Epigenetic therapeutics could revolutionize medicine in the coming decades. (© kentoh/Adobe)
How exactly does your DNA make you who you are?
It's because of epigenetics that identical twins can actually look different and develop different diseases.
Just as software developers don't write apps out of ones and zeros, the interesting parts of the human genome aren't written merely in As, Ts, Cs and Gs. Yes, these are the fundamental letters that make up our DNA and encode the proteins that make our cells function, but the story doesn't end there.
Our cells possess amazing abilities, like eating invading bacteria or patching over a wound, and these abilities require the coordinated action of hundreds, if not thousands, of proteins. Epigenetics, the study of gene expression, examines how multiple genes work at once to make these biological processes happen.
It's because of epigenetics that identical twins – who possess identical DNA -- can actually look different and develop different diseases. Their environments may influence the expression of their genes in unique ways. For example, a research study in mice found that maternal exposure to a chemical called bisphenol A (BPA) resulted in drastic differences between genetically identical offspring. BPA exposure increased the likelihood that a certain gene was turned on, which led to the birth of yellow mice who were prone to obesity. Their genetically identical siblings who were not exposed to BPA were thinner and born with brown fur.
These three mice are genetically identical. Epigenetic differences, however, result in vastly different phenotypes.
(© 1994 Nature Publishing Group, Duhl, D.)
This famous mouse experiment is just one example of how epigenetics may transform medicine in the coming years. By studying the way genes are turned on and off, and maybe even making those changes ourselves, scientists are beginning to approach diseases like cancer in a completely new way.
With few exceptions, most of the 1 trillion cells that make up your body contain the same DNA instructions as all the others. How does each cell in your body know what it is and what it has to do? One of the answers appears to lie in epigenetic regulation. Just as everyone at a company may have access to all the same files on the office Dropbox, the accountants will put different files on their desktop than the lawyers do.
Our cells prioritize DNA sequences in the same way, even storing entire chromosomes that aren't needed along the wall of the nucleus, while keeping important pieces of DNA in the center, where it is most accessible to be read and used. One of the ways our cells prioritize certain DNA sequences is through methylation, a process that inactivates large regions of genes without editing the underlying "file" itself.
As we learn more about epigenetics, we gain more opportunities to develop therapeutics for a broad range of human conditions, from cancer to metabolic disorders. Though there have not been any clinical applications of epigenetics to immune or metabolic diseases yet, cancer is one of the leading areas, with promising initial successes.
One of the challenges of cancer treatments is that different patients may respond positively or negatively to the same treatment. With knowledge of epigenetics, however, doctors could conduct diagnostic tests to identify a patient's specific epigenetic profile and determine the best treatment for him or her. Already, commercial kits are available that help doctors screen glioma patients for an epigenetic biomarker called MGMT, because patients with this biomarker have shown high rates of success with certain kinds of treatments.
Other epigenetic advances go beyond personalized screening to treatments targeting the mechanism of disease. Some epigenetic drugs turn on genes that help suppress tumors, while others turn on genes that reveal the identity of tumor cells to the immune system, allowing it to attack cancerous cells.
Direct, targeted control of your epigenome could allow doctors to reprogram cancerous or aging cells.
The study of epigenetics has also been fundamental to the field of aging research. The older you get, the more methylation marks your DNA carries, and this has led to the distinction between biological aging, or the state of your cells, and chronological aging, or how old you actually are.
Just as our DNA can get miscopied and accumulate mutations, errors in DNA methylation can lead to so-called "epimutations". One of the big hypotheses in aging research today is that the accumulation of these random epimutations over time is responsible for what we perceive as aging.
Studies thus far have been correlative - looking at several hundred sites of epigenetic modifications in a person's cell, scientists can now roughly discern the age of that person. The next set of advances in the field will come from learning what these epigenetic changes individually do by themselves, and if certain methylations are correlated with cellular aging. General diagnostic terms like "aging" could be replaced with "abnormal methylation at these specific locations," which would also open the door to new therapeutic targets.
Direct, targeted control of your epigenome could allow doctors to reprogram cancerous or aging cells. While this type of genetic surgery is not feasible just yet, current research is bringing that possibility closer. The Cas9 protein of genome-editing CRISPR/Cas9 fame has been fused with epigenome modifying enzymes to target epigenetic modifications to specific DNA sequences.
A therapeutic of this type could theoretically undo a harmful DNA methylation, but would also be competing with the cell's native machinery responsible for controlling this process. One potential approach around this problem involves making beneficial synthetic changes to the epigenome that our cells do not have the capacity to undo.
Also fueling this frontier is a new approach to understanding disease itself. Scientists and doctors are now moving beyond the "one defective gene = one disease" paradigm. Because lots of diseases are caused by multiple genes going haywire, epigenetic therapies could hold the key to new types of treatments by targeting multiple defective genes at once.
Scientists are still discovering which epigenetic modifications are responsible for particular diseases, and engineers are building new tools for epigenome editing. Given the proliferation of work in these fields within the last 10 years, we may see epigenetic therapeutics emerging within the next couple of decades.
