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.
CandyCodes could provide sweet justice against fake pills
When we swallow a pill, we hope it will work without side effects. Few of us know to worry about a growing issue facing the pharmaceutical industry: counterfeit medications. These pills, patches, and other medical products might look just like the real thing. But they’re often stuffed with fillers that dilute the medication’s potency or they’re simply substituted for lookalikes that contain none of the prescribed medication at all.
Now, bioengineer William Grover at the University of California, Riverside, may have a solution. Inspired by the tiny, multi-colored sprinkles called nonpareils that decorate baked goods and candies, Grover created CandyCodes pill coatings to prevent counterfeits.
The idea was borne out of pandemic boredom. Confined to his home, Grover was struck by the patterns of nonpareils he saw on candies, and found himself counting the number of little balls on each one. “It’s random, how they’re applied,” he says. “I wondered if it ever repeats itself or if each of these candies is unique in the entire world.” He suspected the latter, and some quick math proved his hypothesis: Given dozens of nonpareils per candy in a handful of different colors, it’s highly unlikely that the sprinklings on any two candies would be identical.
He quickly realized his finding could have practical applications: pills or capsules could be coated with similar “sprinkles,” with the manufacturer photographing each pill or capsule before selling its products. Consumers looking to weed out fakes could potentially take a photo with their cell phones and go online to compare images of their own pills to the manufacturer’s database, with the help of an algorithm that would determine their authenticity. Or, a computer could generate another type of unique identifier, such as a text-based code, tracking to the color and location of the sprinkles. This would allow for a speedier validation than a photo-based comparison, Grover says. “It could be done very quickly, in a fraction of a second.”
Researchers and manufacturers have already developed some anti-counterfeit tools, including built-in identifiers like edible papers with scannable QR codes. But such methods, while functional, can be costly to implement, Grover says.
It wouldn’t be paranoid to take such precautions. Counterfeits are a growing problem, according to Young Kim, a biomedical engineer at Purdue University who was not involved in the CandyCodes study. “There are approximately 40,000 online pharmacies that one can access via the Internet,” he says. “Only three to four percent of them are operated legally.” Purchases from online pharmacies rose dramatically during the pandemic, and Kim expects a boom in counterfeit medical products alongside it.
The FDA warns that U.S. consumers can be exposed to counterfeits through online purchases, in particular. The problem is magnified in low- to middle-income nations, where one in 10 medical products are counterfeit, according to a World Health Organization estimate. Cost doesn’t seem to be a factor, either; antimalarials and antibiotics are most often reported as counterfeits or fakes, and generic medications are swapped as often as brand-name drugs, according to the same WHO report.
Counterfeits weren’t tracked globally until 2013; since then, there have been 1,500 reports to the WHO, with actual incidences of counterfeiting likely much higher. Fake medicines have been estimated to result in costs of $200 billion each year, and are blamed for more than 72,000 pneumonia- and 116,000 malaria-related deaths.
Researchers and manufacturers have already developed some anti-counterfeit tools, including built-in identifiers like edible papers with scannable QR codes or barcodes that are stamped onto or otherwise incorporated into pills and other medical products. But such methods, while functional, can be costly to implement, Grover says.
CandyCodes could provide unique identifiers for at least 41 million pills for every person on the planet.
William Grover
“Putting universal codes on each pill and each dosage is attractive,” he says. “The challenge is, how can we do it in a way that requires as little modification to the existing manufacturing process as possible? That's where I hope CandyCodes have an edge. It's not zero modification, but I hope it is as minor a modification of the manufacturing process as possible.”
Kim calls the concept “a clever idea to introduce entropy for high-level security” even if it may not be as close to market as other emerging technologies, including some edible watermarks he’s helped develop. He points out that CandyCodes still needs to be tested for reproducibility and readability.
The possibilities are already intriguing, though. Grover’s recent research, published in Scientific Reports, predicts that unique codes could be used for at least 41 million pills for every person on the planet.
Sadly, CandyCodes’ multicolored bits probably won’t taste like candy. They must be made of non-caloric ingredients to meet the international regulatory standards that govern food dyes and colorants. But Grover hopes CandyCodes represent a simple, accessible solution to a heart-wrenching issue. “This feels like trying to track down and go after bad guys,” he says. “Someone who would pass off a medicine intended for a child or a sick person and pass it off as something effective, I can't imagine anything much more evil than that. It's fun and, and a little fulfilling to try to develop technologies that chip away at that.”
Waste smothering our oceans is worth billions – here’s what we can do with all that sh$t
There’s hardly a person out there who hasn’t heard of the Great Pacific Garbage Patch. That type of pollution is impossible to miss. It stares you in the face from pictures and videos of sea turtles with drinking straws up their noses and acres of plastic swirling in the sea.
It demands you to solve the problem—and it works. The campaign to raise awareness about plastic pollution in the oceans has resulted in new policies, including bans on microplastics in personal care products, technology to clean up the plastic, and even new plastic-like materials that are better for the environment.
But there’s a different type of pollution smothering the ocean as you read this. Unfortunately, this one is almost invisible, but no less damaging. In fact, it’s even more serious than plastic and most people have no idea it even exists. It is literally under our noses, destroying our oceans, lakes, and rivers – and yet we are missing it completely while contributing to it daily. In fact, we exacerbate it multiple times a day—every time we use the bathroom.
It is the way we do our sewage.
Most of us don’t think much about what happens after we flush the toilet. Most of us probably assume that the substances we flush go “somewhere” and are dealt with safely. But we typically don’t think about it beyond that.
