CHAPTER 12
THE WORLD ACCORDING TO PRIONS UNITED STATES/BRITAIN, 1970s to present day
I go to bed every night offering prayers of thanks to the great mad cow in the sky, because it’s BSE that has really put our field in the money.
—PAUL BROWN of the NIH
The mad cow epidemic scarred Europe in ways that are still apparent. The European Union ban on most genetically modified foods is evidence of this hurt, as are the speculations that continue on websites as to where prion diseases came from—the insecticide used on cows against warble fly, space dust, a Japanese biological warfare experiment in Papua New Guinea, or an American plot led by Carleton Gajdusek in cahoots with the CIA.*7
“This time experts have no answers,” the British newspaper Today wrote in 1994, after the first probable case of variant CJD was found—and it was true. But by demonstrating how little they understood prion diseases, prion experts paradoxically positioned themselves for an increase in research money to a level they had only dreamed of. With the public furious at their governments for failing to protect them—mad cow was one of the causes of the fall of John Major’s government in Britain in 1997—nations invested in prion investigations as they never had before. Worldwide funding went from a pittance to $300 million by the mid-2000s. No one wanted to be caught short a second time.
Some of that money went into getting right the epidemiology of prion diseases; other money went into better understanding the risk posed to humans by infected meat; and much of the rest into improving testing of livestock. But prion researchers also understood that if their work was to matter, it had to have wider applicability. Mad cow, and the sense of urgency it brought, would not be with the world forever. So at the same time as money was going into studies on areas like sheep–cow transmission, many millions of pounds, euros, and dollars were also spent on basic prion science. Prion researchers’ hope was to find a place for their discoveries well beyond the infectious and inherited prion diseases that afflict a few thousand people around the globe. They wanted to play a role in curing other diseases and in pioneering innovations in nonbiological fields as well.
That prions might have implications for other diseases was not a new idea. In fact, it was already on Carleton Gajdusek’s mind in 1957, when, newly arrived in Papua New Guinea to study kuru, he promised the NIH that if he could “crack” the disease, “parkinsonism, Huntington’s chorea, multiple sclerosis, etc., etc.” might follow. After he returned to the States and successfully transmitted kuru to chimpanzees in 1965, he tried to make good on his promise, energetically injecting animals with tissue containing other neurological diseases. But of all the neurodegenerative diseases Gajdusek tried to transmit—CJD, multiple sclerosis, ALS, Alzheimer’s, Parkinson’s, and Huntington’s disease, among many others—only CJD proved transmissible. You could not “catch” the others. Gajdusek was enormously disappointed.
When Stanley Prusiner became the leader in prion research, he revived the hope of a world according to prions. Indeed it was a key motive for his renaming the scrapie agent the “prion” in 1982. He was not just trying to get rid of a cumbersome name; he was trying to establish a new disease principle. We say, “He caught a virus” when a person can be suffering from anything from a cold to rabies. Similarly, Prusiner hoped people would say “he has a prion disease,” when a person had anything from CJD to—to what?
The list Prusiner drew up included the neurodegenerative disorders that Gajdusek had pursued—Parkinson’s disease, Huntington’s disease, Alzheimer’s disease, MS—and quite a few others, including immune system disorders like Crohn’s disease and rheumatoid arthritis and metabolic diseases like adult-onset diabetes.
There has long been anecdotal information suggesting that these diseases have something in common. Many can be inherited but also often just seem to happen by chance. Stress seems to worsen them. The frequency of many increases with age. Jakob thought his patients looked as if they had multiple sclerosis, kuru victims look like Parkinson’s sufferers, and the dementia that appears in the prion disease GSS is so similar to Alzheimer’s that GSS is almost always first misdiagnosed as the latter. A 1997 paper showed that a Parkinson’s drug called Eldepryl (generic name Selegeline) helped patients with moderate Alzheimer’s disease, and in 2001 Prusiner’s lab published a paper showing that a mutation in the prion gene could cause a prion disease indistinguishable from Huntington’s with its characteristic jerky movements, clumsiness, and delusional thinking.
