Bovine Retinal Pericytes Research Articles

Oxidative stress in the eye in diabetes

AbstractPurpose The characterize manifestations of oxidative stress in lens and retina in diabetes, and to evaluate the roles for aldose reductase (AR), Na+‐H+‐exchanger‐1 (NHE‐1), and poly(ADP‐ribose) polymerase‐1 (PARP‐1) in oxidative stress in both tissues, cataract formation, and retinal apoptosis.Methods The experiments were performed in streptozotocin‐diabetic rats and high glucose‐exposed cultured human lens epithelial cells (HLEC) and bovine retinal pericytes and endothelial cells (BRP and BREC). Cataract formation was evaluated by indirect ophthalmoscopy and slit lamp examination, oxidative stress by combination of biochemical and immunohistochemical methods, and retinal apoptosis by TUNEL assay in flat‐mounted retinae.Results Diabetes‐induced oxidative‐nitrosative stress manifested by accumulation of free lipid peroxidation products, malondialdehyde and 4‐hydroxyalkenals, as well as 4‐hydroxynonenal protein adducts, and nitrated and poly(ADP‐ribosyl)ated proteins, is present in both diabetic lens and retina as well as in high glucose‐exposed HLEC and BRP and BREC. Depletion of GSH and ascorbate and changes in the glutathione and ascorbate redox states are present in thre lens only. Activation of AR, NHE‐1 and PARP‐1 promotes oxidative damage. Inhibition of AR, NHE‐1, and PARP‐1 prevents diabetes‐induced oxidative stress, and prevents or delays cataractogenesis and retinal apoptosis.Conclusion Ozidative stress is present in lens and retina in diabetes and plays an important role in diabetic ocular comp‐lications. Commercial interest

Microvascular Retinal Endothelial and Pericyte Cell Apoptosis In Vitro: Role of Hedgehog and Notch Signaling

Aberrant retinal blood flow is a hallmark of retinopathies and may be a causative factor in their pathophysiology. In this study, the effects of pulsatile flow on hedgehog and Notch control of retinal endothelial cell and pericyte apoptosis were examined. The levels of hedgehog and Notch signaling components in bovine retinal endothelial cells (BRECs) and pericytes (BRPs) were examined in vitro under static conditions and after exposure to pulsatile flow, with a perfused transcapillary co-culture system. Notch and hedgehog signaling was examined by immunocytochemistry, immunoblot, and real-time PCR. Notch and hedgehog proteins were present in BRECs and BRPs in vitro and in human retinal vasculature in vivo. Inhibition of hedgehog with cyclopamine and Notch with DAPT decreased hedgehog target gene levels and Notch intracellular receptor expression, respectively, concomitant with an increase in BREC and BRP apoptosis. Sonic hedgehog (Shh) mediated upregulation of Notch1 receptor levels was attenuated after cyclopamine treatment in both cell types. Exposure of co-cultured BRECs and BRPs to pulsatile flow increased apoptosis in the BRPs while concurrently decreasing apoptosis in the BRECs. These changes were concomitant with increased expression of Notch and hedgehog signaling components in the BRECs and reduced expression in the BRPs. The flow-induced decrease in apoptosis in the BRECs was associated with increased Notch receptor expression and was reversed after inhibition of hedgehog signaling with cyclopamine and inhibition of Notch signaling after ectopic expression of the CBF-1/RBP-Jκ-binding protein, RPMS-1. Pulsatile flow promotes BREC survival and enhances BRP apoptosis through modulation of Notch and hedgehog pathways. These interactions have important implications for the pathogenesis of retinopathies.

The role of pulsatile flow in controlling microvascular retinal endothelial and pericyte cell apoptosis and proliferation

Aberrant retinal blood flow is a hallmark of various retinopathies and may be a causative factor in the pathology associated with these conditions. We examined the effects of pulsatile flow on bovine retinal endothelial cell (BREC) and bovine retinal pericyte (BRP) apoptosis and proliferation. Co-cultured BRECs and BRPs were exposed to low (0.3 mL/min) or high (25 mL/min) pulsatile flow for 72 h using a perfused transcapillary culture system. Pulsatile flow increased BREC nitric oxide synthase (eNOS) and cyclooxygenase-2 (COX-2) expression and activity concomitant with a significant decrease in pre-pro-endothelin-1 (ET-1) mRNA and peptide. BREC apoptosis was significantly attenuated following exposure to high flow. The inhibition of NOS, COX, and ET receptors significantly reduced the pro-survival effects of flow on BREC. In contrast, BRP apoptosis was significantly enhanced following exposure to high flow. The inhibition of COX and ET receptors significantly attenuated the high flow-induced increase in BRP apoptosis when compared with untreated controls. Treatment of static BREC with NO donor (S-nitroso-N-acetylpenicillamine, SNAP), ET-1, or iloprost inhibited serum deprivation-induced apoptosis, whereas treatment of BRP with ET-1 and iloprost, but not SNAP, was ineffective. High pulsatile flow decreased BRP proliferation, in the absence of any changes in BREC proliferation. Increased pulsatile flow promotes BREC survival and enhances BRP apoptosis through the activation of endothelial-derived vasoactive substances. Altered pulsatile flow does not alter BREC proliferation in co-culture with BRP, whereas BRP proliferation was significantly decreased at high flow rates. These interactions have important implications for vessel growth and regression during retinal vascular pathogenesis.

