Cyclic nucleotides and growth regulation of the mandibular condylar cartilage of the rat in vitro

Small molecule compounds promote the proliferation of chondrocytes and chondrogenic differentiation of stem cells in cartilage tissue engineering

The application of tissue engineering to generate cartilage is limited because of low proliferative ability and unstable phenotype of chondrocytes. The sources of cartilage seed cells are mainly chondrocytes and stem cells. A variety of methods have been used to obtain large numbers of chondrocytes, including increasing chondrocyte proliferation and stem cell chondrogenic differentiation via cytokines, genes, and proteins. Natural or synthetic small molecule compounds can provide a simple and effective method to promote chondrocyte proliferation, maintain a stable chondrocyte phenotype, and promote stem cell chondrogenic differentiation. Therefore, the study of small molecule compounds is of great importance for cartilage tissue engineering. Herein, we review a series of small molecule compounds and their mechanisms that can promote chondrocyte proliferation, maintain chondrocyte phenotype, or induce stem cell chondrogenesis. The studies in this field represent significant contributions to the research in cartilage tissue engineering and regenerative medicine.

The Essentiality of Arachidonic Acid in Infant Development

Arachidonic acid (ARA, 20:4n-6) is an n-6 polyunsaturated 20-carbon fatty acid formed by the biosynthesis from linoleic acid (LA, 18:2n-6). This review considers the essential role that ARA plays in infant development. ARA is always present in human milk at a relatively fixed level and is accumulated in tissues throughout the body where it serves several important functions. Without the provision of preformed ARA in human milk or infant formula the growing infant cannot maintain ARA levels from synthetic pathways alone that are sufficient to meet metabolic demand. During late infancy and early childhood the amount of dietary ARA provided by solid foods is low. ARA serves as a precursor to leukotrienes, prostaglandins, and thromboxanes, collectively known as eicosanoids which are important for immunity and immune response. There is strong evidence based on animal and human studies that ARA is critical for infant growth, brain development, and health. These studies also demonstrate the importance of balancing the amounts of ARA and DHA as too much DHA may suppress the benefits provided by ARA. Both ARA and DHA have been added to infant formulas and follow-on formulas for more than two decades. The amounts and ratios of ARA and DHA needed in infant formula are discussed based on an in depth review of the available scientific evidence.

Expression of integrinalpha5beta1, focal adhesion kinase and integrin-linked kinase in rat condylar cartilage during mandibular lateral displacement

Integrins are cell-surface mechanochemical sensors and transducers involved in various cellular processes in combination with extracellular ligands. The aim of this study was to investigate the effect of mechanical stress on the expression of integrinalpha5beta1 and its downstream kinases, focal adhesion kinase (FAK) and integrin-linked kinase (ILK), in condylar cartilage during mandible lateral shift in young rats. Sixty 4-week-old male Wistar rats were divided at random into five control groups and five experimental groups. All rats in the experimental groups were fitted with a resin plate to functionally displace the mandible 2mm to the left (ipsilateral side). The rats were killed 1, 3, 7, 14 and 28 days after attachment of the appliance. Serial 6-mum sagittal sections were cut through the condylar head and processed for immunostaining of integrinalpha5beta1, FAK and ILK. The results were quantified using an image analysing system. Integrinalpha5beta1 expression in the superior-posterior region of the condylar cartilage on the ipsilateral side increased from 3 to 14 days compared with the contralateral side, with an intermediate level of expression in the control groups. Expression of FAK and ILK was similar to integrinalpha5beta1 expression, and they were also upregulated on the ipsilateral side compared with the contralateral side at the early stages of the experiment. The different mechanical loading on the two sides of the condylar cartilage led to different expression patterns of integrinalpha5beta1, FAK and ILK, which may correlate with the different morphological and histological changes seen between sides during mandibular lateral shift.

Immunohistochemical localization and distribution of proliferating cell nuclear antigen in the rabbit mandibular condyle following experimental induction of anterior disk displacement

The purpose of the present study was to identify proliferating cells in control versus experimental condyles two weeks following experimental induction of anterior disk displacement (ADD) in the rabbit craniomandibular joint (CMJ). The right joint of 15 rabbits was exposed surgically and all diskal attachments were severed except for the posterior attachment. The disk was then repositioned anteriorly and sutured to the zygomatic arch. The left joint served as a sham-operated control. Ten additional joints were used as nonoperated controls. Mandibular condyles were excised two weeks following surgery and processed for proliferating cell nuclear antigen (PCNA) immunostaining. In control and sham operated condyles, PCNA was localized in the nuclei of chondroblasts of the reserve cell layer, chondrocytes of the upper hypertrophic layer and bone marrow cells of the subchondral bone. In contrast to control joints, the PCNA positive cells of the experimental joints were located throughout the osteoarthritic condylar cartilage. In addition, the percentage of PCNA positive cells of the osteoarthritic condylar cartilage was statistically significantly higher when compared to the control group, p < 0.05. It was concluded that surgical induction of ADD in the rabbit CMJ leads to an increase in mitosis of chondrocytes, which lead to cell proliferation and subsequent hyperplasia of the condylar cartilage.

