Daniela Kaufer has reversed the effects of aging in mouse brains. Can she do it in humans?
IT ALL STARTED WITH A MYSTERIOUS ILLNESS.
In the 1990s, thousands of U.S. veterans returning from combat in the Persian Gulf began suffering from what became known as Gulf War Syndrome, an undiagnosed host of chronic neurological symptoms. During the first Gulf War, deployed soldiers had been prescribed a daily dose of the drug pyridostigmine as a prophylactic against nerve gas because it was feared that Iraqi forces would resort to chemical attacks against invading troops. Although no such attack occurred, soldiers reported symptoms including headaches, dizziness, and memory problems.
Israeli neuroscientist Alon Friedman and then-grad student Daniela Kaufer, now a professor at Berkeley, wanted to know the cause. They proposed what Kaufer calls a “wild hypothesis”: that the anti-nerve gas drug had somehow penetrated the protective blood-brain barrier and was wreaking havoc on the soldiers’ brains.
Aptly named, the blood-brain barrier acts as a highly selective gateway between the bloodstream and the brain tissue. And it’s picky for a reason. You really don’t want a lot of the stuff (bacteria, toxins, etc.) that circulates in your blood getting into your grey matter. By and large, the barrier does a great job of keeping bad things out, but Kaufer and Friedman hypothesized that an extremely stressful situation, like active combat, could increase its permeability, allowing unwelcome guests like pathogens to enter. In other words, what if the stress of war had compromised the soldiers’ protective blood-brain barrier, making it sort of … leaky?
Late one night in 1994, the researchers stood hunched over a tub of water in the psychobiology lab at the Hebrew University of Jerusalem, watching a mouse struggle to stay afloat. The water was intentionally cold—not quite active combat, but enough to induce a stress response in the mouse. The experiment itself was fairly simple: Mouse is forced to swim for four minutes. Researchers inject blue dye into mouse’s vein. If mouse’s brain shows blue coloration, then dye from the bloodstream has crossed the blood-brain barrier.
It would turn out to be a seminal moment in their careers. The results were clear. Scans revealed that the traumatized mouse’s brain was full of blue dye. And when Friedman and Kaufer repeated the experiment using pyridostigmine instead of dye, they found evidence of the drug in the mouse brains, as well as increased neuronal excitability—a common sign of cognitive dysfunction. The implications—that stress could break down the brain’s physiological barrier and disrupt brain activity—were radical. Not only did their discovery highlight the fragility of the blood-brain barrier, but they were able to directly tie a “leaky” barrier to cognitive dysfunction, like that seen in Gulf War veterans. And if degeneration of the barrier was associated with dysfunction in overstressed brains, they wondered, what about injured brains, or even aging brains?
Twenty-five years later, decades of work coalesced in some startling discoveries, which Kaufer and Friedman described in two December 2019 papers published in Science Translational Medicine.
The language of the papers is technical and dense, but one key phrase stands out: chronic yet reversible neural dysfunction. As Kaufer said in an interview with Berkeley News: “We can reverse brain aging.”
WE ACCEPT AGING, IF NOT WILLINGLY, at least unquestioningly, because it is inherent to living. We see it all the time in the wrinkling of flesh, the sagging of muscles, the wilting of leaves, the slowing of memory. And yet the underlying forces, the physiological mechanisms that cause this deterioration are mysterious and complex.
So what exactly is aging?
Philosophers have wrestled with this question for millennia. Aristotle posited a foundational theory about aging and death as the “extinction or exhaustion of the vital heat.” This idea was furthered by others like Galen, a second-century Greek philosopher and physician, and Persian polymath Avicenna, who wrote in his Canon of Medicine: “[L]ife itself depends on the innate heat, and growth depends on the innate moisture.”
Life, the ancient philosophers theorized, is rather like an oil lamp, whose inevitable extinction signifies death. Over time, the body’s innate heat (flame) will consume the internal moisture (fuel) until exhausted. It’s perhaps no wonder that the idea of a “Fountain of Youth”—a wellspring of the very liquid of life—emerged as a popular, albeit fantastical, antidote to aging. If aging is merely a depletion of vital fuel, couldn’t immortality just be a matter of refueling from time to time?
