B. Wiggert

Differential binding to soluble nuclear receptors and effects on cell viability of retinol and retinoic acid in cultured retinoblastoma cells.

Abstract Human retinoblastoma cells in culture contain soluble receptors for both 3H-retinol and 3H-retinoic acid which are separate and distinct as assessed by specificity, enzyme susceptibility and binding affinity. Total cellular binding of retinol correlates well with its rapid effect on cell mortality. A limited number of soluble nuclear receptor sites for 3H-retinoic acid but not 3H-retinol are observed after incubation of the 3H-retinoid with intact cells indicating a possible preferential effect of retinoic acid at the gene level.

Choroideremia: A Clinical, Electron Microscopic, and Biochemical Report

An asymptomatic 19-year-old male with choroideremia had diffuse loss of retinal pigment epithelium (RPE) and choroid except for the periphery and macula. Fluorescein angiography of the arteriovenous phase showed absence of retinal pigment epithelium and exaggerated visualization of choroidal vessels in involved areas. The mother was a typical carrier with pigment stippling of the midperipheral retina. Histopathologic examination of affected areas of one eye showed marked degeneration of the outer and midretina with loss of retinal pigment epithelium and Bruchs membrane, absence of choriocapillaris, chorioretinal adhesions and gliosis. Atrophy of inner and mid-choroid was also observed. Pigmented macrophage-like cells had migrated into the outer and midretinal layers. Electron microscopy disclosed macrophage-like cells with trilaminar structures and photoreceptor phagosomes in the RPE and outer retina. Remnants of photoreceptor outer segments were adherent to the plasma membranes of the macrophage-like cells. Biochemical analysis of retinal tissue samples for interphotoreceptor retinoid-binding protein (IRBP) showed marked reduction in the 146K bands in the equator and posterior pole in the patient compared to controls. Cyclic nucleotide content was altered in the retinal equator. Cyclic AMP was several-fold higher in the RPE-choroid complex of the affected eye than in the control.

A developmental study of interphotoreceptor retinoid-binding protein (IRBP) in single and double homozygous rd and rds mutant mouse retinae

Interphotoreceptor retinoid-binding protein (IRBP) was studied using immunochemical and immunocytochemical techniques in retinae of mice with allelic combinations at the rd and rds loci at different stages of development and degeneration. Until postnatal day 7 (P7), IRBP is located intracellularly in developing retinae of the different genotypes. Thereafter, IRBP is present mainly in the interphotoreceptor matrix. As previously noted, cell death is slowest in the heterozygous +/+,rds/+ mutant with loss increasing in order in +/+,rds/rds, rd/rd, rds/rds and rd/rd,+/+ animals. The IRBP content of the total retina also approximates this pattern, with lowest amounts by far in rd/rd, rds/rds and rd/rd,+/+ mutants (after P14). Interestingly though, IRBP loss significantly precedes visual cell loss in the rd/rd,rds/rds retina. In all the mutants, the remaining rod cells in the outer nuclear layer exhibit synthesis of intracellularly located IRBP at late stages of degeneration. In the single homozygous rd/rd,+/+ and the double homozygous rd/rd,rds/rds mutants, IRBP is present intracellularly during the entire degenerative process with somewhat less intracellular IRBP in the rd/rd,rds/rds mutant. Retinae of homozygous +/+,rds/rds and heterozygous +/+,rds/+ animals exhibit a normal distribution pattern of IRBP immunoreactivity until loss of photoreceptor cells becomes pronounced at later stages of the disease. Many of the remaining cells at this time are probably cone elements although they are structurally changed. Double labeling with IRBP and S-antigen demonstrates, in many but not all, the presence of both proteins in the same cell body. Immunocytochemistry clearly demonstrated the presence of IRBP in remaining photoreceptor cells at late stages of the disease. Thus, the biochemically measured loss of IRBP appears to be a complex process neither directly dependent on the loss of photoreceptor outer segments and reduced interphotoreceptor matrix space (e.g. there is a sustained IRBP level in rodless rds mutants) nor simply due to cell death (e.g. in the rd/rd,rds/rds mutant, IRBP loss significantly precedes cell loss). That this IRBP is mainly intracellular, however, may indicate an abnormality in secretion which, combined with other factors, induces a degenerated and less differentiated phenotype.