Specific properties of the extracellular chondroitin sulphate proteoglycans in the mandibular condylar growth centre in pigs

The developing condylar cartilage of the temporomandibular joint responds to changes in load by adaptive growth. Because local regulatory events taking place during growth processes are not well understood, investigation of extracellular matrix composition could provide new information about which matrix molecules are involved in the regulation of growth processes in this avascular tissue. The large chondroitin sulphate-rich proteoglycans in the mandibular condyle were compared to the proteoglycans in the weight-bearing femoral condyle of juvenile domestic pigs with respect to their buoyant density, chemical composition and immunological identity after isolation by dissociative extraction and CsCl density-gradient centrifugation. The distribution of these proteoglycans was studied in cryosections of mandibular condyle by immunohistochemistry using polyclonal antibodies produced against pig large proteoglycans. In the mandibular condyle, predominantly in the articular zone, the relative amount of proteoglycans with a low glycosaminoglycan content was greater than in femoral cartilage. The large proteoglycan immunologically related to aggrecan gave a protein core of 450 kDa after enzymatic deglycosylation and clearly possessed less keratan sulphate than in femoral aggrecan. Furthermore, the mandibular tissue contained another large proteoglycan with a protein core of 550 kDa after enzymatic deglycosylation, which was immunologically related to the fibroblast-like versican. Immunohistochemistry showed aggrecan increasing in amount inferiorly. In contrast, "versican' was exclusively found in the fibrous and differentiation layers. Aggrecan is mainly responsible for shock absorption and versican and its homologues may be involved in the control of cell proliferation and differentiation. Thus the matrix components of the mandibular condyle seem to be adapted to its special functional needs including parallel articulation and growth.

Mechanical loading triggers specific biochemical responses in mandibular condylar chondrocytes

The effect of mechanical loading on the phosphorylation state of condylar cartilage proteins was investigated by high resolution electrophoretic analysis of 32P-labelled proteins from mechanically stimulated rat mandibular condylar chondrocytes. Specific dephosphorylation (and/or loss) of an acidic, 35-36 kDa protein(s) and of proteins overlapping with members of the ras superfamily of small GTP-binding proteins was observed. These responses may constitute part of a mechanically induced transduction system which establishes the differentiated phenotype.

The influence of altered occlusion on the condylar cartilage of the mandible and on the growth of the entire skull

The effect of the loss of the suspensory zones of the upper jaw on the cartilage of the mandibular condyles and on the growth of both the viscerocranium and the neurocranium was examined after tooth crowns had been reduced in Wistar rats. We measured the thickness of the individual layers of the condylar cartilage and its total thickness. Alterations in the developmental processes involving the condylar cartilage expressed themselves as accelerated maturation, particularly in the centrally compressed areas of the cartilage. Alterations in occlusion influenced the development of the viscerocranium, whereas no influence on the growth of the neurocranium was detected.

On the importance of cAMP and Ca++ in mandibular condylar growth and adaptation

The origin of the mandibular condylar cartilage is not periosteal, like that of the other secondary cartilages; this cartilage originates in a cellular blastema of its own. Despite the fact that the development of secondary cartilages, in general, is dependent on mechanical irritation, that of the condylar cartilage is not. The low level of function experienced postnatally seems to favor growth, but because the proliferation cells of the condylar cartilage are multipotential, they switch their differentiation pathway in the direction of osteoblasts in the absence of function, and growth of the cartilage ceases. This regulation of differentiation is mediated by maturation of the cartilage cells. If function is not present, maturation advances rapidly, and the mature cartilage induces bone formation instead of cartilage. Cyclic AMP and Ca are important mediators in this process, because they affect the advancement of maturation.

Craniofacial alterations following electrolytic lesions of the trigeminal motor nucleus in actively growing rats

The objective of this study was to define further the role of the trigeminal motor nucleus (TMNu) in the postnatal ontogeny of the mammalian craniofacial skeleton. To that end, 42 male Sprague-Dawley rats underwent stereotaxic surgery at 40 days of age; 21 received small electrolytic lesions to their left-side TMNu (lesioned group) while 21 had TMNu stimulation with no actual electrolytic lesion produced (sham group). Seven rats from each group were killed at 28, 56, and 84 days postoperative to analyze trigeminal motoneuron (TMNe) count, masticatory muscle weight, and osteological growth vector data. At all three time periods, lesioned animals showed significant differences 1) between the surgery and nonsurgery sides, and 2) from sham animals. However, sham animals also demonstrated significant between-side differences for medial pterygoid muscle weight (56 days), mandibular height (28 and 56 days), and mandibular length data (84 days); these data suggested that even relatively slight damage to TMNe can create morphological changes within the craniofacial complex. Snout deviation in a lesioned rat towards the opposite side from all other lesioned animals was correlated with unique damage to its pontine reticular formation; this suggested that the observed morphological alterations of the craniofacial complex may have been due not only to TMNu damage, but also to changed expressions of the masticatory central pattern generator (CPG). Morphological alterations of the craniofacial skeleton resulting from lesions to the TMNu were likely due to changed neuromuscular activity patterns of the masticatory muscles and their biomechanical effects upon bone.