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PurposeWe sought to define the role of Wwtr1 in murine ocular structure and function and determine the role of mechanotransduction in Fuchs' endothelial corneal dystrophy (FECD), with emphasis on interactions between corneal endothelial cells (CEnCs) and Descemet's membrane (DM).MethodsA Wwtr1 deficient mouse colony was established, and advanced ocular imaging, atomic force microscope (AFM), and histology/immunofluorescence were performed. Corneal endothelial wound healing was assessed using cryoinjury and phototherapeutic keratectomy in Wwtr1 deficient mice. Expression of WWTR1/TAZ was determined in the corneal endothelium from normal and FECD-affected patients; WWTR1 was screened for coding sequence variants in this FECD cohort.ResultsMice deficient in Wwtr1 had reduced CEnC density, abnormal CEnC morphology, softer DM, and thinner corneas versus wildtype controls by 2 months of age. Additionally, CEnCs had altered expression and localization of Na/K-ATPase and ZO-1. Further, Wwtr1 deficient mice had impaired CEnC wound healing. The WWTR1 transcript was highly expressed in healthy human CEnCs comparable to other genes implicated in FECD pathogenesis. Although WWTR1 mRNA expression was comparable between healthy and FECD-affected patients, WWTR1/TAZ protein concentrations were higher and localized to the nucleus surrounding guttae. No genetic associations were found in WWTR1 and FECD in a patient cohort compared to controls.ConclusionsThere are common phenotypic abnormalities seen between Wwtr1 deficient and FECD-affected patients, suggesting that Wwtr1 deficient mice could function as a murine model of late-onset FECD. Despite the lack of a genetic association between FECD and WWTR1, aberrant WWTR1/TAZ protein subcellular localization and degradation may play critical roles in the pathogenesis of FECD.

Glucocorticoid-induced glaucoma is a secondary open-angle glaucoma. About 40% of the general population may develop elevated intraocular pressure on prolonged glucocorticoid treatment secondary to damages in the trabecular meshwork (TM), a tissue that regulates intraocular pressure. Therefore, identifying the key molecules responsible for glucocorticoid-induced ocular hypertension is crucial. In this study, Dickkopf-related protein 1 (Dkk1), a canonical Wnt signaling inhibitor, was found to be elevated in the aqueous humor and TM of glaucoma patients. At the signaling level, Dkk1 enhanced glucocorticoid receptor (GR) signaling, whereas Dkk1 knockdown or Wnt signaling activators decreased GR signaling in human TM cells as indicated by luciferase assays. Similarly, activation of the GR signaling inhibited Wnt signaling. At the protein level, glucocorticoid-induced extracellular matrix was inhibited by Wnt activation using Wnt activators or Dkk1 knockdown in primary human TM cells. In contrast, inhibition of canonical Wnt signaling by β-catenin knockdown increased glucocorticoid-induced extracellular matrix proteins. At the physiological level, adenovirus-mediated Wnt3a expression decreased glucocorticoid-induced ocular hypertension in mouse eyes. In summary, Wnt and GR signaling inhibit each other in the TM, and canonical Wnt signaling activators may prevent the adverse effect of glucocorticoids in the eye.

Re-epithelialization of wounds is a critical element of wound closure. Growth factors have been used in combination with conventional wound management to promote closure, but the method of delivery has been limited to the topical application of ointment formulations. Cytoactive factors delivered in this way have short resident times in wounds and have met with limited success. Here, we demonstrate that methods used to covalently immobilize proteins on synthetic materials can be extended to immobilize cytoactive factors such as the epidermal growth factor (EGF) onto the wound beds of genetically diabetic mice that exhibit impaired healing. Full-thickness splinted excisional wounds were created in diabetic (db/db) mice with a well-defined silicone splint to limit wound contracture. Wound surfaces were treated with a reducing agent to expose sulfhydryl groups and subsequently treated with EGF modified with a heterobifunctional crosslinker. This allowed for the covalent immobilization of the EGF to the wound surface. The conjugation chemistry was validated in vitro and in vivo. In a separate group of mice, wounds were topically treated twice daily with soluble EGF. The mice were evaluated over 11 days for wound closure. This covalent immobilization strategy resulted in EGF being retained on the wound surface for 2 days and significantly increased epithelial wound closure by 20% compared to wounds treated with topical EGF or topical vehicle. Covalent immobilization was not only therapeutically effective but also delivered a markedly reduced load of growth factor to the wound surface compared to topical application (when only 180 ng of EGF was immobilized onto the wound surface in comparison with 7200 ng of topically applied EGF over a period of 11 days). No adverse effects were observed in treated wounds. Results obtained provide proof of concept for the effectiveness of covalent immobilization in the treatment of dysregulated wounds. The covalent immobilization of cytoactive factors represents a potentially transformative approach to the management of difficult chronic wounds.

PURPOSE: Cells in the trabecular meshwork sense and respond to a myriad of physical forces through a process known as mechanotransduction. Whilst the effect of substratum stiffness or stretch on TM cells have been investigated in the context of transforming growth factor (TGF-β), Wnt and YAP/TAZ pathways, the role of Notch signaling, an evolutionarily conserved pathway, recently implicated in mechanotransduction, has not been investigated in trabecular meshwork (TM) cells. Here, we compare the endogenous expression of Notch pathway molecules in TM cells from glaucomatous and non-glaucomatous donors, segmental flow regions, and when subjected to cyclical strain, or grown on hydrogels of varying rigidity. METHODS: Primary TM from glaucomatous (GTM), non-glaucomatous (NTM) donors, and from segmental flow regions [high flow (HF), low flow (LF)], were utilized between passages 2-6. Cells were (i) plated on tissue culture plastic, (ii) subjected to cyclical strain (6h and 24h), or (iii) cultured on 3kPa and 80kPa hydrogels. mRNA levels of Notch receptors/ligands/effectors in the TM cells was determined by qRT-PCR. Phagocytosis was determined as a function of substratum stiffness in NTM-HF/LF cells in the presence or absence of 100 nM Dexamethasone treatment. RESULTS: Innate expression of Notch pathway genes were significantly overexpressed in GTM cells with no discernible differences observed between HF/LF cells in either NTM or GTM cells cultured on plastic substrates. With 6h of cyclical strain, a subset of Notch pathway genes presented with altered expression. Expression of Notch receptors/ligands/receptors/inhibitors progressively declined with increasing stiffness and this correlated with phagocytic ability of NTM cells. Dexamethasone treatment decreased phagocytosis regardless of stiffness or cells isolated from segmental outflow regions. CONCLUSIONS: We demonstrate here that the Notch expression in cultured TM cells differ intrinsically between GTM vs NTM, and by substratum cues (cyclical strain and stiffness). Of import, the most apparent differences in gene expression were observed as a function of substratum stiffness which closely followed phagocytic ability of cells. Interestingly, on soft substrates (mimicking normal TM stiffness) Notch expression and phagocytosis was highest, while both expression and phagocytosis was significantly lower on stiffer substrates (mimicking glaucomatous stiffness) regardless of DEX treatment. Such context dependent changes suggest Notch pathway may play differing roles in disease vs homeostasis. Studies focused on understanding the mechanistic role of Notch (if any) in outflow homeostasis are thus warranted.

