The Northern white rhinoceros Nola, the last one in the U.S. at that time in 2015, pictured here with author Jeanne Loring and Oliver Ryder (in truck), with a film crew and keepers in the San Diego Zoo's savanna. Nola sadly passed away that year.
I am a stem cell scientist. In my day job I work on developing ways to use stem cells to treat neurological disease – human disease. This is the story about how I became part of a group dedicated to rescuing the northern white rhinoceros from extinction.
The earth is now in an era that is called the "sixth mass extinction." The first extinction, 400 million years ago, put an end to 86 percent of the existing species, including most of the trilobites. When the earth grew hotter, dustier, or darker, it lost fish, amphibians, reptiles, plants, dinosaurs, mammals and birds. Each extinction event wiped out 80 to 90 percent of the life on the planet at the time. The first 5 mass extinctions were caused by natural disasters: volcanoes, fires, a meteor. But humans can take credit for the 6th.
Because of human activities that destroy habitats, creatures are now becoming extinct at a rate that is higher than any previously experienced. Some animals, like the giant panda and the California condor, have been pulled back from the brink of extinction by conserving their habitats, breeding in captivity, and educating the public about their plight.
But not the northern white rhino. This gentle giant is a vegetarian that can weigh up to 5,000 pounds. The rhino's weakness is its horn, which has become a valuable commodity because of the mistaken idea that it grants power and has medicinal value. Horns are not medicine; the horns are made of keratin, the same protein that is in fingernails. But as recently as 2017 more than 1,000 rhinos were slaughtered each year to harvest their horns.
All 6 rhino species are endangered. But the northern white has been devastated. Only two members of this species are alive now: Najin, age 32, and her daughter Fatu, 21, live in a protected park in Kenya. They are social animals and would prefer the company of other rhinos of their kind; but they can't know that they are the last two survivors of their entire species. No males exist anymore. The last male, Sudan, died in 2018 at age 45.
We are celebrating a huge milestone in the efforts to use stem cells to rescue the rhino.
I became involved in the rhino rescue project on a sunny day in February, 2008 at the San Diego Wild Animal Park in Escondido, about 30 miles north of my lab in La Jolla. My lab had relocated a couple of months earlier to Scripps Research Institute to start the Center for Regenerative Medicine for human stem cell research. To thank my staff for their hard work, I wanted to arrange a special treat. I contacted my friend Oliver Ryder, who is director of the Institute for Conservation Research at the zoo, to see if I could take them on a safari, a tour in a truck through the savanna habitat at the park.
This was the first of the "stem cell safaris" that the lab would enjoy over the next few years. On the safari we saw elands and cape buffalo, and fed giraffes and rhinos. And we talked about stem cells; in particular, we discussed a surprising technological breakthrough recently reported by the Japanese scientist Shinya Yamanaka that enabled conversion of ordinary skin cells into pluripotent stem cells.
Pluripotent stem cells can develop into virtually any cell type in the body. They exist when we are very young embryos; five days after we were just fertilized eggs, we became blastocysts, invisible tiny balls of a few hundred cells packed with the power to develop into an entire human being. Long before we are born, these cells of vast potential transform into highly specialized cells that generate our brains, our hearts, and everything else.
Human pluripotent stem cells from blastocysts can be cultured in the lab, and are called embryonic stem cells. But thanks to Dr. Yamanaka, anyone can have their skin cells reprogrammed into pluripotent stem cells, just like the ones we had when we were embryos. Dr. Yamanaka won the Nobel Prize for these cells, called "induced pluripotent stem cells" (iPSCs) several years later.
On our safari we realized that if we could make these reprogrammed stem cells from human skin cells, why couldn't we make them from animals' cells? How about endangered animals? Could such stem cells be made from animals whose skin cells had been being preserved since the 1970s in the San Diego Zoo's Frozen Zoo®? Our safari leader, Oliver Ryder, was the curator of the Frozen Zoo and knew what animal cells were stored in its giant liquid nitrogen tanks at −196°C (-320° F). The Frozen Zoo was established by Dr. Kurt Benirschke in 1975 in the hope that someday the collection would aid in rescue of animals that were on the brink of extinction. The frozen collection reached 10,000 cell lines this year.
We returned to the lab after the safari, and I asked my scientists if any of them would like to take on the challenge of making reprogrammed stem cells from endangered species. My new postdoctoral fellow, Inbar Friedrich Ben-Nun, raised her hand. Inbar had arrived only a few weeks earlier from Israel, and she was excited about doing something that had never been done before. Oliver picked the animals we would use. He chose his favorite animal, the critically endangered northern white rhinoceros, and the drill, which is an endangered primate related to the mandrill monkey,
When Inbar started work on reprogramming cells from the Frozen Zoo, there were 8 living northern rhinoceros around the world: Nola, Angalifu, Nesari, Nabire, Suni, Sudan, Najin, and Fatu. We chose to reprogram Fatu, the youngest of the remaining animals.
