Alzheimer’s disease: Cerebral glaucoma?

NAD+ Supplementation Improves Mitochondrial Functions and Normalizes Glaucomatous Trabecular Meshwork Features

Glaucoma is characterized by pathological elevation of intraocular pressure (IOP) due to dysfunctional trabecular meshwork (TM), which is the primary cause of irreversible vision loss. There are currently no effective treatment strategies for glaucoma. Mitochondrial function plays a crucial role in regulating IOP within the TM. In this study, primary TM cells treated with dexamethasone were used to simulate glaucomatous changes, showing abnormal cellular cytoskeleton, increased expression of extracellular matrix, and disrupted mitochondrial fusion and fission dynamics. Furthermore, glaucomatous TM cell line GTM3 exhibited impaired mitochondrial membrane potential and phagocytic function, accompanied by decreased oxidative respiratory levels as compared to normal TM cells iHTM. Mechanistically, lower NAD+ levels in GTM3, possibly associated with increased expression of key enzymes CD38 and PARP1 related to NAD+ consumption, were observed. Supplementation of NAD+ restored mitochondrial function and cellular viability in GTM3 cells. Therefore, we propose that the aberrant mitochondrial function in glaucomatous TM cells may be attributed to increased NAD+ consumption dependent on CD38 and PARP1, and NAD+ supplementation could effectively ameliorate mitochondrial function and improve TM function, providing a novel alternative approach for glaucoma treatment.

Controversial Past, Splendid Present, Unpredictable Future: A Brief Review of Alzheimer Disease History

Background: The concept of Alzheimer disease (AD)-since its histological discovery by Alzheimer to the present day-has undergone substantial modifications. Methods: We conducted a classical narrative review of this field with a bibliography selection (giving preference to Medline best match). Results: The following subjects are reviewed and discussed: Alzheimer's discovery, Kraepelin's creation of a new disease that was a rare condition until the 1970's, the growing interest and investment in AD as a major killer in a society with a large elderly population in the second half of the 20th century, the consolidation of the AD clinicopathological model, and the modern AD nosology based on the dominant amyloid hypothesis among many others. In the 21st century, the development of AD biomarkers has supported a novel biological definition of AD, although the proposed therapies have failed to cure this disease. The incidence of dementia/AD has shown a decrease in affluent countries (possibly due to control of risk factors), and mixed dementia has been established as the most frequent etiology in the oldest old. Conclusions: The current concept of AD lacks unanimity. Many hypotheses attempt to explain its complex physiopathology entwined with aging, and the dominant amyloid cascade has yielded poor therapeutic results. The reduction in the incidence of dementia/AD appears promising but it should be confirmed in the future. A reevaluation of the AD concept is also necessary.

Ocular manifestations of central insulin resistance

Central insulin resistance, the diminished cellular sensitivity to insulin in the brain, has been implicated in diabetes mellitus, Alzheimer's disease and other neurological disorders. However, whether and how central insulin resistance plays a role in the eye remains unclear. Here, we performed intracerebroventricular injection of S961, a potent and specific blocker of insulin receptor in adult Wistar rats to test if central insulin resistance leads to pathological changes in ocular structures. 80 mg of S961 was stereotaxically injected into the lateral ventricle of the experimental group twice at 7 days apart, whereas buffer solution was injected to the sham control group. Blood samples, intraocular pressure, trabecular meshwork morphology, ciliary body markers, retinal and optic nerve integrity, and whole genome expression patterns were then evaluated. While neither blood glucose nor serum insulin level was significantly altered in the experimental or control group, we found that injection of S961 but not buffer solution significantly increased intraocular pressure at 14 and 24 days after first injection, along with reduced porosity and aquaporin 4 expression in the trabecular meshwork, and increased tumor necrosis factor α and aquaporin 4 expression in the ciliary body. In the retina, cell density and insulin receptor expression decreased in the retinal ganglion cell layer upon S961 injection. Fundus photography revealed peripapillary atrophy with vascular dysregulation in the experimental group. These retinal changes were accompanied by upregulation of pro-inflammatory and pro-apoptotic genes, downregulation of anti-inflammatory, anti-apoptotic, and neurotrophic genes, as well as dysregulation of genes involved in insulin signaling. Optic nerve histology indicated microglial activation and changes in the expression of glial fibrillary acidic protein, tumor necrosis factor α, and aquaporin 4. Molecular pathway architecture of the retina revealed the three most significant pathways involved being inflammation/cell stress, insulin signaling, and extracellular matrix regulation relevant to neurodegeneration. There was also a multimodal crosstalk between insulin signaling derangement and inflammation-related genes. Taken together, our results indicate that blocking insulin receptor signaling in the central nervous system can lead to trabecular meshwork and ciliary body dysfunction, intraocular pressure elevation, as well as inflammation, glial activation, and apoptosis in the retina and optic nerve. Given that central insulin resistance may lead to neurodegenerative phenotype in the visual system, targeting insulin signaling may hold promise for vision disorders involving the retina and optic nerve.

