Angiopoietin-2 Causes Pericyte Dropout in the Normal Retina

Abstract

Pericyte loss is an early pathologic feature of diabetic retinopathy, consistently present in retinae of diabetic humans and animals. Because pericyte recruitment and endothelial cell survival are controlled, in part, by the angiopoietin/Tie2 ligand/receptor system, we studied the expression of angiopoietin-2 and -1 in relation to the evolution of pericyte loss in diabetic rat retinae, using quantitative retinal morphometry, and in retinae from mice with heterozygous angiopoietin deficiency (Ang-2 LacZ knock-in mice). Finally, recombinant angiopoietin-2 was injected into eyes of nondiabetic rats, and pericyte numbers were quantitated in retinal capillaries. Angiopoietin-1 protein was present in the normal maturing retina and was upregulated 2.5-fold in diabetic retinae over 3 months of diabetes. In contrast, angiopoietin-2 protein was consistently upregulated more than 30-fold in the retinae of diabetic rats, preceding the onset of pericyte loss. Heterozygous angiopoietin-2 deficiency completely prevented diabetes-induced pericyte loss and reduced the number of acellular capillary segments. Injection of angiopoietin-2 into the eyes of normal rats induced a dose-dependent pericyte loss. These data show that upregulation of angiopoietin-2 plays a critical role in the loss of pericytes in the diabetic retina. Diabetes 53

Effect of R-(+)-α-lipoic acid on experimental diabetic retinopathy

“…One mechanism by which diabetic pericyte loss can be reduced or even prevented is by the inhibition of Ang-2. Ang-2 is upregulated prior to the onset of pericyte dropout in the diabetic rat, Ang-2 deficiency prevents pericyte dropout, and intravitreal Ang-2 injection induces pericyte dropout in non-diabetic rats [22]. R-(+)-α-lipoic acid normalises Ang-2 expression in hyperglycaemia, suggesting a mechanism by which pericyte preservation could be explained, and linking Ang-2 regulation to the overproduction of mitochondrial ROS.…”

“…Protein concentrations were determined using a standard protocol for protein assay (Bio-Rad, Munich, Germany). Samples (15 μg per retinal extract) were run on 4-15% SDS-PAGE gel electrophoresis, blocked with 10% non-fat milk in PBS, and membranes incubated with antibodies against methylglyoxal-derived imidazole-type AGE, RAGE, NFκB p 65, N ɛ -carboxymethyllysine (CML), VEGF and Ang-2 as described [6,17,22]. O-linked N-acetylglucosamine (OGlcNAc) glycosylated proteins were determined using a monoclonal antibody against O-GlcNAc residues attached to serine or threonine residues of retinal proteins.…”

“…Pericytes, which are known to protect capillaries from regression, are lost from the very beginning of retinopathy. One possibility is the induction of cell death via the receptor for AGE (RAGE)-nuclear factor kappa B (NFκB) pathway [20,21]; another is the active elimination of pericytes from the endothelium by factors such as angiopoietin-2 (Ang-2) [22]. Therefore, our aim was to assess qualitatively and quantitatively the impact of R-(+)-α-lipoic acid on biochemical and cell biological parameters which are abnormal in the diabetic retina, and on major structural parameters of experimental diabetic retinopathy.…”

Microangiopathy and visual deficits characterize the retinopathy of a spontaneously hypertensive rat model with type 2 diabetes and metabolic syndrome

“…34 In this regard, the fact that changes in pericytes could not be detected with the techniques applied in our study represents a limitation of our study. Nevertheless, on the basis of our observed alterations in the microvasculature of obese animals, future studies might focus on potential changes affecting pericytes by applying more specialized techniques 36,37 and could thereby expand the knowledge of microangiopathy in the context of the metabolic syndrome.…”

A review of therapies for diabetic macular oedema and rationale for combination therapy

“…Ang-2 levels are regulated at the level of transcription by different cytokines including VEGF, as well as hypoxia and high-glucose levels, [61][62][63][64] and stored in Weibel-Palade bodies before rapid release. 65 It is elevated in eyes with clinically significant DMO [66][67][68] as well as proliferative DR (PDR), 69,70 and is thought to induce loss of vascular endothelial (VE)-cadherin through phosphorylation.…”