Posted on by Dr. Francis Collins
Most of us can point to a few unwanted scars on our bodies. Every scar tells a story, but people are spending billions of dollars each year trying to hide or get rid of them . What if there was a way to get the wounds on our skin to heal without scarring in the first place?
In a recent paper in the journal Science, a team of NIH-supported researchers has taken an important step in this direction. Working with mice, the researchers deciphered some of the key chemical and physical signals that cause certain skin cells to form tough, fibrous scars while healing a wound . They also discovered how to reprogram them with a topical treatment and respond to injuries more like fetal skin cells, which can patch up wounds in full, regrowing hair, glands, and accessory structures of the skin, and all without leaving a mark.
Of course, mice are not humans. Follow-up research is underway to replicate these findings in larger mammals with skin that’s tighter and more akin to ours. But if the preclinical data hold up, the researchers say they can test in future human clinical trials the anti-scarring drug used in the latest study, which has been commercially available for two decades to treat blood vessel disorders in the eye.
The work comes from Michael Longaker, Shamik Mascharak, and colleagues, Stanford Medicine, Palo Alto, CA. But, to be more precise, the work began with a research project that Longaker was given back in 1987, while a post doc in the lab of Michael Harrison, University of California, San Francisco.
Harrison, a surgeon then performing groundbreaking prenatal surgery, noticed that babies born after undergoing surgery in the womb healed from their surgeries without any scarring. He asked his postdoc to find out why, and Longaker has been trying to answer that question and understand scar formation ever since.
Longaker and his Stanford colleague Geoffrey Gurtner suspected that the difference between healing inside and outside the womb had something to do with tension. Inside the womb, the skin of the unborn is bathed in fluid and develops in a soft, tension-free state. Outside the womb, human skin is exposed to continuous environmental stresses and must continuously remodel and grow to remain viable, which creates a high level of skin tension.
Following up on Longaker and Gurtner’s suspicion, Mascharak found in a series of mouse experiments that a particular class of fibroblast, a type of cell in skin and other connective tissues, activates a gene called Engrailed-1 during scar formation . To see if mechanical stress played a role in this process, Mascharak and team grew mouse fibroblast cells on either a soft, stress-free gel or on a stiff plastic dish that produced mechanical strain. Importantly, they also tried growing the fibroblasts on the same strain-inducing plastic, but in the presence of a chemical that blocked the mechanical-strain signal.
Their studies showed that fibroblasts grown on the tension-free gel didn’t activate the scar-associated genetic program, unlike fibroblasts growing on the stress-inducing plastic. With the chemical that blocked the cells’ ability to sense the mechanical strain, Engrailed-1 didn’t get switched on either.
They also showed the opposite. When tension was applied to healing surgical incisions in mice, it led to an increase in the number of those fibroblast cells expressing Engrailed-1 and thicker scars.
The researchers went on to make another critical finding. The mechanical stress of a fresh injury turns on a genetic program that leads to scar formation, and that program gets switched on through another protein called Yes-associated protein (YAP). When they blocked this protein with an existing eye drug called verteporfin, skin healed more slowly but without any hint of a scar.
It’s worth noting that scars aren’t just a cosmetic issue. Scars differ from unwounded skin in many ways. They lack hair follicles, glands that produce oil and sweat, and nerves for sensing pain or pressure. Because the fibers that make up scar tissue run parallel to each other instead of being more intricately interwoven, scars also lack the flexibility and strength of healthy skin.
These new findings therefore suggest it may one day be possible to allow wounds to heal without compromising the integrity of the skin. The findings also may have implications for many other medical afflictions that involve scarring, such as liver and lung fibrosis, burns, scleroderma, and scarring of heart tissue after a heart attack. That’s also quite a testament to sticking with a good postdoc project, wherever it may lead. One day, it may even improve public health!
 Human skin wounds: A major and snowballing threat to public health and the economy. Sen CK, Gordillo GM, Roy S, Kirsner R, Lambert L, Hunt TK, Gottrup F, Gurtner GC, Longaker MT. Wound Repair Regen. 2009 Nov-Dec;17(6):763-771.
 Preventing Engrailed-1 activation in fibroblasts yields wound regeneration without scarring.
Mascharak S, desJardins-Park HE, Davitt MF, Griffin M, Borrelli MR, Moore AL, Chen K, Duoto B, Chinta M, Foster DS, Shen AH, Januszyk M, Kwon SH, Wernig G, Wan DC, Lorenz HP, Gurtner GC, Longaker MT. Science. 2021 Apr 23;372(6540):eaba2374.
 Skin fibrosis. Identification and isolation of a dermal lineage with intrinsic fibrogenic potential. Rinkevich Y, Walmsley GG, Hu MS, Maan ZN, Newman AM, Drukker M, Januszyk M, Krampitz GW, Gurtner GC, Lorenz HP, Weissman IL, Longaker MT. Science. 2015 Apr 17;348(6232):aaa2151.
