Quality and Agreement With Scientific Consensus of ChatGPT Information Regarding Corneal Transplantation and Fuchs Dystrophy

PURPOSE

ChatGPT is a commonly used source of information by patients and clinicians. However, it can be prone to error and requires validation. We sought to assess the quality and accuracy of information regarding corneal transplantation and Fuchs dystrophy from 2 iterations of ChatGPT, and whether its answers improve over time.

METHODS

A total of 10 corneal specialists collaborated to assess responses of the algorithm to 10 commonly asked questions related to endothelial keratoplasty and Fuchs dystrophy. These questions were asked from both ChatGPT-3.5 and its newer generation, GPT-4. Assessments tested quality, safety, accuracy, and bias of information. Chi-squared, Fisher exact tests, and regression analyses were conducted.

RESULTS

We analyzed 180 valid responses. On a 1 (A+) to 5 (F) scale, the average score given by all specialists across questions was 2.5 for ChatGPT-3.5 and 1.4 for GPT-4, a significant improvement ( P < 0.0001). Most responses by both ChatGPT-3.5 (61%) and GPT-4 (89%) used correct facts, a proportion that significantly improved across iterations ( P < 0.00001). Approximately a third (35%) of responses from ChatGPT-3.5 were considered against the scientific consensus, a notable rate of error that decreased to only 5% of answers from GPT-4 ( P < 0.00001).

CONCLUSIONS

The quality of responses in ChatGPT significantly improved between versions 3.5 and 4, and the odds of providing information against the scientific consensus decreased. However, the technology is still capable of producing inaccurate statements. Corneal specialists are uniquely positioned to assist users to discern the veracity and application of such information.

Current state of endothelial cell therapy

PURPOSE OF REVIEW

Currently, there is heightened interest surrounding endothelial cell therapy for the treatment of corneal edema. The purpose of this review article is to describe and summarize the background information as well as the research surrounding the emerging treatment modalities for endothelial cell therapy.

RECENT FINDINGS

Marked advancements have been made in the translational research in this area, and increasing refinements have been demonstrated in the treatment protocols for cell therapy. Human clinical trials in this field are ongoing, specifically, in the area of injected human corneal endothelial cells (HCECs), with early results showing favorable safety and efficacy profiles.

SUMMARY

Efficient and effective delivery of HCECs to patients with corneal edema and dysfunction now appears feasible, and the results from ongoing human clinical trials are much anticipated. Adjunct therapeutics-in the form of pharmacological agents and/or surgical techniques, such as descemetorhexis-will likely continue to play an important role in defining the future of endothelial cell therapy.

Effect of Anterior Chamber Air on Central Corneal Thickness in Human Donor Eyes

PURPOSE

The purpose of this study was to describe the effects of intracameral air on corneal edema.

METHODS

A laboratory investigation was performed on human donor corneas. Baseline pachymetry measurements through anterior segment optical coherence tomography and endothelial cell density were obtained for all corneas. Each pair of corneas was separated and randomly assigned to undergo air injection or Optisol-GS into a BIONIKO artificial anterior chamber for 5 minutes at physiologic intraocular pressure confirmed by digital palpation. Photographs were obtained immediately on connection of the cornea to the artificial anterior chamber and on completion of the 5 minutes of treatment, with anterior chamber air being exchanged for Optisol-GS. Pretreatment and posttreatment photographs were obtained. Immediately after treatment, pachymetry was again obtained on all corneas. Pachymetry data underwent statistical analysis.

RESULTS

Corneal pachymetry improved from 690.5 ± 126.6 to 576.1 ± 87.2 μm, yielding a 114.4 ± 50.4 μm improvement of pachymetry in the group with air injected into the anterior chamber. This was a significant improvement of pachymetry when compared with the group with Optisol-GS injected into the anterior chamber, which showed an improvement from 662.3 ± 126.5 to 613.5 ± 108.0 μm, yielding an improvement of 48.8 ± 34.3 μm.

CONCLUSIONS

Injection of air into the anterior chamber leads to a significant decrease in corneal pachymetry. We thereby propose that injecting air intracamerally is an effective intraoperative intervention when visualization is negatively affected by corneal edema.

Comparison of corneal endothelial cell density and morphology with Optisol GS and Life4C storage media in the eye bank: a 5-year retrospective analysis

Purpose

Optisol GS and Life4C are corneal storage media used by eye banks worldwide. We sought to determine if either solution was associated with superior corneal endothelial cell density (ECD) or morphology in a large cohort of donor corneas.

Methods

From January 2016 through December 2020, 10,316 corneas from 5,624 unique donors were acquired and analyzed at Rocky Mountain Lions Eye Bank. In April 2019, Life4C replaced Optisol GS as the sole storage medium. We compared ECD and morphology before and after April 2019, and excluded corneas processed within the transition period. Univariable and multivariable regression analyses accounted for age, sex, tobacco use, heavy alcohol use, and diabetes. Only right corneas were analyzed to account for the correlation between eyes.

Results

Of 5042 right corneas analyzed, 3486 were stored in Optisol GS and 1556 in Life4C. There was no significant difference in ECD across groups (2794 vs. 2793 cells/mm2 in Optisol GS and Life4C, p=0.88). In multivariate analyses, there was no significant difference in corneal ECD (0.6 cells/mm2 higher with Life4C, p=0.96) or hexagonality (0.22% higher with Life4C, p=0.31). However, the coefficient of variation was significantly lower in the Life4C group (-0.0039, p=0.03). After adjustment for above factors, corneas in Life4C demonstrated a 3.1% decreased likelihood of exhibiting CV values greater than 0.40 (p=0.009).

Conclusions

This study demonstrates comparable and favorable outcomes using both storage media and confirms their overall efficacy. The decreased CV in Life4C is not of clinically significant magnitude, but merits further research in clinical and long-term settings.

Scheimpflug Corneal Tomography Anterior Chamber Depth in Descemet Stripping Endothelial Keratoplasty Recipients

PURPOSE

Our study investigates whether preoperative anterior chamber depth (ACD) measured by Scheimpflug tomography could serve as a potential predictor of graft failure in eyes undergoing Descemet stripping endothelial keratoplasty (DSEK).

METHODS

A retrospective review was conducted on patients who underwent primary or repeat DSEK between January 2020 and August 2021 at Bascom Palmer Eye Institute. Charts from 378 primary and 192 repeat DSEK patients were reviewed and ultimately 47 primary and 21 repeat DSEK patients met criteria for inclusion. Data collection included demographics, preoperative ACD, best-corrected visual acuity, and length of follow-up.

RESULTS

Demographics were similar between groups, and there was no significant difference in the average best-corrected visual acuity between the single and repeat DSEK groups preoperatively. Baseline preoperative ACD was greatest in the single DSEK group (3.51 ± 0.90 mm) when compared to baseline preoperative ACD in the repeat DSEK group (3.01 ± 0.67 mm, P = 0.003). The preoperative mean ACD was smallest in the repeat DSEK group before the second DSEK (2.94 ± 0.48 mm, P = 0.001). Preoperative baseline ACD was the only variable to affect graft survival time significantly (P = 0.012). The incidence of glaucoma diagnosis was similar in both groups (42.5% vs. 42.8%, P = 0.471). The diagnosis of glaucoma and presence of incisional glaucoma surgery did not affect the graft survival time (P = 0.129, P = 0.559) or need for repeat DSEK.

CONCLUSIONS

Smaller baseline preoperative Scheimpflug ACD measurement may be a possible predictor of the need for repeat DSEK. Our study found that Scheimpflug ACD decreases with subsequent DSEK failure.

Outcomes of Secondary Intraocular Lens Implantation and Descemet Stripping Endothelial Keratoplasty-Comparing Staged Versus Combined Surgical Approach

PURPOSE

The aim of this study was to compare the outcomes of staged versus combined surgical approach for secondary intraocular lens (IOL) implantation and Descemet stripping endothelial keratoplasty (DSEK).

METHODS

This is a retrospective review of 124 eyes from 124 patients who underwent either staged or combined secondary IOL implantation in addition to DSEK over a 5-year period at 2 academic tertiary referral centers, between January 1, 2014, and October 1, 2019. Corrected distance visual acuity (CDVA), presence of graft detachment, primary graft failure (PGF), and cystoid macular edema were documented and analyzed.

