Reduction in trabecular meshwork stem cell content in donor eyes with primary open angle glaucoma

Age-related reduction in the functional properties of adult stem cells located in the peripheral region of human retinal pigment epithelium

PURPOSE

Adult stem cells (SCs) with self-renewal and multilineage potential have been reported upon culturing human retinal pigment epithelial (RPE) cells. The current study aimed to identify the location of SCs in human RPE and to elucidate the age-related changes.

METHODS

Peripheral, equatorial, and central RPE cells from donors of three age groups were analyzed for their sphere-forming, clonal, and label-retaining cell properties. Furthermore, native human RPE flatmounts were immunostained for SC and proliferating cell markers.

RESULTS

Cells with higher sphere-forming and clonal ability were identified only in young donors (<30 years) and were restricted to the periphery. Upon culturing, cells from peripheral and equatorial regions had the label-retaining cell (LRC) property. With aging, the LRCs were restricted to the periphery and were reduced. In young donors, Ki67 + proliferating cells were not observed in native RPE. However, such cells were observed in the peripheral RPE of older donors correlating with the need for regeneration. The native RPE cells were negative for SC marker expression.

CONCLUSION

The above findings highlighted the presence of SCs with the ability to proliferate in the peripheral RPE and a reduction in these functional properties of SCs with aging.

Aging, Cellular Senescence, and Glaucoma

Aging is one of the most serious risk factors for glaucoma, and according to age-standardized prevalence, glaucoma is the second leading cause of legal blindness worldwide. Cellular senescence is a hallmark of aging that is defined by a stable exit from the cell cycle in response to cellular damage and stress. The potential mechanisms underlying glaucomatous cellular senescence include oxidative stress, DNA damage, mitochondrial dysfunction, defective autophagy/mitophagy, and epigenetic modifications. These phenotypes interact and generate a sufficiently stable network to maintain the cell senescent state. Senescent trabecular meshwork (TM) cells, retinal ganglion cells (RGCs) and vascular endothelial cells reportedly accumulate with age and stress and may contribute to glaucoma pathologies. Therapies targeting the suppression or elimination of senescent cells have been found to ameliorate RGC death and improve vision in glaucoma models, suggesting the pivotal role of cellular senescence in the pathophysiology of glaucoma. In this review, we explore the biological links between aging and glaucoma, specifically delving into cellular senescence. Moreover, we summarize the current data on cellular senescence in key target cells associated with the development and clinical phenotypes of glaucoma. Finally, we discuss the therapeutic potential of targeting cellular senescence for the management of glaucoma.

iPSCs-Based Therapy for Trabecular Meshwork

The trabecular meshwork (TM) of the eye serves as an essential tissue in controlling aqueous humor (AH) outflow and intraocular pressure (IOP) homeostasis. However, dysfunctional TM cells and/or decreased TM cellularity is become a critical pathogenic cause for primary open-angle glaucoma (POAG). Consequently, it is particularly valuable to investigate TM characteristics, which, in turn, facilitates the development of new treatments for POAG. Since 2006, the advancement in induced pluripotent stem cells (iPSCs) provides a new tool to (1) model the TM in vitro and (2) regenerate degenerative TM in POAG. In this context, we first summarize the current approaches to induce the differentiation of TM-like cells from iPSCs and compare iPSC-derived TM models to the conventional in vitro TM models. The efficacy of iPSC-derived TM cells for TM regeneration in POAG models is also discussed. Through these approaches, iPSCs are becoming essential tools in glaucoma modeling and for developing personalized treatments for TM regeneration.

A novel glaucoma approach: Stem cell regeneration of the trabecular meshwork

Glaucoma is the leading cause of global irreversible blindness, necessitating research for new, more efficacious treatment options than currently exist. Trabecular meshwork (TM) cells play an important role in the maintenance and function of the aqueous outflow pathway, and studies have found that there is decreased cellularity of the TM in glaucoma. Regeneration of the TM with stem cells has been proposed as a novel therapeutic option by several reports over the last few decades. Stem cells have the capacity for self-renewal and the potential to differentiate into adult functional cells. Several types of stem cells have been investigated in ocular regenerative medicine: tissue specific stem cells, embryonic stem cells, induced pluripotent stem cells, and adult mesenchymal stem cells. These cells have been used in various glaucoma animal models and ex vivo models and have shown success in IOP homeostasis and TM cellularity restoration. They have also demonstrated stability without serious side effects for a significant period of time. Based on current knowledge of TM pathology in glaucoma and existing literature regarding stem cell regeneration of this tissue, we propose a human clinical study as the next step in understanding this potentially revolutionary treatment paradigm. The ability to protect and replace TM cells in glaucomatous eyes could change the field forever.