Controversies and Future Directions of Ocular Biomarkers in Alzheimer Disease

Disentangling the neurological basis of chronic ocular pain using clinical, self-report, and brain imaging data: use of K-means clustering to explore patient phenotypes

Introduction

The factors that mediate the expression of ocular pain and the mechanisms that promote chronic ocular pain symptoms are poorly understood. Central nervous system involvement has been postulated based on observations of pain out of proportion to nociceptive stimuli in some individuals. This investigation focused on understanding functional connectivity between brain regions implicated in chronic pain in persons reporting ocular pain symptoms.

Methods

We recruited a total of 53 persons divided into two cohorts: persons who reported no ocular pain, and persons who reported chronic ocular pain, irrespective of ocular surface findings. We performed a resting state fMRI investigation that was focused on subcortical brain structures including the trigeminal nucleus and performed a brief battery of ophthalmological examinations.

Results

Persons in the pain cohort reported higher levels of pain symptoms relating to neuropathic pain and ocular surface disease, as well as more abnormal tear metrics (stability and tear production). Functional connectivity analysis between groups evinced multiple connections exemplifying both increases and decreases in connectivity including regions such as the trigeminal nucleus, amygdala, and sub-regions of the thalamus. Exploratory analysis of the pain cohort integrating clinical and brain function metrics highlighted subpopulations that showed unique phenotypes providing insight into pain mechanisms.

Discussion

Study findings support centralized involvement in those reporting ocular-based pain and allude to mechanisms through which pain treatment services may be directed in future research.

Topologically convergent and divergent large scale complex networks among Alzheimer's disease spectrum patients: A systematic review

Alzheimer's disease (AD) is associated with disruption at the level of a large-scale complex network. To explore the underlying mechanisms in the progression of AD, graph theory was used to quantitatively analyze the topological properties of structural and functional connections. Although an increasing number of studies have shown altered global and nodal network properties, little is known about the topologically convergent and divergent patterns between structural and functional networks among AD-spectrum patients. In this review, we summarized the topological patterns of the large-scale complex networks using multimodal neuroimaging graph theory analysis in AD spectrum patients. Convergent deficits in the connectivity characteristics were primarily in the default mode network (DMN) itself both in the structural and functional networks, while a divergent changes in the neighboring regions of the DMN were also observed between the patient groups. Together, the application of graph theory to large-scale complex brain networks provides quantitative insights into topological principles of brain network organization, which may lead to increasing attention in identifying the underlying neuroimaging pathological changes and predicting the progression of AD.

Investigating Causality and Shared Genetic Architecture between Neurodegenerative Disorders and Inflammatory Bowel Disease

Published observational studies have revealed the connection between neurodegenerative disorders and inflammatory bowel disease (IBD), whereas the causal association remains largely unclear. Our study aims to assess the causality and identify the shared genetic architecture between neurodegenerative disorders and IBD. Two-sample Mendelian randomization analyses were performed to assess the causality between IBD and neurodegenerative disorders (amyotrophic lateral sclerosis [ALS], Alzheimer's disease [AD], Parkinson's disease [PD], and multiple sclerosis [MS]). Shared genetic loci, functional interpretation, and transcriptomic profiles were further investigated in ALS and IBD. We identified that genetic predisposition to IBD was suggestively associated with lower odds of ALS (odds ratio [OR] 0.96, 95% confidence interval [CI] 0.94 to 0.99). In contrast, IBD was not genetically associated with an increased risk of AD, PD, or MS (and vice versa). Two shared genetic loci (rs6571361 and rs7154847) were derived, and SCFD1, G2E3, and HEATR5A were further identified as novel risk genes with enriched functions related to membrane trafficking. G2E3 was differentially expressed and significantly correlated with SCFD1 in patients with ALS or IBD. Our study reveals the suggestively protective role of IBD on ALS, and does not support the causality of AD, PD, or MS on IBD (and vice versa). Our findings indicate possible shared genetic architecture and pathways between ALS and IBD. These results provide insights into the pathogenesis and therapeutics of IBD and neurodegenerative disorders.

