This post contains material from an older one, updated based on new discoveries.
There are many things you don’t want gathering in large numbers, including locusts, rioters, and brain proteins. Our nerve cells contain many proteins that typically live in solitude, but occasionally gather in their thousands to form large insoluble clumps. These clumps can be disastrous. They can wreck neurons, preventing them from firing normally and eventually killing them.
Such clumps are the hallmarks of many brain diseases. The neurons of Alzheimer’s patients are riddled with tangles of a protein called tau. Those of Parkinson’s patients contain bundles, or fibrils, of another protein called alpha-synuclein. The fibrils gather into even larger clumps called Lewy bodies.
Now, Virginia Lee from the University of Pennsylvania School of Medicine has confirmed that the alpha-synuclein fibrils can spread through the brains of mice. As they spread, they corrupt local proteins and gather them into fresh Lewy bodies, behaving like gangs that travel from town to town, inciting locals into forming their own angry mobs. And as these mobs spread through the mouse brains, they reproduce two of the classic features of Parkinson’s disease: the death of neurons that produce dopamine, and movement problems.
This is the clearest evidence yet that alpha-synuclein can behave like prions, the proteins that cause mad cow disease, scrapie and Creutzfeld-Jacob disease (CJD). Prions are also misshapen proteins that convert the shape of normal peers. But there is a crucial distinction: prions are infectious. They don’t just spread from cell to cell, but from individual to individual. As far as we know, alpha-synuclein can’t do that.
Prions are villains worthy of any comic book. They are infectious misshapen proteins that can convert their normal peers into their own twisted images with a touch. As their numbers grow, they gather in large groups and destroy brain tissue. They cause diseases such as mad cow disease, Creutzfeld-Jacob disease (CJD) and scrapie.
And they’re not alone. It seems that many brain diseases are also caused by clusters of misfolded proteins that can seed fresh groups of themselves. The list includes Alzheimer’s, Parkinson’s and Lou Gehrig’s diseases. None of these are infectious – the proteins behind them can’t spread from one individual to another, but there is mounting evidence that they can trigger waves of corrupted shapes within a single brain.
I wrote about the latest such evidence in Alzheimer’s disease for The Scientist. Here’s a taster. Head over there for more.
There’s something unfeasibly sinister about prions. These infectious entities are incredibly simple, but they can cause fatal and untreatable diseases like mad cow disease, CJD, and others. Prions are malformed versions of a protein called PrP. Like all other proteins, they’re made of chains of amino acids that fold into complex shapes. Prions fold incorrectly, and they encourage normal PrP to do so. These deformed proteins gather in large clumps that wreck brain tissue. Once this process begins, we have no way of stopping it. Prions are little more than bits of renegade origami, but they can bring down that most complex of biological structures – your brain.
It gets worse.
Before they spread to the brain, prions often multiply in the lymphatic system –the group of organs that includes the spleen, lymph nodes, appendix and tonsils. Vincent Béringue from the French National Institute for Agricultural Research has found that prions can hide in these tissues, turning individuals into silent carriers even if they never actually develop disease. Worse still, the spleen provides an easy entry-point for prions, allowing them to jump more easily from one species to another.