Paul Hiscott

The aim of this study was to investigate the temporal and spatial expression of the matricellular protein SPARC (Secreted Protein, Acidic and Rich in Cysteine; also known as osteonectin) in human retinal pigment epithelial (RPE) cells, and compare the results with Bruch's membrane thickness, employing immuno-histochemistry. Eyes from 36 human donors, 16 being 65 years old, were included in the study. Intensity of SPARC immunoreactivity was evaluated using Aequitas Image Analysis software with two-way analysis of variance (ANOVA). Bruch's membrane thickness was assessed by profile analysis and the association between RPE SPARC immunoreactivity and Bruch's membrane thickness was investigated by fitting a linear mixed effects model to the data set. Intensity of SPARC immunostaining in RPE cells was significantly lower in older donors (p<0.05 and p<0.001 for posterior and peripheral RPE cells, respectively). The anatomical localisation of the RPE cells also affected the intensity of SPARC staining, which was lower in posterior compared to peripheral cells (p<0.01). No correlation was observed between SPARC immunoreactivity in RPE cells and the thickness of the underlying Bruch's membrane, in either posterior or peripheral regions. Our results suggest that RPE cell SPARC levels decline with age, a change that may play a role in the pathogenesis of age-related diseases such as age-related macular degeneration.

To determine the effects of the matricellular protein SPARC (Secreted Protein, Acidic and Rich in Cysteine) on human retinal pigment epithelial (HRPE) cell behavior in vitro. Proliferation and migration assays were performed on HRPE cells exposed to various concentrations of SPARC. Additionally, HRPE cells were seeded on top of collagen matrices (a 2D model of the retinal scarring disorder known as proliferative vitreoretinopathy or PVR) and were exposed to SPARC over a 7 day period. Changes in matrix contraction were recorded. HRPE cell proliferation was significantly inhibited at 1 and 10 microg/ml SPARC (p<0.01). SPARC protein did not stimulate HRPE cell migration at any of the concentrations used. SPARC did not significantly affect fibronectin-induced HRPE cell migration at SPARC concentrations up to 10 microg/ml. HRPE cell-seeded collagen matrices demonstrated a significant inhibition of matrix contraction by 1 and 10 microg/ml SPARC (t-test; p<0.02 and 0.001, respectively) compared to controls. SPARC protein has anti-proliferative effects on HRPE cells in vitro. In addition, SPARC appears to have an inhibitory effect on HRPE-mediated contraction of 2D collagen matrices. These results are consistent with an important role for SPARC in modulating cell behavior in vitro and may indicate a role for SPARC in modifying HRPE cell activities during the development of PVR and other proliferative retinal diseases.

BACKGROUND/AIMS Epiretinal and retrolental proliferation may occur during prolonged use of the novel tamponade agent perfluorohexyloctane (F₆H₈). This study aims to determine whether there is any histological evidence that F₆H₈has a role in the formation of these membranes. METHODS Eight epiretinal membranes and three opaque posterior lens capsules were excised from patients in whom F₆H₈ had been used as a long term retinal tamponade agent. The membranes and capsules were examined employing light microscopic methods, including immunohistochemistry. RESULTS The epiretinal membranes showed histological features typical of proliferative vitreoretinopathy (PVR) epiretinal membranes, but they also exhibited a dense macrophagic infiltration. In addition, three of the membranes contained multinucleated cells. Macrophages represented up to 30% of the cells present and appeared to contain large intracytoplasmic vacuoles. Similar cells were seen on the back of the posterior lens capsule in one specimen and all three capsules had posterior migration of lens epithelium. CONCLUSION The pathological findings are not simply those of PVR. The macrophage infiltration suggests that there may be a biological reaction to F₆H₈ which could reflect its surmised propensity to emulsify. Further investigations concerning the cellular response to this promising tamponade agent are warranted.