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Did you know that heart cells can turn into bone inside the human body? Heart tissue and bone tissue have very different jobs, so why does this happen? Michael Aranda hosts in this informative episode of SciShow starring the human heart!
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Michael: Minerals like calcium and phosphate keep your bones tough and rigid, so your limbs can be attached properly, and your body’s not just a squishy mess of tissue.

But sometimes minerals can build up where they’re not supposed to. In fact, after a heart attack, some of your heart tissue could effectively turn into bone. This might sound kind of like a mutant superpower, but it’s actually really dangerous, and has perplexed scientists for a while.

But a new study published in the journal Cell Stem Cell suggests that these bony calcium deposits are just an unfortunate byproduct of the heart trying to heal itself. It’s no surprise that heart tissue and bone tissue have really different jobs. Heart muscle has to be flexible and beat in a rhythm to keep your blood circulating.

Your heartbeat is controlled by electrical signals that spread through the muscle cells that make up different heart chambers. So when heart tissue turns all stiff and mineralized, it can’t conduct those signals as well, and your heart can’t keep that smooth, steady beat – a condition called heart block. And there’s currently no medical treatment to break down these calcium deposits if they form. This bone-like tissue can form after a heart attack, where blood flow gets blocked, so the cells get deprived of oxygen and start to die.

We know that the heart can kind of repair itself when it gets injured. In fact, in an earlier paper, this team of researchers showed that some heart cells can even switch jobs to try and patch things up. See, usually, all mature cells take on a specific function and stay that way forever. But rarely, with the right signal from the body, certain cells can change forms. In this case, the turncoats are called cardiac fibroblasts, a type of connective cell, which can become blood vessel cells after an injury.

And in the study published this week, these researchers found that cardiac fibroblasts can also become cells that act just like osteoblasts, the cells responsible for depositing minerals in your bones. To figure this out, they took heart fibroblasts from mice with calcified hearts and put them in healthy mice hearts. They observed that these osteoblast-like cells started depositing calcium, and mineralizing other cells.

They’re still not completely sure why heart cells would start spewing out minerals, but it’s probably an accident. Maybe the fibroblasts are trying to switch jobs one way to be helpful, they mess up, and go down a different developmental path. The researchers hope that by understanding how heart cells can make this mistake, they’ll be able to develop drugs that block this sort of calcium buildup in patients.

Lots of scientists are researching really small things that can go wrong in human bodies, but plenty are also looking at planet-wide issues. For example, some fish populations are plummeting because of things like commercial fishing and climate change. And it’s not like you can just stick your head underwater and count them to check on the damage.

So, in a new paper, a team of Danish researchers think a soda bottle full of seawater might have the power to tell us how many and what kinds of fish are in the ocean. One strategy to keep tabs on fish populations is trawling, or dragging a big net across the seafloor and seeing what you scoop up. But it has its problems: only part of the ocean floor is flat enough to drag a net across, some bigger animals can easily avoid the nets, it’s pretty invasive, and it’s not all that fast.

Researchers can also ask commercial fishing companies how much they’ve caught, and try to estimate fish populations that way. But this is the twenty-first century, and we have cool sciencey toys now, like quick, cheap, accurate DNA sequencing. Fish shed DNA in the water all the time, just like we humans leave bits and pieces of ourselves wherever we go.

So instead of scooping up the fish, a team of Danish researchers figured they could just scoop up a bunch of environmental DNA, or eDNA, from the water, and match it to known tissue samples and sequences. They ran a traditional trawling study side-by-side with this eDNA study, pulling up two liters of water – a soda-bottle sized amount – everywhere they dropped a net. And, for the most part, the eDNA was able to tell them what was in that part of the ocean.

eDNA sequencing did miss some rare fish that trawling caught, suggesting that two liters of water just didn’t have enough of their DNA in it. Plus, the scientists are still figuring out how the amount of DNA can be used to estimate the actual number of fish in the water. But in the case of one species, the Greenland shark, the eDNA method may actually have done a better job than trawling.

The researchers say that Greenland sharks are big enough to avoid trawling nets. But that issue doesn’t apply to their DNA, so it might provide a better estimate of their numbers. Mostly, because eDNA sequencing is much less invasive than trawling, these scientists think it’s a promising option for future fish studies, even though it still needs some refining.

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