Chemokine Mediated Monocyte Trafficking into the Retina: Role of Inflammation in Alteration of the Blood-Retinal Barrier in Diabetic Retinopathy

Abstract

Inflammation in the diabetic retina is mediated by leukocyte adhesion to the retinal vasculature and alteration of the blood-retinal barrier (BRB). We investigated the role of chemokines in the alteration of the BRB in diabetes. Animals were made diabetic by streptozotocin injection and analyzed for gene expression and monocyte/macrophage infiltration. The expression of CCL2 (chemokine ligand 2) was significantly up-regulated in the retinas of rats with 4 and 8 weeks of diabetes and also in human retinal endothelial cells treated with high glucose and glucose flux. Additionally, diabetes or intraocular injection of recombinant CCL2 resulted in increased expression of the macrophage marker, F4/80. Cell culture impedance sensing studies showed that purified CCL2 was unable to alter the integrity of the human retinal endothelial cell barrier, whereas monocyte conditioned medium resulted in significant reduction in cell resistance, suggesting the relevance of CCL2 in early immune cell recruitment for subsequent barrier alterations. Further, using Cx3cr1-GFP mice, we found that intraocular injection of CCL2 increased retinal GFP+ monocyte/macrophage infiltration. When these mice were made diabetic, increased infiltration of monocytes/macrophages was also present in retinal tissues. Diabetes and CCL2 injection also induced activation of retinal microglia in these animals. Quantification by flow cytometry demonstrated a two-fold increase of CX3CR1+/CD11b+ (monocyte/macrophage and microglia) cells in retinas of wildtype diabetic animals in comparison to control non-diabetic ones. Using CCL2 knockout (Ccl2−/−) mice, we show a significant reduction in retinal vascular leakage and monocyte infiltration following induction of diabetes indicating the importance of this chemokine in alteration of the BRB. Thus, CCL2 may be an important therapeutic target for the treatment of diabetic macular edema.

Adeno-Associated Virus Overexpression of Angiotensin-Converting Enzyme-2 Reverses Diabetic Retinopathy in Type 1 Diabetes in Mice

“…These cells were increased in streptozotocin-control by approximately threefold to fourfold compared with nondiabetic or ACE2-treated diabetic, consistent with previous findings. 65,66 Also consistent with our findings (Figure 5), DR has generally been found to be associated with increased microglia number near retinal vasculature in the inner retinal layers and in the outer plexiform layer, 25,67 normally localizing anterior to the outer nuclear layer. 52 This organization within the ganglion cell layer is consistent with the finding, in individuals with DR, that microglia accumulate around regions of vascular damage 25 and that vascular lesions in the diabetic retina are nonuniform in distribution.…”

Analysis of Outer Nuclear and External Limiting Membrane Layers Pattern on Spectral-Domain Optical Coherence Tomography in Patients with Posterior Uveitis with or without Cystoid Macular Edema

“…The presence of activated monocytes/macrophages in the extravascular space is evidence of the ability of leukocytes to breach the blood retina barrier by diapedesis and establish an inflammatory reaction within the retinal tissues. Their cytological data could explain the thickening of the outer plexiform layer observed in our group 2 eyes [5]. They did not perform any retinal imaging studies but taking their results into consideration along with our observations, we could postulate that the outer plexiform layer is probably the initial site of CME.…”

“…Rangasamy and colleagues observed monocytes/macrophages adhering to the outer surface of retinal capillaries, most likely in the active process of extravasation [5]. The presence of activated monocytes/macrophages in the extravascular space is evidence of the ability of leukocytes to breach the blood retina barrier by diapedesis and establish an inflammatory reaction within the retinal tissues.…”

“…It has already been described that the external retina layer, particularly the outer plexiform layer as the origin of the development of CME, but actually we have little information on the accuracy of the outer retina layer which is reached [5]. Therefore, it would be valuable to identify whether there are circumstances in which the tests are likely to be complementary, rather than redundant, in evaluating uveitis.…”

Epigallocatechin-3-gallate protects retinal vascular endothelial cells from high glucose stress in vitro via the MAPK/ERK-VEGF pathway

“…The common pathological changes caused by DR include the breakdown of the retinal blood-retinal barrier, retinal neovascularization, macular edema, and retinal detachment (Rangasamy et al, 2014;Liu et al, 2014b). The risk factors for DR include hyperglycemia, polyol metabolism, glycosylation, and diacylglycerol (Safi et al, 2014).…”