Retinal pigment epithelial (RPE) cells form a functional complex with photoreceptor neurons of the retina, interacting through the interphotoreceptor matrix (IPM). We now provide evidence that the gene for pigment epithelium-derived factor (PEDF), a protein possessing neurotrophic and neuronal-survival activities, is highly expressed by both fetal and young adult RPE cells. PEDF mRNA is present in RPE cells of the human eye at 17 weeks of gestation, demonstrating its potential for action in vivo during early retinal development. The PEDF protein is secreted in vivo where it constitutes a part of the fetal and adult IPM surrounding photoreceptor outer segments. A polyclonal PEDF antibody recognizes at least four isoforms of secreted human and bovine PEDF by two dimensional gel analysis, and detects a similar 50 kDa protein in the IPM of several other vertebrate species. Within soluble extracts of RPE cells, however, where little, if any, of the 50 kDa species can be detected, an immunoreactive 36 kDa protein is observed by Western blot analysis. By immunofluorescence, PEDF is localized intracellularly in association with the nucleus, presumptive secretory granules, and cytoskeletal elements of cultured RPE cells with PEDF and actin antibodies colocalizing to the same cytoskeletal structures. During initial stages of attachment, PEDF and actin also concentrate at the tips of pseudopods extended by the cultured RPE cells. However, with successive passages, synthesis, and secretion of the PEDF protein as well as transcription of its mRNA decrease and are lost by about 10 passages. In parallel, cultured RPE cells lose their proliferative potential and change from an epithelial-like morphology in early passages to a more fibroblast-like appearance by about the 10th passage. PEDF is thus apparently present intracellularly and extracellularly in both fetal and early adult periods where it could be involved in cellular differentiation and survival and with its loss, in the onset of senescence.
Prolonged periods of high-intensity visible light exposure lead to photoreceptor cell degeneration, but the mechanism of damage is not understood. Increased clusterin mRNA levels have been found in several models of apoptosis, as well as in neurodegeneration. We report here that changes in clusterin mRNA levels are also associated with light-induced retinal damage in adult male albino rats. Animals previously maintained in darkness or a weak cyclic light environment were exposed to intense visible green light for up to 24 h. Some rats were pretreated with a synthetic antioxidant, dimethylthiourea (DMTU), which reduces photoreceptor cell degeneration. Clusterin mRNA steady-state levels increased with the duration of light exposure in both cyclic light and dark reared animals, suggesting that an apoptotic mechanism may be involved. Animals pretreated with DMTU showed a delay in the initial increase in clusterin mRNA levels, suggesting that oxidative damage is involved in the damage mechanism. However, the incomplete suppression of increasing steady-state clusterin mRNA levels by DMTU suggests that either oxidative damage triggers a second pathway or multiple damage mechanisms are induced in the retina by light exposure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.