Scientists want the salamander's secret: how they regenerate tissue
All organisms have the capacity to repair or regenerate tissue damage. None can do it better than salamanders or newts, which can regenerate an entire severed limb.
That feat has amazed and delighted man from the dawn of time and led to endless attempts to understand how it happens – and whether we can control it for our own purposes. An exciting new clue toward that understanding has come from a surprising source: research on the decline of cells, called cellular senescence.
Senescence is the last stage in the life of a cell. Whereas some cells simply break up or wither and die off, others transition into a zombie-like state where they can no longer divide. In this liminal phase, the cell still pumps out many different molecules that can affect its neighbors and cause low grade inflammation. Senescence is associated with many of the declining biological functions that characterize aging, such as inflammation and genomic instability.
Oddly enough, newts are one of the few species that do not accumulate senescent cells as they age, according to research over several years by Maximina Yun. A research group leader at the Center for Regenerative Therapies Dresden and the Max Planck Institute of Molecular and Cell Biology and Genetics, in Dresden, Germany, Yun discovered that senescent cells were induced at some stages of regeneration of the salamander limb, “and then, as the regeneration progresses, they disappeared, they were eliminated by the immune system,” she says. “They were present at particular times and then they disappeared.”
Senescent cells added to the edges of the wound helped the healthy muscle cells to “dedifferentiate,” essentially turning back the developmental clock of those cells into more primitive states.
Previous research on senescence in aging had suggested, logically enough, that applying those cells to the stump of a newly severed salamander limb would slow or even stop its regeneration. But Yun stood that idea on its head. She theorized that senescent cells might also play a role in newt limb regeneration, and she tested it by both adding and removing senescent cells from her animals. It turned out she was right, as the newt limbs grew back faster than normal when more senescent cells were included.
Senescent cells added to the edges of the wound helped the healthy muscle cells to “dedifferentiate,” essentially turning back the developmental clock of those cells into more primitive states, which could then be turned into progenitors, a cell type in between stem cells and specialized cells, needed to regrow the muscle tissue of the missing limb. “We think that this ability to dedifferentiate is intrinsically a big part of why salamanders can regenerate all these very complex structures, which other organisms cannot,” she explains.
Yun sees regeneration as a two part problem. First, the cells must be able to sense that their neighbors from the lost limb are not there anymore. Second, they need to be able to produce the intermediary progenitors for regeneration, , to form what is missing. “Molecularly, that must be encoded like a 3D map,” she says, otherwise the new tissue might grow back as a blob, or liver, or fin instead of a limb.
Wound healing
Another recent study, this time at the Mayo Clinic, provides evidence supporting the role of senescent cells in regeneration. Looking closely at molecules that send information between cells in the wound of a mouse, the researchers found that senescent cells appeared near the start of the healing process and then disappeared as healing progressed. In contrast, persistent senescent cells were the hallmark of a chronic wound that did not heal properly. The function and significance of senescence cells depended on both the timing and the context of their environment.
The paper suggests that senescent cells are not all the same. That has become clearer as researchers have been able to identify protein markers on the surface of some senescent cells. The patterns of these proteins differ for some senescent cells compared to others. In biology, such physical differences suggest functional differences, so it is becoming increasingly likely there are subsets of senescent cells with differing functions that have not yet been identified.
There are disagreements within the research community as to whether newts have acquired their regenerative capacity through a unique evolutionary change, or if other animals, including humans, retain this capacity buried somewhere in their genes.
Scientists initially thought that senescent cells couldn’t play a role in regeneration because they could no longer reproduce, says Anthony Atala, a practicing surgeon and bioengineer who leads the Wake Forest Institute for Regenerative Medicine in North Carolina. But Yun’s study points in the other direction. “What this paper shows clearly is that these cells have the potential to be involved in tissue regeneration [in newts]. The question becomes, will these cells be able to do the same in humans.”
