Retinal glial cell immunoreactivity and neuronal cell changes in rats with STZ-induced diabetes

Manifestation of Pathology in Animal Models of Diabetic Retinopathy Is Delayed from the Onset of Diabetes

Diabetic retinopathy (DR) is the most common complication that develops in patients with diabetes mellitus (DM) and is the leading cause of blindness worldwide. Fortunately, sight-threatening forms of DR develop only after several decades of DM. This well-documented resilience to DR suggests that the retina is capable of protecting itself from DM-related damage and also that accumulation of such damage occurs only after deterioration of this resilience. Despite the enormous translational significance of this phenomenon, very little is known regarding the nature of resilience to DR. Rodent models of DR have been used extensively to study the nature of the DM-induced damage, i.e., cardinal features of DR. Many of these same animal models can be used to investigate resilience because DR is delayed from the onset of DM by several weeks or months. The purpose of this review is to provide a comprehensive overview of the literature describing the use of rodent models of DR in type-1 and type-2 diabetic animals, which most clearly document the delay between the onset of DM and the appearance of DR. These readily available experimental settings can be used to advance our current understanding of resilience to DR and thereby identify biomarkers and targets for novel, prevention-based approaches to manage patients at risk for developing DR.

Local modulation of thyroid hormone signaling in the retina affects the development of diabetic retinopathy

Thyroid hormone (TH) dyshomeostasis is associated with poor prognosis in acute and prolonged illness, but its role in diabetic retinopathy (DR) has never been investigated. Here, we characterized the TH system in the retinas of db/db mice and highlighted regulatory processes in MIO-M1 cells. In the db/db retinas, typical functional traits and molecular signatures of DR were paralleled by a tissue-restricted reduction of TH levels. A local condition of low T3 (LT3S) was also demonstrated, which was likely to be induced by deiodinase 3 (DIO3) upregulation, and by decreased expression of DIO2 and of TH receptors. Concurrently, T3-responsive genes, including mitochondrial markers and microRNAs (miR-133-3p, 338-3p and 29c-3p), were downregulated. In MIO-M1 cells, a feedback regulatory circuit was evidenced whereby miR-133-3p triggered the post-transcriptional repression of DIO3 in a T3-dependent manner, while high glucose (HG) led to DIO3 upregulation through a nuclear factor erythroid 2-related factor 2-hypoxia-inducible factor-1 pathway. Finally, an in vitro simulated condition of early LT3S and hyperglycemia correlated with reduced markers of both mitochondrial function and stress response, which was reverted by T3 replacement. Together, the data suggest that, in the early phases of DR, a DIO3-driven LT3S may be protective against retinal stress, while, in the chronic phase, it not only fails to limit HG-induced damage, but also increases cell vulnerability likely due to persistent mitochondrial dysfunction.

Microstructure abnormity in the optic nerve of type 1 diabetic rats revealed by diffusion tensor imaging study

Diabetic retinopathy (DR) is one of a major complication of type 1 diabetes mellitus (T1DM) and a leading cause of blindness. Evidence of animal study has shown that it is not only a microvasucular lesion of the eye, but also a neurodegeneration disease of the visual system. However, the in vivo imaging evidence of axonal degeneration in the diabetic optic nerve is scarce. Diffusion tensor imaging (DTI) technique has been proved to be an effective tool to track the integrity of the nerve fibers in the central nervous system. In this study, type 1 diabetes was induced by intraperitoneally injecting a single dose of streptozotocin (STZ) into Sprague-Dawley rats. DTI combined with histological assessments was carried out on the optic nerve to clarify the microstructural alterations underlying DTI indices changes at 4 weeks (4 w), 8 weeks (8 w) and 12 weeks (12 w) after STZ induction. The retinal changes were analyzed by pathological evaluations at 4 weeks (4 w) and 12 weeks (12 w) after STZ induction. DTI results showed significantly decreased mean diffusivity (MD) and axial diffusivity (Da) in diabetic optic nerve compared to controls at 12 w. Atrophy in diabetic nerves was monitored by high resolution T₂-weighted images. Axonal degeneration without myelin loss of the optic nerve was confirmed by histological examination. Moreover, there are positive correlations between decreased diffusivities (MD and Da) in the optic nerve and reduced total axolemmal area. The diabetic rats showed intense glial activity since 4 w and thinning of the thickness in inner plexiform layer and nerve fiber layer at 12 w in the retina. In conclusion, DTI could in vivo monitor the progression of optic nerve degeneration in diabetes and the findings in our study would help supply axonal protection for DR in preclinical practice.

