The development of blood-retinal barrier during the interaction of astrocytes with vascular wall cells

Astrocytes are intimately involved in the formation and development of retinal vessels. Astrocyte dysfunction is a major cause of blood-retinal barrier injury and other retinal vascular diseases. In this study, the development of the retinal vascular system and the formation of the blood-ret-inal barrier in mice were investigated using immunolfuorescence staining, gelatin-ink perfusion, and transmission electron microscopy. The results showed that the retinal vascular system of mice develops from the optic disc after birth, and radiates out gradually to cover the entire retina, taking the papilla optica as the center. First, the superifcial vasculature is formed on the inner retinal layer;then, the vasculature extends into the inner and outer edges of the retinal inner nuclear layer, forming the deep vasculature that is parallel to the superifcial vasculature. The blood-retinal barrier is mainly composed of endothelium, basal lamina and the end-feet of astrocytes, which become mature during mouse development. Initially, the naive endothelial cells were immature with few organelles and many microvilli. The basal lamina was uniform in thickness, and the glial end-feet surrounded the outer basal lamina incompletely. In the end, the blood-retinal barrier matures with smooth endothelia connected through tight junctions, rela-tively thin and even basal lamina, and relatively thin glial cell end-feet. These ifndings indicate that the development of the vasculature in the retina follows the rules of“center to periphery”and“superifcial layer to deep layers”. Its development and maturation are spatially and tempo-rally consistent with the functional performance of retinal neurons and photosensitivity. The blood-retinal barrier gradually becomes mature via the process of interactions between astro-cytes and blood vessel cells.

Involvement of moesin phosphorylation in ischemia/reperfusion induced inner blood-retinal barrier dysfunction

AIM: To investigate the role of moesin and its underlying signal transduction in retinal vascular damage induced by retinal ischemia-reperfusion(RIR) insult.METHODS: C57 BL/6 mice were subjected to continued ischemia for 45 min, followed by blood reperfusion. The expression and phosphorylation of moesin in retinal vessels were detected by immunohistochemistry and Western blotting. The inner blood-retinal barrier was evaluated using FITCdextran leakage assay on whole-mount retina. Further studies were conducted to explore the effects of p38 mitogen-activated protein kinase(MAPK) pathway on the involvement of moesin in RIR-evoked retinal vascular hyperpermeability response. RESULTS: It revealed that RIR induced moesin phosphorylation in a time-dependent manner after reperfusion. The phosphorylation of moesin was alleviated by inhibitions of p38 MAPK, while this treatment also ameliorated the dysfunction of inner blood-retinal barrier. CONCLUSION: The results suggest that moesin is involved in RIR-evoked retinal vascular endothelial dysfunction and the phosphorylation of moesin is triggered via p38 MAPK activation.

Upregulated inflammatory associated factors and blood-retinal barrier changes in the retina of type 2diabetes mellitus model

AIM： To examine the expression of high mobility group box-1（HMGB-1） and intercellular adhesion molecule-1（ICAM-1） in the retina and the hippocampal tissues; and further to evaluate the association of these two molecules with the alterations of blood-retinal barrier（BRB） and blood-brain barrier（BBB） in a rat model of type 2 diabetes.METHODS： The type-2 diabetes mellitus（DM） model was established with a high-fat and high-glucose diet combined with streptozotocin（STZ）. Sixteen weeks after DM induction, morphological changes of retina and hippocampus were observed with hematoxylin-eosin staining, and alternations of BRB and BBB permeability were measured using Evans blue method. Levels of HMGB-1 and ICAM-1 in retina and hippocampus were detected by Western blot. Serum HMGB-1 levels were determined by enzyme-linked immunosorbent assay（ELISA）.RESULTS： A significantly higher serum fasting blood glucose level in DM rats was observed 2wk after STZ injection（P 〈0.01）. The serum levels of fasting insulin,Insulin resistance homeostatic model assessment（IRHOMA）,total cholesterol（TC）, total triglycerides（TG） and low density lipoprotein cholesterol（LDL-C） in the DM rats significantly higher than those in the controls（all P 〈0.01）.HMGB-1（0.96±0.03, P 〈0.01） and ICAM-1（0.76±0.12, P 〈0.05） levels in the retina in the DM rats were significantly higher than those in the controls. HMGB-1（0.83±0.13, P 〈0.01） and ICAM-1（1.15 ±0.08, P 〈0.01） levels in the hippocampal tissues in the DM rats were alsosignificantly higher than those in the controls. Sixteen weeks after induction of DM, the BRB permeability to albumin-bound Evans blue dye in the DM rats was significantly higher than that in the controls（P 〈0.01）.However, there was no difference of BBB permeability between the DM rats and controls. When compared to the controls, hematoxylin and eosin staining showed obvious irregularities in the DM rats.CONCLUSION： BRB permeability increases significantly in rats with type-2 DM, which may be associated with the up-regulated retinal expression of HMGB-1 and ICAM-1.

