Regulation of stearoyl coenzyme A desaturase expression in human retinal pigment epithelial cells by retinoic acid.

Stearoyl-CoA desaturase (SCD) is a regulatory enzyme involved in the synthesis of the monounsaturated fatty acids palmitoleate and oleate. The regulation of SCD is of physiological importance because the ratio of saturated fatty acids to unsaturated fatty acids is thought to modulate membrane fluidity. Differential display analysis of retinal pigment epithelial (ARPE-19) cells identified SCD as a gene regulated by retinoic acid. Two SCD transcripts of 3.9 and 5.2 kilobases in size were found to be expressed in these cells by Northern blot analysis. All-trans-retinoic acid (all-trans-RA) increased SCD mRNA expression in a dose- and time-dependent manner; an approximately 7-fold increase was observed with 1 microm all-trans-RA at 48 h. SCD mRNA expression was also increased by 9-cis-retinoic acid (9-cis-RA) as well as 4-(E-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl)-1-propenyl)benzoic acid (TTNPB), a retinoic acid receptor (RAR)-specific agonist. AGN194301, a RAR alpha-specific antagonist, suppressed the SCD expression induced by all-trans-RA, TTNPB, and 9-cis-RA. These results indicate the involvement of RAR alpha in the induction of SCD expression by retinoic acid. However, AGN194204, a RXR (retinoid X receptor) pan agonist, also increased SCD mRNA expression. This increase was not blocked by AGN194301, suggesting that an RAR-independent mechanism may also be involved. Thus, SCD expression in retinal pigment epithelial cells is regulated by retinoic acid, and the regulation appears to be mediated through RAR and RXR.

Oxidative stress induces heme oxygenase-1 immunoreactivity in Müller cells of mouse retina in organ culture.

PURPOSE: Heme oxygenase (HO)-1 immunoreactivity (IR) was examined in normal untreated retina and in retinal explants after in vitro treatment with stress agents. METHODS: Enucleated eyes from young adult C3H mice were immediately fixed and cryosectioned and the retina sections processed for immunocytochemistry with antibodies against HO-1 and glial fibrillary acidic protein (GFAP). From other eyes retinas were isolated and maintained in organ culture, either untreated for 4 days maximum or for 21 hours during which the explants were treated the first 3 hours with selected doses of sodium arsenate or hydrogen peroxide. Thereafter, the explants were processed identically with the normal tissue. RESULTS: In the normal retina, HO-1 and GFAP IR was very low. The culturing itself resulted in an increase in both HO-1 and GFAP immunolabeling in Müller cells of explanted retinas. Both sodium arsenate and hydrogen peroxide further induced strong HO-1 IR in Müller cells but not in other retinal cells. In contrast to HO-1, GFAP staining in Müller cells was not altered as a result of treatment, either by sodium arsenate or hydrogen peroxide at any concentration used. CONCLUSIONS: The results show for the first time that HO-1 can be induced in the retina in vitro by conditions of oxidative stress and that enzyme expression is confined exclusively to Müller cells.

Molecular characterization and developmental expression of NORPEG, a novel gene induced by retinoic acid.

We have characterized NORPEG, a novel gene from human retinal pigment epithelial cells (ARPE-19), in which its expression is induced by all-trans-retinoic acid. Two transcripts ( approximately 3 and approximately 5 kilobases in size) have been detected for this gene, which is localized to chromosome band 5p13.2-13.3. Placenta and testis showed the highest level of expression among various human tissues tested. Six ankyrin repeats and a long coiled-coil domain are present in the predicted sequence of the NORPEG protein, which contains 980 amino acid residues. This approximately 110-kDa protein was transiently expressed in COS-7 cells as a FLAG fusion protein and immunolocalized to the cytoplasm. Confocal microscopic analysis of the NORPEG protein in ARPE-19 cells showed threadlike projections in the cytoplasm reminiscent of the cytoskeleton. Consistent with this localization, the expressed NORPEG protein showed resistance to solubilization by Triton X-100 and KCl. An ortholog of NORPEG characterized from mouse encoded a protein that showed 91% sequence similarity to the human NORPEG protein. The expression of Norpeg mRNA was detected in mouse embryo at embryonic day 9.5 by in situ hybridization, and the expression appears to be developmentally regulated. In adult mouse, the highest level of expression was detected in the seminiferous tubules of testis.

Expression of multiple forms of clusterin during light-induced retinal degeneration.