RESULTS

The CDVA for the 1- to 2- month follow-up period was significantly better in the staged group compared with the combined group ( P = 0.011). By the postoperative 6- to 9-month follow-up period, there was no significant difference in the CDVA between the groups ( P = 0.591). There was no significant difference in the incidence of PGF or graft detachment between the 2 groups ( P > 0.05). In addition, there was no significant difference in the CDVA or rate of postoperative complications between the different methods of IOL fixation.

CONCLUSIONS

The short-term visual outcomes were significantly better in eyes that underwent staged secondary IOL implantation and DSEK versus the combined surgical approach, although the difference was no longer present at 6 to 9 months. There was no difference in the rate of PGF or graft detachment between the 2 groups.

Outcomes of Nontuberculous Mycobacterial Keratitis After Clear Corneal Incision Phacoemulsification Surgery: A Case Series of 6 Eyes in South Florida

PURPOSE

The purpose of this study was to present the successful management and outcomes in a series of 6 cases of culture-positive nontuberculous mycobacterial keratitis after clear corneal incision phacoemulsification surgery.

METHODS

This is a case series of 6 consecutive eyes that presented at the Cornea Division at an academic institution, diagnosed with culture-positive nontuberculous mycobacterial keratitis after phacoemulsification surgery.

RESULTS

Six eyes of 5 patients were included. The mean interval from cataract surgery to presentation was 7.7 weeks. All cases presented with intrastromal abscesses adjacent to corneal incisions, and 2 had scleral extension of the infection. Isolated organisms were Mycobacterium abscessus (n = 4), Mycobacterium chelonae (n = 1), and Mycobacterium mucogenicum (n = 1). All cases were treated with topical amikacin 8 mg/mL for 10.5 weeks on average. All cases received either oral clarithromycin at 500 mg twice-daily dosage or oral azithromycin at 500 mg daily. Two patients with scleral abscesses underwent surgical debridement with amniotic membrane grafts. All 6 eyes achieved infection resolution and good visual recovery, with the final visual acuity ranging from 20/20 to 20/60. None of the patients experienced recurrence of infection.

CONCLUSIONS

Prompt medical treatment with combined topical and oral therapy can lead to infection resolution and favorable visual recovery. Early surgical intervention can ensure good outcomes in cases of scleral extension.

Scheimpflug Corneal Densitometry Values and Severity of Guttae in Relation to Visual Acuity in Fuchs Endothelial Corneal Dystrophy

PURPOSE

The purpose of this study was to investigate the association between corneal densitometry (CD) values from Scheimpflug tomography imaging, severity of guttae, and visual acuity in eyes with Fuchs endothelial corneal dystrophy (FECD).

METHODS

This was a retrospective, cross-sectional study. Patients with FECD were examined at the Bascom Palmer Eye Institute from January 2015 to September 2019. We extracted CD values at central annuli of 0-2, 2-6, 6-10 and 10-12 mm from Scheimpflug tomography images. We investigated the association of corrected distance visual acuity (CDVA) with CD values, severity of guttae, central corneal thickness (CCT), cataract grade, refractive error, corneal edema grade, age, and gender using multivariate generalized estimating equation regression models.

RESULTS

One hundred ninety-two eyes from 110 patients were included in this study. Increase in central CD values at the 0 to 2 mm zone (P < 0.001), severity of guttae (P = 0.046), age (P < 0.001), cataract grade (P < 0.001), corneal edema grade (P < 0.001), and type of refractive error (P = 0.008) were significantly associated with decreased CDVA. Central corneal thickness, sex, and the peripheral CD values (2-6, 6-10, and 10-12 mm) were not significantly associated with CDVA (P > 0.05) in the final multivariate regression model.

CONCLUSIONS

Our study demonstrates that central CD values at 0 to 2 mm and severity of guttae are each associated with decreased CDVA in FECD. These findings carry implications for patients with FECD considering surgical intervention for phacoemulsification alone, Descemet stripping only, or endothelial cell transplantation and provide a multifactorial perspective on vision loss in FECD.

Outcomes of Femtosecond Laser-Assisted Cataract Surgery Compared to Conventional Phacoemulsification in Eyes with Pseudoexfoliation Syndrome

OBJECTIVE

To compare the outcomes including complications, in a large cohort of eyes with pseudoexfoliation syndrome that underwent Femtosecond Laser-Assisted Cataract Surgery (FLACS) versus conventional phacoemulsification.

DESIGN

Retrospective cohort study.

PARTICIPANTS

A total of 513 eyes from 366 patients with pseudoexfoliation syndrome that underwent cataract surgery between April 1, 2014, and December 31, 2018.

METHODS

Charts were reviewed for preoperative examination findings, intraoperative complications, and post-operative outcomes. Best-corrected visual acuity (BCVA) was measured by logMAR and compared between groups at one month and the final follow-up visit.

RESULTS

Of 513 eyes, 71 (13.8%) underwent FLACS, and 442 (86.2%) eyes underwent conventional cataract surgery. Between the two groups, there was no difference in the incidence of vitreous prolapse, capsular tear, pupillary expansion device usage, capsular tension support device usage, or postoperative cystoid macular edema (p > .05 for all). At the final visit, there was no significant difference in BCVA between FLACS and conventional phacoemulsification groups (mean logMAR 0.26 vs. 0.25, p = .87).

CONCLUSIONS

When comparing FLACS and conventional phacoemulsification in eyes with pseudoexfoliation syndrome, no difference was seen in the incidence of complications. BCVA was comparable between the two groups. Zonular weakness significantly increased the risk of complications in both groups.

Acute Corneal Transplant Rejection After COVID-19 Vaccination

PURPOSE

The purpose of this report was to describe 4 cases of acute corneal transplant rejection occurring in association with coronavirus disease 2019 (COVID-19) mRNA vaccination.

METHODS

Four patients with prior keratoplasty developed presumed immunologic rejection after the mRNA-1273 vaccination for coronavirus 2 (SARS-CoV-2). Case 1 had received Descemet membrane endothelial keratoplasty 6 months ago and presented with endothelial graft rejection 3 weeks after the first vaccine dose. Case 2 had undergone penetrating keratoplasty 3 years previously and presented with acute endothelial rejection 9 days after the second vaccine dose. Case 3 had prior Descemet stripping automated endothelial keratoplasty (DSAEK) and began experiencing symptoms of endothelial graft rejection 2 weeks after the second vaccine dose. Case 4 presented with endothelial rejection of the penetrating keratoplasty graft 2 weeks after the second vaccine dose.

RESULTS

Frequent topical corticosteroids alone were initiated in all 4 cases. In case 1, the endothelial rejection line appeared fainter with improvement in visual acuity and corneal edema 5 weeks after diagnosis. Case 2 experienced complete resolution of corneal stromal edema and rejection line 6 weeks after diagnosis. Cases 3 and 4 have both experienced initial improvement with steroid treatment as well.

CONCLUSIONS

These cases suggest acute corneal endothelial rejection may occur soon after either dose of the COVID-19 mRNA vaccine. Prompt initiation of aggressive topical steroid therapy may result in complete resolution of clinical signs and symptoms. Further studies are needed to elucidate the causal mechanism of corneal graft rejection after COVID-19 vaccination.

Presence of SARS-CoV-2 Viral RNA in Aqueous Humor of Asymptomatic Individuals

PURPOSE

The purpose of this study was to determine whether severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is detectable in the aqueous of asymptomatic individuals presenting for ophthalmic surgery.

DESIGN

Prospective cross-sectional study.

METHODS

Setting and participants: all patients undergoing anterior segment surgery at an ambulatory surgical center (ASC) belonging to a tertiary academic center in South Florida during a 102-day period between June and September 2020 received nasal swab testing for SARS-CoV-2 and underwent a relevant review of symptoms prior to surgery, with negative results required for both in order to proceed with surgery. Main outcomes and measurements: a small sample of aqueous humor (approximately 0.2 cc) was acquired at the beginning of anterior segment surgery from all participants. Aqueous humor was analyzed for SARS-CoV-2 viral ribonucleic acid (RNA) using real-time reverse transcriptase polymerase chain reaction. Demographic information was acquired from participants for secondary analyses.

