Histopathologic study of autosomal dominant vitreoretinochoroidopathy in a 26-year-old woman

The clinicopathologic findings were obtained from enucleated eyes, obtained post mortem, of a 26-year-old woman with autosomal dominant vitreoretinochoroidopathy. Light microscopy demonstrated atrophic, disorganized peripheral retina with retinal blood vessels obscured by pigmented cells surrounding periodic acid-Schiff-positive deposits. Peripheral retinal pigment epithelial cells showed multilayering and pigmentation, with a thickened basal lamina. By electron microscopy, the peripheral retinal vessel endothelium was replaced by an arrangement of morphologically polarized pigmented cells of presumed retinal pigment epithelial origin oriented with their basal surfaces toward a fibrillar matrix occupying the vessel lumen. The similarity of the findings in this young patient to those of an aged patient described previously suggest that autosomal dominant vitreoretinochoroidopathy is an early-onset dystrophy of the peripheral retina with minimal subsequent progression, characterized by a retinal pigment epithelial response that includes marked intraretinal migration and extracellular matrix deposition.

Blue light-induced reactivity of retinal age pigment. In vitro generation of oxygen-reactive species

Exposure of the eye to intense light, particularly blue light, can cause irreversible, oxygen-dependent damage to the retina. However, no key chromophores that trigger such photooxidative processes have been identified yet. We have found that illumination of human retinal pigment epithelium (RPE) cells with light induces significant uptake of oxygen that is both wavelength- and age-dependent. Analysis of photoreactivity of RPE cells and their age pigment lipofuscin indicates that the observed photoreactivity in RPE cells is primarily due to the presence of lipofuscin, which, under aerobic conditions, generates several oxygen-reactive species including singlet oxygen, superoxide anion, and hydrogen peroxide. We have also found that lipofuscin-photosensitized aerobic reactions lead to enhanced lipid peroxidation as measured by accumulation of lipid hydroperoxides and malondialdehyde in illuminated pigment granules. Hydrogen peroxide is only a minor product of aerobic photoexcitation of lipofuscin. We postulate that lipofuscin is a potential photosensitizer that may increase the risk of retinal photodamage and contribute to the development of age-related maculopathy.

Comparison of fluorescein angiography with microvascular anatomy of macaque retinas

Recent anatomic work has shown that the capillary network of the fovea is multilaminar. We have identified the elements of this network that are visualized by fluorescein angiography and those that are missed. Fluorescein angiograms of monkey retinas (Macaca fascicularis) with good visualization of individual capillaries were obtained by standard clinical techniques. Retinal whole mounts were prepared from the same animals. Anatomic drawings made from the whole mounts were used to identify which parts of the capillary network were visualized angiographically. Angiographic estimates of dimensions of the foveal avascular zone corresponded closely to the anatomy. Capillary visibility declined rapidly from near perfect visualization at the edge of the foveal avascular zone to less than 40% by 900 microns eccentricity. While all the widest capillary segments (diameter 6.1-7.0 microns) were visualized, only 43% of the modal group of capillary segments (diameter 4.1-4.5 microns) were detected. When a relatively homogeneous population of capillaries was analyzed (diameters limited to the narrow range of 4.0-5.0 microns), visualization declined monotonically with depth in the retina. Capillary segments in the nerve fiber plane were visualized more than four times as effectively as segments of comparable diameter in the deepest vascular plane. High quality angiograms accurately delineate the foveal avascular zone, but they visualize only a fraction of the adjacent multilaminar network. Therefore, current techniques may not detect the earliest nonperfusion of capillaries in vaso-occlusive diseases. Capillary visibility is a joint function of diameter and of retinal depth. The decline in visualization with retinal depth implies that light scattering in the retina degrades the angiographic image.

An improved version of the hairpin ribozyme functions as a ribonucleoprotein complex

Most RNA molecules that are endowed with catalytic activity function in the form of ribonucleoproteins within cells. These complexes are frequently large, poorly defined, and difficult to study. As a model system to study biological catalysis by ribonucleoproteins, we have modified the hairpin ribozyme by inserting an RNA structure that serves as a binding site for bacteriophage R17 coat protein in the form of an extension to ribozyme helix 4, which lies at the periphery of the catalytic domain. In the absence of protein, we find that incorporation of the protein-binding domain increases the catalytic efficiency of the hairpin ribozyme by 2-fold for the cleavage reaction and 16-fold for the ligation reaction. This increase in activity correlates with an increase in the proportion of molecules which fold into the active tertiary structure, as measured by a UV cross-linking assay. Mobility-shift and filter-binding assays of complex formation show that R17 coat protein binds to the chimeric ribozyme with a dissociation constant essentially identical to that of the isolated protein-binding domain; no binding of the protein to the unmodified ribozyme could be detected. The kinetics of cleavage and ligation reactions are not altered by the presence of saturating concentrations of coat protein, and competition studies demonstrate that the protein remains bound to the ribozyme throughout the catalytic cycle. These studies establish that the hairpin ribozyme can be engineered to function efficiently in the form of a ribonucleoprotein in vitro and will serve as the basis for future experimentation to understand mechanisms of protein modulation of catalytic RNA activity, and to introduce other protein-binding domains, for example, HIV-1 rev-binding and tar elements, which may be useful for influencing subcellular localization, regulating intracellular activity, or generating ribozymes that also function as "decoys" in antiviral applications.

Novel system for analysis of group I 3' splice site reactions based on functional trans-interaction of the P1/P10 reaction helix with the ribozyme's catalytic core

A group I intron from a bacterial tRNA precursor has been converted into an RNA enzyme that catalyzes the efficient polymerization of oligoribonucleotide analogs of tRNA exons using a reaction scheme consisting of multiple cycles of reverse and forward exon ligation reactions. Here, we present results showing that this system represents a novel and useful tool for the analysis of 3' splice site reactions of group I ribozymes. First, analysis of variant substrates containing base substitutions in group I secondary structure elements P1, P9.0 and P10 confirms that exon polymerization is dependent on these structures, and therefore constitutes an appropriate and relevant model system for studying the exon ligation step of splicing. Second, to probe interactions between the intron's catalytic core and the bases and backbone of the P1/P10 reaction helix, two successful strategies for separating the internal guide sequence from the intron core were devised. One such strategy uses a construct in which the reaction helix interacts functionally with the catalytic core using only tertiary contacts. Further stabilization of this interaction through the inclusion of a 7 bp intermolecular P2 helix generates increased reaction efficiency. Third, when provided with two reaction helices, the ribozyme synthesizes mixed polymers through a mechanism that involves sequential binding and release of the duplexes. Fourth, in these reactions, turnover of the external guide sequence requires unwinding and annealing of the P2 helix, suggesting that P2 unwinding may occur during group I splicing. These results provide novel experimental tools to probe the relatively poorly understood 3' splice site reactions of group I introns, and may be relevant to ribozyme-catalyzed assembly and recombination of oligomers in prebiotic scenarios.