Candesartan Attenuates Diabetic Retinal Vascular Pathology by Restoring Glyoxalase-I Function

OBJECTIVEAdvanced glycation end products (AGEs) and the renin-angiotensin system (RAS) are both implicated in the development of diabetic retinopathy. How these pathways interact to promote retinal vasculopathy is not fully understood. Glyoxalase-I (GLO-I) is an enzyme critical for the detoxification of AGEs and retinal vascular cell survival. We hypothesized that, in retina, angiotensin II (Ang II) downregulates GLO-I, which leads to an increase in methylglyoxal-AGE formation. The angiotensin type 1 receptor blocker, candesartan, rectifies this imbalance and protects against retinal vasculopathy.RESEARCH DESIGN AND METHODSCultured bovine retinal endothelial cells (BREC) and bovine retinal pericytes (BRP) were incubated with Ang II (100 nmol/l) or Ang II+candesartan (1 μmol/l). Transgenic Ren-2 rats that overexpress the RAS were randomized to be nondiabetic, diabetic, or diabetic+candesartan (5 mg/kg/day) and studied over 20 weeks. Comparisons were made with diabetic Sprague-Dawley rats.RESULTSIn BREC and BRP, Ang II induced apoptosis and reduced GLO-I activity and mRNA, with a concomitant increase in nitric oxide (NO•), the latter being a known negative regulator of GLO-I in BRP. In BREC and BRP, candesartan restored GLO-I and reduced NO•. Similar events occurred in vivo, with the elevated RAS of the diabetic Ren-2 rat, but not the diabetic Sprague-Dawley rat, reducing retinal GLO-I. In diabetic Ren-2 rats, candesartan reduced retinal acellular capillaries, inflammation, and inducible nitric oxide synthase and NO•, and restored GLO-I.CONCLUSIONSWe have identified a novel mechanism by which candesartan improves diabetic retinopathy through the restoration of GLO-I.

GLUT-1 Expression in Bovine Retinal Capillary Endothelial Cells and Pericytes Exposed to Advanced Glycation End Products

Glucose uptake and glucose transporter GLUT-1 expressions are characteristic of retinal capillary endothelial cells and pericytes in response to high glucose. In this study, the effects of advanced glycation end product (AGE-BSA) exposure on these parameters were tested. Primary cultures of bovine retinal capillary endothelial cells (BRECs) and bovine retinal capillary pericytes (BRPs) were exposed to AGE-BSA (100 μg/mL) for 6 days. Glucose uptake was measured using U (14)C-glucose and the GLUT-1 mRNA expression by RT-PCR. GLUT-1 protein was detected by immunofluorescence and subjected to FACS analysis. The authors observed that there was no significant decrease in the GLUT-1 protein expression, and this was confirmed by glucose uptake by (14)C-labeled glucose in both BRECs and BRPs. Even though there was a slight decrease in the mRNA expression of GLUT-1 in AGE-BSA-treated cells compared with both untreated control and BSA treated, the decrease was not significant. This is the first report to show that there is no difference in glucose uptake in BRECs and BRPs on exposure to AGE-BSA.