Time-dependent changes in hypoxia- and gliosis-related factors in experimental diabetic retinopathy

Diabetes causes various biochemical changes in the retina; long-term changes in the factors associated with hypoxia and gliosis have rarely been reported. The present study was conducted to explore the changes in these factors in a time-dependent manner in experimental diabetic retinopathy (DR). Diabetes was induced in Sprague-Dawley rats by intraperitoneal injection of streptozotocin. The expression of the following factors was examined using immunofluorescence and western blot analysis at 0.5, 1, 2, 4 and 6 months after diabetes onset: hypoxia-inducible factor-1alpha (HIF-1alpha), vascular endothelial growth factor (VEGF), erythropoietin (EPO), erythropoietin receptor (EPOR), glial fibrillary acidic protein (GFAP), vimentin, glutamate-aspartate transporter (GLAST) and glutamine synthase (GS). The expression of factors such as HIF-1alpha, VEGF, EPO, EPOR, GFAP and vimentin, was up-regulated with the progression of diabetes in the diabetic rat retinas compared to the expression in normal control retinas, whereas the expression of GS and GLAST was down-regulated. Changes in EPO and EPOR appeared 2 weeks after diabetes onset. HIF-1alpha, VEGF and GFAP started to increase at 1 month and vimentin at 4 months after diabetes onset. GS and GLAST started to decrease at 1 month after diabetes onset. The expression of these factors, which are involved in the processes of hypoxia and gliosis, varied at different stages of DR. The time-course change may be helpful in the evaluation of the progression of DR, and it may indicate the optimal intervention time points for DR.

One month of hyperglycemia alters spectral responses of the zebrafish photopic electroretinogram

Prolonged hyperglycemia can alter retinal function, ultimately resulting in blindness. Adult zebrafish adults exposed to alternating conditions of 2% glucose/0% glucose display a 3× increase in blood sugar levels. After 4 weeks of treatment, electroretinograms (ERGs) were recorded from isolated, perfused, in vitro eyecups. Control animals were exposed to alternating 2% mannitol/0% mannitol (osmotic control) or to alternating water (0% glucose/0% glucose; handling control). Two types of ERGs were recorded: (1) native ERGs measured using white-light stimuli and medium without synaptic blockers; and (2) spectral ERGs measured with an AMPA/kainate receptor antagonist, isolating photoreceptor-to-ON-bipolar-cell synapses, and a spectral protocol that separated red (R), green (G), blue (B) and UV cone signals. Retinas were evaluated for changes in layer thickness and for the inflammatory markers GFAP and Nf-κB (RelA or p65). In native ERGs, hyperglycemic b- and d-waves were lower in amplitude than the b- and d-waves of mannitol controls. Alteration of waveshape became severe, with b-waves becoming more transient and ERG responses showing more PIII-like (a-wave) characteristics. For spectral ERGs, waveshape appeared similar in all treatment groups. However, a1- and b2-wave implicit times were significantly longer, and amplitudes were significantly reduced, in response to hyperglycemic treatment, owing to the functional reduction in signals from R, G and B cones. Nf-κB increased significantly in hyperglycemic retinas, but the increase in GFAP was not significant and retinal layer thickness was unaffected. Thus, prolonged hyperglycemia triggers an inflammatory response and functional deficits localized to specific cone types, indicating the rapid onset of neural complications in the zebrafish model of diabetic retinopathy.

Summary: Zebrafish can be used to examine diabetic complications, including vision loss. Here, in zebrafish, we show that prolonged (4 week) hyperglycemia causes an inflammatory response associated with functional deficits localized to specific cone types.