RESULTS

A total of 70 samples were acquired. Of those, 39 samples were excluded due to insufficient material or inconclusive results. Of 31 samples that were successfully analyzed, 6 (19.4%) demonstrated detectable SARS-CoV-2 RNA. None of the 6 individuals (0%) with detectable viral RNA in aqueous humor reported symptoms during the year, compared to 2 of 25 individuals (8%) with negative samples (P = 1). Positive samples were distributed throughout the study period, including both the first and the last days of enrollment.

CONCLUSIONS

The presence of SARS-CoV-2 viral RNA in aqueous despite negative nasal swab testing confirmed its presence beyond the blood-ocular barrier in asymptomatic individuals and raises the possibility that the virus may persist in immunoprivileged spaces despite an absence of symptoms.

Refractive Outcomes in Fuchs' Endothelial Corneal Dystrophy: Conventional and Femtosecond Laser-Assisted Cataract Surgery

Purpose

To investigate the refractive outcomes of eyes with Fuchs’ endothelial corneal dystrophy (FECD) following phacoemulsification.

Methods

This is a retrospective chart review of patients with FECD who underwent phacoemulsification. Manifest refraction at the early postoperative period (1–6 weeks) and late postoperative period (3–12 months) was collected. The spherical equivalent (SE) and variance of SE from target in diopters (D) were analyzed.

Results

A total of 219 eyes from 175 FECD patients (73 FLACS, 146 conventional phacoemulsification) were included. In the early postoperative period, when comparing variance from intended target, 62% (n=126) had a SE variance of ≤0.5 D, 22% (n=44) >0.5 D and ≤1 D, and 17% (n=34) >1 D. In the late postoperative period, 62% (n=85) had a SE variance of ≤0.5 D, 19% (n=26) >0.5 D and ≤1 D, and 20% (n=27) >1 D. There was no difference in the variance of SE comparing FLACS versus conventional phacoemulsification in either the early postoperative period (p=0.78) or the late postoperative period (p=0.29).

Conclusion

Patients with mild-to-moderate FECD had favorable refractive outcomes with phacoemulsification. There was no difference in refractive outcomes in eyes with FECD between the group that underwent FLACS versus the group that underwent conventional phacoemulsification.

Femtosecond Laser-Assisted Cataract Surgery: Does It Improve Outcomes in Fuchs Endothelial Corneal Dystrophy?

The role of femtosecond laser -assisted cataract surgery in patients with Fuchs endothelial corneal dystrophy remains poorly defined. This invited commentary examines the current evidence surrounding this often-debated topic.

Preloading Trifolded Grafts for Descemet Membrane Endothelial Keratoplasty Affects Scroll Formation

PURPOSE

The trifolded, endothelium-in approach to Descemet membrane endothelial keratoplasty (DMEK) facilitates tissue insertion into the anterior chamber. We hypothesized that preloading the trifolded donor grafts in a cartridge for 48 hours before insertion would induce biomechanical changes that decrease their scrolling tendency compared with those loaded immediately before insertion.

METHODS

Ten Descemet membrane donor grafts, peeled and cut to 8.0 mm, were prepared by a single eye bank technician. Each graft was trifolded and pulled into a DMEK cartridge and stored for 48 hours. They were then pulled with microforceps into a petri dish filled with balanced salt solution. A video was recorded of the graft becoming a scroll over a 2-minute period. Each graft, serving as its own control, was then trifolded, pulled into the cartridge, and the process repeated. Images from 1, 5, 10, 60, and 120 seconds were extracted from video recording of the procedures. Scroll width was analyzed by graders masked to group assignment. A paired t test was used to determine differences in scroll width at each time point between the 48-hour and instant trifolding conditions.

RESULTS

All grafts scrolled after removal from the cartridge into balanced salt solution. We measured a significant difference at all time points 1 through 120 seconds (4.02 preloaded vs. 2.91-mm instant trifold, P = 0.035).

CONCLUSIONS

Preloading DMEK grafts in a trifolded configuration for 48 hours reduces the scrolling tendency of Descemet membrane for at least 2 minutes.

A modified surgical technique for Descemet's stripping automated endothelial keratoplasty (DSAEK) in altered or abnormal anatomy

Purpose

This paper describes a modified technique for the Descemet's Stripping Automated Endothelial Keratopasty (DSAEK) surgery in eyes with abnormal or altered anatomy. Certain anatomic abnormalities increase the level of surgical complexity, and lead to increased risk of donor lenticule detachment. These challenges include aniridia, abnormal iris, aphakia and hypotony from previous vitrectomy.

Observations

The Sheets glide was trimmed to 4mm in width and inserted into the clear-corneal wound. The “needle-push”/Fichman glide technique was used to insert the DSAEK donor graft. The modification of the technique involves maintaining the Sheets glide in the eye for the duration of the intraoperative air bubble. After confirming desired orientation of the graft, air was injected into the anterior chamber, creating a large air bubble between the graft and the Sheets glide. After 10 minutes, the Sheets glide was removed, and the main wound was closed.

Conclusions and Importance

This technique overcomes the challenges of posterior air bubble migration and posterior dislocation of the donor lenticule in eyes with altered anatomy.

Graft-size selection and anisometropia reduction in penetrating keratoplasty (PKP)

PURPOSE

To compare the amount of myopia induced by same-size donor-to-host penetrating keratoplasty with that of the amount of myopia induced by over-sized donor-to-host penetrating keratoplasty.

SETTING

Tertiary referral academic center.

DESIGN

Retrospective cohort study.

METHODS

Charts from patients who underwent penetrating keratoplasty by the same technique at Bascom Palmer Eye Institute between Nov 1, 2002, and January 1, 2006, were reviewed. The patients underwent optical penetrating keratoplasty using 12 interrupted 10-0 nylon sutures and a 12-bite continuous 10-0 nylon suture by a single surgeon (R.K.F.). The surgical technique used would be considered standard of care at most institutions. The Institutional Review Board, University of Miami Human Subjects Research Office, approved the study protocol. The donor graft was over-sized by 0.25mm in eyes when the intended final refractive target was greater than -1.00 diopters spherical equivalent (SE). The same-size donor graft was used when the intended final refractive target was less than -1.00 diopters SE. The selection of donor graft size was entirely based upon clinical parameters, meaning that the intended final refractive target was determined per each patient's fellow eye refraction, with the intention of reducing anisometropia. All patients received postoperative refraction and corneal topography. These measurements were performed at 6-8 weeks when the initial removal of sutures commenced, then at 6 months, then after completion of selective suture removal, then again at 12 months.

RESULTS

At 12 months, the over-sized group resulted in -1.35 diopters (SD = 2.25) SE of refraction, and the same-size group resulted in -0.14 diopters (SD = 2.42) SE. This approached statistical significance (p = 0.052) in comparison to -1.00 diopters spherical equivalent.

CONCLUSIONS

Using a donor graft that is over-sized by 0.25mm results in refraction of -1.00 diopters SE or more of myopia. Using a same-size donor-graft results in refraction of less than -1.00 diopters SE. Therefore, careful graft-size selection can result in a more favorable clinical outcome-namely, reduction in anisometropia-in patients undergoing penetrating keratoplasty.

Outcomes of conventional phacoemulsification versus femtosecond laser-assisted cataract surgery in eyes with Fuchs endothelial corneal dystrophy

PURPOSE

To compare the outcomes in eyes with Fuchs endothelial corneal dystrophy after standard phacoemulsification with those of femtosecond laser-assisted cataract surgery.

SETTING

Bascom Palmer Eye Institute, Miami, Florida, USA.

DESIGN

Retrospective case series.

METHODS

Charts from patients diagnosed with Fuchs endothelial corneal dystrophy who had phacoemulsification cataract surgery at Bascom Palmer Eye Institute between January 1, 2014, and January 1, 2017, were reviewed. The Institutional Review Board, University of Miami Human Subjects Research Office, approved the study protocol. Complicated surgeries and cases with concurrent keratoplasty, previous keratoplasty or glaucoma surgery, or a follow-up shorter than 3 months were excluded. The corrected distance visual acuity (CDVA), central corneal thickness (CCT), and corneal edema at each visit were analyzed. Clinically significant corneal decompensation was defined by corneal edema with CDVA worse than 20/50 lasting more than 3 months, any case resulting in keratoplasty, or both.

