Retinal fibrosis in diabetic retinopathy

Eyeing the Extracellular Matrix in Vascular Development and Microvascular Diseases and Bridging the Divide between Vascular Mechanics and Function

The extracellular matrix (ECM) is critical in all aspects of vascular development and health: supporting cell anchorage, providing structure, organization and mechanical stability, and serving as a sink for growth factors and sustained survival signals. Abnormal changes in ECM protein expression, organization, and/or properties, and the ensuing changes in vascular compliance affect vasodilator responses, microvascular pressure transmission, and collateral perfusion. The changes in microvascular compliance are independent factors initiating, driving, and/or exacerbating a plethora of microvascular diseases of the eye including diabetic retinopathy (DR) and vitreoretinopathy, retinopathy of prematurity (ROP), wet age-related macular degeneration (AMD), and neovascular glaucoma. Congruently, one of the major challenges with most vascular regenerative therapies utilizing localized growth factor, endothelial progenitor, or genetically engineered cell delivery, is the regeneration of blood vessels with physiological compliance properties. Interestingly, vascular cells sense physical forces, including the stiffness of their ECM, through mechanosensitive integrins, their associated proteins and the actomyosin cytoskeleton, which generates biochemical signals that culminate in a rapid expression of matricellular proteins such as cellular communication network 1 (CCN1) and CCN2 (aka connective tissue growth factor or CTGF). Loss or gain of function of these proteins alters genetic programs of cell growth, ECM biosynthesis, and intercellular signaling, that culminate in changes in cell behavior, polarization, and barrier function. In particular, the function of the matricellular protein CCN2/CTGF is critical during retinal vessel development and regeneration wherein new blood vessels form and invest a preformed avascular neural retina following putative gradients of matrix stiffness. These observations underscore the need for further in-depth characterization of the ECM-derived cues that dictate structural and functional properties of the microvasculature, along with the development of new therapeutic strategies addressing the ECM-dependent regulation of pathophysiological stiffening of blood vessels in ischemic retinopathies.

Aging Fits the Disease Criteria of the International Classification of Diseases

The disease criteria used by the World Health Organization (WHO) were applied to human biological aging in order to assess whether aging can be classified as a disease. These criteria were developed for the 11th revision of the International Classification of Diseases (ICD) and included disease diagnostics, mechanisms, course and outcomes, known interventions, and linkage to genetic and environmental factors. RESULTS: Biological aging can be diagnosed with frailty indices, functional, blood-based biomarkers. A number of major causal mechanisms of human aging involved in various organs have been described, such as inflammation, replicative cellular senescence, immune senescence, proteostasis failures, mitochondrial dysfunctions, fibrotic propensity, hormonal aging, body composition changes, etc. We identified a number of clinically proven interventions, as well as genetic and environmental factors of aging. Therefore, aging fits the ICD-11 criteria and can be considered a disease. Our proposal was submitted to the ICD-11 Joint Task force, and this led to the inclusion of the extension code for "Ageing-related" (XT9T) into the "Causality" section of the ICD-11. This might lead to greater focus on biological aging in global health policy and might provide for more opportunities for the new therapy developers.

Inherited Eye Diseases with Retinal Manifestations through the Eyes of Homeobox Genes

Retinal development is under the coordinated control of overlapping networks of signaling pathways and transcription factors. The paper was conceived as a review of the data and ideas that have been formed to date on homeobox genes mutations that lead to the disruption of eye organogenesis and result in inherited eye/retinal diseases. Many of these diseases are part of the same clinical spectrum and have high genetic heterogeneity with already identified associated genes. We summarize the known key regulators of eye development, with a focus on the homeobox genes associated with monogenic eye diseases showing retinal manifestations. Recent advances in the field of genetics and high-throughput next-generation sequencing technologies, including single-cell transcriptome analysis have allowed for deepening of knowledge of the genetic basis of inherited retinal diseases (IRDs), as well as improve their diagnostics. We highlight some promising avenues of research involving molecular-genetic and cell-technology approaches that can be effective for IRDs therapy. The most promising neuroprotective strategies are aimed at mobilizing the endogenous cellular reserve of the retina.

