Progenitor Cells of the Mandibular Condylar Cartilage

Abstract

The secondary cartilage of the mandibular condyle is unique as it undergoes endochondral ossification during growth and robustly remodels in response to changes in its mechanical loading environment. This cartilage is derived from mesenchymal progenitor cells that express markers of early osteoblast differentiation, namely alkaline phosphatase (ALP) and runt-related transcription factor 2 (Runx2). Interestingly, these progenitor cells then differentiate into cartilage with appropriate mechanical loading. Our laboratory has determined that these cells can be labeled by osteoblast progenitor cell markers, including the 3.6 fragment of the rat collagen type 1. However, the role these mesenchymal progenitor cells play in adult mandibular condylar cartilage maintenance and adaptation, as well as the existence of a more potent progenitor cell population within the mandibular condylar cartilage, remain in question. Further characterization of these cells is necessary to determine their potency and regenerative capacity to elucidate their potential for regenerative therapy.

Figure 1

1A. The mandibular condylar cartilage is comprised of four zones. Mesenchymal progenitor cells are found in the polymorphic zone and can be marked by the 3.6kb fragment of the rat collagen type I promoter (3.6Col1) and/or the alpha-smooth muscle actin (α-SMA) promoter. 1B. Mesenchymal progenitor cells require mechanical loading cues to differentiate into fibrocartilage.