RESULTS

The study comprised 207 eyes of 207 patients (64 femtosecond laser-assisted cataract surgery, 143 conventional phacoemulsification). Demographics, baseline guttata and cataract grades, and follow-up time (mean 30 months) were similar between groups (P > .05). The proportion of cases progressing to clinically significant decompensation (13%) was similar between groups (P > .05). Univariate Cox survival analysis also found no difference (hazard ratio, 1.0; 95% confidence interval, 0.4-2.7; P = .96).

CONCLUSIONS

Compared with conventional phacoemulsification, femtosecond laser-assisted cataract surgery did not lower the rate of corneal decompensation in eyes with mild to moderate Fuchs endothelial corneal dystrophy.

Effects of temperature and fluid media on the scroll width size of the Descemet's membrane endothelial keratoplasty (DMEK) donor graft

Aim

Our study was conducted to evaluate whether higher temperature leads to increased – or wider – scroll widths of the Descemet’s membrane endothelial keratoplasty (DMEK) donor graft.

Purpose

To investigate the effects of temperature and fluid media on the DMEK donor graft scroll widths.

Materials and methods

This research work was a laboratory investigation. Baseline cell count was taken via specular microscopy for the donor corneas at room temperature (20°C–25°C). The endothelium sides of the donor corneas were stained with Trypan Blue Solution 0.4% for 30 s, and the Descemet’s membranes were stripped. The DMEK donor grafts were placed into three different fluid media – Optisol^®, Balanced Salt Solution (BSS), and BSS PLUS^® (BSS Plus). The DMEK donor grafts were then transferred into cold temperature (4°C) for 60 min, after which the donor grafts’ scroll widths were examined and measured. The donor grafts were then warmed in the incubator and brought to physiological temperature (35°C–37°C), and their scroll widths were examined and measured again.

Results

In 30 measurements of ten tissues across three temperature and fluid conditions, the average scroll width measured 1.73 mm, ranging from 1.1 to 2.9 mm. In a mixed linear model, the scroll widths increased with temperature (P=0.02). There was no significant difference in scroll widths among the three solutions (P=0.84, mixed linear model).

Conclusion

We observed an increase in DMEK donor graft scroll widths with higher temperatures. The usage of BSS Plus as media solution could also lead to smaller DMEK donor graft scroll widths, compared with BSS, but our study does not establish this.

Dimerization leads to changes in APP (amyloid precursor protein) trafficking mediated by LRP1 and SorLA

Proteolytic cleavage of the amyloid precursor protein (APP) by α-, β- and γ-secretases is a determining factor in Alzheimer's disease (AD). Imbalances in the activity of all three enzymes can result in alterations towards pathogenic Aβ production. Proteolysis of APP is strongly linked to its subcellular localization as the secretases involved are distributed in different cellular compartments. APP has been shown to dimerize in cis-orientation, affecting Aβ production. This might be explained by different substrate properties defined by the APP oligomerization state or alternatively by altered APP monomer/dimer localization. We investigated the latter hypothesis using two different APP dimerization systems in HeLa cells. Dimerization caused a decreased localization of APP to the Golgi and at the plasma membrane, whereas the levels in the ER and in endosomes were increased. Furthermore, we observed via live cell imaging and biochemical analyses that APP dimerization affects its interaction with LRP1 and SorLA, suggesting that APP dimerization modulates its interplay with sorting molecules and in turn its localization and processing. Thus, pharmacological approaches targeting APP oligomerization properties might open novel strategies for treatment of AD.

Cataracts induced by neodymium-yttrium-aluminium-garnet laser lysis of vitreous floaters

BACKGROUND

Neodymium-yttrium-aluminium-garnet (Nd:YAG) laser vitreolysis has been proposed as a treatment modality for symptomatic vitreous floaters. The purpose of this paper is to report two cases of cataracts associated with posterior capsular compromise, induced by Nd:YAG laser vitreolysis for symptomatic vitreous floaters.

METHOD

Case series.

RESULTS

Two patients who underwent ND:YAG laser vitreolysis for symptomatic floaters, presented with decline in visual acuity in the treated eye after the laser procedure. At the slit-lamp biomicroscope, each patient was found to have a posterior subcapsular cataract in the treated eye, with obvious loss of integrity of the posterior capsule. These two patients underwent cataract extraction by the same surgeon via phacoemulsification. Both eyes were found to have a defect in the posterior capsule intraoperatively. In both cases, a three-piece acrylic intraocular lens implant was placed in the sulcus, achieving optic capture. The best-corrected visual acuity (BCVA) was 20/20 in both patients, at 1 month following the surgery. At 2 months, one patient had a BCVA of 20/15. The second patient maintained a BCVA of 20/20 at 3 months.

CONCLUSIONS

Secondary cataract formation accompanied by loss of integrity of the posterior capsule is a potential complication of Nd:YAG laser vitreolysis for symptomatic floaters.

Amiodarone Offsets the Cardioprotective Effects of Ischaemic Preconditioning against Ischaemia/Reperfusion Injury

Both ischaemic preconditioning (IPC) and amiodarone protect against myocardial ischaemia. We examined whether a combination of IPC and amiodarone demonstrated an additive protective effect in isolated rat hearts ( n = 40). The controls (group I) were subjected to ischaemia/reperfusion injury; group II was subjected to cycles of IPC prior to ischaemia/reperfusion injury; group III was subjected to ischaemia in the presence of amiodarone (10−10 mol/l); and group IV was subjected to IPC followed by ischaemia in the presence of amiodarone (10−10 mol/l). Amiodarone produced the best preserved left ventricular end-systolic pressure and dP/dtmax, less developed ventricular stiffness, the shortest arrhythmia duration, and the smallest infarct size among the groups. All of the myocardial protective effects against ischaemia/reperfusion injury were diminished or abolished when IPC and amiodarone were applied sequentially.

A subset of NSAIDs lower amyloidogenic Abeta42 independently of cyclooxygenase activity

Epidemiological studies have documented a reduced prevalence of Alzheimer's disease among users of nonsteroidal anti-inflammatory drugs (NSAIDs). It has been proposed that NSAIDs exert their beneficial effects in part by reducing neurotoxic inflammatory responses in the brain, although this mechanism has not been proved. Here we report that the NSAIDs ibuprofen, indomethacin and sulindac sulphide preferentially decrease the highly amyloidogenic Abeta42 peptide (the 42-residue isoform of the amyloid-beta peptide) produced from a variety of cultured cells by as much as 80%. This effect was not seen in all NSAIDs and seems not to be mediated by inhibition of cyclooxygenase (COX) activity, the principal pharmacological target of NSAIDs. Furthermore, short-term administration of ibuprofen to mice that produce mutant beta-amyloid precursor protein (APP) lowered their brain levels of Abeta42. In cultured cells, the decrease in Abeta42 secretion was accompanied by an increase in the Abeta(1-38) isoform, indicating that NSAIDs subtly alter gamma-secretase activity without significantly perturbing other APP processing pathways or Notch cleavage. Our findings suggest that NSAIDs directly affect amyloid pathology in the brain by reducing Abeta42 peptide levels independently of COX activity and that this Abeta42-lowering activity could be optimized to selectively target the pathogenic Abeta42 species.

Microarray analysis of gene expression in human donor corneas

OBJECTIVES

To use microarray analysis to identify genes expressed in human donor corneas and to create a preliminary, comprehensive database of human corneal gene expression.

METHODS

A complementary DNA (cDNA) library was constructed from transplant-quality, human donor corneas. Biotin-labeled RNA was transcribed from the cDNA library and hybridized in duplicate to microarrays containing approximately 5600 human genes. Results were analyzed using a gene database of the National Institutes of Health, Bethesda, Md. Reverse transcriptase polymerase chain reaction analysis was performed to confirm corneal expression of genes identified by microarray analysis.

