Biomedical subjects

Donald J Zack

Publications and source records attributed to Donald J Zack.

44 records · Page 3Linked to original sources

PubMed2002

Identification of novel bovine RPE and retinal genes by subtractive hybridization.

PURPOSE: Understanding of the specialized function of the retinal pigment epithelium (RPE) can be aided by the identification and characterization of genes that are preferentially expressed in the RPE. With this aim, we undertook a systematic effort to identify and begin characterization of such genes. METHODS: A subtracted bovine RPE cDNA library was generated through subtractive hybridization using a single-stranded circular bovine RPE cDNA library as target and biotinylated mRNA from bovine heart and liver as alternate drivers. Approximately one thousand of the resulting subtracted cDNA clones were partially sequenced and analyzed, and a non-redundant set of one hundred of these cDNAs were examined for tissue expression pattern using a mini-Northern blot procedure and for identity by sequence analysis. RESULTS: The subtraction method successfully allowed the enrichment of cDNAs that are preferentially expressed in the RPE. Out of the analyzed clones, expression of forty-five clones was verifiable by Northern blotting. Of these, a significant proportion of cDNAs were preferentially expressed in the RPE. We observed that the expression of some subtracted cDNAs was restricted to the retina and no expression was detected in the RPE. These retinal clones were obtained in addition to RPE clones presumably because the initial RPE RNA population was contaminated with a small proportion of retinal RNA. Two thirds of the identified RPE and retinal cDNAs are likely to represent novel genes because they do not have homology to known genes in the databases. CONCLUSIONS: Genes that are specifically or predominantly expressed in the RPE/retina are likely to be important for retinal function. We have identified novel cDNAs from bovine RPE and retina by subtractive hybridization. These cDNAs can be used as starting material for the identification of corresponding human genes expressed in the RPE and retina. The human genes thus identified are likely to contain good candidate genes for retinal disease.

Animals↗

PubMed2002

Functional analysis of cone-rod homeobox (CRX) mutations associated with retinal dystrophy.

Mutations in the photoreceptor transcription factor cone-rod homeobox (CRX) have been identified in patients with several forms of retinal degenerative disease. To investigate the mechanisms by which these mutations cause photoreceptor degeneration, CRX constructs representing eleven known mutations, as well as a set of C-terminal deletions, were generated and tested for their ability to activate a rhodopsin-luciferase reporter in a transient cell transfection assay. To further define functional domains, several Gal4dbd-Crx fusions were similarly tested using a Gal4 response element containing heterologous promoter. This analysis demonstrated that the C-terminal region, between amino acids 200 and 284, is essential for CRX-mediated transcriptional activation. Consistent with this, four mutants carrying C-terminal truncations demonstrated significantly reduced transcriptional activation. Confirming the importance of the homeodomain (HD), four of the five mutants carrying HD missense mutations displayed altered transactivating activity, either decreased (three) or increased (one). In vitro protein-DNA binding assays (EMSAs) with CRX-HD peptides representing the three HD mutants with decreased transactivating activity, indicated that the alteration was due to reduced, but not abolished, DNA binding to CRX targets. Taken together, these results support the hypothesis that CRX mutations involved in human photoreceptor degeneration act by impairing CRX-mediated transcriptional regulation of the photoreceptor genes. However, a clear relationship between the magnitude of biochemical abnormality and degree of disease severity was not observed, suggesting that other genetic and environmental modifiers may also contribute to the disease phenotype.

Amino Acid Sequence↗

PubMed2002

Butterfly-shaped pattern dystrophy: a genetic, clinical, and histopathological report.

OBJECTIVES: To identify the disease-causing mutation in a large family segregating dominantly inherited butterfly-shaped pattern dystrophy (BPD) and to describe the microscopic pathological changes observed in a member of this family. METHODS: Seventeen individuals at risk for dominantly inherited BPD in a family were examined and blood samples obtained. Linkage analysis and mutation screening of the human retinal degeneration slow (RDS)/peripherin locus were performed. Light and electron microscopic examinations were performed on 1 postmortem eye of 1 affected individual. RESULTS: Four individuals demonstrated macular degenerative changes with diminished visual acuity, and 3 others exhibited early signs of atrophy without visual deficits. Microscopic examination of the left eye of 1 patient revealed an area of total loss of the retinal pigment epithelium (RPE) and photoreceptor cell layer with intact choriocapillaris and lipofuscin-containing cells in the subretinal space. Outside the area of RPE atrophy, the RPE was greatly distended by lipofuscin. The disease locus in this family was mapped to 6p21.2, the region of the RDS/peripherin gene. Further analysis identified a G-->A change at nucleotide position 637 of RDS/peripherin, predicting a novel Cys213Tyr substitution in all affected members of the family. CONCLUSIONS: This study describes a new RDS/peripherin mutation for BPD and provides the first combined genetic-pathological study of this condition, to our knowledge. CLINICAL RELEVANCE: Accumulation of lipofuscin in RPE is a prominent feature of several retinal disorders, including age-related macular degeneration. Further elucidation of the cellular and molecular mechanism of BPD may provide insight into pathogenesis and lead to novel treatment approaches for this and other macular degenerations.

