Even with 15 percent of their hearts removed, newborn mice possess the extraordinary ability to mend themselves, researchers report today in the journal Science. It’s the first time that mammals outside of the womb have shown the regenerative ability to repair the heart.
Only newborn mice could regenerate part of their hearts, and they lost this ability after about a week after birth. Still, the results were quite impressive: Olson’s team removed 15 percent of the heart one day after birth, and when the researchers checked up three weeks later, the whole heart was repaired in 99 percent of the mice. Until now, scientists had seen fish and amphibians regenerate heart tissue as adults, but only embryonic mammals had been spotted doing the same.
“When a person has a heart attack and heart muscle cells are lost, the heart loses pump function, causing heart failure and eventual death,” said Eric Olson, a molecular biologist at Southwestern Medical Centre in Dallas, Texas. “Now that we know that the mammalian heart indeed possesses the potential to regenerate, at least early in life, we can begin to search for drugs or genes or other things that might reawaken this potential in the adult heart of mice and eventually of humans.” [The Guardian]
First they have to understand what the newborn rodent’s bodies are up to. Initially, Olson and colleagues weren’t sure how the mice were mending themselves—with stem cells, or cells that had already become muscle cells. But the appearance of the cells gave them away, says Dr. Stephen Badylak, who wasn’t involved in the study.
Injecting stem cells into injured mouse muscle not only helped the muscle heal, but gave the mice enhanced muscle mass for years to come.
The study, published in Science Translational Medicine, used skeletal muscle stem cells from young donor mice and injected them into injured muscles of mature mice. Researchers figured that the stem cells would be able to create new muscle cells in the recipient mouse, but the question was: could these new cells be incorporated into the existing muscle on an adult mouse?
After injuring the recipient mouse’s muscle and injecting the cells, the researchers noticed that the injury healed quickly and the mice had larger muscles (about twice the volume, and a 50 percent increase in mass) than before the injury, which they expected. But were surprised to see that the muscle enhancement was sustained throughout the recipient mouse’s lifetime, up to two years.
Researchers have built miniature human livers in the lab, which could lead to better drug discovery and could even point the way toward implantable artificial organs. The mini-livers seem to act like human livers in the lab, but it remains to be seen how well they’ll survive and perform when transplanted into animals or, maybe one day, humans.
“We are excited about the possibilities this research represents, but must stress that we’re at an early stage and many technical hurdles must be overcome before it could benefit patients,” said Shay Soker, Ph.D., professor of regenerative medicine and project director. “Not only must we learn how to grow billions of liver cells at one time in order to engineer livers large enough for patients, but we must determine whether these organs are safe to use in patients.” [Press release].
The researchers at Wake Forest’s Institute for Regenerative Medicine created livers that weigh about 0.2 ounces each. That’s not nearly large enough to keep a human alive (it would need to be about 80 times larger for that), but getting the organ made was a feat in itself. The livers were made using the extracellular scaffolding from an animal liver, after all of the animal’s cells had been gently removed from it.