RESULTS

Duplicate microarrays identified the expression of 1200 genes in human donor corneas. Chromosomal loci had been assigned to 1025 (85%) of these genes. A preliminary database of human corneal gene expression was compiled. A Web site containing these genes was created. Six collagen genes were identified that had not previously been localized within the cornea. Five apoptosis-related genes were identified, 4 of which had not previously been localized within the cornea. Three genes previously shown to cause corneal diseases were identified. Reverse transcriptase polymerase chain reaction analysis of genes identified by microarray analysis confirmed the corneal expression of 2 apoptosis-related genes and 1 collagen gene.

CONCLUSIONS

Microarray analysis of healthy human donor corneas has produced a preliminary, comprehensive database of corneal gene expression. Large-scale analysis of gene expression has the potential to generate large amounts of data, which should be made readily accessible to the scientific community. The Internet offers many potential advantages as a medium for the maintenance of these large data sets.

CLINICAL RELEVANCE

Identification of structural, apoptosis-related, and disease-causing genes within the cornea by microarrays may increase the understanding of normal and abnormal corneal function with likely relevance to corneal diseases and transplants.

Loss of presenilin 1 is associated with enhanced beta-catenin signaling and skin tumorigenesis

Presenilin 1 (PS1) is required for the proteolytic processing of Notch and the beta-amyloid precursor protein (APP), molecules that play pivotal roles in cell-fate determination during development and Alzheimer's disease pathogenesis, respectively. In addition, PS1 interacts with beta-catenin and promotes its turnover through independent mechanisms. Consistent with this activity, we report here that PS1 is important in controlling epidermal cell proliferation in vivo. PS1 knockout mice that are rescued through neuronal expression of human PS1 transgene develop spontaneous skin cancers. PS1-null keratinocytes exhibit higher cytosolic beta-catenin and beta-catenin/lymphoid enhancer factor-1/T cell factor (beta-catenin/LEF)-mediated signaling. This effect can be reversed by reintroducing wild-type PS1, but not a PS1 mutant active in Notch processing but defective in beta-catenin binding. Nuclear beta-catenin protein can be detected in tumors. Elevated beta-catenin/LEF signaling is correlated with activation of its downstream target cyclin D1 and accelerated entry from G(1) into S phase of the cell cycle. This report demonstrates a function of PS1 in adult tissues, and our analysis suggests that deregulation of beta-catenin pathway contributes to the skin tumor phenotype.

The amyloidogenic pathway of amyloid precursor protein (APP) is independent of its cleavage by caspases

Amyloid beta-protein (A beta) is the main constituent of senile plaques in Alzheimer's disease and is derived by proteolysis from the amyloid precursor protein (APP). Generation and secretion of both A beta 40 and A beta 42 isoforms depend largely on internalization of APP and occurs mainly in the endocytic pathway. Evidence has also been presented (Gervais, F. G., Xu, D., Robertson, G. S., Vaillancourt, J. P., Zhu, Y., Huang, J., LeBlanc, A., Smith, D., Rigby, M., Shearman, M. S., Clarke, E. E., Zheng, H., Van der Ploeg, L. H. T., Ruffolo, S. C., Thornberry, N. A., Xanthoudakis, S., Zamboni, R. J., Roy, S., and Nicholson, D. W. (1999) Cell, 97, 395--406) that caspase cleavage of APP at its cytosolic tail affects its processing such that it is redirected to a more amyloidogenic pathway, resulting in enhanced A beta generation. However, caspase cleavage of APP also results in loss of its endocytosis signal (YENP), an event that would predict a decline in internalization and a concomitant decrease, not an increase, in A beta generation. In the present work, we examined whether caspase cleavage of APP is relevant to amyloidogenesis. We found that 1) caspase cleavage of APP results in reduced internalization and, accordingly, a decline in A beta secretion; 2) masking of the caspase site in APP did not affect A beta levels and, 3) caspase activation in cells by serum withdrawal did not increase A beta secretion. Thus, caspase cleavage of APP is unlikely to play a direct role in amyloidogenesis.

Protein kinase C epsilon suppresses Abeta production and promotes activation of alpha-secretase

Deposition of plaques containing Abeta is considered important in the pathogenesis of Alzheimer's disease. Phorbol esters that activate protein kinase C (PKC) promote alpha-secretase-mediated processing of the beta amyloid precursor protein (APP), which generally reduces formation of Abeta. To determine which PKC isozymes mediate this process, we studied CHO cells that express human APP751. Phorbol 12-myristate, 13-acetate (PMA)-stimulated APP secretion, which was reduced by a general PKC inhibitor bisindoylmaleimide I, but not by Gö 6976, which inhibits PKCalpha, beta, gamma, and mu. Since PKCdelta and epsilon were the only other PMA-sensitive isozymes present, we studied cells that express selective peptide inhibitors of these isozymes. Expression of the PKCepsilon inhibitor inhibited PMA-induced APPs secretion and suppression of Abeta production. In contrast, the PKCdelta inhibitor had no effect. These results provide evidence that PKCepsilon decreases Abeta production by promoting alpha-secretase mediated cleavage of APP.

Modulation of amyloid beta-protein clearance and Alzheimer's disease susceptibility by the LDL receptor-related protein pathway

Susceptibility to Alzheimer's disease (AD) is governed by multiple genetic factors. Remarkably, the LDL receptor-related protein (LRP) and its ligands, apoE and alpha2M, are all genetically associated with AD. In this study, we provide evidence for the involvement of the LRP pathway in amyloid deposition through sequestration and removal of soluble amyloid beta-protein (Abeta). We demonstrate in vitro that LRP mediates the clearance of both Abeta40 and Abeta42 through a bona fide receptor-mediated uptake mechanism. In vivo, reduced LRP expression is associated with LRP genotypes and is correlated with enhanced soluble Abeta levels and amyloid deposition. Although LRP has been proposed to be a clearance pathway for Abeta, this work provides the first in vivo evidence that the LRP pathway may modulate Abeta deposition and AD susceptibility by regulating the removal of soluble Abeta.

LDL receptor-related protein (LRP) in Alzheimer's disease: towards a unified theory of pathogenesis

To date, mutations in three genes, beta-amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2), have been found to be causally related to familial Alzheimer's disease (AD). In addition, polymorphisms in three other genes (among others), apolipoprotein E (apoE), alpha2-macroglobulin (alpham), and the low density lipoprotein receptor-related protein (LRP), are implicated to contribute to AD pathogenesis. Interestingly, the encoded gene products are all functionally related in various ways to LRP. Specifically apoE, alpha2m, secreted APP, and amyloid beta-protein (Abeta) complexed to either apoE or alpha2m are ligands of LRP. Furthermore, over-expression of presenilin 1 results in decreased expression of LRP. Since levels of many LRP ligands are increased in Alzheimer's disease and LRP and its ligands are present in senile plaques, decreased LRP function may be a central component in AD pathogenesis. This review explores the current knowledge of LRP in AD and its relationship to the other known AD susceptibility markers.

The nonconserved hydrophilic loop domain of presenilin (PS) is not required for PS endoproteolysis or enhanced abeta 42 production mediated by familial early onset Alzheimer's disease-linked PS variants

Presenilin 1 (PS1) and presenilin 2 (PS2) are polytopic membrane proteins that are mutated in the majority of early onset familial Alzheimer's disease (FAD) cases. Two lines of evidence establish a critical role for PS in the production of beta-amyloid peptides (Abeta). FAD-linked PS mutations elevate the levels of highly amyloidogenic Abeta ending at residue 42 (Abeta42), and cells with ablated PS1 alleles secrete low levels of Abeta. Several recent reports have shown that the hydrophilic loop (HL) domain, located between transmembrane domains 6 and 7, contains sites for phosphorylation, caspase cleavage, and sequences that bind several PS-interacting proteins. In the present report, we examined the metabolism of PS polypeptides lacking the HL domain and the influence of these molecules on Abeta production. We report that the deletion of the HL domain does not have a deleterious effect on the regulated endoproteolysis of PS, saturable accumulation of PS fragments, or the self-association of PS fragments. Abeta production was not significantly altered in cells expressing HL-deleted PS polypeptides compared with cells expressing full-length PS. Importantly, deletion of the HL domain did not affect FAD mutation-mediated elevation in the production of Abeta42. Furthermore, the deletion of the HL domain did not impair the role of PS1 or PS2 in facilitating Notch processing. Thus, our results argue against a biologically or pathologically relevant role for the HL domain phosphorylation and caspase cleavage and the association of PS HL domain-interacting proteins, in amyloid precursor protein metabolism and Abeta production or Notch cleavage.

