Suppression of Ocular Inflammation in Endotoxin–Induced Uveitis by Inhibiting Nonproteolytic Activation of Prorenin

Abstract

Purpose: : Recently, we revealed that angiotensin receptor signaling mediates ocular inflammation and neovascularization. We also found that prorenin undergoes nonproteolytic activation leading to upregulation of the renin–angiotensin system (RAS) when prorenin receptor interacts specifically with the handle region of prorenin. The aim of the present study was to elucidate the role of the receptor–dependent nonproteolytic activation of prorenin in ocular inflammation in endotoxin–induced uveitis (EIU).

Methods: : EIU was induced in Long–Evans rats by a single intraperitoneal injection of 100 µg lipopolysaccharide (LPS). Tissue localization of total prorenin, active prorenin and prorenin receptor in the EIU retina was examined by immunohistochemistry. To block the prorenin receptor–mediated upregulation of RAS, a decoy handle–region peptide (HRP) is intraperitoneally administered 24 hours before and immediately after the injection of LPS. Twenty–four hours after LPS injection, leukocyte adhesion to the retinal vasculature was evaluated with a concanavalin A lectin perfusion–labeling technique. In addition, leukocyte infiltration into the vitreous cavity and protein concentration in the anterior chamber were also measured. Retinal mRNA and protein levels of intercellular adhesion molecule (ICAM)–1, interleukin (IL)–6 and monocyte chemotactic protein (MCP)–1 were examined by RT–PCR and ELISA, respectively.

Results: : Retinal vessels in rats with EIU were strongly positive for prorenin, prorenin receptor and active center of renin. Systemic treatment with HRP resulted in dose– and time–dependent inhibition of the leukocyte adhesion and infiltration and the protein leakage, all of which were increased by the induction of EIU. Retinal mRNA expression and protein levels of ICAM–1, MCP–1 and IL–6, induced in rats with EIU, were also significantly suppressed with application of HRP.

Conclusions: : These findings demonstrate for the first time that nonproteolytically activated prorenin plays a significant role in the development of ocular inflammation in the EIU model. The present study suggests the potential use of HRP, a decoy peptide binding to prorenin receptor, as a therapeutic agent to reduce ocular inflammation.

Keywords: uveitis-clinical/animal model • inflammation • retina