Proliferative capacity of corneal endothelial cells

Abstract

The corneal endothelial monolayer helps maintain corneal transparency through its barrier and ionic “pump” functions. This transparency function can become compromised, resulting in a critical loss in endothelial cell density (ECD), corneal edema, bullous keratopathy, and loss of visual acuity. Although penetrating keratoplasty and various forms of endothelial keratoplasty are capable of restoring corneal clarity, they can also have complications requiring re-grafting or other treatments. With the increasing worldwide shortage of donor corneas to be used for keratoplasty, there is a greater need to find new therapies to restore corneal clarity that is lost due to endothelial dysfunction. As a result, researchers have been exploring alternative approaches that could result in the in vivo induction of transient corneal endothelial cell division or the in vitro expansion of healthy endothelial cells for corneal bioengineering as treatments to increase ECD and restore visual acuity. This review presents current information regarding the ability of human corneal endothelial cells (HCEC) to divide as a basis for the development of new therapies. Information will be presented on the positive and negative regulation of the cell cycle as background for the studies to be discussed. Results of studies exploring the proliferative capacity of HCEC will be presented and specific conditions that affect the ability of HCEC to divide will be discussed. Methods that have been tested to induce transient proliferation of HCEC will also be presented. This review will discuss the effect of donor age and endothelial topography on relative proliferative capacity of HCEC, as well as explore the role of nuclear oxidative DNA damage in decreasing the relative proliferative capacity of HCEC. Finally, potential new research directions will be discussed that could take advantage of and/or improve the proliferative capacity of these physiologically important cells in order to develop new treatments to restore corneal clarity.

Corneal endothelium: developmental strategies for regeneration

“…42 HCECs do not have a significant capacity for in vivo regeneration, thus making them unable to replace dead or damaged cells. 30,43 This occurs because HCECs are arrested in the G1-phase of the cell cycle. Three mechanisms have been identified that contribute to this: (1) cell-cell contact-dependent inhibition, (2) lack of effective growth factor stimulation, and (3) TGF-b2 suppression of S-phase.…”

“…75 The non-enzymatic method is based on the use of ethylenediamine tetraacetic acid (EDTA) to release cell-cell junctions at the same time as it promotes cell division upon exposure to mitogens. 30,70,72,76 In this process, EDTA can also cause cell damage and decrease cell yield. 77 There is a combined method that uses collagenase II to generate preservable HCEC aggregates and a brief treatment with trypsin/EDTA leading to a high proliferation rate with less cell damage.…”

“…28,29 To preserve ocular transparency, endothelial cell density must remain above a critical level, usually between 400 and 500 cells/mm 2 . 30 Adjacent cells communicate through gap junctions and tight junctions, whereas the basal surface is adhered to Descemet's membrane by hemidesmosomes. 31,32 Tight junctions (ZO-1) are supramolecular assemblies, that form intercellular junctions, and are found close to the apical domains of the endothelial cells.…”

“…This allows the endothelium to function as a barrier, forming resistance to the permeability of solutes and fluid through paracellular transport routes. 30,33 There are integral proteins in the cellular membrane, the aquaporins (AQP), which with the Na þ /K þ ATPase pump participate in the fluid movement across the endothelium and function as water selective channels. The isoform AQP-1 is expressed by the corneal endothelial cells and the lens epithelium.…”

Characterization of cryopreserved primary human corneal endothelial cells cultured in human serum-supplemented media

“…Since Stocker et al (1) established a human corneal endothelial cell (HCEC) culture, the potential for cell therapy to treat corneal endothelial dysfunction using HCECs has demonstrated continuous development (2)(3)(4)(5)(6)(7)(8) . The limitations associated with this therapy can be basically divided into two major areas: those related to culturing the cells, such as proliferation, cellular senescence, and fibroblastic transformation and those related to the logistics and techniques for transplanting the cells (2)(3)(4)(5)(6)(7)(8) .…”