Cell death : An anti-rejection drug for the treatment of Huntington’s disease

At the Institut Curie, CNRS and Inserm researchers have shown that Huntington’s disease may be treated using the drug FK506, which is also used clinically to prevent graft rejection. Like Alzheimer’s and Parkinson’s, Huntington’s disease is characterized by the abnormal death of neurons.

The Institut Curie researchers have discovered that FK506 blocks the toxicity of the protein huntingtin, which causes the death of certain neurons leading to disease onset. FK506 is already used in a clinical setting and so is a candidate for fast-track development as a treatment for Huntington’s disease.

This study was published in the February 1, 2006 issue of The Journal of Neuroscience.

Huntington’s disease is a genetic disorder which affects approximately 6 000 people in France and is of concern to over 12 000 carriers of the mutated gene as yet untouched by clinical signs. It is characterized by uncontrolled movements, personality changes, dementia and death 10 to 20 years after onset of the first symptoms (see “Additional information”).

Huntington’s disease results from changes in the IT15 gene, which encodes a protein, huntingtin, whose function is incompletely elucidated. Normal huntingtin contains repeats of the amino acid glutamine, but mutant huntingtin contains more than 35 to 40 glutamines and induces the disease. Symptoms occur earlier as the number of repeats increases.

This abnormal expansion of the polyglutamine tract in huntingtin results in structural changes, and the mutant huntingtin accumulates in neurons thereby causing their dysfunction and ultimately their death.

The same type of mutation causes other neurodegenerative diseases, each involving different regions of the brain. In Huntington’s disease, degeneration occurs in the neurons of the striatum, which are involved in the control of movement.

Raúl Pardo and Emilie Colin at the Institut Curie are studying the mechanisms that lead to neuron death in Huntington’s disease, under the direction of Frédéric Saudou and Sandrine Humbert(1).

They have now shown that calcineurin, a protein abundant in the brain, chemically alters mutant huntingtin, which becomes more toxic for neurons.

They have also discovered that by inhibiting calcineurin, FK506 “corrects” this chemical alteration in mutant huntingtin both in cultured neurons and in an animal model of the disease. FK506 even prevents the death of the striatal neurons. So, FK506 negates the harmful effects of mutant huntingtin in neurons.

FK506 is already used therapeutically to prevent graft rejection, and so may be a candidate for fast-track development as a treatment for Huntington’s disease.