Study of retinal neurodegeneration and maculopathy in diabetic Meriones shawi: A particular animal model with human-like macula

The purpose of this work was to evaluate a potentially useful animal model, Meriones shawi (M.sh)-developing metabolic X syndrome, diabetes and possessing a visual streak similar to human macula-in the study of diabetic retinopathy and diabetic macular edema (DME). Type 2 diabetes (T2D) was induced by high fat diet administration in M.sh. Body weights, blood glucose levels were monitored throughout the study. Diabetic retinal histopathology was evaluated 3 and 7 months after diabetes induction. Retinal thickness was measured, retinal cell types were labeled by immunohistochemistry and the number of stained elements were quantified. Apoptosis was determined with TUNEL assay. T2D induced progressive changes in retinal histology. A significant decrease of retinal thickness and glial reactivity was observed without an increase in apoptosis rate. Photoreceptor outer segment degeneration was evident, with a significant decrease in the number of all cones and M-cone subtype, but-surprisingly-an increase in S-cones. Damage of the pigment epithelium was also confirmed. A decrease in the number and labeling intensity of parvalbumin- and calretinin-positive amacrine cells and a loss of ganglion cells was detected. Other cell types showed no evident alterations. No DME-like condition was noticed even after 7 months. M.sh could be a useful model to study the evolution of diabetic retinal pathology and to identify the role of hypertension and dyslipidemia in the development of the reported alterations. Longer follow up would be needed to evaluate the potential use of the visual streak in modeling human macular diseases.

Chronic insulin treatment of diabetes does not fully normalize alterations in the retinal transcriptome

Background

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. Approximately 95% of patients with Type 1 diabetes develop some degree of retinopathy within 25 years of diagnosis despite normalization of blood glucose by insulin therapy. The goal of this study was to identify molecular changes in the rodent retina induced by diabetes that are not normalized by insulin replacement and restoration of euglycemia.

Methods

The retina transcriptome (22,523 genes and transcript variants) was examined after three months of streptozotocin-induced diabetes in male Sprague Dawley rats with and without insulin replacement for the later one and a half months of diabetes. Selected gene expression changes were confirmed by qPCR, and also examined in independent control and diabetic rats at a one month time-point.

Results

Transcriptomic alterations in response to diabetes (1376 probes) were clustered according to insulin responsiveness. More than half (57%) of diabetes-induced mRNA changes (789 probes) observed at three months were fully normalized to control levels with insulin therapy, while 37% of probes (514) were only partially normalized. A small set of genes (5%, 65 probes) was significantly dysregulated in the insulin-treated diabetic rats. qPCR confirmation of findings and examination of a one month time point allowed genes to be further categorized as prevented or rescued with insulin therapy. A subset of genes (Ccr5, Jak3, Litaf) was confirmed at the level of protein expression, with protein levels recapitulating changes in mRNA expression.

Conclusions

These results provide the first genome-wide examination of the effects of insulin therapy on retinal gene expression changes with diabetes. While insulin clearly normalizes the majority of genes dysregulated in response to diabetes, a number of genes related to inflammatory processes, microvascular integrity, and neuronal function are still altered in expression in euglycemic diabetic rats. Gene expression changes not rescued or prevented by insulin treatment may be critical to the pathogenesis of diabetic retinopathy, as it occurs in diabetic patients receiving insulin replacement, and are prototypical of metabolic memory.

Müller glial dysfunction during diabetic retinopathy in rats is linked to accumulation of advanced glycation end-products and advanced lipoxidation end-products

AIMS/HYPOTHESIS

The impact of AGEs and advanced lipoxidation end-products (ALEs) on neuronal and Müller glial dysfunction in the diabetic retina is not well understood. We therefore sought to identify dysfunction of the retinal Müller glia during diabetes and to determine whether inhibition of AGEs/ALEs can prevent it.

METHODS

Sprague-Dawley rats were divided into three groups: (1) non-diabetic; (2) untreated streptozotocin-induced diabetic; and (3) diabetic treated with the AGE/ALE inhibitor pyridoxamine for the duration of diabetes. Rats were killed and their retinas were evaluated for neuroglial pathology.