Prusiner and other researchers began to point out in the late 1970s that, besides having overlapping symptoms, all these diseases also left dead, misfolded proteins behind. This shared characteristic was not something researchers who specialized in these ailments had ever paid much attention to. They tended to focus on what was unique to the disease they studied—its symptoms, say, or the absence or excess of a given neurotransmitting chemical. That all these diseases caused the buildup of the same gunk in the body was seen as incidental—an insight no more useful for treatment than, say, the knowledge that many infections leave pus.
By contrast, prion researchers thought the dead, misfolded proteins might be the cause of the disease. Most striking to them, most of the diseases produced not just dead, misfolded proteins but dead, misfolded proteins of a particular kind, called amyloid plaques or amyloid fibril sheets. These clumps developed when atoms bonded across the frames of damaged proteins, like the rungs of a fabulously strong ladder. Enzymes couldn’t digest them, and water didn’t dissolve them. There was nothing in biology as tough; it seemed safe to say that no cell could survive their presence. (Researchers call such structures amyloid because they are white and starchy in appearance, amylus being Latin for starch.)
To be sure, the fibrils occurred in different parts of the body in each disease. In Alzheimer’s, the clumps of dead protein were in interstitial spaces in the brain; they were so big you could sometimes see them without a microscope. In Parkinson’s, the proteins cohered in small, thready masses called Lewy bodies. In Huntington’s disease, the dead proteins accumulated in brain neurons. Dead protein clumps didn’t have to be in the brain to do damage, either. For instance, in Type II or adult-onset diabetes, the clumps of dead protein built up in the pancreas. In cardiac amyloidosis, they accumulated in the heart, diminishing the organ’s ability to pump.
Prion researchers now hoped they could bring the techniques they had honed studying the structures and behaviors of prion proteins to these diseases. The amyloid plaque that most closely resembled a prion was the one found in Alzheimer’s disease, so that seemed the logical disease to start with. In the early 1980s, Stanley Prusiner threw his research energies into exploring the overlap between the prion protein and the Alzheimer’s protein. (There was more than a little self-interest in the decision: funding for research on the millions of Alzheimer’s sufferers was a lot easier to find than funding for prion research.) In prion disease, healthy prion proteins convert to disease-causing ones through a process resembling crystallization: one misformed protein touches another, causing it to misform, and so on in a chain reaction. Alzheimer’s proteins turn out to be capable of this behavior, too. If you put a little bit of Alzheimer’s amyloid plaque in a test tube with normally formed Alzheimer’s proteins, the latter will all eventually refold and bond with the original plaque, forming a single large amyloid plaque. Prusiner thought there was even greater overlap between the two proteins, that, in essence, Alzheimer’s were prions, proteins, and he thought he had proven it when, in 1983, working with an Alzheimer’s expert, George Glenner of the University of California–San Diego, he showed that both Alzheimer’s and prion plaques reacted to the same dye. Dyes are used to tease out the structure of proteins, and the fact that prions and Alzheimer’s proteins reacted to the same one suggested that their structures might be identical. Prusiner called the news “astounding”; Glenner, on the other hand, cautioned against leaping to conclusions. “It’s like saying two people are related just because they both have red hair,” he pointed out.
As researchers learned more about the two diseases over the next few years, distinctions emerged and it became clear that Prusiner’s enthusiasm was excessive. With colleagues he traced the prion to the prion gene on Chromosome 21; Glenner traced his Alzheimer protein to an Alzheimer’s protein gene on a different chromosome. The two proteins were composed of different amino acids arranged in a different sequence. What the researchers had was not a single underlying disease but a single disease principle.
When Prusiner and others returned to amyloid plaques a second time, they did so with broader interests: They wanted to know what they were and how they formed. No two diseases gave the same answer. Researchers went through dozens, from ALS to rheumatoid arthritis to adult-onset diabetes, and identified the key protein that misforms in each of them.
