHOP-GADD34 pathway is activated in TM of human and mouse glaucoma. Expression of ATF4 in TM promotes aberrant protein synthesis and ER client protein load, leading to TM dysfunction and cell death. These events lead to IOP elevation and glaucomatous neurodegeneration. ATF4 interacts with CHOP and this interaction is essential for IOP elevation. Notably, genetic depletion or pharmacological inhibition of ATF4-CHOP-GADD34 pathway prevents TM cell death and rescues mouse models of glaucoma by reducing protein synthesis and ER client protein load in TM cells. Importantly, glaucomatous TM cells exhibit significantly increased protein synthesis along with induction of ATF4-CHOP-GADD34 pathway. These studies indicate a pathological role of ATF4-CHOP-GADD34 pathway in glaucoma and provide a possible treatment for glaucoma by targeting this pathway.

CNS axonal degeneration and transport deficits at the optic nerve head precede structural and functional loss of retinal ganglion cells in a mouse model of glaucoma.

BACKGROUND: Glaucoma is a leading neurodegenerative disease affecting over 70 million individuals worldwide. Early pathological events of axonal degeneration and retinopathy in response to elevated intraocular pressure (IOP) are limited and not well-defined due to the lack of appropriate animal models that faithfully replicate all the phenotypes of primary open angle glaucoma (POAG), the most common form of glaucoma. Glucocorticoid (GC)-induced ocular hypertension (OHT) and its associated iatrogenic open-angle glaucoma share many features with POAG. Here, we characterized a novel mouse model of GC-induced OHT for glaucomatous neurodegeneration and further explored early pathological events of axonal degeneration in response to elevated IOP. METHODS: C57BL/6 J mice were periocularly injected with either vehicle or the potent GC, dexamethasone 21-acetate (Dex) once a week for 10 weeks. Glaucoma phenotypes including IOP, outflow facility, structural and functional loss of retinal ganglion cells (RGCs), optic nerve (ON) degeneration, gliosis, and anterograde axonal transport deficits were examined at various stages of OHT. RESULTS: Prolonged treatment with Dex leads to glaucoma in mice similar to POAG patients including IOP elevation due to reduced outflow facility and dysfunction of trabecular meshwork, progressive ON degeneration and structural and functional loss of RGCs. Lowering of IOP rescued Dex-induced ON degeneration and RGC loss, suggesting that glaucomatous neurodegeneration is IOP dependent. Also, Dex-induced neurodegeneration was associated with activation of astrocytes, axonal transport deficits, ON demyelination, mitochondrial accumulation and immune cell infiltration in the optic nerve head (ONH) region. Our studies further show that ON degeneration precedes structural and functional loss of RGCs in Dex-treated mice. Axonal damage and transport deficits initiate at the ONH and progress toward the distal end of ON and target regions in the brain (i.e. superior colliculus). Most of anterograde transport was preserved during initial stages of axonal degeneration (30% loss) and complete transport deficits were only observed at the ONH during later stages of severe axonal degeneration (50% loss). CONCLUSIONS: These findings indicate that ON degeneration and transport deficits at the ONH precede RGC structural and functional loss and provide a new potential therapeutic window for rescuing neuronal loss and restoring health of damaged axons in glaucoma.

Effects of TAK-639, a novel topical C-type natriuretic peptide analog, on intraocular pressure and aqueous humor dynamics in mice.

Primary open-angle glaucoma (POAG) is a leading cause of irreversible blindness, and individuals with ocular hypertension are at risk to develop POAG. Currently, the only modifiable risk factor for glaucoma progression is lowering of intraocular pressure (IOP). A novel mechanism for lowering IOP involves activation of the type B natriuretic peptide receptor (NPR-B), the naturally occurring agonist of which is C-type natriuretic peptide (CNP). Being a cyclic peptide of 22 amino acids, CNP does not readily penetrate the cornea and its ocular hypotensive effect requires intraocular injection. TAK-639 is a synthetic, cornea-permeable, 9-amino acid CNP analog has been studied for the treatment of ocular hypertension and POAG. We assessed TAK-639 in a receptor binding profile and the effects of TAK-639 on NPR-B-mediated cyclic GMP production in cultured transformed human trabecular meshwork (TM) cells (GTM-3). We also evaluated the effects of topical ocular administration of TAK-639 on mouse IOP and aqueous humor dynamics. Among 89 non-natriuretic peptide receptors, transporters, and channels evaluated, TAK-639 at 10 µM displaced ligand binding by more than 50% to only two receptors: the type 2 angiotensin receptor (IC50 = 8.2 µM) and the cholecystokinin A receptor (IC50 = 25.8 µM). In vitro, TAK-639 selectively activates NPR-B (EC50 = 61 ±â€¯11 nM; GTM-3 cells) relative to NPR-A (EC50 = 2179 ±â€¯670 nM; 293T cells). In vivo, TAK-639 lowered mouse IOP by three mechanisms: increase in aqueous humor outflow facility (C), reduction in the aqueous humor formation rate (Fin), and reduction in episcleral venous pressure (Pe). The maximum mean IOP decreases from baseline were -12.1%, -21.0%, and -36.1% for 0.1%, 0.3%, and 0.6% doses of TAK-639, respectively. Maximum IOP-lowering effect was seen at 2 h, and the duration of action was >6 h. With TAK-639 0.6%, at 2 h post-dose, aqueous outflow facility (C) increased by 155.8%, Fin decreased by 41.0%, the uveoscleral outflow rate (Fu) decreased by 52.6%, and Pe decreased by 31.5% (all p < 0.05). No ocular adverse effects were observed. TAK-639 is an efficacious IOP-lowering agent, with a unique combination of mechanisms of action on both aqueous formation and aqueous outflow facility. Further study of this mechanism of treatment may optimize pharmacologic outcomes and provide disease management in patients with POAG and ocular hypertension.