Structure-mapping of the hairpin ribozyme. Magnesium-dependent folding and evidence for tertiary interactions within the ribozyme-substrate complex

We have used chemical modification analysis to probe the solution structure of the hairpin ribozyme. The modifying reagents dimethylsulfate, 1-cyclohexyl-N'-[2-(N-methylmorpholino) ethyl-carbodiimide-p-toluenesulfonate, kethoxal, diethylpyrocarbonate and (2,12-dimethyl-3,7,11,17- tetraazabicyclo [11.3.1]heptadeca-1(17),2,11,13,15-pentaenato) nickel(II) perchlorate were used to probe functional groups that participate in Watson-Crick and non-canonical base-pairs. Our results confirm the existence of four short helices (3 to 6 bp) within the ribozyme-substrate complex, and demonstrate that one intramolecular helix (helix 4) is comprised of three base-pairs rather than the previously suggested five. In the absence of magnesium, the ribozyme is observed to fold into its secondary structure. Upon addition of magnesium, a striking difference in chemical modification is observed, particularly at sites within the ribozyme's large internal loop (loop B) that are essential for catalytic function (bases 21 to 26). Moreover, magnesium-dependent folding clearly destabilizes an A-U base-pair in a region where a proposed bend is required to juxtapose the catalytically essential loops A and B. Upon addition of substrate, no changes are observed in the structure of helix 3, loop B or helix 4. However, strong protection of bases in the substrate-binding domain is observed, including those located across internal loop A. The modification data are consistent with the formation of a previously proposed tertiary structure motif within loop B that includes non-canonical G-A, A-U and A-A base-pairs, and that is identical with those identified by NMR analysis of loop E of 5 S rRNA and the sarcin/ricin loop of 28 S rRNA. Our results indicate that the hairpin ribozyme adopts a stable magnesium-dependent tertiary structure to which the substrate binds without inducing major conformational changes, and that substrate recognition is likely to involve non-canonical base-pairs between the ribozyme and substrate sequences adjacent to the cleavage site.

Separation of phenotypically distinct subpopulations of cultured human retinal pigment epithelial cells

Like most epithelial cells that are isolated from tissues and placed in culture, the phenotype of human retinal pigment epithelial cells (RPE) in vitro is more variable than for the same cells in situ. The phenotypic heterogeneity of the cultures has been attributed to varying stages of differentiation of the cells induced by the culture environment. In this study we show that within the same cultures RPE cells exist as phenotypic variants which are distinct and stable. Two phenotypically distinct subpopulations were identified, one epithelioid and one fusiform, that were present from the first spreading event in primary culture through multiple serial passages and when maintained for extended periods at confluency. Cell aggregation studies indicated differences in cellular adhesions, known determinants of cell shape, between the subpopulations. Methods to separate the subpopulations were developed which are based on the differential trypsin sensitivity of adhesions. The separated subpopulations had the same RPE cytokeratins by immunoblotting, but cytokeratin filaments (and actin filaments) had different organizations. The study indicates that RPE cell cultures contain at least two subpopulations of phenotypically distinct cells under identical culture conditions that can be separated and propagated independently. The phenotypic variants offer a model system for investigating determinants of epithelial cell shape in RPE. Further, the separation methods might be applied to test for phenotypic variants in other types of cultured epithelia.

A modified group I intron can function as both a ribozyme and a 5' exon in a trans-exon ligation reaction

Here, we show that a single RNA molecule derived from a group-I intron can provide the catalytic activity, the substrate recognition domain and the attacking nucleophile in a reaction that mimics the exon ligation step of splicing. To accomplish this reaction, we have linked a 5' exon sequence to the 3' end of an attenuated form of the self-splicing Tetrahymena rRNA intron. The ribozyme (I-E1) attacks an oligoribonucleotide analog of the 3' splice site (I'-E2) to generate a product containing ligated exons (I-E1-E2) and a small intron fragment (I'). Two modified introns were constructed and tested for activity. A construct designed to interact with the 3' splice site through intermolecular P9.0 and P10 helices was found to be inactive due to failure to form a stable ribozyme-substrate complex. A second modified intron and substrate combination was engineered, in which the complex was further stabilized by an intermolecular P9.2 helix. In this case, stable complexes and reaction products were identified. The reaction efficiency was low compared to splicing of the unmodified intron-containing precursor, and will be optimized in future experiments. Following optimization, we believe that this system may be exploited to examine the functional consequences of a wide variety of 3' splice-site modifications, and may provide the basis for development of highly selective trans-acting ribozymes.

Temporal differences in the expression of mRNA for IL-10 and IFN-gamma in the brains and spleens of C57BL/10 mice infected with Toxoplasma gondii

C57BL/10 Sc Sn (B10) mice infected orally with Toxoplasma gondii tissue cysts were killed at regular intervals up to day 116 post infection (p.i.) and their brains excised. These were used either to count the total number of cysts in the brain, for RNA purification or histopathological studies. Mortality levels in a parallel group of T. gondii infected B10 mice were also monitored and regular plasma samples taken to measure specific antibody production. Seventy per cent of mice died within the first 35 days of infection. Thereafter deaths were infrequent. Inflammation in the brain was apparent from day 10 onwards and by day 25 there was widespread astrocyte activation, perivascular cuffing, meningitis and extensive encephalitis. Total cyst numbers increased rapidly from day 15 to day 35 when they peaked. By day 60, however, cyst numbers had dropped dramatically and this decrease continued through to day 116. Using the polymerase chain reaction mRNA transcripts for IFN-gamma were detected from the first time point sampled, day 25 p.i., until the end of the study. Transcripts for IL-10, an inhibitor of IFN-gamma production, release and activity, were not detected until day 70. The predominant antibody detected against T. gondii was IgG2a but not IgG1. Significantly transcripts for IFN-gamma were found in the spleens of infected but not non-infected animals. Our results suggest that an inflammatory response associated with IFN-gamma production in B10 mice eventually controls T. gondii infection. After the cyst burden has dropped dramatically transcripts for IL-10 are detected in the brain, perhaps to suppress inflammation, and limit pathology.

The response of cultured human retinal pigment epithelium to hypoxia: a comparison to other cell types

PURPOSE

To characterize the response of cultured human retinal pigment epithelial (RPE) cells to lowered environmental oxygen.

METHODS

The response of cultured RPE cells to lowered oxygen environments was compared to that of cell types of presumed high (Madin-Darby canine kidney [MDCK] cells, an epithelial cell line) and low (CSF, corneal stromal fibroblasts) aerobic requirements. Cultures in a range of densities were exposed for 7 days to 3%, 8%, or 20% O2 with measurements of adenosine triphosphate (ATP), cell number, and cytochrome oxidase (CO) activity (an enzyme marker of aerobic metabolism).

RESULTS

RPE cells had levels of CO activity and total cellular ATP intermediate between those of CSF (low) and MDCK (high) in all oxygen environments. Hypoxia led to modestly lowered ATP pools and CO activity for RPE cells over a wide range of culture densities. Hypoxia induced a greater cell loss in MDCK cells than in RPE cells, and the effects of hypoxia were greater in dense cultures of both epithelial cell types. Hypoxia had little effect on cell number for CSF.

CONCLUSIONS

The data suggest that cultured RPE cells, though aerobically active, are not as dependent upon oxidative phosphorylation and are more resistant to hypoxia than MDCK cells, a cell type derived from another well-perfused tissue. The authors conclude that RPE cells are unlikely to suffer from hypoxic injury in situ because of a moderate aerobic demand and an abundant oxygen supply.

