Abstract
Previous studies on the degenerative animal model of multiple sclerosis suggested that the copper-chelator cuprizone might directly suppress T-cell functions. Peripheral T-cell function in the cuprizone model has already been explored; therefore, in the present study, we investigated, for the first time, how cuprizone feeding affects the thymus, the organ of T-cell maturation and selection. We found that even one week of cuprizone treatment induced significant thymic atrophy, affecting the cortex over the medulla. Fluorescent microscopy and flow-cytometric analyses of thymi from cuprizone- and vehicle-treated mice indicated that eradication of the cluster of the differentiation-4 (CD4)-CD8 double-positive T-cell subset was behind the substantial cell loss. This result was confirmed with CD3-CD4-CD8 triple-staining experiments. Ultrastructurally, we observed degraded as well as enlarged mitochondria, myelin-bodies, large lipid droplets, and large lysosomes in the thymi of cuprizone-treated mice. Some of these features were similar to those in physiological and steroid-induced accelerated aging. According to our results, apoptosis was mainly of mitochondrial origin mediated by both caspase-3- and apoptosis inducing factor-mediated mechanisms. Additionally, mitogen activated protein kinase activation and increased pro-apoptotic B cell lymphoma-2 family protein expression were the major underlying processes. Our results do not indicate a functional relationship between cuprizone-induced thymus involution and the absence of inflammatory responses or the selective demyelination observed in the cuprizone model. On the other hand, due to the reversible nature of cuprizone’s deleterious effects, the cuprizone model could be valuable in studying thymus regeneration as well as remyelination processes.
Highlights
Administration of the copper chelator cuprizone to young adult C57BL/6 mice induces multifocal demyelination mainly in the corpus callosum and superior cerebellar peduncle [1] without significant T-cell activation in the affected areas [2]
In order to investigate the effect of cuprizone on the thymus, four-week-old male C57BL/6 mice were fed with pulverised chow containing 0.2% of the drug
Since cuprizone treatment resulted in a significant weight loss for the animals as well (Fig 1C), we normalised their thymic mass to their body mass, and found this relative thymus mass still reduced in the cuprizone-treated mice (Fig 1D), indicating a disproportional thymus involution in these animals
Summary
Administration of the copper chelator cuprizone to young adult C57BL/6 mice induces multifocal demyelination mainly in the corpus callosum and superior cerebellar peduncle [1] without significant T-cell activation in the affected areas [2]. According to histopathological studies [3], the pattern of cuprizone-induced demyelination resembles that of type III multiple sclerosis (MS) lesions characterised by oligodendrocyte degeneration and minor inflammation [4]. The mechanism of the oligodendrocyte loss and demyelination in the cuprizone model is not well understood. Cuprizone-induced early formation of mega-mitoachondria in the liver [7] and oligodendrocytes [8], and expressional and functional changes of mitochondrial enzymes [9,10] indicate mitochondrial dysfunction behind the oligodendrocyte loss. There is no explanation for the preferential regional distribution of cuprizone-induced demyelination, and the exclusivity of the cell death toward oligodendrocytes
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