NASA astronaut Frank Rubio floats by the International Space Station’s “window to the world.” Yesterday, he returned from the longest single spaceflight by a U.S. astronaut on record - over one year. Exploring deep space will require even longer missions.
Yesterday, NASA astronaut Frank Rubio returned to Earth after over one year, the longest single spaceflight for a U.S. astronaut. But this is just the start; longer and more complex missions into deep space loom ahead, from returning to the moon in 2025 to eventually sending humans to Mars. Understanding how spaceflight affects the body is vital to success. By studying these impacts, NASA aims to help astronauts perform in space as well as they do on Earth.
The dangers of microgravity are real
A NASA report published in 2016 details a long list of incidents and near-misses caused – at least partly – by space-induced changes in astronauts’ vision and coordination. These issues make it harder to move with precision and to judge distance and velocity.
According to the report, in 1997, a resupply ship collided with the Mir space station, possibly because a crew member bumped into the commander during the final docking maneuver. This mishap caused significant damage to the space station.
Returns to Earth suffered from problems, too. The same report notes that touchdown speeds during the first 100 space shuttle landings were “outside acceptable limits. The fastest landing on record – 224 knots (258 miles) per hour – was linked to the commander’s momentary spatial disorientation.” Earlier, each of the six Apollo crews that landed on the moon had difficulty recognizing moon landmarks and estimating distances. For example, Apollo 15 landed in an unplanned area, ultimately straddling the rim of a five-foot deep crater on the moon, harming one of its engines.
Spaceflight causes unique stresses on astronauts’ brains and central nervous systems. NASA is working to reduce these harmful effects.
NASA
Space messes up your brain
In space, astronauts face the challenges of microgravity, ionizing radiation, social isolation, high workloads, altered circadian rhythms, monotony, confined living quarters and a high-risk environment. Among these issues, microgravity is one of the most consequential in terms of physiological changes. It changes the brain’s structure and its functioning, which can hurt astronauts’ performance.
The brain shifts upwards within the skull, displacing the cerebrospinal fluid, which reduces the brain’s cushioning. Essentially, the brain becomes crowded inside the skull like a pair of too-tight shoes.
That’s partly because of how being in space alters blood flow. On Earth, gravity pulls our blood and other internal fluids toward our feet, but our circulatory valves ensure that the fluids are evenly distributed throughout the body. In space, there’s not enough gravity to pull the fluids down, and they shift up, says Rachael D. Seidler, a physiologist specializing in spaceflight at the University of Florida and principal investigator on many space-related studies. The head swells and legs appear thinner, causing what astronauts call “puffy face chicken legs.”
“The brain changes at the structural and functional level,” says Steven Jillings, equilibrium and aerospace researcher at the University of Antwerp in Belgium. “The brain shifts upwards within the skull,” displacing the cerebrospinal fluid, which reduces the brain’s cushioning. Essentially, the brain becomes crowded inside the skull like a pair of too-tight shoes. Some of the displaced cerebrospinal fluid goes into cavities within the brain, called ventricles, enlarging them. “The remaining fluids pool near the chest and heart,” explains Jillings. After 12 consecutive months in space, one astronaut had a ventricle that was 25 percent larger than before the mission.
Some changes reverse themselves while others persist for a while. An example of a longer-lasting problem is spaceflight-induced neuro-ocular syndrome, which results in near-sightedness and pressure inside the skull. A study of approximately 300 astronauts shows near-sightedness affects about 60 percent of astronauts after long missions on the International Space Station (ISS) and more than 25 percent after spaceflights of only a few weeks.
Another long-term change could be the decreased ability of cerebrospinal fluid to clear waste products from the brain, Seidler says. That’s because compressing the brain also compresses its waste-removing glymphatic pathways, resulting in inflammation, vulnerability to injuries and worsening its overall health.
The effects of long space missions were best demonstrated on astronaut twins Scott and Mark Kelly. This NASA Twins Study showed multiple, perhaps permanent, changes in Scott after his 340-day mission aboard the ISS, compared to Mark, who remained on Earth. The differences included declines in Scott’s speed, accuracy and cognitive abilities that persisted longer than six months after returning to Earth in March 2016.
By the end of 2020, Scott’s cognitive abilities improved, but structural and physiological changes to his eyes still remained, he said in a BBC interview.
“It seems clear that the upward shift of the brain and compression of the surrounding tissues with ventricular expansion might not be a good thing,” Seidler says. “But, at this point, the long-term consequences to brain health and human performance are not really known.”
NASA astronaut Kate Rubins conducts a session for the Neuromapping investigation.
NASA
Staying sharp in space
To investigate how prolonged space travel affects the brain, NASA launched a new initiative called the Complement of Integrated Protocols for Human Exploration Research (CIPHER). “CIPHER investigates how long-duration spaceflight affects both brain structure and function,” says neurobehavioral scientist Mathias Basner at the University of Pennsylvania, a principal investigator for several NASA studies. “Through it, we can find out how the brain adapts to the spaceflight environment and how certain brain regions (behave) differently after – relative to before – the mission.”