A photo-cross-linkable tertiary structure motif found in functionally distinct RNA molecules is essential for catalytic function of the hairpin ribozyme

We have identified an essential UV-sensitive tertiary structure domain within the hairpin ribozyme. Irradiation at 254 nm produces two cross-linked RNA species that are resolved from the unmodified structure by denaturing gel electrophoresis. One cross-link forms at high efficiency and maps between nucleotides G21 and/or A22 and U41, all essential bases located within an internal loop joining helices 3 and 4. A second cross-link forms between nucleotides A20 and U42 as a result of ribozyme dimerization at concentrations greater than 0.5 microM. Both cross-linked species retain cleavage activity and so presumably reflect catalytically proficient structures of the ribozyme. Formation of the intramolecular cross-link is independent of Mg2+ and substrate and is blocked by base substitutions within the reactive domain that inhibit catalysis. A 36-nt RNA fragment containing the photoreactive domain but lacking the substrate binding domain also cross-links with high efficiency and maps between G21 and U41, as observed with the intact molecule. The sequence and cross-linking sites of the UV-sensitive internal loop are strikingly similar to those found in several other RNA molecules, including loop E of 5S rRNA. These results suggest that the loop E-like structure may be a common RNA folding domain that is utilized in a variety of functionally important RNA molecules.

A process approach to memory book training for neurological patients

This article describes a process approach to training memory book usage as a compensatory strategy for neurological patients. Clinicians who recommend memory books to patients need to consider the physical, cognitive, social and emotional strengths and weaknesses of the individual as they assist with the design and implementation of such books. Throughout the process, a major focus of this approach is on the need to raise awareness of memory deficits while minimizing patient resistance. By individualizing a memory book, clients tend to view it as a tool which can maximize their independence. Support from the discharge environment may be necessary in some areas to maintain optimum performance.

Cytochrome oxidase activity in bovine and human retinal pigment epithelium: topographical and age-related differences

Cytochrome c oxidase (CO) is a mitochondrial enzyme complex that was used in this study as a marker enzyme of aerobic metabolism. The activity of the enzyme was measured in the RPE of posterior and peripheral regions of bovine and human eyes. The posterior regions included the bovine area centralis or human macula. To determine if aging affected CO activity, activity was compared in RPE cells from human donors of varying age. An in vitro aging model was also used in which CO activity was measured in bovine and human RPE cells that were aged by repeated culture passage. CO activity was found to be significantly lower in posterior RPE cells from both bovine and human eyes suggesting that aerobic metabolism in RPE cells differs regionally. For human RPE samples, CO activity was lower in posterior cells at all donor ages and no significant age-related changes in CO activity were observed except that the highest activity samples were from older donors. Similarly, RPE cells that were aged in culture showed no significant changes in CO activity per cell although there were some high activity samples among the aged cultures. With aging, RPE cell density at confluency declined resulting in lower total CO activity in the aged epithelial monolayer. The data suggest that the ability of individual RPE cells to generate energy via respiration is maintained in the aged eye, but because RPE cell number declines with age and the activity of remaining RPE cells does not increase commensurately, there may declines in the ability of the aged pigment epithelium to perform tissue-level functions (e.g., transepithelial transport).(ABSTRACT TRUNCATED AT 250 WORDS)

Optimization of an anti-HIV hairpin ribozyme by in vitro selection

We have applied in vitro selection methods to achieve a large increase in the catalytic activity of a hairpin ribozyme targeted against a highly conserved 14-nucleotide sequence within HIV-1 pol RNA. The substrate specificity was changed by mutating 8 bases within the substrate-binding domain of the parental (-)sTRSV ribozyme. The resulting enzyme cleaved the HIV substrate specifically but with a 20-fold reduction in catalytic efficiency (kcat/KM). Following random mutagenesis, ribozymes with increased activity against the target sequence were selected through 10 rounds of in vitro selection. Selective pressure was increased by decreasing MgCl2 and spermidine concentrations, and reducing reaction time. Variant ribozymes with base substitutions A11-->G and U39-->C were selected in the population. These mutations were introduced singly and in combination into the trans-acting anti-HIV ribozyme. Each of the single-base substitutions significantly increased ribozyme activity, while the activity of double mutant was increased to nearly the level of the parental ribozyme. These findings demonstrate that in vitro selection is a powerful and efficient method to optimize ribozymes for the catalytic inactivation of targeted RNA molecules.

Four ribose 2'-hydroxyl groups essential for catalytic function of the hairpin ribozyme

The hairpin ribozyme catalyzes site-specific cleavage of an RNA substrate using a magnesium-dependent transphosphorylation mechanism. Here, we describe experiments designed to test the importance of ribose 2'-hydroxyl groups for ribozyme function. Ribozymes for this work were synthesized in two segments using solid-phase RNA phosphoramidite chemistry. 2'-Deoxyribonucleotides were systematically introduced at each of the 50 positions within the ribozyme, and the catalytic activity of the resulting mixed RNA-DNA polymers was measured. Deletion of the 2'-hydroxyl group at each of four sites (A10, G11, A24, and C25) was found to result in severe inhibition of cleavage activity (kcat/KM decreased by 100- to 1000-fold), although KM measurements and mobility-shift assays showed that substrate binding was not affected. Identical results were obtained upon substitution of these ribonucleotides with 2'-O-methyl derivatives. Inhibition by 2'-modified sugars at G11 or A24 was rescued by increased Mg2+ concentrations, suggesting that these 2'-hydroxyls may function in magnesium binding. Our results demonstrate that the 2'-hydroxyl groups at A10, G11, A24, and C25 provide essential functions for catalysis, possibly forming important tertiary contacts or magnesium coordination sites that are necessary for active site architecture.

2'-Hydroxyl groups important for exon polymerization and reverse exon ligation reactions catalyzed by a group I ribozyme

The functional importance of ribose moieties in both exons and in intron sequences proximal to the 3' splice site of a group I intron has been analyzed using a novel exon polymerization reaction. The ribozyme is a modified version of a self-splicing bacterial tRNA intron (I) that attacks a 20-nucleotide synthetic ligated exon substrate (E1.E2), yielding E1 and I.E2 by reverse exon ligation. A series of repetitive reactions then polymerize E2 on the 3' end of the intron; attack by E1 subsequently generates E1.(E2)n. Systematic deoxyribonucleotide substitution within E1.E2 was used to probe the function of 2'-hydroxyl groups in each exon and the 3'-terminal nucleotides of the intron. We find that ribose at the splice junction (U-1) and at the two adjacent positions with E1 (A-2, C-3) is important for reverse exon ligation. Within E2, deletion of 2'-hydroxyl groups of the nucleotides that form P10 does not affect reactivity. In contrast, ribose at the 3' end of the intron is essential for reverse exon ligation, and the presence of a 2'-OH group in each of the nucleotides comprising P9.0[3'] contributes to reaction efficiency. These results support a model in which specific 2'-hydroxyl groups at and adjacent to the reaction sites form tertiary contacts that serve to stabilize interactions with the catalytic core of the ribozyme. Furthermore, they suggest that the mechanism by which guanosine at the 3' end of the intron is activated for reverse exon ligation is the same as that by which guanosine mononucleotide is activated in the first step of splicing.