Co-Prevalence of Alzheimer's Disease and Age-Related Macular Degeneration Established by Histopathologic Diagnosis

BACKGROUND

Previous epidemiologic studies have suggested an association between AMD and AD, and several therapeutic agents are being developed based on this principle. However, prior studies have provided conflicting results due in part to their reliance on clinical diagnoses that are not based on gold-standard histopathology.

OBJECTIVE

To use histopathologic standards for diagnosis in order to determine the co-prevalence of AD among patients with and without AMD.

METHODS

This is a cross-sectional study of 157 autopsy ocular specimens from patients with and without AMD that were greater than 75 years of age at death. Sarks staging was used to document the severity of AMD, and Braak and Braak staging was used to assess the severity of AD in corresponding brain specimens. The prevalence of AD within different severities of AMD was determined using univariable and multivariable logistic regression.

RESULTS

58% of autopsy eyes had AMD. The prevalence of AD was lower in AMD subjects (63%) compared to non-AMD subjects (73%), even when grouped by severity (all p > 0.15). The likelihood of AD was significantly less in AMD subjects, even after adjusting for age and sex in multivariable analysis (OR 0.47, p = 0.049).

CONCLUSION

Histopathologic diagnoses fail to support an increase in prevalence of AD among subjects with AMD, even when disease severity is considered.

Stem Cell Therapies in Alzheimer's Disease: Applications for Disease Modeling

Alzheimer's disease (AD) is a neurodegenerative disease with complex pathologic and biologic characteristics. Extracellular β-amyloid deposits, such as senile plaques, and intracellular aggregation of hyperphosphorylated tau, such as neurofibrillary tangles, remain the main neuropathological criteria for the diagnosis of AD. There is currently no effective treatment of the disease, and many clinical trials have failed to prove any benefits of new therapeutics. More recently, there has been increasing interest in harnessing the potential of stem cell technologies for drug discovery, disease modeling, and cell therapies, which have been used to study an array of human conditions, including AD. The recently developed and optimized induced pluripotent stem cell (iPSC) technology is a critical platform for screening anti-AD drugs and understanding mutations that modify AD. Neural stem cell (NSC) transplantation has been investigated as a new therapeutic approach to treat neurodegenerative diseases. Mesenchymal stem cells (MSCs) also exhibit considerable potential to treat neurodegenerative diseases by secreting growth factors and exosomes, attenuating neuroinflammation. This review highlights recent progress in stem cell research and the translational applications and challenges of iPSCs, NSCs, and MSCs as treatment strategies for AD. Even though these treatments are still in relative infancy, these developing stem cell technologies hold considerable promise to combat AD and other neurodegenerative disorders. SIGNIFICANCE STATEMENT: Alzheimer's disease (AD) is a neurodegenerative disease that results in learning and memory defects. Although some drugs have been approved for AD treatment, fewer than 20% of patients with AD benefit from these drugs. Therapies based on stem cells, including induced pluripotent stem cells, neural stem cells, and mesenchymal stem cells, provide promising therapeutic strategies for AD.

Retinal Optical Coherence Tomography Metrics Are Unchanged in Verubecestat Alzheimer's Disease Clinical Trial but Correlate with Baseline Regional Brain Atrophy

BACKGROUND

We performed exploratory analyses of retinal thickness data from a clinical trial of the AβPP cleaving enzyme (BACE) inhibitor verubecestat in patients with Alzheimer's disease (AD).

OBJECTIVE

To evaluate: 1) possible retinal thickness changes following BACE inhibition; and 2) possible association between retinal thickness and brain atrophy.

METHODS

Retinal thickness was measured using spectral-domain optical coherence tomography in a 78-week randomized placebo-controlled trial of verubecestat in 1,785 patients with mild-to-moderate AD. Changes from baseline in retinal pigment epithelium, macular grid retinal nerve fiber layer, central subfield retinal thickness, and macular grid volume were evaluated for verubecestat versus placebo. Correlation analyses were performed to investigate the potential association between macular grid retinal nerve fiber layer and central subfield retinal thickness with brain volumetric magnetic resonance imaging (vMRI) data at baseline, as well as correlations for changes from baseline at Week 78 in patients receiving placebo.

