Repair of Retinal Pigment Epithelium and Choriocapillaries after Laser Photocoagulation: Correlations between Scanning Electron, Transmission Electron and Light Microscopy

Abstract

Cell-to-cell interactions between retinal pigment epithelial (RPE) cells and vascular endothelium were examined by scanning electron microscopy, which demonstrates many facets of surface topography. The repair process after laser photocoagulation was characterized by a morphologically heterogeneous population of regenerated RPE cells, including normal-looking cells, macrophage-like cells and large elongated RPE cells. The macrophage-like and normal-looking RPE cells were predominantly seen adjacent to growing new choroidal vessels. Large cells appeared mainly in the vicinity of the extracellular matrix, where no viable new vessels were seen. The observed association between a specific phenotype of regenerated RPE cells and neovascularization may further support the hypothesis that regenerated RPE cells have a dual function, exerting both stimulatory and inhibitory effects on endothelial cells.

Wnt/β-Catenin Signaling Mediates Regeneration of Retinal Pigment Epithelium After Laser Photocoagulation in Mouse Eye

“…The RPE has a proliferative capacity, and it has been demonstrated that local proliferation occurs after injury. 32,33 However, until now, no in vivo study has shown that RPE cell proliferation is induced by Wnt/b-catenin signaling after laser photocoagulation. To measure RPE cell proliferation after laser photocoagulation, the number of EdUpositive cells in the laser-treated area was counted in whole mounts.…”

Pigment-Epithelium-Derived Factor Is Upregulated in Photocoagulated Human Retinal Pigment Epithelial Cells

“…To date, there is a wealth of evidence that thermal photocoagulation of RPE cells stimulates the biosynthesis of various pro-and antiangiogenic mediators [26][27][28] . Yoshimura et al [29] demonstrated that photocoagulation of cultured human RPE cells results in the production of TGF-␤ 2 , a potent inhibitor of vascular endothelial cell proliferation in vitro.…”

Conditioned medium from mixed retinal pigmented epithelium and Muller cell cultures reduces in vitro permeability of retinal vascular endothelial cells

“…Permeability of radiolabelled macromolecular tracers across the EC barrier was determined as follows. Within one hour of laser treatment, a mixture of radiolabelled tracers-[methoxy- 3 (Operation Manual, Packard Instrument Co) was used to calculate radioactivity of the individual radionuclides. A ratio of the radioactivity from each of the lower wells to the total count was determined for each timepoint and expressed as the percentage equilibration.…”

“…Changes in retinal morphology after laser have been well described in rats, 3 rabbits, 4 monkeys, 5 and humans. 6 7 Although some laser energy may directly affect the retinal vessels, it is generally accepted that the major site of absorption is the RPE and choroid.…”