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Cystamine inhibits caspase activity. Implications for the treatment of polyglutamine disorders
Mathieu Lesort1, Matthew Lee, Janusz Tucholski
1Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, 35294-0017, USA. mlesort@uab.edu
Insights
Cystamine inhibits caspase-3 activity, a key factor in Huntington
Area of Science:
- Neuroscience
- Biochemistry
- Pharmacology
Background:
- Huntington's disease (HD) is a fatal neurodegenerative disorder with no effective treatments.
- Current research suggests inhibiting caspase activity or preventing mitochondrial dysfunction may delay HD progression.
- Cystamine, known to inhibit transglutaminase, has shown promise in prolonging survival in HD mouse models.
Purpose of the Study:
- To investigate the direct effect of cystamine on caspase-3 activity.
- To determine if cystamine's inhibition of caspase-3 is dependent on transglutaminase activity.
- To explore cystamine's potential as a therapeutic agent for Huntington's disease by examining its antioxidant effects.
Main Methods:
- Assessed cystamine's inhibition of recombinant active caspase-3 in vitro using enzyme kinetics.
- Evaluated cystamine's effect on caspase-3 activation in cells treated with pro-apoptotic agents.
- Measured caspase-3 activity in cell lines with varying levels of tissue transglutaminase (tTG) expression.
- Quantified changes in glutathione levels following cystamine treatment.
Main Results:
- Cystamine demonstrated a concentration-dependent inhibition of caspase-3 activity, acting as an uncompetitive inhibitor at low concentrations and non-competitive at higher concentrations (IC50 = 23.6 μM).
- Cystamine effectively inhibited caspase-3 activation in situ, independent of transglutaminase activity.
- Cystamine treatment significantly increased intracellular glutathione levels.
Conclusions:
- Cystamine directly inhibits caspase-3 activity, suggesting a novel therapeutic mechanism for Huntington's disease.
- The caspase-inhibiting effects of cystamine are independent of its action on transglutaminase.
- Cystamine may offer neuroprotection in Huntington's disease by inhibiting caspases and boosting antioxidant defenses through increased glutathione.
Abstract:
Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder caused by an abnormally expended polyglutamine domain. There is no effective treatment for HD; however, inhibition of caspase activity or prevention of mitochondria dysfunction delays disease progression in HD mouse models. Similarly administration of cystamine, which can inhibit transglutaminase, prolonged survival of HD mice, suggesting that inhibition of transglutaminase might provide a new treatment strategy. However, it has been suggested that cystamine may inhibit other thiol-dependent enzymes in addition to transglutaminase. In this study we show that cystamine inhibits recombinant active caspase-3 in a concentration-dependent manner. At low concentrations cystamine is an uncompetitive inhibitor of caspase-3 activity, becoming a non-competitive inhibitor at higher concentrations. The IC(50) for cystamine-mediated inhibition of caspase-3 activity in vitro was 23.6 microm. In situ cystamine inhibited in a concentration-dependent manner the activation of caspase-3 by different pro-apoptotic agents. Additionally, cystamine inhibited caspase-3 activity to the same extent in cell lines stably overexpressing wild type tissue transglutaminase (tTG), a mutant inactive tTG, or an antisense for tTG, demonstrating that cystamine inhibits caspase activity independently of any effects it may have on the transamidating activity of tTG. Finally, treatment with cystamine resulted in a robust increase in the levels of glutathione. These findings demonstrate that cystamine may prolong neuronal survival and delay the onset of HD by inhibiting caspases and increasing the level of antioxidants such as glutathione.