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Katherine Andersh, Stephanie B. Syc-Mazurek, Olivia Marola, Richard T Libby; TNF and IL1A are directly neurotoxic to RGCs. Invest. Ophthalmol. Vis. Sci. 2020;61(7):250.
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© ARVO (1962-2015); The Authors (2016-present)
A recent study showed genetic deficiency of three cytokines—complement component 1, subcomponent q (C1q); interleukin 1 alpha (Il1a); and tumor necrosis factor (Tnf)—lessened RGC death after axonal injury. Combined deficiency of Tnf and Il1a appeared to elicit similar levels of RGC protection after optic nerve crush compared to protection conferred by deficiency of all three molecules together. Thus, IL1A and TNF appear to be major factors mediating RGC death after axonal injury. Intravitreal injection of TNF is sufficient to drive RGC death, however, this death is delayed, occurring ~8 weeks post-injection. Whether IL1A is sufficient to drive RGC death in the retina is unknown. Here, we test whether intravitreal injection of IL1A is sufficient to drive RGC death, and whether IL1A enhances TNF-induced RGC death.
Eyes of 2-4 month-old C57BL/6J mice were intravitreally injected with 2 μL of IL1A alone(1 mg/mL), TNF(100 μg/mL), or IL1A and TNF together to determine whether these molecules are directly neurotoxic to RGCs in vivo. Retinal flat mounts were assessed 5 days post-injection for dying cells (cleaved caspase 3; cCASP3) and 14 days post-injection for RGC survival (RBPMS+ cells). Groups were analyzed using a one-way ANOVA with Tukey’s post hoc, P<0.05 was considered significant.
Compared to control retinas, the number of cCASP3+ RGCs was significantly elevated 5 days after combined injection of TNF and IL1A (cells per mm2±SEM; n per group; control: 0; TNF+IL1A: 20±6; n=8; P<0.001). Similarly, combined injection of TNF and IL1A resulted in ~20% RBPMS+ RGC loss 14 days post-injection, but this loss was not observed after injection of TNF or IL1A alone (control: 3895±40, n=26; IL1A: 3811±56, n=9, P=0.35; TNF alone: 3756±77; n=9; P=0.75; TNF+IL1A: 3189±73, n=10; P<0.001).
Intravitreal injection of TNF and IL1A caused a significant increase in the number of dying RGCs 5 days after insult and a decrease in the number of surviving RGCs 14 days after insult. At these time points, TNF or IL1A alone do not alter RGC density. Intravitreal injection of TNF is sufficient to kill ~15-20% of RGCs, however, loss is only apparent 8 weeks post-injection. Therefore, combined application of TNF and IL1A acts in a more rapid manner to drive RGC loss. IL1A has not been previously investigated for its direct neurotoxic effects, and these data show that IL1A contributes to RGC death in the presence of other proinflammatory molecules.
This is a 2020 ARVO Annual Meeting abstract.
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