Mesenchymal Cells in Cartilage Growth and Regeneration “An Immunohistochemical and Electron Microscopic Study”

Abstract

Two common types of cells involved in cartilage growth; the undifferentiated perichondrial cells and chondrocytes. The perichondrial cells provide new external layers of cartilage matrix and are responsible for appositional growth. Chondrocytes proliferate to produce chondrogenic cells which generate a new interstitial cartilage matrix (interstitial cartilage growth). We previously described a third type of cartilage growth which is a mesenchymal cell-dependent type in the cartilage of the air breathing dendritic organ of catfish. The current study aimed to investigate this phenomenon using histochemical techniques, semi-thin sectioning, TEM and immunohistochemical staining. Typical mesenchymal cells penetrated the cartilage of the air breathing organ. Differentiating chondrogenic cells were detected adjacent to mesenchymal cells. Mesenchymal cells were continued with either the perichondrium or the external mesenchyme. Different stages of chondrogenic cells were identified adjacent to mesenchymal cells. Mesenchymal, chondrogenic and mature chondrocytes expressed type II collagen. Chondrogenic cells secrete elastic and safranin O positive cartilage matrix. Cartilage remnants and broken lacunae were observed at the site of mesenchymal cells. Mesenchymal cells, perichondrial cells, and chondrocytes had strong immunoreactivity for MMP-9. Mature chondrocytes undergo death leaving empty lacunae which were penetrated by mesenchymal cells. In conclusion, mesenchymal cells were responsible for cartilage matrix degradation and formation of the new matrix. They play a role in growth and maintenance of cartilage.