Dr. Cuervo and her team had previously shown that a glitch in autophagy may trigger Parkinson's disease by allowing a toxic protein to accumulate. She suspected that something similar was going on in Huntington's disease. After studying two mouse models of Huntington's disease as well as lymphoblasts (white cells) from people with the disease, she and her team found that the mutated huntingtin protein was sabotaging the cell's garbage-collecting efforts.
One mechanism for cleaning up cells involves forming a membrane around the protein or other cellular structure requiring removal. These "garbage bags" (more formally known as autophagosomes) then travel to enzyme-filled sacs known as lysosomes that fuse with the bags and digest their cargo. But the clean-up efforts go awry in Huntington's disease.
Dr. Cuervo and her team found that the defective huntingtin proteins stick to the inner layer of autophagosomes, preventing them from gathering garbage. The result: Autophagosomes arrive empty at the lysosomes; and cellular components that should be recycled instead accumulate, causing toxicity that probably contributes to cell death.
This finding, Dr. Cuervo noted, shows that activating the lysosomes of cells one of the proposed treatments for Huntington's disease won't do any good.
"It doesn't matter how active your lysosomes are if they're not going to receive any cellular components to digest," she said. "Instead, we should focus on treatments to help autophagosomes recognize intracellular garbage, perhaps by minimizing their contact with the defective huntingtin protein. By enhancing the clearance of cellular debris, we may be able to keep Huntington's patients free of symptoms for a longer time."
|Contact: Deirdre Branley|
Albert Einstein College of Medicine