Abstract
BackgroundDisease progression in retinal neurodegeneration is strongly correlated to immune cell activation, which may have either a neuroprotective or neurotoxic effect. Increased knowledge about the immune response profile and retinal neurodegeneration may lead to candidate targets for treatments. Therefore, we have used the explanted retina as a model to explore the immune response and expression of the immune modulator galectin-3 (Gal-3), induced by the cultivation per se and after additional immune stimulation with lipopolysaccharide (LPS), and how this correlates with retinal neurotoxicity.MethodsPost-natal mouse retinas were cultured in a defined medium. One group was stimulated with LPS (100 ng/ml, 24 h). Retinal architecture, apoptotic cell death, and micro- and macroglial activity were studied at the time of cultivation (0 days in vitro (DIV)) and at 3, 4 and 7 DIV using morphological staining, biochemical- and immunohistochemical techniques.ResultsOur results show that sustained activation of macro- and microglia, characterized by no detectable cytokine release and limited expression of Gal-3, is not further inducing apoptosis additional to the axotomy-induced apoptosis in innermost nuclear layer. An elevated immune response was detected after LPS stimulation, as demonstrated primarily by release of immune mediators (i.e. interleukin 2 (IL-2), IL-6, KC/GRO (also known as CLCX1) and tumour necrosis factor-α (TNF-α)), increased numbers of microglia displaying morphologies of late activation stages as well as Gal-3 expression. This was accompanied with increased apoptosis in the two additional nuclear layers, and damage to retinal gross architecture.ConclusionWe demonstrate that an immune response characterized by sustained and increased release of cytokines, along with an increase in Gal-3 expression, is accompanied by significant increased neurotoxicity in the explanted retina. Further investigations using the current setting may lead to increased understanding on the mechanisms involved in neuronal loss in retinal neurodegenerations.
Highlights
The retina constitutes a remote extension of the brain, located at the back of the eye, and is a light-sensitive neural structure enabling vision
Our results show that sustained activation of macro- and microglia, characterized by no detectable cytokine release and limited expression of Gal-3, is not further inducing apoptosis additional to the axotomy-induced apoptosis in innermost nuclear layer
An elevated immune response was detected after LPS stimulation, as demonstrated primarily by release of immune mediators (i.e. interleukin 2 (IL-2), interleukin- 6 (IL-6), KC/GRO and tumour necrosis factor-α (TNF-α)), increased numbers of microglia displaying morphologies of late activation stages as well as Gal-3 expression
Summary
The retina constitutes a remote extension of the brain, located at the back of the eye, and is a light-sensitive neural structure enabling vision. Retinal neurodegenerative diseases, such as glaucoma, diabetic retinopathy and age-related macular degeneration (AMD), lead to loss of neurons, resulting in progressive loss of visual function. In parallel, increasing reports suggest that microglial cells are a crucial component in the acute and chronic disease phases of retinal degeneration [10,11,12,13,14,15,16]. Disease progression in retinal neurodegeneration is strongly correlated to immune cell activation, which may have either a neuroprotective or neurotoxic effect. We have used the explanted retina as a model to explore the immune response and expression of the immune modulator galectin-3 (Gal-3), induced by the cultivation per se and after additional immune stimulation with lipopolysaccharide (LPS), and how this correlates with retinal neurotoxicity
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