RESULTS

Verubecestat did not significantly alter retinal thickness during the trial compared with placebo. At baseline, mean macular grid retinal nerve fiber layer and central subfield retinal thickness were weakly but significantly correlated (Pearson's r values≤0.23, p-values < 0.01) with vMRI of several brain regions including whole brain, hippocampus, and thalamus. At Week 78, correlations between retinal thickness and brain vMRI changes from baseline in the placebo group were small and mostly not statistically significant.

CONCLUSION

BACE inhibition by verubecestat was not associated with adverse effects on retinal thickness in patients with mild-to-moderate AD. Correlations between retinal thickness and brain volume were observed at baseline.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01739348 (registered December 3, 2012; https://clinicaltrials.gov/ct2/show/NCT01739348).

Biochemical Characterization of Mouse Retina of an Alzheimer's Disease Model by Raman Spectroscopy

The presence of biomarkers characteristic for Alzheimer’s disease in the retina is a controversial topic. Raman spectroscopy offers information on the biochemical composition of tissues. Thus, it could give valuable insight into the diagnostic value of retinal analysis. Within the present study, retinas of a double transgenic mouse model, that expresses a chimeric mouse/human amyloid precursor protein and a mutant form of human presenilin 1, and corresponding control group were subjected to ex vivo Raman imaging. The Raman data recorded on cross sections of whole eyes highlight the layered structure of the retina in a label-free manner. Based on the Raman information obtained from en face mounted retina samples, a discrimination between healthy and Alzheimer’s disease retinal tissue can be done with an accuracy of 85.9%. For this a partial least squares-linear discriminant analysis was applied. Therefore, although no macromolecular changes in form of, i.e., amyloid beta plaques, can be noticed based on Raman spectroscopy, subtle biochemical changes happening in the retina could lead to Alzheimer’s disease identification.

Neuroimaging advances regarding subjective cognitive decline in preclinical Alzheimer's disease

Subjective cognitive decline (SCD) is regarded as the first clinical manifestation in the Alzheimer’s disease (AD) continuum. Investigating populations with SCD is important for understanding the early pathological mechanisms of AD and identifying SCD-related biomarkers, which are critical for the early detection of AD. With the advent of advanced neuroimaging techniques, such as positron emission tomography (PET) and magnetic resonance imaging (MRI), accumulating evidence has revealed structural and functional brain alterations related to the symptoms of SCD. In this review, we summarize the main imaging features and key findings regarding SCD related to AD, from local and regional data to connectivity-based imaging measures, with the aim of delineating a multimodal imaging signature of SCD due to AD. Additionally, the interaction of SCD with other risk factors for dementia due to AD, such as age and the Apolipoprotein E (ApoE) ɛ4 status, has also been described. Finally, the possible explanations for the inconsistent and heterogeneous neuroimaging findings observed in individuals with SCD are discussed, along with future directions. Overall, the literature reveals a preferential vulnerability of AD signature regions in SCD in the context of AD, supporting the notion that individuals with SCD share a similar pattern of brain alterations with patients with mild cognitive impairment (MCI) and dementia due to AD. We conclude that these neuroimaging techniques, particularly multimodal neuroimaging techniques, have great potential for identifying the underlying pathological alterations associated with SCD. More longitudinal studies with larger sample sizes combined with more advanced imaging modeling approaches such as artificial intelligence are still warranted to establish their clinical utility.