Electrochemical devices that transform electrical energy to mechanical energy through an electrochemical process have numerous applications ranging from soft robotics and micropumps to autofocus microlenses and bioelectronics. To date, achievement of large deformation strains and fast response times remains a challenge for electrochemical actuator devices operating in liquid wherein drag forces restrict the actuator motion and electrode materials/structures limit the ion transportation and accumulation. We report results for electrochemical actuators, electrochemical mass transfers, and electrochemical dynamics made from organic semiconductors (OSNTs). Our OSNTs electrochemical device exhibits high actuation performance with fast ion transport and accumulation and tunable dynamics in liquid and gel-polymer electrolytes. This device demonstrates an excellent performance, including low power consumption/strain, a large deformation, fast response, and excellent actuation stability. This outstanding performance stems from enormous effective surface area of nanotubular structure that facilitates ion transport and accumulation resulting in high electroactivity and durability. We utilize experimental studies of motion and mass transport along with the theoretical analysis for a variable–mass system to establish the dynamics of the electrochemical device and to introduce a modified form of Euler-Bernoulli’s deflection equation for the OSNTs. Ultimately, we demonstrate a state-of-the-art miniaturized device composed of multiple microactuators for potential biomedical application. This work provides new opportunities for next generation electrochemical devices that can be utilized in artificial muscles and biomedical devices.

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

Early-onset Fuchs endothelial corneal dystrophy (FECD) has been associated with nonsynonymous mutations in collagen VIII α2 (COL8A2), a key extracellular matrix (ECM) protein in Descemet’s membrane (DM). Two knock-in strains of mice have been generated to each express a mutant COL8A2 protein (Col8a2(L450W/L450W) and Col8a2(Q455K/Q455K)) that recapitulate the clinical phenotype of early-onset FECD including endothelial cell loss, cellular polymegathism and pleomorphism, and guttae. Due to abnormalities in ECM protein composition and structure in FECD, the stiffness of DM in Col8a2 knock-in mice and wildtype (WT) controls was measured using atomic force microscopy at 5 and 10 months of age, coinciding with the onset of FECD phenotypic abnormalities. At 5 months, only sporadic guttae were identified via in vivo confocal microscopy (IVCM) in Col8a2(Q455K/Q455K) mice, otherwise both strains of Col8a2 transgenic mice were indistinguishable from WT controls in terms of endothelial cell density and size. By 10 months of age, Col8a2(L450W/L450W) and Col8a2(Q455K/Q455K) mice developed reduced corneal endothelial density, increased endothelial cell area and guttae, with the Col8a2(Q455K/Q455K) strain exhibiting a more severe phenotype. However, at 5 months of age, prior to the development endothelial cell abnormalities, Col8a2(L450W/L450W) and Col8a2(Q455K/Q455K) mice knock-in mice had reduced tissue stiffness of DM that was statistically significant in the Col8a2(Q455K/Q455K) mice when compared with wildtype controls. These data indicate that alterations in the tissue compliance of DM precede phenotypic changes in endothelial cell count and morphology and may play a role in onset and progression of FECD.

Purpose: To identify the effects of a single copy deletion of Yap1 (Yap1+/−) in the mouse eye, the ocular phenotypic consequences of Yap1+/− were determined in detail. Methods: Complete ophthalmic examinations, as well as corneal esthesiometry, the phenol red thread test, intraocular pressure, and Fourier-domain optical coherence tomography were performed on Yap1+/− and age-matched wild-type (WT) mice between eyelid opening (2 weeks after birth) and adulthood (2 months and 1 year after birth). Following euthanasia, enucleated eyes were characterized histologically. Results: Microphthalmia with small palpebral fissures, corneal fibrosis, and reduced corneal sensation were common findings in the Yap1+/− mice. Generalized corneal fibrosis precluded clinical examination of the posterior structures. Histologically, thinning and keratinization of the corneal epithelium were observed in the Yap1+/− mice in comparison with the WT mice. Distorted collagen fiber arrangement and hypercellularity of keratocytes were observed in the stroma. Descemet’s membrane was extremely thin and lacked an endothelial layer in the Yap1+/− mice. The iris was adherent to the posterior cornea along most of its surface creating a distorted contour. Most of the Yap1+/− eyes were microphakic with swollen fibers and bladder cells. The retinas of the Yap1+/− mice were normal at 2 weeks and 2 months of age, but the presence of retinal abnormalities, including retinoschisis and detachment, was markedly increased in the Yap1+/− mice at 1 year of age. Conclusions: The results show that the heterozygous deletion of the Yap1 gene in mice leads to complex ocular abnormalities, including microphthalmia, corneal fibrosis, anterior segment dysgenesis, and cataract.

The transformation of quiescent keratocytes to activated fibroblasts and myofibroblasts (KFM transformation) largely depends on transforming growth factor beta (TGFβ) signaling. Initiation of the TGFβ signaling cascade results from binding of TGFβ to the labile type I TGFβ receptor (TGFβRI), which is stabilized by the 90 kDa heat shock protein (Hsp90). Since myofibroblast persistence within the corneal stroma can result in stromal haze and corneal fibrosis in patients undergoing keratorefractive therapy, modulation of TGFβ signaling through Hsp90 inhibition would represent a novel approach to prevent myofibroblast persistence. In vitro, rabbit corneal fibroblasts (RCFs) or stratified immortalized human corneal epithelial cells (hTCEpi) were treated with a Hsp90 inhibitor (17AAG) in the presence/absence of TGFβ1. RCFs were cultured either on tissue culture plastic, anisotropically patterned substrates, and hydrogels of varying stiffness. Cellular responses to both cytoactive and variable substrates were assessed by morphologic changes to the cells, and alterations in expression patterns of key keratocyte and myofibroblast proteins using PCR, Western blotting and immunocytochemistry. Transepithelial electrical resistance (TEER) measurements were performed to establish epithelial barrier integrity. In vivo, the corneas of New Zealand White rabbits were wounded by phototherapeutic keratectomy (PTK) and treated with 17AAG (3× or 6× daily) either immediately or 7 days after wounding for 28 days. Rabbits underwent clinical ophthalmic examinations, SPOTS scoring and advanced imaging on days 0, 1, 3, 7, 10, 14, 21 and 28. On day 28, rabbits were euthanized and histopathology/immunohistochemistry was performed. In vitro data demonstrated that 17AAG inhibited KFM transformation with the de-differentiation of spindle shaped myofibroblasts to dendritic keratocyte-like cells accompanied by significant upregulation of corneal crystallins and suppression of myofibroblast markers regardless of TGFβ1 treatment. RCFs cultured on soft hydrogels or patterned substrates exhibited elevated expression of α-smooth muscle actin (αSMA) in the presence of 17AAG. Treatment of hTCEpi cells disrupted zonula occludens 1 (ZO-1) adherens junction formation. In vivo, there were no differences detected in nearly all clinical parameters assessed between treatment groups. However, rabbits treated with 17AAG developed greater stromal haze formation compared with controls, irrespective of frequency of administration. Lastly, there was increased αSMA positive myofibroblasts in the stroma of 17AAG treated animals when compared with controls. Hsp90 inhibition promoted reversion of the myofibroblast to keratocyte phenotype, although this only occurred on rigid substrates. By contrast, in vivo Hsp90 inhibition was detrimental to corneal wound healing likely due to impairment in corneal epithelial closure and barrier function restoration. Collectively, our data demonstrated a strong interplay in vitro between biophysical cues and soluble signaling molecules in determining corneal stromal cell phenotype.

Glaucoma is a multi-factorial disease often associated with elevated intraocular pressure and increased rigidity of the trabecular meshwork (TM). Stiffening of inner wall endothelial cells of the Schlemm’s canal (SC) has also been documented with glaucoma. Such stiffening is often associated with changes in the extracellular matrix and thus plays a critical role in maintenance of aqueous outflow homeostasis. Considering that biomechanics and topographical cues from the matrix significantly influence cellular responses, it is imperative to understand the biomechanical attributes of the TM. Here, we review relevant studies that have measured the elastic moduli of the TM from humans and a variety of non-human animal models including the various methods used. The reported elastic moduli vary from kilopascal to megapascal range depending on the method utilized in excised tissues. Multiple attempts are currently underway for in vivo quantifications which would significantly be beneficial for diagnosis of the disease. We conclude the chapter by discussing briefly the cellular consequences to the dynamically changing matrix stiffness and its implication in disease etiology and progression.

