Methylene Blue Modulates Huntingtin Aggregation Intermediates and Is Protective in Huntington's Disease Models

Department of Biological Chemistry, Psychiatry and Human Behavior, University of California, Irvine, California 92697, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.75). 08/2012; 32(32):11109-19. DOI: 10.1523/JNEUROSCI.0895-12.2012
Source: PubMed

ABSTRACT Huntington's disease (HD) is a devastating neurodegenerative disorder with no disease-modifying treatments available. The disease is caused by expansion of a CAG trinucleotide repeat and manifests with progressive motor abnormalities, psychiatric symptoms, and cognitive decline. Expression of an expanded polyglutamine repeat within the Huntingtin (Htt) protein impacts numerous cellular processes, including protein folding and clearance. A hallmark of the disease is the progressive formation of inclusions that represent the culmination of a complex aggregation process. Methylene blue (MB), has been shown to modulate aggregation of amyloidogenic disease proteins. We investigated whether MB could impact mutant Htt-mediated aggregation and neurotoxicity. MB inhibited recombinant protein aggregation in vitro, even when added to preformed oligomers and fibrils. MB also decreased oligomer number and size and decreased accumulation of insoluble mutant Htt in cells. In functional assays, MB increased survival of primary cortical neurons transduced with mutant Htt, reduced neurodegeneration and aggregation in a Drosophila melanogaster model of HD, and reduced disease phenotypes in R6/2 HD modeled mice. Furthermore, MB treatment also promoted an increase in levels of BDNF RNA and protein in vivo. Thus, MB, which is well tolerated and used in humans, has therapeutic potential for HD.

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    ABSTRACT: Summary The redox dye, methylene blue (MB) is proved to have beneficial effects in various models of neurodegenerative diseases. Here we investigated the effects of MB (100nM, 300nM and 1μM) on key bioenergetic parameters and on H2O2 production/elimination in isolated guinea-pig brain mitochondria under normal as well as respiration-impaired conditions. As measured by High Resolution Oxygraph the rate of resting oxygen consumption was increased, but the ADP-stimulated respiration was unaffected by MB with either substrate (glutamate-malate, succinate or alpha-glycerophosphate) used for supporting mitochondrial respiration. In mitochondria treated with inhibitors of complex I or complex III MB moderately but significantly increased the rate of ATP production, restored ΔΨm and increased the rate of Ca(2+)-uptake. The effects of MB are consistent with transferring electrons from upstream components of the electron transport chain to cytochrome c, which is energetically favorable when the flow of electrons in the respiratory chain is compromised. On the other hand, MB significantly increased the production of H2O2 measured by Amplex UltraRed fluorimetry in all conditions; both in resting, ATP-synthesizing and respiration-impaired mitochondria with each substrate combination supporting respiration. Furthermore, it also decreased the elimination of H2O2. Generation of H2O2, without superoxide formation, observed in the presence of MB is interpreted as a result of reduction of molecular oxygen to H2O2 by the reduced MB. The elevated generation and impaired elimination of H2O2 should be considered for the overall oxidative state of mitochondria treated with MB.
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    ABSTRACT: Polyglutamine diseases are a group of inherited neurodegenerative disorders that are caused by an abnormal expansion of a trinucleotide CAG repeat, which encodes a polyglutamine tract in the protein-coding region of the respective disease genes. To date, nine polyglutamine diseases are known, including Huntington's disease, spinal and bulbar muscular atrophy, dentatorubral-pallidoluysian atrophy and six forms of spinocerebellar ataxia. These diseases share a salient molecular pathophysiology including the aggregation of the mutant protein followed by the disruption of cellular functions such as transcriptional regulation and axonal transport. The intraneuronal accumulation of mutant protein and resulting cellular dysfunction are the essential targets for the development of disease-modifying therapies, some of which have shown beneficial effects in animal models. In this review, the current status of and perspectives on therapy development for polyglutamine diseases will be discussed.
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Nov 24, 2014