RESULTS

AGEs and ALEs accumulated at higher levels in diabetic retinas than in controls (p < 0.001). AGE/ALE immunoreactivity was significantly diminished by pyridoxamine treatment of diabetic rats. Diabetes was also associated with the up-regulation of the oxidative stress marker haemoxygenase-1 and the induction of glial fibrillary acidic protein production in Müller glia (p < 0.001). Pyridoxamine treatment of diabetic rats had a significant beneficial effect on both variables (p < 0.001). Diabetes also significantly altered the normal localisation of the potassium inwardly rectifying channel Kir4.1 and the water channel aquaporin 4 to the Müller glia end-feet interacting with retinal capillaries. These abnormalities were prevented by pyridoxamine treatment.

CONCLUSIONS/INTERPRETATION

While it is established that AGE/ALE formation in the retina during diabetes is linked to microvascular dysfunction, this study suggests that these pathogenic adducts also play a role in Müller glial dysfunction.

Diabetic eNOS-knockout mice develop accelerated retinopathy

PURPOSE

Dysfunction of endothelial nitric oxide synthase (eNOS) has been implicated in the pathogenesis of diabetic vascular complications. This study was undertaken to determine the role of eNOS in the development of diabetic retinopathy (DR), by investigating the functional consequences of its deficiency in the diabetic state.

METHODS

Diabetes was induced in eNOS-knockout (eNOS(-/-)) and C57B/6 mice by streptozotocin (STZ) injection. Retinal vasculature was evaluated by albumin extravasation, to quantitatively measure vascular permeability, and by trypsin-digested retinal vascular preparations, to quantify acellular capillaries. Gliosis was evaluated by immunofluorescent techniques. Retinal capillary basement membrane thickness was assessed by transmission electron microscopy. Total retinal nitric oxide level was assessed by measuring nitrate/nitrite using a fluorometric-based assay, iNOS expression was examined by real-time PCR.

RESULTS

Diabetic eNOS(-/-) mice exhibit more severe retinal vascular permeability than age-matched diabetic C57BL/6 mice, detectable as early as 3 weeks after diabetes induction. Diabetic eNOS(-/-) mice also show earlier onset and an increased number of acellular capillaries, sustained gliosis, and increased capillary basement membrane thickness. Total nitric oxide (NO) level was also increased, concomitant with elevated iNOS expression in diabetic eNOS(-/-) retina.

CONCLUSIONS

Diabetic eNOS(-/-) mice exhibit A significantly wider range of advanced retinal vascular complications than the age-matched diabetic C57BL/6 mice, supporting the notion that eNOS-derived NO plays an essential role in retinal vascular function. This mouse model also faithfully replicates many of the hallmarks of vascular changes associated with human retinopathy, thus providing a unique model to aid in understanding the pathologic mechanisms of and to develop effective therapeutic strategies for diabetic retinopathy.

Juxtacellular labeling of tonically active neurons and phasically active neurons in the rat striatum

Tonically active neurons (TANs) and phasically active neurons (PANs) are widely believed to be the cholinergic interneurons and GABAergic projection neurons, respectively, in the striatum based on in vivo intracellular recordings coupled with morphological examinations of anesthetized rats, and on histochemical, electrophysiological, and labeling studies of in vitro slice preparations. TANs of alert behaving animals exhibit prolonged pause responses to behaviorally significant events. PANs, on the other hand, are mostly inactive when subjects are quiet and not performing any actions, but exhibit burst discharges in response to external stimuli and/or voluntary actions. Several other types of interneurons have also been identified in the striatum, such as parvalbumin-containing GABAergic interneurons (fast-spiking cells), somatostatin-containing interneurons, and calretinin-containing interneurons. To identify the neurochemical and morphological characteristics of TANs and PANs in a more direct manner, we conducted juxtacellular labeling, combining electrophysiology with immunohistochemistry and morphology in anesthetized rats. All of the juxtacellularly labeled TANs (n=3) among those recorded (n=10) were ChAT-positive and had large cell somata with aspiny dendrites. Thus, although our observations are based on a limited number of neurons, our findings provide the most convincing evidence to date that TANs in the striatum are cholinergic neurons. We also found that the majority of PANs are GABA-immunoreactive (46 of 48 tested) and approximately two-thirds had spiny dendrites (30 of 48 tested), indicating that the majority are medium-sized, spiny, GABAergic projection neurons, consistent with general beliefs. Conversely, the remaining one-third of PANs had aspiny dendrites (n=18), indicating that they were interneurons. Therefore, the present study reveals that TANs are cholinergic neurons and that the majority of PANs are medium-sized, spiny, GABAergic projection neurons, while a smaller number are GABAergic interneurons.

