A long-ignored skeletal tissue filled with oil

Abstract

Cartilage is a strong, flexible connective tissue that serves vital support functions in the vertebrate skeletal system. In addition to giving structure to parts of the body, such as the nose, ears, and larynx, cartilage protects bones and joints by absorbing shock and reducing friction (1–3). Current human histology and anatomy textbooks list three types of cartilage—hyaline cartilage, elastic cartilage, and fibrocartilage—that vary in their morphological features, locations in the body, and biomechanical functions (1–3). All three types consist of specialized cartilage cells called chondrocytes and a firm yet pliable extracellular matrix (ECM) that is rich in collagen, proteoglycans, and elastin fibers. On page 154 of this issue, Ramos et al. (4) report the distinctive properties of another type of cartilage characterized by large lipid vacuoles that were first observed more than 150 years ago (5, 6). The discovery may have implications for regenerating cartilages.