Aryl Hydrocarbon Receptor Regulates Apoptosis and Inflammation in a Murine Model of Experimental Autoimmune Uveitis.

Yike Huang,Shaoqiu Jiang,Lu Yang,Xiao Zhu,Aize Kijlstra,Jing Yu,Shengping Hou,Huaping Liang,Junchi He,Suyin Mei,Peizeng Yang,Ke Hu

doi:10.3389/fimmu.2018.01713

Abstract

Uveitis is characterized as a common cause of blindness worldwide. Aryl hydrocarbon receptor (AhR), a ligand-activated nuclear receptor, has been implicated to play a role in human uveitis, although the exact mechanisms remain poorly understood. The purpose of this study was to enhance our knowledge concerning the role of AhR during intraocular inflammation. We immunized wild-type and AhR-knockout C57BL/6J mice with IRBP651–670 to induce experimental autoimmune uveitis (EAU). Disease severity was evaluated with both clinical and histopathological grading. Blood–retinal barrier (BRB) integrity was tested by Evans blue and tight junction proteins qualifications. Apoptosis was measured using TdT-mediated dUTP nick end labeling staining. Macrophage/microglia activation and polarization were studied by immunofluorescence and Western blot. Following EAU induction, AhR−/− mice had more severe clinical and histopathological manifestations of uveitis than AhR+/+ mice. Increased vascular permeability and apoptotic cells were observed in AhR−/− EAU mice when compared with AhR+/+ EAU mice. In addition, AhR−/− EAU mice showed evidence of a significantly increased macrophage/microglia cells and a stronger polarization from the M2 to the M1 phenotype as compared to AhR+/+ EAU mice. The levels of pro-inflammatory cytokines including tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-1β were increased in AhR−/− EAU mice, which was associated with the activation of NF-κB and signal transducers and activators of transcription (STAT) pathways. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an agonist of AhR, caused a significant decrease in the clinical and histopathological manifestations, preserved BRB integrity, reduced apoptotic cells, inhibited macrophage/microglia activation, and shifted their polarization from M1 toward M2. Moreover, decreased expression of pro-inflammatory cytokines including TNF-α, IL-6, and IL-1β and inhibition of NF-κB and STAT pathways were found in EAU mice following TCDD treatment. In conclusion, AhR activation with TCDD exhibits an immunomodulatory effect by reducing BRB breakdown, inhibiting retinal cell apoptosis, and reducing pro-inflammatory cytokine expression during EAU. The underlying mechanism may involve the modulation of macrophages/microglia polarization and the downregulation of NF-κB and STAT pathways.

Highlights

Uveitis, a vision-threatening intraocular inflammatory disease, usually affects people aged 20–50 years [1, 2]
Our results showed that the protein expression of p65, p-STAT1, and p-STAT3 was elevated in the retinas of aryl hydrocarbon receptor (AhR)−/− experimental autoimmune uveitis (EAU) mice compared with AhR+/+ EAU mice and this could be nick end labeling (TUNEL) images of eye sections in naive, vehicle, and TCDD-treated mice
AhR-knockout mice exhibited more severe clinical and histological manifestations of intraocular inflammation when compared with wild-type mice after EAU induction with a uveitogenic peptide of the retinal protein IRBP

Summary

Introduction

A vision-threatening intraocular inflammatory disease, usually affects people aged 20–50 years [1, 2]. Immune privilege is a complex phenomenon that involves multiple components, starting with the sequestration of antigens behind an efficient blood–retinal barrier (BRB), thereby inhibiting the activation and function of acquired and innate immune cells [11]. Recent studies have shown that innate immune cells including macrophages and microglia are involved in antigen presentation during EAU [15]. In addition to bloodborne inflammatory cells, retinal microglia show phagocytic and pathogenic features similar to those exhibited by macrophages. Activated macrophages and retinal microglia release pathogenic factors, such as tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS), resulting in the nitration of cytochrome c which is known to cause apoptosis in EAU [17,18,19]. Factors that may affect apoptosis following an inflammatory response include the activation of the aryl hydrocarbon receptor (AhR) [21]

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