High glucose‐induced apoptosis in bovine retinal pericytes is associated with transforming growth factor β and βIG‐H3: βIG‐H3 induces apoptosis in retinal pericytes by releasing Arg‐Gly‐Asp peptides

Transforming growth factor beta (TGF-beta) plays an important role in diabetic retinopathy. betaIG-H3 is a downstream target molecule of TGF-beta that may participate in the pathogenesis of diabetic retinopathy and in particular in the loss of pericytes during early pathological changes. We observed bovine retinal pericytes apoptosis and the increased expression of TGF-beta and betaIG-H3 induced by high concentrations of glucose in the cell culture media. An anti-TGF-beta antibody was used to block glucose-induced retinal pericytes apoptosis. Retinal pericytes were also transfected with cDNA encodings either wild-type or mutant betaIG-H3 lacking Arg-Gly-Asp (RGD) sequences in order to validate the effects of betaIG-H3 and RGD signalling on retinal pericytes apoptosis. A cell death-detecting enzyme-linked immunosorbent assay revealed that 25 mM glucose significantly increased cell death compared with 5.5 mM glucose after 5 or 7 days of exposure (P < 0.01). High glucose significantly increased the TGF-beta levels as compared with 5.5 mM glucose after 5 days, and betaIG-H3 levels after 3, 5 and 7 days of exposure (P < 0.01). TGF-beta increased cell death and betaIG-H3 levels in a dose-dependent manner, with a maximal effect observed at 1 ng/mL. An anti-TGF-beta antibody nearly completely blocked high glucose-induced cell death. Wild-type betaIG-H3-transfected cells showed a significant increase in cell death as compared with mutant betaIG-H3-transfected (Mycb-c) cells, untransfected or mock-transfected cells. These results suggest that hyperglycaemia-induced expression of TGF-beta and betaIG-H3 contributes to accelerated retinal pericytes apoptosis. betaIG-H3 induces pericytes apoptosis through its RGD motif, which may constitute an important pathogenic mechanism leading to pericytes loss in diabetic retinopathy.

Metabolic memory and diabetic retinopathy: Role of inflammatory mediators in retinal pericytes

Diabetic retinopathy shares many characteristics features of a low grade chronic inflammatory disease. Its progression resists arrest when good metabolic control is re-established after a period of poor metabolic control, suggesting a 'metabolic memory' phenomenon. The aim of this study is to investigate the effect of reversal of high glucose to normal glucose on the inflammatory mediators in pericytes, the site of histopathology in diabetic retinopathy. Bovine retinal pericytes were incubated in high glucose (20 mM) for 2 days followed by normal glucose (5 mM) for 4 days (2 --> 4), or in high glucose for 4 days followed by normal glucose for 4 days (4 --> 4) or 8 days (4 --> 8). Pericytes incubated in continuous normal or high glucose for 2-12 days served as controls. Continuous high glucose exposure for 2-12 days significantly elevated gene expressions and protein concentrations of IL-1 beta, NF-kB, VEGF, TNF-alpha, TGF-beta and ICAM-1 in retinal pericytes. Four days of normal glucose that followed 2 days of high glucose (2 --> 4) had marginal, but significant, beneficial effect on the increases in these inflammatory mediators. Four days of normal glucose in 4 --> 4 group failed to reverse increases in inflammatory mediators and cell apoptosis remained elevated, but addition of dexamethasone during normal glucose exposure ameliorated such increases. However, when normal glucose exposure, after 4 days of high glucose was extended to 8 days (4 --> 8), increases in these mediators were significantly decreased. Hyperglycemia-induced elevations in inflammatory mediators in retinal microvascular cells resist reversal after re-institution of normal glucose conditions. Both, the duration of the initial exposure to high glucose, and normal glucose that follows high glucose, are critical in determining the outcome of the alterations in the inflammatory mediators.

Differential TGF-β Signaling in Retinal Vascular Cells: A Role in Diabetic Retinopathy?

Purpose. An early hallmark of preclinical diabetic retinopathy is thickening of the capillary basal lamina (BL). TGF-beta, a multipotent cytokine acting through its receptors ALK5 and -1, has been postulated to be involved in this phenomenon. In light of this possible role, TGF-beta signaling and its downstream molecular effects were characterized in cultured vascular endothelial cells and pericytes of the retina. Methods. Bovine retinal endothelial cells and pericytes were stimulated with TGF-beta1 in the presence or absence of SD-208, a specific inhibitor of the TGF-beta type I receptor ALK5, or ALK5 small interfering (si)RNA. TGF-beta-signaling pathways were characterized by analysis of phosphorylated Smad2 or -1/5/8 proteins and TGF-beta target genes (PAI-1, fibronectin, CTGF, Smad7, and Id1) and protein (fibronectin). Results. ALK5 was expressed in both cell types, whereas ALK1 was exclusively expressed in endothelial cells. In endothelial cells, TGF-beta induced Smad2 phosphorylation at high concentrations, which was efficiently blocked by ALK5 inhibition. In contrast, in pericytes, Smad2 phosphorylation was rapidly induced at low concentrations of TGF-beta. The ALK1-Smad1/5/8 pathway was activated by TGF-beta in endothelial cells only. TGF-beta caused ALK5-mediated upregulation of PAI-1, Smad7, and fibronectin and in pericytes at lower TGF-beta concentrations than in endothelial cells. CTGF mRNA expression was induced only in pericytes. Fibronectin protein was confirmed to be regulated by TGF-beta in both cell types. Conclusions. TGF-beta signaling in retinal endothelial cells and pericytes show that these cells, and in particular the pericytes, have the essential characteristics to allow for a role of TGF-beta in BL thickening in preclinical diabetic retinopathy.

