Increased expression of endothelial antigen PAL-E in human diabetic retinopathy correlates with microvascular leakage

AIMS/HYPOTHESIS: The Pathologische Anatomie Leiden-Endothelium (PAL-E) antigen is a marker for loss of the blood-brain barrier function in brain tumours. It is endothelium specific and is associated with the endothelial plasmalemmal vesicles (caveolae) involved in transcellular transport. To test whether blood-retinal barrier loss in diabetic retinopathy is associated with cellular changes in the endothelium, the expression of antigen PAL-E in relation to microvascular leakage in human diabetic retinopathy was investigated. METHODS: Immunohistochemical staining of frozen tissue sections of postmortem eyes obtained from 30 persons without and 41 persons with diabetes mellitus was carried out with monoclonal antibodies against PAL-E and CD31 and with antibodies against endogenous fibrinogen, albumin and IgG as indicators of vascular leakage. RESULTS: Patchy or uniform microvascular PAL-E staining was observed in the retina of 17 of the 41 eyes of diabetic patients and in 2 of the 30 normal control eyes. In the diabetic eyes, PAL-E staining co-localized with microvascular staining for endogenous fibrinogen, albumin and IgG. Strong staining for PAL-E was observed in sites without blood-tissue barriers, like the choroid. CONCLUSIONS/INTERPRETATION: In microvessels with an intact blood-retina barrier the endothelial antigen PAL-E is absent. Its expression is increased in retinal vessels of patients with diabetic retinopathy and correlates with microvascular leakage of plasma proteins. This phenotypic shift involving an antigen associated with caveolae suggests that dysfunction of the endothelium forms the cellular basis for microvascular leakage in diabetic retinopathy, rather than passive endothelial damag

Role of VEGF-A in endothelial phenotypic shift in human diabetic retinopathy and VEGF-A-induced retinopathy in monkeys

The endothelium-specific antigen PAL-E, associated with transport vesicles in non-barrier endothelium, is almost absent from barrier capillaries in the normal brain and retina. We have recently demonstrated that only leaking retinal capillaries in diabetic retinopathy (DR) in humans characteristically express PAL-E. Here we investigated the relation between the expression of the PAL-E antigen and vascular endothelial growth factor-A (VEGF) in human post-mortem eyes of individuals with diabetes mellitus (DM) and in experimental VEGF-induced retinopathy in cynomolgus monkeys. Cryosections were cut of eyes of 41 individuals with and 30 individuals without DM and eyes of 2 cynomolgus monkeys who received 4 injections of 0.5 microg VEGF in the vitreous of one eye and PBS in the other. The sections were stained with antibodies against VEGF, PAL-E and endogenous markers for microvascular leakage. Specific retinal vascular staining for VEGF was only observed in 10 out of the 41 cases with DM. These 10 cases also had marked uniform PAL-E staining and widespread vascular leakage. In contrast, diabetic patients without microvascular leakage and controls were negative for VEGF and PAL-E. Likewise, PAL-E was found only in the leaky retinal vessels of monkey eyes injected with VEGF. These results indicate that increased expression of the PAL-E antigen in retinal endothelium in conditions with microvascular leakage is related to VEGF and suggest that VEGF directly or indirectly induces PAL-E. PAL-E expression may reflect important endothelial changes involved in the disturbance of the blood-retina barrier in D

Histopathology of an infantile-onset spongiform leukoencephalopathy with a discrepantly mild clinical course

Recently, we described an as yet unidentified white matter disorder in eight patients which probably has an autosomal recessive mode of inheritance. The disease was characterized by megalencephaly and leukoencephalopathy with onset during the 1st year of life and a delayed onset of slowly progressive neurological dysfunction. No basic biochemical defect could be identified. Brain biopsy was performed in one of the patients and the histopathological findings are described in the present report. A spongiform leukoencephalopathy was revealed, without cortical involvement. Most vacuoles were covered by single five-layered membranes, representing single myelin lamellae. Some vacuoles were partially covered by multi-lamellar myelin sheaths or oligodendroglial cell extensions. The vacuoles were never found in the middle or inner parts of myelin sheaths, but involved the outermost lamellae of myelin sheaths only, whereas the remainder of the myelin sheaths remained undisturbed. The histopathological findings place the disease among the vacuolating myelinopathies, although it is distinct from the well-known forms. Possible pathophysiological mechanisms are splitting of the outermost myelin lamellae at the intraperiod line or a disturbance of compaction of the outermost myelin lamellae at the intraperiod lin

Vascular localization of heparan sulfate proteoglycans in retinas of patients with diabetes mellitus and in VEGF-induced retinopathy using domain-specific antibodies