Purpose The purpose of this study was to determine whether genipin-induced crosslinked cell-derived matrix (XCDM) precipitates fibrotic phenotypes in human trabecular meshwork (hTM) cells by dysregulating β-catenin and Yes-associated protein (YAP)/ transcriptional coactivator with PDZ-binding motif (TAZ) signaling pathways. Methods Cell-derived matrices were treated with control or genipin for 5 hours to obtain respective uncrosslinked (CDM) and XCDMs and characterized. hTM cells were seeded on these matrices with/without Wnt pathway modulators in serum-free media for 24 hours. Elastic modulus, gene, and protein (whole cell and subcellular fractions) expressions of signaling mediators and targets of Wnt/β-catenin and YAP/TAZ pathways were determined. Results At the highest genipin concentration (10% XCDM), XCDM had increased immunostaining of N-e(γ-glutamyl)-lysine crosslinks, appeared morphologically fused, and was stiffer (5.3-fold, P < 0.001). On 10% XCDM, hTM cells were 7.8-fold (P < 0.001) stiffer, total β-catenin was unchanged, pβ-catenin was elevated, and pGSK3β was suppressed. Although 10% XCDM had no effect on cytoplasmic β-catenin levels, it reduced nuclear β-catenin, cadherin 11, and key Wnt target genes/proteins. The 10% XCDM increased total TAZ, decreased pTAZ, and increased cytoplasmic TAZ levels in hTM cells. The 10% XCDM increased total YAP, reduced nuclear YAP levels, and critical YAP/TAZ target genes/proteins. Wnt activation rescued hTM cells from 10% XCDM-induced stiffening associated with increased nuclear β-catenin. Conclusions Increased cytoplasmic TAZ may inhibit β-catenin from its nuclear shuttling or regulating cadherin 11 important for aqueous homeostasis. Elevated cytoplasmic TAZ may inhibit YAP's probable homeostatic function in the nucleus. Together, TAZ's cytoplasmic localization may be an important downstream event of how increased TM extracellular matrix (ECM) crosslinking may cause increased stiffness and ocular hypertension in vivo. However, Wnt pathway activation may ameliorate ocular hypertensive phenotypes induced by crosslinked ECM.

Progressive corneal endothelial disease eventually leads to corneal edema and vision loss due to the limited regenerative capacity of the corneal endothelium in vivo and is a major indication for corneal transplantation. Despite the relatively high success rate of corneal transplantation, there remains a pressing global clinical need to identify improved therapeutic strategies to address this debilitating condition. To evaluate the safety and efficacy of novel therapeutics, there is a growing demand for pre-clinical animal models of corneal endothelial dysfunction. In this review, experimentally induced, spontaneously occurring and genetically modified animal models of corneal endothelial dysfunction are described to assist researchers in making informed decisions regarding the selection of the most appropriate animal models to meet their research goals.

Purpose Glycosaminoglycans (GAGs) are important components of the corneal stroma, and their spatiotemporal arrangement regulates the organization of collagen fibrils and maintains corneal transparency. This study was undertaken to determine the consequences of hyaluronidase (HAse) injected into the corneal stroma on stromal stiffness and ultrastructure. Methods Equal volumes of HAse or balanced salt solution (vehicle) were injected intrastromally into the corneas of New Zealand white rabbits. Ophthalmic examination and multimodal imaging techniques, including Fourier-domain optical coherence tomography and in vivo confocal microscopy (IVCM), were performed at multiple time points to evaluate the impact of HAse treatment in vivo. Atomic force microscopy and transmission electron microscopy (TEM) were used to measure corneal stiffness and collagen's interfibrillar spacing, respectively. Results Central corneal thickness progressively decreased after HAse injection, reaching its lowest value at day 7, and then returned to normal by day 42. The HAse did not impact the corneal endothelium but transiently altered keratocyte morphology at days 1 and 7, as measured by IVCM. HAse-injected corneas became stiffer by day 1 postinjection, were stiffest at day 7, and returned to preinjection values by day 90. Changes in stromal stiffness correlated with decreased interfibrillar spacing as measured by TEM. Conclusions Degradation of GAGs by HAse decreases the corneal thickness and increases stromal stiffness through increased packing of the collagen fibrils in a time-dependent manner. Translational relevance Intrastromal HAse injection appears relatively safe in the normal cornea, but its impact on corneal biomechanics and structure under pathologic conditions requires further study.

Redox state sustained by reactive oxygen species (ROS) is crucial for regeneration; however, the interplay between oxygen (O2), ROS and hypoxia-inducible factors (HIF) remains elusive. Here we observe, using an optic-based probe (optrode), an elevated and steady O2 influx immediately upon amputation. The spatiotemporal O2 influx profile correlates with the regeneration of Xenopus laevis tadpole tails. Inhibition of ROS production but not ROS scavenging decreases O2 influx. Inhibition of HIF-1α impairs regeneration and stabilization of HIF-1α induces regeneration in the refractory period. In the regeneration bud, hypoxia correlates with O2 influx, ROS production, and HIF-1α stabilization that modulate regeneration. Further analyses reveal that heat shock protein 90 is a putative downstream target of HIF-1α while electric current reversal is a de facto downstream target of HIF-1α. Collectively, the results show a mechanism for regeneration via the orchestration of O2 influx, ROS production, and HIF-1α stabilization., Reactive oxygen species (ROS) and hypoxia-inducible factors (HIF) mediate regeneration but how is unclear. Here, the authors use an optic-based probe (‘optrode’) to monitor oxygen (O2) during Xenopus tail regeneration, identifying crosstalk between O2 influx, ROS production, and HIF-1α stabilization.

Purpose\ud To develop a mechanical model in which a contact lens is swept over ocular surface cells under conditions that mimic the force and speed of the blink, and to investigate the resulting biological changes.\ud \ud Methods\ud A computer controlled mechanical instrument was developed to hold a dish containing 3D cultured stratified human ocular surface epithelial cells, across which an arm bearing a contact lens was swept back and forth repeatedly at a speed and force mimicking the human blink. Cells were subjected to repeated sweep cycles for up to 1 h at a speed of 120 mm/s with or without an applied force of 19.6 mN (to mimic pressure exerted by upper eyelid), after which the cell layer thickness was measured, the cell layer integrity was investigated using fluorescent quantum dots (6 and 13 nm) and the phosphorylation levels of various protein kinases were analyzed by human phospho-kinase arrays. Data for selected kinases were further quantitated by enzyme immunoassays.\ud \ud Results\ud The thickness of the cell layers did not change after exposure to sweep cycles with or without applied force. Quantum dots (6 and 13 nm) were able to penetrate the layers of cells exposed to sweep cycles but not layers of untreated control cells. The phosphorylation levels of HSP27 and JNK1/2/3 increased for cells exposed to sweep cycles with applied force compared to untreated control cells.\ud \ud Conclusions\ud The in vitro mechanical instrument is a useful tool to investigate the effects of blinking on the ocular surface.