Light deprivation reduces the severity of experimental diabetic retinopathy

Illumination of the retina is a major determinant of energy expenditure by its neurons. However, it remains unclear whether light exposure significantly contributes to the pathophysiology of common retinal disease. Driven by the premise that light exposure reduces the metabolic demand of the retina, recent clinical trials failed to demonstrate a benefit for constant illumination in the treatment of diabetic retinopathy. Here, we instead ask whether light deprivation or blockade of visual transduction could modulate the severity of this common cause of blindness. We randomized adult mice with two different models of diabetic retinopathy to 1-3 months of complete dark housing. Unexpectedly, we find that diabetic mice exposed to short or prolonged light deprivation have reduced diabetes-induced retinal pathology, using measures of visual function, compared to control animals in standard lighting conditions. To corroborate these results, we performed assays of retinal vascular health in diabetic Gnat1^-/- and Rpe65^-/- mice, which lack phototransduction. Both mutants displayed less diabetes-associated retinal vascular disease compared to respective wild-type controls. Collectively, these results suggest that light-induced visual transduction promotes the development of diabetic retinopathy and implicate photoreceptors as an early source of visual pathology in diabetes.

Utilizing network pharmacology to explore the underlying mechanism of Radix Salviae in diabetic retinopathy

INTRODUCTION

Radix Salviae (Dan-shen in pinyin), a classic Chinese herb, has been extensively used to treat diabetic retinopathy in clinical practice in China for many years. However, the pharmacological mechanisms of Radix Salviae remain vague. The aim of this study was to decrypt the underlying mechanisms of Radix Salviae in the treatment of diabetic retinopathy using a systems pharmacology approach.

METHODS

A network pharmacology-based strategy was proposed to elucidate the underlying multi-component, multi-target, and multi-pathway mode of action of Radix Salviae against diabetic retinopathy. First, we collected putative targets of Radix Salviae based on the Traditional Chinese Medicine System Pharmacology database and a network of the interactions among the putative targets of Radix Salviae and known therapeutic targets of diabetic retinopathy was built. Then, two topological parameters, "degree" and "closeness certainty" were calculated to identify the major targets in the network. Furthermore, the major hubs were imported to the Database for Annotation, Visualization and Integrated Discovery to perform a pathway enrichment analysis.

RESULTS

A total of 130 nodes, including 18 putative targets of Radix Salviae, were observed to be major hubs in terms of topological importance. The results of pathway enrichment analysis indicated that putative targets of Radix Salviae mostly participated in various pathways associated with angiogenesis, protein metabolism, inflammatory response, apoptosis, and cell proliferation. The putative targets of Radix Salviae (vascular endothelial growth factor, matrix metalloproteinases, plasminogen, insulin-like growth factor-1, and cyclooxygenase-2) were recognized as active factors involved in the main biological functions of treatment, which implied that these were involved in the underlying mechanisms of Radix Salviae on diabetic retinopathy.

CONCLUSIONS

Radix Salviae could alleviate diabetic retinopathy via the molecular mechanisms predicted by network pharmacology. This research demonstrates that the network pharmacology approach can be an effective tool to reveal the mechanisms of traditional Chinese medicine from a holistic perspective.

Vascular changes in diabetic retinopathy-a longitudinal study in the Nile rat

Diabetic retinopathy is the most common microvascular complication of diabetes and is a major cause of blindness, but an understanding of the pathogenesis of the disease has been hampered by a lack of accurate animal models. Here, we explore the dynamics of retinal cellular changes in the Nile rat (Arvicanthis niloticus), a carbohydrate-sensitive model for type 2 diabetes. The early retinal changes in diabetic Nile rats included increased acellular capillaries and loss of pericytes that correlated linearly with the duration of diabetes. These vascular changes occurred in the presence of microglial infiltration but in the absence of retinal ganglion cell loss. After a prolonged duration of diabetes, the Nile rat also exhibits a spectrum of retinal lesions commonly seen in the human condition including vascular leakage, capillary non-perfusion, and neovascularization. Our longitudinal study documents a range and progression of retinal lesions in the diabetic Nile rat remarkably similar to those observed in human diabetic retinopathy, and suggests that this model will be valuable in identifying new therapeutic strategies.