Why proteins form destructive amyloid plaques that injure the cell in the first place is itself an intriguing question. The damage may be a side effect of the general flexibility proteins exhibit: they fold in multiple ways because they have to accomplish many things, and if a physiologically active molecule can fold so many ways, chances are that a few of those ways will be harmful within the small space of a cell. Protein researchers all over the world are working on this problem in their respective diseases today, trying to block proteins from turning into amyloids and amyloids from overwhelming cells. In addition, there are researchers who think that an amyloid does not itself damage the cell but rather protects it by isolating otherwise damaging proteins, restricting them in a bond so strong that, as one protein chemist noted, it is “essentially indestructible under physiological conditions.”
Intriguingly, researchers have also verified Gajdusek’s old hunch that prions aren’t the only transmissible protein—amyloid A amyloidosis, an opportunistic disease that strikes people with chronic inflammations such as rheumatoid arthritis, turns out to share this property. You can inject it into mice and the protein will replicate and the mouse will develop the disease, just as with prions; and the disease can even be transmitted orally. There are also hints that other amyloid plaque diseases such as Alzheimer’s can be transmitted—the English prion researchers Rosalind Ridley and Harry Baker reported that they transmitted Alzheimer plaques in 1993. George Glenner, Prusiner’s collaborator, died of cardiac amyloidosis in 1995 and, among others, the Alzheimer’s researcher Rudolph Tanzi, of Harvard Medical School, wonders whether Glenner may have been infected somehow while working on the protein. If other protein diseases do turn out to be transmissible, it may force researchers to disassemble the boundary between diseases that infect you and diseases that just happen, between those that pursue you and those you acquire by life habits, old age, or environmental toxins. It is possible we will one day talk about people catching MS, Alzheimer’s, and even diabetes—or at least a propensity for these diseases.
“The amazing thing is how long it took us to see all these things that were right in front of our face,” says Fred Cohen, a molecular chemist at the University of California–San Francisco whose lab works with Prusiner’s. “The parallels were obvious.”
If prionlike diseases are infectious, though, they are not so in the traditional way. They are not “alive”—infection in their case is purely a mechanical process. The theory of prions threatens to diminish our uniqueness in the universe, which is one reason that—like Galileo’s insistence that the earth moves around the sun—it had trouble finding acceptance. It was another example of—in the words of the German chemist Friedrich Wöhler, who discovered in 1828 that he could synthesize the body’s chemicals perfectly well in a test tube—“the great tragedy of science, the slaying of a beautiful hypothesis by an ugly fact.” The hypothesis was that life is ineffable, uniquely alive; the reality is that it is just chemical. Or, as Justus von Liebig wrote in 1855, life is nothing more than “chemical processes dependent upon common chemical forces.”
It should not be surprising then that a branch of biology that traces disease to nonliving, mechanical processes had also turned out to be useful in engineering. Chemists are familiar with conformational influence, which they call nucleation. Briefly, nucleation is the tendency of molecules to arrange themselves, typically in an orderly fashion, around a first fixed point: this process gives material remarkable strength. Silk is a product of nucleation, and so is the abalone shell, its nacreous surface three thousand times stronger than if it were made of nonnucleated material. In fact, J. S. Griffith got the idea that would turn out to be the basis of prion theory from mechanical physics, from the way checkers, if shaken on a checkerboard with one checker in a fixed position, will assume an orderly pattern around the original checker. The prion researcher Byron Caughey co-authored an interesting paper on nucleation in 1995, in which he compared prions to Ice-9. Ice-9, an invention of the novelist Kurt Vonnegut in his novel Cat’s Cradle, is a variant of water that freezes at a higher temperature. In the novel, a madman deliberately releases Ice-9 seeds, which, through nucleation, cause all the water in the world to freeze. (Vonnegut got his ideas from his brother Bernard, who is credited with discovering cloud seeding to increase rainfall, another example of nucleation.)
Papers like Caughey’s and novels like Vonnegut’s suggest how seductive nucleation is to the imagination, one reason it has attracted Carleton Gajdusek. Gajdusek’s mind continued to be fertile, even during his time in jail. He enjoyed incarceration, in fact; he loved how simple it made his life, never having to know where his wallet was or which of his clothes were clean. “No hotel could offer more punctual and polite service,” he wrote in his journal in 1997. The warden let him do his work in the common room after lights out, and his personal writings blossomed. “At the rate I am going, 1997 will be the most verbose journal of my life,” he noted happily in its pages.