Ocular hypertension is a causal risk-factor to developing glaucoma. This is associated with stiffening of the trabecular meshwork (TM), the primary site of resistance to aqueous-humor-outflow. The mechanisms underlying this stiffening or how pathologic extracellular matrix (ECM) affects cell function are poorly understood. It is recognized that mechanotransduction systems allow cells to sense and translate the intrinsic biophysical properties of ECM into intracellular signals to control gene transcription, protein expression, and cell behavior. Using an anterior segment perfusion model, we document that there are significantly more low flow regions that are much stiffer, and fewer high flow regions that are less stiff in glaucomatous TM (GTM) when compared to non-glaucomatous TMs (NTM). GTM tissue also has fewer cells overall when compared with NTM tissue. In order to study the role of pathologic ECM in glaucoma disease progression, we conducted studies using cell derived matrices (CDM). First, we characterized the mechanics, composition and organization of fibronectin in ECM deposited by GTM and NTM cells treated with glucocorticosteroids. Then, we determined that these GTM-derived ECM are able to induce stiffening of normal NTM cells, and alter their gene/protein expression to resemble that of a glaucomatous phenotype. Further, we demonstrate that GTM-derived ECM causes endoplasmic reticular stress in NTM. They also became resistant to being reorganized by these NTM cells. These phenomena were exacerbated by ECMs obtained from steroid treated glaucoma model groups. Collectively, our data demonstrates that CDMs represent a novel tool for the study of bidirectional interactions between TM cells and their immediate microenvironment. Statement of Significance Extracellular matrix (ECM) changes are prevalent in a number of diseases. The precise mechanisms by which changes in the ECM contribute to disease progression is unclear, primarily due to absence of appropriate models. Here, using glaucoma as a disease model, we document changes in cell derived matrix (CDM) and tissue mechanics that contribute to the pathology. Subsequently, we determine the effect that ECMs from diseased and healthy individuals have on healthy cell behaviors. Data emanating from this study demonstrate that CDMs are a potent tool for the study of cell-ECM interactions.

The human anterior segment perfusion culture model is a valuable tool for studying the trabecular meshwork (TM) and aqueous humor outflow in glaucoma. The traditional model relies on whole eye globes resulting in high cost and limited availability. Here, we developed a glue-based method which enabled us to use human corneal rims for perfusion culture experiments. Human corneal rim perfusion culture plates were 3D printed. Human corneal rims containing intact TM were attached and sealed to the plate using low viscosity and high viscosity glues, respectively. The human corneal rims were perfused using the constant flow mode, and the pressure changes were recorded using a computerized system. Outflow facility, TM stiffness, and TM morphology were evaluated. When perfused at rates from 1.2 to 3.6 μl/min, the outflow facility was 0.359 ± 0.216 μl/min/mmHg among 10 human corneal rims. The stiffness of the TM in naïve human corneal rim was similar to that of perfusion cultured human corneal rim. Also, the stiffness of TM of corneal rims perfused with dexamethasone was significantly higher than the control. Human corneal rims with glue contamination in the TM could be differentiated by high baseline intraocular pressure as well as high TM stiffness. Histology studies showed that the TM tissues perfused with plain medium appeared normal. We believed that our glued-based method is a useful tool and low-cost alternative to the traditional anterior segment perfusion culture model.

Ocular hypertension has been attributed to increased resistance to aqueous outflow often as a result of changes in trabecular meshwork (TM) extracellular matrix (ECM) using in vivo animal models (for example, by genetic manipulation) and ex vivo anterior segment perfusion organ cultures. These are, however, complex and difficult in dissecting molecular mechanisms and interactions. In vitro approaches to mimic the underlying substrate exist by manipulating either ECM topography, mechanics, or chemistry. These models best investigate the role of individual ECM protein(s) and/or substrate property, and thus do not recapitulate the multi-factorial extracellular microenvironment; hence, mitigating its physiological relevance for mechanistic studies. Cell-derived matrices (CDMs), however, are capable of presenting a 3D-microenvironment rich in topography, chemistry, and whose mechanics can be tuned to better represent the network of native ECM constituents in vivo. Critically, the composition of CDMs may also be fine-tuned by addition of small molecules or relevant bioactive factors to mimic homeostasis or pathology. Here, we first provide a streamlined protocol for generating CDMs from TM cell cultures from normal or glaucomatous donor tissues. Second, we document how TM cells can be pharmacologically manipulated to obtain glucocorticoid-induced CDMs and how generated pristine CDMs can be manipulated with reagents like genipin. Finally, we summarize how CDMs may be used in mechanistic studies and discuss their probable application in future TM regenerative studies.

The cornea is the most external layer of the eye and serves two important roles in (1) the refraction of light and (2) protection from the outside environment, both of which are highly dependent on the collagen assembly of the corneal stroma. This study sought to determine the collagen fiber arrangement of the canine corneal stroma and correlate the stromal organization with tissue stiffness in the anterior and posterior cornea. Collagen organization of the canine cornea was visualized through second-harmonic generation (SHG) imaging, and tissue stiffness of the anterior and posterior corneal stroma was determined by atomic force microscopy. Analysis of the canine anterior corneal stroma using SHG imaging documented intertwining of the collagen fibers with a high degree of fiber branching, with a more lamellar and non-branching posterior stroma. The anterior stroma had significantly higher tissue stiffness in both dogs and humans, when compared with the posterior corneal stroma (canine median: 1.3 kPa vs. 0.3 kPa, human median: 14.6 kPa vs. 2.1 kPa, respectively). There was a direct correlation between corneal collagen stromal organization and tissue stiffness in the dog, which was consistent with other mammalian species previously examined and likely reflects the need for maintenance of rigidity and corneal curvature.

Elevated intraocular pressure (IOP) is the primary risk factor for glaucoma and is the only treatable feature of the disease. There is a correlation between elevated pressure and homeostatic reductions in the aqueous humor outflow resistance via changes in the extracellular matrix of the trabecular meshwork. It is unclear how these extracellular matrix changes affect segmental patterns of aqueous humor outflow, nor do we understand their causal relationship. The goal of this study was to determine whether there are changes in the segmental outflow regions with perfusion in normal eyes, and whether these regions change during the IOP homeostatic response to elevated pressure. Using human anterior segment perfusion organ culture, we measured the amount of high flow (HF), intermediate flow (MF), and low flow (LF) regions before and after 7 days of perfusion at either physiologic pressure ("1x") or at elevated pressure ("2x"). We found a small but significant decrease in the amount of HF regions over 7 days perfusion at 1x pressure, and a twofold increase in the amount of MF regions over 7 days perfusion at 2x pressure. Small positional differences, or shifts in the specific location of HF, MF, or LF, occurred on a per eye basis and were not found to be statistically significant across biological replicates. Differences in the amount of segmental flow regions of contralateral eyes flowed at 1x pressure for 7 days were small and not statistically significant. These results demonstrate that perfusion at physiologic pressure had little effect on the distribution and amount of HF, MF and LF regions. However, the overall amount of MF regions is significantly increased in response to perfusion at elevated pressure during IOP homeostatic resistance adjustment. The amount of both HF and LF regions was decreased accordingly suggesting a coordinated response in the TM to elevated pressure.

Glaucoma remains only partially understood, particularly at the level of intraocular pressure (IOP) regulation. Trabecular meshwork (TM) and Schlemm's canal inner wall endothelium (SCE) are key to IOP regulation and their characteristics and behavior are the focus of much investigation. This is becoming more apparent with time. We and others have studied the TM and SCE's extracellular matrix (ECM) extensively and unraveled much about its functions and role in regulating aqueous outflow. Ongoing ECM turnover is required to maintain IOP regulation and several TM ECM manipulations modulate outflow facility. We have established clearly that the outflow pathway senses sustained pressure deviations and responds by adjusting the outflow resistance correctively to keep IOP within an appropriately narrow range which will not normally damage the optic nerve. The glaucomatous outflow pathway has in many cases lost this IOP homeostatic response, apparently due at least in part, to loss of TM cells. Depletion of TM cells eliminates the IOP homeostatic response, while restoration of TM cells restores it. Aqueous outflow is not homogeneous, but rather segmental with regions of high, intermediate and low flow. In general, glaucomatous eyes have more low flow regions than normal eyes. There are distinctive molecular differences between high and low flow regions, and during the response to an IOP homeostatic pressure challenge, additional changes in segmental molecular composition occur. In conjunction with these changes, the biomechanical properties of the juxtacanalicular (JCT) segmental regions are different, with low flow regions being stiffer than high flow regions. The JCT ECM of glaucomatous eyes is around 20 times stiffer than in normal eyes. The aqueous humor outflow resistance has been studied extensively, but neither the exact molecular components that comprise the resistance nor their exact location have been established. Our hypothetical model, based on considerable available data, posits that the continuous SCE basal lamina, which lies between 125 and 500 nm beneath the SCE basal surface, is the primary source of normal resistance. On the surface of JCT cells, small and highly controlled focal degradation of its components by podosome- or invadopodia-like structures, PILS, occurs in response to pressure-induced mechanical stretching. Sub-micron sized basement membrane discontinuities develop in the SCE basement membrane and these discontinuities allow passage of aqueous humor to and through SCE giant vacuoles and pores. JCT cells then relocate versican with its highly charged glycosaminoglycan side chains into the discontinuities and by manipulation of their orientation and concentration, the JCT and perhaps the SCE cells regulate the amount of fluid passage. Testing this outflow resistance hypothesis is ongoing in our lab and has the potential to advance our understanding of IOP regulation and of glaucoma.

