Yvonne Ou

The Transmembrane Domains of Ectoapyrase (CD39) Affect Its Enzymatic Activity and Quaternary Structure

Mammalian ectoapyrase (CD39) is an integral membrane protein with two transmembrane domains and a large extracellular region. The enzymatic activity of ectoapyrase is inhibited by most detergents used for membrane protein solubilization. In contrast, the enzymatic activities of soluble E-type ATPases, including potato tuber (Solanum tuberosum) apyrase and parasite ecto-ATPase, are not affected by detergents. Here we show that ectoapyrase is a tetramer and that detergents that reduce the activity of the enzyme promote dissociation of the tetramer to monomers. We expressed a secreted form of the ectoapyrase in COS-7 cells by fusing the signal peptide of murine CD4 with the extracellular domain of the ectoapyrase. The soluble ectoapyrase is catalytically active and its activity is not affected by detergents. Mutants of the ectoapyrase with only the NH2- or the COOH-terminal transmembrane domain are membrane-bound, and their activity is no longer affected by detergents. The enzymatic activity of all of the mutant proteins is less than that of the native enzyme. These results suggest that the proper contacts between the transmembrane domains of the monomers in the tetramer are necessary for full enzymatic activity.

Transcriptional Modification by a CASK-Interacting Nucleosome Assembly Protein

CASK acts as a coactivator for Tbr-1, an essential transcription factor in cerebral cortex development. Presently, the molecular mechanism of the CASK coactivation effect is unclear. Here, we report that CASK binds to another nuclear protein, CINAP, which binds histones and facilitates nucleosome assembly. CINAP, via its interaction with CASK, forms a complex with Tbr-1, regulating expression of the genes controlled by Tbr-1 and CASK, such as NR2b and reelin. A knockdown of endogenous CINAP in hippocampal neurons reduces the promoter activity of NR2b. Moreover, NMDA stimulation results in a reduction in the level of CINAP protein, via a proteasomal degradation pathway, correlating with a decrease in NR2b expression in neurons. This study suggests that reduction of the CINAP protein level by synaptic stimulation contributes to regulation of the transcriptional activity of the Tbr-1/CASK/CINAP protein complex and thus modifies expression of the NR2b gene.

Glaucoma, Alzheimer disease and other dementia: A longitudinal analysis

Purpose: To evaluate the risk of developing Alzheimer disease (AD) or other dementia in patients diagnosed with open-angle glaucoma (OAG) in a nationally representative longitudinal sample of elderly persons. Methods: This retrospective cohort study (January 1, 1994–December 31, 2007) used Medicare 5% claims data. We identified beneficiaries aged 68+ years who had at least two claims with diagnoses of OAG and no Alzheimer or other dementia in 1994, using a 3-year look-back period between 1991 and 1993 (n = 63,235) and beneficiaries matched on age, sex, race, and Charlson index without a diagnosis of OAG throughout the observational period (n = 63,235), using propensity score matching. Using a Cox Proportional Hazards model, we analyzed time to AD diagnosis and time to AD or other dementia diagnosis. Results: Elderly individuals diagnosed with OAG did not have an increased rate of AD and other dementia diagnosis compared to those without OAG during a 14-year follow-up period, even after controlling for relevant covariates present at baseline. Conclusions: Individuals aged 68+ years diagnosed with OAG have a decreased rate of AD or other dementia diagnosis compared to control patients without an OAG diagnosis. Although OAG and AD are both age-related neurodegenerative diseases, our findings do not support a positive association.

Outcomes of Ahmed Glaucoma Valve Implantation in Children With Primary Congenital Glaucoma

OBJECTIVES To evaluate the long-term efficacy of intraocular pressure reduction and complications of Ahmed glaucoma valve (AGV) implantation in children with primary congenital glaucoma. METHODS The medical records of patients with primary congenital glaucoma who underwent AGV implantation with a minimum follow-up of 6 months were reviewed. The primary outcome measure was cumulative probability of success, defined as intraocular pressure greater than 5 mm Hg and less than 23 mm Hg and at least a 15% reduction from the preoperative intraocular pressure, without serious complications, additional glaucoma surgery, or loss of light perception. RESULTS Thirty eyes of 19 children with primary congenital glaucoma who underwent AGV implantation with a minimum follow-up of 6 months were reviewed. The children had a mean (SD) age of 1.8 (2.6) years, a mean (SD) preoperative intraocular pressure of 28.4 (6.7) mm Hg, and a mean (SD) follow-up time of 57.6 (48.0) months. The cumulative probability of success was 63% in 1 year and 33% in 5 years. After a second AGV implantation, the cumulative probability of success was 86% in 1 and 2 years and 69% in 5 years. Hispanic ethnicity (P = .02) and being female (P = .005) were associated with increased risk of failure. CONCLUSIONS Thirty-three percent of AGV implantations in children with primary congenital glaucoma were successful after 5 years of follow-up. With the implantation of a second AGV, the 5-year success rate increased to 69%.

