In a study that sheds new light on the causes of Parkinson's disease, researchers report that brain cells in Parkinson's patients abandon their energy-producing machinery¹, the mitochondria（线粒体） . A shutdown in fuel can have devastating² effects on brain cells, which consume roughly 20 percent of the body's energy despite making up only 2 percent of body weight. The findings indicate that boosting the mitochondria with FDA approved drugs early on may prevent or delay the onset³ of Parkinson's. The study will be published in the one-year anniversary issue of the journal Science Translational Medicine, on Wednesday October 6 2010. Science Translational Medicine is published by AAAS, the nonprofit science society.

Affecting roughly 5 million people worldwide, Parkinson's disease is a relentless⁴（无情的，残酷的） condition that starts killing⁵ dopamine（多巴胺） neurons in the brain many years before the onset of hallmark symptoms like tremors⁶（震动，颤抖） , muscle rigidity⁷ and slow movements. Thus, much-needed drugs to slow or halt the disease would have the greatest benefit for patients if they are given early on, before too many dopamine neurons die.

Clemens Scherzer from Brigham and Women's Hospital and Harvard Medical School, along with an international team of researchers, now show that a root cause of Parkinson's disease may lie in 10 gene⁸ sets related to energy production that spur neurons in the brain to "divorce" their mitochondria and related energy-producing pathways.

These gene sets are controlled by a master regulator--the PGC-1alpha gene. Moreover, abnormal expression of these genes⁹ likely occurs during the initial stages of Parkinson's disease, long before the onset of symptoms, the study shows. Targeting PGC-1alpha may thus be an effective way to slow down or halt the earliest stages of Parkinson's, staving off permanent damage and neuronal loss.

"The most exciting result from our study for me is the discovery of PGC-1alpha as a new therapeutic¹⁰ target for early intervention¹¹ in Parkinson's disease. PGC-1alpha is a master switch that activates¹³ hundreds of mitochondrial genes, including many of those needed to maintain and repair the power plants in the mitochondria," Scherzer said.

FDA-approved medications that activate¹² that PGC-1alpha are already available for widespread diseases like diabetes¹⁴. These medications may jumpstart the development of new Parkinson's drugs; instead of having to start from scratch, pharmaceutical¹⁵（制药的） companies may be able to dust off their drug libraries and find look-alike drugs capable of targeting PGC-1alpha in the brain.

"As we wrap up our first year of publishing the journal, the new study from Zheng et al. exemplifies the goal of Science Translational Medicine, applying knowledge and technology from different fields-such as neuroscience, genomics and bioinformatics-to achieve new discoveries," said Editor Katrina Kelner.

Previous studies have linked defects in mitochondrial activity to Parkinson's disease, but they generally have not provided such a comprehensive, specific set of genes as Scherzer and colleagues now report. The researchers analyzed¹⁶ a part of the brain called the substantia nigra（黑质，黑暗） in 185 tissue samples from deceased Parkinson's patients.

The substantia nigra (Latin for "black substance") contains dopamine-producing neurons. Scherzer and colleagues used a laser beam to precisely¹⁷ 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 cellular¹⁸ processes related to mitochondrial function and energy production. Suppressing these genes is likely to severely¹⁹ damage components²⁰ required for brain energy metabolism²¹. 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 malfunctions²² 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 deficient²³.

Why would the brain, being so highly energy dependent, abandon its entire energy-producing apparatus²⁴（装置，设备） ? That seems to be the core mystery of Parkinson's disease. Some think that mitochondrial activity may be affected²⁵ 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 pervasive²⁶（普遍的，蔓延的） electron transport chain deficit²⁷ 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.