Most of us also probably don’t think about what’s in the ocean or lakes we swim in. Since others are swimming, jumping in is just fine. But our waterways are far from clean. In fact, at times they are incredibly filthy. In the US, we are dumping 1.2 trillion of gallons of untreated sewage into the environment every year. Just New York City alone discharges 27 billion gallons into the Hudson River basin annually.
How does this happen? Part of it is the unfortunate side effect of our sewage system design that dates back to over a century ago when cities were smaller and fewer people were living so close together.
Back then, engineers designed the so-called “combine sewer overflow systems,” or CSOs, in which the storm water pipes are connected to the sanitary sewer pipes. In normal conditions, the sewage effluent from homes flows to the treatment plants where it gets cleaned and released into the waterways. But when it rains, the pipe system becomes so overwhelmed with water that the treatment plant can’t process it fast enough. So the treatment plant has to release the excess water through its discharge pipes—directly, without treatment, into streams, rivers and the ocean.
The 1.2 trillion gallons of CSO releases isn’t even the full picture. There are also discharges from poorly maintained septic systems, cesspools and busted pipes of the aging wastewater infrastructure. The state of Hawaii alone has 88,000 cesspools that need replacing and are currently leaking 53 million gallons of raw sewage daily into their coastal waters. You may think twice about swimming on your Hawaii vacations.
Overall, the US is facing a $271 billion backlog in wastewater infrastructure projects to update these aging systems. Across the Western world, countries are facing similar challenges with their aging sewage systems, especially the UK and European Union.
That’s not to say that other parts of the planet are in better shape. Out of the 7+ billion people populating our earth, 4.2 billion don’t have access to safe sanitation. Included in this insane number are roughly 2 billion people who have no toilet at all. Whether washed by rains or dumped directly into the waterways, a lot of this sludge pollutes the environment, the drinking water, and ultimately the ocean.
Pipes pour water onto a rocky shore in Jakarta, Indonesia.
Tom Fisk
What complicates this from an ocean health perspective is that it’s not just poop and pee that gets dumped into nearby waterways. It is all the things we put in and on our bodies and flush down our drains. That vicious mix of chemicals includes caffeine, antibiotics, antidepressants, painkillers, hormones, microplastics, cocaine, cooking oils, paint thinners, and PFAS—the forever chemicals present in everything from breathable clothing to fire retardant fabrics of our living room couches. Recent reports have found all of the above substances in fish—and then some.
Why do we allow so much untreated sewage spill into the sea? Frankly speaking, for decades scientists and engineers thought that the ocean could handle it. The mantra back then was “dilution is the solution to pollution,” which might’ve worked when there were much fewer people living on earth—but not now. Today science is telling us that this old approach doesn’t hold. That marine habitats are much more sensitive than we had expected and can’t handle the amount of wastewater we are discharging into them.
The excess nitrogen and phosphorus that the sewage (and agricultural runoff) dumps into the water causes harmful algal blooms, more commonly known as red or brown tides. The water column is overtaken by tiny algae that sucks up all the oxygen from the water, creating dead zones like the big fish kills in the Gulf of Mexico. These algae also cause public health issues by releasing gases toxic to people and animals, including dementia, neurological damage, and respiratory illness. Marshes and mangroves end up with weakened root systems and start dying off. In a wastewater modeling study I published last year, we found that 31 percent of salt marshes globally were heavily polluted with human sewage. Coral reefs get riddled with disease and overgrown by seaweed.
We could convert sewage into high-value goods. It can be used to generate electricity, fertilizer, and drinking water. The technologies not only exist but are getting better and more efficient all the time.
Moreover, by way of our sewage, we managed to transmit a human pathogen—Serratia marcescens, which causes urinary, respiratory and other infections in people—to corals! Recent reports from the Florida Keys are showing white pox disease popping up in elk horn corals caused by S.marcescens, which somehow managed to jump species. Many recent studies have documented just how common this type of pollution is across the globe.
Yet, there is some good news in that abysmal sewage flow. Just like with plastic pollution, realizing that there’s a problem is the first step, so awareness is key. That’s exactly why I co-founded Ocean Sewage Alliance last year—a nonprofit that aims to “re-potty train the world” by breaking taboos in talking about the poop and pee problem, as well as uniting experts from various key sectors to work together to end sewage pollution in coastal areas.
To end this pollution, we have to change the ways we handle our sewage. Even more exciting is that by solving the sewage problem we can create all sorts of economic benefits. In 2015, human poop was valued at $9.5 billion a year globally, which today would be $11.5 billion per year.
What would one do with that sh$t?
We could convert it into high-value goods. Sewage can be used to generate electricity, fertilizer, and drinking water. The technologies not only exist but are getting better and more efficient all the time. Some exciting examples include biodigesters and urine diversion (or peecycling) systems that can produce fertilizer and biogas, essentially natural gas. The United Nations estimates that the biogas produced from poop could provide electricity for 138 million homes. And the recovered and cleaned water can be used for irrigation, laundry and flushing toilets. It can even be refined to the point that it is safe for drinking water – just ask the folks in Orange County, CA who have been doing so for the last few decades.
How do we deal with all the human-made pollutants in our sewage? There is technology for that too. Called pyrolysis, it heats up sludge to high temperatures in the absence of oxygen, which causes most of the substances to degrade and fall apart.
There are solutions to the problems—as long as we acknowledge that the problems exist. The fact that you are reading this means that you are part of the solution already. The next time you flush your toilet, think about where this output may flow. Does your septic system work properly? Does your local treatment plant discharge raw sewage on rainy days? Can that plant implement newer technologies that can upcycle waste? These questions are part of re-potty training the world, one household at a time. And together, these households are the force that can turn back the toxic sewage tide. And keep our oceans blue.