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We're closer than ever to growing life in artificial wombs, and we've learned a bit more about how glucose and protein affect exercise endurance.

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If you pay attention to science news, you may have seen some sci-fi-looking pictures of a wrinkly, underdeveloped pink lamb in a plastic sack.

These pictures, published with a study in Nature Communications last month, are of something called the biobag. This technology could someday have the potential to incubate a premature human fetus until it’s a little more ready for the world.

In other words, it’s an artificial womb. Researchers at the Children’s Hospital of Philadelphia developed the biobag to try and save the lives of infants born anytime before 28 weeks, even as early as 22 or 23 weeks. Premature infants face a host of complications, but their tiny, underdeveloped lungs are especially at risk.

In the womb, a fetus floats in watery amniotic fluid filled with a bunch of complex molecules that help its development. It gets all the oxygen it needs through its umbilical cord that connects its circulatory system to its mother’s. Around 24 weeks in, the lung structures that swap out oxygen and carbon dioxide, called alveoli, start developing.

But there aren’t enough of them for normal breathing yet. So if a premature infant takes a breath of harsh, dry air, the immature alveoli can be badly overworked and start to scar, which could lead to chronic lung disease. That’s where the biobag comes in: this single-use plastic bag system is designed to dunk the fetus in lab-made amniotic fluid within seconds of delivery to keep their lungs away from air.

It’s also designed to provide a connection to oxygen and a lab-made cocktail of fats, sugars, amino acids, and minerals that get pumped in through the fetus’s umbilical cord by its own heartbeat and movement. This mimics the natural womb environment to keep up with all of their growing needs. The researchers tested their technology on 8 premature lambs at a stage of development similar to a 23-week-old human fetus.

The lambs stayed in the bags for 4 weeks, because that was how long the researchers had permission to run the experiment, according to institutional animal protocols. But they think the lambs probably could’ve grown up more. Using the bag system, the premature lambs matured, getting bigger and growing wool.

At the end of the experiment, the researchers dissected them and found that their brains, lungs, and other organs looked to be in working order. Animal trials of the biobag are still ongoing, and there are plenty of things they still want to iron out. For example, the synthetic amniotic fluid they used for this study was a simple solution of electrolytes, meaning dissolved charged substances like salts and phosphate, while the real thing has much more complex molecules that support development.

That said, the biobag is not, and won’t be, a replacement for a living womb from beginning to end. It only keeps a fetus going through the last few weeks. And while the bag system admittedly looks a little creepy, the researchers intend to make it even more womb-like, and eventually want to test how it can care for premature human babies.

And this is maybe a little less exciting than saving infant lives, but we’re learning a lot about adult bodies too, like what’s going on when you “hit a wall” during exercise. Endurance athletes like long-distance runners and cyclists know the feel. You’re cruising along just fine, until suddenly, it’s like you’ve smashed into a brick wall, Wile E.

Coyote style. Your brain is telling your muscles to move, but your muscles just don’t wanna. And a new study in the journal Cell Metabolism has uncovered a molecule involved in why this happens, and maybe a way to stop it.

Hitting the wall has to do with the amount of energy available to your body. Your body makes use of energy in two main forms: the chemical bonds in carbohydrates, which are sugars and starches, and fats. Your body breaks those bonds to extract the energy, which we colloquially call “burning”.

Fat has more energy stored in it, but sugar is easier to burn, so it’s a trade-off. And different body tissues fall on different sides. While your muscles can burn fat for energy, they use sugar, specifically glucose, a lot.

And the rest of your body, especially your brain, needs a steady level of glucose to keep working too. Hitting the wall happens when you use too much of the readily-available glucose. Your brain goes, “Wait, hold on; I’m outta gas here, and I’m gonna need you to stop, like moving, right now.” And to figure out how this happens, a team of researchers has been experimenting with a protein called PPAR-delta-, which helps our bodies manage energy.

It’s found in many tissues, but in muscle it seems to help us build endurance. When mice were genetically engineered to not have any PPAR-delta- in their muscles, they couldn’t build endurance no matter how much they trained. Then, the mice were given a drug called GW, which causes the PPAR-delta- gene in their muscles to switch on.

These mice were capable of running on a tiny little mouse treadmill with no training for nearly two hours longer than their couch potato friends who didn’t get the drug. The reason, the researchers say, is that PPAR-delta affects a bunch of genes involved in your metabolism. Basically, it ramps up fat burning in the muscles, while conserving glucose.

That way, your brain doesn’t feel like it’s going to run out and “hit a wall”. So the researchers admit that some athletes might be tempted to activate PPAR-delta with drugs instead of spending a whole lot of time training. But, they say, a drug like GW could also have therapeutic possibilities for people who struggle with exercise because of age or chronic disease, but we still need more research for sure.

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