Researchers have discovered a new type of tissue, a soft and flexible ‘fatty cartilage’ that could revolutionize the treatment of traumatic injuries, birth defects, and cartilage-damaging diseases like osteoarthritis, rheumatoid arthritis and lupus.
Along with bone, cartilage is an essential component of our skeletal system. Some of its important functions include providing shape and support to structures such as the ears, nose and windpipe, and acting as a shock absorber in the joints.
Now, an international team of researchers led by the University of California, Irvine (UC Irvine) has discovered a new type of skeletal tissue, a fatty cartilage called ‘lipocartilage,’ that has the potential to revolutionize the fields of regenerative medicine and tissue engineering.
“Lipocartilage’s resilience and stability provide a compliant, elastic quality that’s perfect for flexible body parts such as earlobes or the tip of the nose, opening exciting possibilities in regenerative medicine and tissue engineering, particularly for facial defects or injuries,” said Maksim Plikus, a professor of developmental and cell biology at UC Irvine and the study’s corresponding author.
Cartilage’s biomechanical properties – it is strong but flexible – are due to cells called chondrocytes secreting large amounts of collagen-rich extracellular matrix (ECM), which surrounds the cells. However, during a previous study, while the researchers were examining mouse ears to find answers about hair growth, they noticed cells with internal fat stores throughout the rodent’s ear cartilage. Looking closer, they found that the new kind of tissue was also present in the nose, voice box, and chest of mice. So, the researchers set out to understand this lipocartilage better.
Although the cells were initially thought to be adipocytes, cells that make up adipose or fatty tissue, the researchers found that they were instead a distinct kind of fat-filled skeletal cell called a lipochondrocyte. They ascertained that the cells’ fat-containing storage units (vacuoles) were robust and super-stable. In mice, individual lipochondrocytes didn’t change in size, whether the animals were overfed to the point of obesity or starved. This is unlike adipocytes, which, in obesity, will fill their lipid vacuoles and grow in size or empty them and shrink during periods of starvation. This meant that, regardless of food availability, lipocartilage maintained its durable, flexible properties, which the researchers likened to bubble wrap.
“The discovery of the unique lipid biology of lipocartilage challenges long-standing assumptions in biomechanics and opens doors to countless research opportunities,” said Raul Ramos, a postdoctoral researcher in UC Irvine’s Laboratory for Developmental and Regenerative Biology and the study’s lead author. “Future directions include gaining an understanding of how lipochondrocytes maintain their stability over time and the molecular programs that govern their form and function, as well as insights into the mechanisms of cellular aging. Our findings underscore the versatility of lipids beyond metabolism and suggest new ways to harness their properties in tissue engineering and medicine.”
In addition to rodents, lipocartilage was found in the ears of other mammals, especially those with thin, membrane-like ears, such as bats and marsupials. The researchers also confirmed that abundant lipid droplets form in human cartilage cells grown in the lab from embryonic stem cells.
The researchers see great potential for the use of lipocartilage in the future.
“Currently, cartilage reconstruction often requires harvesting tissue from the patient’s rib – a painful and invasive procedure,” Plikus said. “In the future, patient-specific lipochondrocytes could be derived from stem cells, purified and used to manufacture living cartilage tailored to individual needs. With the help of 3D printing, these engineered tissues could be shaped to fit precisely, offering new solutions for treating birth defects, trauma and various cartilage diseases.”
The study was published in the journal Science.
Source: UC Irvine