Thiamine and benfotiamine prevent apoptosis induced by high glucose‐conditioned extracellular matrix in human retinal pericytes

Early and selective loss of pericytes and thickening of the basement membrane are hallmarks of diabetic retinopathy. We reported reduced adhesion, but no changes in apoptosis, of bovine retinal pericytes cultured on extracellular matrix (ECM) produced by endothelial cells in high glucose (HG). Since human and bovine pericytes may behave differently in conditions mimicking the diabetic milieu, we verified the behaviour of human retinal pericytes cultured on HG-conditioned ECM. Pericytes were cultured in physiological/HG on ECM produced by human umbilical vein endothelial cells in physiological/HG, alone or in the presence of thiamine and benfotiamine. Adhesion, proliferation, apoptosis, p53 and Bcl-2/Bax ratio (mRNA levels and protein concentrations) were measured in wild-type and immortalized human pericytes. Both types of pericytes adhered less to HG-conditioned ECM and plastic than to physiological glucose-conditioned ECM. DNA synthesis was impaired in pericytes cultured in HG on the three different surfaces but there were no differences in proliferation. DNA fragmentation and Bcl-2/Bax ratio were greatly enhanced by HG-conditioned ECM in pericytes kept in both physiological and HG. Addition of thiamine and benfotiamine to HG during ECM production completely prevented these damaging effects. Apoptosis is strongly increased in pericytes cultured on ECM produced by endothelium in HG, probably due to impairment of the Bcl-2/Bax ratio. Thiamine and benfotiamine completely revert this effect. This behaviour is therefore completely different from that of bovine pericytes, underlining the importance of establishing species-specific cell models to study the mechanisms of diabetic retinopathy.

Anticataract effect as a predictor of drug efficacy against early diabetes‐induced retinal changes

Abstract Purpose To evaluate if anticataract effect predicts drug efficacy against early diabetes‐induced retinal changes, using STZ‐diabetic rat model and cultured retinal microvascular cells. Methods Mature control and STZ‐diabetic rats received one of the following treatments (a prevention approach): 1) the aldose reductase inhibitor (ARI) fidarestat, 2) the PARP inhibitors, 1,5‐isoquinolinediol or GPI‐15427; 3) the Na+/H+‐exchanger‐1 (NHE‐1) inhibitor cariporide; and 4) two agents, counteracting endoplasmic reticulum stress,trimethylamine N‐oxide dehydrate or 4‐phenylbutyric acid. The duration of diabetes was 12 wks. Cataract formation was monitored by indirects ophthalmoscopy and slit lamp examination.Oxidative stress and apoptosis were assessed as early diabetes‐induced retinal changes in rat retinae and cultured bovine retinal pericytes and endothelial cells. Results An ARI treatment completely prevented cataract formation in STZ‐diabetic rats, whereas three other treatments delayed, but did not prevent, diabetes‐induced cataractogenesis. All four classes of agents counteracted diabetes‐induced apoptosis in rat retinae, and the ARI, PARP inhibitor, and NHE‐1 inhibitor treatments prevented high glucose and NEFA‐induced apoptosis in pericytes and endothelial cells. Fidarestat, PARP inhibitors, and cariporide treatments also counteracted diabetes‐related oxidative stress in the retinae and cultured retinal microvascular cells. The effect of agents counteracting endoplasmic reticulum stress on retinal oxidative stress has not been explored. Conclusion Anticataract effect ia a likely predictor of the efficacy of experimental pharmacological agents against, at least, early diabetes‐associated retinal changes which may facilitate diabetes drug discovery. Commercial interest

Different apoptotic responses of human and bovine pericytes to fluctuating glucose levels and protective role of thiamine