Contributions of inflammatory processes to the development of the early stages of diabetic retinopathy

Diabetes causes metabolic and physiologic abnormalities in the retina, and these changes suggest a role for inflammation in the development of diabetic retinopathy. These changes include upregulation of iNOS, COX-2, ICAM-1, caspase 1, VEGF, and NF-κB, increased production of nitric oxide, prostaglandin E2, IL-1β, and cytokines, as well as increased permeability and leukostasis. Using selective pharmacologic inhibitors or genetically modified animals, an increasing number of therapeutic approaches have been identified that significantly inhibit development of at least the early stages of diabetic retinopathy, especially occlusion and degeneration of retinal capillaries. A common feature of a number of these therapies is that they inhibit production of inflammatory mediators. The concept that localized inflammatory processes play a role in the development of diabetic retinopathy is relatively new, but evidence that supports the hypothesis is accumulating rapidly. This new hypothesis offers new insight into the pathogenesis of diabetic retinopathy, and offers novel targets to inhibit the ocular disease.

Early electroretinographic features of streptozotocin-induced diabetic retinopathy

BACKGROUND

This study set out to document the early electrophysiological and immunohistochemical changes that occur in the retina of experimentally induced diabetic rats.

METHODS

Diabetes was induced in rats by intraperitoneal injection of 60 mg/kg of streptozotocin (STZ). Electroretinogram readings were taken monthly under either short-duration or long-duration stimuli for up to 3 months after STZ. Oscillatory potentials (OP) and the amplitudes and implicit times of a- and b-waves were analysed, and b-wave amplitudes were analysed using a Naka-Rushton fit. Scotopic a-waves were analysed with photoreceptor models, and Rmp3 (the maximum a-wave amplitude) and S (sensitivity) were calculated. Three months after STZ injection, immunohistochemistry for glial fibrillary acidic protein was performed on the retinas of the STZ-treated rats and age-matched controls.

RESULTS

The implicit OP times were significantly longer in the diabetic rats as compared with the controls, and this difference was noted as early as 1 month following STZ treatment. Other electrophysiological parameters, such as OP amplitudes, a- and b-wave amplitude as well as the implicit times, did not differ from controls at this stage. The sacrificed STZ-treated rats also demonstrated marked enhancement of glial fibrillary acidic protein immunoreactivity, suggesting that at least in experimentally induced diabetic retinopathy there is increased Müller cell reactivity.

CONCLUSION

The results of this study indicated that functional alterations in the retina develop rapidly after the onset of diabetes. Analysis of each electroretinogram component may be useful in further investigating the development mechanisms of diabetic retinopathy.

Lower somatostatin expression is an early event in diabetic retinopathy and is associated with retinal neurodegeneration

OBJECTIVE

To test the hypothesis that a reduction of somatostatin (SST) in the retina exists in patients without clinically detectable diabetic retinopathy and that it is associated with retinal neurodegeneration.

RESEARCH DESIGN AND METHODS

Human diabetic postmortem eyes (n = 10) without clinically detectable retinopathy were compared with eyes (n = 10) from nondiabetic donors. SST mRNA (RT-PCR) and SST-28 immunoreactivity (confocal laser) were measured separately in neuroretina and retinal pigment epithelium (RPE). In addition, SST-28 (radioimmunoassay) was measured in the vitreous fluid. Glial fibrillar acidic protein (GFAP) was assessed by immunofluorescence and Western blot. Apoptotic cells were quantified using transferase-mediated dUTP nick-end labeling.

RESULTS

A higher expression of SST was detected in RPE than neuroretina in both groups. SST mRNA levels and SST-28 immunoreactivity were significantly lower in both RPE and the neuroretina from diabetic donors compared with nondiabetic donors. These results were in agreement with those obtained by measuring SST-28 in the vitreous fluid of the same donors. Increased GFAP and a higher degree of apoptosis were observed in diabetic retinas compared with nondiabetic retinas. These changes were most evident in patients with the higher deficit of SST.