PURPOSE: Clusterin has been associated with active cell death in several different model systems, including animal models of retinal degeneration. Clusterin is also expressed in normal tissues, a finding that leads to the question of how it could then play a cell death-specific role during tissue regression. To address this paradox, we have examined clusterin expression during light-induced retinal damage in rats. METHODS: Normal albino rats were reared in darkness and then exposed to intense visible light to induce retinal degeneration. Clusterin expression was then examined at various times after light treatment. Standard molecular techniques including Northern analysis, immunohistochemistry, and Western analysis were employed. RESULTS: Northern analysis established that the largest increase in clusterin expression occurs after a decrease in interphotoreceptor retinoid binding protein, IRBP, expression (an indication of a photoreceptor cell dysfunction) and after an increase in heme oxygenase 1, HO-1, expression (an oxidative stress inducible gene), suggesting that induction of clusterin expression is an oxidative stress response. Immuno-histochemical analysis with two different clusterin-specific antibodies, anti(SGP-2) and anti(301), localized distinct forms of clusterin to Müller cells and degenerating photo-receptor cells. Western analysis demonstrated degeneration associated isoforms of clusterin in light treated retina that are not present in normal retina. CONCLUSION: Clusterin over-expression is characteristic of a retinal degeneration phenotype and we propose that clusterin action may be defined by the nature in which it is modified. We hypothesize that alternate processing leads to retinal degeneration-specific forms of the protein (65, 61, and 50 kDa) that are not present in normal retina.

Circadian-dependent retinal light damage in rats.

PURPOSE: To determine the relative susceptibility of rats to retinal light damage at different times of the day or night. METHODS: Rats maintained in a dim cyclic light or dark environment were exposed to a single dose of intense green light beginning at various times. Normally, light exposures were for 8 or 3 hours, respectively, although longer and shorter periods were also used. Some animals were treated with the synthetic antioxidant dimethylthiourea (DMTU) before or after the onset of light. The extent of visual cell loss was estimated from measurements of rhodopsin and retinal DNA levels 2 weeks after light treatment. The time course of retinal DNA fragmentation, and the expression profiles of heme oxygenase-1 (HO-1) and interphotoreceptor retinol binding protein (IRBP) were determined 1 to 2 days after exposure. RESULTS: When dark-adapted, cyclic light-reared or dark-reared rats were exposed to intense light during normal nighttime hours (2000-0800) the loss of rhodopsin or photoreceptor cell DNA was approximately twofold greater than that found in rats exposed to light during the day (0800-2000). The relative degree of light damage susceptibility persisted in cyclic light-reared rats after dark adaptation for up to 3 additional days. For rats reared in a reversed light cycle, the light-induced loss of rhodopsin was also reversed. Longer duration light treatments revealed that dim cyclic light-reared rats were three- to fourfold more susceptible to light damage at 0100 than at 1700 and that dark-reared animals were approximately twofold more susceptible. Intense light exposure at 0100 resulted in greater retinal DNA fragmentation and the earlier appearance of apoptotic DNA ladders than at 1700. The extent of retinal DNA damage also correlated with an induction of retinal HO-1 mRNA and with a reduction in IRBP transcription. Antioxidant treatment with DMTU was effective in preventing retinal light damage when given before but not after the onset of light. CONCLUSIONS: These results confirm earlier work showing greater retinal light damage in rats exposed at night rather than during the day and extend those findings by demonstrating that a single, relatively short, intense light exposure causes a circadian-dependent, oxidatively induced loss of photoreceptor cells. The light-induced loss of photoreceptor cells is preceded by DNA fragmentation and by alterations in the normal transcriptional events in the retina and within the photoreceptors. The expression profile of an intrinsic retinal factor(s) at the onset of light exposure appears to be important in determining light damage susceptibility.

Overexpression of heme oxygenase in neuronal cells, the possible interaction with Tau.