Adult↗

PubMed2002

Inducible expression of vascular endothelial growth factor in adult mice causes severe proliferative retinopathy and retinal detachment.

Transgenic mice with vascular endothelial growth factor (VEGF) driven by the rhodopsin promoter (rho/VEGF mice) develop neovascularization that originates from the deep capillary bed of the retina and grows into the subretinal space. In rho/VEGF mice, VEGF expression in photoreceptors begins between postnatal days 5 and 7, the period when the deep capillary bed is developing. An important question is whether or not the developmental stage of the deep capillary bed is critical for occurrence of neovascularization. Also, although rho/VEGF mice are extremely useful for the study of ocular neovascularization, there are some applications for which the early onset of VEGF expression is a disadvantage. In this study, we used the reverse tetracycline transactivator (rtTA) inducible promoter system coupled to either the rhodopsin or interphotoreceptor retinoid-binding protein (IRBP) promoter to control the time of onset of VEGF transgene expression in photoreceptors. In the absence of doxycycline, adult double-transgenic rho/rtTA-TRE/VEGF or IRBP/rtTA-TRE/VEGF mice showed little VEGF transgene expression and no phenotype. The addition of doxycycline to the drinking water resulted in prominent transgene expression and evidence of neovascularization within 3 to 4 days. Like rho/VEGF mice, the neovascularization originated from the deep capillary bed of the retina, but it was more extensive and caused outer retinal folds followed by total retinal detachment. Real-time polymerase chain reaction and enzyme-linked immunosorbent assay demonstrated that the mice with inducible expression of VEGF that developed retinal detachment had much higher ocular levels of VEGF mRNA and protein compared to rho/VEGF mice that manifest a much milder phenotype. These data demonstrate that regardless of developmental stage of the vascular bed, increased expression of VEGF in the retina is sufficient to cause neovascularization, and high levels of expression cause severe neovascularization and traction retinal detachment. Mice with inducible expression of VEGF in the retina provide a valuable new model of ocular neovascularization.

Animals↗

PubMed2002

Protein Phosphatase 1 binds strongly to the retinoblastoma protein but not to p107 or p130 in vitro and in vivo.

PURPOSE: To identify and characterize retinoblastoma protein (pRb) binding proteins that may influence retinoblast proliferation and retinal pigment epithelial cell survival. METHODS: The yeast two-hybrid system was used to screen a bovine retinal cDNA library and to characterize positive clones. DNA sequencing and site-directed mutagenesis were used for further analysis. Co-immunoprecipitation experiments were used to confirm the results of the two-hybrid system in vivo. RESULTS: In the two-hybrid system, Protein Phosphatase 1alpha1 (PP1alpha1) binds the retinoblastoma protein. Unlike several other pRb binding proteins, PP1alpha1 binds only weakly to the Rb family member p107, and does not demonstrate detectable binding to p130. Confirming the two-hybrid results, endogenous PP1 in a human retinal pigment epithelial (RPE) cell line co-immunoprecipitates with endogenous pRb but not p107 or p130. Site directed mutagenesis of two pRb binding motifs in PP1alpha1 from LXSXE to LXCXE leads to slight increases in its two-hybrid interaction with pRb but does not alter its binding preference for pRb over the other family members. The complete sequence of bovine PP1alpha1 is reported. CONCLUSIONS: The strong two-hybrid interaction between PP1alpha1 and pRb, but not p107 or p130, suggests that the phosphorylation status of members of the pRb family may be regulated by different phosphatases, contributing to fine control of cell cycle progression. Conversely, PP1 activity may be specifically regulated by pRb and not p107 or p130. Mutagenesis studies suggest that PP1alpha1's LXSXE motif is not responsible for its binding preference for pRb over p107 and p130. Disruption of the PP1-pRb interaction may influence retinoblastoma tumorigenesis as well as RPE cell proliferation and survival.

Amino Acid Sequence↗

PubMed2002

Pigment epithelium-derived factor suppresses ischemia-induced retinal neovascularization and VEGF-induced migration and growth.