VITAMIN A RECEPTORS: RETINOL BINDING IN NEURAL RETINA AND PIGMENT EPITHELIUM

Abstract— With sucrose density gradient analysis, bovine retinal cytosol demonstrates 2S and 7S retinol‐binding species; binding in pigment epithelial cytosol is predominantly to a 2S species. Binding of retinol to the 2S component in retina is unaffected by retinoic acid or retinyl palmitate whereas the ester effectively competes for 2S binding in pigment epithelium. Specific retinol binding can also be demonstrated by gel filtration on Sepharose 4B; no high molecular weight (> 100–200,000) retinol binding species are observed by this technique. Both the 2S and 7S binding species in retinal cytosol are protein in nature and differentially susceptible to proteolysis. The 2S and 7S species appear to be separate and distinct since chaotropic agents such as sodium thiocyanate or KCl and CaCl2 do not seem to convert the 7S species into 2S subunits. Scatchard plot analysis indicates high affinity retinol binding to the 2S receptor. Computer analysis of the binding data yields Ka=3 × 108, n = 1, a molecular size of 16,200 and ΔG0=−9.5 kcal/mol.

Oxidative Damage and Responses in Retinal Nuclei Arising from Intense Light Exposure

Prolonged or high intensity visible light exposure leads to photoreceptor cell damage and loss by incompletely understood mechanisms. In the rat retina, the sequence of events associated with intense light damage is triggered by the bleaching of rhodopsin (1), and the extent of damage is modulated by other photoreceptor cell proteins involved in visual transduction (2). Thus, environmental light-rearing conditions that alter the steady state levels of rhodopsin, α-transducin and s-antigen (arrestin) can affect the ultimate fate of visual cells (2,3). However, irrespective of their prior light-rearing environment, when rats are pretreated with natural or synthetic antioxidants, retinal light damage is less than in unsupplemented animals (4–8). This indicates that intense light exposure also results in oxidative reactions within the photoreceptor cell.

Nuclear Uptake of Retinoids: Autoradiographic Evidence in Retinoblastoma Cells In Vitro

The special role of vitamin A (retinol) in vision is well known (Wald, 1968). The more general role that vitamin A plays in differentiation and maintenance of epithelial tissues is less well understood. There are several interesting analogies, however, between vitamin A and the steroid hormones which may enable us to better understand the vitamin’s general mechanism of action (Wolf and De Luca, 1970). Both vitamin A and the hormones affect tissue development and growth and have specific intracellular receptors in target tissues (Bashor et al., 1973), including the neural retina (Wiggert et al., 1977~). We have recently presented preliminary biochemical evidence that retinoic acid, a normal metabolite of retinol, is preferentially taken up by nuclei ofretinoblastoma cells in culture (Wiggert et al., 1977b), again in a manner similar to the well-known accumulation of steroid hormones in target cell nuclei. In the present communication, we would like to present further evidence using alternative techniques that retinoic acid, but not retinol, is preferentially taken up in retinoblastoma nuclei and that it may be the “active” retinoid in these cultured human cells.

Morphological and Biochemical Studies of the Retinal Degeneration in the Vitiligo Mouse

The vitiligo mouse has been studied since the mid 1980’s for the depigmentary condition of its skin and fur. As such, it is a promising model for the human skin disease vitiligo ( 1 ). Vitiligo may occur in isolation or in combination with other disorders, including retinal degeneration (Vogt-Koyanagi-Harada syndrome) (2). In 1988, Dr. Richard Sidman and co-workers provided a preliminary report in Mouse News Letter that the vitiligo mouse had a slow progressive retinal degeneration (3). We obtained breeding pairs from Dr. Sidman and set out to characterize the retinal degeneration in this mouse and to determine the etiology of the disease with the hope of eventually designing strategies to treat the disorder. This chapter will review our findings about the morphologic, electrophysiologic and biochemical characteristics of this mutant with particular emphasis on promising results from studies of retinoid metabolism.