The government released Gajdusek on five years’ probation in 1998, with permission to serve the time abroad. Then seventy-four, he had gained an enormous amount of weight; his brother described him as looking like “a great Buddha.” Once unstoppable, as he trekked through the Highland jungles, he now had trouble walking. He went directly to his lawyer’s office, got his passport, had a party at Dulles Airport with friends (among them several other Nobelists), and flew to France. “He wishes to roll around among different labs like Diogenes in a barrel,” one European scientist said at the time.
Gajdusek, who now lives in Amsterdam, is content in his exile. He is open—obsessive—about his long-hidden sexuality. “I am a pedagogic pedophiliac pediatrician,” he greeted me in 2003 when I called to arrange a meeting. Mostly he spends his time reading and thinking about big ideas, the sort that always appealed to him more than lab work.
One subject of his inquiry is how life-forms can replicate without DNA. According to Gajdusek: “life is nucleation, conformational change, and replication.” At the same time, so is nonlife. He asks whether nucleating forces explain the arrangement of stars in a galaxy, and whether fossils could serve as templates for the re-creation of vanished life-forms.
Among the other questions that interest Gajdusek is the mystery of why prions—or “nucleating amyloids,” as he calls them, still resisting Prusiner’s term—are so hard to disinfect. The probability that prions have no DNA cannot really explain this robustness: even prion ash is infectious. Gajdusek theorizes that there is a nanoscopic bit of clay or silica in the prion that captures the form of the protein after the rest of the structure has been incinerated. These molecular templates—“atomic ghost replicas,” in Gajdusek’s words—wait for new intact prions that will adapt to their shape to begin the infection cycle again. “In this case,” Gajdusek wrote in a 2001 paper, “we can really speak of the fantasy of a ‘virus’ from the inorganic world.”
Self-assembling biological systems like protein plaques and nonbiological ones like crystals are a new frontier, and many researchers have taken up the challenge. One is a professor of biomedical engineering at MIT named Shuguang Zhang. Zhang is an unabashed disciple of Gajdusek; he keeps a blow-up of the Nobel laureate on his shelf. Zhang is trying to put nucleation to work in medicine. Biology has always lacked a modeling mechanism that is more complicated than a petri dish, in which experiments are easy to execute but not very true to life, but less complicated than a living animal, in which experiments are true to life but hard to execute. Zhang is using nucleation to create a third way. He has developed watery protein solutions that can form three-dimensional scaffolds. He has also shown how these scaffolds can speed healing when injected into the body, functioning like dissolving stitches, and other times how they can enter the body, organize to open a cell wall, and then dissolve to allow it to close again after a medication bonded to the molecules has entered. These two examples are only the beginning of what self-assembling proteins might accomplish in medicine, according to Zhang. Colleagues are trying to zap molecules with radio transmitters to get them to assume different shapes in the body. They hope one day to persuade stem cells on scaffoldings to grow into muscles or neurons.
There are plenty of potential applications for self-assembling systems outside the body as well—tiny systems using the forces of nucleation could be useful for everything from plastics that build themselves to tiny circuits that can assemble themselves at the molecular level, on a computer chip. The trick, according to Zhang, is to appropriate the work nature has already done—to glean the secrets of the tiny machine that is the cell and co-opt its genius to one’s own purposes. Opposition has already sprung up to self-assembling systems too, the worry being that we have no idea how safe any of this technology is and what its effect on our bodies or the environment may be. Opponents point to the Buckyball, a self-assembling, soccer ball–shaped carbon nanomolecule. Once thought to be harmless, it now turns out to persist in the environment for considerable time when released, invading the cells of living things with unknown consequences. We tap the power of the cell at our peril, though Zhang is not worried. “We have had the Stone Age, the Bronze Age, and the plastic age,” he says. “The future is the designed material age.”