Humans Might Be Able To Regrow Cartilage

8:29 minutes

a black and white x-ray of a foot and ankle. you can see where the bones meet and where the joints are
An x-ray of a normal right foot. Credit: Public Domain, Wikimedia Commons

Cartilage is the connective tissue that provides padding between your joints. As we age, the wearing down of cartilage can lead to different types of arthritis. It’s been long believed that once humans lose cartilage, it can never grow back. Now, a team of researchers investigated this idea, and found that the cartilage in our ankles might be able to turnover more easily compared to our hips and knees. Their results were published in the journal Science Advances. Rheumatologist Virginia Byers Kraus, who was an author on the study, discusses how human cartilage might be able to regenerate and what this means for future treatments.

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Segment Guests

Virginia Byers Kraus

Virginia Byers Kraus is a Professor of Medicine, Orthopaedics and Pathology at Duke University in Durham, North Carolina.

Segment Transcript

IRA FLATOW: I’m Ira Flatow. This is Science Friday. If you’re of a certain age or if you have arthritis, you worry about your cartilage wearing out, right? But you’ve probably heard that you can’t regrow your cartilage. When it wears out, it’s gone. And that can lead to different types of arthritis or worsening arthritis.

Well, listen to this. A team of researchers wanted to investigate this idea about, well, can you regrow this stuff? They used molecular clocks to figure out the age of the cartilage in our bodies from our hips to our knees to our ankles. And they found that the cartilage in your ankle was younger, younger than the cartilage in your hips.

And their results were published this week in the journal Science Advances. So what does this turnover rate tell us about cartilage repair? My next guest is an author on that study. Dr. Virginia Byers Kraus is a Professor of Medicine, Orthopedics, and Pathology at Duke University in Durham, North Carolina. Welcome to Science Friday.


IRA FLATOW: Isn’t cartilate a living tissue, right? Why is it so difficult for us to regrow it then?

VIRGINIA BYERS KRAUS: It absolutely is living. It’s full of cells. But what’s unusual about cartilage is it doesn’t have any blood supply and it doesn’t have any nerve tissue. So that’s why it can be degenerating for long periods of time without there being that many signals in terms of something’s going wrong.

IRA FLATOW: How does it survive without any blood supply? Why wouldn’t it just rot in your body like a foreign object?

VIRGINIA BYERS KRAUS: Well, this is why exercise is so important for the joint nutrition. Because it gets its nutrients from the fluid inside the joint, which moves in and out of the cartilage, brings the nutrients in and out to the cells with each dynamic motion.

IRA FLATOW: So are you saying that even if we have arthritis and when we’re aching, we should still continue to do exercise?

VIRGINIA BYERS KRAUS: Yes, as much as possible. And when people are really severely affected, we send them to the pool where they only weigh 1/8 in the pool what they weigh on land, which is even better than on the moon. And that way, they can move their joints through ranges of motion without that deleterious load.

IRA FLATOW: That’s very interesting. Let’s talk about cartilage aging. How does it age over time?

VIRGINIA BYERS KRAUS: So over time, all your tissues accumulate chemical modifications. And in cartilage that is particularly true. Because a lot of these cartilages are very long-lasting. And what we found, our surprise, as you mentioned, was that the proteins in the ankle appeared to be much younger in older people than their knee cartilage or their hip cartilage. Which told us that the ankle is in a high state of continuous repair, like a house that’s being refurbished continuously. And the knees are somewhere intermediate. But the hips have very low repair capacity.

IRA FLATOW: So are the ankles then making new cartilage, or are they just keeping the old stuff healthier?

VIRGINIA BYERS KRAUS: So they’re doing both. They’re getting rid of the old and they’re replacing it with new. So they’re constantly turning it over and keeping it fresh.

IRA FLATOW: Do we know how that happens? And could we then do that for the rest of the joints in our bodies?

VIRGINIA BYERS KRAUS: Well, we wracked our brains about this. And we finally hit upon a beautiful paper in 2016, some work that looked at three different animals that could regenerate their limbs. Even though the animals were widely separated in evolutionary time by millions of years, they posited that those factors that were controlling limb regeneration that were shared across the three of them might be the master regulators of limb regeneration.

