Changes in Type I and Type II Collagen Expression in Rat Mandibular Condylar Cartilage Associated with Aging and Dietary Loading.

AIMS: To evaluate the usefulness of diet board feeding as a model for temporomandibular joint (TMJ) research, characterize dietary loading-related morphometric changes in the mandibular condylar cartilage of aging rats, and investigate changes in type I and type II collagen expression in different age, sex, and diet groups. METHODS: Material was collected from a study that examined the effects of 1-year and 2-year diet board feeding on rats. In diet board feeding, rats must gnaw wood to reach their food, leading to a higher masticatory workload. The material analyzed was comprised of 150 TMJ samples from 75 Hsd:Sprague Dawley rats grouped according to feeding method (diet board [experimental group] or ad libitum [control group]), sex, and experiment length (1 or 2 years). The rats were sacrificed at the age of 15 or 26 months (15-M rats or 26-M rats). From the TMJ samples, 5-µm-thick sections were cut parallel to the sagittal plane of the mandibular condyle. Histomorphometric analysis of the thickness of the condylar cartilage and the number of cartilage cells was performed after toluidine blue staining. Immunohistochemical staining included type I and type II collagen antigens. Differences in the thickness of the cellular layer and the number of cells in the condylar cartilage were analyzed by means of a repeated-measures analysis of variance (ANOVA) model, and differences in the type of collagen with a one-way random-effects ANOVA model. RESULTS: Condylar cartilage was significantly thicker in the 15-M diet board-fed rats than in the 15-M control rats and in the 26-M rats than in the 15-M rats. The number of cells was larger in the 26-M female rats than in the 26-M male rats. Type I collagen expression was significantly higher in the 15-M diet board-fed female rats than in the 15-M controls. Type II collagen showed increased expression in older rats compared to younger rats. CONCLUSION: Condylar cartilage is sensitive to the interplay between loading, aging, and sex of middle-aged and older rats. High loading of condylar cartilage increased the thickness of cartilage in younger rats.

Effect of Estrogen and Food Hardness on Metabolism and Turnover of Condylar Cartilage.

AIMS: To clarify the effect of estrogen and food hardness on condylar cartilage and the cartilage-bone interface. METHODS: A total of 56 rats were divided into four groups: (1) ovariectomized rats fed a normal (pressed pellet) food, (2) ovariectomized rats fed a soft (powder) food, (3) control rats fed a normal (pressed pellet) food, and (4) control rats fed a soft (powder) food. Some rats (n = 29) were sacrificed at the age of 67 days and others (n = 27) at the age of 87 days, and then 5-µm-thick sagittal paraffin sections were prepared from each temporomandibular joint (TMJ). Toluidine blue staining, in situ hybridization with type X collagen, terminal deoxynucleotidyl transferase and deoxyuridine triphosphate nick end labeling (TUNEL-assay), and tartrate-resistant acid phosphatase (TRAP) histochemistry were performed. Immunohistochemical analyses included cathepsin K, adiponectin, proliferating cell nuclear antigen (PCNA), and type X collagen staining. Analysis of variance and appropriate post-hoc tests were used in all analyses. RESULTS: Ovariectomy and normal food consistency increased the thickness of condylar cartilage (P < .001), PCNA expression (P < .001) and type X collagen expression (P < .001). Ovariectomy decreased the number (P < .05) and size of osteoclasts (P < .01). Soft food increased the number of cartilage cells stained positively against adiponectin (P < .01). CONCLUSION: Decreased estrogen level and normal food hardness increase the thickness of condylar cartilage by various mechanisms.

Effect of estrogen and dietary loading on condylar cartilage.

AIMS: To study the effect of estrogen deficiency and altered temporomandibular joint loading on the histomorphology of condylar cartilage and on the expression of types II and X collagen and matrix metalloproteinase-3 (MMP-3). METHODS: Thirty-six female rats were divided into four groups: ovariectomized rats on a normal diet, nonovariectomized control rats on a normal diet, ovariectomized rats on a soft diet, and nonovariectomized control rats on a soft diet. Ovariectomy was performed at the age of 60 days. Repeated-measures ANOVA was used to analyze the data. RESULTS: The condylar cartilage in the ovariectomized normal diet group showed a significantly higher number of cells than in the nonovariectomized control rats (P < .001). The proportional amount of MMP-3 expression was significantly higher in the ovariectomized rats than in the nonovariectomized control rats in both diet groups (P < .001). The area covered by types II and X collagen was significantly higher in the experimental groups than in the control groups (P < .01). CONCLUSION: Condylar cartilage is sensitive to both estrogen level and dietary loading.

Effect of estrogen and altered diet hardness on the expression of estrogen receptor alpha and matrix metalloproteinase-8 in rat condylar cartilage.

AIMS: To examine the effect of decreased estrogen level and altered diet hardness on condylar cartilage morphology of the rat temporomandibular joint (TMJ) and on the expression of condylar cartilage estrogen receptor alpha (ERa) and matrix metalloproteinase-8 (MMP-8). METHODS: A total of 36 female rats was divided into four groups: ovariectomized rats fed a normal diet, non-ovariectomized controls fed a normal diet, ovariectomized rats fed a soft diet, and non-ovariectomized controls fed a soft diet. Ovariectomy was performed at the age of 60 days. Seven days after the operation, the rats were sacrificed. Repeated measures ANOVA and Duncan's multiple comparison tests were used for statistical analysis. RESULTS: The ovariectomized rats had thicker cartilage layers than the controls, both in the normal diet and soft diet groups. The thinnest cartilage layers were found in the control rats fed with the soft diet. The thickness of the chondroblastic layer was significantly higher (P < .001) in the normal-diet rats than in the soft-diet rats in both ovariectomized and non-ovariectomized groups. The thickness of the proliferative layer was significantly higher (P < .001) in the ovariectomized soft-diet rats than in the soft-diet control rats. The proportional amount of ERa was statistically significantly higher (P < .001) in the condylar cartilage of the ovariectomized rats than in the non-ovariectomized control rats both in the normal- and soft-diet groups. The proportional amount of ERa was statistically significantly higher (P < .001) in the ovariectomized normal-diet rats than in the ovariectomized soft-diet rats. The proportional number of MMP-8-positive cells was statistically significantly higher (P < .001) in the condylar cartilage of ovariectomized rats fed the soft diet than in non-ovariectomized control rats fed the soft diet. Control rats fed with the normal diet had a higher proportional amount of MMP-8 positive cells than control rats fed with the soft diet (P < .05). CONCLUSION: The rat TMJ condylar cartilage is sensitive to changes in estrogen levels and altered diet hardness.