Novel RNA polymerization reaction catalyzed by a group I ribozyme

We have converted a bacterial tRNA precursor containing a 205 nt self-splicing group I intron into a RNA enzyme that catalyzes polymerization of an external RNA substrate. The reaction involves transesterification steps analogous to both the forward and reverse exon ligation steps of group I splicing; as such it depends entirely on 3' splice site reactions. The RNA substrate is a 20 nt analogue of the ligated exons (E1.E2), whose 3' end resembles the 3' terminus of the intron RNA enzyme (IVS). The splice junction of the substrate is attacked by the 3' end of the intron, then the molecule displaces the original 3' terminal guanosine so that the new 3' terminus is brought into the active site and used as the attacking nucleophile in the next reaction. Polymerization occurs via a series of covalent enzyme-linked intermediates of the structure IVS.(E2)n, where n = 1 to > or = 18. The 5' exon accumulates during the course of the reaction and can attack the covalent intermediates to produce elongation products of structure E1.(E2)n, regenerating the intron RNA enzyme in unchanged form. In this manner, the enzyme converts 20 nt oligoribonucleotides into polyribonucleotides up to at least 180 nt by 10 nt increments. These results have significant implications for the evolution of RNA-based self-replicating systems.

In vitro aging of bovine and human retinal pigment epithelium: number and activity of the Na/K ATPase pump

We have previously observed that the density of Na/K ATPase pumps is lower in RPE cells in the posterior pole of both bovine and human eyes. The posterior pole in human eyes includes the macula, a region which is predisposed to aging pathology. In this study we examined the effect of age on the sodium pump using cultures of bovine (bRPE) and human (hRPE) RPE cells that were aged in vitro by repeated passage. The cultures were assayed for cell number, protein, pump density (specific binding of [3H]ouabain) and pump activity (specific uptake of 86Rb) at confluency at each passage. In culture, bRPE had more pumps per cell (3.2 x 10(6)) than hRPE (1.2 x 10(6)), but the bRPE pumps were less active so the pumping capacity per cell was nearly equal. Bovine RPE aged more rapidly in vitro (survived fewer passages) than hRPE. With aging, RPE cells from both species showed declines in cell number at confluency. Pump number and pump activity per cell remained constant. Because cell number declined, the pumping capacity per unit area of confluent epithelium was diminished with culture aging. RPE cell number is known to decline with age in situ, especially in the macula. If Na/K ATPase pump number and activity per RPE cell remain constant with aging in vivo as shown here in vitro, the effective pumping capacity of the RPE per unit area of 'monolayer' would decline in aged eyes.(ABSTRACT TRUNCATED AT 250 WORDS)

Essential nucleotide sequences and secondary structure elements of the hairpin ribozyme

In vitro selection experiments have been used to isolate active variants of the 50 nt hairpin catalytic RNA motif following randomization of individual ribozyme domains and intensive mutagenesis of the ribozyme-substrate complex. Active and inactive variants were characterized by sequencing, analysis of RNA cleavage activity in cis and in trans, and by substrate binding studies. Results precisely define base-pairing requirements for ribozyme helices 3 and 4, and identify eight essential nucleotides (G8, A9, A10, G21, A22, A23, A24 and C25) within the catalytic core of the ribozyme. Activity and substrate binding assays show that point mutations at these eight sites eliminate cleavage activity but do not significantly decrease substrate binding, demonstrating that these bases contribute to catalytic function. The mutation U39C has been isolated from different selection experiments as a second-site suppressor of the down mutants G21U and A43G. Assays of the U39C mutation in the wild-type ribozyme and in a variety of mutant backgrounds show that this variant is a general up mutation. Results from selection experiments involving populations totaling more than 10(10) variants are summarized, and consensus sequences including 16 essential nucleotides and a secondary structure model of four short helices, encompassing 18 bp for the ribozyme-substrate complex are derived.

Modulation of sodium-potassium adenosine triphosphatase in cultured bovine retinal pigment epithelium by potassium

PURPOSE

The aim of the study was to examine the extracellular potassium concentration [K+]o as a modulator of the retinal pigment epithelium (RPE) contribution to ion homeostasis in the subretinal space by measuring sodium-potassium adenosine triphosphatase (Na+/K+ ATPase) pump number and activity in cultured bovine RPE in the presence of different concentrations of extracellular potassium.

METHODS

Pump number was quantified by measuring specific binding of 3H-ouabain to bovine RPE exposed to low (0.5-2.5 mmol) or control (5.0 mmol) [K+]o over 72 hr. Na+/K+ ATPase activity in low and control [K+]o was quantified by measurement of 86Rb+ uptake.

RESULTS

Low [K+]o increased RPE pump number in a dose- and time-dependent manner, with lesser effects on denser than on sparser cultures. [K+]-modulation of pump number was reversible and did not occur in the presence of the protein synthesis inhibitor cycloheximide. In RPE exposed to low [K+]o for 72 hr, pump activity was decreased compared with the control but increased toward control levels when re-exposed to control [K+]o. The total potassium transported per cell was 60% of control in low [K+]o but increased to slightly above control when re-exposed to control [K+]o.

CONCLUSIONS

In cultured RPE cells, both Na+/K+ ATPase pump number and pump activity are affected by changes in [K+]o, with greater modulation in sparser cultures. If similar events occur in situ, the sodium pump in RPE may respond to changes in subretinal potassium ion concentration, especially if the RPE cell number is reduced as in aging or disease.

Ionic requirements for RNA binding, cleavage, and ligation by the hairpin ribozyme

Metal ion requirements for RNA binding, cleavage, and ligation by the hairpin ribozyme have been analyzed. RNA cleavage is observed when Mg2+, Sr2+, or Ca2+ are added to a 40 mM Tris-HCl buffer, indicating that these divalent cations were capable of supporting the reaction. No reaction was observed when other ions (Mn2+, Co2+, Cd2+, Ni2+, Ba2+, Na+, K+, Li+, NH4+, Rb+, and Cs+) were tested. In the absence of added metal ions, spermidine can induce a very slow ribozyme-catalyzed cleavage reaction that is not quenched by chelating agents (EDTA and EGTA) that are capable of quenching the metal-dependent reaction. Addition of Mn2+ to a reaction containing 2 mM spermidine increases the rate of the catalytic step by at least 100-fold. Spermidine also reduces the magnesium requirement for the reaction and strongly stimulates activity at limiting Mg2+ concentrations. There are no special ionic requirements for formation of the initial ribozyme-substrate complex--analysis of complex formation using native gels and kinetic assays shows that the ribozyme can bind substrate in 40 mM Tris-HCl buffer. Complex formation is inhibited by both Mn2+ and Co2+. Ionic requirements for the ribozyme-catalyzed ligation reaction are very similar to those for the cleavage reaction. We propose a model for catalysis by the hairpin ribozyme that is consistent with these findings. Formation of an initial ribozyme-substrate complex occurs without the obligatory involvement of divalent cations. Ions (e.g., Mg2+) can then bind to form a catalytically proficient complex, which reacts and dissociates.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro selection and evolution of RNA: applications for catalytic RNA, molecular recognition, and drug discovery

In vitro selection and in vitro evolution methods represent powerful tools for isolating functional RNA molecules, and are proving to have wide applications in biology. Selection in the absence of living cells is possible because some RNA molecules possess a selectable "phenotype" (catalytic activity or ligand binding) as well as a "genotype" (nucleotide sequence). This review discusses the basic principles of in vitro selection technology and the application of these methods to isolate RNA molecules with interesting and novel properties. Selection techniques have been used to analyze the structure and function of catalytic RNA molecules (ribozymes), and to isolate novel catalytic structures not found in nature. They are also useful for studying protein-RNA interactions and for isolating RNA molecules that bind specifically to peptides and other ligands. The isolation of RNA molecules with new binding functionalities (aptamers) for both large and small molecules has exciting potential for discovery of new drugs and diagnostic reagents.