And so they found a list of 108 micro RNA that they think are the master regulators of that process. So we looked into those factors. And we found that several of the ones that we tested– which were some of their highest and most abundant ones– were highest in the ankle, were intermediate in the knee, and were low in the hip and correlated very well with the protein age and the amount of those chemical modifications that had accumulated.

IRA FLATOW: So could you move around that micro RNA to different places?

VIRGINIA BYERS KRAUS: Exactly. That’s what’s so exciting is that we now have a list of 108 regenerative micro RNA that could be injected into the joint to boost the natural repair response. Because we’re already making those for ourselves.

IRA FLATOW: Let me give out our number. 844-724-8255 if you’d like to talk about cartilage and arthritis and things, 844-724-8255.

One of the treatments you hear about for cartilage damage is stem cells. Can we use stem cells to regrow cartilage?

VIRGINIA BYERS KRAUS: So a lot of work is being done very diligently to try to look at that. And in fact, the current state of knowledge suggests that stem cells are in the surface of cartilage more than anywhere else. And that’s where we’ve found the most robust regenerative capacity. So we compared the top, the middle, and the deep parts of cartilage. So one thought is that it’s the stem cell production of micro RNA that might, in part, be the factor that is actually regenerating the tissue.

IRA FLATOW: Is there anything that you can eat? Because you always hear– on television, on the internet, wherever– people selling you stuff that will regenerate or save your cartilage. Is there any truth to that?

VIRGINIA BYERS KRAUS: Well, a number of dietary factors probably do impact the health of the joint. So a good nutritious diet, vitamins. But most of all, optimal weight. So it’s eating not too much that is probably the most important factor.

IRA FLATOW: And also getting that exercise, as you say, so that you can regenerate the cartilage.


IRA FLATOW: The ideal animal model to study human cartilage and joints, I’ve learned from reading your research, is the guinea pig.

VIRGINIA BYERS KRAUS: The guinea pig is so similar to humans, possibly because they also, like us, they tend to like to eat a lot. And they also can be sedentary. And they develop a form of knee osteoarthritis that looks extremely similar to what humans get just naturally. And guinea pigs get it naturally. So one great next step is to take these micro RNA and test in that animal to see if one could actually slow or completely prevent the osteoarthritis that they naturally develop over the first year of their lives.

IRA FLATOW: Are those tests underway yet?

VIRGINIA BYERS KRAUS: So we’re hopeful to be getting more funding to try to pursue those. There has been one study that was just recently published in a mouse model, injury model, which is another cause of osteoarthritis. And it looks like one of the micro RNA that just so happened to be on the list of regenerative micro RNA, it seemed to have some beneficial effects at blocking osteoarthritis. So we think that that strategy has got some great potential.

IRA FLATOW: Is there any inheritance or genetics to what kinds of cartilage you inherit, whether it’s going to last longer than another?

VIRGINIA BYERS KRAUS: So that’s a fascinating question. It also seems to tie into what we’ve just been talking about. The most widely accepted and validated genetic mutation that’s related to osteoarthritis is a growth factor called GDF-5. And even a 10% reduction in the amount of that growth factor over a lifetime seems to increase people’s susceptibility to getting osteoarthritis. So we do think that the repair capacity, innate repair capacity, is very much related to people’s susceptibility.

IRA FLATOW: Is it possible to transfer the younger cartilage in your ankles to other parts of your body that might need it more?

VIRGINIA BYERS KRAUS: Well, whenever you make a hole in cartilage, you’ll always then have the conundrum of having to try to fix it. So it sure would be nicer to be able to find some synthetic solution or make, for instance, the micro RNA that are injectable so that you wouldn’t have to create a second wound to cause an additional problem.

IRA FLATOW: Yeah, that would be the better solution. And we’ll watch out for later news with this. I want to wish you luck. And thank you very much for taking the time to talk with us.


IRA FLATOW: Virginia Byers Kraus is Professor of Medicine and Orthopedics and Pathology at Duke University. That’s there in Durham, North Carolina.

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