So how did this new cell escape scientists and doctors for so long? In a way, it didn't. Plicous and his graduate student scoured centuries of scientific papers for any lost traces of fatty cartilage. He found a clue in an 1854 German book by Franz Leydig, a contemporary of Charles Darwin. “Anything and everything he could put under the microscope, he did,” says Plicous. Leydig's book described fat-like cells in a cartilage sample from a rat ear. But 19th-century equipment could not go further than that observation, and, realizing that a more accurate census of skeletal tissue could be valuable to medicine, Plicous resolved to solve the matter.
His team began their investigation by looking at the cartilage located between thin layers of skin in a mouse's ear. A green dye that preferentially stains fatty molecules reveals a network of squishy blobs. They isolated these lipid-laden cells and analyzed their contents. All your cells have the same library of genes, but those genes are not always active. What genes did these cells express? Which proteins move around inside? That data showed that lipochondrocytes actually, molecularly, look very different from fat cells.
He next asked how lipochondrocytes behave. Fat cells have an unremarkable function in the body: storing energy. When your body stores energy, cellular stores of lipids increase; When your body burns fat, the cells shrink. It turns out that lipochondrocytes do no such thing. Researchers studied the ears of rats placed on high-fat versus calorie-restricted diets. Despite rapid weight gain or loss, there was no change in lipochondrocytes in the ears.
“That immediately suggested that they must have a completely different role that has nothing to do with metabolism,” says Plicous. “It has to be structural.”
Lipochondrocytes are like balloons filled with vegetable oil. They are soft and amorphous but still resist compression. It contributes significantly to the structural properties of cartilage. Based on data from rodents, the tensile strength, flexibility and stiffness of cartilage increased by 77 to 360 percent when comparing cartilage tissue with and without lipochondrocytes – suggesting that these cells make cartilage more flexible.
And structural gifts appear to benefit all types of species. For example, in the outer ear of Pallas's long-tongued bat, lipocartilage is the base of a series of ruffles, which scientists believe helps them tune to precise wavelengths of sound.
The team has also discovered lipochondrocytes in human fetal cartilage. And Lee says this finding finally explains something that reconstructive surgeons commonly see: “There's always a little bit of slippage in the cartilage,” she says, especially in young children. “You can feel it, you can see it. It's very clear.”
New findings suggest that lipochondrocytes fine-tune the biomechanics of some of our cartilage. A rigid scaffold of cartilage proteins without lipids is more durable and is used to build weight-bearing joints in your neck, back, and yes, you guessed it – ribs, traditional sources of cartilage for implants. Is one of. “But when it comes to more complex things that need to be really flexible, bouncy, elastic — the ear, the tip of the nose, the larynx,” says Plikus, that's where lipocartilage shines.
As for procedures that involve modifying these body parts, Plicus envisions one day growing lipocartilage organoids in a dish and 3D-printing them in any desired shape. However, Li urges caution: “Despite 30 or 40 years of study, we are not very good at making complex tissues,” she says.
Although such an operation is still a way off, studies show that it is possible to grow lipochondrocytes from embryonic stem cells and safely isolate them for transplantation. Lee anticipates that regulators won't greenlight using fetal cells to grow tissue for a non-life-threatening condition, but he says if researchers can grow transplantable tissue from patient-derived adult cells So she will be more optimistic. (Plicus says they've filed a new patent application for a cover using stem cells from adult tissue.)
Lipochondrocytes update our understanding of what cartilage should look and feel like – and why. “When we're, say, trying to make a nose, sometimes we can use [lipid-filled cells] For a little bit of padding.” Lee says. Lipocartilage could one day fill that void as growable, implantable tissue — or it could inspire better biomimetic materials. “It could both “Maybe.” “It's exciting to think about. That's probably the one thing we're missing.”