MRI findings suggestive of Alzheimer's disease in patients with primary open angle glaucoma - a single sequence analysis using rapid 3D T1 spoiled gradient echo

OBJECTIVE

Primary open-angle glaucoma (POAG) is a degenerative optic neuropathy disease which has somewhat similar pathophysiology to Alzheimer's disease (AD). This study aims to determine the presence of medial temporal atrophy and parietal lobe atrophy in patients with POAG compared to normal controls using medial temporal atrophy (MTA) scoring and posterior cortical atrophy (PCA) scoring system on T1 magnetization-prepared rapid gradient-echo.

METHODS

50 POAG patients and 50 normal subjects were recruited and an MRI brain with T1-magnetization-prepared rapid gradient-echo was performed. Medial temporal lobe and parietal lobe atrophy were by MTA and PCA/Koedam scoring. The score of the PCA and MTA were compared between the POAG group and the controls.

RESULTS

There was a significant statistical difference between PCA score in POAG and the healthy control group (p-value = 0.026). There is no statistical difference between MTA score in POAG compared to the healthy control group (p-value = 0.58).

CONCLUSION

This study suggests a correlation between POAG and PCA score. Potential application of this scoring method in clinical diagnosis and monitoring of POAG patients.

ADVANCES IN KNOWLEDGE

The scoring method used in AD may also be applied in the diagnosis and monitoring of POAGMRI brain, specifically rapid volumetric T1 spoiled gradient echo sequence, may be applied in POAG assessment.

Brain Functional Network Analysis of Patients with Primary Angle-Closure Glaucoma

Objectives. Recent resting-state functional magnetic resonance imaging (fMRI) studies have focused on glaucoma-related neuronal degeneration in structural and spontaneous functional brain activity. However, there are limited studies regarding the differences in the topological organization of the functional brain network in patients with glaucoma. In this study, we aimed to assess both potential alterations and the network efficiency in the functional brain networks of patients with primary angle-closure glaucoma (PACG). Methods. We applied resting-state fMRI data to construct the functional connectivity network of 33 patients with PACG ( $54.21\pm 7.21\text{years}$ ) and 33 gender- and age-matched healthy controls ( $52.42\pm 7.80\text{years}$ ). The differences in the global and regional topological brain network properties between the two groups were assessed using graph theoretical analysis. Partial correlations between the altered regional values and clinical parameters were computed for patients with PACG. Results. No significant differences in global topological measures were identified between the two groups. However, significant regional alterations were identified in the patients with PACG, including differences within visual and nonvisual (somatomotor and cognition-emotion) regions. The normalized clustering coefficient and normalized local efficiency of the right superior parietal gyrus were significantly correlated with the retinal fiber layer thickness (RNFLT) and the vertical cup to disk ratio (V C/D). In addition, the normalized node betweenness of the left middle frontal gyrus (orbital portion) was significantly correlated with the V C/D in the patients with PACG. Conclusions. Our results suggest that regional inefficiency with decrease and compensatory increase in local functional properties of visual and nonvisual nodes preserved the brain network of the PACG at the global level.

Assessing the Performance of Daily Intake of a Homotaurine, Carnosine, Forskolin, Vitamin B2, Vitamin B6, and Magnesium Based Food Supplement for the Maintenance of Visual Function in Patients with Primary Open Angle Glaucoma

Background

Glaucoma is a multifactorial optic neuropathy, which causes a continuous loss of retinal ganglion cells. Given the neurodegenerative nature of glaucoma, the necessity for neuroprotective intervention still arises, to be added alongside hypotonic therapy.

Objective

The objective of this study was to assess the effect of daily intake of a homotaurine, carnosine, forskolin, vitamins B1, B2, and B6, folic acid, and magnesium based supplement (GANGLIOLIFE®) on the progression rates of the visual field in patients with progressive POAG despite good tonometric compensation and to assess the most suitable dosage.

Methods

This is a monocentric nonrandomized experimental clinical study. Patients with mean deviation (MD) ranging from -2 dB to -15 dB with MD progression ≥1 dB in the previous year and IOP values of ≤18 mm Hg were included. All the patients underwent supplement therapy for a period of 6 months. For the first 2 months, they took 2 tablets a day, and for the following 4 months, 1 tablet a day. The patients were assessed before the start of treatment, time 0 (T ₀), after 2 months (T ₁), and after 6 months (T ₂) of therapy. At each check-up, patients were given a full eye test including perimetry, RNFL, and GCC using FD-OCT, PERG, contrast sensitivity, and QoL evaluation using the Glaucoma Symptom Scale questionnaire and National Eye Institute Visual Function Questionnaire 25.

Results

31 patients with a mean age of 70.80 ± 8.77 were included. At T ₁ and T ₂, the mean values of MD were lessened (MD = -5.37 ± -2.91, P < 0.01, and MD = -5.48 ± 3.15, P < 0.05, respectively) compared to T ₀ (MD = -5.98 ± 2.83). Patients also demonstrated a significant reduction in IOP (P < 0.01), improved light sensitivity (P < 0.01) and contrast sensitivity (P < 0.05), and a better quality of life (P < 0.05).