Substrate selection rules for the hairpin ribozyme determined by in vitro selection, mutation, and analysis of mismatched substrates

Substrate recognition by the hairpin ribozyme has been proposed to involve two short intermolecular helices, termed helix 1 and helix 2. We have used a combination of three methods (cleavage of mismatched substrates, in vitro selection, and site-specific mutational analysis) to systematically determine the substrate recognition rules for this RNA enzyme. Assays measuring substrate cleavage in trans under multiple turnover conditions were conducted using the wild-type ribozyme and substrates containing mismatches in all sites potentially recognized by the ribozyme. Molecules containing single- and multiple-base mismatches in helix 2 at sites distant from the cleavage site (g-4c, u-5a, g-4c: u-5a) were cleaved with reduced efficiency, whereas those with mismatches proximal to the cleavage site (c-2a, a-3c, c-2a: a-3c) were not cut. Analogous results were obtained for helix 1, where mismatches distal from the cleavage site (u+7a, u+8a, u+9a, u+7a: u+8a: u+9a) were used much more efficiently than those proximal to the cleavage site (c+4a, u-5a, g+6c, c+4a: u+5a: g+6c). In vitro selection experiments were carried out to identify active variants from populations of molecules in which either helix 1 or helix 2 was randomized. Results constitute an artificial phylogenetic data base that proves base-pairing of nucleotides at five positions within helix 1 and three positions within helix 2 and reveals a significant sequence bias at 3 bp (c+4.G6, c-2.G11, and a-3.U12). This sequence bias was confirmed at two sites by measuring relative cleavage rates of all 16 possible dinucleotide combinations at base pairs c+4.G6 and c-2.G11.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of potassium transport in cultured retinal pigment epithelium and retinal glial cells by serum and epidermal growth factor

The ionic environment of retinal photoreceptors is partially controlled by potassium transporters on retinal glial and retinal pigment epithelial cells (RPE). In this study, serum and epidermal growth factor (EGF) were examined as modulators of potassium transport in confluent cultures of human RPE and rabbit retinal glia. EGF is a known mitogen for confluent RPE cultures and was shown here to also stimulate [3H]thymidine incorporation in cultures of retinal glia. For potassium transport studies 86Rb was used as a tracer during a 17-min incubation. For both retinal cell types the mean total 86Rb uptake in 10% serum was approximately 60% above basal, serum-free controls. For EGF, tested in several experiments in a concentration range from 1 to 100 ng/ml, maximal total uptake was 33 and 24% above controls for RPE and glia, respectively. Inhibitor studies suggested that basal and serum-stimulated uptake for both cell types occurred by the ouabain-sensitive Na-K ATPase pump and by the furosemide- or bumetanide-sensitive Na-K-Cl cotransporter. EGF-stimulated uptake appeared to be due predominantly to the cotransporter. The data suggest that serum components and EGF, which may be available to retina-derived cells under pathologic conditions, may not only stimulate proliferation but may also act as short-term modulators of potassium ion movement and thus affect physiologic processes that are sensitive to ion homeostasis.

Extensive phosphorothioate substitution yields highly active and nuclease-resistant hairpin ribozymes

The catalytic function of the hairpin ribozyme has been investigated by modification-interference analysis of both ribozyme and substrate, using ribonucleoside phosphorothioates. Thiophosphate substitutions in two ribozyme domains were examined by using a novel and highly efficient two-piece ribozyme assembled from two independently synthesized oligoribonucleotides. The catalytic proficiency of the two-piece construct (KM = 48 nM, kcat = 2.3 min-1) is nearly identical to that of the one-piece ribozyme. The two-piece ribozyme is essentially unaffected by substitution with thiophosphates 5' to all guanosines, cytidines, and uridines. In contrast, incorporation of multiple adenosine phosphorothioates in the 5' domain of the ribozyme decreases ribozyme activity by a factor of 25. Modification-interference experiments using ribozymes partially substituted with adenosine phosphorothioate suggest that thiophosphates 5' to A7, A9 and A10 interfere with cleavage to a greater extent than substitutions at other sites within the molecule, but the effect is modest. Within the substrate, phosphorothioate substitution does not directly interfere with cleavage, rather, increasing thiophosphate content decreases the stability of the ribozyme-substrate complex. We describe the construction of a hairpin ribozyme containing dinucleotide extensions at its 5' and 3' ends. Full substitution of this molecule with G and C phosphorothioates results in a ribozyme with greatly enhanced stability against cellular ribonucleases without significant loss of catalytic efficiency.

In vitro selection of active hairpin ribozymes by sequential RNA-catalyzed cleavage and ligation reactions

In vitro selection methods provide rapid and extremely powerful tools for elucidating interactions within and between macromolecules. Here, we describe the development of an in vitro selection procedure that permits the rapid isolation and evaluation of functional hairpin ribozymes from a complex pool of sequence variants containing an extremely low frequency of catalytically proficient molecules. We have used this method to analyze the sequence requirements of two regions of the ribozyme-substrate complex: a 7-nucleotide internal loop within the ribozyme that is essential for catalytic function and substrate sequences surrounding the cleavage-ligation site. Results indicate that only 3 of the 16,384 internal loop variants examined have high cleavage and ligation activity and that the ribozyme has a strong requirement for guanosine immediately 3' to the cleavage-ligation site.

Collagen shield delivery of tissue plasminogen activator: functional and pharmacokinetic studies of anterior segment delivery

BACKGROUND

Postoperative fibrin formation remains a major complication associated with intraocular surgery, especially after vitreoretinal surgery for proliferative vitreoretinopathy, proliferative diabetic retinopathy, trauma, or endophthalmitis. Tissue plasminogen activator (tPA) has been shown, both in experimental studies and clinical trials, to specifically dissolve formed intraocular fibrin after intracameral or intravitreal injection. We studied collagen shield delivery of tPA to the anterior segment and vitreous of rabbit eyes to evaluate a noninvasive delivery modality.

METHODS

Anterior segment fibrin clots were formed in rabbit eyes by injecting citrated rabbit plasma. The tPA hydrated collagen shields, or control shields, were then placed on the rabbit corneas and the extent of fibrin clot was followed. In other rabbit eyes, tPA hydrated collagen shields were placed on the rabbit corneas and an enzyme-linked immunosorbent assay (ELISA) was utilized to determine aqueous, vitreous, and blood levels of tPA over time.