Of course, it’s not quite that simple. For one, every part of the body ages differently. In the brain alone, there are billions of neurons, pathways, and chemical reactions that each function—or dysfunction—in their own way. Put in simplest terms, Peter Sudmant, an assistant professor of integrative biology at Berkeley, says this: “Brain aging is two things. It’s the decline of these biological processes that keep ourselves and our neurons healthy. But it’s also the physical manifestation of these things—whether it’s memory loss or cognitive decline. … And those things are completely, inextricably linked.”
Our populations are aging beyond what was once imaginable. A century ago, the average life expectancy of an American was 55.4 years—since 2012, it has reached an all-time high of 78.9. With longer life spans has come an alarming increase in degenerative brain disorders. Alzheimer’s, the most common form of dementia, is ranked in the top ten causes of death in the United States, with nearly 6 million people currently diagnosed. The National Institutes of Health is expected to spend $2.8 billion in 2020 on Alzheimer’s research alone.
And yet, while decline is inevitable, disease is not. Everyone’s brains atrophy as cells shrink and connections deteriorate, but not everyone develops Alzheimer’s or dementia. Every oil lamp burns down, but not every oil lamp tips over and lights the room on fire.
There’s enormous potential in this distinction. There’s also one very important question that Daniela Kaufer has dedicated her life to trying to answer: If the path from brain deterioration to neurologic dysfunction is identified, can it be manipulated or even blocked?
The answer could change our very understanding of aging itself.
THREE WEEKS INTO CALIFORNIA’S lockdown, Kaufer and I finally “meet” over Zoom. Our screens connect, and she begins to talk immediately, her quick, staccato voice commanding the glitchy audio as we commiserate about working from home. It’s a major headache for her—bills still need to be paid, lab mice still need to be fed—but she’s more concerned about her students and their projects. “The students I see are really struggling,” she says, her tone softening. “I think it’s much more difficult for them.”
Kaufer, who grew up in Israel, has always been a bit of a pioneer. Neither of her parents went to college and there were no scientists in the family, but she fixated on neuroscience from an early age.
“I don’t remember ever wanting to do anything else,” she says. “I don’t know where it came from. I was fascinated by the brain … but I don’t think I knew what that meant.”
When she and Alon Friedman published in 1996, their findings about Gulf War Syndrome met with tepid response. From her recollection, publishing was an uphill battle, as they faced resistance from skeptical peers. Leaky blood-brain barriers had first been implicated in cognitive decline of aging patients back in the 1970s. But the results of prior studies were mixed. Even when researchers observed a correlation, they weren’t able to prove that deterioration of the barrier was the direct cause. Many scientists still believed the barrier to be a fairly static structure, the permeability of which didn’t change significantly over the course of a person’s life. Others were interested in its permeability only as a tool for transporting drugs, like tumor-killing chemicals, into the brain. Kaufer and Friedman had their own ideas.
“At some point, we started thinking that we really want to know what happens when it’s open,” says Kaufer. “And can this actually be something that plays a role in the mechanism of the disease generation?”
She decided to investigate further. After completing her Ph.D. in molecular biochemistry at the Hebrew University and postdoctoral work at Stanford, she accepted a position at Berkeley in 2005.
IN HER LAB AT CAL, SHE CONTINUED experiments in mice, confirming that increased permeability of the blood-brain barrier correlated with a host of neurological symptoms. But which ingredient of the inflowing blood was the agent of dysfunction? Was it the blood cells themselves, or something smaller, like DNA or proteins? She went to work, selectively injecting each into the mouse’s brain, and zeroed in on a prime suspect: albumin. (A common blood protein, albumin is normally filtered out by the blood-brain barrier.) By labeling the protein with a fluorescent tag, she was able to observe it binding to TGF-β receptors and being taken up by certain star-shaped brain cells called astrocytes. Eventually, she identified an entire chain of events—a “TGF-β signaling pathway”—that albumin activated in the brain.