Conclusions

Treatment with a supplement which includes homotaurine, carnosine, forskolin, vitamins B1, B2, and B6, folic acid, and magnesium has been shown to be able to slow down the rate of progression of functional damage and improve visual function after 2 and 6 months of daily intake. Quality of life showed significant improvement.

Neuroprotective effects of brain-derived neurotrophic factor against amyloid beta 1-40-induced retinal and optic nerve damage

Brain-derived neurotrophic factor (BDNF) could be considered a potential neuroprotective therapy in amyloid beta (Aβ)-associated retinal and optic nerve degeneration. Hence, in this study we investigated the neuroprotective effect of BDNF against Aβ1-40-induced retinal and optic nerve injury. In this study, exposure to Aβ1-40 was associated with retinal and optic nerve injury. TUNEL staining showed significant reduction in the apoptotic cell count in the BDNF-treated group compared with Aβ1-40 group. H&E-stained retinal sections also showed a striking reduction in neuronal cells in the ganglion cell layer (GCL) of retinas fourteen days after Aβ1-40 exposure. By contrast, number of retinal cells was preserved in the retinas of BDNF-treated animals. After Aβ1-40 exposure, visible axonal swelling was observed in optic nerve sections. However, the BDNF-treated group showed fewer changes in optic nerve; axonal swelling was less frequent and less marked. In the present study, exposure to Aβ was associated with oxidative stress, whereas levels of retinal glutathione (GSH), superoxide dismutase (SOD) and catalase were significantly increased in BDNF-treated than in Aβ1-40-treated rats. Both visual object recognition tests using an open-field arena and a Morris water maze showed that BDNF improved rats' ability to recognise visual cues (objects with different shapes) after Aβ1-40 exposure, thus demonstrating that the visual performance of rats was relatively preserved following BDNF treatment. In conclusion, intravitreal treatment with BDNF prevents Aβ1-40-induced retinal cell apoptosis and axon loss in the optic nerve of rats by reducing retinal oxidative stress and restoring retinal BDNF levels.

Evaluation of Retinal Nerve Fiber Layer Thickness, Electroretinogram and Visual Evoked Potential in Patients with Alzheimer's Disease

OBJECTIVE

To study the retinal nerve fibre layer (RNFL) thickness and visual electrophysiology testing in patients with Alzheimer's disease (AD).

METHODS

A cross-sectional, hospital-based study: 25 AD subjects and 25 controls were recruited. Candidates who fulfil the criteria with normal ocular examinations were made to proceed with scanning laser polarimetry, pattern electroretinogram (PERG), and pattern visual evoked potential (PVEP) examinations of the right eye. RNFL thickness, PERG, and PVEP readings were evaluated.

RESULTS

In AD, the mean of average RNFL thickness was 45.28 μm, SD = 3.61, P < 0.001 (P < 0.05), while the superior RNFL thickness was 54.44 μm, SD = 2.85, P < 0.001 (P < 0.05) and inferior RNFL thickness was 47.11 μm, SD = 4.52, P < 0.001 (P < 0.05). For PERG, the mean P50 latency was 63.88 ms, SD = 7.94, P < 0.001 (P < 0.05) and the mean amplitudes of P50 waves were 1.79 μV, SD = 0.64, P < 0.001 (P < 0.05) and N95 waves were 2.43 μV, SD = 0.90, P < 0.001 (P < 0.05). For PVEP, the mean latency of P100 was 119.00 ms, SD = 9.07, P < 0.001 (P < 0.05), while the mean latency of N135 was 145.20 ms, SD = 8.53, P < 0.001 (P < 0.05). The mean amplitude of P100 waves was 3.71 μV, SD = 1.60, P < 0.001 (P < 0.05), whereas the mean amplitude of N135 waves was 3.67 μV, SD = 2.02, P < 0.001 (P < 0.05). RNFL thickness strongly correlates with PERG readings, with P50 latency R = 0.582, R2 = 0.339, P=0.002 (P < 0.05), amplitude of P50 wave at R = 0.749, R2 = 0.561, P ≤ 0.001 (P < 0.05), and amplitude of N95 wave at R = 0.500, R2 = 0.250, P=0.011 (P < 0.05). No significant difference and correlation were observed on PVEP readings.

CONCLUSION

The mean of the average, superior and inferior RNFL thickness were significantly lower in the AD group compared with control. There is also significant difference of PERG and PVEP parameters between AD and controls. Regression analysis showed average RNFL thickness having significantly linear relationship with the PERG parameters.

