Laryngeal cartilages undergo a slow ossification process during aging, making them an excellent model for studying cartilage mineralization and ossification processes. Pig laryngeal cartilages are similar to their human counterparts in shape and size, also undergo mineralization, facilitating the study of cartilage mineralization. We investigated the processes of cartilage mineralization and ossification and compared these with the known processes in growth plates. Thyroid cartilages from glutaraldehyde-perfused male minipigs and from domestic pigs were used for X-ray, light microscopic, and transmission electron microscopic analyses. We applied different fixation and postfixation solutions to preserve cell shape, proteoglycans, and membranes. In contrast to the ossifying human thyroid cartilage, predominantly cartilage mineralization was observed in minipig and domestic pig thyroid cartilages. The same subset of chondrocytes responsible for growth plate mineralization is also present in thyroid cartilage mineralization. Besides mineralization mediated by matrix vesicles, a second pattern of cartilage mineralization was observed in thyroid cartilage only. Here, the formation and growth of crystals were closely related to collagen fibrils, which served as guide rails for the expansion of mineralization. It is hypothesized that the second pattern of cartilage mineralization may be similar to a maturation of mineralized cartilage after initial matrix vesicles-mediated cartilage mineralization.
Keywords: cartilage mineralization; cattle; domestic pigs; electron microscopy; laryngeal cartilages; minipigs; ossification; thyroid cartilage.