Effect of pyridone agent on blood-retinal barrier in diabetic mice

AIM： To evaluate the therapeutic effect of fluorofenidone on disrupted blood-retinal barrier in the diabetic mice and uncover its underlying mechanism. METHODS： db/db mice were randomly chosen for treatment with daily doses of fluorofenidone or placebo at 5-week-old, treatment continued until mice reach 24-week- old. Then, expression of transcriptiona factor insulin gene enhancer binding protein-1 （Islet-I） and vascular endothelial growth factor （VEGF） in murine retinas were evaluated. Retinal vascular permeability was assessed by examining the level of albumin in db/db murine retinas. Furthermore, the retinal vessel tight junction was estimated by checking the level of occludin in the murine retinal tissues. RESULTS： After occurrence of diabetic retinopthy in db/ db mice, expressions of transcritpional factor Islet-1 was found to be upregulated in db/db murine retinas compared with non-diabetic controls. Similar to expression pattern of Islet-l, VEGF were also demonstrated to be increased in retinas of db/db mice, which was accompanied by increased retinal vascular leakage and decreased tight junction protein level. Systemetic administration of fluorofenidone repaired broken retinal vascular tight junction by restoring occludin expression in db/db retinal tissue. Consequently, retinal vascular premeability were indicated to be reduced by examining the transudative albumin level in diabetic retinal tissues. Both Islet-1 and VEGF expression were inhibited in the retinas of db/db mice after treatment with fluorofenidone. CONCLUSION： Fluorofenidone significantly protectes retinal tight junction and reduces retinal vascular leakage. The phenomenon can be partially attributed to reducing overexpression of Islet-1 and VEGF in diabetic retinal tissues.

RNA interference targeting NOX4 protects visual function in an experimental model of retinal detachment by alleviating blood-retinal barrier damage

AIM:To observe the effects of the inhibition of NADPH oxidase 4(NOX4)expression on the retinal vascular barriers and visual function after retinal detachment(RD).METHODS:RD model was established 3 wk after adenoassocianed virus vector injection.The retinal tissue was harvested 3 d after RD,and the death of retinal vascular endothelial cells and photoreceptors was observed using electron microscopy.The NOX4 expression was detected by Western blot.Confocal microscopy was used to observe a retinal patch that had been perfused with Evans blue.A modified water maze test was used to detect the time required to find the platform on the water surface.The visual function of the rats was evaluated and reactive oxygen species(ROS)expression was detected by a fluorescence microplate reader.RESULTS:The retinal patch showed that NOX4 interference significantly reduced the destruction of the tight junctions between the retinal endothelium of RD rats and reduced leakage.Western blotting showed decreased expression of the NOX4 protein and decreased expression of ROS in retinal tissue;the Morris water maze test results showed that NOX4 interference significantly decreased the escape latency of the rats.CONCLUSION:NOX4 interference reduces the production of ROS in retinal vascular endothelial cells after experimental RD,thereby protecting the blood-retinal barrier and protecting visual function.