A second cytotoxic proteolytic peptide derived from amyloid beta-protein precursor

The amyloid beta-protein precursor gives rise to the amyloid beta-protein, the principal constituent of senile plaques and a cytotoxic fragment involved in the pathogenesis of Alzheimer disease. Here we show that amyloid beta-protein precursor was proteolytically cleaved by caspases in the C terminus to generate a second unrelated peptide, called C31. The resultant C31 peptide was a potent inducer of apoptosis. Both caspase-cleaved amyloid beta-protein precursor and activated caspase-9 were present in brains of Alzheimer disease patients but not in control brains. These findings indicate the possibility that caspase cleavage of amyloid beta-protein precursor with the generation of C31 may be involved in the neuronal death associated with Alzheimer disease.

Amyloid-beta peptides interact with plasma proteins and erythrocytes: implications for their quantitation in plasma

Amyloid beta peptides are bound rapidly in the plasma complicating an accurate assessment of their in vivo abundance by immunoassay procedures. The extent of Abeta immunoassay interference was used to estimate the Abeta binding capacity of purified plasma proteins, erythrocytes and whole plasma. Human serum albumin bound Abeta peptides rapidly with a 1:1 stoichiometry and at physiological concentrations was capable of binding over 95% of an input of 5 ng/ml Abeta. Purified alpha2-macroglobulin was able to bind Abeta peptides and at physiological concentration bound 73% of 5 ng/ml of Abeta. Erythrocytes also sequestered the Abeta peptides, showing a preference for binding Abeta 1-42. Incubation of 5 ng/ml of Abeta in plasma revealed that about 30% of the peptides were still detectable by immunoassay, presumably reflecting the binding of Abeta peptides with albumin and other plasma molecules. Thus, our studies reveal that both the soluble and formed elements of the blood are capable of sequestering Abeta peptides. To avoid underestimating plasma Abeta values, we employed an improved column chromatography method under denaturing conditions to liberate Abeta from its associations with plasma proteins. Quantification of Abeta 40 and 42 levels in plasma from both normal and AD individuals after chromatography showed a large overlap between AD and control groups, despite the very large pool of Abeta present in the AD brains. The potential origins of the plasma Abeta pool are discussed.

Expression of beta-amyloid precursor protein-CD3gamma chimeras to demonstrate the selective generation of amyloid beta(1-40) and amyloid beta(1-42) peptides within secretory and endocytic compartments

Amyloid beta-protein (Abeta) is the main constituent of amyloid fibrils found in senile plaques and cerebral vessels in Alzheimer's disease (AD) and is derived by proteolysis from the beta-amyloid precursor protein (APP). We have analyzed the amyloidogenic processing of APP using chimeric proteins stably transfected in Chinese hamster ovary cells. The extracellular and transmembrane domains of APP were fused to the cytoplasmic region derived from the CD3 gamma chain of the T cell antigen receptor (CD3gamma). CD3gamma contains an endoplasmic reticulum (ER) retention motif (RKK), in the absence of which the protein is targeted to lysosomes without going through the cell surface (Letourneur, F., and Klausner, R.D. (1992) Cell 69, 1143-1157). We used the wild-type sequence of CD3gamma to create an APP chimera predicted to remain in the ER (gammaAPP(ER)). Deletion of the RKK motif at the C terminus directed the protein directly to the lysosomes (gammaAPP(LYS)). A third chimera was created by removing both lysosomal targeting signals in addition to RKK (gammaAPP(DeltaDelta)). This last construct does not contain known targeting signals and consequently accumulates at the cell surface. We show by immunofluorescence and by biochemical methods that all three APP chimeras localize to the predicted compartments within the cell, thus providing a useful model to study the processing of APP. We found that Abeta(1-40) is generated in the early secretory and endocytic pathways, whereas Abeta(1-42) is made mainly in the secretory pathway. More importantly, we provide evidence that, unlike in neuronal models, both ER/intermediate compartment- and endocytic-derived Abeta forms can enter the secretable pool. Finally, we directly demonstrate that lysosomal processing is not involved in the generation or secretion of either Abeta(1-40) or Abeta(1-42).

Mutagenesis identifies new signals for beta-amyloid precursor protein endocytosis, turnover, and the generation of secreted fragments, including Abeta42

It has long been assumed that the C-terminal motif, NPXY, is the internalization signal for beta-amyloid precursor protein (APP) and that the NPXY tyrosine (Tyr743 by APP751 numbering, Tyr682 in APP695) is required for APP endocytosis. To evaluate this tenet and to identify the specific amino acids subserving APP endocytosis, we mutated all tyrosines in the APP cytoplasmic domain and amino acids within the sequence GYENPTY (amino acids 737-743). Stable cell lines expressing these mutations were assessed for APP endocytosis, secretion, and turnover. Normal APP endocytosis was observed for cells expressing Y709A, G737A, and Y743A mutations. However, Y738A, N740A, and P741A or the double mutation of Y738A/P741A significantly impaired APP internalization to a level similar to that observed for cells lacking nearly the entire APP cytoplasmic domain (DeltaC), arguing that the dominant signal for APP endocytosis is the tetrapeptide YENP. Although not an APP internalization signal, Tyr743 regulates rapid APP turnover because half-life increased by 50% with the Y743A mutation alone. Secretion of the APP-derived proteolytic fragment, Abeta, was tightly correlated with APP internalization, such that Abeta secretion was unchanged for cells having normal APP endocytosis but significantly decreased for endocytosis-deficient cell lines. Remarkably, secretion of the Abeta42 isoform was also reduced in parallel with endocytosis from internalization-deficient cell lines, suggesting an important role for APP endocytosis in the secretion of this highly pathogenic Abeta species.

Presenilin 1 facilitates the constitutive turnover of beta-catenin: differential activity of Alzheimer's disease-linked PS1 mutants in the beta-catenin-signaling pathway

Although an association between the product of the familial Alzheimer's disease (FAD) gene, presenilin 1 (PS1), and beta-catenin has been reported recently, the cellular consequences of this interaction are unknown. Here, we show that both the full length and the C-terminal fragment of wild-type or FAD mutant PS1 interact with beta-catenin from transfected cells and brains of transgenic mice, whereas E-cadherin and adenomatous polyposis coli (APC) are not detected in this complex. Inducible overexpression of PS1 led to increased association of beta-catenin with glycogen synthase kinase-3beta (GSK-3beta), a negative regulator of beta-catenin, and accelerated the turnover of endogenous beta-catenin. In support of this finding, the beta-catenin half-life was dramatically longer in fibroblasts deficient in PS1, and this phenotype was completely rescued by replacement of PS1, demonstrating that PS1 normally stimulates the degradation of beta-catenin. In contrast, overexpression of FAD-linked PS1 mutants (M146L and DeltaX9) failed to enhance the association between GSK-3beta and beta-catenin and interfered with the constitutive turnover of beta-catenin. In vivo confirmation was demonstrated in the brains of transgenic mice in which the expression of the M146L mutant PS1 was correlated with increased steady-state levels of endogenous beta-catenin. Thus, our results indicate that PS1 normally promotes the turnover of beta-catenin, whereas PS1 mutants partially interfere with this process, possibly by failing to recruit GSK-3beta into the PS1-beta-catenin complex. These findings raise the intriguing possibility that PS1-beta-catenin interactions and subsequent activities may be consequential for the pathogenesis of AD.