Vascular cells in diabetes are subjected to daily fluctuations from high to low glucose. We aimed at investigating whether pulsed exposure to different glucose concentrations influences apoptosis in human retinal pericytes (HRP) versus bovine retinal pericytes (BRP), with consequences on the onset of diabetic retinopathy, and the possible protective role of thiamine. BRP and HRP (wild-type and immortalized) were grown in physiological/high glucose for 7 days, and then returned to physiological glucose for another 24, 48 or 72 h. Cells were also kept intermittently at 48-h intervals in high/normal glucose for 8 days, with/without thiamine/benfotiamine. Apoptosis was determined through ELISA, TUNEL, Bcl-2, Bax and p53 expression/concentration. Continuous exposure to high glucose increased apoptosis in BRP, but not HRP. BRP apoptosis normalized within 24 h of physiological glucose re-entry, while HRP apoptosis increased within 24-48 h of re-entry. Intermittent exposure to high glucose increased apoptosis in HRP and BRP. Bcl-2/Bax results were consistent with DNA fragmentation, while p53 was unchanged. Thiamine and benfotiamine countered intermittent high glucose-induced apoptosis. Human pericytes are less prone to apoptosis induced by persistently high glucose than bovine cells. However, while BRP recover after returning to physiological levels, HRP are more vulnerable to both downwardly fluctuating glucose levels and intermittent exposure. These findings reinforce the hypotheses that (1) glycaemic fluctuations play a role in the development of diabetic retinopathy and (2) species-specific models are needed. Thiamine and benfotiamine prevent human pericyte apoptosis, indicating this vitamin as an inexpensive approach to the prevention and/or treatment of diabetic complications.

Poly(ADP-Ribose)Polymerase Inhibition Counteracts Cataract Formation and Early Retinal Changes in Streptozotocin-Diabetic Rats

This study evaluated the role for poly(ADP-ribose) polymerase (PARP) in diabetes-induced cataractogenesis and early retinal changes. Control and streptozotocin (STZ)-diabetic rats were treated with or without the PARP inhibitors 1,5-isoquinolinediol (ISO; 3 mg kg(-1) d(-1) intraperitoneally) and 10-(4-methyl-piperazin-1-ylmethyl)-2H-7-oxa-1,2-diaza-benzo[de]anthracen-3-1 (GPI-15427, 30 mg kg(-1) d(-1) orally) for 10 weeks after the first 2 weeks without treatment. Lens clarity was evaluated by indirect ophthalmoscopy and slit lamp examination, and retinal changes were evaluated by immunohistochemistry and Western blot analysis. In in vitro studies, cultured human lens epithelial cells and bovine retinal pericytes and endothelial cells were exposed to high glucose or palmitate. PARP is expressed in lens, and poly(ADP-ribosyl)ated proteins are primarily localized in the 38- to 87-kDa range of the protein spectrum, with several minor bands at 17 to 38 kDa. The 38- to 87-kDa and the 17- to 38-kDa poly(ADP-ribosyl)ated protein expression increased by 74% and 275%, respectively, after 4 weeks of diabetes and by approximately 65% early after exposure of lens epithelial cells to 30 mM glucose. Both PARP inhibitors delayed, but did not prevent, the formation of diabetic cataract. The number of TUNEL-positive nuclei in flatmounted retinas increased approximately 4-fold in STZ diabetic rats, and this increase was prevented by ISO and GPI-15427. Both PARP inhibitors reduced diabetes-induced retinal oxidative-nitrosative and endoplasmic reticulum stress and glial activation. GPI-15427 (20 microM) prevented oxidative-nitrosative stress and cell death in palmitate-exposed pericytes and endothelial cells. PARP activation is implicated in the formation of diabetic cataract and in early retinal changes. These findings provide a rationale for the development of PARP inhibitors for the prevention of diabetic ocular complications.

Altered expression of genes related to blood–retina barrier disruption in streptozotocin-induced diabetes

Disruption of the blood–retina barrier (BRB) is an early phenomenon in preclinical diabetic retinopathy (PCDR). Two vascular permeability pathways may be affected, the paracellular pathway involving endothelial cell tight junctions, and the endothelial transcellular pathway mediated by endocytotic vesicles (caveolae). The relative contribution of both pathways to vascular permeability in PCDR is unknown. We compared transcription levels in entire rat retina of genes related to these pathways between control conditions and after 6 and 12 weeks of streptozotocin-induced diabetes, as well as in bovine retinal endothelial cells (BRECs) exposed to VEGF and bovine retinal pericytes (BRPCs), using real-time quantitative RT-PCR. To confirm endothelial-specificity, immunohistochemical staining was performed in rat retina, and mRNA transcript levels were compared between BRECs and BRPCs. mRNA and protein of most paracellular transport-related genes were specifically expressed by retinal endothelial cells, whereas vesicle transport-related mRNA and proteins were present in various retinal cell types, including endothelial cells. Expression of selected endothelial cell tight junction genes and particularly that of occludin and claudin-5 was reduced in the diabetic retina and in BRECs after exposure to VEGF. Expression of 6 out of 11 vesicular transport-related genes was upregulated after induction of diabetes. Of these, only plasmalemma vesicle-associated protein (PV-1) was exclusively expressed in BRECs and not in BRPCs. PV-1 transcription was markedly induced in diabetic retina and by VEGF in BRECs. Caveolin-1 immunostaining was primarily found in the retinal vasculature, and its mRNA levels in BRECs were highly abundant and VEGF-inducible. Whereas the endothelial tight junction genes occludin and claudin-5 showed a transient downregulation, we observed long-term upregulation in diabetic retina and VEGF-induced expression in BRECs of the vesicular transport-related genes caveolin-1 and PV-1. The altered gene expression profiles observed in this study suggest a transient induction of the paracellular pathway and prolonged involvement of transcellular endothelial transport mechanisms in the increased permeability of retinal capillaries in PCDR.