Vascular endothelial growth factor-165b protects the blood-retinal barrier from damage after acute high intraocular pressure in rats

AIM:To elucidate the role of vascular endothelial growth factor-165b(VEGF-165b)in blood-retinal barrier(BRB)injury in the rat acute glaucoma model.METHODS:In this study,the rat acute high intraocular pressure(HIOP)model was established before and after intravitreous injection of anti-VEGF-165b antibody.The expression of VEGF-165b and zonula occludens-1(ZO-1)in rat retina was detected by double immunofluorescence staining and Western blotting,and the breakdown of BRB was detected by Evans blue(EB)dye.RESULTS:The intact retina of rats expressed VEGF-165b and ZO-1 protein,which were mainly located in the retinal ganglion cell layer and the inner nuclear layer and were both co-expressed with vascular endothelial cell markers CD31.After acute HIOP,the expression of VEGF-165b was up-regulated;the expression of ZO-1 was down-regulated at 12h and then recovered at 3d;EB leakage increased,peaking at 12h.After intravitreous injection of anti-VEGF-165b antibody,the expression of VEGF-165b protein was no significantly changed;and the down-regulation of the expression of ZO-1 was more obvious;EB leakage became more serious,peaking at 3d.EB analysis also showed that EB leakage in the peripheral retina was greater than that in the central retina.CONCLUSION:The endogenous VEGF-165b protein may protect the BRB from acute HIOP by regulating the expression of ZO-1.The differential destruction of BRB after acute HIOP may be related to the selective loss of retinal ganglion cells.

Dynamic changes of inducible nitric oxide synthase expression in rat's retina and its role on blood-retinal barrier injury after acute high intraocular pressure

AIM: To clarify the role of inducible nitric oxide synthase(i NOS) in blood-retinal barrier(BRB) injury after acute high intraocular pressure(IOP) in rats.METHODS: Forty-two Sprague-Dawley(SD) rats were randomized into 7 groups [control(Cont), 3, 6, 12, 24, 48, and 72 h, n=6]. Except Cont group, other groups’ retina tissue was obtained at corresponding time points after a model of acute high IOP have been established in rats. The expression of i NOS and tight junction protein zonula occludens(ZO)-1 was detected by Western blotting. Evans blue(EB;3%) was injected into the great saphenous vein to detect the leakage of EB by spectrophotometer. Nine rats were divided into Cont, 6 h, 12 h groups, the expression of i NOS was localized by immunofluorescence. In order to verify the role of i NOS in the damage to BRB, thirty-six rats were randomly divided into 4 groups [Cont, Cont+inhibitor(Inh), 6 h and 6 h+Inh, n=9]. After treatment with the i NOSspecific inhibitor 1400 W, the expression of i NOS and ZO-1 and the leakage of BRB were detected again.RESULTS: The immunofluorescence results showed that the expression of i NOS was observed in the Cont group and 6 h group, but not in the 12 h group. i NOS was mainly expressed in the retinal nerve fiber layer, ganglion cell layer and inner nuclear layer and that it did not colocalize with the retinal ganglion cell marker Neu N but was co-expressed with the vascular endothelial cell marker CD31. Western blotting showed that in the early period(3 h, 6 h) after acute high IOP, the expression of i NOS was upregulated, then the down-regulation of i NOS were tested in the follow-up timing spots. ZO-1 expression showed a continuous downregulation after 6 h. The quantitative results for EB showed that the amount of EB leakage began to increase at 3 h after acute high IOP. At 6 h, the leakage of EB was lower, but at 12 h, the leakage of EB was highest, after which it gradually recovered but remained higher than that in the Cont group. The expression of i NOS was down-regulated after 1400 W treatment. ZO-1 expression was not significantly changed in the Cont+Inh group and the 6 h group, and significantly down-regulated in the 6 h+Inh group, and the leakage of EB was significantly increased after 1400 W treatment.CONCLUSION: These results suggest that the upregulation of i NOS expression in the early stage after acute high IOP may have a protective effect on BRB injury.