To do this, he says, “Astronauts will perform NASA’s cognition test battery before, during and after six- to 12-month missions, and will also perform the same test battery in an MRI scanner before and after the mission. We have to make sure we better understand the functional consequences of spaceflight on the human brain before we can send humans safely to the moon and, especially, to Mars.”
As we go deeper into space, astronauts cognitive and physical functions will be even more important. “A trip to Mars will take about one year…and will introduce long communication delays,” Seidler says. “If you are on that mission and have a problem, it may take eight to 10 minutes for your message to reach mission control, and another eight to 10 minutes for the response to get back to you.” In an emergency situation, that may be too late for the response to matter.
“On a mission to Mars, astronauts will be exposed to stressors for unprecedented amounts of time,” Basner says. To counter them, NASA is considering the continuous use of artificial gravity during the journey, and Seidler is studying whether artificial gravity can reduce the harmful effects of microgravity. Some scientists are looking at precision brain stimulation as a way to improve memory and reduce anxiety due to prolonged exposure to radiation in space.
Other scientists are exploring how to protect neural stem cells (which create brain cells) from radiation damage, developing drugs to repair damaged brain cells and protect cells from radiation.
To boldly go where no astronauts have gone before, they must have optimal reflexes, vision and decision-making. In the era of deep space exploration, the brain—without a doubt—is the final frontier.
Additionally, NASA is scrutinizing each aspect of the mission, including astronaut exercise, nutrition and intellectual engagement. “We need to give astronauts meaningful work. We need to stimulate their sensory, cognitive and other systems appropriately,” Basner says, especially given their extreme confinement and isolation. The scientific experiments performed on the ISS – like studying how microgravity affects the ability of tissue to regenerate is a good example.
“We need to keep them engaged socially, too,” he continues. The ISS crew, for example, regularly broadcasts from space and answers prerecorded questions from students on Earth, and can engage with social media in real time. And, despite tight quarters, NASA is ensuring the crew capsule and living quarters on the moon or Mars include private space, which is critical for good mental health.
Exploring deep space builds on a foundation that began when astronauts first left the planet. With each mission, scientists learn more about spaceflight effects on astronauts’ bodies. NASA will be using these lessons to succeed with its plans to build science stations on the moon and, eventually, Mars.
“Through internally and externally led research, investigations implemented in space and in spaceflight simulations on Earth, we are striving to reduce the likelihood and potential impacts of neurostructural changes in future, extended spaceflight,” summarizes NASA scientist Alexandra Whitmire. To boldly go where no astronauts have gone before, they must have optimal reflexes, vision and decision-making. In the era of deep space exploration, the brain—without a doubt—is the final frontier.
Swiss researchers have found a type of brain cell that appears to be a hybrid of the two other main types — and it could lead to new treatments for brain disorders.
A new brain cell: Researchers at the Wyss Center for Bio and Neuroengineering and the University of Lausanne believe they’ve definitively proven that some astrocytes do actively participate in neurotransmission, making them a sort of hybrid of neurons and glial cells.
According to the researchers, this third type of brain cell, which they call a “glutamatergic astrocyte,” could offer a way to treat Alzheimer’s, Parkinson’s, and other disorders of the nervous system.
“Its discovery opens up immense research prospects,” said study co-director Andrea Volterra.
The study: Neurotransmission starts with a neuron releasing a chemical called a neurotransmitter, so the first thing the researchers did in their study was look at whether astrocytes can release the main neurotransmitter used by neurons: glutamate.
By analyzing astrocytes taken from the brains of mice, they discovered that certain astrocytes in the brain’s hippocampus did include the “molecular machinery” needed to excrete glutamate. They found evidence of the same machinery when they looked at datasets of human glial cells.
Finally, to demonstrate that these hybrid cells are actually playing a role in brain signaling, the researchers suppressed their ability to secrete glutamate in the brains of mice. This caused the rodents to experience memory problems.
“Our next studies will explore the potential protective role of this type of cell against memory impairment in Alzheimer’s disease, as well as its role in other regions and pathologies than those explored here,” said Andrea Volterra, University of Lausanne.
But why? The researchers aren’t sure why the brain needs glutamatergic astrocytes when it already has neurons, but Volterra suspects the hybrid brain cells may help with the distribution of signals — a single astrocyte can be in contact with thousands of synapses.
“Often, we have neuronal information that needs to spread to larger ensembles, and neurons are not very good for the coordination of this,” researcher Ludovic Telley told New Scientist.
Looking ahead: More research is needed to see how the new brain cell functions in people, but the discovery that it plays a role in memory in mice suggests it might be a worthwhile target for Alzheimer’s disease treatments.
The researchers also found evidence during their study that the cell might play a role in brain circuits linked to seizures and voluntary movements, meaning it’s also a new lead in the hunt for better epilepsy and Parkinson’s treatments.
“Our next studies will explore the potential protective role of this type of cell against memory impairment in Alzheimer’s disease, as well as its role in other regions and pathologies than those explored here,” said Volterra.
