85 research outputs found
Retinal biomarkers of Alzheimer’s disease: insights from transgenic mouse models
In this paper, we use the retina as a window into the central nervous system and in particular to assess changes in the retinal tissue associated with the Alzheimer’s disease. We imaged the retina of wild-type (WT) and transgenic mouse model (TMM) of Alzheimer’s disease with optical coherence tomography and classify retinas into the WT and TMM groups using support vector machines with the radial basis function kernel. Predictions reached an accuracy over 80% at the age of 4 months and over 90% at the age of 8 months. Texture analysis of computed fundus reference images suggests a more heterogeneous organization of the retina in transgenic mice at the age of 8 months in comparison to controls.This study was supported by the Neuroscience Mantero Belard Prize 2015 (Santa
Casa da Misericórdia)(MB-1049-2015), by The Portuguese Foundation for Science
and Technology (PEst-UID/NEU/04539/2013), by FEDER-COMPETE
(POCI-01-0145-FEDER-007440) and Centro 2020 Regional Operational Programme
(CENTRO-01-0145-FEDER-000008: BrainHealth 2020).info:eu-repo/semantics/publishedVersio
Disruption of a neural microcircuit in the rod pathway of the mammalian retina by diabetes mellitus
Diabetes leads to dysfunction of the neural retina before and independent of classical microvascular diabetic retinopathy, but previous studies have failed to demonstrate which neurons and circuits are affected at the earliest stages. Here, using patch-clamp recording and two-photon Ca2+ imaging in rat retinal slices, we investigated diabetes-evoked changes in a microcircuit consisting of rod bipolar cells and their dyad postsynaptic targets, AII and A17 amacrine cells, which play an essential role in processing scotopic visual signals. AII amacrines forward their signals to ON- and OFF-cone bipolar cells and A17 amacrines provide GABAergic feedback inhibition to rod bipolar cells. Whereas Ca2+-permeable AMPA receptors mediate input from rod bipolar cells to both AII and A17 amacrines, diabetes changes the synaptic receptors on A17, but not AII amacrine cells. This was expressed as a change in pharmacological properties and single-channel conductance of the synaptic receptors, consistent with an upregulation of the AMPA receptor GluA2 subunit and reduced Ca2+ permeability. In addition, two-photon imaging revealed reduced agonist-evoked influx of Ca2+ in dendritic varicosities of A17 amacrine cells from diabetic compared with normal animals. Because Ca2+-permeable receptors in A17 amacrine cells mediate synaptic release of GABA, the reduced Ca2+ permeability of these receptors in diabetic animals leads to reduced release of GABA, followed by disinhibition and increased release of glutamate from rod bipolar cells. This perturbation of neuron and microcircuit dynamics can explain the decreased dynamic range and sensitivity of scotopic vision that has been observed in diabetes.publishedVersio
Diabetic hyperglycemia reduces Ca2+ permeability of extrasynaptic AMPA receptors in AII amacrine cells
There is increasing evidence that diabetic retinopathy is a primary neuropathological disorder that precedes the microvascular pathology associated with later stages of the disease. Recently, we found evidence for altered functional properties of synaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in A17, but not AII, amacrine cells in the mammalian retina, and the observed changes were consistent with an upregulation of the GluA2 subunit, a key determinant of functional properties of AMPA receptors, including Ca2+ permeability and current-voltage (I-V) rectification properties. Here, we have investigated functional changes of extrasynaptic AMPA receptors in AII amacrine cells evoked by diabetes. With patch-clamp recording of nucleated patches from retinal slices, we measured Ca2+ permeability and I–V rectification in rats with ∼3 wk of streptozotocin-induced diabetes and age-matched, noninjected controls. Under bi-ionic conditions (extracellular Ca2+ concentration = 30 mM, intracellular Cs+ concentration = 171 mM), the reversal potential (Erev) of AMPA-evoked currents indicated a significant reduction of Ca2+ permeability in diabetic animals [Erev = −17.7 mV, relative permeability of Ca2+ compared with Cs+ (PCa/PCs) = 1.39] compared with normal animals (Erev = −7.7 mV, PCa/PCs = 2.35). Insulin treatment prevented the reduction of Ca2+ permeability. I–V rectification was examined by calculating a rectification index (RI) as the ratio of the AMPA-evoked conductance at +40 and −60 mV. The degree of inward rectification in patches from diabetic animals (RI = 0.48) was significantly reduced compared with that in normal animals (RI = 0.30). These results suggest that diabetes evokes a change in the functional properties of extrasynaptic AMPA receptors of AII amacrine cells. These changes could be representative for extrasynaptic AMPA receptors elsewhere in AII amacrine cells and suggest that synaptic and extrasynaptic AMPA receptors are differentially regulated.acceptedVersio
Diabetes changes ionotropic glutamate receptor subunit expression level in the human retina
