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Laurel G. Jackson, Karen M. Joos, Rebecca M. Sappington; Cytokine Modulation in a Rat Model of Acute, Intermittent Ocular Hypertension. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2465.
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Alterations in cytokine production have been reported in a variety of glaucoma models, including chronic and acute animal models and in vitro models. For these models, cytokine levels were examined following constant elevations in pressure. Here we examine retinal production of cytokines in a rat model of intermittent ocular hypertension.
In Sprague Dawley rats, intraocular pressure (IOP) was transiently elevated (35mmHg) in one eye for one hour/day, six days a week over the course of six weeks. IOP remained normal in the fellow eye, which served as an internal control. A multi-plex protein array was used to quantify cytokine levels in protein lysates from experimental and control retina. Cytokines examined by the array were interleukin-1alpha (IL-1α), interleukin-1beta (IL-1β), interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-6 (IL-6), interleukin-10 (IL-10), interferon gamma (IFNγ), tumor necrosis factor alpha (TNFα) and granulocyte macrophage colony stimulating factor (GM-CSF). We used semi-quantitative western blotting to further analyze IL-1β, IL-4, IL-6 and TNFα. T-tests and the Shapiro-Wilk normality test were used for statistical analyses.
IL-1α and IL-1β were elevated ≥ 1.5-fold in the experimental retina of three or more animals. In contrast, IL-10 decreased ≥ 50% in experimental retina of three or more animals. Interestingly, IL-6 and TNFα increased ≥ 1.5-fold in some animals and decreased ≥ 50% or more in other animals. No change between experimental and control retina was noted in three or more animals for IL-2, IL-4 and GM-CSF. In our samples, IL-1β, IL-4, IL-6 and TNFα were present in the highest concentrations and were selected for further analysis. Despite equal loading of total protein, retinal samples exhibited different levels of general protein expression, as determined by beta-actin. As a result, directional changes in cytokine production varied for some individual animals. Across animals, densitometry analysis of western blots for IL-1β (P = 0.26) and IL-4 (P = 0.16) revealed no significant difference between experimental and control retina. In contrast, IL-6 expression increased 22% (P = 0.04) in experimental versus control retina. TNFα also exhibited a trend towards elevated levels (P = 0.06) in experimental retina.
When compared with previous work, our data suggests that intermittent elevations in IOP induce changes in cytokine production that are greatly reduced in breadth and magnitude compared to constant pressure models.
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