In a collaborative study, researchers from Kyushu University and Harvard Medical School have identified proteins that can turn or “reprogram” fibroblasts — the most commonly found cells in skin and connective tissue — into cells with similar properties to limb progenitor cells. Publishing in Developmental Cell (“Direct reprogramming of non-limb fibroblasts to cells with properties of limb progenitors”), the researchers’ findings have enhanced our understanding of limb development and have set the stage for regenerative therapy in the future.
Globally, close to 60 million people are living with limb loss. Amputations can result from various medical conditions such as tumors, infections, and birth defects, or due to trauma from industrial accidents, traffic accidents, and natural disasters such as earthquakes. People with limb injuries often rely on synthetic materials and metal prostheses, but many researchers are studying the process of limb development, with the aim of bringing regenerative therapy, or natural tissue replacement, one step closer as a potential treatment.
“During limb development in the embryo, limb progenitor cells in the limb bud give rise to most of the different limb tissues, such as bone, muscle, cartilage and tendon. It’s therefore important to establish an easy and accessible way of making these cells,” explains Dr. Yuji Atsuta, lead researcher who began tackling this project at Harvard Medical School and continues it as a lecturer at Kyushu University’s Graduate School of Sciences.
Currently, a common way to obtain limb progenitor cells is directly from embryos, which, in the case of human embryos, raises ethical concerns. Alternatively, they can be made using induced pluripotent stem cells — adult cells which are reprogrammed into an embryonic-like state, and which can later be coaxed into specific tissue types. The new method developed by Atsuta and colleagues, which directly reprograms fibroblast cells into limb progenitor cells and bypasses induced pluripotent stem cells, simplifies the process and reduces costs. It also mitigates the concern of cells turning cancerous, which often occurs with induced pluripotent stem cells.
In the initial phase of the study, the researchers looked at what genes were expressed in the early limb buds in mice and chicken embryos. Almost all cells in the body, including fibroblasts and limb progenitor cells, contain identical genomic DNA, but the different properties and functions of each cell type emerge during development due to changes in gene expression (in other words, which genes are active, and which proteins are produced by the cell). One way that gene expression is controlled in cells is by specific proteins, called transcription factors.
The research group identified 18 genes, mostly transcription factors, that are more highly expressed in the early limb bud compared to other tissues. They cultured fibroblasts from mouse embryos and introduced these 18 genes into the fibroblasts using viral vectors so that the cells produced these 18 protein factors. They found that the modified fibroblasts took on the properties and showed similar gene expression to naturally-occurring limb progenitor cells found in limb buds.
Next, over a series of experiments, the researchers narrowed down their selection and determined that only three protein factors were essential to reprogram mouse fibroblasts into limb progenitor-like cells: Prdm16, Zbtb16, and Lin28a. A fourth protein, Lin41, helped the cultured limb progenitor cells grow and multiply more rapidly.
The researchers not only confirmed that the reprogrammed limb progenitor cells had similar gene expression to natural limb progenitor cells, but also had similar ability. “These reprogrammed cells are not only molecular mimics; we have confirmed their potential to develop into specialized limb tissues, both in laboratory dishes (in vitro) and also in living organisms (in vivo),” says Atsuta. “Testing in vivo was particularly challenging, as we had to transplant the reprogrammed mouse cells into the limb buds of chicken embryos.”
In these experiments, the researchers used lentiviruses, which insert genes directly into the infected cells’ genome, raising the risk that the cells can become cancer. Instead, the team is considering other safer vectors, such as adeno-associated viruses or plasmids, which deliver genes to the cells without inserting genes into the genome.
Atsuta’s lab group is now trying to apply this method to human cells, for future therapeutic applications, and also to snakes, whose ancestors had limbs that were subsequently lost during evolution. “Interestingly, the reprogrammed limb progenitor cells generated limb bud-like organoids, so it seems possible to generate limb tissues in species that no longer possess them. The study of limbless snakes can uncover new pathways and knowledge in developmental biology.”
News
Studies detail high rates of long COVID among healthcare, dental workers
Researchers have estimated approximately 8% of Americas have ever experienced long COVID, or lasting symptoms, following an acute COVID-19 infection. Now two recent international studies suggest that the percentage is much higher among healthcare workers [...]