RESULTS

Collagen shield tPA delivery shortened the time to fibrin clot lysis by 50% (mean clearance time = 49 +/- 23 hours; P less than .05). ELISA for tPA levels noted measurable vitreous levels by 2 hours after tPA hydrated collagen shield application with a peak at 24 hours. Aqueous tPA levels were not measurable until 18 hours after tPA collagen shield application and peaked at 36 hours. Vitreous tPA levels were greater than aqueous tPA levels at all time points (P less than .05). No evidence of corneal edema or opacification, hemorrhage, or cataract was seen.

CONCLUSIONS

These results document the efficacy and safety of tPA delivery to the aqueous and vitreous via a hydrated collagen shield in this animal model.

Novel guanosine requirement for catalysis by the hairpin ribozyme

THERE is much interest in the development of 'designer ribozymes' to target destruction of RNAs in vitro and in vivo. Engineering of ribozymes with novel specificities requires detailed knowledge of the ribozyme-substrate interaction, and a rigorous evaluation of sequence specificity. The hairpin ribozyme catalyses an efficient and reversible site-specific cleavage reaction. We have used mutagenesis and in vitro selection strategies to show that RNA cleavage and ligation has an absolute requirement for guanosine immediately 3' to the cleavage-ligation site. This G is not required for efficient substrate binding, rather, its 2-amino group is an essential component of the active site required for catalysis.

Binding and cleavage of nucleic acids by the "hairpin" ribozyme

The "hairpin" ribozyme derived from the minus strand of tobacco ringspot virus satellite RNA [(-)sTRSV] efficiently catalyzes sequence-specific RNA hydrolysis in trans (Feldstein et al., 1989; Hampel & Triz, 1989; Haseloff & Gerlach, 1989). The ribozyme does not cleave DNA. An RNA substrate analogue containing a single deoxyribonucleotide residue 5' to the cleavage site (A-1) binds to the ribozyme efficiently but cannot be cleaved. A DNA substrate analogue with a ribonucleotide at A-1 is cleaved; thus A-1 provides the only 2'-OH required for cleavage. These results support cleavage via a transphosphorylation mechanism initiated by attack of the 2'-OH of A-1 on the scissile phosphodiester. The ribozyme discriminates between DNA and RNA in both binding and cleavage. Results indicate that the 2'-OH of A-1 functions in complex stabilization as well as cleavage. The ribozyme efficiently cleaves a phosphorothioate diester linkage, suggesting that the pro-Rp oxygen at the scissile phosphodiester does not coordinate Mg2+.

Methanol poisoning. A rodent model with structural and functional evidence for retinal involvement

Methanol ingestion can lead to visual impairment, central nervous system dysfunction, or death. The extent of ocular involvement has been difficult to determine because the toxicity is restricted to humans and nonhuman primates due to species differences in methanol metabolism. A rodent model of methanol toxicity recently developed by us was used to evaluate retinal dysfunction in methanol poisoning. Formic acidemia and visual toxic reactions developed in methanol-intoxicated rats. Electroretinographic analysis indicated a significant early deficit in b-wave amplitude followed by a temporally delayed, lesser reduction in a-wave amplitude. Histologic evaluation of the eyes 60 hours after methanol administration revealed generalized retinal edema and vacuolation in the photoreceptors and retinal pigment epithelium. Ultrastructural examination showed swelling and disruption of the mitochondria in photoreceptor inner segments, optic nerve, and the retinal pigment epithelium. These studies document direct retinal involvement in this nonprimate model of methanol toxicity.

Retinal pigment epithelial cells of the posterior pole have fewer Na/K adenosine triphosphatase pumps than peripheral cells

The density of Na/K adenosine triphosphatase (ATPase) pumps in retinal pigment epithelial (RPE) cells in different retinal regions was quantified by measuring the binding of 3H-ouabain to RPE in cow and human eyecups. In bovine eyes, pump density was estimated in RPE samples isolated from three retinal regions outlined with a 7-mm trephine: one from the posterior pole in the area centralis and two from the superior, equatorial retina representing unpigmented (in the tapetum) and pigmented zones. In human eyes, RPE samples were isolated from a posterior region centered around the macula and one superior region. Ouabain binding to RPE of the posterior pole of both species was approximately 40-60% lower than binding to RPE of more peripheral regions in the same eyes. For bovine eyes, ouabain binding did not differ between pigmented and unpigmented cells of the superior retina, suggesting that reduced binding in the relatively amelanotic posterior cells was not related to levels of pigmentation. For human RPE, binding to posterior cells was lower in eyes from donors of all ages (range, 17-90 yr). The data suggest that Na/K ATPase pump site density is lower in posterior RPE cells of both bovine and human eyes, perhaps due to a regional difference in requirements for ionic regulation.

The effect of culture density and proliferation rate on the expression of ouabain-sensitive Na/K ATPase pumps in cultured human retinal pigment epithelium

The number and activity of ouabain-sensitive Na/K ATPase pumps expressed by many cell types in vitro, including human retinal pigment epithelial cells (RPE), have been shown to decline with increasing culture density. Cell proliferation also declined as cultures became dense so it was unclear if pump number was modulated by cell proliferation or culture confluency. By exposing RPE cultures to various feeding regimens, using culture medium containing or lacking serum, it was possible to produce RPE cultures with a range of culture densities and growth rates. These were analyzed for proliferative activity by quantifying [3H]thymidine incorporation and for Na/K ATPase pump number by measuring specific [3H]ouabain binding. The results suggest that pump number is modulated by culture density and, further, that the density-dependent regulation of pump number requires serum. Although density-dependent modulation of culture growth is also serum requiring, cell proliferation and pump number did not appear to be related; cultures of similar density which differed significantly in growth rate had similar numbers of pumps. The view that elevated numbers of pumps were not necessarily found in proliferating cells was further supported by qualitative examination of radioautographs of cells dually labeled with [3H]thymidine and [3H]ouabain. Cycling cells which had [3H]thymidine-labeled nuclei did not have notably higher labeling with [3H]ouabain. However, [3H]ouabain labeling, as an indicator of pump site number and distribution, did vary among cells in an RPE population and also within individual cells. This latter observation suggests that unpolarized RPE cells in sparse cultures may have regionally different requirements for ionic regulation.

Modulation of growth in retina-derived cells by extracellular matrices

Intravitreal membranes from patients with proliferative vitreoretinopathy (PVR) consist partly of retinal glial (RG) and retinal pigment epithelial (RPE) cells surrounded by varying amounts of extracellular matrix (ECM). The contribution of the ECM to the growth of PVR membranes is unknown. This study was undertaken to determine if proliferation in cultured RPE and RG cells is affected by different substrates, including some ECM materials which have been identified in PVR membranes. Substrates tested included type I collagen, basement membrane Matrigel, and poly-D-lysine, as well as uncharacterized cell type-specific matrices deposited by cultured RPE and RG cells. Proliferation was quantified by 3H-thymidine incorporation and radioautography 24 hours after plating and by cell counts after 14 days in the presence of serum. Relative to uncoated culture plastic, growth of RPE cells was inhibited by Matrigel, enhanced by poly-D-lysine, and unaffected by type I collagen. In contrast, growth in RG cells was inhibited by type I collagen and unaffected by the other substrates. Analysis of the timing of DNA synthesis after plating suggested that the substrates which affected RPE growth did so by altering the fraction of cycling cells rather than the cell cycle time. For the cell-derived matrices, heterotypic matrix (matrix produced by the other retinal cell type) enhanced the growth of both RPE and RG. The results suggest that the ECM may modify the growth of cells contributing to PVR membranes. Of note is that the cell-derived matrices reciprocally stimulated growth of RG and RPE cells, cell types which may interact in PVR membranes.

