Behaviour of cells of condylar cartilage of foetal mouse mandible maintained in vitro

Differential gene expression in the perichondrium and cartilage of the neonatal mouse temporomandibular joint

Our goal was to discover genes differentially expressed in the perichondrium (PC) of the mandibular condylar cartilage (MCC) that might enhance regenerative medicine or orthopaedic therapies directed at the tissues of the temporomandibular joint. We used targeted gene arrays (osteogenesis, stem cell) to identify genes preferentially expressed in the PC and the cartilaginous (C) portions of the MCC in 2-day-old mice. Genes with higher expression in the PC sample related to growth factor ligand-receptor interactions [FGF-13 (6.4x), FGF-18 (4x), NCAM (2x); PGDF receptors, transforming growth factor (TGF)-beta and IGF-1], the Notch isoforms (especially Notch 3 and 4) and their ligands or structural proteins/proteoglycans [collagen XIV (21x), collagen XVIII (4x), decorin (2.5x)]. Genes with higher expression in the C sample consisted mostly of known cartilage-specific genes [aggrecan (11x), procollagens X (33x), XI (14x), IX (4.5x), Sox 9 (4.4x) and Indian hedgehog (6.7x)]. However, the functional or structural roles of several genes that were expressed at higher levels in the PC sample are unclear [myogenic factor (Myf) 9 (9x), tooth-related genes such as tuftelin (2.5x) and dentin sialophosphoprotein (1.6x), VEGF-B (2x) and its receptors (3-4x) and sclerostin (1.7x)]. FGF, Notch and TGF-beta signalling may be important regulators of MCC proliferation and differentiation; the relatively high expression of genes such as Myf6 and VEGF-B and its receptors suggests a degree of unsuspected plasticity in PC cells.

Electrical stimulation of masseter muscles maintains condylar cartilage in long-term organ culture

When condylar cartilage is maintained under nonfunctional organ culture conditions, its phenotypic expression is altered to a premature form with less expression of the type II collagen characteristic of mature chondroblasts. The aim of this study was to examine whether, by electrical stimulation of the major masticatory muscle, the masseter muscle, chondrogenic expression could be maintained under organ culture conditions in which the jaws with the craniomandibular joint were cultured in one block. Sixty BALB/c mice of both sexes were divided randomly into three groups of equal size. Two groups were decapitated at the age of 5 days. The cranial base and mandible were dissected out in one block, and the explant was placed on its cut surface on a culture dish. The masseter muscles of the explants in one group were stimulated with an electric pulsing device delivering an AC current of a frequency of 0.7 Hz and an amplitude of 5V with hourly active and silent periods. Five experimental and five control explants were fixed after culture periods of 1, 3, 7, and 14 days. The mice in the third group were used as in vivo controls. By electrical stimulation of the masseter muscle, the phenotypic characteristics of the condylar chondroblasts, such as the deposition of type II collagen and the thickness of the cartilage layers, closely resembled the situation in vivo, while the controls in a non-functional environment gradually lost their characteristic form.

Growth of the mandibular condylar cartilage of the rat in serum-free organ culture

To evaluate the intrinsic capacity for growth, the mandibular condylar cartilage of 4-day-old rats was cultured in a serum-free, chemically-defined medium for 28 days and compared with the condylar cartilage cultured in a serum-supplemented medium and with the normal growth in vivo. Under the serum-free culture conditions, cell proliferation, differentiation into functional chondroblasts and matrix formation continued, but chondroclasia and osteogenesis were absent. This resulted, after 28 days of culture, in an enlarged condylar cartilage with altered proportions, a severe reduction of the prechondroblastic and the transitional zone and a considerable increase of the hypertrophic zone. It appears that the serum-free culture system is unfavourable for endochondral osteogenesis and lacks factors modulating the rate of proliferation, differentiation and maturation of the prechondroblasts. In the functional environment of the condyle, humoral or mechanical factors seem to exert this essential modulating influence on the condylar-cartilage growth.

Mandibular growth retardation in corticosteroid-treated juvenile mice

Juvenile mice were treated for up to eight weeks with weekly doses of a synthetic analogue of cortisol:triamcinolone hexacetonide. The mandibular condylar cartilage was studied histologically and histochemically at regular intervals. Morphometric measurements were performed along the mandibular posterior vertical dimension (condylar process and ramus). By the second injection significant morphological changes were noted in the condylar cartilage, followed by retardation of bone growth. The most distinctive feature in the cartilage of triamcinolone-treated mice was a marked increase in the dimension of its mineralized zone concomitant with a significant increase in the number of hypertrophic chondrocytes. The role of condylar cartilage in mandibular growth is discussed.