Surgical Management of Pediatric Glaucoma

Pediatric glaucoma surgery is challenging because of the differences in anatomy from the adult, differences in the behavior of the tissues of a childs glaucomatous eye, the variety in causes of the disease, and difficulties with postoperative management. Goniotomy and trabeculotomy are the preferred initial treatments for primary congenital glaucoma. Trabeculectomy with adjunctive mitomycin C is more likely to succeed in older, phakic patients, but carries the long-term risk of bleb-associated endophthalmitis. Glaucoma drainage devices may be preferred in younger children and in patients with aphakic glaucoma, but these devices can cause tube-related complications. Lastly, cyclodestructive procedures are reserved for patients in whom filtering surgery has failed, given its more unpredictable effects and serious complications.

Selective Vulnerability of Specific Retinal Ganglion Cell Types and Synapses after Transient Ocular Hypertension

Key issues concerning ganglion cell type-specific loss and synaptic changes in animal models of experimental glaucoma remain highly debated. Importantly, changes in the structure and function of various RGC types that occur early, within 14 d after acute, transient intraocular pressure elevation, have not been previously assessed. Using biolistic transfection of individual RGCs and multielectrode array recordings to measure light responses in mice, we examined the effects of laser-induced ocular hypertension on the structure and function of a subset of RGCs. Among the α-like RGCs studied, αOFF-transient RGCs exhibited higher rates of cell death, with corresponding reductions in dendritic area, dendritic complexity, and synapse density. Functionally, OFF-transient RGCs displayed decreases in spontaneous activity and receptive field size. In contrast, neither αOFF-sustained nor αON-sustained RGCs displayed decreases in light responses, although they did exhibit a decrease in excitatory postsynaptic sites, suggesting that synapse loss may be one of the earliest signs of degeneration. Interestingly, presynaptic ribbon density decreased to a greater degree in the OFF sublamina of the inner plexiform layer, corroborating the hypothesis that RGCs with dendrites stratifying in the OFF sublamina may be damaged early. Indeed, OFF arbors of ON-OFF RGCs lose complexity more rapidly than ON arbors. Our results reveal type-specific differences in RGC responses to injury with a selective vulnerability of αOFF-transient RGCs, and furthermore, an increased susceptibility of synapses in the OFF sublamina. The selective vulnerability of specific RGC types offers new avenues for the design of more sensitive functional tests and targeted neuroprotection. SIGNIFICANCE STATEMENT Conflicting reports regarding the selective vulnerability of specific retinal ganglion cell (RGC) types in glaucoma exist. We examine, for the first time, the effects of transient intraocular pressure elevation on the structure and function of various RGC types. Among the α-like RGCs studied, αOFF-transient RGCs are the most vulnerable to transient transient intraocular pressure elevation as measured by rates of cell death, morphologic alterations in dendrites and synapses, and physiological dysfunction. Specifically, we found that presynaptic ribbon density decreased to a greater degree in the OFF sublamina of the inner plexiform layer. Our results suggest selective vulnerability both of specific types of RGCs and of specific inner plexiform layer sublaminae, opening new avenues for identifying novel diagnostic and treatment targets in glaucoma.

Factors that Influence Intraocular Pressure Changes after Myopic and Hyperopic LASIK and Photorefractive Keratectomy: A Large Population Study

PURPOSE To describe the factors that influence the measured intraocular pressure (IOP) change and to develop a predictive model after myopic and hyperopic LASIK and photorefractive keratectomy (PRK) in a large population. DESIGN Retrospective, observational case series. PARTICIPANTS Patients undergoing primary PRK or LASIK with a refractive target of emmetropia between January 1, 2008, and October 5, 2011. METHODS The Optical Express database was queried for all subjects. Data were extracted on procedure specifics, preoperative central corneal thickness (CCT), IOP (using noncontact tonometry), manifest refraction, average keratometry, age, gender, and postoperative IOP at 1 week, 1 month, and 3 months. A linear mixed methods model was used for data analysis. MAIN OUTCOME MEASURES Change in IOP from preoperatively to 1 month postoperatively. RESULTS A total of 174 666 eyes of 91 204 patients were analyzed. Hyperopic corrections experienced a smaller IOP decrease than myopic corrections for both PRK and LASIK (P<0.0001). Patients who underwent LASIK had a 0.94 mmHg (95% confidence interval [CI], 0.89-0.98) greater IOP decrease than patients who underwent PRK (P<0.0001), reflecting the effect of the lamellar flap. The decrease in IOP was linearly related to preoperative manifest spherical equivalent (MSE) for myopic PRK and LASIK (P<0.0001), weakly correlated with preoperative MSE after hyperopic LASIK, and not related to preoperative MSE after hyperopic PRK. The single greatest predictor of IOP change was preoperative IOP across all corrections. By using the available data, a model was constructed to predict postoperative IOP change at 1 month; this was able to explain 42% of the IOP change after myopic LASIK, 34% of the change after myopic PRK, 25% of the change after hyperopic LASIK, and 16% of the change after hyperopic PRK. CONCLUSIONS Myopic procedures lower measured IOP more than hyperopic procedures; this decrease was proportional to the amount of refractive error corrected. Independent of the refractive correction, the creation of the lamellar LASIK flap decreased measured IOP by 0.94 mmHg. A best-fit model for IOP change was developed that may allow better interpretation of post-laser vision correction IOP values.