A new Graph Gaussian embedding method for analyzing the effects of cognitive training

Identifying heterogeneous cognitive impairment markers at an early stage is vital for Alzheimer's disease diagnosis. However, due to complex and uncertain brain connectivity features in the cognitive domains, it remains challenging to quantify functional brain connectomic changes during non-pharmacological interventions for amnestic mild cognitive impairment (aMCI) patients. We present a quantitative method for functional brain network analysis of fMRI data based on the multi-graph unsupervised Gaussian embedding method (MG2G). This neural network-based model can effectively learn low-dimensional Gaussian distributions from the original high-dimensional sparse functional brain networks, quantify uncertainties in link prediction, and discover the intrinsic dimensionality of brain networks. Using the Wasserstein distance to measure probabilistic changes, we discovered that brain regions in the default mode network and somatosensory/somatomotor hand, fronto-parietal task control, memory retrieval, and visual and dorsal attention systems had relatively large variations during non-pharmacological training, which might provide distinct biomarkers for fine-grained monitoring of aMCI cognitive alteration. An important finding of our study is the ability of the new method to capture subtle changes for individual patients before and after short-term intervention. More broadly, the MG2G method can be used in studying multiple brain disorders and injuries, e.g., in Parkinson's disease or traumatic brain injury (TBI), and hence it will be useful to the wider neuroscience community.

Characterization of the retinal changes of the 3×Tg-AD mouse model of Alzheimer’s disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder whose diagnosis remains a notable challenge. The literature suggests that cerebral changes precede AD symptoms by over two decades, implying a significantly advanced stage of AD by the time it is usually diagnosed. In the study herein, texture analysis was applied to computed optical coherence tomography ocular fundus images to identify differences between a group of the transgenic mouse model of the Alzheimer’s disease (3×Tg-AD) and a group of wild-type mice, at the ages of one and two-months-old. A substantial difference between groups was found at both time-points across all neuroretina’s layers. Here, the inner nuclear layer stands out both in the level of statistically significant differences and on the extension of these differences which span through the imaged area. Also, the progression of AD is suggested to be spotted by texture analysis as demonstrated by the significant difference found in the inner plexiform and the outer nuclear layers from the age of one to the age of two-months-old. These findings demonstrate the potential of the use of the retina and texture analysis to the diagnosis of AD and monitor AD progression. Besides, the differences between groups found in this study suggest that the 3×Tg-AD model may be inappropriate to study early changes associated with the AD and other animal models should be tested following the same path and rationale. Moreover, these results also suggest that the human genes present in these transgenic mice may have an impact on the neurodevelopment of offspring which would justify the significant changes found at the age of one-month-old.

Retinal analysis of a mouse model of Alzheimer's disease with multicontrast optical coherence tomography

Significance. Recent Alzheimer's disease (AD) patient studies have focused on retinal analysis, as the retina is the only part of the central nervous system that can be imaged noninvasively by optical methods. However, as this is a relatively new approach, the occurrence and role of retinal pathological features are still debated. Aim. The retina of an APP/PS1 mouse model was investigated using multicontrast optical coherence tomography (OCT) in order to provide a documentation of what was observed in both transgenic and wild-type mice. Approach. Both eyes of 24 APP/PS1 transgenic mice (age: 45 to 104 weeks) and 15 age-matched wild-type littermates were imaged by the custom-built OCT system. At the end of the experiment, retinas and brains were harvested from a subset of the mice (14 transgenic, 7 age-matched control) in order to compare the in vivo results to histological analysis and to quantify the cortical amyloid beta plaque load. Results. The system provided a combination of standard reflectivity data, polarization-sensitive data, and OCT angiograms. Qualitative and quantitative information from the resultant OCT images was extracted on retinal layer thickness and structure, presence of hyper-reflective foci, phase retardation abnormalities, and retinal vasculature. Conclusions. Although multicontrast OCT revealed abnormal structural properties and phase retardation signals in the retina of this APP/PS1 mouse model, the observations were very similar in transgenic and control mice.

Retinal thickness as a potential biomarker in patients with amyloid-proven early- and late-onset Alzheimer's disease

Introduction

Retinal thickness measured with optical coherence tomography has been proposed as a noninvasive biomarker for Alzheimer's disease (AD). We therefore measured retinal thickness in well-characterized AD and control participants, considering ophthalmological confounders.

