The substantia nigra (Latin for "black substance") contains dopamine-producing neurons. Scherzer and colleagues used a laser beam to precisely cut out the dopamine neurons that are abnormal in Parkinson's. Next, the team looked at gene activity in these dopamine neurons and identified gene sets-groups of genes involved in one biological process-that are associated with Parkinson's disease. At the end of this tour-de-force analysis, 10 gene sets linked to Parkinson's emerged. All of these gene sets had a common thread-the master regulator gene PGC-1alpha.

The 10 gene sets encode proteins responsible for cellular processes related to mitochondrial function and energy production. Suppressing these genes is likely to severely damage components required for brain energy metabolism. One of these components is the electron transport chain; a set of reactions controlled by mitochondria that generates the energy cells need to function. Other studies have hinted that one of the five complexes making up the electron transport chain malfunctions in Parkinson's. Yet, Scherzer and colleagues found that not just one, but virtually all of the components needed by mitochondria to build the electron transport chain are deficient.

Why would the brain, being so highly energy dependent, abandon its entire energy-producing apparatus? That seems to be the core mystery of Parkinson's disease. Some think that mitochondrial activity may be affected by a combination of genes and the environment.

"I believe that environmental chemicals, risk genes, and aging-each having a small effect when taken separately-in combination may lead to the pervasive electron transport chain deficit we found in common Parkinson's disease and to which dopamine neurons might be intrinsically more susceptible," said senior author Clemens Scherzer, Assistant Professor of Neurology at Harvard Medical School.

Source: American Association for the Advancement of Science