Joining the Dots in Genetic Parkinson's Disease

Some people are more predisposed to suffer Parkinson's disease than others, a fraction of those due to mutations in genes involved in mitochondrial quality control. The state of mitochondrial function shows up as an important component of many different conditions and indeed in aging itself. In Parkinson's disease it is thought that mitochondrial dysfunction contributes to the conditions in which the population of dopamine-producing neurons in the brain die off, producing the characteristic symptoms of the disease.

It may be that more of Parkinson's disease is genetic than was previously thought, and the odds of that being the case increase as the chain of molecular machinery involved in mitochondrial quality control is followed and new components identified. This sort of work also helps clarify the mechanisms associated with mitochondrial dysfunction in aging:

Mitofusin 2 (Mfn2) is known for its role in fusing mitochondria together, so they might exchange mitochondrial DNA in a primitive form of sexual reproduction. "Mitofusins look like little Velcro loops. They help fuse together the outer membranes of mitochondria. Mitofusins 1 and 2 do pretty much the same thing in terms of mitochondrial fusion. What we have done is describe an entirely new function for Mfn2."

Mitochondria work to import a molecule called PINK. Then they work to destroy it. When mitochondria get sick, they can't destroy PINK and its levels begin to rise. Once PINK levels get high enough, they make a chemical change to Mfn2, which sits on the surface of mitochondria. This chemical change is called phosphorylation. Phosphorylated Mfn2 on the surface of the mitochondria can then bind with a molecule called Parkin that floats around in the surrounding cell.

Once Parkin binds to Mfn2 on sick mitochondria, Parkin labels the mitochondria for destruction. The labels then attract special compartments in the cell that "eat" and destroy the sick mitochondria. As long as all links in the quality-control system work properly, the cells' damaged power plants are removed, clearing the way for healthy ones. "But if you have a mutation in PINK, you get Parkinson's disease. And if you have a mutation in Parkin, you get Parkinson's disease. About 10 percent of Parkinson's disease is attributed to these or other mutations that have been identified." The discovery of Mfn2's relationship to PINK and Parkin opens the doors to a new genetic form of Parkinson's disease.



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