Selective Regulation of Heme Oxygenase-1 Expression and Function by Insulin through IRS1/Phosphoinositide 3-Kinase/Akt-2 Pathway

Heme oxygenase 1 (HO-1) is a representative mediator of antioxidants and cytoprotectants against various stress stimuli including oxidants in vascular cells. Intensive insulin treatment can delay the onset and progression of diabetic retinopathy and other vascularopathies, yet little is known about insulin regulation of anti-apoptotic and antioxidant molecules such as HO-1 in vascular cells. Intravitreous injection or in vitro addition of insulin increased HO-1 protein expression in rat retina and in cultured bovine retinal pericytes, retinal endothelial cells, and retinal pigment epithelial cells. In bovine retinal pericytes, insulin induced mRNA and protein expression of HO-1 in a time- and concentration-dependent manner. Using HO-1 promoter analysis, the luciferase reporter assay showed that induction of HO-1 expression by insulin is mediated by additional response elements in the ho-1 promoter gene, which was not responsive to antioxidants. Insulin-induced HO-1 mRNA expression through activation of PI3-kinase/Akt pathway without affecting ERK and p38 MAPK. Overexpression of an adenoviral vector of native IRS1, IRS2, and Akt dominant negative or small interfering RNA transfection of Akt1 and Akt2 targeted gene demonstrated that insulin regulated HO-1 expression via IRS1 and Akt2 pathway, selectively. Further, insulin treatment prevented H(2)O(2)-induced NF-kappaB and caspase-8 activation and apoptosis via the IRS1/PI3K/Akt2/HO-1 pathway in the pericytes. In conclusion, we suggest that the anti-apoptotic properties of insulin are mediated partly by increasing HO-1 expression at transcriptional level via IRS1/PI3K/Akt2 activation, a potential explanation for how insulin is retarding the progression of microvascular complications induced by diabetes.

Identification of a Retinal Aldosterone System and the Protective Effects of Mineralocorticoid Receptor Antagonism on Retinal Vascular Pathology

Blockade of the renin-angiotensin-aldosterone system (RAAS) is being evaluated as a treatment for diabetic retinopathy; however, whether the mineralocorticoid receptor (MR) and aldosterone influence retinal vascular pathology is unknown. We examined the effect of MR antagonism on pathological angiogenesis in rats with oxygen-induced retinopathy (OIR). To determine the mechanisms by which the MR and aldosterone may influence retinal angiogenesis; inflammation and glucose-6-phosphate dehydrogenase (G6PD) were evaluated in OIR and cultured bovine retinal endothelial cells (BRECs) and bovine retinal pericytes (BRPs). In OIR, MR antagonism (spironolactone) was antiangiogenic. Aldosterone may mediate the pathogenic actions of MR in the retina, with 11beta-hydroxysteroid dehydrogenase type 2 mRNA being detected and with aldosterone stimulating proliferation and tubulogenesis in BRECs and exacerbating angiogenesis in OIR, which was attenuated with spironolactone. The MR and aldosterone modulated retinal inflammation, with leukostasis and monocyte chemoattractant protein-1 mRNA and protein in OIR being reduced by spironolactone and increased by aldosterone. A reduction in G6PD may be an early response to aldosterone. In BRECs, BRPs, and early OIR, aldosterone reduced G6PD mRNA, and in late OIR, aldosterone increased mRNA for the NAD(P)H oxidase subunit Nox4. A functional retinal MR-aldosterone system was evident with MR expression, translocation of nuclear MR, and aldosterone synthase expression, which was modulated by RAAS blockade. We make the first report that MR and aldosterone influence retinal vasculopathy, which may involve inflammatory and G6PD mechanisms. MR antagonism may be relevant when developing treatments for retinopathies that target the RAAS.