Blood-retinal barrier as a converging pivot in understanding the initiation and development of retinal diseases

Clinical ophthalmologists consider each retinal disease as a completely unique entity.However,various retinal diseases,such as uveitis,age-related macular degeneration,diabetic retinopathy,and primary open-angle glaucoma,share a number of common pathogenetic pathways.Whether a retinal disease initiates from direct injury to the blood-retinal barrier(BRB)or a defect/injury to retinal neurons or glia that impairs the BRB secondarily,the BRB is a pivotal point in determining the prognosis as self-limiting and recovering,or developing and progressing to a clinical phenotype.The present review summarizes our current knowledge on the physiology and cellular and molecular pathology of the BRB,which underlies its pivotal role in the initiation and development of common retinal diseases.

Tight junction disruption and the pathogenesis of the chronic complications of diabetes mellitus:A narrative review

The chronic complications of diabetes mellitus constitute a major public health problem.For example,diabetic eye diseases are the most important cause of blindness,and diabetic nephropathy is the most frequent cause of chronic kidney disease worldwide.The cellular and molecular mechanisms of these chronic complications are still poorly understood,preventing the development of effective treatment strategies.Tight junctions(TJs)are epithelial intercellular junctions located at the most apical region of cell-cell contacts,and their main function is to restrict the passage of molecules through the paracellular space.The TJs consist of over 40 proteins,and the most important are occludin,claudins and the zonula occludens.Accumulating evidence suggests that TJ disruption in different organs,such as the brain,nerves,retina and kidneys,plays a fundamental pathophysiological role in the development of chronic complications.Increased permeability of the blood-brain barrier and the blood-retinal barrier has been demonstrated in diabetic neuropathy,brain injury and diabetic retinopathy.The consequences of TJ disruption on kidney function or progression of kidney disease are currently unknown.In the present review,we highlighted the molecular events that lead to barrier dysfunction in diabetes.Further investigation of the mechanisms underlying TJ disruption is expected to provide new insights into therapeutic approaches to ameliorate the chronic complications of diabetes mellitus.

Lycium barbarum polysaccharides related RAGE and Aβ levels in the retina of mice with acute ocular hypertension and promote maintenance of blood retinal barrier

Our previous study verified the protective effects of Lycium barbarum polysaccharides(LBP)on retinal neurons and blood vessels in acute ocular hypertension(AOH)mice.To investigate the effect of LBP on the reactivity of retinal glial cells,an AOH mouse model was established in one eye by maintaining ocular hypertension of 90 mm Hg for 60 minutes.Either LBP solution(1 mg/kg)or phosphate-buffered saline was administrated to the mice by gavage daily,starting 7 days before the AOH insult and continuing until the mice were sacrificed for specimen collection on day 4 post-insult.After AOH insult,increased numbers of astrocytes and microglia were observed,together with decreased expression of the following glial cell biomarkers in the retinal ganglion cells of AOH mice:glial fibrillary acidic protein,glutamine synthetase,aquaporin-4,S-100 proteins,ionized calcium-binding adaptor molecule 1,amyloid precursor protein and receptor of advanced glycosylation end-products.After intervention with LBP,the above changes were significantly reduced.Remarkably,morphological remodeling of blood vessel-associated retinal astrocytes,marked by glial fibrillary acidic protein,was also observed.These results,taken together,suggest that LBP regulated the production of amyloid-βand expression of receptor of advanced glycosylation end-products,as well as mediating the activity of retinal glial cells,which may lead to the promotion of better maintenance of the blood-retinal barrier and improved neuronal survival in AOH insult.This study was approved by the Committee for the Use of Live Animals in Teaching and Research(approval No.CULTRA-#1664-08).

Hydrogen sulfide intervention in cystathionine-β-synthase mutant mouse helps restore ocular homeostasis