The posterior face of the cornea consists of the corneal endothelium, a monolayer of cuboidal cells that secrete and attach to Descemet’s membrane, an exaggerated basement membrane. Dysfunction of the endothelium compromises the barrier and pump functions of this layer that maintain corneal deturgesence. A large number of corneal endothelial dystrophies feature irregularities in Descemet’s membrane, suggesting that cells create and respond to the biophysical signals offered by their underlying matrix. This review provides an overview of the bidirectional relationship between Descemet’s membrane and the corneal endothelium. Several experimental methods have characterized a richly topographic and compliant biophysical microenvironment presented by the posterior surface of Descemet’s membrane, as well as the ultrastructure and composition of the membrane as it builds during a lifetime. We highlight the signaling pathways involved in the mechanotransduction of biophysical cues that influence cell behavior. We present the specific example of Fuchs’ Corneal Endothelial Dystrophy as a condition in which a dysregulated Descemet’s membrane may influence the progression of disease. Finally, we discuss some disease models and regenerative strategies that may facilitate improved treatments for corneal dystrophies.

Purpose Lysophosphatidic acid (LPA) and soluble interleukin-6 receptor (sIL6R) are elevated in primary open angle glaucoma (POAG). LPA and IL6 modulate in response to biomechanical stimuli and converge on similar fibrotic phenotypes. Thus, we determined whether LPA and IL6 trans-signaling (IL6/sIL6R) interact via Yes-associated protein (YAP)/Transcriptional coactivator with a PDZ-binding motif (TAZ) or Signal transducer and activator of transcription 3 (STAT3) pathways in human trabecular meshwork (hTM) cells. Methods Confluent primary hTM cells were serum starved for 24 hours, and treated with vehicle, LPA (20 µM), IL6 (100 ng/mL)/sIL6R (200 ng/mL), or both (LPA + IL6/sIL6R) for 24 hours, with or without a YAP inhibitor (verteporfin; 2 µM) or STAT3 inhibitor (2 µM). Expression of key receptors and ligands, signaling mediators, actomyosin machinery, cell contractility, and extracellular matrix (ECM) targets of both signaling pathways was determined by immunocytochemistry, RT-qPCR, and Western blotting. Results LPA and IL6 trans-signaling coupling overexpressed/activated receptors and ligands, glycoprotein-130, IL6, and autotaxin; signaling mediators, YAP, TAZ, Pan-TEAD, and phosphorylated STAT3 (pSTAT3); actomyosin and contractile machinery components, myosin light chain 2 (MLC2), phosphorylated MLC2, rho-associated protein kinase 1, filamentous actin, and α-smooth muscle actin; and fibrotic ECM proteins, collagen I and IV, fibronectin, laminin, cysteine-rich angiogenic inducer 61, and connective tissue growth factor in hTM cells; mostly beyond LPA or IL6 trans-signaling alone. Verteporfin inhibited YAP, TAZ, and pSTAT3, with concomitant abrogation of aforementioned fibrotic targets; the STAT3 inhibitor was only partially effective. Conclusions These data suggest synergistic crosstalk between LPA and IL6 trans-signaling, mediated by YAP, TAZ, and pSTAT3. By completely inhibiting these mediators, verteporfin may be more efficacious in ameliorating LPA and/or IL6 trans-signaling-induced ocular hypertensive phenotypes in hTM cells.

Purpose To determine the temporal effects of dexamethasone (DEX) and glucocorticoid-induced matrix (GIM) on integrins/integrin adhesomes, caveolins, cytoskeletal-related proteins, and stiffness in human trabecular meshwork (hTM) cells. Methods Primary hTM cells were plated on plastic dishes (TCP), treated with vehicle (Veh) or 100 nM DEX in 1% serum media for 1, 3, 5, and 7 day(s). Concurrently, hTM cells were also plated on vehicle control matrices (VehMs) and GIMs for similar time points; VehMs and GIMs had been generated from chronic cultures of Veh-/DEX-stimulated hTM cells and characterized biochemically. Subsets of cells prior to plating on TCP or VehMs / GIMs served as baseline. Protein expression of mechanoreceptors, cytoskeletal-related proteins, and elastic moduli of hTM cells were determined. Results Compared with Veh, DEX temporally overexpressed αV, β3, and β5 integrins from day 3 to day 7, and integrin linked kinase at day 7, in hTM cells. However, DEX decreased β1 integrin at day 1 and day 7, while increasing Cavin1 at day 7, in a time-independent manner. Further, DEX temporally upregulated α-smooth muscle actin(α-SMA) and RhoA at day 7 and day 5, respectively; while temporally downregulating Cdc42 at day 3 and day 7 in hTM cells. Conversely, GIM showed increased immunostaining of fibronectin extra-domain A and B isoforms. Compared with VehM, GIM temporally increased αV integrin, Cavin1, and RhoA from day 3 to day 7, at day 3 and day 7, and at day 5, respectively, in hTM cells. Further, GIM overexpressed α-SMA at day 3 and day 7, and stiffened hTM cells from day 1 to day 7, in a time-independent fashion. Conclusions Our data highlight crucial mechanoreceptors, integrin adhesomes, and actin-related proteins that may temporally sustain fibrotic phenotypes precipitated by DEX and/or GIM in hTM cells.

Segmental flow in the human trabecular meshwork is a well-documented phenomenon but in depth mechanistic investigations of high flow (HF) and low flow (LF) regions are restricted due to the small amount of tissue available from a single donor. To address this issue we have generated and characterized multiple paired HF and LF cell strains. Here paired HF and LF cell strains were generated from single donors. Cells were characterized for growth and proliferation, as well as gene and protein expression of potential segmental region markers. Cells isolated from HF and LF regions have similar growth and proliferation rates. Gene expression data reveals vascular cell adhesion protein 1 (VCAM1), thrombospondin 2 (THBS2), and tissue inhibitor of metalloproteinase 1 (TIMP1) are potential markers of LF cells in vitro. Protein expression of VCAM1, THBS2 and TIMP1 are complex and may reflect the dynamic nature of the TM. Initial protein expression levels of these genes is either similar between HF and LF cells (VCAM1, THBS2), or higher in HF compared to LF in some strains (TIMP1). However, after long term culture LF cells express higher levels of VCAM1, TIMP1 and THBS2 protein compared to HF cells. HF and LF cell strains are a powerful new tool that enable understanding segmental flow allowing for multiple experiments on the same genetic background.