PURPOSE: The Steno hypothesis (Deckert et al. ) states that in diabetes mellitus (DM), changes in vascular heparan sulfate proteoglycan (HSPG) expression are involved in systemic endothelial dysfunction and increased capillary permeability. In diabetes-induced glomerular capillary leakage, loss of HSPG and its side chains has been documented. This study aimed to investigate whether microvascular leakage in diabetic retinopathy (DR) is also associated with altered expression of HSPG in retinal microvessels. METHODS: Serial cryosections of post-mortem eyes of 22 subjects with DM and 7 controls were stained with antibodies against the core proteins of the basement membrane HSPGs agrin (Abs Bl31 and JM72) and perlecan (Ab 1948), and four antibodies against heparan sulfate side chains (HS) (Abs JM403, HepSS1, JM13, 3G10). Moreover, we investigated Cynomolgus monkey eyes injected with vascular endothelial growth factor (VEGF)-A, as a model of retinal microvas-cular leakage. The endothelial antigen PAL-E was used to detect microvascular leakage. RESULTS: In the retina of all controls and DM cases, agrin and perlecan core proteins and HS as recognized by JM403 and 3G10 were expressed in the walls of microvessels. Staining for JM13 was variable between cases, but unrelated to microvascular leakage as determined by PAL-E. Staining for HepSS1 was absent in all human retinal microvessels. In monkey retinas, HSPG staining was identical to that in human retinal tissues, except for the staining for HepSS1, which was found absent in control monkey eyes but which was positive in VEGF-injected eyes. CONCLUSIONS: Increased microvascular permeability in human DR is not associated with changes in expression of the HSPGs studied, whereas high amounts of VEGF may induce increased expression of the HS side chain epitope recognized by HepSS1. These results suggest that the mechanism underlying retinal leakage is different from diabetic glomerular capillary leakage

Vascular endothelial growth factors and angiogenesis in eye disease

The vascular endothelial growth factor (VEGF) family of growth factors controls pathological angiogenesis and increased vascular permeability in important eye diseases such as diabetic retinopathy (DR) and age-related macular degeneration (AMD). The purpose of this review is to develop new insights into the cell biology of VEGFs and vascular cells in angiogenesis and vascular leakage in general, and to provide the rationale and possible pitfalls of inhibition of VEGFs as a therapy for ocular disease. From the literature it is clear that overexpression of VEGFs and their receptors VEGFR-1, VEGFR-2 and VEGFR-3 is causing increased microvascular permeability and angiogenesis in eye conditions such as DR and AMD. When we focus on the VEGF receptors, recent findings suggest a role of VEGFR-1 as a functional receptor for placenta growth factor (PIGF) and vascular endothelial growth factor-A (VEGF)-A in pericytes and vascular smooth muscle cells in vivo rather than in endothelial cells, and strongly suggest involvement of pericytes in early phases of angiogenesis. In addition, the evidence pointing to distinct functions of VEGFs in physiology in and outside the vasculature is reviewed. The cellular distribution of VEGFR-1, VEGFR-2 and VEGFR-3 suggests various specific functions of the VEGF family in normal retina, both in the retinal vasculature and in neuronal elements. Furthermore, we focus on recent findings that VEGFs secreted by epithelia, including the retinal pigment epithelium (RPE), are likely to mediate paracrine vascular survival signals for adjacent endothelia. In the choroid, derailment of this paracrine relation and overexpression of VEGF-A by RPE may explain the pathogenesis of subretinal neovascularisation in AMD. On the other hand, this paracrine relation and other physiological functions of VEGFs may be endangered by therapeutic VEGF inhibition, as is currently used in several clinical trials in DR and AMD. (C) 2003 Elsevier Science Ltd. All rights reserve

Synergistic action of heparin and serum on basic fibroblast growth factor-modulated DNA synthesis and mitochondrial activity of cultured bovine corneal endothelial cells

Basic fibroblast growth factor (bFGF) is a major mitogen and chemoattractant for many cell types. The synergistic role of fetal bovine serum (FBS) and heparin on the modulation of tissue-cultured bovine corneal endothelial cells by bFGF was studied. Cell modulation was assessed by DNA synthesis ([3H]thymidine incorporation), mitochondrial activity (MTT assay), mitochondrial volume (transmission electron microscope study), and cell shape in mitotically competent cells and cells mitotically inhibited by 5-fluorouracil, mitomycin C, and irradiation. The dose-dependent stimulation of bFGF was found to be different for DNA synthesis and mitochondrial activity, the maximal effective dose being 1 and 10 ng/ml, respectively. Supplementation of bFGF with FBS enhanced both DNA synthesis and mitochondrial activity and caused a shift in the dose response to lower bFGF concentrations for the DAN synthesis, but not for the mitochondrial activity. Supplementation of bFGF with heparin resulted in an additional response for the mitochondrial activity, but not for the DNA synthesis. In addition, bFGF increased mitochondrial volume and induced elongation of the cells. These processes were further enhanced by the addition of heparin to bFGF. These results suggest that serum and heparin have a differential effect on mitogenic and non-mitogenic cells processes modulated by bFG