William Jagust, a professor of public health and neuroscience at Berkeley, compares this phenomenon to a chain of billiard balls lined up in front of a pocket. In this scenario, he says, “Albumin is one of the balls that hits the TGF-β ball, and that TGF-β ball hits another ball,” and on and on until the final ball is pushed into the pocket. “This is fundamentally the idea of a cascade,” he says. However, if you can stop one ball you can break the chain. By identifying the precise sequence of events, and the key billiard balls involved, Kaufer had taken a big first step toward intervention.
For the next few years, she published paper after paper, collaborating on projects that tied blood-brain barrier disruption, and activation of the TGF-β pathway, to strokes, epilepsy, and certain genetic disorders. She discovered that deterioration of the barrier was a driving force of cognitive decline in diseases like Parkinson’s and following traumatic brain injury, from, say, repeated head blows in contact sports. She started to see parallels between dysfunction in young, injured brains and old, diseased brains.
“Think Muhammad Ali and NFL victims of chronic, traumatic encephalopathy,” Kaufer would later write. “These young brains look a lot like aged, neurodegeneration-riddled brains. What if the same mechanism is responsible for natural aging?”
Kaufer, like centuries of philosophers before her, became fascinated with the question of what, exactly, causes brain aging. It seemed to be something other than just natural decline since there was so much natural variability, with some minds staying sharp while others struggled to recall basic facts. From MRI scans, Friedman confirmed what they already suspected: the blood-brain barrier deteriorates with age, but not uniformly; in people over the age of 70, 60 percent show some decay.
Kaufer and Friedman wanted to make the connection that no one else had. If albumin was really causing the dysfunction—memory loss, seizures, confusion—they should be able to induce or prevent those symptoms by manipulating the uptake of the protein.
TO INVESTIGATE, THEY LAUNCHED A SERIES of experiments. In the first trial, they injected albumin into the brains of young mice and found that, within a week, they were behaving like old mice—their brains showed inflammation, they had a decreased ability to learn new tasks like navigating mazes, and they were more prone to seizures. In the second trial, they turned off the gene for the TGF-β protein receptor, which prevented albumin from binding and thus blocked the entire signaling pathway. This worked, too—the young mice retained their youthful brains even when exposed to albumin. In the third trial, the researchers again turned off the gene for the protein receptor, but in a population of middle-aged mice. “That was great,” Kaufer says. Despite being older, the mice showed less brain aging over time. “They had molecular signatures of a young brain. They learned like a young mouse.”
It was the fourth trial that took everyone by surprise. Designed as a control, the experiment would test the effects of blocking the protein receptor in mice whose brains are already very aged. The researchers expected no change in the mice’s cognitive abilities because, as Kaufer put it, “At this point the damage has already happened, you can’t really reverse that.” But, in fact, a week after turning off the TGF-β pathway, the older mice were learning like younger mice, suffering fewer seizures, and exhibiting all the molecular markers of young brains. For these older mice, cognitive decline hadn’t merely been prevented or stopped, it had actually been reversed.
The implications of the discovery were profound, suggesting as it did that failing minds could be restored to youthful acuity with a single genetic tweak. “This was really very encouraging,” Kaufer would later write. “Isn’t that exactly what we all want? To learn the maze just like this young mouse?”
The only problem was that what they’d done in the mice—knock out the receptor-coding gene—wasn’t likely to happen in humans anytime soon. If they wanted to test this therapy in people, they needed a different strategy. And that’s where Barry Hart came in.
A medicinal chemist in Palo Alto, Hart had been working on a drug for cancer that just so happened to selectively block the TGF-β receptor in astrocytes. As Kaufer recalls, Hart read some of her papers and sent her an email that said, “I have something that I think could be a really interesting drug as a clinical candidate. Do you want to try it?” Kaufer drove down to Palo Alto to meet him for coffee, and Hart handed her a vial of the drug. It worked remarkably well on her mice. After seven days of treatment with the small-molecule drug, called IPW, the aged brains of the older mice looked younger, they were less prone to seizures, and they performed better on cognitive tasks like maze running.