PURPOSE: To determine the effect of pigment epithelium-derived factor (PEDF) in a mouse model of ischemia-induced retinal neovascularization and on vascular endothelial growth factor (VEGF)--induced migration and growth of cultured microvascular endothelial cells. METHODS: Human recombinant PEDF was expressed in the human embryonic kidney 293 cell line and purified by ammonium sulfate precipitation and cation exchange chromatography. C57BL/6 mice were exposed to 75% oxygen from postnatal day (P)7 to P12 and then returned to room air. Mice received intravitreal injections of 2 microg PEDF in one eye and vehicle in the contralateral eye on P12 and P14. At P17, mice were killed and eyes enucleated for quantitation of retinal neovascularization. The mitogenic and motogeneic effects of VEGF on cultured bovine retinal and adrenal capillary endothelial cells were examined in the presence or absence of PEDF, using cell counts and migration assays. RESULTS: Two species of human recombinant PEDF, denoted A and B, were purified to apparent homogeneity. PEDF B appeared to comigrate on SDS-PAGE with PEDF from human vitreous samples. Changes in electrophoretic mobility after peptide-N-glycosidase F (PNGase F) digestion suggest that both PEDF forms contain N-linked carbohydrate. Analyses of the intact proteins by liquid chromatography-electrospray mass spectrometry (LC-ESMS) revealed the major molecular weight species for PEDF A (47,705 +/- 4) and B (46,757 +/- 5). LC-ESMS analysis of tryptic peptides indicated that PEDF A and B exhibit differences in glycopeptides containing N-acetylneuraminic acid (NeuAc) and N-acetylhexosamine (HexNAc). Intravitreal administration of either species of PEDF significantly inhibited retinal neovascularization (83% for PEDF A and 55% for PEDF B; P = 0.024 and 0.0026, respectively). PEDF A and B (20 nM) suppressed VEGF-induced retinal microvascular endothelial cell proliferation by 48.8% and 41.4%, respectively, after 5 days (P < 0.001) and VEGF-induced migration by 86.5% +/- 16.7% and 78.1% +/- 22.3%, respectively, after 4 hours (P = 0.004 and P = 0.008, respectively). CONCLUSIONS: These data indicate that elevated concentrations of PEDF inhibit VEGF-induced retinal endothelial cell growth and migration and retinal neovascularization. These findings suggest that localized administration of PEDF may be an effective approach for the treatment of ischemia-induced retinal neovascular disorders.

Animals↗

PubMed2002

Caspase activation and amyloid precursor protein cleavage in rat ocular hypertension.

PURPOSE: Retinal ganglion cell (RGC) death in glaucoma involves apoptosis. Activation of caspases and abnormal processing of amyloid precursor protein (APP) are important events in other chronic neurodegenerations, such as Alzheimer's disease (AD). The retinal expression and activation of caspases and the patterns of caspase-3-mediated APP processing in ocular hypertensive models of rat glaucoma were investigated. METHODS: RGC death was produced in one eye by chronic exposure to increased intraocular pressure (IOP) or by optic nerve transection. Elevated IOP was produced by obstruction of aqueous humor outflow with laser coagulation or limbal hypertonic saline injection. Caspase activity and APP processing in the retina were examined by RNase protection assay (RPA), immunocytochemistry, immunoblot assay, and colorimetric assay. RESULTS: RPA revealed elevations of caspase-3 mRNA, as well as other apoptosis-related mRNAs. Immunocytochemistry showed caspase-3 activation in RGCs damaged by ocular hypertension. The generation of the caspase-3-mediated APP cleavage product (DeltaC-APP) was also increased in ocular hypertensive RGCs. Western immunoblot assay and colorimetry revealed significantly more activated caspase-3 in ocular hypertensive retinas than in control retinas. The activated form of caspase-8, an initiator caspase, and amyloid-beta, a product of APP proteolysis and a component of senile plaques in AD, were detected in RGCs by immunohistochemistry significantly more often in ocular hypertensive than in control retinas. The amounts of full-length APP were reduced and amyloid-beta-containing fragments were increased in ocular hypertensive retinas by Western immunoblot assay. CONCLUSIONS: Rat RGCs subjected to chronic ocular hypertension demonstrate caspase activation and abnormal processing of APP, which may contribute to the pathophysiology of glaucoma.

Amyloid beta-Peptides↗

PubMed2002

AAV-mediated gene transfer of pigment epithelium-derived factor inhibits choroidal neovascularization.

PURPOSE: Adeno-associated viral (AAV) vectors have been used to express several different proteins in the eye. The purpose of this study was to determine whether AAV-mediated intraocular gene transfer of pigment epithelium-derived factor (PEDF) inhibits the development of choroidal neovascularization (CNV) in a murine model. METHODS: C57BL/6 mice were given intravitreous or subretinal injections of a PEDF expression construct packaged in an AAV vector (AAV-chicken beta-actin promoter-exon 1-intron 1[CBA]-PEDF) or control vector (AAV-CBA-green fluorescent protein[GFP]). After 4 or 6 weeks, the Bruch's membrane was ruptured by laser photocoagulation at three sites in each eye. After 14 days, the area of CNV at each rupture site was measured by image analysis. Intraocular levels of PEDF were measured by enzyme-linked immunosorbent assay. RESULTS: Four to six weeks after intraocular injection of AAV-CBA-PEDF, levels of PEDF in whole-eye homogenates were 6 to 70 ng. The average area of CNV at sites of the Bruch's membrane rupture showed no significant difference in eyes injected with AAV-CBA-PEDF compared with uninjected eyes. In contrast, 4 to 6 weeks after intraocular injection of 1.5 x 10(9) or 2.0 x 10(10) particles of AAV-CBA-PEDF, the area of CNV at the Bruch's membrane rupture sites had significantly decreased compared with CNV area at rupture sites in eyes injected with AAV-CBA-GFP. CONCLUSIONS: These data suggest that intraocular expression of PEDF or other antiangiogenic proteins with AAV vectors may provide a new treatment approach for ocular neovascularization.

Animals↗