Establishment of human trabecular meshwork cell cultures using nontransplantable corneoscleral rims

An Overview of Current Glaucomatous Trabecular Meshwork Models

PURPOSE

To provide an overview of the existing alternative models for studying trabecular meshwork (TM).

METHODS

Literature review.

RESULTS

The TM is a complex tissue that regulates aqueous humor outflow from the eye. Dysfunction of the TM is a major contributor to the pathogenesis of open-angle glaucoma, a leading cause of irreversible blindness worldwide. The TM is a porous structure composed of trabecular meshwork cells (TMC) within a multi-layered extracellular matrix (ECM). Although dysregulation of the outflow throughout the TM represents the first step in the disease process, the underlying mechanisms of TM degeneration associate cell loss and accumulation of ECM, but remain incompletely understood, and drugs targeting the TM are limited. Therefore, experimental models of glaucomatous trabeculopathy are necessary for preclinical screening, to advance research on this disease's pathophysiology, and to develop new therapeutic strategies targeting the TM. Traditional animal models have been used extensively, albeit with inherent limitations, including ethical concerns and limited translatability to humans. Consequently, there has been an increasing focus on developing alternative in vitro models to study the TM. Recent advancements in three-dimensional cell culture and tissue engineering are still in their early stages and do not yet fully reflect the complexity of the outflow pathway. However, they have shown promise in reducing reliance on animal experimentation in certain aspects of glaucoma research.

CONCLUSION

This review provides an overview of the existing alternative models for studying TM and their potential for advancing research on the pathophysiology of open-angle glaucoma and developing new therapeutic strategies.

Primary Human Trabecular Meshwork Model for Pseudoexfoliation

The lack of an animal model or an in vitro model limits experimental options for studying temporal molecular events in pseudoexfoliation syndrome (PXF), an age related fibrillopathy causing trabecular meshwork damage and glaucoma. Our goal was to create a workable in vitro model of PXF using primary human TM (HTM) cell lines simulating human disease. Primary HTM cells harvested from healthy donors (n = 3), were exposed to various concentrations (5 ng/mL, 10 ng/mL, 15 ng/mL) of transforming growth factor-beta1 (TGF-β1) for different time points. Morphological change of epithelial–mesenchymal transition (EMT) was analyzed by direct microscopic visualization and immunoblotting for EMT markers. Expression of pro-fibrotic markers were analyzed by quantitative RT-PCR and immunoblotting. Cell viability and death in treated cells was analyzed using FACS and MTT assay. Protein complex and amyloid aggregate formation was analyzed by Immunofluorescence of oligomer11 and amyloid beta fibrils. Effect of these changes with pharmacological inhibitors of canonical and non-canonical TGF pathway was done to analyze the pathway involved. The expression of pro-fibrotic markers was markedly upregulated at 10 ng/mL of TGF-β1 exposure at 48–72 h of exposure with associated EMT changes at the same time point. Protein aggregates were seen maximally at these time points that were found to be localized around the nucleus and in the extracellular matrix (ECM). EMT and pro-fibrotic expression was differentially regulated by different canonical and non-canonical pathways suggesting complex regulatory mechanisms. This in vitro model using HTM cells simulated the main characteristics of human disease in PXF like pro-fibrotic gene expression, EMT, and aggregate formation.

An injectable peptide hydrogel for reconstruction of the human trabecular meshwork

Glaucoma is a leading cause of irreversible blindness worldwide. Current treatments of glaucoma involve lowering the IOP by means of decreasing aqueous humor production or increasing non-trabecular aqueous humor outflow with the help of IOP-lowering eye drops, nanotechnology enabled glaucoma drainage implants, and trabeculectomy. However, there is currently no effective and permanent cure for this disease. In order to investigate new therapeutic strategies, three dimensional (3D) biomimetic trabecular meshwork (TM) models are in demand. Therefore, we adapted MAX8B, a peptide hydrogel system to bioengineer a 3D trabecular meshwork scaffold. We assessed mechanical and bio-instructive properties of this engineered tissue matrix by using rheological analysis, 3D cell culture and imaging techniques. The scaffold material exhibited shear-thinning ability and biocompatibility for proper hTM growth and proliferation indicating a potential utilization as an injectable implant. Additionally, by using a perfusion system, MAX8B scaffold was tested as an in vitro platform for investigating the effect of Dexamethasone (Dex) on trabecular meshwork outflow facility. The physiological response of hTM cells within the scaffold to Dex treatment clearly supported the effectiveness of this 3D model as a drug-testing platform, which can accelerate discovery of new therapeutic targets for glaucoma. STATEMENT OF SIGNIFICANCE: Artificial 3D-TM (3-dimentional Trabecular Meshwork) developed here with hTM (human TM) cells seeded on peptide-hydrogel scaffolds exhibits the mechanical strength and physiological properties mimicking the native TM tissue. Besides serving a novel and effective 3D-TM model, the MAX8B hydrogel could potentially function as an injectable trabecular meshwork implant.