An international team of researchers, led by investigators at the University of California (UC) Irvine, has uncovered a new type of skeletal tissue that could transform the field of regenerative medicine and tissue engineering. Known as “lipocartilage,” this tissue is found in mammals’ ears, noses, and throats, and has unique properties that make it exceptionally resilient and flexible.
“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 senior author Maksim Plikus, PhD, a professor of developmental and cell biology at UC Irvine.
The research, published in Science, demonstrates that lipocartilage is composed of fat-filled cells called “lipochondrocytes,” that provide very stable internal support, while allowing the tissue to remain soft and springy, similar to the bubbles in packing material. Unlike ordinary fat cells, these specialized cells maintain stable lipid reservoirs, keeping their size constant regardless of food availability. This ability helps maintain the tissue’s strength and flexibility, which allows it to stay soft and pliable.
Unlike typical cartilage, which relies on an external extracellular matrix for structural support, lipocartilage has internal, self-generated stability. Lipochondrocytes produce lipid-filled vacuoles that support the tissue, and these vacuoles are “locked” in place due to a unique genetic process that prevents the breakdown of fats. This discovery provides new and divergent information about the role of lipids in skeletal tissues and could have wide-reaching implications for tissue engineering.
The study shows that lipocartilage precursor cells express a combination of genes typically seen in both cartilage and fat cells. Through a process called de novo lipogenesis, these cells synthesize lipid vacuoles from glucose, unlike adipocytes, which absorb fat from the bloodstream. Even when subjected to changes in diet or caloric intake, lipocartilage does not shrink or expand, unlike typical fat tissues, which readily change their size based on metabolic conditions.
“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,” said Raul Ramos, the study’s lead author and a postdoctoral researcher in the Plikus lab.
The research team also discovered that in certain mammals, such as bats, lipocartilage is arranged in intricate shapes, such as parallel ridges in bat ears, that enhance their hearing by modulating sound waves. In addition, they identified lipocartilage in human cartilage cells grown in vitro from embryonic stem cells, pointing to its potential for use in humans.
Researchers are now studying the molecular processes that enable lipocartilage’s stability and its potential uses in regenerative medicine. Advances in 3D printing technology could allow for the creation of personalized, living cartilage tissues tailored to individual needs.
These new findings could help researchers develop patient-specific cartilage for reconstructive surgeries. Current methods often require harvesting cartilage from a patient’s rib, but the ability to use stem cells to generate customized lipocartilage tissue could lead to less invasive, personalized treatments for cartilage defects, trauma, and diseases.