AIM: To investigate the applications of hydrogen sulfide(H2 S) in eye-specific ailments in mice.METHODS: Heterozygous cystathionine-β-synthase(CBS+/-) and wild-type C57 BL/6 J(WT) mice fed with or without high methionine diet(HMD) were administered either phosphate buffered saline(PBS) or the slow-release H2 S donor: GYY4137. Several analyses were performed to study GYY4137 effects by examining retinal lysates for key protein expressions along with plasma glutamate and glutathione estimations. Intraocular pressure(IOP) was monitored during GYY4137 treatment; barium sulfate and bovine serum albumin conjugated fluorescein isothiocyanate(BSA-FITC) angiographies were performed for examining vasculature and its permeability post-treatment. Visionguided behavior was also tested employing novel object recognition test(NORT) and light-dark box test(LDBT) recordings.RESULTS: CBS deficiency(CBS+/-) coupled with HMD led disruption of methionine/homocysteine(Hcy) metabolism leading to hyperhomocysteinemia(HHcy) in CBS+/-mice as reflected by increased Hcy, and s-adenosylhomocysteine hydrolase(SAHH) levels. Unlike CBS, cystathionine-γ lyase(CSE), methylenetetrahydrofolate reductase(MTHFR) levels which were reduced but compensated by GYY4137intervention. Heightened oxidative and endoplasmic reticulum(ER) stress responses were mitigated by GYY4137 effects along with enhanced glutathione(GSH) levels. Increased glutamate levels in CBS+/-strain were prominent than WT mice and these mice also exhibited higher IOP that was lowered by GYY4137 treatment. CBS deficiency also resulted in vision-guided behavioral impairment as revealed by NORT and LDBT findings. Interestingly, GYY4137 was able to improve CBS+/-mice behavior together with lowering their glutamate levels. Blood-retinal barrier(BRB) appeared compromised in CBS+/-with vessels' leakage that was mitigated in GYY4137 treated group. This corroborated the results for occludin(an integral plasma membrane protein of the cellular tight junctions) stabilization.CONCLUSION: Findings reveal that HHcy-induced glutamate excitotoxicity, oxidative damage, ER-stress and vascular permeability alone or together can compromise ocular health and that GYY4137 could serve as a potential therapeutic agent for treating HHcy induced ocular disorders.

Infl iximab relieves blood retinal barrier breakdown through the p38 MAPK pathway in a diabetic rat model

AIM： To clarify the mechanism of infliximab treatment in diabetic macular edema （DME） and to provide a new alternative therapy for DME. METHODS： Rats were randomly divided into the control group, the model group and the infliximab treatment group. A diabetic rat model was created. The concentration of TNF-α in the vitreous body was detected by ELISA. The expressions of B-Raf, p38, claudin-1 and occludin in the retina were detected by Western blot. The integrity of the blood retinal barrier （BRB） was measured using Evan＇s blue as a tracer. RESULTS： After three months and six months of the diabetes model, the vitreous TNF-α level in the model group was higher than that of the control group. It was also higher in treated group than that of the control group but was lower than that of the model group. The differences among the three groups were statistically significant （at 3mo, F=857.098, P〈0.001; 6mo, F=1261.897, P〈0.001）. The retina B-Raf and p38 levels in the model group were higher than that of the control group. They were also higher in treated group than that of the control group but were lower than that of the model group. The differences among the three groups were statistically significant （B-Raf at 3mo, F=106.596, P〈0.001 and at 6mo, F=200.681, P〈0.001; p38 at 3mo, F=41.662, P〈0.001 and at 6mo, F=67.979, P〈0.001）. The retina claudin-1 and occludin levels in the model group were lower than that of the control group. They were also lower in treated group than that of the control group but were higher than that of the model group. The differences among three groups were statistically significant （claudin-1 at3mo, F=-139.088, P〈0.001 and at 6mo, F=128.415, P〈0.001; occludin at 3mo, F=-92.733, P〈0.001 and at 6mo, F--104.478, P〈0.001）. The retinal Evans blue leakage in the model group was higher than that of the control group. It was also higher in treated group than that of the control group but was lower than that of the model group. The differences among the three groups were statistically significant （at 3mo, F=-447.946, P〈0.001; at 6mo, F＇=-1610.732, P〈0.001）. CONCLUSION： In-α diabetic rat model, infliximab may relieve TNF-α induced BRB breakdown via the B-Raf and p38 signaling pathway.

