Tag Archives: regenerative medicine

Researchers successfully regrow limbs on frogs. They want to do the same thing with humans

Most animals have pretty good injury repair capabilities, but when it comes to lost limbs, only a select few can regrow them. The rest, including humans, have little they can do to repair such injuries. But as a new study shows, with the right treatments, our bodies may be hacked and “convinced” to regrow lost limbs. Although the study focused on frogs, which are obviously very different from humans, the proof-of-concept study suggests that this approach could work on many animals, including humans.

The African clawed frog (Xenopus laevis). Image via Wiki Commons.

Limb regeneration is a new frontier in biomedical science. It’s something we’ve long considered outside the realm of possibility, restricted only to superheroes and myth, but research is bringing it closer and closer to reality.

While many things differentiate humans from frogs, neither we nor they are able to regenerate limbs. So researchers at Tufts University and Harvard University’s Wyss Institute used frogs (specifically, the African clawed frog or Xenopus laevis) as a proof of concept. X. laevis is often used in research as it is easy to handle, lays eggs throughout the year, and for a model organism, shares a close evolutionary relationship with humans.

The researchers triggered the regrowth of a lost leg using a five-drug cocktail that they applied in a wearable silicone bioreactor dome that sealed the drugs over the stump for just 24 hours. After the treatment was administered, the regenerative process was kickstarted, and over the course of an 18-month period, the frogs regrew an almost fully functional leg.

“It’s exciting to see that the drugs we selected were helping to create an almost complete limb,” said Nirosha Murugan, research affiliate at the Allen Discovery Center at Tufts and first author of the paper. “The fact that it required only a brief exposure to the drugs to set in motion a months-long regeneration process suggests that frogs and perhaps other animals may have dormant regenerative capabilities that can be triggered into action.”

The experiment was repeated on dozens of frogs, and while not all of them regrew limbs, most did — including bone tissue and even toe-like structures at the end of the limb (though these weren’t supported by bone). It’s not a magic elixir, and the treatment is not perfect, but the drug cocktail delivered through the wearable bioreactor really does seem capable of regrowing limbs.

Regrowth of soft tissue. The MDT group (bottom) represents the five-drug cocktail treatment. Image credits: Murugan et al (2022).

The researchers essentially hacked the biological pathways that enable the growth and organization of tissue — much like in an embryo. This is why the treatment was only applied once, over the course of a day; meanwhile, other approaches involve numerous interventions over the course of the process.

“The remarkable complexity of functional limbs suggests that the fastest path toward this goal may lie in triggering native, self-limiting modules of organogenesis, not continuous micromanagement of the lengthy process at the cell and molecular levels,” the researchers write in the study. “We implemented this via a short exposure of limb amputation wounds to a wearable bioreactor containing a payload of five select biochemical factors.”

The first stage is the formation of a mass of stem cells at the end of the stump, which was then used to gradually reconstruct the limb. It’s essential that this structure is covered with the dome as quickly as possible after amputation to ensure its protection and activation. This treatment would be ideally applied right after amputation.

“Mammals and other regenerating animals will usually have their injuries exposed to air or making contact with the ground, and they can take days to weeks to close up with scar tissue,” said David Kaplan, Stern Family Professor of Engineering at Tufts and co-author of the study. “Using the BioDome cap in the first 24 hours helps mimic an amniotic-like environment which, along with the right drugs, allows the rebuilding process to proceed without the interference of scar tissue.”

At first, researchers tried using the protective dome with a single drug, progesterone. Progesterone is a steroid hormone involved in the menstrual cycle, pregnancy, and embryogenesis of humans and other species. This alone triggered some limb growth, but the resulting limb was essentially a non-functional spike. Each of the other four drugs fills a different role, ranging from reducing inflammation and the stopping of scar tissue formation to the promotion of growth of new nerves, blood vessels, and muscles. It’s the combination of all these together that leads to a nigh-functional limb.

Researchers note that while the limbs weren’t 100% identical to “normal” limbs, they featured digits, webbing, and detailed skeletal and muscular features. Overall, the results show the successful “kickstarting” of regenerative pathways

The plan now is to move on to mammal research. Despite the differences between frogs and mammals, researchers say that the biggest difference lies in the “early events of wound healing” — if these early processes can be understood and replicated, then there’s no apparent reason why this couldn’t be applied to mammals, and ultimately humans as well.

“The goal of triggering latent tissue-building routines to regrow limbs in humans may be achieved by identifying and exploiting principles observed in highly regenerative organisms,” the researchers conclude.

The study was published in the journal Science Advances.

mouse age reversal

Old organ regenerated to youthful state in elderly mice using gene manipulation

mouse age reversal

Photo: guardian

The popular myth of the fountain of youth tells the story of a magical spring that restores youth to anyone who drinks from it. Scientists working with longevity research have made important strides forward in recent years, however all of these efforts concentrate on prolonging life and slowing the effects old age has on the body, not reversing them. A breakthrough by researchers at University of Edinburgh may cause a paradigm shift in regenerative medicine after an old organ in elderly mice was regenerated into a youthful state, simply by manipulating a single gene.

The thymus is a specialized organ in the immune system. The functions of the thymus are the “schooling” of T-lymphocytes (T cells), which are critical cells of the adaptive immune system, and the production and secretion of thymosins, hormones which control T-lymphocyte activities and various other aspects of the immune system.

With old age, however, the thymus becomes progressively smaller making the body more vulnerable to infections and diseases. In fact, by the age of 70 the thymus is just a tenth of the size in adolescence. So, the team at the MRC Centre for Regenerative Medicine at the University of Edinburgh thought of a way to regenerate the thymus.