Increased expression of heme oxygenase-1 (HO-1) is a common feature in a number of neurodegenerative diseases. Interestingly, the spatial distribution of HO-1 expression in diseased brain is essentially identical to that of pathological expression of tau. In this study, we explored the relationship between HO-1 and tau, using neuroblastoma cells stably transfected with sense and antisense HO-1 constructs as well as with the vector alone. In transfected cells overexpressing HO-1, the activity of heme oxygenase was increased, and conversely, the level of tau protein was dramatically decreased when compared with antisense HO-1 or CEP transfected cells. The suppression of tau protein expression was almost completely reversed by zinc-deuteroporphyrin, a specific inhibitor of heme oxygenase activity. The activated forms of ERKs (extracellular signal-regulated kinases) were also decreased in cells overexpressing HO-1 although no changes in the expression of total ERK-1/2 proteins were observed. These data are in agreement with the finding that the expression of tau is regulated through signal cascades including the ERKs, whose activities are modulated by oxidative stresses. The expression of tau and HO-1 may be regulated by oxidative stresses in a coordinated manner and play a pivotal role in the cytoprotection of neuronal cells.

Heme-binding by Drosophila retinoid- and fatty acid-binding glycoprotein (RFABG), a member of the proapolipophorin gene family.

We previously have cloned and characterized a retinoid- and fatty acid-binding glycoprotein (RFABG) isolated from the heads of Drosophila melanogaster. The protein is composed of two glycosylated subunits (Mr = >200,000 and 70,000) and is a member of the proapolipophorin gene family. Spectral analysis of purified RFABG revealed an absolute absorbance peak at 405 nm, which is typical for a heme-containing protein. The aim of the present study was to characterize the heme-binding properties of RFABG. Upon saturation of the protein solution with carbon monoxide followed by dithionite reduction, a red shift of the Soret peak to 424 nm and the characteristic alpha- and beta- bands at 567 and 539 nm were observed. Native RFABG contains approximately 0.175 moles of heme (mol/mol) indicating that purified RFABG is primarily the apoprotein. Hemin-agarose affinity chromatography of the native RFABG followed by Western blot analysis showed a single immunoreactive band at 70 kDa, indicating that the heme-binding domain resides in the 70 kDa subunit. Although retinoid and fatty acid also bind to the 70 kDa subunit, no competition was observed when an excess of heme was added to a solution of retinoid or fatty acid bound to RFABG. Heme added to a solution of purified RFABG bound in a saturable manner with an affinity of 3.8 x 10(-7) m.Thus, the current study clearly demonstrates that retinoid- and fatty acid-binding glycoprotein is a novel heme-binding protein, which may be involved in the transport and/or metabolism of heme in Drosophila.

Identification of a new member of transforming growth factor-beta superfamily in Drosophila: the first invertebrate activin gene.

Activins, a subgroup of the transforming growth factor-beta (TGF-beta) superfamily, have been extensively studied in vertebrates for their roles in growth and development. However, activins are not thought to be expressed in invertebrates. The identification of the first invertebrate activin gene is reported here. A genomic clone representing 102 F region of the Drosophila chromosome 4 is found to encode a putative activin beta. The predicted protein sequence has a multibasic protease site that would generate a mature C-terminal peptide containing 113 amino acids showing > 60% similarity to the vertebrate activin beta B (inhibin beta B) sequences. A TGF-beta family signature as well as all 9 cysteine residues conserved in the vertebrate activins are also present in this mature peptide sequence. Northern blot and RT-PCR analyses indicated that the activin beta gene is expressed in embryo, larva and adult stages of Drosophila.

Light history and age-related changes in retinal light damage.

PURPOSE: To determine the effects of age and long-term light- or dark-rearing environments on acute, intense-light-mediated retinal degeneration. METHODS: Male albino rats were maintained in a dim cyclic light environment or in darkness for as long as 1 year. When aged 2, 4, 8, and 12 months, some rats were given the synthetic antioxidant dimethylthiourea (DMTU) by intraperitoneal injection and were exposed to intense visible light for as long as 24 hours. Uninjected control rats were exposed to light at the same time. Other rats were treated with light of lower intensity for various periods. Two weeks after intense-light treatment, photoreceptor cell degeneration was estimated by determining the level of rhodopsin and by measuring the content of photoreceptor cell DNA. Light-induced changes in retinal DNA were analyzed immediately after exposure by neutral gel electrophoresis and by 8-hydroxy-deoxyguanosine measurements. Expression of the antioxidative stress protein heme oxygenase-1 (HO-1) was determined by northern blot analysis of mRNA in retinal extracts. RESULTS: At all ages, rats reared in cyclic dim-light conditions had lower rhodopsin levels than did rats reared in darkness; photoreceptor cell DNA levels were unaffected by the rearing environment. Senescent losses in rhodopsin and retinal DNA were significant after rats were 12 months old. Dim-light-reared rats exhibited an age-related increase in retinal light damage susceptibility, whereas dark-reared rats were equally susceptible to damage at all ages. In both types of rats, the mechanism of light-induced cell death involved an apoptotic process, visualized by the pattern of DNA fragments on electrophoretic gels. The process also induced the expression of HO-1 mRNA. Photoreceptor cell loss determined by biochemical measurement, DNA fragmentation, and HO-1 induction were dramatically reduced by the administration of DMTU. CONCLUSIONS: The age-related increase in susceptibility to retinal light damage in rats is influenced by their long-term daily light history. Decreasing retinal irradiance by dark-rearing eliminates the age-related increase in light damage, suggesting a correlation between light environment and retinal gene expression associated with damage. In all rats, retinal light damage resulted in a pattern of DNA fragmentation consistent with apoptotic cell death and in an increased expression of HO-1 mRNA. Antioxidant treatment greatly reduced apoptosis and HO-1 expression. This indicates that light damage involves an oxidative process that may also trigger apoptosis in the retina. The rat aging model may provide useful insights into the role of light environment associated with retinal degeneration in an aging human population.

