{"text":[[{"start":7.89,"text":"The writer is a science commentator"}],[{"start":11.469999999999999,"text":"The phrase “skin-deep” is often used dismissively, to refer to something as superficial or lacking complexity. That feels like a misnomer when it comes to skin itself."}],[{"start":28.06,"text":"It is an astonishing organ, essentially a multi-layered, waterproof body bag that keeps other organs in but pathogens and the outside world out. Our skin typically accounts for about 15 per cent of body weight and renews itself every month. We each shed millions of skin cells every day."}],[{"start":50.55,"text":"A wealth of different types of cells lurk beyond the epidermis, the outer layer that contains mostly keratinocytes: hair follicles, pigment cells, immune cells, sweat glands, blood vessels and fat cells; nerve fibres, for sensory perception; the muscular structures responsible for goosebumps; and fibroblasts, which make collagen and other connective tissue. "}],[{"start":77.8,"text":"Skin can regenerate if damaged but the jostling between these many cells means that not all grow back. Without that full complement, repaired skin loses some of its function and can become scarred, stiff and painful. "}],[{"start":95.59,"text":"Now, scientists at Harvard University experimenting on mice have uncovered a method that could one day allow wounds to heal without scarring. The technique involves dialling down excessive nerve growth, so that other cells can bloom. If proven in humans, it could improve the prospects for both healing and wound-related pain."}],[{"start":119.67,"text":"Scientists have long suspected that the key to perfect wound healing lies somewhere in embryonic development. Injured foetuses heal without scars, and babies that are operated on in utero also show seamless skin repairs, with all the various cell types restored. But this capacity disappears soon after birth, with later skin healing characterised by sometimes stiff and painful scar tissue and a sparser sprinkling of cell types. For example, the healed area might lack hair follicles and sweat glands."}],[{"start":157.31,"text":"Biologists Ya-Chieh Hsu, Hannah Tam and colleagues decided to investigate this process. They clipped out small pieces of skin from mice at different stages of development, both before and after birth — marking the areas with fluorescent beads and henna ink — and examined how the skin regrew. While regeneration happened seamlessly in animals wounded before birth, with healed areas only visible via the markings, the picture was different for mice wounded five days or more after being born. "}],[{"start":192.94,"text":"In those cases, the regeneration was more chaotic, with the injury site packed with epidermal cells, immune cells and abnormal bundles of collagen fibres that lacked the “basket-weave” pattern of uninjured skin. Several other cell types failed to regrow. "}],[{"start":213.63,"text":"And crucially, just like an emptied patch of land that is colonised by weeds, the wound site was overrun with nerve fibres. When the scientists used Botox as a kind of weedkiller — to block the signals encouraging nerves to sprout — the missing cell types started reappearing. "}],[{"start":234.82,"text":"Tam and Hsu published the results online last month in the journal Cell, concluding that “skin initially possesses a remarkable capacity for organ-level regeneration that becomes progressively blocked with development, rather than irreversibly lost”. "}],[{"start":252.17,"text":"They pin much of this blocking on a signalling gene known as CXCL12, which promotes cross-talk between fibroblasts and nerves. The key to improving organ-level regeneration, the researchers believe, lies in tamping down this cellular chatter, so that the skin can revert to an earlier, more orderly state of repair. "}],[{"start":274.27,"text":"“Our findings suggest that excessive nerve growth early after injury contributes to scarring,” Hsu told me. Wounds in humans, she added, show similar frantic nerve growth early on and could potentially be tamed in the same way: “We do not yet know whether this applies directly to humans, but we are optimistic . . . In principle, CXCL12 activity could be reduced using small-molecule inhibitors or blocking antibodies, and we are actively exploring these approaches in the lab.” By putting the brakes on nerve growth, it might also address injury-related pain."}],[{"start":314.71,"text":"Extreme nerve regrowth could be an evolutionary survival response to wounding, Hsu suggests: it would sensitise the area and potentially prevent further damage, even if it came at the cost of regenerating other cells. "}],[{"start":331.78999999999996,"text":"With skin and brain constantly communicating, our outer wrapping is a portal for feeling and interpreting the outside world, even when we are on the inside. Embryos can get goosebumps, Tam says. "}],[{"start":348.64,"text":"The world of skin is very much more than skin-deep. "}],[{"start":360.78999999999996,"text":""}]],"url":"https://audio.ftcn.net.cn/album/a_1775777654_7186.mp3"}