PARP, Na+/H+‐exchanger‐1, and early diabetes‐induced retinal changes

Abstract Purpose To evaluate the roles for PARP and Na+/H+‐exchanger‐1 (NHE‐1) in early diabetes‐induced changes in the retina and retinal capillary cells Methods Control (C) and STZ‐diabetic (D) rats were treated with/without the PARP inhibitors, 1,5‐isoquinolinediol (ISO, 3 mgkg‐1d‐1 i.p.) or 10‐(4‐Methyl‐piperazin‐1‐ylmethyl)‐2H‐7‐oxa‐1,2‐diaza‐benzo[de]‐anthracen‐3‐one (GPI 15427, 30 mgkg‐1d‐1), for 10 wks after 2 wks without treatment. Apoptosis was evaluated in flat‐mounted retinas by TUNEL assay, and nitrotyrosine (NT), poly(ADP‐ribose) (PAR), GFAP, BiP/GRP78 and GRP94 expressions by immunohistochemistry and Western blot analyses. Primary bovine retinal pericytes and endothelial cells were cultured with/without 0.6 mM palmitate, or in 5 mM or 30 mM glucose. Apoptosis was assessed by TUNEL and caspase‐3 assays, superoxide production by ethidium fluorescence, and NT and PAR by immunocytochemistry. Results In the PARP study, the number of TUNEL‐positive nuclei was increased ~4‐fold in D, and this increase was prevented in D+ISO and D+GPI 15427. PARP inhibitors counteracted oxidative‐nitrosative and endoplasmic reticulum stresses, and glial activation. Palmitate dose dependently increased superoxide production in cultured retinal cells. GPI 15427, 20 microM, prevented FFA‐induced increase in the rate of apoptosis, and alleviated NT and PAR accumulation in both pericytes and endothelial cells. In the NHE‐1 study, the specific NHE‐1 inhibitor cariporide (10 microM) prevented high glucose‐induced apoptosis, and alleviated oxidative‐nitrosative stress and PAR accumulation in bovine retinal pericytes. In vivo studies in the STZ‐diabetic rat model are in progress. Conclusion PARP and NHE‐1 play an important role in early diabetes‐induced changes in retina and retinal capillary cells.

Aldose reductase inhibitor fidarestat counteracts diabetes-associated cataract formation, retinal oxidative-nitrosative stress, glial activation, and apoptosis

This study was aimed at evaluating the potent and specific aldose reductase inhibitor fidarestat, on diabetes-associated cataract formation, and retinal oxidative-nitrosative stress, glial activation, and apoptosis. Control and streptozotocin-diabetic rats were treated with or without fidarestat (16 mg kg(-1)d(-1)) for 10 weeks after an initial 2-week period without treatment. Lens changes were evaluated by indirect ophthalmoscopy and portable slit lamp. Nitrotyrosine, poly(ADP-ribose), and glial fibrillary acidic protein expression were assessed by immunohistochemistry. The rate of apoptosis was quantified in flat-mounted retinas by TUNEL assay with immunoperoxidase staining. To dissect the effects of high glucose exposure in retinal microvascular cells, primary bovine retinal pericytes and endothelial cells were cultured in 5 or 30 mM glucose, with or without fidarestat (10 microM) for 3-14 days. Apoptosis was assessed by TUNEL assay, nitrotyrosine and poly(ADP-ribose) by immunocytochemistry, and Bax and Bcl-2 expression by Western blot analyses. Fidarestat treatment prevented diabetic cataract formation and counteracted retinal nitrosative stress, and poly(ADP-ribose) polymerase activation, as well as glial activation. The number of TUNEL-positive nuclei (mean +/- SEM) was increased approximately 4-fold in diabetic rats vs. controls (207+/-33 vs. 49+/-4, p<0.01), and this increase was partially prevented by fidarestat (106+/-34, p<0.05 vs. untreated diabetic group). The apoptotic cell number increased with the prolongation of exposure of both pericytes and endothelial cells to high glucose levels. Fidarestat counteracted nitrotyrosine and poly(ADP-ribose) accumulation and apoptosis in both cell types. Antiapoptotic effect of fidarestat in high glucose-exposed retinal pericytes was not associated with the inhibition of Bax or increase in Bcl-2 expression. In conclusion, the findings, i) support an important role for aldose reductase in diabetes-associated cataract formation, and retinal oxidative-nitrosative stress, glial activation, and apoptosis, and ii) provide a rationale for the development of aldose reductase inhibitors, and, in particular, fidarestat, for the prevention and treatment of diabetic ocular complications.