As our knowledge of senescent cells increases, Atala thinks we need to embrace a new analogy to help understand them: humans in retirement. They “have acquired a lot of wisdom throughout their whole life and they can help younger people and mentor them to grow to their full potential. We're seeing the same thing with these cells,” he says. They are no longer putting energy into their own reproduction, but the signaling molecules they secrete “can help other cells around them to regenerate.”
There are disagreements within the research community as to whether newts have acquired their regenerative capacity through a unique evolutionary change, or if other animals, including humans, retain this capacity buried somewhere in their genes. If so, it seems that our genes are unable to express this ability, perhaps as part of a tradeoff in acquiring other traits. It is a fertile area of research.
Dedifferentiation is likely to become an important process in the field of regenerative medicine. One extreme example: a lab has been able to turn back the clock and reprogram adult male skin cells into female eggs, a potential milestone in reproductive health. It will be more difficult to control just how far back one wishes to go in the cell's dedifferentiation – part way or all the way back into a stem cell – and then direct it down a different developmental pathway. Yun is optimistic we can learn these tricks from newts.
Senolytics
A growing field of research is using drugs called senolytics to remove senescent cells and slow or even reverse disease of aging.
“Senolytics are great, but senolytics target different types of senescence,” Yun says. “If senescent cells have positive effects in the context of regeneration, of wound healing, then maybe at the beginning of the regeneration process, you may not want to take them out for a little while.”
“If you look at pretty much all biological systems, too little or too much of something can be bad, you have to be in that central zone” and at the proper time, says Atala. “That's true for proteins, sugars, and the drugs that you take. I think the same thing is true for these cells. Why would they be different?”
Our growing understanding that senescence is not a single thing but a variety of things likely means that effective senolytic drugs will not resemble a single sledge hammer but more a carefully manipulated scalpel where some types of senescent cells are removed while others are added. Combinations and timing could be crucial, meaning the difference between regenerating healthy tissue, a scar, or worse.
Two Conservative Icons Gave Opposite Advice on COVID-19. Those Misinformed Died in Higher Numbers, New Study Reports.
The news sources that you consume can kill you - or save you. That's the fundamental insight of a powerful new study about the impact of watching either Sean Hannity's news show Hannity or Tucker Carlson's Tucker Carlson Tonight. One saved lives and the other resulted in more deaths, due to how each host covered COVID-19.
Carlson took the threat of COVID-19 seriously early on, more so than most media figures on the right or left.
This research illustrates the danger of falling for health-related misinformation due to judgment errors known as cognitive biases. These dangerous mental blindspots stem from the fact that our gut reactions evolved for the ancient savanna environment, not the modern world; yet the vast majority of advice on decision making is to "go with your gut," despite the fact that doing so leads to so many disastrous outcomes. These mental blind spots impact all areas of our life, from health to politics and even shopping, as a survey by a comparison purchasing website reveals. We need to be wary of cognitive biases in order to survive and thrive during this pandemic.
Sean Hannity vs. Tucker Carlson Coverage of COVID-19
Hannity and Tucker Carlson Tonight are the top two U.S. cable news shows, both on Fox News. Hannity and Carlson share very similar ideological profiles and have similar viewership demographics: older adults who lean conservative.
One notable difference, however, relates to how both approached coverage of COVID-19, especially in February and early March 2020. Researchers at the Becker Friedman Institute for Economics at the University of Chicago decided to study the health consequences of this difference.
Carlson took the threat of COVID-19 seriously early on, more so than most media figures on the right or left. Already on January 28, way earlier than most, Carlson spent a significant part of his show highlighting the serious dangers of a global pandemic. He continued his warnings throughout February. On February 25, Carlson told his viewers: "In this country, more than a million would die."
By contrast, Hannity was one of the Fox News hosts who took a more extreme position in downplaying COVID-19, frequently comparing it to the flu. On February 27, he said "And today, thankfully, zero people in the United States of America have died from the coronavirus. Zero. Now, let's put this in perspective. In 2017, 61,000 people in this country died from influenza, the flu. Common flu." Moreover, Hannity explicitly politicized COVID-19, claiming that "[Democrats] are now using the natural fear of a virus as a political weapon. And we have all the evidence to prove it, a shameful politicizing, weaponizing of, yes, the coronavirus."