Recombinant adenovirus is an appropriate vector for endocytotic protein trafficking studies in cultured neurons

Endocytosis of full-length beta-amyloid precursor protein (APP) from the plasma membrane contributes to beta-amyloid peptide (Abeta) secretion, and, hence, potentially contributes to the molecular pathogenesis of Alzheimer's disease. We recently have demonstrated that central neuronal APP is endocytosed in a common vesicular compartment with recycling synaptic vesicle integral membrane proteins, but is then sorted away from synaptic vesicles for retrograde transport to the neuronal soma. For this report, we explore whether recombinant adenovirus can be used to modulate APP expression in cultured central neurons to study APP processing by the endocytotic pathway in these cells. Using a replication-deficient recombinant adenovirus that expresses a lacZ reporter (Ad5/CMV-lacZ), we demonstrate high efficiency of transfection (30-35%) at low viral titer (10-20 MOI), with no significant neuronal toxicity or cytoarchitectural change. In addition, we demonstrate that infection with the control virus does not result in re-direction of endogenous neuronal APP from usual endocytotic pathways. We have prepared, using the same genomic background as the control virus, an adenoviral vector that expresses the neuronal isoform of human APP (Ad5/CMV-APP). Infection with Ad5/CMV-APP at 10-20 MOI results in significantly increased immunoreactivity for endocytosed APP with preservation of usual endocytotic trafficking. These results demonstrate that recombinant adenovirus at low titer is an appropriate and effective vector for protein trafficking/processing studies in cultured central neurons.

Contrasting role of presenilin-1 and presenilin-2 in neuronal differentiation in vitro

Presenilin-1 (PS1) and presenilin-2 (PS2), the major genes of familial Alzheimer's disease, are homologous to sel-12, a Caenorhabditis elegans gene involved in cell fate decision during development. Recently, wild-type and mutant presenilins have been associated also with apoptotic cell death. By using stable transfection of antisense cDNAs, we studied the functions of PS1 and PS2 during neuronal differentiation in the NTera2 human teratocarcinoma (NT2) cell line. Expression of antisense PS1 resulted in a failure of the clones to differentiate into neurons after retinoic acid induction, whereas cells transfected with antisense PS2 differentiated normally. Concomitantly, antisense PS1 clones were associated with increased apoptosis both under basal conditions and during the early period of neuronal differentiation after retinoic acid treatment. Overexpression of bcl-2 in antisense PS1 clones reduced cell death and resulted in a recovery of neuronal differentiation. These studies suggest that PS1 plays a role in differentiation and cell death and that PS1 and PS2 have differing physiological roles in this experimental paradigm.

Presenilin 1 regulates the processing of beta-amyloid precursor protein C-terminal fragments and the generation of amyloid beta-protein in endoplasmic reticulum and Golgi

Progressive cerebral deposition of the amyloid beta-protein (Abeta) is believed to play a pivotal role in the pathogenesis of Alzheimer's disease (AD). The highly amyloidogenic 42-residue form of Abeta (Abeta42) is the first species to be deposited in both sporadic and familial AD. Mutations in two familial AD-linked genes, presenilins 1 (PS1) and 2 (PS2), selectively increase the production of Abeta42 in cultured cells and the brains of transgenic mice, and gene deletion of PS1 shows that it is required for normal gamma-secretase cleavage of the beta-amyloid precursor protein (APP) to generate Abeta. To establish the subcellular localization of the PS1 regulation of APP processing to Abeta, fibroblasts from PS1 wild-type (wt) or knockout (KO) embryos as well as Chinese hamster ovary (CHO) cells stably transfected with wt or mutant PS1 were subjected to subcellular fractionation on discontinuous Iodixanol gradients. APP C-terminal fragments (CTF) were markedly increased in both endoplasmic reticulum- (ER-) and Golgi-rich fractions of fibroblasts from KO mice; moreover, similar increases were documented directly in KO brain tissue. No change in the subcellular distribution of full-length APP was detectable in fibroblasts lacking PS1. In CHO cells, a small portion of APP, principally the N-glycosylated isoform, formed complexes with PS1 in both ER- and Golgi-rich fractions, as detected by coimmunoprecipitation. When the same fractions were analyzed by enzyme-linked immunosorbent assays for Abetatotal and Abeta42, Abeta42 was the major Abeta species in the ER fraction (Abeta42:Abetatotal ratio 0.5-1.0), whereas absolute levels of both Abeta42 and Abeta40 were higher in the Golgi fraction and the Abeta42:Abetatoal ratio was 0.05-0.16 there. Mutant PS1 significantly increased Abeta42 levels in the Golgi fraction. Our results indicate PS1 and APP can interact in the ER and Golgi, where PS1 is required for proper gamma-secretase processing of APP CTFs, and that PS1 mutations augment Abeta42 levels principally in Golgi-like vesicles.

Subcellular distribution and turnover of presenilins in transfected cells

The mechanisms by which mutations in presenilin-1 (PS1) and presenilin-2 (PS2) result in the Alzheimer's disease phenotype are unclear. Full-length PS1 and PS2 are each processed into stable proteolytic fragments after their biosynthesis in transfected cells. PS1 and PS2 have been localized by immunocytochemistry to the endoplasmic reticulum (ER) and Golgi compartments, but previous studies could not differentiate between the full-length presenilin proteins and their fragments. We carried out subcellular fractionation of cells stably transfected with PS1 or PS2 to determine the localization of full-length presenilins and their fragments. Full-length PS1 and PS2 were principally distributed in ER fractions, whereas the N- and C-terminal fragments were localized predominantly to the Golgi fractions. In cells expressing the PS1 mutant lacking exon 9 (DeltaE9), we observed only full-length molecules that were present in the ER and Golgi fractions. The turnover rate was considerably slower for the DeltaE9 holoprotein, apparently due to decreased degradation within the ER. Our results suggest that that full-length presenilin proteins are primarily ER resident molecules and undergo endoproteolysis within the ER. The fragments are subsequently transported to the Golgi compartment, where their turnover rate is much slower than that of the full-length presenilin in the ER.

The beta-amyloid precursor protein of Alzheimer's disease enhances neuron viability and modulates neuronal polarity

beta-Amyloid precursor protein (betaPP) can reside at neuron and glial cell surfaces or undergo proteolytic processing into secreted fragments. Although betaPP has been studied extensively, its precise physiological role is unknown. A line of transgenic knock-out mice selectively deficient in betaPP survive and breed but exhibit motor dysfunction and brain gliosis, consistent with a physiological role for betaPP in neuron development. To elucidate these functions, we cultured hippocampal neurons from wild-type and betaPP-deficient mice and compared their ability to attach, survive, and develop neurites. We found that hippocampal neurons from betaPP-deficient mice had diminished viability and retarded neurite development. We also compared the effects of betaPP secretory products, released from wild-type astrocytes, on process outgrowth from wild-type and betaPP-deficient hippocampal neurons. Outgrowth was enhanced at 1 d in the presence of wild-type astrocytes, as compared with betaPP-deficient astrocytes. However, by 3 d, neurons had shorter axons but more minor processes with more branching when cocultured with wild-type astrocytes, as compared with betaPP-deficient astrocytes. Our data demonstrate that cell-associated neuronal betaPP contributes to neuron viability, axonogenesis, and arborization and that betaPP secretory products modulate axon growth, dendrite branching, and dendrite numbers.

Characterization of amyloid beta protein species in cerebral amyloid angiopathy of a squirrel monkey by immunocytochemistry and enzyme-linked immunosorbent assay

We analyzed the composition of amyloid beta protein (A beta) species in cerebral amyloid angiopathy (CAA) of an aged squirrel monkey. Immunocytochemistry demonstrated that the cerebral cortex contained no lesions other than widespread CAA with A beta40 as its apparent major component. However, enzyme-linked immunosorbent assay revealed that A beta42(43) predominated over A beta40 in a formic acid-extracted cortical fraction. These findings suggest possible underestimation of A beta42(43) levels in some previous immunocytochemical investigations.