Through sheer determination and trial and error, Inbar got the reprogramming technique to work, and in 2011 we published the first report of iPSCs from endangered species in the scientific journal Nature Methods. The cover of the journal featured a drawing of an ark packed with animals that might someday be rescued through iPSC technology. By 2011, one of the 8 rhinos, Nesari, had died.
This kernel of hope for using iPSCs to rescue rhinos grew over the next 10 years. The zoo built the Rhino Rescue Center, and brought in 6 females of the closely related species, the southern white rhinoceros, from Africa. Southern white rhino populations are on the rise, and it appears that this species will survive, at least in captivity. The females are destined to be surrogate mothers for embryos made from northern white rhino cells, when eventually we hope to generate sperm and eggs from the reprogrammed stem cells, and fertilize the eggs in vitro, much the same as human IVF.
The author, Jeanne Loring, at the Rhino Rescue Center with one of the southern white rhino surrogates.
David Barker
As this project has progressed, we've been saddened by the loss of all but the last two remaining members of the species. Nola, the last northern white rhino in the U.S., who was at the San Diego Zoo, died in 2015.
But we are celebrating a huge milestone in the efforts to use stem cells to rescue the rhino. Just over a month ago, we reported that by reprogramming cells preserved in the Frozen Zoo, we produced iPSCs from stored cells of 9 northern white rhinos: Fatu, Najin, Nola, Suni, Nadi, Dinka, Nasima, Saut, and Angalifu. We also reprogrammed cells from two of the southern white females, Amani and Wallis.
We don't know when it will be possible to make a northern white rhino embryo; we have to figure out how to use methods already developed for laboratory mice to generate sperm and eggs from these cells. The male rhino Angalifu died in 2014, but ever since I saw beating heart cells derived from his very own cells in a culture dish, I've felt hope that he will one day have children who will seed a thriving new herd of northern white rhinos.
This fall, Robert Reinhart of Boston University published a study finding that electrical stimulation can boost memory - and Reinhart was surprised to discover the effects lasted a full month.
Scientists believe brain circuits tend to uncouple as we age. Since brain neurons communicate by exchanging electrical impulses with each other, the breakdown of these links and associations could be what causes the “senior moment”—when you can’t remember the name of the movie you just watched.
In 2019, Boston University researchers led by Robert Reinhart, director of the Cognitive and Clinical Neuroscience Laboratory, showed that memory loss in healthy older adults is likely caused by these disconnected brain networks. When Reinhart and his team stimulated two key areas of the brain with mild electrical current, they were able to bring the brains of older adult subjects back into sync — enough so that their ability to remember small differences between two images matched that of much younger subjects for at least 50 minutes after the testing stopped.
Reinhart wowed the neuroscience community once again this fall. His newer study in Nature Neuroscience presented 150 healthy participants, ages 65 to 88, who were able to recall more words on a given list after 20 minutes of low-intensity electrical stimulation sessions over four consecutive days. This amounted to a 50 to 65 percent boost in their recall.
Even Reinhart was surprised to discover the enhanced performance of his subjects lasted a full month when they were tested again later. Those who benefited most were the participants who were the most forgetful at the start.
An older person participates in Robert Reinhart's research on brain stimulation.
Robert Reinhart
Reinhart’s subjects only suffered normal age-related memory deficits, but NIBS has great potential to help people with cognitive impairment and dementia, too, says Krista Lanctôt, the Bernick Chair of Geriatric Psychopharmacology at Sunnybrook Health Sciences Center in Toronto. Plus, “it is remarkably safe,” she says.
Lanctôt was the senior author on a meta-analysis of brain stimulation studies published last year on people with mild cognitive impairment or later stages of Alzheimer’s disease. The review concluded that magnetic stimulation to the brain significantly improved the research participants’ neuropsychiatric symptoms, such as apathy and depression. The stimulation also enhanced global cognition, which includes memory, attention, executive function and more.
This is the frontier of neuroscience.
The two main forms of NIBS – and many questions surrounding them
There are two types of NIBS. They differ based on whether electrical or magnetic stimulation is used to create the electric field, the type of device that delivers the electrical current and the strength of the current.
Transcranial Current Brain Stimulation (tES) is an umbrella term for a group of techniques using low-wattage electrical currents to manipulate activity in the brain. The current is delivered to the scalp or forehead via electrodes attached to a nylon elastic cap or rubber headband.
Variations include how the current is delivered—in an alternating pattern or in a constant, direct mode, for instance. Tweaking frequency, potency or target brain area can produce different effects as well. Reinhart’s 2022 study demonstrated that low or high frequencies and alternating currents were uniquely tied to either short-term or long-term memory improvements.
Sessions may be 20 minutes per day over the course of several days or two weeks. “[The subject] may feel a tingling, warming, poking or itching sensation,” says Reinhart, which typically goes away within a minute.
