Huntingtin inclusion bodies are iron‐dependent centers of oxidative events

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Abstract
Recently, we reported that the transient expression of huntingtin exon1 polypeptide containing polyglutamine tracts of various sizes (httEx1‐polyQ) in cell models of Huntington disease generated an oxidative stress whose intensity was CAG repeat expansion‐dependent. Here, we have analyzed the intracellular localization of the oxidative events generated by the httEx1‐polyQ polypeptides. Analysis of live COS‐7 cells as well as neuronal SK‐N‐SH and PC12 cells incubated with hydroethidine or dichlorofluorescein diacetate revealed oxidation of these probes at the level of the inclusion bodies formed by httEx1‐polyQ polypeptides. The intensity and frequency of the oxidative events among the inclusions were CAG repeat expansion‐dependent. Electron microscopic analysis of cell sections revealed the presence of oxidation‐dependent morphologic alterations in the vicinity of httEx1‐polyQ inclusion bodies. Moreover, a high level of oxidized proteins was recovered in partially purified inclusions. We also report that the iron chelator deferroxamine altered the structure, localization and oxidative potential of httEx1‐polyQ inclusion bodies. Hence, despite the fact that the formation of inclusion bodies may represent a defense reaction of the cell to eliminate httEx1 mutant polypeptide, this phenomenon appears inherent to the generation of iron‐dependent oxidative events that can be deleterious to the cell.