Upregulation of Lysyl Oxidase Expression in Vitreous of Diabetic Subjects: Implications for Diabetic Retinopathy

Animal studies have shown diabetes-induced lysyl oxidase (LOX) upregulation promotes blood-retinal-barrier breakdown and retinal vascular cell loss associated with diabetic retinopathy (DR). However, it is unclear whether changes in LOX expression contribute to the development and progression of DR. To determine if vitreous LOX levels are altered in patients with DR, 31 vitreous specimens from subjects with advanced proliferative DR (PDR), and 27 from non-diabetics were examined. The two groups were age- and gender-matched (57 ± 12 yrs vs. 53 ± 18 yrs; 19 males and 12 females vs. 17 males and 10 females). Vitreous samples obtained during vitrectomy were assessed for LOX levels using ELISA. LOX was detected in a larger number of PDR subjects (58%) than in non-diabetic subjects (15%). Additionally, ELISA measurements showed a significant increase in LOX levels in the diabetic subjects with PDR, compared to those of non-diabetic subjects (68.3 ± 112 ng/mL vs. 2.1 ± 8.2 ng/mL; p < 0.01). No gender difference in vitreous LOX levels was observed in either the diabetic or non-diabetic groups. Findings support previous reports of increased LOX levels in retinas of diabetic animals and in retinal vascular cells in high glucose condition, raising the prospect of targeting LOX overexpression as a potential target for PDR treatment.

Diabetic Retinopathy, lncRNAs, and Inflammation: A Dynamic, Interconnected Network

Diabetic retinopathy (DR) is reaching epidemic levels globally due to the increase in prevalence of diabetes mellitus (DM). DR also has detrimental effects to quality of life, as it is the leading cause of blindness in the working-age population and the most common cause of vision loss in individuals with DM. Over several decades, many studies have recognized the role of inflammation in the development and progression of DR; however, in recent years, accumulating evidence has also suggested that non-coding RNAs, especially long non-coding (lncRNAs), are aberrantly expressed in diabetes and may play a putative role in the development and progression of DR through the modulation of gene expression at the transcriptional, post-transcriptional, or epigenetic level. In this review, we will first highlight some of the key inflammatory mediators and transcription factors involved in DR, and we will then introduce the critical roles of lncRNAs in DR and inflammation. Following this, we will discuss the implications of lncRNAs in other epigenetic mechanisms that may also contribute to the progression of inflammation in DR.

A Combination Therapy Targeting Endoglin and VEGF-A Prevents Subretinal Fibro-Neovascularization Caused by Induced Müller Cell Disruption

Purpose

Subretinal fibroneovascularization is one of the most common causes of vision loss in neovascular AMD (nAMD). Anti-VEGF therapy effectively inhibits vascular leak and neovascularization but has little effect on fibrosis. This study aimed to identify a combination therapy to concurrently inhibit subretinal neovascularization and prevent fibrosis.

Methods

We generated transgenic mice in which induced disruption of Müller cells leads to subretinal neovascularization, which is reliably accompanied by subretinal fibrosis. We conducted Western blots and immunohistochemistry to study changes in transforming growth factor-β (TGFβ) signaling including endoglin, a coreceptor essential for TGFβ signaling, and then tested the effects of monthly intravitreal injection of anti-VEGF-A and anti-endoglin, either alone or in combination, on the development of subretinal fibroneovascularization in our transgenic mice.

Results

Müller cell disruption increased expression of TGFβ1, TGFβ type 1 receptor, and phosphorylated-Smad3. Endoglin was strongly expressed in subretinal fibroneovascular tissue. Fluorescein angiography and measurements of retinal vascular permeability indicated that intravitreal anti-VEGF-A in combination with anti-endoglin treatment more efficiently inhibited vascular leak compared with either monotherapy. Immunostaining of retinal wholemounts with antibodies against glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1 indicated that the combination therapy also effectively prevented subretinal fibrosis and inhibited microglial activation. Luminex cytokine assays indicated that intravitreal anti-VEGF-A and anti-endoglin treatment, either alone or in combination, reduced the production of IL33 and macrophage inflammatory protein-3α.

