Abstract
Purpose: :
Cigarette smoking, oxidative stress and inflammation play a major role in age-related macular degeneration (AMD), the leading cause of blindness in the elderly. Drusen below the retinal pigment epithelium (RPE) are a risk factor for progression of dry to blinding wet AMD. Yet, the mechanisms involved remain undefined. We recently reported a declined monocyte chemoattractant-1 (MCP-1) production by injured RPE following prolonged exposure to cigarette smoke-derived hydroquinone (HQ)-induced oxidative stress and by RPE from smoker AMD patients therefore highlighting the importance of this cytokine in AMD pathophysiology. To better understand the role of the RPE in inflammatory retinal conditions in the context of smoking, we investigated whether sustained HQ-induced oxidative stress modulates MCP-1 expression in lipopolysaccharide (LPS)-stimulated RPE in vivo and the signaling pathways involved.
Methods: :
C57BL/6 female mice were divided into 3 groups (n=8/group): Group 1: control mice received regular drinking tap water; Group 2: mice received a single intraperitoneal (i.p.) injection of 2 mg/kg LPS and regular drinking tap water (sacrificed 24 hours after injection); Group 3: mice treated with 0.8% HQ in drinking water for 5 days and received a single i.p. injection of 2 mg/kg LPS on day 5. At the end of the experimental period, mice were euthanized and eyes were removed and microdissected for recovery of RPE sheets. MCP-1 mRNA expression was analyzed by real-time PCR. Protein expression of MCP-1, total and phosphorylated Nuclear Factor-KappaB (NF-ΚB) p65, mitogen activated protein kinases (MAPK) ERK, p38 and JNK was assessed by Western blot. Research was conducted in compliance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research.
Results: :
HQ potently inhibited LPS-induced MCP-1 mRNA and protein expression in mouse RPE sheets. Also, HQ blocked LPS-mediated ERK, p38, JNK and NF-ΚB p65 phosphorylation.
Conclusions: :
Our findings suggest that HQ possesses immunosuppressive properties in the retina by downregulating LPS-induced MCP-1 production via NF-ΚB and MAPK inhibition in mouse RPE sheets. Diminished expression of MCP-1 during inflammatory stimulus may impair the recruitment of scavenging macrophages responsible for clearing debris from the sub-RPE space which could be an underlying factor promoting drusen accumulation and progression to wet AMD in smokers.
Keywords: age-related macular degeneration • retinal pigment epithelium • inflammation