Early diabetic retinopathy is characterized by changes in subtle visual functions such as contrast sensitivity and dark adaptation. The outcome of several studies suggests that glutamate is involved in retinal neurodegeneration during diabetes. We hypothesized that the protein levels of ionotropic glutamate receptor subunits are altered in the retina during diabetes. Therefore, we investigated whether human diabetic patients have altered immunoreactivity of ionotropic glutamate receptor subunits in the retina.http://www.sciencedirect.com/science/article/B6SYR-4RS9SS1-1/1/232d6ae7147919a2286326863ee69f1
Elevated glucose changes the expression of ionotropic glutamate receptor subunits and impairs calcium homeostasis in retinal neural cells
PURPOSE. Altered glutamatergic neurotransmission and calcium
homeostasis may contribute to retinal neural cell dysfunction
and apoptosis in diabetic retinopathy (DR). The purpose of this
study was to determine the effect of high glucose on the
protein content of -amino-3-hydroxy-5-methylisoxazole-4-propionic
acid (AMPA) and kainate glutamate receptor subunits,
particularly the GluR2 subunit, because it controls Ca2 permeability
of AMPA receptor-associated channels. The effect of
high glucose on the concentration of cytosolic free calcium
([Ca2 ]i) was also investigated.
METHODS. The protein content of GluR1, GluR2, GluR6/7, and
KA2 subunits was assessed by Western blot. Cobalt staining
was used to identify cells containing calcium/cobalt-permeable
AMPA receptors. The [Ca2 ]i changes evoked by KCl or kainate
were recorded by live-cell confocal microscopy in R28
cells and in primary cultures of rat retina, loaded with fluo-4.
RESULTS. In primary cultures, high glucose significantly decreased
the protein content of GluR1 and GluR6/7 subunits
and increased the protein content of GluR2 and KA2 subunits.
High glucose decreased the number of cobalt-positive cells,
suggesting a decrease in calcium permeability through AMPA
receptor-associated channels. In high-glucose–treated cells,
changes in [Ca2 ]i were greater than in control cells, and the
recovery to basal levels was delayed. However, in the absence
of Na , to prevent the activation of voltage-sensitive calcium
channels, the [Ca2 ]i changes evoked by kainate in the presence
of cyclothiazide, which inhibits AMPA receptor desensitization,
were significantly lower in high-glucose–treated cells
than in control cultures, further indicating that AMPA receptors
were less permeable to calcium. Mannitol, used as an
osmotic control, did not cause significant changes compared
with the control.
CONCLUSIONS. The results suggest that elevated glucose may
alter glutamate neurotransmission and calcium homeostasis in
the retina, which may have implications for the mechanisms of
vision loss in DR.Foundation for Science and Technology, Portugal and FEDER (Grant POCTI/CBO/38545/01), The Juvenile Diabetes Research Foundation, The American Diabetes Association and the Pennsylvania Lions Sight Conservation and Eye Eye Research Foundation
Longitudinal normative OCT retinal thickness data for wild-type mice, and characterization of changes in the 3×Tg-AD mice model of Alzheimer's disease
Mice are widely used as models for many diseases, including eye and neurodegenerative diseases. However, there is a lack of normative data for retinal thickness over time, especially at young ages. In this work, we present a normative thickness database from one to four-months-old, for nine layers/layer-aggregates, including the total retinal thickness, obtained from the segmentation of spectral-domain optical coherence tomography (SD-OCT) data from the C57BL6/129S mouse strain. Based on fifty-seven mice, this normative database provides an opportunity to study the ageing of control mice and characterize disease models' ageing, such as the triple transgenic mouse model of Alzheimer's disease (3×Tg-AD) used in this work. We report thickness measurements, the differences in thickness per layer, demonstrate a nasal-temporal asymmetry, and the variation of thickness as a function to the distance to the optic disc center. Significant differences were found between the transgenic group's thickness and the normative database for the entire period covered in this study. Even though it is well accepted that retinal nerve fiber layer (RNFL) thinning is a hallmark of neurodegeneration, our results show a thicker RNFL-GCL (RNFL-Ganglion cell layer) aggregate for the 3×Tg-AD mice until four-months-old.This study was supported by The Portuguese Foundation for Science and Technology (FCT) through PTDC/ EMD-EMD/28039/2017, UIDB/04950/2020, Pest-UID/ NEU/04539/2019, and by FEDER-COMPETE through POCI-01-0145-FEDER-028039.info:eu-repo/semantics/publishedVersio
Diabetes changes the levels of ionotropic glutamate receptors in the rat retina
Purpose: Diabetic retinopathy (DR) is a leading cause of vision loss and blindness among adults between the age 20 to
74. Changes in ionotropic glutamate receptor subunit composition can affect retinal glutamatergic neurotransmission and,
therefore, contribute to visual impairment. The purpose of this study was to investigate whether diabetes leads to changes
in ionotropic glutamate receptor subunit expression at the protein and mRNA level in the rat retina.