Conclusions

Our findings offer a potentially novel combination approach to concurrently managing subretinal neovascularization and fibrosis in nAMD.

Nutraceuticals for the Treatment of Diabetic Retinopathy

Diabetic retinopathy (DR) is one of the most common complications of diabetes mellitus and is characterized by degeneration of retinal neurons and neoangiogenesis, causing a severe threat to vision. Nowadays, the principal treatment options for DR are laser photocoagulation, vitreoretinal surgery, or intravitreal injection of drugs targeting vascular endothelial growth factor. However, these treatments only act at advanced stages of DR, have short term efficacy, and cause side effects. Treatment with nutraceuticals (foods providing medical or health benefits) at early stages of DR may represent a reasonable alternative to act upstream of the disease, preventing its progression. In particular, in vitro and in vivo studies have revealed that a variety of nutraceuticals have significant antioxidant and anti-inflammatory properties that may inhibit the early diabetes-driven molecular mechanisms that induce DR, reducing both the neural and vascular damage typical of DR. Although most studies are limited to animal models and there is the problem of low bioavailability for many nutraceuticals, the use of these compounds may represent a natural alternative method to standard DR treatments.

Lymphatic Vascular Structures: A New Aspect in Proliferative Diabetic Retinopathy

Diabetic retinopathy (DR) is the most common diabetic microvascular complication and major cause of blindness in working-age adults. According to the level of microvascular degeneration and ischemic damage, DR is classified into non-proliferative DR (NPDR), and end-stage, proliferative DR (PDR). Despite advances in the disease etiology and pathogenesis, molecular understanding of end-stage PDR, characterized by ischemia- and inflammation-associated neovascularization and fibrosis, remains incomplete due to the limited availability of ideal clinical samples and experimental research models. Since a great portion of patients do not benefit from current treatments, improved therapies are essential. DR is known to be a complex and multifactorial disease featuring the interplay of microvascular, neurodegenerative, metabolic, genetic/epigenetic, immunological, and inflammation-related factors. Particularly, deeper knowledge on the mechanisms and pathophysiology of most advanced PDR is critical. Lymphatic-like vessel formation coupled with abnormal endothelial differentiation and progenitor cell involvement in the neovascularization associated with PDR are novel recent findings which hold potential for improved DR treatment. Understanding the underlying mechanisms of PDR pathogenesis is therefore crucial. To this goal, multidisciplinary approaches and new ex vivo models have been developed for a more comprehensive molecular, cellular and tissue-level understanding of the disease. This is the first step to gain the needed information on how PDR can be better evaluated, stratified, and treated.

Adiponectin: A potential candidate for treating fibrosis in posterior segment of the eye

Fibrosis in ocular tissues causes severe visual deterioration and blindness in patients with glaucoma, cataract, age related macular degeneration (AMD) and diabetic retinopathy (DR). Currently available anti-fibrotic agents exhibit undesirous cytotoxic effects and thus prove ineffective to treat post-surgical fibrosis. Accordingly, there is a need to develop efficient and novel anti-fibrotic agents. Adiponectin (APN), an adipokine from adipocytes is increased in the aqueous and vitreous humor of the patients with micro-angiopathy and chronic inflammation. Furthermore, it is reported to be elevated in the subretinal fluid, vitreous and epiretinal membrane of patients with AMD, proliferative vitreoretinopathy (PVR) and proliferative diabetic retinopathy (PDR) respectively. Since APN has anti-angiogenic activity and reduces VEGF levels, we hypothesize that APN might regulate the angio-fibrotic switch and drive the formation of fibrovascular membrane at advanced stages of AMD, PVR and PDR. Intriguingly, APN is shown to inhibit liver, cardiac and pulmonary fibrosis, yet it accelerates renal fibrosis. Therefore, the factors such as tissue and cell type, disease specific pathological milieu and the choice of APN receptor interaction could determine the pro- or anti-fibrotic nature of APN. We speculate that APN could play a profibrotic role in the posterior segment of the eye.