Methods

We included 57 amyloid-proven AD cases and 85 cognitively normal, amyloid-negative controls. All subjects underwent retinal thickness measurements with spectral domain optical coherence tomography and an ophthalmological assessment to exclude ocular disease.

Results

Retinal thickness did not discriminate cases from controls, including stratified analyses for early- versus late-onset AD. We found significant associations between macular thickness and global cortical atrophy [β -0.358; P = .01] and parietal cortical atrophy on magnetic resonance imaging [β -0.371; P < .01] in AD cases.

Discussion

In this study, representing the largest optical coherence tomography cohort with amyloid-proven AD cases, we show that retinal thickness does not discriminate AD from controls, despite evident changes on clinical, neuroimaging, and CSF measures, querying the use of retinal thickness measurements as an AD biomarker.

Reflections on the Utility of the Retina as a Biomarker for Alzheimer's Disease: A Literature Review

As a part of the central nervous system, the retina may reflect both physiologic processes and abnormalities related to diseases of the brain. Indeed, a concerted effort has been put forth to understand how Alzheimer's disease (AD) pathology may manifest in the retina as a means to assess the state of the AD brain. The development and refinement of ophthalmologic techniques for studying the retina in vivo have produced evidence of retinal degeneration in AD diagnosed patients. In this review, we will discuss retinal imaging techniques implemented to study the changes in AD retina as well as highlight the recent efforts made to correlate such findings to other clinical hallmarks of AD to assess the viability of the retina as a biomarker for AD.

Efficacy and neural mechanism of acupuncture treatment in older adults with subjective cognitive decline: study protocol for a randomised controlled clinical trial

INTRODUCTION

Subjective cognitive decline (SCD) refers to individuals' perceived decline in memory and/or other cognitive abilities relative to their previous level of performance, while objective neuropsychological deficits are not observed. SCD may represent a preclinical phase of Alzheimer's disease. At this very early stage of decline, intervention could slow the rate of incipient decline to prolong and preserve cognitive and functional abilities. However, there is no effective treatment recommended for individuals with SCD. Acupuncture, as a non-pharmacological intervention, has been widely employed for patients with cognitive disorders.

METHODS AND ANALYSIS

The proposed study is a randomised, assessor-blinded and placebo-controlled study that investigates the efficacy and mechanism of acupuncture in SCD. Sixty patients with SCD will be randomly allocated either into an acupuncture group or a sham acupuncture group. They will receive 24 sessions of real acupuncture treatment or identical treatment sessions using a placebo needle. Global cognitive changes based on a multidomain neuropsychological test battery will be evaluated to detect the clinical efficacy of acupuncture treatment at baseline and end of treatment. MRI scans will be used to explore acupuncture-related neuroplasticity changes. Correlation analyses will be performed to investigate the relationships between the changes in brain function and symptom improvement.

ETHICS AND DISSEMINATION

The trial was approved by the research ethics committee. The results of the study will be published in a peer-reviewed academic journal and will also be disseminated electronically through conference presentations.

TRIAL REGISTRATION NUMBER

NCT03444896.

Comorbidity of age-related macular degeneration with Alzheimer's disease: A histopathologic case-control study

Introduction

Previous studies evaluating the association between clinically diagnosed Alzheimer’s disease (AD) and age-related macular degeneration (AMD) have generated conflicting results. This study is the first to assess whether AMD prevalence is higher in AD patients than non-AD controls by using histopathology to definitively diagnose AD.

Methods

This was a retrospective case-control study utilizing diagnostic information extracted from autopsy reports of patients age 75 and above, including 115 with a neuropathological diagnosis of AD and 57 age-matched normal controls.

Results

The rate of AMD was not significantly higher in AD cases (53.0%) than in controls (59.6%) (z = 0.820, p = 0.794). AMD severity as determined by Sarks score was similar between AD patients and controls (χ² = 2.96, p = 0.706). There was also no significant association between Braak stage of AD severity and AMD (χ² = 4.55, p = 0.602).