Melting Arctic Ice May Unleash Ancient Deadly Diseases, Scientists Warn
Melting Arctic ice increases human and animal interactions, raising the risk of infectious disease spread. Researchers urge early intervention and surveillance. Climate change is opening new pathways for the spread of infectious diseases such [...]
Scientists May Have Found a Secret Weapon To Stop Pancreatic Cancer Before It Starts
Researchers at Cold Spring Harbor Laboratory have found that blocking the FGFR2 and EGFR genes can stop early-stage pancreatic cancer from progressing, offering a promising path toward prevention. Pancreatic cancer is expected to become [...]
Breakthrough Drug Restores Vision: Researchers Successfully Reverse Retinal Damage
Blocking the PROX1 protein allowed KAIST researchers to regenerate damaged retinas and restore vision in mice. Vision is one of the most important human senses, yet more than 300 million people around the world are at [...]
Differentiating cancerous and healthy cells through motion analysis
Researchers from Tokyo Metropolitan University have found that the motion of unlabeled cells can be used to tell whether they are cancerous or healthy. They observed malignant fibrosarcoma [...]
This Tiny Cellular Gate Could Be the Key to Curing Cancer – And Regrowing Hair
After more than five decades of mystery, scientists have finally unveiled the detailed structure and function of a long-theorized molecular machine in our mitochondria — the mitochondrial pyruvate carrier. This microscopic gatekeeper controls how [...]
Unlocking Vision’s Secrets: Researchers Reveal 3D Structure of Key Eye Protein
Researchers have uncovered the 3D structure of RBP3, a key protein in vision, revealing how it transports retinoids and fatty acids and how its dysfunction may lead to retinal diseases. Proteins play a critical [...]
5 Key Facts About Nanoplastics and How They Affect the Human Body
Nanoplastics are typically defined as plastic particles smaller than 1000 nanometers. These particles are increasingly being detected in human tissues: they can bypass biological barriers, accumulate in organs, and may influence health in ways [...]
Measles Is Back: Doctors Warn of Dangerous Surge Across the U.S.
Parents are encouraged to contact their pediatrician if their child has been exposed to measles or is showing symptoms. Pediatric infectious disease experts are emphasizing the critical importance of measles vaccination, as the highly [...]
AI at the Speed of Light: How Silicon Photonics Are Reinventing Hardware
A cutting-edge AI acceleration platform powered by light rather than electricity could revolutionize how AI is trained and deployed. Using photonic integrated circuits made from advanced III-V semiconductors, researchers have developed a system that vastly [...]
A Grain of Brain, 523 Million Synapses, Most Complicated Neuroscience Experiment Ever Attempted
A team of over 150 scientists has achieved what once seemed impossible: a complete wiring and activity map of a tiny section of a mammalian brain. This feat, part of the MICrONS Project, rivals [...]
The Secret “Radar” Bacteria Use To Outsmart Their Enemies
A chemical radar allows bacteria to sense and eliminate predators. Investigating how microorganisms communicate deepens our understanding of the complex ecological interactions that shape our environment is an area of key focus for the [...]
Psychologists explore ethical issues associated with human-AI relationships
It's becoming increasingly commonplace for people to develop intimate, long-term relationships with artificial intelligence (AI) technologies. At their extreme, people have "married" their AI companions in non-legally binding ceremonies, and at least two people [...]
When You Lose Weight, Where Does It Actually Go?
Most health professionals lack a clear understanding of how body fat is lost, often subscribing to misconceptions like fat converting to energy or muscle. The truth is, fat is actually broken down into carbon [...]
How Everyday Plastics Quietly Turn Into DNA-Damaging Nanoparticles
The same unique structure that makes plastic so versatile also makes it susceptible to breaking down into harmful micro- and nanoscale particles. The world is saturated with trillions of microscopic and nanoscopic plastic particles, some smaller [...]
AI Outperforms Physicians in Real-World Urgent Care Decisions, Study Finds
The study, conducted at the virtual urgent care clinic Cedars-Sinai Connect in LA, compared recommendations given in about 500 visits of adult patients with relatively common symptoms – respiratory, urinary, eye, vaginal and dental. [...]