Molecular Mechanisms Mediating Diabetic Retinal Neurodegeneration: Potential Research Avenues and Therapeutic Targets

Diabetic retinopathy (DR) is a devastating complication of diabetes with a prevalence rate of 35%, and no effective treatment options. Since the most visible clinical features of DR are microvascular irregularities, therapeutic interventions often attempt to reduce microvascular injury, but only after permanent retinal damage has ensued. However, recent data suggests that diabetes initially affects retinal neurons, leading to neurodegeneration as an early occurrence in DR, before onset of the more noticeable vascular abnormalities. In this review, we delineate the sequence of initiating events leading to retinal degeneration in DR, considering neuronal dysfunction as a primary event. Key molecular mechanisms and potential biomarkers associated with retinal neuronal degeneration in diabetes are discussed. In addition to glial reactivity and inflammation in the diabetic retina, the contribution of neurotrophic factors, cell adhesion molecules, apoptosis markers, and G protein signaling to neurodegenerative pathways warrants further investigation. These studies could complement recent developments in innovative treatment strategies for diabetic retinopathy, such as targeting retinal neuroprotection, promoting neuronal regeneration, and attempts to re-program other retinal cell types into functional neurons. Indeed, several ongoing clinical trials are currently attempting treatment of retinal neurodegeneration by means of such novel therapeutic avenues. The aim of this article is to highlight the crucial role of neurodegeneration in early retinopathy progression, and to review the molecular basis of neuronal dysfunction as a first step toward developing early therapeutic interventions that can prevent permanent retinal damage in diabetes. ClinicalTrials.gov: NCT02471651, NCT01492400.

Chebulagic acid and Chebulinic acid inhibit TGF-β1 induced fibrotic changes in the chorio-retinal endothelial cells by inhibiting ERK phosphorylation

PURPOSE

Diabetic retinopathy (DR) is characterized by pro-inflammatory, pro-angiogenic and pro-fibrotic environment during the various stages of the disease progression. Basement membrane changes in the retina and formation of fibrovascular membrane are characteristically seen in DR. In the present study the effect of Alcoholic (AlE) extracts of Triphala an ayurvedic herbal formulation and its chief compounds, Chebulagic (CA), Chebulinic (CI) and Gallic acid (GA) were evaluated for TGFβ1-induced anti-fibrotic activity in choroid-retinal endothelial cells (RF/6A).

METHOD

RF/6A cells were treated with TGFβ1 alone or co-treated with AlE, CA, CI or GA. The mRNA and protein expression of fibrotic markers (αSMA, CTGF) were assessed by qPCR and western blot/ELISA. Functional changes were assessed using proliferation assay and migration assay. To deduce the mechanism of action, downstream signaling was assessed by western blot analysis along with in silico docking studies.

RESULT

AlE (50 μg/ml) CA and CI at 10 μM reduced the expression of pro-fibrotic genes (αSMA and CTGF) induced by TGFβ1, by inhibiting ERK phosphorylation. GA did not inhibit TGFβ1 mediated changes in RF/6A cells. In silico experiments shows that CA and CI has favourable binding energy to bind with TGFβ receptor and inhibit the downstream signaling, while GA did not.

CONCLUSION

Hence this study identifies Triphala and its chief compounds CA and CI as potential adjuvants in the management of DR.