Residual vision activation and the brain-eye-vascular triad: Dysregulation, plasticity and restoration in low vision and blindness - a review

Vision loss due to ocular diseases such as glaucoma, optic neuropathy, macular degeneration, or diabetic retinopathy, are generally considered an exclusive affair of the retina and/or optic nerve. However, the brain, through multiple indirect influences, has also a major impact on functional visual impairment. Such indirect influences include intracerebral pressure, eye movements, top-down modulation (attention, cognition), and emotionally triggered stress hormone release affecting blood vessel dysregulation. Therefore, vision loss should be viewed as the result of multiple interactions within a “brain-eye-vascular triad”, and several eye diseases may also be considered as brain diseases in disguise. While the brain is part of the problem, it can also be part of the solution. Neuronal networks of the brain can “amplify” residual vision through neuroplasticity changes of local and global functional connectivity by activating, modulating and strengthening residual visual signals. The activation of residual vision can be achieved by different means such as vision restoration training, non-invasive brain stimulation, or blood flow enhancing medications. Modulating brain functional networks and improving vascular regulation may offer new opportunities to recover or restore low vision by increasing visual field size, visual acuity and overall functional vision. Hence, neuroscience offers new insights to better understand vision loss, and modulating brain and vascular function is a promising source for new opportunities to activate residual vision to achieve restoration and recovery to improve quality of live in patients suffering from low vision.

Spectral-Domain OCT Measurements in Alzheimer's Disease: A Systematic Review and Meta-analysis

TOPIC

OCT is a noninvasive tool to measure specific retinal layers in the eye. The relationship of retinal spectral-domain (SD) OCT measurements with Alzheimer's disease (AD) and mild cognitive impairment (MCI) remains unclear. Hence, we conducted a systematic review and meta-analysis to examine the SD OCT measurements in AD and MCI.

CLINICAL RELEVANCE

Current methods of diagnosing early AD are expensive and invasive. Retinal measurements of SD OCT, which are noninvasive, technically simple, and inexpensive, are potential biomarkers of AD.

METHODS

We conducted a literature search in PubMed and Excerpta Medica Database to identify studies published before December 31, 2017, that assessed the associations between AD, MCI, and measurements of SD OCT: ganglion cell-inner plexiform layer (GC-IPL), ganglion cell complex (GCC), macular volume, and choroidal thickness, in addition to retinal nerve fiber layer (RNFL) and macular thickness. We used a random-effects model to examine these relationships. We also conducted meta-regression and assessed heterogeneity, publication bias, and study quality.

RESULTS

We identified 30 eligible studies, involving 1257 AD patients, 305 MCI patients, and 1460 controls, all of which were cross-sectional studies. In terms of the macular structure, AD patients showed significant differences in GC-IPL thickness (standardized mean difference [SMD], -0.46; 95% confidence interval [CI], -0.80 to -0.11; I² = 71%), GCC thickness (SMD, -0.84; 95% CI, -1.10 to -0.57; I² = 0%), macular volume (SMD, -0.58; 95% CI, -1.03 to -0.14; I² = 80%), and macular thickness of all inner and outer sectors (SMD range, -0.52 to -0.74; all P < 0.001) when compared with controls. Peripapillary RNFL thickness (SMD, -0.67; 95% CI, -0.95 to -0.38; I² = 89%) and choroidal thickness (SMD range, -0.88 to -1.03; all P < 0.001) also were thinner in AD patients.

CONCLUSIONS

Our results confirmed the associations between retinal measurements of SD OCT and AD, highlighting the potential usefulness of SD OCT measurements as biomarkers of AD.

Association between Open-Angle Glaucoma and the Risks of Alzheimer's and Parkinson's Diseases in South Korea: A 10-year Nationwide Cohort Study

We aimed to investigate the risks of Alzheimer’s (AD) and Parkinson’s disease (PD) in the 10 years following diagnosis of open-angle glaucoma (OAG) using a nationwide cohort. This propensity score-matched retrospective cohort study included 1,025,340 subjects from the Korean National Health Insurance Service National Sample Cohort database. The OAG group (n = 1,469) included patients who were initially diagnosed with OAG between 2004 and 2007, and the subjects in the comparison group were matched in a 1:5 ratio using propensity scores. Cox regression analyses were performed to investigate the risks of developing AD or PD. The diagnosis of OAG was significantly associated with an increased incidence of AD (hazard ratio [HR] = 1.403, 95% confidence interval [CI] 1.180–1.669, p < 0.001), but not PD (HR = 0.995, 95% CI 0.620–1.595, p = 0.983) after adjusting for possible confounding factors. In subgroup analyses, participants with OAG aged ≥65 years were more likely to develop AD compared with those aged <65 years, and female OAG patients had a greater risk of developing AD than males. Patients diagnosed with OAG have a higher risk of developing AD, but not PD, and the risk differed according to age and sex.