Glucocorticoid Receptor Transactivation Is Required for Glucocorticoid-Induced Ocular Hypertension and Glaucoma.

Purpose: Glucocorticoid (GC)-induced ocular hypertension (GC-OHT) is a serious side effect of prolonged GC therapy that can lead to glaucoma and permanent vision loss. GCs cause a plethora of changes in the trabecular meshwork (TM), an ocular tissue that regulates intraocular pressure (IOP). GCs act through the glucocorticoid receptor (GR), and the GR regulates transcription both through transactivation and transrepression. Many of the anti-inflammatory properties of GCs are mediated by GR transrepression, while GR transactivation largely accounts for GC metabolic effects and side effects of GC therapy. There is no evidence showing which of the two mechanisms plays a role in GC-OHT. Methods: GRdim transgenic mice (which have active transrepression and impaired transactivation) and wild-type (WT) C57BL/6J mice received weekly periocular dexamethasone acetate (DEX-Ac) injections. IOP, outflow facilities, and biochemical changes to the TM were determined. Results: GRdim mice did not develop GC-OHT after continued DEX treatment, while WT mice had significantly increased IOP and decreased outflow facilities. Both TM tissue in eyes of DEX-treated GRdim mice and cultured TM cells isolated from GRdim mice had reduced or no change in the expression of fibronectin, myocilin, collagen type I, and α-smooth muscle actin (α-SMA). GRdim mouse TM (MTM) cells also had a significant reduction in DEX-induced cytoskeletal changes, which was clearly seen in WT MTM cells. Conclusions: We provide the first evidence for the role of GR transactivation in regulating GC-mediated gene expression in the TM and in the development of GC-OHT. This discovery suggests a novel therapeutic approach for treating ocular inflammation without causing GC-OHT and glaucoma.

BMP and Activin Membrane Bound Inhibitor Regulates the Extracellular Matrix in the Trabecular Meshwork.

Purpose: The trabecular meshwork (TM) has an important role in the regulation of aqueous humor outflow and IOP. Regulation of the extracellular matrix (ECM) by TGFß2 has been studied extensively. Bone morphogenetic protein (BMP) and activin membrane-bound inhibitor (BAMBI) has been shown to inhibit or modulate TGFß2 signaling. We investigate the role of TGFß2 and BAMBI in the regulation of TM ECM and ocular hypertension. Methods: Mouse TM (MTM) cells were isolated from B6;129S1-Bambitm1Jian/J flox mice, characterized for TGFß2 and dexamethasone (DEX)-induced expression of fibronectin, collagen-1, collagen-4, laminin, α-smooth muscle actin, cross-linked actin networks (CLANs) formation, and DEX-induced myocilin (MYOC) expression. MTM cells were transduced with Ad5.GFP to identify transduction efficiency. MTM cells and mouse eyes were transduced with Ad5.Null, Ad5.Cre, Ad5.TGFß2, or Ad5.TGFß2 + Ad5.Cre to evaluate the effect on ECM production, IOP, and outflow facility. Results: MTM cells express TM markers and respond to DEX and TGFß2. Ad5.GFP at 100 MOI had the highest transduction efficiency. Bambi knockdown by Ad5.Cre and Ad5.TGFß2 increased fibronectin, collagen-1, and collagen-4 in TM cells in culture and tissue. Ad5.Cre, Ad5.TGFß2, and Ad5.TGFß2 + Ad5.Cre each significantly induced ocular hypertension and lowered aqueous humor outflow facility in transduced eyes. Conclusions: We show for the first time to our knowledge that knockdown of Bambi alters ECM expression in cultured cells and mouse TM, reduces outflow facility, and causes ocular hypertension. These data provide a novel insight into the development of glaucomatous TM damage and identify BAMBI as an important regulator of TM ECM and ocular hypertension.

