Cytokine and Complement Response in the Glaucomatous βB1-CTGF Mouse Model.

Sabrina Reinehr,Rudolf Fuchshofer,Dennis Koch,Ana M Mueller-Buehl,H Burkhard Dick,Johanna D Doerner,Stephanie C Joachim

doi:10.3389/fncel.2021.718087

Abstract

Glaucoma is a complex neurodegenerative disease leading to a loss of retinal ganglion cells (RGCs) and optic nerve axons. An activation of the complement system seems to contribute to cell loss in this disease. Hence, we investigated a possible initiation of the complement system and the cytokine response in the βB1-CTGF glaucoma model. In these mice, intraocular pressure is elevated, which is the main glaucoma risk factor in patients, and RGC loss occurs at 15 weeks of age. Therefore, quantitative real-time PCR and immunohistological experiments were performed in 5-, 10-, and 15-week-old βB1-CTGF animals and their corresponding wildtypes (WT) to analyze the expression of several complement system factors. We could show that mRNA levels of the terminal complement pathway components C3 and C5 (Hc) were upregulated at 10 weeks. In accordance, more C3+ and membrane attack complex+ cells were observed in transgenic retinae. Further, the C5a receptor anaphylatoxin receptor (C5ar) and the complement component C5a receptor 1 (C5ar1; CD88) mRNA levels were upregulated in 10- and 15-week-old βB1-CTGF mice. Interestingly, all three activation routes of the complement system were elevated in βB1-CTGF mice at some age. Especially C1q, as a marker of the classical pathway, was significantly increased at all investigated ages. Furthermore, mRNA expression levels of interferon-γ (Infg) were upregulated at 5 weeks, while Cxcl1 and Cxcl2 mRNA levels were upregulated at 10 and 15 weeks. The mRNA levels of the chemokines Cxcl10 were increased at all ages in βB1-CTGF mice. These results lead to the assumption that in these transgenic mice, a complement activation mainly through the classical pathway as well as a cytokine response plays a major role in cell death.

Highlights

The complement system forms an integral part of the early immune response
An elevated intraocular pressure (IOP) is the main risk factor for this disease and hallmarks are a loss of retinal ganglion cells (RGCs) as well as a degeneration of optic nerve axons (Casson et al, 2012)
Assembling of membrane attack complex (MAC) can result in an activation of pro-inflammatory cytokines, such as interleukin (IL)-1, tumor necrosis factor α (TNFα), CCL2, interferon-γ (INF-γ), or IL-8 (CXCL8) (Schonermark et al, 1991; Liu et al, 2011; Xie et al, 2019)

Summary

Introduction

The classical, the lectin, and the alternative, can activate the terminal pathway including the membrane attack complex (MAC) (Walport, 2001; Bayly-Jones et al, 2017). Recent data indicates that all retinal cells are able to express components of the complement system (Pauly et al, 2019). Albeit it resembles a double-edged sword since its activation can either benefit or harm the host and is probably involved in several retinal diseases. A recent study suggests that elevated levels of IL8 can be considered a risk factor used for detecting and managing glaucoma (Chono et al, 2018)

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