Proliferation and Migration of Peripheral Retinal Pigment Epithelial Cells Are Associated with the Upregulation of Wingless-Related Integration and Bone Morphogenetic Protein Signaling in Dark Agouti Rats.

OBJECTIVE: The aim of this study was to investigate the possible migration of proliferating peripheral retinal pigment epithelial (RPE) cells and their association with differential gene expressions. MATERIALS AND METHODS: The RPE layer was obtained from the inner aspect of the eyeball of dark agouti rats (12-13 weeks old) and was mounted on glass slides. The peripheral RPE cell proliferation was evaluated using bromodeoxyuridine immunohistochemistry (n = 10). The cell migration was examined using the Dil tracer technique (n = 40) at the end of weeks 6, 10, 14 and 18. Affymetrix microarray analysis was used to investigate differential gene expressions in peripheral and central RPE cells, which was authenticated by RT-PCR using 4 RPE-specific genes (n = 10). RESULTS: In this study, peripheral RPE cells divided and appeared in clusters, but equatorial and central RPE cells rarely divided. The peripheral RPE cells migrated to the central RPE region in a time-dependent manner up to the end of week 14, but not later. The microarray analysis showed the expression of 9,645 out of a total of 35,220 genes studied. Among the 9,645 genes, 573 were differentially expressed (438 were upregulated and 135 were downregulated) in peripheral RPE cells as compared to central RPE cells. Of these 573 genes, 56 were associated with signaling pathways related to the regulation of cell proliferation, including Pax6, TGFß, BMP and Wnt, and 404 were associated with pathways of cell migration. CONCLUSIONS: In this study, peripheral RPE cells divided and migrated to the central region. This process was associated with differential gene expressions in these cells.

Glatiramer acetate elevates cell production in the mature retinal pigment epithelium.

The retinal-pigmented epithelium (RPE) is critical for visual function. Throughout life, central RPE cells are lost but replenished by peripheral cell production. Glatiramer acetate increases neuronal production in mature brains and is thought to erode age-related deposits in the human retina that are risk factors for macular degeneration. Here, we ask whether this agent also elevates RPE production in mature rat eyes. If so, it may be used to replenish these cells in damaged eyes. Glatiramer acetate was given systemically for 14 days combined with Bromodeoxyuridine (BrdU) to mark cell division. One eye was then processed for the cell cycle marker Ki67 and the other for BrdU. Glatiramer acetate significantly elevated the number of RPE cells in the cell cycle, with more labeled with Ki67. There were also significantly more BrdU-labeled cells over the 14 days, confirming that some cells divided. However, while Ki67 positive cell numbers increased by approximately 100% following examination at one time point, BrdU cell numbers increased by only 3% when averaged per day. Hence, glatiramer acetate induces cells to proliferate, but many may fail either to complete division or to survive. This may have long-term consequences for this tissue.

Mature peripheral RPE cells have an intrinsic capacity to proliferate; a potential regulatory mechanism for age-related cell loss.

BACKGROUND: Mammalian peripheral retinal pigmented epithelium (RPE) cells proliferate throughout life, while central cells are senescent. It is thought that some peripheral cells migrate centrally to correct age-related central RPE loss. METHODOLOGY/PRINCIPAL FINDINGS: We ask whether this proliferative capacity is intrinsic to such cells and whether cells located centrally produce diffusible signals imposing senescence upon the former once migrated. We also ask whether there are regional differences in expression patterns of key genes involved in these features between the centre and the periphery in vivo and in vitro. Low density RPE cultures obtained from adult mice revealed significantly greater levels of proliferation when derived from peripheral compared to central tissue, but this significance declined with increasing culture density. Further, exposure to centrally conditioned media had no influence on proliferation in peripheral RPE cell cultures at the concentrations examined. Central cells expressed significantly higher levels of E-Cadherin revealing a tighter cell adhesion than in the peripheral regions. Fluorescence-labelled staining for E-Cadherin, F-actin and ZO-1 in vivo revealed different patterns with significantly increased expression on central RPE cells than those in the periphery or differences in junctional morphology. A range of other genes were investigated both in vivo and in vitro associated with RPE proliferation in order to identify gene expression differences between the centre and the periphery. Specifically, the cell cycle inhibitor p27(Kip1) was significantly elevated in central senescent regions in vivo and mTOR, associated with RPE cell senescence, was significantly elevated in the centre in comparison to the periphery. CONCLUSIONS: These data show that the proliferative capacity of peripheral RPE cells is intrinsic and cell-autonomous in adult mice. These differences between centre and periphery are reflected in distinct patterns in junctional markers. The regional proliferation differences may be inversely dependent to cell-cell contact.

Held under arrest: Many mature albino RPE cells display polyploidal features consistent with abnormal cell cycle retention.

A population of peripheral retinal pigment epithelium (RPE) cells in mature pigmented rats are retained in the cell cycle and divide, as determined by Ki67 and BrdU labeling. Their cell cycle rate is approximately 5 days. Ten times as many Ki67 positive cells are found in albinos compared with pigmented animals, but it is not known if they actually divide or only express cell cycle markers. In spite of the increased number of cells expressing cell cycle markers, we show here using BrdU, that levels of cell division in albino RPE are similar to those in pigmented animals and have a similar cell cycle rate. Hence, cell cycle activity does not progress through to cell division in the majority of albino RPE cells. Peripheral RPE cells in albinos are different from those in pigmented animals. Many have very large distorted or highly fragmented nuclei. These data along with patterns of Ki67 and BrdU labeling are consistent with such cells being retained abnormally in the cell cycle, replicating their DNA, but not able to progress through to full cell division. Hence, there are two populations of RPE cells in albinos, those undergoing normal cell division and those that appear to be arrested in the cell cycle. These abnormalities are present from early postnatal stages.