The Role of Wnt/ß-Catenin Signaling and K-Cadherin in the Regulation of Intraocular Pressure.

Purpose: Wnt/ß-catenin signaling in the trabecular meshwork (TM) is required for maintaining normal intraocular pressure (IOP), although the mechanism(s) behind this are unknown. We hypothesize that Wnt/ß-catenin signaling regulates IOP via ß-catenin's effects on cadherin junctions. Methods: Nonglaucomatous primary human TM (NTM) cells were treated with or without 100 ng/ml Wnt3a, 1 µg/ml sFRP1, or both for 4 to 48 hours. Cells were immunostained for ß-catenin, total cadherins, or cadherin isoforms. Membrane proteins or whole-cell lysates were isolated for Western immunoblotting and probed for cadherin isoforms. RNA was extracted for cDNA synthesis and qPCR analysis of cadherin expression. Some NTM cells were cultured on electric plates for cell impedance assays. Ad5.CMV recombinant adenoviruses encoding K-cadherin, and/or sFRP1 were injected into eyes of 4- to 6-month-old female BALB/cJ mice (n = 8-10). Conscious IOPs were assessed for 35 days. Results: Upon Wnt3a treatment, total cadherin expression increased and ß-catenin accumulated at the TM cell membrane and on processes formed between TM cells. qPCR showed that Wnt3a significantly increased K-cadherin expression in NTM cells (P < 0.01, n = 3), and Western immunoblotting showed that Wnt3a increased K-cadherin in NTM cells, which was inhibited by the addition of sFRP1. Cell impedance assays showed that Wnt3a treatment increased transcellular resistance and anti-K-cadherin siRNA decreased transcellular resistance (P < 0.001, n = 4-6). Our in vivo study showed that K-cadherin significantly decreased sFRP1-induced ocular hypertension (P < 0.05, n = 6). Western immunoblotting also showed that K-cadherin alleviated sFRP1-induced ß-catenin decrease in mouse anterior segments. Conclusions: Our results suggest that cadherins play important roles in the regulation of TM homeostasis and IOP via the Wnt/ß-catenin pathway.

Knockout of tissue transglutaminase ameliorates TGFß2-induced ocular hypertension: A novel therapeutic target for glaucoma?

Glaucoma is a vision threatening optic neuropathy that affects millions of people worldwide. In primary open angle, increased intraocular pressure (IOP) is the main risk factor for the development of this disease. Studies investigating the causes and mechanisms of increased IOP show fibrotic changes in the trabecular meshwork (TM) that are different from those of age-matched controls. Tissue transglutaminase (TGM2), an extracellular matrix (ECM) crosslinking enzyme, covalently crosslinks ECM proteins and causes excessive ECM protein deposition in the TM that could cause increased IOP. Previous literature reports increased expression of TGM2 in glaucomatous eyes compared to controls. We recently have shown that overexpression of TGM2 causes increased ECM crosslinking in the TM, increases IOP, and decreases aqueous humor (AH) outflow facility in mouse eyes. Therefore, we wanted to study the effect of TGM2 knockout (KO) on IOP in TGM2 floxed mice. Ad5.Cre transduction caused partial KO of TGM2, which decreased TGM2 expression in the TM region of mouse eyes. TGM2 KO significantly decreased IOP by itself and also in TGFß2 induced ocular hypertensive mice. TGM2 KO also restores the outflow facility in TGFß2 transduced eyes. Overall, TGM2 KO rescued the TGFß2-induced ocular hypertensive phenotype. Thus, TGM2 may offer potential as a new therapeutic target for glaucoma.

Glucocorticoid receptor GRß regulates glucocorticoid-induced ocular hypertension in mice.

Prolonged glucocorticoid (GC) therapy can cause GC-induced ocular hypertension (OHT), which if left untreated progresses to iatrogenic glaucoma and permanent vision loss. The alternatively spliced isoform of glucocorticoid receptor GRß acts as dominant negative regulator of GR activity, and it has been shown that overexpressing GRß in trabecular meshwork (TM) cells inhibits GC-induced glaucomatous damage in TM cells. The purpose of this study was to use viral vectors to selectively overexpress the GRß isoform in the TM of mouse eyes treated with GCs, to precisely dissect the role of GRß in regulating steroid responsiveness. We show that overexpression of GRß inhibits GC effects on MTM cells in vitro and GC-induced OHT in mouse eyes in vivo. Ad5 mediated GRß overexpression reduced the GC induction of fibronectin, collagen 1, and myocilin in TM of mouse eyes both in vitro and in vivo. GRß also reversed DEX-Ac induced IOP elevation, which correlated with increased conventional aqueous humor outflow facility. Thus, GRß overexpression reduces effects caused by GCs and makes cells more resistant to GC treatment. In conclusion, our current work provides the first evidence of the in vivo physiological role of GRß in regulating GC-OHT and GC-mediated gene expression in the TM.