Amyloid β Enhances Migration of Endothelial Progenitor Cells by Upregulating CX3CR1 in Response to Fractalkine, Which May Be Associated With Development of Choroidal Neovascularization

Abstract

Objective-Deposits that accumulate beneath retinal pigment epithelium, called drusen, are early signs of age-related macular degeneration (AMD). We have shown that amyloid ␤ (A␤) is present in drusen, and A␤ may be involved in AMD development. We have also shown that endothelial progenitor cells (EPCs) may contribute to the development of choroidal neovascularization (CNV). Thus, the purpose of this study was to investigate the role played by CX3CR1, a chemokine receptor, in EPC migration and CNV formation. Methods and Results-EPCs collected from human umbilical cords were found to express higher levels of CX3CR1 than human umbilical vein endothelial cells, and exposure of EPCs to A␤ caused further upregulation of CX3CR1. This upregulation was decreased by blocking fractalkine, a ligand of CX3CR1. Exposure of EPCs to fractalkine increased their migration, but pretreatment with A␤ enhanced the migration. The fractalkine-induced EPC migration was more inhibited by EPCs derived from CX3CR1 Ϫ/Ϫ mice than wild-type mice. The area of laser-induced CNV was significantly smaller in wild-type mice that received bone marrow transplantation from CX3CR1 Ϫ/Ϫ mice than in those that received transplantation from wild-type mice. Conclusion-These data suggest that A␤ enhances EPC migration through the upregulation of CX3CR1. This upregulation might play a role in development of CNV. (Arterioscler Thromb Vasc Biol. 2011;31:e11-e18.)Key Words: angiogenesis Ⅲ cell physiology Ⅲ vascular biology Ⅲ age-related macular degeneration Ⅲ endothelial progenitor cells A ge-related macular degeneration (AMD) is the leading cause of irreversible vision decrease in the elderly worldwide. [1][2][3][4] The decrease of vision results from geographical atrophy or choroidal neovascularization (CNV) in the macula of the eye. During the development of CNV, new vessels develop from the choroidal vessels and penetrate the thick matrix of the Bruch membrane and pass into the avascular subretinal space.Among the earliest signs of AMD are subretinal extracellular deposits, known as drusen, which accumulate beneath the retinal pigment epithelium (RPE). 5 Epidemiological studies have shown that the presence of many discrete or confluent drusen significantly increases the risk of developing CNV. 6,7 We have found that amyloid ␤ (A␤) peptides are present in drusen, and we have suggested that their presence is the primary stimulus for the development of AMD. 8 The A␤ peptides vary in length from 39 to 43 amino acid residues and are produced by the sequential proteolytic processing of precursors of amyloid proteins. 9 Interestingly, A␤ is the main component of the senile plaques found in the brains of Alzheimer's patients. 9 -11 The results of our study on senescent neprilysin gene-disrupted mice that lack the A␤-degrading enzyme showed that there was a significant increase in the deposition of A␤ in the subretinal space. 8 This is relevant to this study because these mice developed several characteristics of human eyes at the early stage AMD, although they...

Neuronal Cx3cr1 Deficiency Protects against Amyloid β-Induced Neurotoxicity

“…Cx3cl1 is a plasma membrane protein that can be cleaved to release the N-terminal chemokine domain, which signals either in a paracrine or autocrine manner through Cx3cr1. Since inflammatory cytokines and Aβ itself enhance Cx3cl1 signalling preceding cell death in various disease models [ 7 , 10 , 21 , 22 ], we asked whether Aβ (1–42) also potentiates Cx3cl1 cleavage in microglia-depleted cultured neurons. ELISA analysis of media from wild-type neuronal cultures that had been treated with 200 nM Aβ (1–42) for 24 hours demonstrated a marked increase in soluble Cx3cl1 compared to media from vehicle-treated controls, whereas Cx3cl1 mRNA transcript levels did not differ significantly from baseline.…”

“…Previous studies have shown that excitotoxic stimuli, including Aβ administration, potentiate Cx3cr1 signaling; however, downstream effects of receptor activation are confounding. While activating microglial Cx3cr1 has been reported to limit neurotoxic proinflammatory mediators, suppression of Cx3cl1 signaling ameliorates neurotoxicity [ 7 , 10 , 21 , 22 ].…”

Laser-induced choroidal neovascularization model to study age-related macular degeneration in mice

“…Both neutrophil and macrophage depletion reduce CNV formation [14][15][16] . The recruitment of BM-derived cells (endothelial progenitor cells, pericytes, mesenchymal stem cells) in CNV lesions has been reported 5,[17][18][19] and mimics the vasculogenic process observed in human patients 17 . Vascular endothelial growth factor (VEGF-A) rapidly emerged as a potent angiogenic factor involved in CNV formation, diverting much of the focus of research.…”

Effects of concentration of amyloid β (Aβ) on viability of cultured retinal pigment epithelial cells

“…This study was solely based on an in vitro approach in which RPE culture was the main component, and we mainly focused on molecular changes. While RPE dysfunction caused by Aβ is essential to the pathogenesis of AMD, choroidal endothelial cells may also play an important role [40]. But cross talk between the RPE cells and choroidal cells was not investigated in our study.…”