Discussion

No significant effect of AD diagnosis or pathologic severity on AMD comorbidity was found, suggesting that any shared mechanisms between AMD and AD may be nondeterministic.

Retinal thickness as potential biomarker in posterior cortical atrophy and typical Alzheimer's disease

BACKGROUND

Retinal thickness can be measured non-invasively with optical coherence tomography (OCT) and may offer compelling potential as a biomarker for Alzheimer's disease (AD). Retinal thinning is hypothesized to be a result of retrograde atrophy and/or parallel neurodegenerative processes. Changes in the visual pathway are of particular interest in posterior cortical atrophy (PCA), the most common atypical AD phenotype predominantly affecting the parietal-occipital cortices. We therefore evaluated retinal thickness as non-invasive biomarker of neurodegeneration in well-characterized participants with posterior cortical atrophy (PCA) and typical Alzheimer's disease (tAD).

METHODS

Retinal thickness measures were acquired from 48 patient participants (N = 25 PCA; N = 23 tAD) fulfilling consensus diagnostic criteria and 70 age-matched controls. Participants were recruited between 2014 and 2016. All participants underwent optical coherence tomography (OCT) imaging, including measurement of peripapillary retinal nerve fiber layer (pRNFL) thickness and total macular thickness (mRT). Participants did not show evidence of any significant ophthalmological conditions. Subgroup analyses were performed in participants with available MRI and CSF measures, providing evidence of neurodegeneration and underlying AD pathology respectively.

RESULTS

There was no evidence of overall between-group differences in pRNFL thickness (mean PCA 98.7 ± 12.2; tAD 99.9 ± 8.7; controls 99.6 ± 10.0 μm, one-way analysis of variance (ANOVA) p = 0.92) or total mRT (mean PCA 266.9 ± 16.3; tAD 267.8 ± 13.6; controls 269.3 ± 13.6 μm, one-way ANOVA p = 0.75). Similarly, subgroup analysis with MRI biomarkers (PCA = 18, tAD = 17, controls = 31) showing neurodegeneration, and CSF biomarkers (PCA = 18, tAD = 14, controls = 13) supporting underlying AD pathology did not provide evidence of overall between-group differences in pRNFL or mRT measures (all p > 0.3).

CONCLUSIONS

Retinal thickness did not discriminate tAD and PCA from controls or from one another despite unequivocal differences on standard clinical, neuro-imaging and CSF measures. Findings from this well-characterized sample, including cases with PCA, do not support the hypothesis that retinal neurodegeneration, measured using conventional OCT, is a useful biomarker for AD or PCA.

Folate/Vitamin B Alleviates Hyperhomocysteinemia-Induced Alzheimer-Like Pathologies in Rat Retina

Hyperhomocysteinemia (Hhcy) is an independent risk factor for Alzheimer's disease (AD). Visual dysfunction is commonly found and is positively correlated with the severity of cognitive defects in AD patients. Our previous study demonstrated that Hhcy induces memory deficits with AD-like tau and amyloid-β (Aβ) pathologies in the hippocampus, and supplementation with folate and vitamin B12 (FB) prevents the Hhcy-induced AD-like pathologies in the hippocampus. Here, we investigated whether Hhcy also induces AD-like pathologies in the retina and the effects of FB. An Hhcy rat model was produced by vena caudalis injection of homocysteine for 14 days, and the effects of FB were assessed by simultaneous supplementation with FB in drinking water. We found that Hhcy induced vessel damage with Aβ and tau pathologies in the retina, while simultaneous supplementation with FB remarkably attenuated the Hhcy-induced tau hyperphosphorylation at multiple AD-related sites and Aβ accumulation in the retina. The mechanisms involved downregulation of amyloid precursor protein (APP), presenilin-1, beta-site APP-cleaving enzyme 1, and protein phosphatase-2A. Our data suggest that the retina may serve as a window for evaluating the effects of FB on hyperhomocysteinemia-induced Alzheimer-like pathologies.