Rejuvenating elderly mice

Previous research showed that a gene, called Foxn1, naturally gets shut down as the thymus ages, so the Edinburgh researchers concentrated on boosting the gene back to youthful levels. A drug that targets this protein and instructs stem cell-like cells to rebuild the organ was made and given to elderly mice. The results were striking: just by manipulating this single gene, the thymus in elderly mice increased in size and made more T-cells. It almost completely regenerated.

“Our results suggest that targeting the same pathway in humans may improve thymus function and therefore boost immunity in elderly patients, or those with a suppressed immune system. However, before we test this in humans we need to carry out more work to make sure the process can be tightly controlled,” said Clare Blackburn, Professor of Tissue Stem Cell Biology, MRC Centre for Regenerative Medicine.

It’s not clear why the thymus shrinks with age, but one theory says it’s because more energy is diverted towards reproduction once entering adolescence. As such, if human trials are to begin, there needs to be a tightly controlled setting to ensure no negative side-effects are encountered. The discovery could also offer hope to patients with DiGeorge syndrome, a genetic condition that causes the thymus to not develop properly.

“One of the key goals in regenerative medicine is harnessing the body’s own repair mechanisms and manipulating these in a controlled way to treat disease. This interesting study suggests that organ regeneration in a mammal can be directed by manipulation of a single protein, which is likely to have broad implications for other areas of regenerative biology,” said Dr Rob Buckle, Head of Regenerative Medicine, Medical Research Council.

But what about other organs? The heart, lungs, liver, maybe there’s a way to regenerate these by gene manipulation as easily as it was for the thymus. The full paper can be read here.

Also worth noting is a different path that leads to the same destination – reactivating the enzyme telomerase, which repairs damaged tissue and reverses signs of aging, as shown by studies on mice at the Dana-Farber Cancer Institute, Harvard Medical School. A synergy between the two methods may propel medicine into a new age.

Decellularized Mouse Heart: Lu et. al

Scientists engineer heart in the lab that beats on its own

Regenerative medicine has come a long way, and while important strides forward have been made, scientists are still toiling with ways to completely grow organs in labs. There are millions of people worldwide suffering from afflictions to organs like the liver, lungs or heart – for many of them a transplant is they’re only chance at living a normal life again and even survive. Less than 1% of those on the waiting list actually receive a transplant, however, because of the sheer disproportion between donors and patients. Elaborating means of growing new organs in the lab ready for transplant and save lives is thus imperious. Work is though and slow, but signs are we’re getting there.

The latest breakthrough comes from researchers at University of Pittsburgh who recently report they’ve cultured a heart that can beat on its own. Unlike other cultured organs like the lungs or liver (still primitive, somewhat working, but not ready for transplant), the heart is the most difficult organ to build. Why? The heart beats, and building a heart in the lab that beats isn’t enough. It needs to beat at a certain rate, something controlled by the cardiovascular system, which needs to be reproduced. So you need to build a whole new system, not just the organ itself. Onto the scientists’ work, however.

Decellularized Mouse Heart:  Lu et. al

Decellularized Mouse Heart: Lu et. al

Like other regenerative efforts, the researchers used induced pluripotent stem cells to culture their heart. These cells are very similar to stem cells, only they’re collected from adult cells and forced to express certain genes. Using cells collected from blood, skin, stomach, even urine (we reported earlier how a group of researchers grew teeth-like structures using such cells), scientists can turn these into iPSCs and then morph them into whatever they like. So, basically, most of the features of stem cells (the differences between iPSCs and stem cells are still not fully understood), without the drawbacks – controversial embryonic collection, hard to come by etc. Most importantly, however, because the pluripotent stem cells are collected from mature cells – i.e. from the patient who needs the transplant – an organ grown from these will have a much slighter chance at being rejected by the host body.

“Scientists have been looking to regenerative medicine and tissue engineering approaches to find new solutions for this important problem. The ability to replace a piece of tissue damaged by a heart attack, or perhaps an entire organ, could be very helpful for these patients,” said Lei Yang, the lead researcher.

The approach Lei and his team used, however, is different in one key aspect from other iPSC-centered heart regeneration efforts. They first let the stem cells begin to develop for six days, such that some of them may differentiate into  cardiovascular progenitor cells.

The heart of mouse was subsequently collected and had all its cells removed besides the underling structure – leaving a sort of scaffold. Onto this scaffold the cardiovascular cells developed from human induced stem cells were laid. So, contrary to previous methods where the risk of some stem cells developing into liver cells for instance is present, the Pittsburgh team’s approach rendered more functioning heart cells – the denser the heart cells are in the organ the better the chance it has of working closer to the natural thing.

“This process makes MCPs, which are precursor cells that can further differentiate into three kinds of cells the heart uses, including cardiomyocytes, endothelial cells and smooth muscle cells,” Dr. Yang explained. “Nobody has tried using these MCPs for heart regeneration before. It turns out that the heart’s extracellular matrix – the material that is the substrate of heart scaffold – can send signals to guide the MCPs into becoming the specialized cells that are needed for proper heart function.”

Finally, the heart had enough cells to power itself and beat on its own (check the embedded video in this article) – a breakthrough moment in science. It still needs a tremendous amount of refining though. For one, as states earlier, it needs to beat a certain rate, and besides the cardiovascular system which needs to be finely regenerated, you need to have a precise density of cardiovascular cells. For human transplants, there’s another challenge. You need to have scaffolds made from other human hearts.  The next move for Yang and his colleagues will be to use as a scaffolding a stripped-down heart from a human cadaver available for research.

“One of our next goals is to see if it’s feasible to make a patch of human heart muscle,” he added. “We could use patches to replace a region damaged by a heart attack. That might be easier to achieve because it won’t require as many cells as a whole human-sized organ would.”

Findings appeared in the journal Nature Communications. source: Pitts Uni