CONCLUSIONS

Underproduction of SST is an early event in the eyes of diabetic patients and is associated with glial activation and neural death. In addition, our results suggest that RPE is an important source of SST in the human eye. The possible role of the lower production of SST in the pathogenesis of diabetic retinopathy requires further investigation.

Critical role of inducible nitric oxide synthase in degeneration of retinal capillaries in mice with streptozotocin-induced diabetes

AIMS/HYPOTHESIS

Diabetes results in the upregulation of the production of several components of the inflammatory response in the retina, including inducible nitric oxide synthase (iNOS). The aim of this study was to investigate the role of iNOS in the pathogenesis of the early stages of diabetic retinopathy using iNOS-deficient mice (iNos (-/-)).

MATERIALS AND METHODS

iNos (-/-) mice and wild-type (WT; C57BL/6J) mice were made diabetic with streptozotocin or kept as non-diabetic controls. Mice were killed at different time points after the induction of diabetes for assessment of vascular histopathology, cell loss in the ganglion cell layer (GCL), retinal thickness, and biochemical and physiological abnormalities.

RESULTS

The concentrations of nitric oxide, nitration of proteins, poly(ADP-ribose) (PAR)-modified proteins, endothelial nitric oxide synthase, prostaglandin E(2), superoxide and leucostasis were significantly (p < 0.05) increased in retinas of WT mice diabetic for 2 months compared with non-diabetic WT mice. All of these abnormalities except PAR-modified proteins in retinas were inhibited (p < 0.05) in diabetic iNos (-/-) mice. The number of acellular capillaries and pericyte ghosts was significantly increased in retinas from WT mice diabetic for 9 months compared with non-diabetic WT controls, these increases being significantly inhibited in diabetic iNos (-/-) mice (p < 0.05 for all). Retinas from WT diabetic mice were significantly thinner than those from their non-diabetic controls, whereas diabetic iNos (-/-) mice were protected from this abnormality. We found no evidence of cell loss in the GCL of diabetic WT or iNos (-/-) mice. Deletion of iNos had no beneficial effect on diabetes-induced abnormalities on the electroretinogram.

CONCLUSIONS/INTERPRETATION

We demonstrate that the inflammatory enzyme iNOS plays an important role in the pathogenesis of vascular lesions characteristic of the early stages of diabetic retinopathy in mice.

Microglial changes occur without neural cell death in diabetic retinopathy

Very early neuroglial changes have been observed to precede major vascular changes in the retina of diabetic patients and animal models. We investigated the sequence of these neuroglial changes further, in mice with alloxan-induced diabetes. Diabetes was induced by a single injection of Alloxan into C57/Bl6 mice, which subsequently received daily insulin injections. Diabetic and control animals were weighed and their blood glucose levels were determined weekly. Electroretinographic recordings and scanner laser ophthalmoscope (SLO) examinations were carried out 15 days, one month and three months after the onset of diabetes. Diabetes induction was confirmed by the presence of glucose in the urine, a tripling of blood glucose level, weight loss and an increase in glycated haemoglobin levels. Three months after diabetes onset, the electroretinogram b/a wave amplitude ratio was decreased at the highest light intensities and oscillatory potentials were delayed. The retinal fundus and vessels remained unchanged. No cell apoptosis was detected in vertical and horizontal sections of the retina by TUNEL or immunocytochemistry for the active caspase 3. No increase in GFAP-immunostaining indicative of a glial reaction was observed in Müller glial cells. By contrast, changes in the morphology of microglial cells were observed, with marked shortening of the dendrites. Thus, the microglial reaction occurs very early in progression to diabetic retinopathy, at about the same time as early electroretinographic modifications. The absence of apoptotic cells, contrasting with previous results in mice with streptozotocin-induced diabetes, is consistent with insulin neuroprotection.