Methods: Changes in the expression of ionotropic glutamate receptor subunits were investigated at the mRNA and protein
levels in retinas of streptozotocin (STZ)-induced diabetic and age-matched control rats. Animals were euthanized one,
four and 12 weeks after the onset of diabetes. Retinal protein extracts were prepared, and the receptor subunit levels were
assessed by western blotting. Transcript levels were assessed by real-time quantitative PCR.
Results: Transcript levels of most ionotropic glutamate receptor subunits were not significantly changed in the retinas of
diabetic rats, as compared to age-matched controls but protein levels of α-amino-3-hydroxyl-5-methyl-4-isoxazole-
propionate (AMPA), kainate, and N-methyl-D-aspartic acid receptors (NMDA) receptors were found to be altered.
Conclusions: The results provide evidence that diabetes affects the retinal content of ionotropic glutamate receptor
subunits at the protein level. The possible implications of these changes on retinal physiology and visual impairment in
DR are discusse
Having a Coffee Break: The Impact of Caffeine Consumption on Microglia-Mediated Inflammation in Neurodegenerative Diseases
Caffeine is the major component of coffee and the most consumed psychostimulant in the world and at nontoxic doses acts as a nonselective adenosine receptor antagonist. Epidemiological evidence suggests that caffeine consumption reduces the risk of several neurological and neurodegenerative diseases. However, despite the beneficial effects of caffeine consumption in human health and behaviour, the mechanisms by which it impacts the pathophysiology of neurodegenerative diseases still remain to be clarified. A promising hypothesis is that caffeine controls microglia-mediated neuroinflammatory response associated with the majority of neurodegenerative conditions. Accordingly, it has been already described that the modulation of adenosine receptors, namely, the A2A receptor, affords neuroprotection through the control of microglia reactivity and neuroinflammation. In this review, we will summarize the main effects of caffeine in the modulation of neuroinflammation in neurodegenerative diseases
Sweet Stress: Coping With Vascular Dysfunction in Diabetic Retinopathy
Oxidative stress plays key roles in the pathogenesis of retinal diseases, such as diabetic retinopathy. Reactive oxygen species (ROS) are increased in the retina in diabetes and the antioxidant defense system is also compromised. Increased ROS stimulate the release of pro-inflammatory cytokines, promoting a chronic low-grade inflammation involving various signaling pathways. An excessive production of ROS can lead to retinal endothelial cell injury, increased microvascular permeability, and recruitment of inflammatory cells at the site of inflammation. Recent studies have started unraveling the complex crosstalk between retinal endothelial cells and neuroglial cells or leukocytes, via both cell-to-cell contact and secretion of cytokines. This crosstalk is essential for the maintenance of the integrity of retinal vascular structure. Under diabetic conditions, an aberrant interaction between endothelial cells and other resident cells of the retina or invading inflammatory cells takes place in the retina. Impairment in the secretion and flow of molecular signals between different cells can compromise the retinal vascular architecture and trigger angiogenesis. In this review, the synergistic contributions of redox-inflammatory processes for endothelial dysfunction in diabetic retinopathy will be examined, with particular attention paid to endothelial cell communication with other retinal cells
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