Changes of Visual Pathway and Brain Connectivity in Glaucoma: A Systematic Review

Background: Glaucoma is a leading cause of irreversible blindness worldwide. The increasing interest in the involvement of the cortical visual pathway in glaucomatous patients is due to the implications in recent therapies, such as neuroprotection and neuroregeneration. Objective: In this review, we outline the current understanding of brain structural, functional, and metabolic changes detected with the modern techniques of neuroimaging in glaucomatous subjects. Methods: We screened MEDLINE, EMBASE, CINAHL, CENTRAL, LILACS, Trip Database, and NICE for original contributions published until 31 October 2017. Studies with at least six patients affected by any type of glaucoma were considered. We included studies using the following neuroimaging techniques: functional Magnetic Resonance Imaging (fMRI), resting-state fMRI (rs-fMRI), magnetic resonance spectroscopy (MRS), voxel- based Morphometry (VBM), surface-based Morphometry (SBM), diffusion tensor MRI (DTI). Results: Over a total of 1,901 studies, 56 case series with a total of 2,381 patients were included. Evidence of neurodegenerative process in glaucomatous patients was found both within and beyond the visual system. Structural alterations in visual cortex (mainly reduced cortex thickness and volume) have been demonstrated with SBM and VBM; these changes were not limited to primary visual cortex but also involved association visual areas. Other brain regions, associated with visual function, demonstrated a certain grade of increased or decreased gray matter volume. Functional and metabolic abnormalities resulted within primary visual cortex in all studies with fMRI and MRS. Studies with rs-fMRI found disrupted connectivity between the primary and higher visual cortex and between visual cortex and associative visual areas in the task-free state of glaucomatous patients. Conclusions: This review contributes to the better understanding of brain abnormalities in glaucoma. It may stimulate further speculation about brain plasticity at a later age and therapeutic strategies, such as the prevention of cortical degeneration in patients with glaucoma. Structural, functional, and metabolic neuroimaging methods provided evidence of changes throughout the visual pathway in glaucomatous patients. Other brain areas, not directly involved in the processing of visual information, also showed alterations.

The Role of Microglia in Retinal Neurodegeneration: Alzheimer's Disease, Parkinson, and Glaucoma

Microglia, the immunocompetent cells of the central nervous system (CNS), act as neuropathology sensors and are neuroprotective under physiological conditions. Microglia react to injury and degeneration with immune-phenotypic and morphological changes, proliferation, migration, and inflammatory cytokine production. An uncontrolled microglial response secondary to sustained CNS damage can put neuronal survival at risk due to excessive inflammation. A neuroinflammatory response is considered among the etiological factors of the major aged-related neurodegenerative diseases of the CNS, and microglial cells are key players in these neurodegenerative lesions. The retina is an extension of the brain and therefore the inflammatory response in the brain can occur in the retina. The brain and retina are affected in several neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and glaucoma. AD is an age-related neurodegeneration of the CNS characterized by neuronal and synaptic loss in the cerebral cortex, resulting in cognitive deficit and dementia. The extracellular deposits of beta-amyloid (Aβ) and intraneuronal accumulations of hyperphosphorylated tau protein (pTau) are the hallmarks of this disease. These deposits are also found in the retina and optic nerve. PD is a neurodegenerative locomotor disorder with the progressive loss of dopaminergic neurons in the substantia nigra. This is accompanied by Lewy body inclusion composed of α-synuclein (α-syn) aggregates. PD also involves retinal dopaminergic cell degeneration. Glaucoma is a multifactorial neurodegenerative disease of the optic nerve, characterized by retinal ganglion cell loss. In this pathology, deposition of Aβ, synuclein, and pTau has also been detected in retina. These neurodegenerative diseases share a common pathogenic mechanism, the neuroinflammation, in which microglia play an important role. Microglial activation has been reported in AD, PD, and glaucoma in relation to protein aggregates and degenerated neurons. The activated microglia can release pro-inflammatory cytokines which can aggravate and propagate neuroinflammation, thereby degenerating neurons and impairing brain as well as retinal function. The aim of the present review is to describe the contribution in retina to microglial-mediated neuroinflammation in AD, PD, and glaucomatous neurodegeneration.

Histological, morphometric, protein and gene expression analyses of rat retinas with ischaemia-reperfusion injury model treated with sildenafil citrate

The aim of this study was to better understand the role of apoptosis in a retinal ischaemia-reperfusion injury model and to determine whether sildenafil citrate treatment can prevent retinal cell apoptosis. Thirty-six rats were divided into a control group (n = 6) and two experimentally induced ischaemia-reperfusion groups (7 and 21 days; n = 15 per group). The induced ischaemia-reperfusion groups were treated with sildenafil for 7 and 21 days (n = 10 per group), and 10 animals were treated with a placebo for the same period (n = 5 per group). Paracentesis of the anterior chamber was performed with a 30-G needle attached to a saline solution (0.9%) bag positioned at a height of 150 cm above the eye for 60 min. Intraocular pressure was measured by rebound tonometer (TonoVet® ). The eyes were analysed by histology and morphometry, and by immunohistochemistry and qRT-PCR for expression of Caspase-7, Caspase-6, Caspase-9, Tnf-r2, Fas-l, Bcl-2 and Bax. Sildenafil-treated animals showed lower levels of histopathological changes (inflammatory, cellular and tissue) than their placebo-treated counterparts at both 7 and 21 days. The retinal ganglion cell layer (RGC) was preserved in the sildenafil groups (SG), with a cell count closer to control than in the placebo groups (PG). Caspase-7 expression was significantly higher in both treated groups at 7 days compared to controls. Gene expression levels in both treatment groups differed from the controls, but in SG Bax and Caspase-6 expression levels were similar to control animals. These results suggest that the main mechanism of retinal cell death in this model is apoptosis, as there is an increase in pro-apoptotic factors and decrease in the anti-apoptotic ones. Also, sildenafil seems to protect the retinal ganglion cell layer from apoptosis. Cell survival was evident in the histological and morphometric analyses, and sildenafil treatment had a protective effect in the apoptosis pathways, with gene expression levels in SG similar to the controls.