However, after President Donald Trump declared COVID-19 a national emergency in mid-March, Hannity -- and other Fox News hosts -- changed their tune to align more with Carlson's, acknowledging the serious dangers of the virus.
The Behavior and Health Consequences
The Becker Friedman Institute researchers investigated whether the difference in coverage impacted behaviors. They conducted a nationally representative survey of over 1,000 people who watch Fox News at least once a week, evaluating both viewership and behavior changes in response to the pandemic, such as social distancing and improving hygiene.
Next, the study compared people's behavior changes to viewing patterns. The researchers found that "viewers of Hannity changed their behavior five days later than viewers of other shows, while viewers of Tucker Carlson Tonight changed their behavior three days earlier than viewers of other shows." The statistical difference was more than enough to demonstrate significance; in other words, it was extremely unlikely to occur by chance -- so unlikely as to be negligible.
Did these behavior changes lead to grave consequences? Indeed.
The paper compared the popularity of each show in specific counties to data on COVID-19 infections and deaths. Controlling for a wide variety of potential confounding variables, the study found that areas of the country where Hannity is more popular had more cases and deaths two weeks later, the time that it would take for the virus to start manifesting itself. By March 21st, the researchers found, there were 11 percent more deaths among Hannity's viewership than among Carlson's, again with a high degree of statistical significance.
The study's authors concluded: "Our findings indicate that provision of misinformation in the early stages of a pandemic can have important consequences for health outcomes."
Such outcomes stem from excessive trust that our minds tend to give those we see as having authority, even if they don't possess expertise in the relevant subject era.
Cognitive Biases and COVID-19 Misinformation
It's critically important to recognize that the study's authors did not seek to score any ideological points, given the broadly similar ideological profiles of the two hosts. The researchers simply explored the impact of accurate and inaccurate information about COVID-19 on the viewership. Clearly, the false information had deadly consequences.
Such outcomes stem from excessive trust that our minds tend to give those we see as having authority, even if they don't possess expertise in the relevant subject era -- such as media figures that we follow. This excessive trust - and consequent obedience - is called the "authority bias."
A related mental pattern is called "emotional contagion," in which we are unwittingly infected with the emotions of those we see as leaders. Emotions can motivate action even in the absence of formal authority, and are particularly important for those with informal authority, including thought leaders like Carlson and Hannity.
Thus, Hannity telling his audience that Democrats used anxiety about the virus as a political weapon led his audience to reject fears of COVID-19, even though such a reaction and consequent behavioral changes were the right response. Carlson's emphasis on the deadly nature of this illness motivated his audience to take appropriate precautions.
Authority bias and emotional contagion facilitate the spread of misinformation and its dangers, at least when we don't take the steps necessary to figure out the facts. Such steps can range from following best fact-checking practices to getting your information from news sources that commit publicly to being held accountable for truthfulness. Remember, the more important and impactful such information may be for your life, the more important it is to take the time to evaluate it accurately to help you make the best decisions.
[Editor's Note: This is the fifth episode in our Moonshot series, which explores cutting-edge scientific developments that stand to fundamentally transform our world.]
Kira Peikoff was the editor-in-chief of Leaps.org from 2017 to 2021. As a journalist, her work has appeared in The New York Times, Newsweek, Nautilus, Popular Mechanics, The New York Academy of Sciences, and other outlets. She is also the author of four suspense novels that explore controversial issues arising from scientific innovation: Living Proof, No Time to Die, Die Again Tomorrow, and Mother Knows Best. Peikoff holds a B.A. in Journalism from New York University and an M.S. in Bioethics from Columbia University. She lives in New Jersey with her husband and two young sons. Follow her on Twitter @KiraPeikoff.