Purpose Wnt is a spatiotemporally regulated signaling pathway whose inhibition is associated with glaucoma, elevated intraocular pressure (IOP), and cell stiffening. Whether such changes are permanent or may be reversed is unclear. Here, we determine if activation of Wnt pathway after inhibition reverses the pathologic phenotype. Methods Primary human trabecular meshwork (hTM) cells from nonglaucomatous donors were cultured for 12 days in the absence or presence of Wnt modulators: (i) LGK974 (Porcn inhibitor, 10 µM); (ii) LY2090314 (pGSK3β inhibitor, 250 nM); or (iii) 9 days of LGK974 followed by 3 days of LY2090314. Wnt modulation were determined by Western blotting and extracellular matrix (ECM) related genes were evaluated by quantitative PCR. Cytoskeletal morphology was determined by immunofluorescence and cell stiffness by atomic force microscopy. Results Wnt activation was confirmed by downregulation of pGSK3β (0.3-fold; P < 0.01), overexpression of AXIN2 (6.7-fold; P < 0.001), and LEF1 (3.8-fold; P < 0.001). Wnt inhibition resulted in dramatic changes in F-actin, which were resolved with subsequent Wnt activation. Concurrently, cell stiffness that was elevated with Wnt inhibition (11.86 kPa; P < 0.01) decreased with subsequent Wnt activation (4.195 kPa; P < 0.01) accompanied by significant overexpression of phosphorylated YAP (1.8-fold; P < 0.001) and TAZ (1.4-fold; P < 0.001). Additionally, Wnt activation after inhibition significantly repressed ECM genes (SPARC and CTGF, P < 0.01), cross-linking genes (LOX and TGM2, P < 0.05), inhibitors of matrix metalloproteinases (TIMP1 and PAI1, P < 0.001), and overexpressed MMP 1/9/14 (P < 0.01). Conclusions These data strongly demonstrate that, in normal hTM cells, activation of the Wnt pathway reverses the pathological phenotype caused by Wnt inhibition and may thus be a viable therapeutic for lowering IOP.

Reactive molecular oxygen (O(2)) plays important roles in bioenergetics and metabolism and is implicated in biochemical pathways underlying angiogenesis, fertilization, wound healing and regeneration. Here we describe how to use the scanning micro-optrode technique (SMOT) to measure extracellular fluxes of dissolved O(2). The self-referencing O(2)-specific micro-optrode (also termed micro-optode and optical fiber microsensor) is a tapered optical fiber with an O(2)-sensitive fluorophore coated onto the tip. The O(2) concentration is quantified by fluorescence quenching of the fluorophore emission upon excitation with blue–green light. The micro-optrode presents high spatial and temporal resolutions with improved signal-to-noise ratio (in the picomole range). In this protocol, we provide step-by-step instructions for micro-optrode calibration, validation, example applications and data analysis. We describe how to use the technique for cells (Xenopus oocyte), tissues (Xenopus epithelium and rat cornea), organs (Xenopus gills and mouse skin) and appendages (Xenopus tail), and provide recommendations on how to adapt the approach to different model systems. The basic, user-friendly system presented here can be readily installed to reliably and accurately measure physiological O(2) fluxes in a wide spectrum of biological models and physiological responses. The full protocol can be performed in ~4 h.

Purpose Transforming growth factor β1 (TGFβ1) is elevated in wounds after injury and promotes the transdifferentiation of quiescent cells in the stroma (keratocytes, to activated fibroblasts and subsequently myofibroblasts-KFM transformation). Coactivators of transcription, YAP (Yes-associated protein) and TAZ (Transcriptional coactivator with PDZ-binding motif), are mechanotransducers that intersect with the TGFβ pathway via interactions with Smad proteins. Here, we examined the distinct role of YAP and TAZ on TGFβ1 induced myofibroblast transformation of primary human corneal fibroblasts (HCFs). Methods A knockdown approach was used to silence YAP and TAZ individually in HCFs. Forty-eight hours post siRNA transfection, cells were cultured in the presence or absence of 2 ng/ml TGFβ1 for 24h. The cells were subjected to nuclear and cytoplasmic fractionation. The expression of α-smooth muscle actin (αSMA), Smad 2, 3 and 4, CTGF and phospho-Smad2, 3, and 4 were assessed by qPCR and Western blotting. Results TGFβ1 stimulation resulted in the decreased phosphorylation of YAP in the cytosol, and increased levels of phosphorylated TAZ and Smad2/3/4 in the nucleus. Knockdown of TAZ resulted in elevated YAP expression but not vice versa. Additionally, knockdown of TAZ but not YAP resulted in upregulation of αSMA expression in the presence and absence of TGFβ1. In the presence of TGFβ1 YAP knockdown increased Smad2/3/4 expression and Smad4 phosphorylation, while TAZ knockdown had no effect on Smad2/3/4 expression and phosphorylation. YAP knockdown inhibited CTGF expression while TAZ knockdown resulted in its increased expression. Finally, simultaneous knockdown of YAP and TAZ resulted in cell death. Conclusion Our findings suggest that YAP and TAZ function as distinct modulators of TGFβ1 induced myofibroblast transformation and have different roles in signalling. Specifically, TAZ limits YAP's ability to mediate KFM transformation via Smad proteins. The data also suggest that while having distinct effects, YAP and TAZ have redundant or combinatorial functions critical to cell survival. These results suggest that a loss of TAZ may help drive corneal haze and fibrosis and that the balance between YAP/TAZ is essential in controlling myofibroblast differentiation.

The transformation of keratocytes and fibroblasts to myofibroblasts is important to corneal wound healing as well as formation of stromal haze. The purpose of this study was to determine the effect of latrunculin B, an actin cytoskeleton disruptor in conjunction with a fundamental biophysical cue, substrate stiffness, on myofibroblast transformation in vitro and in vivo. Rabbit corneal fibroblasts were cultured on substrates of differing compliance (1.5, 22, and 71 kPa) and tissue culture plastic (TCP; > 1 GPa) in media containing 0 or 10 ng/ml TGFβ1 for 72 h. Cells were treated with 0.4 μM Lat-B or DMSO for 30 min every 24 h for 72 h. RNA was collected from cells and expression of alpha-smooth muscle actin (α-SMA), keratocan, and ALDH1A1 determined using qPCR; immunocytochemistry was used to assess α-SMA protein expression. A rabbit phototherapeutic keratectomy (PTK) model was used to assess the impact of 0.1% Lat-B (n = 3) or 25% DMSO (vehicle control, n = 3) on corneal wound healing by assessment of epithelial wound size with fluorescein stain and semi-quantitative stromal haze scoring by an observer masked to treatment group as well as Fourier-domain optical coherence tomography (FD-OCT) at set time points. Statistical analysis was completed using one-way or two-way analysis of variance. Treatment with Lat-B versus DMSO resulted in significantly less αSMA mRNA (P ≤ 0.007) for RCF cells grown on 22 and 71 kPa substrates as well as TCP without or with TGFβ1, and significantly decreased α-SMA protein expression in RCFs cultured on the intermediate (22 kPa) stiffness in the absence (P = 0.028) or presence (P = 0.018) of TGFβ1. Treatment with Lat-B versus DMSO but did not significantly alter expression of keratocan or ALDH1A1 mRNA in RCFs (P > 0.05) in the absence or presence of TGFβ1, but RCFs grown on stiff hydrogels (71 kPa) had significantly more keratocan mRNA expression versus the 22 kPa hydrogel or TCP (P

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

Purpose The extracellular matrix (ECM) of the trabecular meshwork (TM) modulates resistance to aqueous humor outflow, thereby regulating IOP. Glaucoma, a leading cause of irreversible blindness worldwide, is associated with changes in the ECM of the TM. The elastic modulus of glaucomatous TM is larger than age-matched normal TM; however, the biomechanical properties of segmental low (LF) and high flow (HF) TM regions and their response to elevated pressure, are unknown. Methods We perfused human anterior segments at two pressures using an ex vivo organ culture system. After extraction, we measured the elastic modulus of HF and LF TM regions by atomic force microscopy and quantitated protein differences by proteomics analyses. Results The elastic modulus of LF regions was 2.3-fold larger than HF regions at physiological (1×) pressure, and 7.4-fold or 3.5-fold larger than HF regions at elevated (2×) pressure after 24 or 72 hours, respectively. Using quantitative proteomics, comparisons were made between HF and LF regions at 1× or 2× pressure. Significant ECM protein differences were observed between LF and HF regions perfused at 2×, and between HF regions at 1× compared to 2× pressures. Decorin, TGF-β-induced protein, keratocan, lumican, dermatopontin, and thrombospondin 4 were common differential candidates in both comparisons. Conclusions These data show changes in biomechanical properties of segmental regions within the TM in response to elevated pressure, and levels of specific ECM proteins. Further studies are needed to determine whether these ECM proteins are specifically involved in outflow resistance and IOP homeostasis.