MMPI correlates among post-acute TBI patients

A retrospective study examined predictors of MMPI responses for a sample of 66 post-acute traumatic brain-injured patients. Years of education was found to be correlated to four clinical scales and two validity scales with the more educated subjects reporting less psychopathological symptoms. Those with higher Verbal IQs tended to score higher on the Hysteria scale and the Repression scale. Those with higher Performance IQs were found to be endorsing more items on the Hypochondriasis, Hysteria and Organic Symptoms scales. The Verbal-Performance (V-P) difference score was not found to be significantly predictive of indices of defensiveness. Depression was found to vary over time peaking between 1 and 3 years after injury. The results were discussed in terms of their implications for clinicians.

Clearance of experimental vitreous hemorrhage after panretinal cryotherapy is related to macrophage influx

We investigated the effect of panretinal cryotherapy on blood clearance and on the inflammatory cellular response in rabbit eyes with experimental vitreous hemorrhage. Eyes treated with cryotherapy demonstrated less extensive vitreous opacity and more rapid clearance of blood than untreated eyes. The peak inflammatory cellular response measured by counts or radiolabeled cells in the optic nerve was 2.5 times greater in the cryotherapy-treated eyes. Panretinal cryotherapy may promote the clearance of vitreous hemorrhage by stimulating the influx of increased numbers of phagocytic inflammatory cells.

A 3' splice site-binding sequence in the catalytic core of a group I intron

Ribozymes use specific RNA-RNA interactions for substrate binding and active-site formation. Self-splicing group I introns have approximately 70 nucleotides constituting the core, a region containing sequences and structures indispensable for catalytic function. The catalytic core must interact with the substrates used for the two steps of the self-splicing reaction, that is, guanosine, the 5'-splice-site helix (P1) and the 3' splice site. Mutational evidence suggests that core sequences near segment J6/7 that joins the base-paired stems P6 and P7, and the bulged base of P7(5'), participate in binding guanosine substrate, but nothing is known about the interactions between the core, the 5'-splice-site helix and the 3' splice site. On the basis of comparative sequence data, it has been suggested that two specific bases in the catalytic core of group I introns might form a binding sequence for the 3' splice site. Here we present genetic evidence that such a binding site exists in the core of the Tetrahymena large subunit ribosomal RNA intron. We demonstrate that this pairing, termed P9.0, is functionally important in the exon ligation step of self-splicing, but is not itself responsible for 3'-splice-site selection.

Stimulation of DNA synthesis in human and bovine RPE by peptide growth factors: the response to TNF-alpha and EGF is dependent upon culture density

A range of concentrations of several peptide mitogens was tested for growth activity on bovine and human RPE cells under serum free conditions by analysis of 3H-thymidine incorporation within the first 24 hrs of exposure to the agents. For cultures which were subconfluent or in early confluence, TNF-alpha, a product of activated macrophages, was the most effective mitogen; little or no growth stimulation was observed for PDGF, EGF, NGF, IGF-1, IL-1B, bFGF or TGF-beta 1. For TNF-alpha and EGF the growth response was analyzed in cultures of varying density. TNF-alpha was more active in sparse RPE cultures whereas EGF stimulation was greater in dense cultures. The response to growth factors was similar in RPE cells from the two species sources, but the apparent magnitude of the response was greater for bovine cells because the growth rate in serum free medium, which was used as the basal reference, was lower for bovine RPE. It is concluded that culture conditions, especially the timing of the assay and the level of confluence of the cells, affect the detection of a growth response to peptide mitogens. Although several of the agents which were tested did not stimulate DNA synthesis in RPE in this study, they may nonetheless promote growth when assayed in combination with other agents or they may affect other biological functions of RPE cells.

Selection of the 3'-splice site in group I introns

A model for selection of 3'-splice sites in splicing of RNA precursors containing group I introns is presented. The key feature of this model is a newly identified tertiary interaction between the catalytic core of the intron and the 3'-splice site. This tertiary pairing would bring the 3'-splice site into the core of the intron, which is known to contain RNA sequences and structures essential for catalyzing the splicing reactions. The proposed tertiary interaction can coexist with P10, a pairing between 3'-exon sequences and the 'internal guide sequence' near the 5'-end of the intron. The model predicts that three RNA-RNA interactions are important in selection of 3'-splice sites: (i) binding of intron sequences with the core; (ii) pairing of exon sequences with the internal guide sequence; and (iii) binding of the terminal guanosine to an unknown site within the core.

Compensatory mutations demonstrate that P8 and P6 are RNA secondary structure elements important for processing of a group I intron

Compensatory mutations have been constructed which demonstrate that P8 and P6, two of nine proposed base-pairing interactions characteristic of group I introns, exist within the folded structure of the Tetrahymena thermophila rRNA intervening sequence, and that these secondary structure elements are important for splicing in E. coli and self-splicing in vitro. Two-base mutations in the 5' and 3' segments of P8 are predicted to disrupt P8 and a strong splicing-defective phenotype is observed in each case. A compensatory four-base mutation in P8 is predicted to restore pairing, and results in the restoration of splicing activity to nearly wild type levels. Thus, we conclude that P8 exists and is essential for splicing. In contrast to the strong phenotypes generally exhibited by mutations which disrupt RNA secondary structure, a two-base mutation in L8, the loop between P8[5'] and P8[3'], results in only a slight decrease in splicing activity. We also tested P6, a pairing which is proposed to consist of only two base-pairs in this intron. A two-base mutation in P6[3'] reduces splicing activity to a greater extent than does a two-base mutation in P6[5']. Comparison of the activities of these mutants and a compensatory P6 four-base mutant support the existence of P6, and suggest that the P6 pairing may be particularly important in the exon ligation step of splicing.

Growth in retinal glial cells in vitro is affected differentially by two types of cell contact-mediated interactions

Contact among rabbit retinal glial cells in subconfluent culture was previously shown to stimulate DNA synthesis [J. M. Burke (1983) Exp. Cell Res. 146, 204-206]. In this study nonliving surface membranes and metabolic coupling were investigated as mediators of the contact-dependent phenomenon. To evaluate surface membranes, preparations of fixed glial cells and fixed fibroblasts of several types were added in varying numbers to sparse cultures of glia or fibroblasts. In agreement with published data, fibroblast proliferation was inhibited by the fixed cells in a dose-dependent manner. Growth in glial cells was similarly inhibited. Fixed cells of both types were approximately equally effective in suppressing proliferation in cells of both types. No number of fixed cells was identified which, when added to glial cultures, stimulated glial proliferation. In contrast, metabolic coupling among glial cells was associated with increased DNA synthesis. Coupling was detected radioautographically as a flux of labeled precursor molecules from a prelabeled to a recipient population of glial cells in coculture. The cocultures were secondarily incubated with [3H]thymidine to label the nuclei of S-phase recipient cells. In the cocultures there was a higher rate of nuclear labeling in coupled than in uncoupled recipient glial cells. The results suggest that growth in subconfluent retinal glial cell cultures is modulated differentially by two types of interactions which require cell contact: growth is inhibited by interaction among nonliving cell surfaces but stimulated by metabolic cooperation among living cells.