Retinal α-synuclein deposits in Parkinson's disease patients and animal models

Despite decades of research, accurate diagnosis of Parkinson's disease remains a challenge, and disease-modifying treatments are still lacking. Research into the early (presymptomatic) stages of Parkinson's disease and the discovery of novel biomarkers is of utmost importance to reduce this burden and to come to a more accurate diagnosis at the very onset of the disease. Many have speculated that non-motor symptoms could provide a breakthrough in the quest for early biomarkers of Parkinson's disease, including the visual disturbances and retinal abnormalities that are seen in the majority of Parkinson's disease patients. An expanding number of clinical studies have investigated the use of in vivo assessments of retinal structure, electrophysiological function, and vision-driven tasks as novel means for identifying patients at risk that need further neurological examination and for longitudinal follow-up of disease progression in Parkinson's disease patients. Often, the results of these studies have been interpreted in relation to α-synuclein deposits and dopamine deficiency in the retina, mirroring the defining pathological features of Parkinson's disease in the brain. To better understand the visual defects seen in Parkinson's disease patients and to propel the use of retinal changes as biomarkers for Parkinson's disease, however, more conclusive neuropathological evidence for the presence of retinal α-synuclein aggregates, and its relation to the cerebral α-synuclein burden, is urgently needed. This review provides a comprehensive and critical overview of the research conducted to unveil α-synuclein aggregates in the retina of Parkinson's disease patients and animal models, and thereby aims to aid the ongoing discussion about the potential use of the retinal changes and/or visual symptoms as biomarkers for Parkinson's disease.

Ocular amyloid imaging at the crossroad of Alzheimer's disease and age-related macular degeneration: implications for diagnosis and therapy

Alzheimer's disease (AD) and age-related macular degeneration (AMD) are important disorders of aging, but significant challenges remain in diagnosis and therapy. Amyloid-beta (Aβ), found in the brain and a defining feature of AD, has also been observed in the retina in both AD and AMD. While current diagnostic modalities for detecting Aβ in the brain are costly or invasive, Aβ in the retina can be noninvasively and conveniently imaged using modern photonic imaging systems such as optical coherence tomography (OCT). Moreover, since many of these retinal changes occur before degenerative changes can be detected in the brain, ocular amyloid biomarkers could be utilized to detect AD as well as AMD in their earliest stages when therapy may be most effective in halting disease progression. Novel technologies to quantify retinal biomarkers have the potential to facilitate early diagnosis and noninvasive monitoring of disease progression with important therapeutic implications.

Human Tau Expression Does Not Induce Mouse Retina Neurodegeneration, Suggesting Differential Toxicity of Tau in Brain vs. Retinal Neurons

The implication of the microtubule-associated protein (MAP) Tau in the ocular manifestations of Alzheimer’s disease (AD) is elusive due to the lack of relevant animal model. However, signs of AD have been reported in the brain of transgenic mice expressing human Tau (hTau). To assess whether hTau is sufficient to induce AD pathogenesis in the retina as well, in the present study, we compared the retinal structure and function of KO mice deprived of Tau (mTKO) with those of transgenic mice expressing hTau. Our results revealed that hTau is particularly abundant in the inner nuclear layer (INL) cells of the retina. By electroretinogram (ERG) recording, light-induced retinal cell activation was not altered in hTau compared with mTKO littermates. Surprisingly, the ERG response mediated by cone photoreceptor stimulation was even stronger in hTau than in mTKO retinae. Immunofluorescent analysis of retinal sections allowed us to observe thicker inner retina in hTau than in mTKO eyes. By Western Blotting (WB), the upregulation of mTOR that was found in hTau mice may underlie retinal structure and function increases. Taken together, our results not only indicate that hTau expression is not toxic for retinal cells but they also suggest that it may play a positive role in visual physiology. The use of hTau may be envisaged to improve visual recovery in ocular diseases affecting the retinal function such as glaucoma or diabetic retinopathy.