Differential expression of breast cancer-resistance protein,lung resistance protein,and multidrug resistance protein 1 in retinas of streptozotocin-induced diabetic mice

AIM：To investigate the altering expression profiles of efflux transporters such as breast cancer-resistance protein（BCRP）,lung resistance protein（LRP）,and multidrug resistance protein 1（MDR1） at the inner blood-retinal barrier（BRB） during the development of early diabetic retinopathy（DR） and/or aging in mice.METHODS：Relative m RNA and protein expression profiles of these three efflux transporters in the retina during the development of early DR and/or aging in mice were examined.The differing expression profiles of Zonula occludens 1（ ZO-1） and vascular endothelial growth factor-A（ VEGFA） in the retina as well as the perfusion characterization of fluorescein isothiocyanate（FITC）-dextran and Evans blue were examined to evaluate the integrity of the inner BRB.RESULTS：There were significant alterations in these three efflux transporters＇ expression profiles in the m RNA and protein levels of the retina during the development of diabetes mellitus and/or aging.The development of early DR was confirmed by the expression profiles of ZO-1 and VEGFA in the retina as well as the compromised integrity of the inner BRB.CONCLUSION：The expression profiles of some efflux transporters such as BCRP,LRP,and MDR1 in mice retina during diabetic and/or aging conditions are tested,and the attenuated expression of BCRP,LRP,and MDR1 along with the breakdown of the inner BRB is found,which may be linked to the pathogenesis of early DR.

pH-Responsive polymer boosts cytosolic siRNA release for retinal neovascularization therapy

Small interfering RNA(siRNA)has a promising future in the treatment of ocular diseases due to its high efficiency,specificity,and low toxicity in inhibiting the expression of target genes and proteins.However,due to the unique anatomical structure of the eye and various barriers,delivering nucleic acids to the retina remains a significant challenge.In this study,we rationally design PACD,an A-B-C type non-viral vector copolymer composed of a hydrophilic PEG block(A),a siRNA binding block(B)and a pH-responsive block(C).PACDs can self-assemble into nanosized polymeric micelles that compact siRNAs into polyplexes through simple mixing.By evaluating its pH-responsive activity,gene silencing efficiency in retinal cells,intraocular distribution,and anti-angiogenesis therapy in a mouse model of hypoxia-induced angiogenesis,we demonstrate the efficiency and safety of PACD in delivering siRNA in the retina.We are surprised to discover that,the PACD/siRNA polyplexes exhibit remarkable intracellular endosomal escape efficiency,excellent gene silencing,and inhibit retinal angiogenesis.Our study provides design guidance for developing efficient nonviral ocular nucleic acid delivery systems.

Preventive effect of chrysin on experimental autoimmune uveitis triggered by injection of human IRBP peptide 1-20 in mice

Uveitis is a common cause of blindness worldwide.Experimental autoimmune uveitis(EAU)is an animal model of noninfectious uveitis.Chrysin(5,7-dihydroxyflavone)is a member of the flavonoid family and has anti-inflammatory effects.We immunized C57BL/6J mice with human interphotoreceptor retinoid-binding protein peptide 1–20 to induce EAU.Chrysin was administered intragastrically at 25 mg/kg daily to the chrysin-treated mice from 3 days before immunization to 21 days after immunization.Vehicle was administered to the mice in the control group according to the same protocol.Lower clinical and histopathological scores,increased integrity of the blood–retinal barrier(BRB)and higher expression of tight junction proteins were observed in the chrysin-treated mice.Chrysin significantly decreased the proportions of Th1,Th17 and CD4^(+)CD3^(+)CD62L^(+)Th0 cells,and increased the proportion of Treg cells.Both macrophage infiltration and the expression of inducible nitric oxide synthase in the retina were efficiently inhibited by chrysin treatment.In chrysin-treated mice,the expression of interferon-γ,interleukin(IL)-17A,IL-6,IL-1βand tumor necrosis factor-αwas reduced in the retina,whereas higher levels of transforming growth factor-βwere detected.Furthermore,NF-κBp65 was downregulated after chrysin treatment.In conclusion,as an anti-inflammatory molecule,chrysin exerts a preventive effect on EAU by modulating the balance among helper T-cell subsets and suppressing ocular inflammation,thereby maintaining the integrity of the BRB.