The Alternative Complement System Mediates Cell Death in Retinal Ischemia Reperfusion Injury.

Saori Inafuku,Kip M Connor,Garrett Klokman

doi:10.3389/fnmol.2018.00278

Abstract

Ischemia reperfusion (IR) injury induces retinal cell death and contributes to visual impairment. Previous studies suggest that the complement cascade plays a key role in IR injury in several systemic diseases. However, the role of the complement pathway in the ischemic retina has not been investigated. The aim of this study is to determine if the alternative complement cascade plays a role in retinal IR injury, and identify which components of the pathway mediate retinal degeneration in response to IR injury. To accomplish this, we utilized the mouse model of retinal IR injury, wherein the intraocular pressure (IOP) is elevated for 45 min, collapsing the retinal blood vessels and inducing retinal ischemia, followed by IOP normalization and subsequent reperfusion. We found that mRNA expression of complement inhibitors complement receptor 1-related gene/protein-y (Crry), Cd55 and Cd59a was down-regulated after IR. Moreover, genetic deletion of complement component 3 (C3−/−) and complement factor b (Fb−/−) decreased IR-induced retinal apoptosis. Because vascular dysfunction is central to IR injury, we also assessed the role of complement in a model of shear stress. In human retinal endothelial cells (HRECs), shear stress up-regulated complement inhibitors Cd46, Cd55, and Cd59, and suppressed complement-mediated cell death, indicating that a lack of vascular flow, commonly observed in IR injury, allows for complement mediated attack of the retinal vasculature. These results suggested that in retinal IR injury, the alternative complement system is activated by suppression of complement inhibitors, leading to vascular dysfunction and neuronal cell death.

Highlights

Ischemia reperfusion (IR) injury is a complex pathophysiological phenomenon that is initiated by the loss of blood flow to a tissue and resultant ischemia followed by the subsequent return of blood flow, which results in oxidative stress and downstream cytotoxic inflammatory effects
When the needle was removed from the anterior chamber, blood flowed in from the central retinal artery instantaneously, allowing retinal vessels to revert to their normal width and the retina to regain its original color (Figure 1C and Supplementary Video 3)
To investigate whether the complement pathway is involved in IR injury-induced retinal cell death, we evaluated the expression of complement inhibitors complement receptor 1-related gene/protein-y (Crry), Cd55 and Cd59a in C57BL6 mice, factor b (Fb)−/− mice and component 3 (C3)−/− mice at 6 h after IR surgery or sham surgery

Summary

Introduction

Ischemia reperfusion (IR) injury is a complex pathophysiological phenomenon that is initiated by the loss of blood flow to a tissue and resultant ischemia followed by the subsequent return of blood flow, which results in oxidative stress and downstream cytotoxic inflammatory effects. Current therapeutic approaches for IR injury focus on returning retinal blood flow through the use of anticoagulants, vasodilators, and laser treatment, or by alleviating oxidative stress using free radical scavengers (Osborne et al, 2004). The alternative complement pathway is a key mediator of endogenous immune surveillance and tissue homeostasis. The alternative complement pathway remains in a constant state of low-level activation, which allows for continuous probing of cells. The classical and lectin pathways do not maintain this low-level activation (Pangburn and Müller-Eberhard, 1980; Pangburn et al, 1981; Bexborn et al, 2008; Ricklin et al, 2010)

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