Role of Inflammation in Diabetic Retinopathy

Diabetic retinopathy is a common complication of diabetes and remains the leading cause of blindness among the working-age population. For decades, diabetic retinopathy was considered only a microvascular complication, but the retinal microvasculature is intimately associated with and governed by neurons and glia, which are affected even prior to clinically detectable vascular lesions. While progress has been made to improve the vascular alterations, there is still no treatment to counteract the early neuro-glial perturbations in diabetic retinopathy. Diabetes is a complex metabolic disorder, characterized by chronic hyperglycemia along with dyslipidemia, hypoinsulinemia and hypertension. Increasing evidence points to inflammation as one key player in diabetes-associated retinal perturbations, however, the exact underlying molecular mechanisms are not yet fully understood. Interlinked molecular pathways, such as oxidative stress, formation of advanced glycation end-products and increased expression of vascular endothelial growth factor have received a lot of attention as they all contribute to the inflammatory response. In the current review, we focus on the involvement of inflammation in the pathophysiology of diabetic retinopathy with special emphasis on the functional relationships between glial cells and neurons. Finally, we summarize recent advances using novel targets to inhibit inflammation in diabetic retinopathy.

NF-κβ: A Potential Target in the Management of Vascular Complications of Diabetes

Diabetes is a metabolic disorder affecting large percentage of population worldwide. NF-κβ plays key role in pathogenesis of vascular complications of diabetes. Persistent hyperglycemia activates NF-κβ that triggers expression of various cytokines, chemokines and cell adhesion molecules. Over-expression of TNF-α, interleukins, TGF-β, Bcl2 and other pro-inflammatory proteins and pro-apoptotic genes by NF-κβ is key risk factor in vascular dysfunction. NF-κβ over-expression also triggers calcification of endothelial cells leading to endothelial dysfunction and further vascular complications. Inhibition of NF-κβ pro-inflammatory pathway is upcoming novel target for management of vascular complications of diabetes. Various natural and synthetic inhibitors of NF-κβ have been studied in management of diabetic complications. Recent preclinical and clinical studies validate NF-κβ as promising target in the management of vascular complications of diabetes.

Protective Effect of Tang Wang One Decoction on the Retinal Vessels of Diabetic Rats

Objective. This study aimed to determine the influence of Tang Wang One Decoction (TWOD) on the retinal vessels of diabetic rats. Methods. The hemorheology of diabetic rats was observed. Morphological studies of retinal vessels were conducted using optical microscopy and electron microscopy. Immunological histochemistry assay was used to measure the expression levels of MMP-9, occludin, and claudin-5. Results. Obvious pathological damage was observed in the retinal vessels of diabetic rats. TWOD positively affected the hemorheology and morphology of retinal vessels. The decoction also decreased the expression of MMP-9 and increased the expression of occludin and claudin-5. Conclusions. The results suggest that the retinal protective effects of TWOD might be related to downregulation of MMP-9 and upregulation of occludin and claudin-5.

Association between microfibrillar-associated protein 4 (MFAP4) and micro- and macrovascular complications in long-term type 1 diabetes mellitus

AIMS

To evaluate microfibrillar-associated protein 4 (MFAP4) as a marker of micro- and macrovascular complications in patients with type 1 diabetes.

METHODS

This cross-sectional study included 203 persons with a long duration of type 1 diabetes from a population-based cohort ascertained in the former Funen County, Denmark. Detection of plasma-MFAP4 (pMFAP4) was performed by the AlphaLISA Technique. Diabetic retinopathy (DR) was graded in accordance with the Early Treatment Diabetic Retinopathy Study adaptation of the modified Airlie House classification. A monofilament test was used to test for neuropathy, and nephropathy was evaluated in a single spot urine sample. Data describing macrovascular disease were obtained from the Danish National Patient Register.

RESULTS

Median age and duration of diabetes were 58.7 and 43 years, respectively, and 61% were males. High levels of pMFAP4 were found in participants of old age, in women and in non-smokers (p < 0.05). In a multiple logistic regression model, patients with high levels of pMFAP4 were more likely to have diabetic neuropathy (OR 2.47 for quartile 4 versus quartile 1, 95% CI 1.01-6.03). No association was found between pMFAP4 and proliferative diabetic retinopathy, nephropathy or macrovascular disease.

CONCLUSIONS

No association between pMFAP4 and macrovascular vascular complications was found. However, high levels of pMFAP4 correlated independently with diabetic neuropathy. Further studies on the predictive value of increased circulating MFAP4 in diabetic neuropathy are warranted.