The other main approach to NIBS is Transcranial Magnetic Simulation (TMS). It involves the use of an electromagnetic coil that is held or placed against the forehead or scalp to activate nerve cells in the brain through short pulses. The stimulation is stronger than tES but similar to a magnetic resonance imaging (MRI) scan.
The subject may feel a slight knocking or tapping on the head during a 20-to-60-minute session. Scalp discomfort and headaches are reported by some; in very rare cases, a seizure can occur.
No head-to-head trials have been conducted yet to evaluate the differences and effectiveness between electrical and magnetic current stimulation, notes Lanctôt, who is also a professor of psychiatry and pharmacology at the University of Toronto. Although TMS was approved by the FDA in 2008 to treat major depression, both techniques are considered experimental for the purpose of cognitive enhancement.
“One attractive feature of tES is that it’s inexpensive—one-fifth the price of magnetic stimulation,” Reinhart notes.
Don’t confuse either of these procedures with the horrors of electroconvulsive therapy (ECT) in the 1950s and ‘60s. ECT is a more powerful, riskier procedure used only as a last resort in treating severe mental illness today.
Clinical studies on NIBS remain scarce. Standardized parameters and measures for testing have not been developed. The high heterogeneity among the many existing small NIBS studies makes it difficult to draw general conclusions. Few of the studies have been replicated and inconsistencies abound.
Scientists are still lacking so much fundamental knowledge about the brain and how it works, says Reinhart. “We don’t know how information is represented in the brain or how it’s carried forward in time. It’s more complex than physics.”
Lanctôt’s meta-analysis showed improvements in global cognition from delivering the magnetic form of the stimulation to people with Alzheimer’s, and this finding was replicated inan analysis in the Journal of Prevention of Alzheimer’s Disease this fall. Neither meta-analysis found clear evidence that applying the electrical currents, was helpful for Alzheimer’s subjects, but Lanctôt suggests this might be merely because the sample size for tES was smaller compared to the groups that received TMS.
At the same time, London neuroscientist Marco Sandrini, senior lecturer in psychology at the University of Roehampton, critically reviewed a series of studies on the effects of tES on episodic memory. Often declining with age, episodic memory relates to recalling a person’s own experiences from the past. Sandrini’s review concluded that delivering tES to the prefrontal or temporoparietal cortices of the brain might enhance episodic memory in older adults with Alzheimer’s disease and amnesiac mild cognitive impairment (the predementia phase of Alzheimer’s when people start to have symptoms).
Researchers readily tick off studies needed to explore, clarify and validate existing NIBS data. What is the optimal stimulus session frequency, spacing and duration? How intense should the stimulus be and where should it be targeted for what effect? How might genetics or degree of brain impairment affect responsiveness? Would adjunct medication or cognitive training boost positive results? Could administering the stimulus while someone sleeps expedite memory consolidation?
Using MRI or another brain scan along with computational modeling of the current flow, a clinician could create a treatment that is customized to each person’s brain.
While Sandrini’s review reported improvements induced by tES in the recall or recognition of words and images, there is no evidence it will translate into improvements in daily activities. This is another question that will require more research and testing, Sandrini notes.
Scientists are still lacking so much fundamental knowledge about the brain and how it works, says Reinhart. “We don’t know how information is represented in the brain or how it’s carried forward in time. It’s more complex than physics.”
Where the science is headed
Learning how to apply precision medicine to NIBS is the next focus in advancing this technology, says Shankar Tumati, a post-doctoral fellow working with Lanctôt.
There is great variability in each person’s brain anatomy—the thickness of the skull, the brain’s unique folds, the amount of cerebrospinal fluid. All of these structural differences impact how electrical or magnetic stimulation is distributed in the brain and ultimately the effects.
Using MRI or another brain scan along with computational modeling of the current flow, a clinician could create a treatment that is customized to each person’s brain, from where to put the electrodes to determining the exact dose and duration of stimulation needed to achieve lasting results, Sandrini says.
Above all, most neuroscientists say that largescale research studies over long periods of time are necessary to confirm the safety and durability of this therapy for the purpose of boosting memory. Short of that, there can be no FDA approval or medical regulation for this clinical use.
Lanctôt urges people to seek out clinical NIBS trials in their area if they want to see the science advance. “That is how we’ll find the answers,” she says, predicting it will be 5 to 10 years to develop each additional clinical application of NIBS. Ultimately, she predicts that reigning in Alzheimer’s disease and mild cognitive impairment will require a multi-pronged approach that includes lifestyle and medications, too.
Sandrini believes that scientific efforts should focus on preventing or delaying Alzheimer’s. “We need to start intervention earlier—as soon as people start to complain about forgetting things,” he says. “Changes in the brain start 10 years before [there is a problem]. Once Alzheimer’s develops, it is too late.”