Vascular permeability in experimental diabetes is associated with reduced endothelial occludin content: vascular endothelial growth factor decreases occludin in retinal endothelial cells. Penn State Retina Research Group.
TL;DR: These data show that diabetes selectively reduces retinal occludin protein expression and increases BRB permeability, and suggest that the elevated VEGF in the vitreous of patients with diabetic retinopathy increases vascular permeability by downregulating occlUDin content.
Abstract: Blood-retinal barrier (BRB) breakdown is a hallmark of diabetic retinopathy, but the molecular changes that cause this pathology are unclear. Occludin is a transmembrane component of interendothelial tight junctions that may regulate permeability at the BRB. In this study, we examined the effects of vascular endothelial growth factor (VEGF) and diabetes on vascular occludin content and barrier function. Sprague-Dawley rats were made diabetic by intravenous streptozotocin injection, and age-matched animals served as controls. After 3 months, BRB permeability was quantified by intravenous injection of fluorescein isothiocyanate-bovine serum albumin (FITC-BSA), Mr 66 kDa, and 10-kDa rhodamine-dextran (R-D), followed by digital image analysis of retinal sections. Retinal fluorescence intensity for FITC-BSA increased 62% (P < or = 0.05), but R-D fluorescence did not change significantly. Occludin localization at interendothelial junctions was confirmed by immunofluorescence, and relative protein content was determined by immunoblotting of retinal homogenates. Retinal occludin content decreased approximately 35% (P < or = 0.03) in the diabetic versus the control animals, whereas the glucose transporter GLUT1 content was unchanged in rat retinas. Additionally, treatment of bovine retinal endothelial cells in culture with 0.12 nmol/l or 12 nmol/l VEGF for 6 h reduced occludin content 46 and 54%, respectively. These data show that diabetes selectively reduces retinal occludin protein expression and increases BRB permeability. Our findings suggest that the elevated VEGF in the vitreous of patients with diabetic retinopathy increases vascular permeability by downregulating occludin content. Decreased tight junction protein expression may be an important means by which diabetes causes increased vascular permeability and contributes to macular edema.
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TL;DR: Understanding how BBB TJ might be affected by various factors holds significant promise for the prevention and treatment of neurological diseases.
Abstract: The blood-brain barrier (BBB) is the regulated interface between the peripheral circulation and the central nervous system (CNS). Although originally observed by Paul Ehrlich in 1885, the nature of the BBB was debated well into the 20th century. The anatomical substrate of the BBB is the cerebral microvascular endothelium, which, together with astrocytes, pericytes, neurons, and the extracellular matrix, constitute a "neurovascular unit" that is essential for the health and function of the CNS. Tight junctions (TJ) between endothelial cells of the BBB restrict paracellular diffusion of water-soluble substances from blood to brain. The TJ is an intricate complex of transmembrane (junctional adhesion molecule-1, occludin, and claudins) and cytoplasmic (zonula occludens-1 and -2, cingulin, AF-6, and 7H6) proteins linked to the actin cytoskeleton. The expression and subcellular localization of TJ proteins are modulated by several intrinsic signaling pathways, including those involving calcium, phosphorylation, and G-proteins. Disruption of BBB TJ by disease or drugs can lead to impaired BBB function and thus compromise the CNS. Therefore, understanding how BBB TJ might be affected by various factors holds significant promise for the prevention and treatment of neurological diseases.
2,374 citations
Cites background from "Vascular permeability in experiment..."
...vascular permeability and reduced occludin content in the retinal microvasculature (which is similar to that of the brain) (Antonetti et al., 1998) and at the BBB (Chehade et al....
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...…effects and a known risk factor for ischemic stroke (Goldstein et al., 2001), is also associated with increased vascular permeability and reduced occludin content in the retinal microvasculature (which is similar to that of the brain) (Antonetti et al., 1998) and at the BBB (Chehade et al., 2002)....
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TL;DR: The glycation of plasma proteins such as albumin, fibrinogen, globulins and collagen to form different types of AGEs is discussed and the role of A GEs in the pathogenesis of diabetic complications including retinopathy, cataract, neuropathy, nephropathy and cardiomyopathy is discussed.
Abstract: During long standing hyperglycaemic state in diabetes mellitus, glucose forms covalent adducts with the plasma proteins through a non-enzymatic process known as glycation. Protein glycation and formation of advanced glycation end products (AGEs) play an important role in the pathogenesis of diabetic complications like retinopathy, nephropathy, neuropathy, cardiomyopathy along with some other diseases such as rheumatoid arthritis, osteoporosis and aging. Glycation of proteins interferes with their normal functions by disrupting molecular conformation, altering enzymatic activity, and interfering with receptor functioning. AGEs form intra- and extracellular cross linking not only with proteins, but with some other endogenous key molecules including lipids and nucleic acids to contribute in the development of diabetic complications. Recent studies suggest that AGEs interact with plasma membrane localized receptors for AGEs (RAGE) to alter intracellular signaling, gene expression, release of pro-inflammatory molecules and free radicals. The present review discusses the glycation of plasma proteins such as albumin, fibrinogen, globulins and collagen to form different types of AGEs. Furthermore, the role of AGEs in the pathogenesis of diabetic complications including retinopathy, cataract, neuropathy, nephropathy and cardiomyopathy is also discussed.