Pseudoexfoliation syndrome is a systemic disorder of the extracellular matrix (ECM) with ocular manifestations in the form of chronic open angle glaucoma. Elevated levels of TGFβ3 in the aqueous humor of individuals with pseudoexfoliation glaucoma (PEX) have been reported. The influence of TGFβ3 on the biochemical composition and biomechanics of ECM of human trabecular meshwork (HTM) cells was investigated. HTM cells from eye bank donor eyes were isolated, plated on aminosilane functionalized glass substrates and cultured in the presence or absence of 1 ng/mL TGFβ3 for 4 weeks. After incubation, samples were decellularized and decellularization was verified by immunostaining. The mechanics of the remaining ECM that was deposited by the treated or the control cells were measured by atomic force microscopy (AFM). Imaged by AFM, the surface features of the ECM from both sets of samples had a similar roughness/topography (as determined by RMS values) suggesting surface features of the ECM were similar in both cases; however, the ECM from the HTM cells treated with TGFβ3 was between 3- and 5-fold stiffer than that produced by the control HTM cells. Proteins present in the ECM were solubilized and analyzed using liquid chromatography tandem mass spectroscopy (LC-MS/MS). Data indicate that multiple proteins previously reported to be altered in glaucoma were changed in the ECM as a result of the presence of TGFβ3, including inhibitors of the BMP and Wnt signaling pathways. Gremlin1and 4, SERPINE1 and 2, periostin, secreted frizzled related protein (SFRP) 1 and 4, and ANGPTL4 were among those proteins that were overexpressed in the ECM after TGFβ3 treatment.

Laser-induced experimental glaucoma (ExGl) in non-human primates (NHPs) is a common animal model for ocular drug development. While many features of human hypertensive glaucoma are replicated in this model, structural and functional changes in the unlasered portions of trabecular meshwork (TM) of laser-treated primate eyes are understudied. We studied NHPs with ExGl of several years duration. As expected, ExGl eyes exhibited selective reductions of the retinal nerve fiber layer that correlate with electrophysiologic measures documenting a link between morphologic and elctrophysiologic endpoints. Softening of unlasered TM in ExGl eyes compared to untreated controls was observed. The degree of TM softening was consistent, regardless of pre-mortem clinical findings including severity of IOP elevation, retinal nerve fiber layer thinning, or electrodiagnostic findings. Importantly, this softening is contrary to TM stiffening reported in glaucomatous human eyes. Furthermore, microscopic analysis of unlasered TM from eyes with ExGl demonstrated TM thinning with collapse of Schlemm’s canal; and proteomic analysis confirmed downregulation of metabolic and structural proteins. These data demonstrate unexpected and compensatory changes involving the TM in the NHP model of ExGl. The data suggest that compensatory mechanisms exist in normal animals and respond to elevated IOP through softening of the meshwork to increase outflow.

Corneal wound healing is an enormously complex process that requires the simultaneous cellular integration of multiple soluble biochemical cues, as well as cellular responses to the intrinsic chemistry and biophysical attributes associated with the matrix of the wound space. Here, we document how the biomechanics of the corneal stroma are altered through the course of wound repair following keratoablative procedures in rabbits. Further we documented the influence that substrate stiffness has on stromal cell mechanics. Following corneal epithelial debridement, New Zealand white rabbits underwent phototherapeutic keratectomy (PTK) on the right eye (OD). Wound healing was monitored using advanced imaging modalities. Rabbits were euthanized and corneas were harvested at various time points following PTK. Tissues were characterized for biomechanics with atomic force microscopy and with histology to assess inflammation and fibrosis. Factor analysis was performed to determine any discernable patterns in wound healing parameters. The matrix associated with the wound space was stiffest at 7 days post PTK. The greatest number of inflammatory cells were observed 3 days after wounding. The highest number of myofibroblasts and the greatest degree of fibrosis occurred 21 days after wounding. While all clinical parameters returned to normal values 400 days after wounding, the elastic modulus remained greater than pre-surgical values. Factor analysis demonstrated dynamic remodeling of stroma occurs between days 10 and 42 during corneal stromal wound repair. Elastic modulus of the anterior corneal stroma is dramatically altered following PTK and its changes coincide initially with the development of edema and inflammation, and later with formation of stromal haze and population of the wound space with myofibroblasts. Factor analysis demonstrates strongest correlation between elastic modulus, myofibroblasts, fibrosis and stromal haze thickness, and between edema and central corneal thickness. Statement of significance Tissue biomechanics during the course of corneal wound healing is documented for the first time through atomic force microscopy, and is correlated with advanced clinical imaging and immunohistochemistry. Parameters obtained from the study are applied in a multivariate statistical model to cluster the data for better classification and monitor the wound repair process. Elastic modulus of the anterior corneal stroma is dramatically altered following wounding and correlates initially with the development of edema and inflammation, and later with formation of stromal haze and population of the wound space with myofibroblasts. Importantly, the occurrence of myofibroblasts is preceded by changes in tissue mechanics, which is important to consider in light of crosslinking procedures applied to treat corneal diseases.

Mucins are large glycoproteins expressed by epithelial cells of both the conjunctiva and cornea, and principle components of the glycocalyx. They are thought to play an important role in determining the interactions between the cornea/conjunctiva and the overlying tear film. The purpose of this study was to characterize the membrane-associated corneal mucin expression pattern from multiple species commonly used in ophthalmic research and drug development to better define the biochemical attributes of the ocular surface. Humans, rhesus macaques and dogs were found to have a very similar pattern of mucin expression, with mucin 16 (MUC16) being the most prevalent mucin transcript. In contrast, the rabbit had a unique mucin expression pattern with all mucin transcripts expressed at relatively similar levels. To determine if there were spatial differences in expression, peripheral and central corneal epithelium were individually isolated and evaluated for mucin expression. In all species examined, MUC1, MUC4 and MUC16 had higher peripheral corneal expression when compared with central, which reached statistical significance in MUC1 (rhesus and dog). The data demonstrated variation in corneal epithelial membrane-associated mucin expression between species, with the rabbit having a distinct expression pattern. These differences may be reflective of the environment, pathogen exposure or tear film dynamics of the respective species. The species differences, as well as regional mucin expression patterns, characterized in this study further define the biochemical composition of the ocular surface and may play an important role in tear film stability.

