In the vast majority of Parkinsons disease (PD) patients, the disorder arises not because of a genetic defect, but because some external insult triggers the death of dopamine-producing neurons. Now, researchers have reported progress in understanding the mechanism underlying that death, which they say suggests a new treatment pathway.
In both mice and human patients, the researchers have found evidence that neurons die because of a crippling of a particular protective enzyme that eliminates potentially damaging reactive oxygen species normally generated in the cells power plants, called mitochondria.
David Park, of the Ottawa Health Research Institute, and colleagues published their findings in the July 5, 2007 issue of the journal Neuron, published by Cell Press.
The researchers studied the mechanism of PD using a mouse model of the disease, in which a mitochondria-affecting toxin called MPTP is used to produce Parkinsons-like brain pathology. In earlier studies, they had found that MPTP activates protein-snipping enzymes called calpains in mitochondria. They also found evidence that calpains, in turn, activate a cellular switch called Cdk5. The question, however, was how this abnormal activation ultimately kills neurons.
In their new studies, the researchers analyzed neurons to determine that Cdk5 regulates yet another enzyme called Prx2. This enzyme is known as a peroxidase and acts to render harmless the chemically active reactive oxygen species that are produced inside mitochondria in the process of generating energy for the cell.
Specifically, the researchers found that treating neurons with MPTP activates Cdk5 to switch off Prx2. Whats more, they found that activating Prx2 in MPTP-treated mice prevented the loss of dopamine-producing neurons. And they experimentally demonstrated that the action of Cdk5 on Prx2 plays a pivotal role in the neuronal damage from MPTP.