A new picture of aging began to emerge.
Around middle age, the blood-brain barrier starts to deteriorate. As the gateway opens up, chemicals and other substances rush in, triggering a chemical cascade of immune proteins called cytokines. They, in turn, cause neurons to fire a little too excitedly, creating a self-perpetuating loop of inflammation and neural dysfunction. In mice, this might look like seizures and poor performance in maze running. In humans, it often manifests as confusion, memory loss, or difficulty with basic tasks. Kaufer calls this mental chaos the “inflammatory fog”—an apt metaphor because, like fog, it can lift. Beneath the neurological fog of inflammation may be a relatively well-functioning, even youthful brain.
Berkeley neuroscientist William Jagust is cautiously optimistic about the possibility for treatment. “If you’ve talked to scientists, we’re all kind of the same, we all get excited about a new idea. But we all want to see the proof, right?” He thinks Kaufer’s work, in identifying a specific, novel mechanism of aging, is creative and compelling. But he adds, “The fundamental question is: Does this translate to the human situation? And we’re just gonna have to see.”
For one thing, cognitive dysfunction in mice may not be a good model for dementia or neurodegenerative disease in humans. As Jagust explains, there are no known animals that get Alzheimer’s disease naturally.
Still, he thinks they’re on the right track. “You’ve got two parts of the story here that make it worth investigating,” Jagust says. “One is that these [TGF-β] pathways are present in humans. And two is there seems to be evidence for disruption of the blood-brain barrier in humans. I’m not sure you can really get much better than that, in terms of motivating you to dig deeper.”
TO DEVELOP A DRUG TO TREAT HUMANS, Kaufer, Friedman, and Hart have since started a company, Mend Neuroscience. Though shelter-in-place has thrown a wrench in their timeline, Kaufer hopes the company can start clinical trials in a few years.
Even so, we’re far from the proverbial fountain of youth.
Kaufer believes they’ve “made a big step” in elucidating the role of the blood-brain barrier in brain functionality, but she’s not quite ready to rewrite the neurobiology textbooks. As for this idea of reversing aging? She thinks a more accurate description would be “[restoring] youthful function of the brain.”
Peter Sudmant, assistant professor and a collaborator on the paper, also sees promise in therapeutics, not as a way to reverse aging per se but to improve quality of life in aging populations, or people suffering from disease or brain injury. “The thrust of the field right now is increasing health span,” he says, which means “not necessarily increasing our longevity, but that we can hopefully live healthy and mentally fulfilled lives into old age.”
The appeal is enormous, and many people are desperate for therapies to be developed immediately. It’s only been a few months since the publication of Kaufer’s two recent papers, but already she has received countless emails and Facebook messages from would-be patients describing their Alzheimer’s or dementia symptoms and begging to participate in clinical trials. “There were people that wrote things like, ‘I don’t care if it’s approved or not, can you just give me some of the drug?’ ” Another person jokingly offered to wear mouse ears to be eligible. “The most heartbreaking one was somebody saying, ‘My life is not worth much anyway. Just let me try it.’ It is very clear that the human need behind it is enormous.”
She tries to respond to every email, but she knows that she’s years away from clinical trials, let alone FDA approval and a market-ready therapy.
As the company seeks funding, Kaufer is continuing to research new, bigger questions and is particularly excited about the idea of brain resilience. If the blood-brain barrier is as malleable and dynamic as she and others believe, then maybe deterioration and cognitive decline isn’t inevitable. Maybe even something as simple as lowering life stress could forestall leakage.
“What is the take-home message from that?” she asks. “Work on your mental resilience and cognitive resilience all the time. Which means don’t be stressed about work.” Jokingly, she adds, “I guess I should just retire right now and go work on my mental and cognitive resilience.”
For all of our sakes, let’s hope she waits.
Leah Worthington is senior online editor of California.
From the Summer 2020 issue of California.