Genetic defects in β-spectrin and tau sensitize C. elegans axons to movement-induced damage via torque-tension coupling

Our bodies are in constant motion and so are the neurons that invade each tissue. Motion-induced neuron deformation and damage are associated with several neurodegenerative conditions. Here, we investigated the question of how the neuronal cytoskeleton protects axons and dendrites from mechanical stress, exploiting mutations in UNC-70 β-spectrin, PTL-1 tau/MAP2-like and MEC-7 β-tubulin proteins in Caenorhabditis elegans. We found that mechanical stress induces supercoils and plectonemes in the sensory axons of spectrin and tau double mutants. Biophysical measurements, super-resolution, and electron microscopy, as well as numerical simulations of neurons as discrete, elastic rods provide evidence that a balance of torque, tension, and elasticity stabilizes neurons against mechanical deformation. We conclude that the spectrin and microtubule cytoskeletons work in combination to protect axons and dendrites from mechanical stress and propose that defects in β-spectrin and tau may sensitize neurons to damage.

DOI:http://dx.doi.org/10.7554/eLife.20172.001

Patients with Primary Open-Angle Glaucoma May Develop Ischemic Heart Disease More Often than Those without Glaucoma: An 11-Year Population-Based Cohort Study

OBJECTIVES

To investigate whether patients with primary open angle glaucoma (POAG) have a higher proportion of ischemic heart disease (IHD) development.

DESIGN

A population-based retrospective cohort study, using the National Health Insurance Database (NHID) from 1st January, 2001, to 31st December, 2011, in Taiwan.

METHODS

3510 subjects with POAG were enrolled into the POAG group and 14040 subjects without glaucoma into the comparison group. The comparison group consisted of randomly selected individuals, matched with the POAG group based on age, gender, and index date (date of enrollment) at a ratio of 1:4. The participants of both groups should have no IHD before the index date, and they were followed until the end of 2011 to see whether they had new-onset IHD or not. Kaplan-Meier curves were used to compare the cumulative incidence of IHD between the two groups. Frailty model, a specialized form of Cox regression analysis, was used to estimate the crude and adjusted hazard ratio (HR) of IHD. Analyses were adjusted by age, gender, and systemic comorbidities (i.e. diabetes, hypertension, hyperlipidemia, atrial fibrillation and congestive heart failure).

RESULTS

The mean age of the cohort was 57.6±11.0 years. There were slightly more males than females (51.6% vs. 48.4%). A log-rank test comparing Kaplan-Meier curves of the two groups revealed a significantly higher cumulative incidence of IHD in the POAG group (p-value<0.001). In the univariate analysis by Frailty model, POAG patients had a significantly higher hazard of IHD (unadjusted HR = 2.32; 95% confidence interval 1.93 to 2.79). After adjustment, results remained significant (adjusted HR = 1.41; 95% confidence interval 1.16 to 1.72).

CONCLUSION

People with POAG may suffer from IHD more often than those without glaucoma.

Mechanical stress models of Alzheimer's disease pathology

INTRODUCTION

Extracellular accumulation of amyloid-β protein and intracellular accumulation of tau in brain tissues have been described in animal models of Alzheimer's disease (AD) and mechanical stress-based diseases of different mechanisms, such as traumatic brain injury (TBI), arterial hypertension (HTN), and normal pressure hydrocephalus (NPH).

METHODS

We provide a brief overview of experimental models of TBI, HTN, and NPH showing features of tau-amyloid pathology, neuroinflammation, and neuronal loss.

RESULTS

"Alzheimer-like" hallmarks found in these mechanical stress-based models were compared with AD features found in transgenic models.

DISCUSSION

The goal of this review is, therefore, to build on current concepts of onset and progression of AD lesions. We point to the importance of accumulated mechanical stress in brain as an environmental and endogenous factor that pushes protein deposition and neuronal injury over the disease threshold. We further encourage the development of preventing strategies and drug screening based on mechanical stress models.