Control of Drosophila retinoid and fatty acid binding glycoprotein expression by retinoids and retinoic acid: northern, western and immunocytochemical analyses.

In Drosophila, thorough retinoid deprivation is possible, optimizing investigation of the effects of vitamin A metabolites and retinoic acid on the visual system. Retinoids had been found to control transcription and translation of Drosophila's opsin gene. To follow this line of inquiry, we examined the effect of retinoids on the translation and transcription of a Drosophila Retinoid and Fatty Acid Binding Glycoprotein. Western blots showed that this protein is high in retinoid replete flies and low in deprived flies. Flies grown on media capable of activating the opsin gene's transcription and which contain alternate transcription activators including retinoic acid yielded extracts containing significant amounts of Retinoid and Fatty Acid Binding Glycoprotein. Immunocytochemistry confirmed its absence in deprived flies and its presence in flies reared or replaced on these diverse media containing retinoids or general nutrients. Immunocytochemistry localized Retinoid and Fatty Acid Binding Glycoprotein to the Semper (cone) cells and the intraommatidial matrix (the interphotoreceptor matrix of the ommatidium). Positive staining of Semper cells in mutants of the opsin gene and a mutant lacking receptors suggests that Retinoid and Fatty Acid Binding Glycoprotein does not depend on presence of opsin and that it is not synthesized in receptor cells respectively. Northern blots demonstrated greatly diminished mRNA for Retinoid and Fatty Acid Binding Glycoprotein in flies grown on deprivation food relative to flies grown on normal food. Although the synthesis of Retinoid and Fatty Acid Binding Glycoprotein does not require chromophore precursors as does that of opsin, the control of Retinoid and Fatty Acid Binding Glycoprotein and opsin transcription by retinoids including retinoic acid might very well be the same. Our results suggest that Retinoid and Fatty Acid Binding Glycoprotein may be involved in retinoid transport. Also, Semper cells may be analogous to vertebrate retinal pigment epithelium in retinoid metabolism and/or delivery.

Inflammatory cytokines induce intercellular adhesion molecule-1 (ICAM-1) mRNA synthesis and protein secretion by human retinal pigment epithelial cell cultures.

Retinal inflammatory diseases in man are associated with an upregulation in the expression of intercellular adhesion molecule-1 (ICAM-1) in cells within the retina and with an increase in soluble ICAM-1 within the vitreous. These studies suggest that this protein may contribute to immunopathological processes within the eye. The effects of inflammatory mediators on the regulation of the expression and secretion of ICAM-1 by human retinal pigment epithelial cell cultures (HRPE) were investigated in order to identify the possible source of soluble ICAM-1 and the conditions which enhance its production. Immunofluorescence studies on TNF-alpha and/or IFN-gamma treated HRPE cells demonstrated cellular expression of ICAM-1 which was predominantly localized to intercellular junctions. Moreover, treatment of HRPE for 24 h with tumour necrosis factor alpha (TNF-alpha) (10 ng/ml), interferon gamma (IFN-gamma) (500 u/ml), interleukin 1 alpha (IL-1 alpha) (10 ng/ml) and IL-1 beta (10 ng/ml) results in the secretion of ICAM-1, ranging from 9 to 13 ng per 10(6) cells. IFN-gamma acts synergistically with (TNF-alpha) and IL-1 in the secretion of ICAM-1 by HRPE. Only 1.75 ng of soluble ICAM-1 was detected in untreated HRPE cells. In contrast, lipopolysaccharide (LPS), IL-6, IFN-alpha or TGF-beta did not exhibit any influence on ICAM-1 secretion by these cells. Northern blot analysis reveals an increased expression of ICAM-1 mRNA in HRPE stimulated with IFN-gamma, TNF-alpha or IL-1 for 24 h. In untreated cells, ICAM-1 mRNA is not detectable. There is a progressive increase in ICAM-1 mRNA levels in cytokine-treated HRPE, that reaches steady state by 12 h. Furthermore, a close correlation is noted between ICAM-1 mRNA levels and the secretion of ICAM-1 protein, suggesting regulation at the level of gene transcription. ICAM-1 secretion by RPE might actively participate in the immune reactions in the retina, by recruiting and activating lymphocytes, and contribute to the immunopathological processes in inflammatory diseases.