Dry eye syndrome is a multifactorial disease of the ocular surface, with clinical findings that include discomfort, visual disturbance, and tear film instability.1 In the United States, it is estimated that 7.8% of women 50 years of age and older2 and 4.34% of men 50 years of age and older3 are affected by dry eye syndrome. Although the International Dry Eye Workshop categorized the types of dry eye as (1) aqueous-deficient and (2) evaporative,1 dry eye syndrome and other ocular surface disorders also involve the interaction between the cellular surface of the eye and the liquid film constituted by the tears.4 It is widely believed that the stability/instability of tear film depends on the surface properties of the epithelium, especially its wettability or degree of retention of tear film in contact with the ocular surface.5–7 Although wetting properties have conventionally been attributed to the presence of a hydrophilic glycocalyx,8 specifically to the highly O-glycosylated membrane-associated mucins of the ocular surface (principally MUC1, MUC4, and MUC16),9 to our knowledge, there are no studies that directly correlate the expression and spatial distribution of cell associated mucins to the physicochemical surface properties of the ocular surface. Immortalized corneal epithelial cell lines have been reported to differentiate, stratify, and express significant amounts of mucins when cultured as a confluent monolayer of cells and stimulated with 10% fetal bovine serum and 10 ng/mL epithelial growth factor (EGF).10 In this work we induced stratification of an hTERT immortalized corneal epithelial (hTCEpi) cell line11 over a period of 6 days and characterized the expression of mucins to correlate with the surface properties of the cells. A standard method to evaluate surface properties is the sessile drop contact angle technique.5–7,12 This widely used method is performed by measuring the contact angle between a drop of liquid and a solid in air. However, measurements of the contact angle of water drops on cell cultures or tissues are misleading because the thin film of liquid covering the surface on hydrated cells impedes the measurement of an angle. Furthermore, if the cell surface is allowed to dry, the contact angle changes values, depending on the moisture level, as observed by Tiffany,7 suggesting the loss of the native state of the cell's surface. To overcome some of the challenges intrinsic to using water as the probe, other liquids can be used to characterize surfaces, such as polar liquids (e.g., glycerol or formamide) or nonpolar lipids (e.g., diiodomethane or benzene). However, polar liquids can disturb the cells due to the difference in osmolarity between the liquid and the cytosol, whereas many nonpolar liquids interact with the phospholipids of the cellular membrane, disrupting it.13 Therefore, the choice of fluid(s) used to measure contact angles of cell surfaces bathed in a fluid environment is critical in determining the interfacial properties. In this work, we used the two-liquid system, where cells are immersed in an isotonic physiologic buffer, and the contact angle is recorded using a nonreactive nonpolar liquid (perfluorocarbon) deposited on the cell surface (Fig. 1A). We also performed the captive bubble method, where the surface of interest is inverted and an air bubble is trapped in contact with the surface (Fig. 1B). Both of these methods permit the measurement of the contact angle and the contact angle hysteresis, which is a measurement that correlates to the uniformity of the surface. For smooth and uniform surfaces, droplets have unique contact angles. However, on heterogeneous surfaces, such as biological surfaces, droplets become pinned by defects and possess an advancing and a receding angle of contact, which may be recorded by tilting the apparatus (Fig. 1C). The intrinsic biochemical make up and surface topography of the ocular surface contribute to this heterogeneity, and the extent to which this promotes the retention of the tear film at the ocular surface is understudied. These measurements allow evaluation of the surface properties at different maturation levels of the glycocalyx during the stratification process of immortalized human corneal epithelial cells. Figure 1 (A) Use of two-liquid method to measure contact angle. In this system, the bulk fluid is PBS and the droplet is a perfluorocarbon. (B) Captive bubble method used to measure contact angle. (C) Tilting of the apparatus to measure the advancing and receding ...

Conducting polymer hydrogel is fabricated atop gold or ITO electrodes and is functionalized with monoclonal antibodies. Binding of interferon-γ molecules causes redox properties of conductive hydrogel to change in a concentration-dependent fashion without the need for washing or sample handling steps. This conductive hydrogel remains functional in a fouling media such as whole blood.

Purpose Treatment with corticosteroids can result in ocular hypertension and may lead to the development of steroid-induced glaucoma. The extent to which biomechanical changes in trabecular meshwork (TM) cells and extracellular matrix (ECM) contribute toward this dysfunction is poorly understood. Methods Primary human TM (HTM) cells were cultured for either 3 days or 4 weeks in the presence or absence of dexamethasone (DEX), and cell mechanics, matrix mechanics and proteomics were determined, respectively. Adult rabbits were treated topically with either 0.1% DEX or vehicle over 3 weeks, and mechanics of the TM were determined. Results Treatment with DEX for 3 days resulted in a 2-fold increase in HTM cell stiffness, and this correlated with activation of extracellular signal-related kinase 1/2 (ERK1/2) and overexpression of α-smooth muscle actin (αSMA). Further, the matrix deposited by HTM cells chronically treated with DEX is approximately 4-fold stiffer, more organized, and has elevated expression of matrix proteins commonly implicated in glaucoma (decorin, myocilin, fibrillin, secreted frizzle-related protein [SFRP1], matrix-gla). Also, DEX treatment resulted in a 3.5-fold increase in stiffness of the rabbit TM. Discussion This integrated approach clearly demonstrates that DEX treatment increases TM cell stiffness concurrent with elevated αSMA expression and activation of the mitogen-activated protein kinase (MAPK) pathway, stiffens the ECM in vitro along with upregulation of Wnt antagonists and fibrotic markers embedded in a more organized matrix, and increases the stiffness of TM tissues in vivo. These results demonstrate glucocorticoid treatment can initiate the biophysical alteration associated with increased resistance to aqueous humor outflow and the resultant increase in IOP.

Dysfunction of the human trabecular meshwork (HTM) plays a central role in the age-associated disease glaucoma, a leading cause of irreversible blindness. The etiology remains poorly understood but cellular senescence, increased stiffness of the tissue, and the expression of Wnt antagonists such as secreted frizzled related protein-1 (SFRP1) have been implicated. However, it is not known if senescence is causally linked to either stiffness or SFRP1 expression. In this study, we utilized in vitro HTM senescence to determine the effect on cellular stiffening and SFRP1 expression. Stiffness of cultured cells was measured using atomic force microscopy and the morphology of the cytoskeleton was determined using immunofluorescent analysis. SFRP1 expression was measured using qPCR and immunofluorescent analysis. Senescent cell stiffness increased 1.88±0.14 or 2.57±0.14 fold in the presence or absence of serum, respectively. This was accompanied by increased vimentin expression, stress fiber formation, and SFRP1 expression. In aggregate, these data demonstrate that senescence may be a causal factor in HTM stiffening and elevated SFRP1 expression, and contribute towards disease progression. These findings provide insight into the etiology of glaucoma and, more broadly, suggest a causal link between senescence and altered tissue biomechanics in aging-associated diseases.

Wnt antagonism has been linked to glaucoma and intraocular pressure regulation, as has increased stiffness of human trabecular meshwork (HTM) tissue. We have shown culturing HTM cells on substrates that mimic the elevated stiffness of glaucomatous tissue leads to elevated expression of the Wnt antagonist secreted frizzled related protein 1 (SFRP1), suggesting a linkage between SFRP1 and HTM mechanobiology. In this study, we document biomechanical consequences of Wnt antagonism on HTM cells. Cells were treated with the Wnt antagonists (SFRP1, KY02111, and LGK-974) for 8 days and allowed to recover for 4 days. After recovery, intrinsic cell stiffness and activation of the Wnt pathway via β-catenin staining and blotting were assayed. Basal cell stiffness values were 3.71±0.37, 4.33±3.07, and 3.07±kPa (median±S.D.) for cells derived from 3 donors. Cell stiffness increased after 0.25μg/mL (4.32±5.12, 8.86±8.51, 4.84±3.15kPa) and 0.5μg/mL (16.75±5.59, 13.18±7.99, and 8.54±5.77kPa) SFRP1 treatment. Stiffening was observed after 10μM KY02111 (10.72±5.63 and 6.57±5.53kPa) as well as LGK-974 (9.60±7.41 and 11.40±9.24kPa) treatment compared with controls (3.79±1.01 and 5.16±2.14kPa). Additionally, Wnt inhibition resulted in decreased β-catenin staining and increased phosphorylation at threonine 41 after recovery. In conclusion, this work demonstrates a causal relationship between Wnt inhibition and cell stiffening. Additionally, these findings suggest transient Wnt inhibition resulted in durable modulation of the mechanical phenotype of HTM cells. When placed in context with previous results, these findings provide a causal link between Wnt antagonism and cell stiffness and suggest a feedback loop contributing to glaucoma progression.