Comparative Studies on the Morphology of Chondrocytes, Adipocytes and Adipochondrocytes in New Zealand White Rabbits

Abstract

Adult cartilage comes in three different types: hyaline cartilage, elastic cartilage, and fibrocartilage. In several forms of cartilage, chondrocytes are described as a one-cell population. Chondrocytes are the manufacturers of the surrounding ECM and collagen type II fibers in hyaline cartilage besides the elastic fibers in elastic cartilage. Whereas the white adipocytes mainly compose the white adipose tissue and they are specialized in production, storage and mobilization of triglycerides. Early studies explored a unique type of chondrocyte in mouse, rat, and rabbit auricular cartilage having morphology similar to white adipocytes and identified it as "adipochondrocyte". The objective of the current study was to explore the differences between chondrocyte, adipocyte and adipochondrocyte morphologies in white New Zealand rabbits and to ascertain if adipochondrocyte is more comparable to chondrocyte or adipocyte morphology. The auricles, articular cartilage of carpal joint, and pre-renal white fat of adult male white rabbits were harvested and processed for histological examination with light and transmission electron microscopy. The adipochondrocytes appeared as hypertrophic white adipocyte-like chondrocytes occupied the auricular cartilage plate of the white New Zealand rabbits, similar to the characteristic "signet ring" appearance of the white adipocytes in pre-renal white fat. The adipochondrocytes were housed in lacunae within an ECM similar to chondrocytes of articular cartilage. The TEM examination had illuminated that the adipochondrocyte cytoplasm contained large lipid globule that flattened the eccentric nucleus and sparse organelles. Further studies are suggested to exploring molecular and functional features of adipochondrocytes, chondrocytes and adipocytes.