Abstract
Purpose :
C-X-C motif chemokine receptor 5 (CXCR5) is a transmembrane G protein-coupled receptor (RPCR) belonging to the CXC chemokine receptor family and blinding to ligand Cxcl13. The function of the CXCL13-CXCR5 axis in the eye remains largely unknown. Recently, we demonstrated that aged CXCR5 knockout mice (CXCR5−/−) develop retinal degeneration (RD) with age, recapitulating many aspects of human age-macular degeneration (AMD), however, mechanisms of this process remain elusive. Here we present findings that CXCR5 is expressed in retinal pigment epithelial cells (RPE) and required for the function in maintaining retinal pigment epithelial (RPE) cells homeostasis and blood-retinal barrier (BRB) through PI3K-AKT-FOXO1 pathway.
Methods :
Immunohistochemistry (IHC) was used to study the human donors and mouse eye sections. IPS derived human RPE cells and primary RPE (pRPE) cultures from wild type (WT) and CXCR5-/- mice were evaluated using IHC, Western blot (WB) and Electric Cell-substrate Impedance Sensing (ECIS) analysis.
Results :
IHC analysis of healthy human donor eye sections has demonstrated the expression of CXCR5 and CXCL13 in the RPE layer. Results in adult and aged mice demonstrated a decrease of CXCR5-CXCL13 expression with age. Mouse pRPE cell cultures and IPS derived human RPE cells demonstrated the expression of CXCR5, which is reduced under oxidative stress conditions and hypoxia. The Cxcr5-/- RPE cells lose the hexagonal shape and become spindle-like. WB and IHC analysis of the pRPE cultures from wild type (WT) and CXCR5-/- mice demonstrated a decrease of ZO-1, RPE65, AKT, PI3K expression in CXCR5-/- RPE cells, with an increase of nuclear phospho-FOXO1, MITF and Vimentin as well as b-amyloid, expression in CXCR5-/- pRPE cells. The loss of barrier function was further confirmed using ECIS that demonstrated significant (P<0.001) decrease in resistance of CXCR5-/- RPE cells monolayer. Lack of CXCR5 increased pRPE culture's sensitivity to oxidative stress and hypoxia-induced cell death (P<0.001).
Conclusions :
These observations suggest that the CXCL13-CXCR5 axis plays an important role in RPE cell homeostasis, CXCR5-/- RPE cells lack differentiation and undergo epithelial-mesenchymal transformation (EMT). Loss of the CXCR5-CXCL13 axis function in the RPE cells may be a component of RD pathologies such as AMD and retinitis pigmentosa.
This is a 2020 ARVO Annual Meeting abstract.