Title: Adipochondrocytes in rabbit auricular cartilage
ArXiv ID: 1802.01375
Date: 2019-03-15
Authors: : - Ahmed M. El-Sayed - Mohamed A. Al-Ghamdi - Hany S. Farag - Mohamed F. Hassanien
📝 Abstract
Chondrocytes are described as one cell population in different cartilage types. The auricular cartilage in mouse and rat contains unique chondrocytes similar in morphology to white adipocytes and known as lipochondrocytes. Lipochondrocytes were not mentioned in other species. The current study aimed to explore the existence of this cell type in rabbits. The auricles of adult male white rabbits were harvested and processed for histological examination with light and electron microscopy. With the light microscopy, the auricular cartilage of adult rabbits contained central large rounded adipocyte-like chondrocytes, termed in the current study adipochondrocytes The adipochondrocytes were embedded in relatively wide lacunae and had large lipid droplets with a rim of cytoplasm. The scanning electron microscopy confirmed this result. With the transmission electron microscopy, the adipochondrocytes showed dark nucleus and electron-dense cytoplasm with few organelles and cytoplasmic processes. The adipochondrocytes of the auricular cartilage in adult rabbits were unique cell type and different from chondrocytes in other cartilage subtypes. This result should be considered during cartilage transplant. Further studies are suggested to investigate the development and physiological roles of adipochondrocytes in the auricular cartilage in rabbits.
💡 Deep Analysis
📄 Full Content
Cartilage is an avascular type of connective tissue exists in three subtypes; hyaline, elastic and fibrocartilage. The cartilage subtypes have different anatomical locations. For example, hyaline cartilage is found on articular surfaces, in the respiratory tract, and in ribs. Elastic cartilage is present in the external ear and epiglottis, while the fibrocartilage predominates in the intervertebral discs, and in the ligaments and tendons (Mescher 2015) . Each cartilage subtype was made by a single cell type (chondrocytes) which embedded inside lacunae, and extracellular matrix (ECM), which produced and maintained by the chondrocytes themselves (Ahmed 2007). The ECM consists of glycosaminoglycans (GAGs), proteoglycans and fibers. Based on the predominance of each structure of the ECM, the cartilage three subtypes could be differentiated (Naumann et al., 2002). In general, the elastic cartilage is mostly cellular with a little ECM (Ito et al., 2001). Furthermore, the elastic cartilage in adult rats and mice is unique. Its chondrocytes are occupied by large fat droplets resembling the white adipocytes and its ECM is sparse but rich in elastic fibers and never been mineralized (Sanzone and Reith 1976, Kostovic-Knezevic et al., 1981, Mallinger and Böck 1985, Bradamante et al., 1991). The chondrocytes in the ear pinnae of mice (auricular cartilage) were termed as "Lipochondrocytes" (Sanzone and Reith 1976). Lipochondrocytes were not mentioned in other species. It is not clear if this type of chondrocytes is specific to mice and rats or could be found in the auricular cartilage of other species. We hypothesized that these cells could be found in small mammalian species thus, the current study was undertaken with the aim of exploring these cells in the auricular cartilage of rabbit.
The current study was conducted in the Laboratory of Histology Department in the Faculty of Veterinary Medicine, South Valley University, Qena, Egypt from January 2017 to July 2017.
Apparently healthy, mature (6-month old) male New Zealand White rabbits (n=15) were obtained from the farm of the Faculty of Agriculture, South Valley University, Qena, Egypt. The animals were euthanized with ether then small pieces (0.5 mm) from the auricles were dissected. Some specimens were immediately fixed in either 10% neutral buffered formalin (NPF; pH=7.4) for 24 hours for the light microscopy or in 2.5% glutaraldehyde for 48 hours at 4C°, then in 1% osmium tetroxide for 2 hours for examination with the scanning (SEM) and transmission (TEM) electron microscopy.
NBF-fixed samples were dehydrated in ascending grades of ethanol, embedded in paraffin. Paraffin sections (5µm thickness) were cut with a rotary microtome (Leica RM2255) and stained with hematoxylin and eosin (H&E) as a general stain, periodic acid-schiff (PAS) for neutral GAGs, alcian blue for acidic GAGs, combined PAS-alcian blue for both types of GAGs, safranin-O for proteoglycans, Masson’s trichrome for collagen fibers and orcein stains for elastic fibers detection (Jones et al. 2008). Sections were examined with the light microscope (Leica DMLS). Photographs were captured with Leica digital camera (Leica ICC50) using ×4, ×10, ×40 and ×100 objectives in JPEG format.
Fixed specimens were dehydrated in ascending grades of ethanol. The specimens were dried, coated with gold in a sputter coater and examined with the SEM (JEOL 5500) at the Central Laboratory of the SVU.
Fixed specimens were dehydrated in ascending grades of ethanol and embedded in Spurr’s resin. Semithin and ultrathin sections were taken with a glass knife. Semithin sections (0.5 µm thickness) were stained with toluidine blue and ultrathin sections (80-100 nm) were stained with lead citrate and uranyl acetate, then examined with the TEM (JEOL1010) at the Central Laboratory of the SVU.
The thickness of the auricular cartilage, the diameters of the lacunae and lipid droplets of adipochondrocytes, the adipochondrocyte/ ECM ratio area and cellular density (the number of cells in a specific area) were measured using the free imageJ software (https://imagej.nih.gov/ij/)
. The results were analyzed by EXCELL 2016 and expressed as mean ±SE.
The auricular cartilage plate of the white rabbits consisted of hypertrophic white adipocyte-like chondrocytes inside their rounded to oval lacunae. These cells were termed “Adipochondrocytes” in the current study. The adipochondrocytes occupied most of the central zone of the auricular cartilage and were separated from each other by a sparse ECM and surrounded by flattened collagenous tissue of perichondrium. In addition, smaller ovoid cells were squeezed between the central hypertrophied adipochondrocytes and the perichondrium, and contained varying amounts of lipid droplets (Fig. 1A-C). The cytoplasm of adipochondrocytes was mostly occupied by single large rounded to oval lipid droplets. The lipid droplets of the adipochondrocytes dissolved during paraffin section preparation, leaving empt