1,029 citations
TL;DR: In this paper, the safety and efficacy of dexamethasone intravitreal implant (DEX implant; OZURDEX, Allergan, Inc., Irvine, CA) compared with sham in eyes with vision loss due to macular edema (ME) associated with BRVO or central retinal vein occlusion (CRVO).
955 citations
TL;DR: Recent findings that VEGFs secreted by epithelia, including the retinal pigment epithelium (RPE), are likely to mediate paracrine vascular survival signals for adjacent endothelia may explain the pathogenesis of subretinal neovascularisation in AMD.
884 citations
TL;DR: Recent findings on the cellular and molecular mechanisms by which ROS signal events leading to impairment of endothelial barrier function and promotion of leukocyte adhesion are discussed.
Abstract: Reactive oxygen species (ROS) are generated at sites of inflammation and injury, and at low levels, ROS can function as signaling molecules participating as signaling intermediates in regulation of fundamental cell activities such as cell growth and cell adaptation responses, whereas at higher concentrations, ROS can cause cellular injury and death. The vascular endothelium, which regulates the passage of macromolecules and circulating cells from blood to tissues, is a major target of oxidant stress, playing a critical role in the pathophysiology of several vascular diseases and disorders. Specifically, oxidant stress increases vascular endothelial permeability and promotes leukocyte adhesion, which are coupled with alterations in endothelial signal transduction and redox-regulated transcription factors such as activator protein-1 and nuclear factor-κB. This review discusses recent findings on the cellular and molecular mechanisms by which ROS signal events leading to impairment of endothelial barrier fun...
760 citations
Cites background from "Vascular permeability in experiment..."
...VEGF treatment (15–90 min) of endothelial cells has resulted in tyrosine phosphorylation of VE-cadherin, b-catenin, plakoglobin (g-catenin), p120, and platelet endothelial cell adhesion molecule-1 (PECAM-1) from human umbilical vein endothelial cells (52) and occludin-1 and ZO-1 from bovine retinal endothelial cells (10)....
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References
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TL;DR: The data suggest that VEGF plays a major part in mediating active intraocular neovascularization in patients with ischemic retinal diseases, such as diabetic retinopathy and retinal-vein occlusion.
Abstract: Background Retinal ischemia induces intraocular neovascularization, which often leads to glaucoma, vitreous hemorrhage, and retinal detachment, presumably by stimulating the release of angiogenic molecules. Vascular endothelial growth factor (VEGF) is an endothelial-cell-specific angiogenic factor whose production is increased by hypoxia. Methods We measured the concentration of VEGF in 210 specimens of ocular fluid obtained from 164 patients undergoing intraocular surgery, using both radioimmunoassays and radioreceptor assays. Vitreous proliferative potential was measured with in vitro assays of the growth of retinal endothelial cells and with VEGF-neutralizing antibody. Results VEGF was detected in 69 of 136 ocular-fluid samples from patients with diabetic retinopathy, 29 of 38 samples from patients with neovascularization of the iris, and 3 of 4 samples from patients with ischemic occlusion of the central retinal vein, as compared with 2 of 31 samples from patients with no neovascular disorders (P<0.00...
3,714 citations
TL;DR: An integral membrane protein localizing at tight junctions is now identified, which is designated as "occludin," which was revealed by a hydrophilicity plot that was very similar to that of connexin, an integral membraneprotein in gap junctions.
Abstract: Recently, we found that ZO-1, a tight junction-associated protein, was concentrated in the so called isolated adherens junction fraction from the liver (Itoh, M., A. Nagafuchi, S. Yonemura, T. Kitani-Yasuda, Sa. Tsukita, and Sh. Tsukita. 1993. J. Cell Biol. 121:491-502). Using this fraction derived from chick liver as an antigen, we obtained three monoclonal antibodies specific for a approximately 65-kD protein in rats. This antigen was not extractable from plasma membranes without detergent, suggesting that it is an integral membrane protein. Immunofluorescence and immunoelectron microscopy with these mAbs showed that this approximately 65-kD membrane protein was exclusively localized at tight junctions of both epithelial and endothelial cells: at the electron microscopic level, the labels were detected directly over the points of membrane contact in tight junctions. To further clarify the nature and structure of this membrane protein, we cloned and sequenced its cDNA. We found that the cDNA encoded a 504-amino acid polypeptide with 55.9 kDa. A search of the data base identified no proteins with significant homology to this membrane protein. A most striking feature of its primary structure was revealed by a hydrophilicity plot: four putative membrane-spanning segments were included in the NH2-terminal half. This hydrophilicity plot was very similar to that of connexin, an integral membrane protein in gap junctions. These findings revealed that an integral membrane protein localizing at tight junctions is now identified, which we designated as "occludin."
