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.
Biohackers Made a Cheap and Effective Home Covid Test -- But No One Is Allowed to Use It
Last summer, when fast and cheap Covid tests were in high demand and governments were struggling to manufacture and distribute them, a group of independent scientists working together had a bit of a breakthrough.
Working on the Just One Giant Lab platform, an online community that serves as a kind of clearing house for open science researchers to find each other and work together, they managed to create a simple, one-hour Covid test that anyone could take at home with just a cup of hot water. The group tested it across a network of home and professional laboratories before being listed as a semi-finalist team for the XPrize, a competition that rewards innovative solutions-based projects. Then, the group hit a wall: they couldn't commercialize the test.
They wanted to keep their project open source, making it accessible to people around the world, so they decided to forgo traditional means of intellectual property protection and didn't seek patents. (They couldn't afford lawyers anyway). And, as a loose-knit group that was not supported by a traditional scientific institution, working in community labs and homes around the world, they had no access to resources or financial support for manufacturing or distributing their test at scale.
But without ethical and regulatory approval for clinical testing, manufacture, and distribution, they were legally unable to create field tests for real people, leaving their inexpensive, $16-per-test, innovative product languishing behind, while other, more expensive over-the-counter tests made their way onto the market.
Who Are These Radical Scientists?
Independent, decentralized biomedical research has come of age. Also sometimes called DIYbio, biohacking, or community biology, depending on whom you ask, open research is today a global movement with thousands of members, from scientists with advanced degrees to middle-grade students. Their motivations and interests vary across a wide spectrum, but transparency and accessibility are key to the ethos of the movement. Teams are agile, focused on shoestring-budget R&D, and aim to disrupt business as usual in the ivory towers of the scientific establishment.
Ethics oversight is critical to ensuring that research is conducted responsibly, even by biohackers.
Initiatives developed within the community, such as Open Insulin, which hopes to engineer processes for affordable, small-batch insulin production, "Slybera," a provocative attempt to reverse engineer a $1 million dollar gene therapy, and the hundreds of projects posted on the collaboration platform Just One Giant Lab during the pandemic, all have one thing in common: to pursue testing in humans, they need an ethics oversight mechanism.
These groups, most of which operate collaboratively in community labs, homes, and online, recognize that some sort of oversight or guidance is useful—and that it's the right thing to do.
But also, and perhaps more immediately, they need it because federal rules require ethics oversight of any biomedical research that's headed in the direction of the consumer market. In addition, some individuals engaged in this work do want to publish their research in traditional scientific journals, which—you guessed it—also require that research has undergone an ethics evaluation. Ethics oversight is critical to ensuring that research is conducted responsibly, even by biohackers.
Bridging the Ethics Gap
The problem is that traditional oversight mechanisms, such as institutional review boards at government or academic research institutions, as well as the private boards utilized by pharmaceutical companies, are not accessible to most independent researchers. Traditional review boards are either closed to the public, or charge fees that are out of reach for many citizen science initiatives. This has created an "ethics gap" in nontraditional scientific research.
Biohackers are seen in some ways as the direct descendents of "white hat" computer hackers, or those focused on calling out security holes and contributing solutions to technical problems within self-regulating communities. In the case of health and biotechnology, those problems include both the absence of treatments and the availability of only expensive treatments for certain conditions. As the DIYbio community grows, there needs to be a way to provide assurance that, when the work is successful, the public is able to benefit from it eventually. The team that developed the one-hour Covid test found a potential commercial partner and so might well overcome the oversight hurdle, but it's been 14 months since they developed the test--and counting.
In short, without some kind of oversight mechanism for the work of independent biomedical researchers, the solutions they innovate will never have the opportunity to reach consumers.
In a new paper in the journal Citizen Science: Theory & Practice, we consider the issue of the ethics gap and ask whether ethics oversight is something nontraditional researchers want, and if so, what forms it might take. Given that individuals within these communities sometimes vehemently disagree with each other, is consensus on these questions even possible?
We learned that there is no "one size fits all" solution for ethics oversight of nontraditional research. Rather, the appropriateness of any oversight model will depend on each initiative's objectives, needs, risks, and constraints.
We also learned that nontraditional researchers are generally willing (and in some cases eager) to engage with traditional scientific, legal, and bioethics experts on ethics, safety, and related questions.
We suggest that these experts make themselves available to help nontraditional researchers build infrastructure for ethics self-governance and identify when it might be necessary to seek outside assistance.
Independent biomedical research has promise, but like any emerging science, it poses novel ethical questions and challenges. Existing research ethics and oversight frameworks may not be well-suited to answer them in every context, so we need to think outside the box about what we can create for the future. That process should begin by talking to independent biomedical researchers about their activities, priorities, and concerns with an eye to understanding how best to support them.
Christi Guerrini, JD, MPH studies biomedical citizen science and is an Associate Professor at Baylor College of Medicine. Alex Pearlman, MA, is a science journalist and bioethicist who writes about emerging issues in biotechnology. They have recently launched outlawbio.org, a place for discussion about nontraditional research.
Sept. 13th Event: Delta, Vaccines, and Breakthrough Infections
This virtual event will convene leading scientific and medical experts to address the public's questions and concerns about COVID-19 vaccines, Delta, and breakthrough infections. Audience Q&A will follow the panel discussion. Your questions can be submitted in advance at the registration link.
DATE:
Monday, September 13th, 2021
12:30 p.m. - 1:45 p.m. EDT
REGISTER:
Dr. Amesh Adalja, M.D., FIDSA, Senior Scholar, Johns Hopkins Center for Health Security; Adjunct Assistant Professor, Johns Hopkins Bloomberg School of Public Health; Affiliate of the Johns Hopkins Center for Global Health. His work is focused on emerging infectious disease, pandemic preparedness, and biosecurity.
Dr. Nahid Bhadelia, M.D., MALD, Founding Director, Boston University Center for Emerging Infectious Diseases Policy and Research (CEID); Associate Director, National Emerging Infectious Diseases Laboratories (NEIDL), Boston University; Associate Professor, Section of Infectious Diseases, Boston University School of Medicine. She is an internationally recognized leader in highly communicable and emerging infectious diseases (EIDs) with clinical, field, academic, and policy experience in pandemic preparedness.
Dr. Akiko Iwasaki, Ph.D., Waldemar Von Zedtwitz Professor of Immunobiology and Molecular, Cellular and Developmental Biology and Professor of Epidemiology (Microbial Diseases), Yale School of Medicine; Investigator, Howard Hughes Medical Institute. Her laboratory researches how innate recognition of viral infections lead to the generation of adaptive immunity, and how adaptive immunity mediates protection against subsequent viral challenge.
Dr. Marion Pepper, Ph.D., Associate Professor, Department of Immunology, University of Washington. Her lab studies how cells of the adaptive immune system, called CD4+ T cells and B cells, form immunological memory by visualizing their differentiation, retention, and function.
This event is the third of a four-part series co-hosted by Leaps.org, the Aspen Institute Science & Society Program, and the Sabin–Aspen Vaccine Science & Policy Group, with generous support from the Gordon and Betty Moore Foundation and the Howard Hughes Medical Institute.
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.