Interaction between amyloid precursor protein and presenilins in mammalian cells: implications for the pathogenesis of Alzheimer disease

Mutations in the presenilin 1 (PS1) and presenilin 2 (PS2) genes increase the production of the highly amyloidogenic 42-residue form of amyloid beta-protein (Abeta42) in a variety of cell lines and transgenic mice. To elucidate the molecular mechanism of this effect, wild-type (wt) or mutant PS1 and PS2 genes were stably transfected into Chinese hamster ovary cells expressing endogenous or transfected beta-amyloid precursor protein (APP). By immunoprecipitation/Western blot analysis, APP was consistently found to coimmunoprecipitate with PS1 or PS2 proteins. Several distinct PS1, PS2, or APP antibodies precipitated PS-APP complexes that were detectable by blotting with either APP or PS antibodies. Importantly, complex formation could be detected at endogenous protein levels in nontransfected cells. In various Chinese hamster ovary cell lines, the amounts of APP coprecipitated by PS antibodies were proportional to the expression levels of both APP and PS. APP-PS complexes also were recovered from human 293 and HS683 cells. Full maturation of APP was not required for the interaction; most APP molecules complexed with PS were solely N-glycosylated. Treatment of cells with brefeldin A or incubation at 20 degrees C did not block complex formation, suggesting that the association between APP and PS occurs in part in the endoplasmic reticulum. Complex formation was detected for both wt and mutant PS and APP proteins. Deletion of the APP C-terminal domain did not abrogate complex formation, suggesting that the interaction does not occur in the cytoplasmic domains of the proteins. Our results demonstrate that wt and mutant PS1 and PS2 proteins form complexes with APP in living cells, strongly supporting the hypothesis that mutant PS interacts with APP in a way that enhances the intramembranous proteolysis of the latter by a gamma-secretase cleaving at Abeta42.

Enhanced production and oligomerization of the 42-residue amyloid beta-protein by Chinese hamster ovary cells stably expressing mutant presenilins

Mutations in the presenilin 1 (PS1) and presenilin 2 (PS2) genes cause the most common and aggressive form of early onset familial Alzheimer's disease. To elucidate their pathogenic mechanism, wild-type (wt) or mutant (M146L, C410Y) PS1 and wt or mutant (M239V) PS2 genes were stably transfected into Chinese hamster ovary cells that overexpress the beta-amyloid precursor protein (APP). The identity of the 43-45-kDa PS1 holoproteins was confirmed by N-terminal radiosequencing. PS1 was rapidly processed (t1/2 = 40 min) in the endoplasmic reticulum into stable fragments. Wild-type and mutant PS2 holoproteins exhibited similar half lives (1.5 h); however, their endoproteolytic fragments showed both mutation-specific and cell type-specific differences. Mutant PS1 or PS2 consistently induced a 1.4-2.5-fold increase (p < 0.001) in the relative production of the highly amyloidogenic 42-residue form of amyloid beta-protein (Abeta42) as determined by quantitative immunoprecipitation and by enzyme-linked immunosorbent assay. In mutant PS1 and PS2 cell lines with high increases in Abeta42/Abetatotal ratios, spontaneous formation of low molecular weight oligomers of Abeta42 was observed in media, suggesting enhanced Abeta aggregation from the elevation of Abeta42. We conclude that mutant PS1 and PS2 proteins enhance the proteolysis of beta-amyloid precursor protein by the gamma-secretase cleaving at Abeta residue 42, thereby promoting amyloidogenesis.

Phorbol esters affect multiple steps in beta-amyloid precursor protein trafficking and amyloid beta-protein production

BACKGROUND

Amyloid beta-protein (A beta), the major constituent of amyloid deposits found in Alzheimer's disease, is derived from the beta-amyloid precursor protein (beta PP). Constitutive proteolysis by alpha-secretase and secretion of soluble beta PP (beta PPs) are stimulated by protein kinase C (PKC) activation, whereas A beta production and release are inhibited. The cellular mechanism that underlies the PKC-mediated down-regulation of A beta generation is unclear. Because endocytic processing of beta PP from the cell surface is a major pathway of A beta production, the effect of PKC activation by phorbol 12,13-dibutyrate (PDBu) on endocytic trafficking of beta PP was examined.

MATERIALS AND METHODS

In this study, trafficking of beta PP was assayed in Chinese hamster ovary cells (CHO) cells stably transfected with full-length beta PP751.

RESULTS

Treatment with PDBu resulted in a rapid and striking reduction of up to 80% in the amount of beta PP at the cell surface. This loss of cell-surface molecules could not be accounted for by changes in the trafficking of cell-surface beta PP molecules, as determined by a radiolabeled antibody assay. Rather, the decrease in beta PP was due primarily to a reduction in the sorting of beta PP to the cell surface. This alteration was correlated with accelerated intracellular alpha-secretase-mediated beta PP cleavage and accelerated beta PP trafficking in the exocytic pathway.

CONCLUSIONS

The data suggest that the displacement of beta PP away from the cell surface after phorbol ester treatment reduces the substrate available for endocytic processing and in turn, results in the inhibition of A beta production.

Isolation and characterization of Drosophila presenilin homolog

Presenilin-1 (PS1) and presenilin-2 (PS2) are associated with a majority of early onset familial Alzheimer's disease (FAD). Sequence analysis of PS1/2 has revealed integral transmembrane proteins which are highly homologous to the protein coded by sel-12, a Caenorhabditis elegans gene involved in the lin-12/Notch signaling pathway. The normal function of PS1/2, as well as the pathogenesis caused by mutations of these genes in FAD, are unknown however. We have identified a Drosophila presenilin homolog (DPS) and mapped the chromosomal location of this gene. DPS shows 53% amino acid identity to PS1/2 and 45% to the sel-12 product. Strong amino acid conservations appear at the position associated with FAD. In embryonic stages, DPS is expressed primarily in the CNS.

Cell surface amyloid beta-protein precursor colocalizes with beta 1 integrins at substrate contact sites in neural cells

Amyloid beta-protein (A beta), the principal constituent of the senile plaques seen in Alzheimer's disease (AD), is derived by proteolysis from the beta-amyloid precursor protein (beta PP). The distribution and trafficking of cell surface beta PP are of particular interest because some of these molecules are direct precursors of secreted A beta and because the localization of beta PP at the cell surface may be related directly to its physiological functions. Recently, we reported that, in cultured hippocampal neurons, cell surface beta PP is preferentially expressed on axons in a striking discontinuous pattern. In this study, we describe the colocalization of cell surface beta PP and integrins in primary cultured cells. In rat hippocampal neurons, cell surface beta PP was colocalized selectively with alpha 1 beta 1 and alpha 5 beta 1 integrin heterodimers at these characteristic segmental locations. In rat cortical astrocytes, both cell surface beta PP and beta 1 integrin were located at the cell periphery in the "spreading" stage shortly after plating. In "flattened" astrocytes cultured for several days, beta PP was found in punctate deposits called point contacts. In these sites, beta PP was colocalized with alpha 1 beta 1, but not with alpha 5 beta 1 integrin heterodimers, the latter of which were situated at focal contact sites. In both neurons and astrocytes examined after shearing, clathrin and alpha-adaptin were colocalized with beta PP on the surface that directly contacts the substratum. These results are consistent with the putative role of beta PP in cell adhesion and suggests that beta PP either interacts with selected integrins or shares similar cellular machinery to promote cell adhesion.

Trafficking of cell-surface beta-amyloid precursor protein: evidence that a sorting intermediate participates in synaptic vesicle recycling

We recently demonstrated that the Alzheimer's beta-amyloid precursor protein (APP) is internalized from the axonal cell surface. In this study, we use biochemical and cell biological methods to characterize endocytotic compartments that participate in trafficking of APP in central neurons. APP is present in presynaptic clathrin-coated vesicles purified from bovine brain, together with the recycling synaptic vesicle integral membrane proteins synaptophysin, synaptotagmin, and SV2. In contrast, APP is largely excluded from synaptic vesicles purified from rat brain. In primary cerebellar macroneurons, cell-surface APP is internalized with recycling synaptic vesicle integral membrane proteins but is subsequently sorted away from synaptic vesicles and transported retrogradely to the neuronal soma. Internalized APP partially co-localizes with rab5a-containing compartments in axons and with V-ATPase-containing compartments in both axons and neuronal soma. These results provide direct biochemical evidence that an obligate sorting compartment participates in the regeneration of synaptic vesicles during exo/endocytotic recycling at nerve terminals but do not preclude concurrent "kiss-and-run" recycling. Moreover, APP is now, to our knowledge, the first demonstrated example of an axonal cell-surface protein that is internalized with recycling synaptic vesicle membrane proteins but is subsequently sorted away from synaptic vesicles.