2,469 citations
TL;DR: A series of stages in the development of renal changes in diabetes, characterized by early hyperfunction and hypertrophy, are defined, which may be useful both in clinical work and in research activities.
Abstract: Alterations in renal function and structure are found even at the onset of diabetes mellitus. Studies performed over the last decade now allow definition of a series of stages in the development of renal changes in diabetes. Such a classification may be useful both in clinical work and in research activities. Stage 1 is characterized by early hyperfunction and hypertrophy. These changes are found at diagnosis, before insulin treatment. Increased urinary albumin excretion, aggravated during physical exercise, is also a characteristic finding. Changes are at least partly reversible by insulin treatment. Stage 2 develops silently over many years and is characterized by morphologic lesions without signs of clinical disease. However, kidney function tests and morphometry on biopsy specimens reveal changes. The function is characterized by increased GFR. During good diabetes control, albumin excretion is normal; however, physical exercise unmasks changes in albuminuria not demonstrable in the resting situation. During poor diabetes control albumin excretion goes up both at rest and during exercise. A number of patients continue in stage 2 throughout their lives. Stage 3, incipient diabetic nephropathy, is the forerunner of overt diabetic nephropathy. Its main manifestation is abnormally elevated urinary albumin excretion, as measured by radioimmunoassay. A level higher than the values found in normal subjects but lower than in clinical disease is the main characteristic of this stage, which appeared to be between 15 and 300 micrograms/min in the baseline situation. A slow, gradual increase over the years is a prominent feature in this very decisive phase of renal disease in diabetes when blood pressure is rising. The increased rate in albumin excretion is higher in patients with increased blood pressure. GFR is still supranormal and antihypertensive treatment in this phase is under investigation, using the physical exercise test. Stage 4 is overt diabetic nephropathy, the classic entity characterized by persistent proteinuria (greater than 0.5 g/24 h). When the associated high blood pressure is left untreated, renal function (GFR) declines, the mean fall rate being around 1 ml/min/mo. Long-term antihypertensive treatment reduces the fall rate by about 60% and thus postpones uremia considerably. Stage 5 is end-stage renal failure with uremia due to diabetic nephropathy. As many as 25% of the population presently entering the end-stage renal failure programs in the United States are diabetic. Diabetic nephropathy and diabetic vasculopathy constitute a major medical problem in society today.
870 citations
TL;DR: Expression of wild-type and mutant occludin appears to have activated an existing mechanism that allows selective paracellular flux in the presence of electrically sealed tight junctions.
Abstract: Tight junctions, the most apical of the intercellular junctions that connect individual cells in a epithelial sheet, are thought to form a seal that restricts paracellular and intramembrane diffusion. To analyze the functioning of tight junctions, we generated stable MDCK strain 2 cell lines expressing either full-length or COOH-terminally truncated chicken occludin, the only known transmembrane component of tight junctions. Confocal immunofluorescence and immunoelectron microscopy demonstrated that mutant occludin was incorporated into tight junctions but, in contrast to full-length chicken occludin, exhibited a discontinuous junctional staining pattern and also disrupted the continuous junctional ring formed by endogenous occludin. This rearrangement of occludin was not paralleled by apparent changes in the junctional morphology as seen by thin section electron microscopy nor apparent discontinuities of the junctional strands observed by freeze-fracture. Nevertheless, expression of both wild-type and mutant occludin induced increased transepithelial electrical resistance (TER). In contrast to TER, particularly the expression of COOH-terminally truncated occludin led to a severalfold increase in paracellular flux of small molecular weight tracers. Since the selectivity for size or different types of cations was unchanged, expression of wild-type and mutant occludin appears to have activated an existing mechanism that allows selective paracellular flux in the presence of electrically sealed tight junctions. Occludin is also involved in the formation of the apical/basolateral intramembrane diffusion barrier, since expression of the COOH-terminally truncated occludin was found to render MDCK cells incapable of maintaining a fluorescent lipid in a specifically labeled cell surface domain.
853 citations
TL;DR: Understanding and manipulating permeability will require a more detailed molecular characterization of tight junction proteins and in particular a characterization of how cell signaling regulates their attachment to the perijunctional cytoskeleton.
Abstract: Tight junctions create a regulated paracellular barrier to the movement of water, solutes, and immune cells between both epithelial and endothelial cells. Recent progress has been made in identifying the proteins that create this barrier. The transmembrane protein occludin is an excellent candidate for the sealing protein and is bound on the cytoplasmic membrane surface to the proteins ZO-1 and ZO-2. Functions for ZO-1 and ZO-2 are suggested by their invertebrate homologues, one of which is a tumor suppressor and another is required in epidermal growth factor receptor signaling. Multiple cellular signaling pathways affect assembly and sealing of junctions. Dynamic regulation of perijunctional actin has emerged as a unifying hypothesis for controlling paracellular permeability. Understanding and manipulating permeability will require a more detailed molecular characterization of tight junction proteins and in particular a characterization of how cell signaling regulates their attachment to the perijunctional cytoskeleton.
839 citations