Macroglial and retinal changes in hypercholesterolemic rabbits after normalization of cholesterol levels

This study evaluates hypercholesterolemic rabbits, examining the retinal changes in Müller cells and astrocytes as well as their variations after a period of normal blood-cholesterol values induced by a standard diet. New Zealand rabbits were divided into three groups: G0, fed a standard diet; G1A, fed a 0.5% cholesterol-enriched diet for 8 months; and G1B, fed as G1A followed by standard diet for 6 months. Eyes were processed for transmission electron microscopy and immunohistochemistry (GFAP). While G1B resembled G0 more than did G1A, they shared alterations with G1A: a) as in G1A, Müller cells were GFAP+, filled spaces left by axonal degeneration, formed glial scars and their nuclei were displaced to the nerve-fibre layer. The area occupied by the astrocytes associated with the nerve-fibre bundles (AANFB) and by perivascular astrocytes (PVA) in G1A and G1B was significantly lower than in controls. However, no significant differences in PVA were found between G1A and G1B. In G1B, type I PVA was absent and replaced by hypertrophic type II cells; b) Bruch's membrane (BM) was thinner in G1B than in G1A; c) the retinal pigment epithelium (RPE) cytoplasm contained fewer lipids in G1B than in G1A; d) in G1A and G1B choriocapillaris and retinal vessel showed alterations with respect to G0; e) cell death and axonal degeneration in the retina were similar in G1A and G1B. The substitution of a hyperlipemic diet by a standard one normalizes blood-lipid levels. However, the persistence of damage at retinal vessels and BM-RPE could trigger chronic ischemia.

Latanoprost rescues retinal neuro-glial cells from apoptosis by inhibiting caspase-3, which is mediated by p44/p42 mitogen-activated protein kinase

The purpose of this study was to investigate whether latanoprost, a prostaglandin F2alpha analogue, has a direct anti-apoptotic effect both in retinal neuro-glial cells in culture and in diabetic retina. R28 cells, immortalized retinal neuroglial progenitor cells, were induced apoptosis by 24h serum deprivation. Serum withdrawal made up to 15% of R28 cells pyknotic and activated caspase-3 immunoreactive, and latanoprost acid suppressed apoptosis with dose dependency at an optimum concentration of 1.0 microM (P<0.001). UO126, a mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase kinase (MEK) 1 and 2 inhibitor reversed this effect. Streptozotocin induced one- or three-month diabetic rats received balanced-salt-solution (BSS) in the left eye and latanoprost eye drops in the right for 5 days. Retinal wholemount was subjected to terminal dUTP nick end labeling (TUNEL) staining, whereas eyeballs were enucleated for cleaved caspase-3 immunofluorescence. Retinal homogenates were probed for phospho- or total p44/p42 MAPK and Akt. One- and three-month diabetic retina had 30.2+/-15.3 and 23.6+/-9.0 TUNEL positive cells per 0.5 cm(2), respectively, whereas control retina had few TUNEL positive cells. Latanoprost instillation significantly reduced these cells (10.0+/-3.1 and 11.3+/-3.1 cells per 0.5 cm(2) for 1M and 3M, respectively, P<0.01), whereas BSS did not. Latanoprost also significantly reduced cleaved caspase-3 immunoreactive cells in ganglion cell and inner nuclear layers (P<0.05). Latanoprost increased phosphorylated to total protein ratio of p44/p42 MAPK (P<0.05), but not of Akt. Taken together, the present findings suggest that latanoprost rescues retinal neurons and/or glial cells from apoptosis, which is probably mediated by p44/p42 MAPK through caspase-3 inhibition.

The role of cytokines and trophic factors in epiretinal membranes: Involvement of signal transduction in glial cells

Idiopathic epiretinal membranes (ERMs) in the macular region can cause a reduction in vision and sometimes recurs after surgical removal, but its pathogenic mechanisms are still unknown. On the other hand, the presence of secondary ERMs has been associated with various clinical conditions including proliferative diabetic retinopathy (PDR) and proliferative vitreoretinopathy (PVR). Recent studies have shown a significant association between clinical grades of PDR or PVR, and the expression levels of specific cytokines and/or growth factors in the vitreous fluid. Expression of these factors and their receptors are also observed in secondary ERMs. ERMs are composed of many cell types such as retinal pigment epithelial cells and vascular endothelial cells, however the role of glial cells is yet unclear. Interestingly, glial cells in ERMs express some trophic factor receptors and transcription factors, such as NF-kappaB, suggesting an involvement of glial signal transduction in the pathogenesis of ERMs. In this review, we summarize recent progress regarding the clinical and laboratory findings of ERMs.