Molecular characterization and developmental expression of a retinoid- and fatty acid-binding glycoprotein from Drosophila. A putative lipophorin.

A detailed understanding of the mechanism of lipid transport in insects has been hampered by the inability to identify the proapolipophorin gene that encodes apolipophorins I and II, the principal protein components of lipophorin, the lipid transport vehicle. Here we provide the first molecular description of the Drosophila gene encoding a retinoid- and fatty acid-binding glycoprotein (RFABG) and present evidence that it is a member of the proapolipophorin gene family. The gene, localized to the chromosome 4 (102 F region), encodes a 3351-amino acid protein that could serve as the precursor for the approximately 70-kDa and >200-kDa polypeptides associated with RFABG. The N-terminal sequence of the approximately 70-kDa polypeptide and that predicted for the >200-kDa polypeptide showed high sequence similarity to blowfly apolipophorin II and apolipophorin I, respectively. The RFABG precursor contains a signal peptide and exhibits a multidomain mosaic protein structure, which is typical of extracellular proteins. It has structural domains similar to lipid-binding proteins, namely vitellogenins and apolipoprotein B. The protein also contains a domain similar to the D domain of von Willebrand factor and mucin. The gene is expressed in the Drosophila embryo during development in cells that make up the amnioserosa and fat bodies. Immunolocalizations using specific antibodies against RFABG reveal that the protein is initially dispersed through the embryonic amnioserosa sac and latter concentrated at skeletal muscle-epidermis apodemeal contact junctions during larval development. This novel gene may play an important role in the transport of lipids, including retinoids and fatty acids, in insects.

Transforming growth factor-beta inhibits the cytokine-mediated expression of the inducible nitric oxide synthase mRNA in human retinal pigment epithelial cells.

Human retinal pigment epithelial (RPE) cells in culture respond to a mixture of cytokines (IFN-gamma, IL-1 beta, TNF-alpha) by producing large amounts of nitric oxide. Transforming growth factor-beta, unlike other growth factors, was found to inhibit this response by more than 75%. The expression of mRNA for the inducible form of nitric oxide synthase in RPE cells treated with cytokines was demonstrated by reverse transcription-polymerase chain reaction, sequencing of the PCR product and northern blotting. Transforming growth factor-beta was highly effective in inhibiting (by 75%) the cytokine-induced nitric oxide synthase mRNA expression. This response by RPE may play an important role in the etiology of infectious and inflammatory diseases affecting retina.

Photoreceptor cells in the vitiligo mouse die by apoptosis. TRPM-2/clusterin expression is increased in the neural retina and in the retinal pigment epithelium.