Ouabain-sensitive Na+-K+ ATPase pumps in cultured human retinal pigment epithelium

The expression of Na+-K+ ATPase pumps was studied in cultured human retinal pigment epithelium (RPE). Pump site number was measured by quantitation of the specific binding of [3H]ouabain to cultures of varying density. Specific binding of [3H]ouabain was time- and concentration-dependent, and was inhibited by potassium and by excess unlabeled ouabain. Estimates of pump site number based upon specific [3H]ouabain binding indicated that the number of pumps per RPE cell was maximal in sparse cultures and declined six-fold as cultures became confluent. Pump activity, determined by measurement of specific 86Rb (rubidium) uptake, was also greater in sparse than in dense cultures. Quantitation of [3H]thymidine incorporation as a measure of cell proliferation demonstrated that proliferation in RPE cultures decreased logarithmically as culture density increased. Increased pump site number in cultured RPE, therefore, correlated with increased cell proliferation and decreased culture density. We conclude that human RPE express ouabain-sensitive Na+-K+ ATPase in vitro and maximal expression is observed in sparse, proliferating cultures.

The response styles of post-acute traumatic brain-injured patients on the MMPI

A retrospective descriptive study (n = 44) was conducted on the response styles of post-acute traumatic brain-injured patients on the MMPI. The sample profiles were examined on indices of consistency, random responding, and bias to look good or bad. The results showed that about 20% of the profiles were markedly inconsistent, including two profiles which met the criteria for random responding. Depending on the cut-off score used, between 0 and 9% were identified as biased to look bad, while between 18 and 30% were identified as biased to look good. A mean profile on the primary clinical and research scales was developed and a frequency count of the high two-point codes was conducted. This profile approached clinically significant levels on the Psychopathic deviant, Schizophrenia, Depression, and Mania scales, respectively. The three most frequently occurring two-point codes (2-4, 4-8, and 4-9) have been classified as characterological in nature. The primary implication of these results for clinicians was the need for careful scrutiny of indices of consistency, random responding and bias to look good when interpreting self-report measures such as the MMPI with the TBI population.

Photoablation of ocular melanoma with a high-powered argon endolaser

We studied the use of a 15-W argon blue-green laser in the treatment of choroidal melanoma in a rabbit model. Greene melanoma cells were used to produce 2- to 4-mm thick tumors posteriorly in the suprachoroidal space in pigmented rabbits. Endophotocoagulation delivered through a 600-micron fiberoptic probe was performed to ablate the tumor tissue and a surrounding margin of normal tissue. A vitreous cutter was used simultaneously to remove liberated necrotic debris. The effect of the laser on tumor and normal ocular tissue was evaluated by light microscopy and the extent of the proliferative response by tritiated thymidine radioautography. Application of 100 to 400 pulses of laser energy using treatment parameters of 12 to 14 W of power and 0.1-s pulses resulted in complete ablation of melanoma tissue, overlying retina, and choroid. There was no substantial intraoperative or postoperative hemorrhage. Material liberated during the laser treatment was found to be nonviable. The effect of the laser on tissue appeared localized to within approximately 1.25 mm of the margin of the central lesion. The high-energy argon laser seems to offer a means of effectively ablating melanoma tissue via an internal resection approach.

Molecular genetics of group I introns: RNA structures and protein factors required for splicing--a review

In vivo and in vitro genetic techniques have been widely used to investigate the structure-function relationships and requirements for splicing of group-I introns. Analyses of group-I introns from extremely diverse genetic systems, including fungal mitochondria, protozoan nuclei, and bacteriophages, have yielded results which are complementary and highly consistent. In vivo genetic studies of fungal mitochondrial systems have served to identify cis-acting sequences within mitochondrial introns, and trans-acting protein products of mitochondrial and nuclear genes which are important for splicing, and to show that some mitochondrial introns are mobile genetic elements. In vitro genetic studies of the self-splicing intron within the Tetrahymena thermophila nuclear large ribosomal RNA precursor (Tetrahymena LSU intron) have been used to examine essential and nonessential RNA sequences and structures in RNA-catalyzed splicing. In vivo and in vitro genetic analysis of the intron within the bacteriophage T4 td gene has permitted the detailed examination of mutant phenotypes by analyzing splicing in vivo and self-splicing in vitro. The genetic studies combined with phylogenetic analysis of intron structure based on comparative nucleotide sequence data [Cech 73 (1988) 259-271] and with biochemical data obtained from in vitro splicing experiments have resulted in significant advances in understanding the biology and chemistry of group-I introns.

Regional comparisons of cathepsin D activity in bovine retinal pigment epithelium

Cathepsin D is the lysosomal protease in the retinal pigment epithelium which is presumed to be the major enzyme involved in the degradation of shed discs during the photoreceptor renewal process. In this study, the cathepsin D activity in RPE cells from the posterior area centralis was compared to the activity in cells from the equatorial region of the same bovine eyes. Enzyme activities were measured both in paired fresh RPE isolates from the two retinal regions and in paired regional RPE cultures. Cultures were further analyzed for changes in enzyme activity with time in vitro from 3 to 11 weeks. Analysis of freshly isolated RPE cells from 30 eyes indicated that cells from the area centralis have significantly higher cathepsin D activity than cells from the more peripheral retina. Paired cultures of RPE from the two regions did not express the intraeye topographical differences in enzyme activity which were observed in fresh isolates. There were significant variations in enzyme activity in cultured RPE cells with time in vitro, but activity levels did not show progressive increases or decreases with in vitro aging. After 11 weeks in vitro, but not at earlier times, the enzyme activities in the paired regional cultures from the same eye were highly correlated. The data suggest that the higher levels of cathepsin D activity observed in the freshly isolated RPE from the area centralis result from modulators of enzyme activity which are not present in culture.

Topographical variation in growth in cultured bovine retinal pigment epithelium

Cell cultures of adult bovine retinal pigment epithelium (RPE) were propagated from posterior and equatorial regions of the same eyes to study topographical differences in cell growth. To generate the cultures, the retina was removed, eyecups were incubated in collagenase followed by trephining three zones from the posterior area centralis and three zones from the equatorial region of the tapetal retina. Outgrowth in primary cultures and proliferation in passaged cultures were evaluated in paired cultures derived from the same eyes. Relative to cells from the more peripheral regions, RPE cells from the area centralis showed lower growth potential which was manifested as reduced cell numbers in primary outgrowth and a smaller fraction of serum-responsive cells when cultures were serially passaged. Cells from older donors have been shown to exhibit similar reductions in in vitro growth potential, making it appear as if, with regards to proliferation, RPE from the area centralis is more "aged" than RPE from more peripheral regions of the same eyes.