Mechanical Stress as the Common Denominator between Chronic Inflammation, Cancer, and Alzheimer's Disease

The pathogenesis of common diseases, such as Alzheimer's disease (AD) and cancer, are currently poorly understood. Inflammation is a common risk factor for cancer and AD. Recent data, provided by our group and from others, demonstrate that increased pressure and inflammation are synonymous. There is a continuous increase in pressure from inflammation to fibrosis and then cancer. This is in line with the numerous papers reporting high interstitial pressure in cancer. But most authors focus on the role of pressure in the lack of delivery of chemotherapy in the center of the tumor. Pressure may also be a key factor in carcinogenesis. Increased pressure is responsible for oncogene activation and cytokine secretion. Accumulation of mechanical stress plays a key role in the development of diseases of old age, such as cardiomyopathy, atherosclerosis, and osteoarthritis. Growing evidence suggest also a possible link between mechanical stress in the pathogenesis of AD. The aim of this review is to describe environmental and endogenous mechanical factors possibly playing a pivotal role in the mechanism of chronic inflammation, AD, and cancer.

Autophagy in axonal degeneration in glaucomatous optic neuropathy

The role of autophagy in retinal ganglion cell (RGC) death is still controversial. Several studies focused on RGC body death, although the axonal degeneration pathway in the optic nerve has not been well documented in spite of evidence that the mechanisms of degeneration of neuronal cell bodies and their axons differ. Axonal degeneration of RGCs is a hallmark of glaucoma, and a pattern of localized retinal nerve fiber layer defects in glaucoma patients indicates that axonal degeneration may precede RGC body death in this condition. As models of preceding axonal degeneration, both the tumor necrosis factor (TNF) injection model and hypertensive glaucoma model may be useful in understanding the mechanism of axonal degeneration of RGCs, and the concept of axonal protection can be an attractive approach to the prevention of neurodegenerative optic nerve disease. Since mitochondria play crucial roles in glaucomatous optic neuropathy and can themselves serve as a part of the autophagosome, it seems that mitochondrial function may alter autophagy machinery. Like other neurodegenerative diseases, optic nerve degeneration may exhibit autophagic flux impairment resulting from elevated intraocular pressure, TNF, traumatic injury, ischemia, oxidative stress, and aging. As a model of aging, we used senescence-accelerated mice to provide new insights. In this review, we attempt to describe the relationship between autophagy and recently reported noteworthy factors including Nmnat, ROCK, and SIRT1 in the degeneration of RGCs and their axons and propose possible mechanisms of axonal protection via modulation of autophagy machinery.

The interactions of genes, age, and environment in glaucoma pathogenesis

Glaucoma, a progressive degenerative condition that results in the death of retinal ganglion cells, is one of the leading causes of blindness, affecting millions worldwide. The mechanisms underlying glaucoma are not well understood, although years of studies have shown that the largest risk factors are elevated intraocular pressure, age, and genetics. Eleven genes and multiple loci have been identified as contributing factors. These genes act by a number of mechanisms, including mechanical stress, ischemic/oxidative stress, and neurodegeneration. We summarize the recent advances in the understanding of glaucoma and propose a unified hypothesis for glaucoma pathogenesis. Glaucoma does not result from a single pathological mechanism, but rather a combination of pathways that are influenced by genes, age, and environment. In particular, we hypothesize that, in the presence of genetic risk factors, exposure to environment stresses results in an earlier age of onset for glaucoma. This hypothesis is based upon the overlap of the molecular pathways in which glaucoma genes are involved. Because of the interactions between these processes, it is likely that there are common therapies that may be effective for different subtypes of glaucoma.

The current research status of normal tension glaucoma

Normal tension glaucoma (NTG) is a progressive optic neuropathy that mimics primary open-angle glaucoma, but lacks the findings of elevated intraocular pressure or other mitigating factors that can lead to optic neuropathy. The present review summarized the causes, genetics, and mechanisms underlying NTG in both animal models and human patients. We also proposed that the neurovascular unit is a therapeutic target for NTG management.

Alteration of fractional anisotropy and mean diffusivity in glaucoma: novel results of a meta-analysis of diffusion tensor imaging studies

OBJECTIVES

We hypothesized that a meta-analysis of existing studies may help to reveal significant changes on diffusion tensor imaging (DTI) in patients with glaucoma. Therefore, a meta-analysis was utilized to investigate the possibility that DTI can detect white matter damage in patients with glaucoma.

METHODS

The study design and report adhered to the PRISMA Statement guidelines. DTI studies that compared glaucoma patients and controls were surveyed using PubMed, Web of Science and EMBASE (January 2008 to September 2013). Stata was used to analyze the decrease in fractional anisotropy (FA) and increase in mean diffusivity (MD) in the optic nerve and optic radiation in patients with glaucoma.

RESULTS

Eleven DTI studies were identified through a comprehensive literature search, and 10 independent DTI studies of glaucoma patients were eligible for the meta-analysis. A random effects model revealed a significant FA reduction in the optic nerve and optic radiation, as well as a significant MD increase in the tracts. A heterogeneity analysis suggested that FA may be related to glaucoma severity.

CONCLUSIONS

Our findings revealed that the optic nerve and optic radiation were vulnerable regions in patients with glaucoma and that FA may be correlated with glaucoma severity and age. Furthermore, this study suggests that magnetic resonance imaging in patients with glaucoma may help to provide objective evidence to aid in the diagnosis and management of glaucoma.