PURPOSE: To determine the mechanism of photoreceptor cell death in the vitiligo mouse, a model of retinal degeneration in which the genetic defect is not retina specific but is instead caused by single point mutation in the microphthalmia (mi) gene that codes for a basic helix-loop-helix DNA transcription factor. METHODS: Detection of apoptotic cells was performed in fixed retinal tissue using the TUNEL assay in animals 1, 2, 4, 6, 8, 16, 32, 40, and 52 weeks. Electron microscopic analysis was used to confirm the morphologic hallmarks of apoptosis, and Southern blot analysis was used to detect internucleosomal DNA fragmentation. Additionally, the expression of a gene associated with apoptosis, TRPM-2/clusterin, was examined. RESULTS: At ages beyond the time of normal retinal programmed cell death, vitiligo retinas had significantly more TUNEL-positive photoreceptor cells and more photoreceptor cells with condensed chromatin than controls. DNA internucleosomal fragmentation ladders were present in vitiligo retinas even as late as 15 weeks, a time well beyond developmental apoptosis in controls. TRPM-2/clusterin mRNA levels in vitiligo neural retinas were similar to controls initially but were two times greater than controls by 12 weeks. Surprisingly, TRPM-2/clusterin mRNA levels were elevated in the retinal pigment epithelium in the mutant; the expression at one week was two times greater than normals and remained elevated for many months, even though retinal pigment epithelial cells showed no morphologic evidence of apoptosis. CONCLUSIONS: The morphologic and biochemical data suggest that photoreceptor cells die by apoptosis in vitiligo mice. The increased retinal TRPM-2/clusterin mRNA levels may be a direct response to these events. The increased expression of this gene in the retinal pigment epithelium, however, may reflect its role in tissue regression and membrane remodeling. Mechanisms by which the mi gene defect might result in the vitiligo retinopathy are proposed.

Induction of heme oxygenase-1 mRNA and protein in neocortex and cerebral vessels in Alzheimer's disease.

Previous studies demonstrated the specific association of heme oxygenase (HO)-1 protein to the neurofibrillary pathology of Alzheimer's disease (AD). In this study, we used reverse transcription-polymerase chain reaction methods to show the increased expression of HO-1 but not HO-2 mRNA transcripts in cerebral cortex and cerebral vessels from subjects with AD compared with age-matched non-AD controls. Neither the HO-1 nor the HO-2 mRNA levels was altered in the cerebellum, a brain region usually spared from the pathological alterations of AD. There was no clear evidence that the expression of HO-1 in these tissues was related to postmortem interval, cause of death, or the age of the subjects studied. Using immunoblotting methods, we further showed that HO-1 protein content was increased in neocortical and vascular samples from AD subjects compared with controls. Our findings suggest the specific induction of HO-1 mRNA and protein in the cerebral cortex and cerebral vessels but not HO-2 mRNA or protein in association with the pathological lesions of the disease.

Induction of heme oxygenase 1 in the retina by intense visible light: suppression by the antioxidant dimethylthiourea.

The effect of intense visible light (light damage) on the expression of heme oxygenase 1 (HO-1), a protein induced by oxidative stress, was investigated in the rat retina. A sensitive reverse transcription-PCR assay demonstrated the expression of mRNA for HO-1 as well as HO-2, the noninducible HO form, in the normal retina. As analyzed by Northern blotting, however, HO-1 mRNA was barely detectable under normal circumstances. After exposure to intense visible light, retinas had markedly higher HO-1 mRNA levels than unexposed controls, with increases up to 52- and 98-fold at 12 and 24 hr of exposure, respectively. Intense light exposure also resulted in an increase in HO-1 protein. In contrast, no appreciable change in HO-2 mRNA or protein was observed. The increase in HO-1 message was more pronounced in rats previously reared in the dark than in those reared in a weak cyclic-light environment. A marked decrease from the high level of HO-1 mRNA induced by light insult was observed when the animals were allowed to recover in the dark for 24 hr after light exposure. Most important, treatment of animals with 1,3-dimethylthiourea, a synthetic antioxidant, prior to light exposure effectively blocked the increase in HO-1 mRNA. Thus, HO-1 is a sensitive marker for assessing light-induced insult in the retina. Since increased expression of HO-1 is thought to be a cellular defense against oxidative damage, its expression may play an important role in protecting the retina against light damage.

Expression of mRNA for atrial natriuretic peptide receptor-A in human liver: detection using RT-PCR.

cDNA preparations obtained from human liver poly A+ RNA by reverse transcription were subjected to polymerase chain reaction. Primers used in the reaction were designed from the reported cDNA sequence for human placental atrial natriuretic peptide receptor-A (ANPRA). Sequence analysis of the amplified product (approximately 700 bp) showed 100% identity to the 2476-3189 bp region of the reported cDNA sequence of human placental ANPRA. Northern blot analysis of human liver poly A+ RNA fractions showed a hybridization signal at approximately 4.4 kb, identical to the signal obtained from the poly A+ RNA fractions of human placenta. These results indicate the possible mRNA expression for atrial natriuretic peptide receptor-A in human liver.

Changes in clusterin expression associated with light-induced retinal damage in rats.

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.