Cystamine increases L-cysteine levels in Huntington’s disease transgenic mouse brain and in a PC12 model of polyglutamine aggregation Jonathan H. Fox,* David S. Barber, Bhupinder Singh,* Birgit Zucker,* Mary K. Swindell,* Fran Norflus,* Rodica Buzescu,* Raman Chopra,* Robert J. Ferrante,à , § Aleksey Kazantsev* and Steven M. Hersch* *MassGeneral Institute for Neurodegenerative Disease, Department of Neurology, Massachusetts General Hospital, Charlestown, Massachusetts, USA  Center of Environmental Health and Toxicology, University of Florida, Gainesville, Florida, USA àNeurology, Pathology, and Psychiatry Departments, Boston University School of Medicine, Boston, Massachusetts, USA §Geriatric Research Education and Clinical Center, Bedford VA Medical Center, Massachusetts, USA Abstract Cystamine, a small disulfide-containing chemical, is neuro- protective in a transgenic mouse and a Drosophila model of Huntington’s disease (HD) and decreases huntingtin aggre- gates in an in vitro model of HD. The mechanism of action of cystamine in these models is widely thought to involve inhi- bition of transglutaminase mediated cross-linking of mutant huntingtin in the process of aggregate formation/stabilization. In this study we show that cystamine, both in vitro and in a transgenic mouse model of HD (R6/2), increases levels of the cellular antioxidant L-cysteine. Several oxidative stress mark- ers increase in HD brain. We provide further evidence of oxidative stress in mouse HD by demonstrating compensatory responses in R6/2 HD brains. We found age-dependent increases in forebrain glutathione (GSH), and increased levels of transcripts coding for proteins involved in GSH synthesis and detoxification pathways, as revealed by quantitative PCR analysis. Given the general importance of oxidative stress as a mediator of neurodegeneration we propose that an increase in brain L-cysteine levels could be protective in HD. Further- more, cystamine was dramatically protective against 3-nitro- propionic acid-induced striatal injury in mice. We suggest that cystamine’s neuroprotective effect in HD transgenic mice results from pleiotropic effects that include transglutaminase inhibition and antioxidant activity. Keywords: cystamine, glutathione, Huntington’s disease, L-cysteine, neuroprotection, oxidative stress. J. Neurochem. (2004) 91, 413–422. Huntington’s disease (HD) is a dominantly inherited neuro- degenerative disorder characterized by the loss of striatal projection and cerebro-cortical neurons, with the accumula- tion of intraneuronal aggregates containing the mutant protein huntingtin (Hersch and Ferrante 2003). The HD mutation results from a CAG expansion that enlarges a polyglutamine tract within huntingtin to greater than about 37 residues. The disease is progressive and currently there are no treatments to delay onset or progression. Nevertheless, several compounds have been beneficial in mouse models of HD, providing a number of possible treatments to test in HD patients (Beal and Ferrante 2004). How mutant huntingtin leads to neuronal death is poorly understood. There has been growing evidence that transcrip- tional (Cha 2000; Nucifora et al. 2001; Dunah et al. 2002) and mitochondrial dysfunction (Beal 2000; Panov et al. 2002) and oxidative injury (Browne et al. 1999) play significant roles in HD pathogenesis. The induction of tissue transglutaminase in brain has also been postulated to play a Received May 27, 2004; revised manuscript received June 27, 2004; accepted June 29, 2004. Address correspondence and reprint requests to Steven Hersch, MassGeneral Institute for Neurodegenerative Disease, MGH East Bldg 114-2001, 114 16 th Street, Charlestown, MA 02129, USA. E-mail: Hersch@helix.mgh.harvard.edu. Abbreviations used: BSO, L-buthionine-(S,R)-sulfoximine; CSF, cerebrospinal fluid; FBS, fetal bovine serum; GFP, green fluorescent protein; GSH, glutathione; GSHee, glutathione ethyl-ester; GSSG, glutathione disulfide; HD, Huntington’s disease; 3-NP, 3-nitropropionic acid; PBS, phosphate-buffered saline. Journal of Neurochemistry , 2004, 91, 413–422 doi:10.1111/j.1471-4159.2004.02726.x Ó 2004 International Society for Neurochemistry, J. Neurochem. (2004) 91, 413–422 413