Thank you to GiveWell, an organization that makes it easy to find excellent charities to trust, for sponsoring today’s episode!

Click on the link below to donate, and be sure to use the fundraiser code SCISHOW at checkout to make sure your donation gets matched. [♪ INTRO] One of the biggest questions in medicine right now is how to prevent Alzheimer’s disease. It’s a fatal disease that damages the brain and destroys neurons, first in the areas involved in memory, and then, beyond.

And it affects tens of millions of people worldwide. But every day, researchers are looking for ways to cure or prevent it. And in a paper published Monday in the journal Nature Aging, one team may have found a promising candidate.

It’s called sildenafil. And it is a currently prescribed for a type of high blood pressure and for erectile dysfunction. One reason it’s hard to prevent Alzheimer’s is because scientists don’t fully understand what causes it.

Still, one thing they do know is what the disease looks like in the brain. Brains affected by Alzheimer’s are famous for having clumps or tangles of certain proteins that block communication between neurons. They’re called amyloid plaques and neurofibrillary tangles.

And most of the drugs developed for Alzheimer’s have tried to address at least one of them. But in this new study, the team wasn’t trying to invent an Alzheimer’s drug. They were trying to identify drugs that already exist that might treat the disease.

First, they characterized traits that previous studies have identified as having some relationship to Alzheimer’s -- like specific genes and their protein products. Then, they did a computer-based analysis to see what drugs interact with those traits, what kinds of data are available about them, and how effective they might be. And in the end, their most promising candidate was sildenafil.

Among other things, this drug has already been shown to reduce the severity of neurofibrillary tangles in mouse models of Alzheimer’s. Next, they looked to see if there was any link between sildenafil and Alzheimer’s in a huge medical dataset. They analyzed insurance data from more than 7.2 million people in the US.

And they found that after six years, people who used sildenafil were 69% less likely to have developed Alzheimer’s disease, compared to similar patients who didn’t use the drug. Nice! Or at least, they were 69% less likely to have filed an insurance claim about it, which is a pretty good surrogate.

As for why this would happen, well, the researchers ran tests on neuronal cells to find out. In one experiment, they grew neurons from cells taken from patients with Alzheimer’s and then treated them with sildenafil. And after six days of treatment, one thing they found was that the treated neurons had more neurite growth than the control cells, in other words, the branches coming off their neurons had grown more.

Now, all that said… This paper doesn’t prove that sildenafil prevents Alzheimer’s. This is a promising lead, but to know how effective this drug is, researchers will need to do rigorous, randomized clinical trials. But hey, maybe this is how it starts: Right now, scientists have an interesting connection.

And with a lot of research and testing, it could become more. But there’s a long way to go before we know for sure. In completely different news, scientists have also published new findings about Hydra.

Not the mythological serpents. Not the villains from the Marvel movies. The small, wiggly aquatic animals.

Hydra are famous for being able to regrow their heads, and scientists haven’t known exactly how they do it. But in a paper published Wednesday in Genome Biology and Evolution, a team mapped out the mechanisms behind this feat for the first time. A key part of Hydra biology is the head organizer.

It’s a group of cells in the top of the animal’s head, and it keeps the Hydra... organized. Hydra’s cells are constantly growing and dividing, and the head organizer tells those cells how they should grow, depending on what body part they’re in. It’s also involved in head regeneration, and in reproduction, specifically, in a process called budding.

In budding,a Hydra will get a head organizer in the lower part of its body, which will tell the Hydra to grow a structure called a bud that becomes a new, adult animal. So, this head organizer thing is a big deal. Now, besides mapping out how Hydra regrow their heads, the researchers also investigated how head regeneration and budding are similar.

In both cases, they looked at gene expression — or, what sections of DNA are actively being read and utilized by Hydra’s cells during these processes. After a lot of analysis, this team found that head regrowth and budding involved a lot of the same genes, but they were expressed at different times. Which makes sense: Both processes involve regrowing body parts, but in different ways.

Meanwhile, when the researchers zeroed in on what’s happening only during head regrowth, they found that it’s about as complicated as you’d think! They identified and categorized a huge set of genetic locations potentially involved in this process — like, around 27 thousand of them. Together, all of these elements control what’s happening in the Hydra’s body as it regrows its head.

In a way, the animal is opening up an instruction manual, flipping to the “I just got decapitated; how do I get a new head?” section, and reading what’s there. Now, besides teaching us more about how Hydra work, this study also has implications for evolution. It’s thought that the complexity of multicellular life was driven by gene expression, so, not just what’s in DNA, but how it gets used.

So, studying Hydra and comparing their genes to related animals can tell us something about when different forms of gene expression evolved. In this case, after comparing their results to the results on one of Hydra’s relatives, the researchers suggest that this kind of complex gene expression probably evolved more than 600 million years ago. So, Hydra aren’t just capable of regrowing their heads… they’ve gotten a lot of practice at it.

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