Minireview: Fibronectin in retinal disease

Retinal fibrosis, characterized by dysregulation of extracellular matrix (ECM) protein deposition by retinal endothelial cells, pigment epithelial cells, and other resident cell-types, is a unifying feature of several common retinal diseases. Fibronectin is an early constituent of newly deposited ECM and serves as a template for assembly of other ECM proteins, including collagens. Under physiologic conditions, fibronectin is found in all layers of Bruch's membrane. Proliferative vitreoretinopathy (PVR), a complication of retinal surgery, is characterized by ECM accumulation. Among the earliest histologic manifestations of diabetic retinopathy (DR) is capillary basement membrane thickening, which occurs due to perturbations in ECM homeostasis. Neovascularization, the hallmark of late stage DR as well as exudative age-related macular degeneration (AMD), involves ECM assembly as a scaffold for the aberrant new vessel architecture. Rodent models of retinal injury demonstrate a key role for fibronectin in complications characteristic of PVR, including retinal detachment. In mouse models of DR, reducing fibronectin gene expression has been shown to arrest the accumulation of ECM in the capillary basement membrane. Alterations in matrix metalloproteinase activity thought to be important in the pathogenesis of AMD impact the turnover of fibronectin matrix as well as collagens. Growth factors involved in PVR, AMD, and DR, such as PDGF and TGFβ, are known to stimulate fibronectin matrix assembly. A deeper understanding of how pathologic ECM deposition contributes to disease progression may help to identify novel targets for therapeutic intervention.

In Vivo Evaluation of the Visual Pathway in Streptozotocin-Induced Diabetes by Diffusion Tensor MRI and Contrast Enhanced MRI

Visual function has been shown to deteriorate prior to the onset of retinopathy in some diabetic patients and experimental animal models. This suggests the involvement of the brain's visual system in the early stages of diabetes. In this study, we tested this hypothesis by examining the integrity of the visual pathway in a diabetic rat model using in vivo multi-modal magnetic resonance imaging (MRI). Ten-week-old Sprague-Dawley rats were divided into an experimental diabetic group by intraperitoneal injection of 65 mg/kg streptozotocin in 0.01 M citric acid, and a sham control group by intraperitoneal injection of citric acid only. One month later, diffusion tensor MRI (DTI) was performed to examine the white matter integrity in the brain, followed by chromium-enhanced MRI of retinal integrity and manganese-enhanced MRI of anterograde manganese transport along the visual pathway. Prior to MRI experiments, the streptozotocin-induced diabetic rats showed significantly smaller weight gain and higher blood glucose level than the control rats. DTI revealed significantly lower fractional anisotropy and higher radial diffusivity in the prechiasmatic optic nerve of the diabetic rats compared to the control rats. No apparent difference was observed in the axial diffusivity of the optic nerve, the chromium enhancement in the retina, or the manganese enhancement in the lateral geniculate nucleus and superior colliculus between groups. Our results suggest that streptozotocin-induced diabetes leads to early injury in the optic nerve when no substantial change in retinal integrity or anterograde transport along the visual pathways was observed in MRI using contrast agent enhancement. DTI may be a useful tool for detecting and monitoring early pathophysiological changes in the visual system of experimental diabetes non-invasively.

The importance of glial cells in the homeostasis of the retinal microenvironment and their pivotal role in the course of diabetic retinopathy

Diabetic retinopathy (DR) is a remarkable microvascular complication of diabetes and it has been considered the leading cause of legal blindness in working-age adults in the world. Several overlapping and interrelated molecular pathways are involved in the development of this disease. DR is staged into different levels of severity, from the nonproliferative to the advanced proliferative form. Over the years the progression of DR evolves through a series of changes involving distinct types of specialized cells: neural, vascular and glial. Prior to the clinically observable vascular complications, hyperglycemia and inflammation affect retinal glial cells which undergo a wide range of structural and functional alterations. In this review, we provide an overview of the status of macroglia and microglia in the course of DR, trying to briefly take into account the complex biochemical mechanisms that affect the intimate relationship among neuroretina, vessels and glial cells.