Who's lost first? Susceptibility of retinal ganglion cell types in experimental glaucoma

ABSTRACT The purpose of this article is to summarize our current knowledge about the susceptibility of specific retinal ganglion cell (RGC) types in experimental glaucoma, and to delineate the initial morphological and functional alterations that occur in response to intraocular pressure (IOP) elevation. There has been debate in the field as to whether RGCs with large somata and axons are more vulnerable, with definitive conclusions still in progress because of the wide diversity of RGC types. Indeed, it is now estimated that there are greater than 30 different RGC types, and while we do not yet understand the complete details, we discuss a growing body of work that supports the selective vulnerability hypothesis of specific RGC types in experimental glaucoma. Specifically, structural and functional degeneration of various RGC types have been examined across different rodent models of experimental glaucoma (acute vs. chronic) and different strains, and an emerging consensus is that OFF RGCs appear to be more vulnerable to IOP elevation compared to ON RGCs. Understanding the mechanisms by which this selective vulnerability manifests across different RGC types should lead to novel and improved strategies for neuroprotection and neuroregeneration in glaucoma. HIGHLIGHTSWhether large retinal ganglion cells (RGCs) are more susceptible in glaucoma is controversial.Specific RGC types are selectively vulnerable to intraocular pressure elevation.Different RGC types undergo degenerative events on varying time scales.

Scleral Intraocular Pressure Measurement in Cadaver Eyes Pre- and Postkeratoprosthesis Implantation

PURPOSE We correlated scleral IOP to assigned IOP using pneumatonometry in cadaver eyes before and after Boston type I keratoprosthesis (KPro) implantation. METHODS Corneal IOP and scleral IOP at the superonasal, superotemporal, inferotemporal, and inferonasal quadrants were measured using pneumatonometry in six cadaver eyes cannulated with an infusion line with assigned IOP held at 20, 30, 40, and 50 mm Hg. Measurements of scleral IOP at the same location were repeated after a KPro was implanted. Correlations between scleral IOP and assigned IOP were analyzed for the entire group of eyes, and for each individual eye before and after KPro. One eye was tested by another masked grader for interobserver variability. RESULTS Scleral IOP measured higher than corneal IOP by a mean of 13.2 mm Hg. For group analysis, pre-KPro scleral IOP had a positive and linear correlation with assigned IOP in all quadrants (P < 0.00001), and this correlation was preserved after KPro implantation (P < 0.00001). There was strong interobserver agreement in all measurement sites (P < 0.001). In analyses of individual eyes, scleral IOP measured at the inferotemporal quadrant confirmed the strong linear association between scleral IOP and assigned IOP before and after KPro for all study eyes. A Bland-Altman plot showed that the difference in scleral IOP between pre-KPro and post-KPro eyes fell mostly within ± 5 mm Hg. CONCLUSIONS Scleral IOP measured by pneumatonometry may be used to estimate IOP in cadaver eyes with and without keratoprosthesis. This may be a potential modality for assessing IOP for patients with corneal pathology or keratoprosthesis.

Development of a resident training module for systematic optic disc evaluation in glaucoma.

PurposeTo determine the impact on ophthalmology residents of a training module to teach systematic optic disc (disc) evaluation. MethodsA training module for disc evaluation was developed consisting of: (1) a computer-based evaluation course with 100 illustrative disc photographs featuring normal and glaucomatous discs; (2) 2 different disc photograph test sets to be completed before and after taking the course; and (3) a 1-page checklist emphasizing 8 areas of disc evaluation to guide the residents through the test sets. Each area required identification of 2 to 3 key features pertinent to glaucoma. Points were assigned to each correctly answered item on the checklist by ophthalmology residents of 2 training programs. Residents were also asked to evaluate the disc according to a glaucoma scale. Main outcome measures included precourse and postcourse checklist scores and disc glaucoma evaluation scores. ResultsTwenty-eight residents from 2 training programs completed the training module. Mean checklist scores improved significantly after taking the evaluation course across all residents and in residents who had 2 years of ophthalmology residency experience (P=0.019, 0.017, respectively). Precourse disc glaucoma evaluation score increased 4% to 6% per year of ophthalmology residency training (P=0.023, R2=0.1838). One program had a higher mean postcourse disc glaucoma evaluation score than another (P=0.038). ConclusionsA systematic disc evaluation module for resident training may improve disc evaluation, provide an objective method to assess the residents learning experience, monitor the progress and identify areas of weakness of training, and compare results among groups of residents across different residency programs.