Reduced cortical thickness in primary open-angle glaucoma and its relationship to the retinal nerve fiber layer thickness

Objectives

To examine possible changes in cortical thickness and their relationship to retinal nerve fiber layer (RNFL) thickness in patients with primary open-angle glaucoma (POAG).

Materials and Methods

Thirty-six patients with POAG and 40 matched healthy controls were enrolled in this study. All subjects underwent a comprehensive ophthalmologic examination and a high resolution structural magnetic resonance scan. Cortical thickness analysis was used to assess the changes between patients and controls. Correlations between the thickness of the visual cortex and RNFL thickness were also analyzed. Finally, the relationship between the severity of changes in the visual cortex and RNFL thickness was evaluated by comparing patients with mild and severe groups.

Results

POAG patients showed significant bilateral cortical thinning in the anterior half of the visual cortex around the calcarine sulci (left BA 17 and BA 18, right BA17) and in some smaller regions located in the left middle temporal gyrus (BA37) and fusiform gyrus (BA19). The thickness of the visual cortex correlated positively with RNFL thickness (left, r = 0.44, p = 0.01; right, r = 0.38, p = 0.03). Significant differences between mild and severe groups were observed with regard to both RNFL thickness and the thickness of bilateral visual cortex (p < 0.05).

Conclusion

Our findings indicate that cortical thickness analysis may be sufficiently sensitive to detect cortical alterations in POAG and that the measurement has great potential for clinical application.

Brain involvement in glaucoma: advanced neuroimaging for understanding and monitoring a new target for therapy

On the basis of a large body of experimental data the notion that glaucoma damages retinal ganglion cells and central areas of the visual system has been put forward. The mechanisms underlying glaucomatous involvement of the central areas are not known: the most likely hypothesis is that this event is the result of an anterograde transynaptic neurodegeneration triggered by ganglion cells' death. However, it is possible that in some cases it may be the consequence of a neurodegenerative disease of the central nervous system. In any event, novel mechanisms leading to cell demise might be implicated. The development of powerful neuroimaging techniques in conjunction with sophisticated analysis has recently provided compelling support to the involvement of central stations of the visual pathway in patients suffering of glaucoma. Diffusion Tensor-MRI allows the central damage associated with glaucoma to be assessed and therapeutic efficacy of novel neuroprotective interventions to be quantified.

Diffusion tensor magnetic resonance imaging reveals visual pathway damage that correlates with clinical severity in glaucoma

BACKGROUND

To investigate nerve fibre damage of the visual pathway in patients with primary open-angle glaucoma using tract-based spatial statistical analysis of diffusion tensor imaging and correlate these measures with the clinical severity of glaucoma.

DESIGN

Cross-sectional study.

PARTICIPANTS

Twenty-five individuals with primary open-angle glaucoma and 24 healthy controls were recruited.

METHODS

All subjects underwent detailed ophthalmological examinations, including the cup-to-disc ratio, retinal nerve fibre layer thickness and visual fields test. Diffusion tensor imaging of the visual pathway was performed using a 3.0-T magnetic resonance scanner.

MAIN OUTCOME MEASURES

Diffusivity changes of the nerve fibres in the visual pathway were calculated through tract-based spatial statistical analysis. The mean diffusivity and fractional anisotropy were assessed and compared with ophthalmological measurements.

RESULTS

Compared with controls, bilateral optic tracts and optic radiations in primary open-angle glaucoma patients showed significantly decreased fractional anisotropy and increased mean diffusivity (P < 0.05). In the glaucoma group, the fractional anisotropy of the optic tracts and optic radiations varied consistently with the cup-to-disc ratio, retinal nerve fibre layer thickness and visual function analysis, respectively (P < 0.05). The mean diffusivity of the optic tracts correlated with these ophthalmological measurements (P < 0.05). However, no significant correlation was observed between the mean diffusivity of the optic radiations and the ophthalmological measurements (P > 0.05).

CONCLUSIONS

The optic tracts and optic radiations of primary open-angle glaucoma patients demonstrated radiological evidence of neurodegeneration. This varied with damage to the optic disc and with the loss of visual function. Tract-based spatial statistical analysis of diffusion tensor imaging is an objective and effective tool for detecting the loss of cortical nerve fibres in primary open-angle glaucoma.

Glaucoma and Alzheimer’s disease in the elderly

Primary open angle glaucoma and Alzheimer’s disease have long been established as two separate pathological entities, primarily affecting the elderly. The progressive, irreversible course of both diseases has significant implications on an aging population. As the complex pathophysiology of the two diseases has progressively unraveled over the past two decades, common pathophysiological changes have also been elucidated. Some of these mechanisms have established a strong grounding, whilst others remain principally speculative. The mutual neuropathological changes in primary open angle glaucoma and Alzheimer’s disease have facilitated the development of neuroprotective strategies. While most of these strategies are still in the preclinical phase, they have shown great promise in experimental animal studies. Further understanding of the common pathophysiology of primary open angle glaucoma and Alzheimer’s disease and their timeline may have great implications on early diagnosis and effective therapeutic targeting.