Glypican 4, a Membrane Binding Protein for Bactericidal/Permeability-Increasing Protein Signaling Pathways in Retinal Pigment Epithelial Cells

Originally identified as a lipopolysaccharide binding protein with Gram-negative bactericidal activity in the leukocytes, bactericidal/permeability-increasing protein (BPI) has been shown to induce various effects in retinal cells in vivo and in vitro. The authors recently reported that BPI can induce ERK1/2 and Akt activity and that it increases DNA synthesis in the bovine retinal pigment epithelial (RPE) and pericyte cells. The authors have extended the characterization of BPI interaction with membrane proteins from bovine RPE. Crude membrane pools from RPE were isolated, solubilized, and bound to rBPI(21) affinity column. Bound proteins were separated by SDS-PAGE and stained with Coomassie blue, which showed an intense band at 36 kDa consistently displaced by rBPI(21). Tandem mass spectrometry of the 36-kDa band suggested that cell surface protein glypican 4 (GPC4) serves as a putative BPI-binding protein. Heparitinase, phosphatidylinositol-specific phospholipase C, and anti-GPC4 antibody suppressed BPI-induced ERK and Akt phosphorylation in bovine RPE. Moreover, heparitinase also inhibited BPI actions on VEGF and PDGF-B mRNA expression induced by H(2)O(2). These new findings suggest that GPC4 is a specific binding protein for BPI on RPE to mediate the activation of ERK1/2, Akt, and the mRNA expressions of PDGF-B and VEGF.

Overexpression of integrin-linked kinase in bovine retinal microvascular pericytes induced by glucose

目的 研究高糖培养的牛视网膜微血管周细胞的凋亡和整合蛋白连接酶(ILK)表达的变化及二者的关系.方法 原代培养周细胞,用流式细胞Annexin V检测周细胞的凋亡,用免疫细胞化学和Western blot检测牛视网膜微血管周细胞ILK的表达.结果 用30 mmol/L D-葡萄糖培养24、48、72 h后,牛视网膜微血管周细胞凋亡显著增加,分别为47.6%、58.4%和68.7%且具有时间依赖性.用5 mmol/L D-葡萄糖培养72 h后未见周细胞ILK表达.在30 mmol/L D-葡萄糖或5 μmol/L H2O2条件下培养72 h后,周细胞形态发生改变,ILK表达显著增强,主要分布在细胞质;Western blot检测发现30 mmol/L D-葡萄糖培养的条件下周细胞ILK蛋白水平随时间延长显著增加.结论 高糖可以诱导视网膜微血管周细胞凋亡,高糖条件下周细胞ILK过表达可能参与周细胞的损伤。

Aldose Reductase Inhibition Counteracts Diabetes-Induced Retinal Oxidative Injury, Glial Activation, and Apoptosis

Purpose: To access the role for increased aldose reductase (AR) activity in oxidative injury, glial activation, and apoptosis in retinae of diabetic rats and high glucose-exposed cultured retinal pericytes and endothelial cells. Methods: Control (C) and STZ-diabetic (D) rats were treated with/without the AR inhibitor fidarestat (F, 16 mg/kg/g, for 10 wks after 2 wks without treatment). The rate of apoptosis was assessed in flat-mounted retinas by TUNEL assay with immunoperoxidase staining, and nitrotyrosine (NT), poly(ADP-ribose) [PAR, a marker of poly(ADP-ribose) polymerase activation] and glial fibrillary acidic protein (GFAP) expression in retinal sections by immunohistochemistry. Primary bovine retinal pericytes and endothelial cells were cultured in 5 mM or 30 mM glucose with/without F (10 microM) for 3-14 d. Apoptosis was assessed by TUNEL assay, NT and PAR by immunocytochemistry, and Bax and Bcl-2 expression by Western blot analyses. Results: The number of TUNEL-positive nuclei (Mean ± SEM) was increased ~4-fold in D (207 ± 33 vs 49 ± 4 in C, p < 0.01), and this increase was partially corrected in D+F (106 ± 34, p < 0.05 vs D). The apoptotic cell number increased with prolongation of exposure of both pericytes and endothelial cells to high glucose. F counteracted high glucose-induced apoptosis, and NT and PAR accumulation in both cell types. Antiapoptotic effect of F in high glucose-exposed retinal pericytes was not associated with inhibition of Bax or increase in Bcl-2 expression (endothelial cell studies are in progress). Conclusions: AR inhibition with fidarestat conteracts diabetes-associated retinal oxidative injury, glial activation, and apoptosis.