Skin Health (National Institute of Arthritis and Musculoskeletal and Skin Diseases/NIH)
Michael Longaker (Stanford Medicine, Palo Alto, CA)
Geoffrey Gurtner (Stanford Medicine)
NIH Support: National Institute of General Medical Sciences; National Institute of Dental and Craniofacial Research
Posted on by Dr. Francis Collins
Researchers have become skilled at growing an array of miniature human organs in the lab. Such lab-grown “organoids” have been put to work to better understand diabetes, fatty liver disease, color vision, and much more. Now, NIH-funded researchers have applied this remarkable lab tool to produce mini-lungs to study SARS-CoV-2, the coronavirus that causes COVID-19.
The intriguing bubble-like structures (red/clear) in the mini-lung pictured above represent developing alveoli, the tiny air sacs in our lungs, where COVID-19 infections often begin. In this organoid, the air sacs consist of many thousands of cells, all of which arose from a single adult stem cell isolated from tissues found deep within healthy human lungs. When carefully nurtured in lab dishes, those so-called alveolar epithelial type-2 cells (AT2s) begin to multiply. As they grow, they spontaneously assemble into structures that closely resemble alveoli.
A team led by Purushothama Rao Tata, Duke University School of Medicine, Durham, NC, developed these mini-lungs in a quest to understand how adult stem cells help to regenerate damaged tissue in the deepest recesses of the lungs, where SARS-CoV-2 attacks. In earlier studies, the researchers had shown it was possible for these cells to produce miniature alveoli. But there was a problem: the “soup” they used to nurture the growing cells included ingredients that weren’t well defined, making it hard to characterize the experiments fully.
In the study, now reported in Cell Stem Cell, the researchers found a way to simplify and define that brew. For the first time, they could produce mini-lungs consisting only of human lung cells. By growing them in large numbers in the lab, they can now learn more about SARS-CoV-2 infection and look for new ways to prevent or treat it.
Tata and his collaborators at the University of North Carolina, Chapel Hill, have already confirmed that SARS-CoV-2 infects the mini-lungs via the critical ACE2 receptor, just as the virus is known to do in the lungs of an infected person.
Interestingly, the cells also produce cytokines, inflammatory molecules that have been tied to tissue damage. The findings suggest the cytokine signals may come from the lungs themselves, even before immune cells arrive on the scene.
The heavily infected lung cells eventually self-destruct and die. In an unexpected turn of events, they even induce cell death in some neighboring healthy cells that are not infected. The relevance of the studies to the clinic was boosted by the finding that the gene activity patterns in the mini-lungs are a close match to those found in samples taken from six patients with severe COVID-19.
Now that he’s got the recipe down, Tata is busy making organoids and helping to model COVID-19 infections, with the hope of identifying and testing promising new treatments. It’s clear these mini-lungs are breathing some added life into the basic study of COVID-19.
 Human lung stem cell-based alveolospheres provide insights into SARS-CoV-2-mediated interferon responses and pneumocyte dysfunction. Katsura H, Sontake V, Tata A, Kobayashi Y, Edwards CE, Heaton BE, Konkimalla A, Asakura T, Mikami Y, Fritch EJ, Lee PJ, Heaton NS, Boucher RC, Randell SH, Baric RS, Tata PR. Cell Stem Cell. 2020 Oct 21:S1934-5909(20)30499-9.
Coronavirus (COVID-19) (NIH)
Tata Lab (Duke University School of Medicine, Durham, NC)
NIH Support: National Institute of Allergy and Infectious Diseases; National Heart, Lung, and Blood Institute; National Institute of General Medical Sciences; National Institute of Diabetes and Digestive and Kidney Diseases
Posted on by Dr. Francis Collins
When someone suffers a fully severed spinal cord, it’s considered highly unlikely the injury will heal on its own. That’s because the spinal cord’s neural tissue is notorious for its inability to bridge large gaps and reconnect in ways that restore vital functions. But the image above is a hopeful sight that one day that could change.
Here, a mouse neural stem cell (blue and green) sits in a lab dish, atop a special gel containing a mat of synthetic nanofibers (purple). The cell is growing and sending out spindly appendages, called axons (green), in an attempt to re-establish connections with other nearby nerve cells.
Posted on by Dr. Francis Collins
Certain organisms have remarkable abilities to achieve self-healing, and a fascinating example is the zebrafish (Danio rerio), a species of tropical freshwater fish that’s an increasingly popular model organism for biological research. When the fish’s spinal cord is severed, something remarkable happens that doesn’t occur in humans: supportive cells in the nervous system bridge the gap, allowing new nerve tissue to restore the spinal cord to full function within weeks.
Pretty incredible, but how does this occur? NIH-funded researchers have just found an important clue. They’ve discovered that the zebrafish’s damaged cells secrete a molecule known as connective tissue growth factor a (CTGFa) that is essential in regenerating its severed spinal cord. What’s particularly encouraging to those looking for ways to help the 12,000 Americans who suffer spinal cord injuries each year is that humans also produce a form of CTGF. In fact, the researchers found that applying human CTGF near the injured site even accelerated the regenerative process in zebrafish. While this growth factor by itself is unlikely to produce significant spinal cord regeneration in human patients, the findings do offer a promising lead for researchers pursuing the next generation of regenerative therapies.