J Orofac Pain 32 (2018), No. 3 9. Aug. 2018
J Orofac Pain 32 (2018), No. 3 (09.08.2018)
Changes in Type I and Type II Collagen Expression in Rat Mandibular Condylar Cartilage Associated with Aging and Dietary Loading
Orajärvi, Marko / Laaksonen, Sakari / Hauru, Riikka / Mursu, Eerika / Jonaviciute, Egle / Voipio, Hanna-Marja / Raustia, Aune / Pirttiniemi, Pertti
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 repeatedmeasures 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.
Keywords: age-related changes, diet board, joint loading, mandibular condylar cartilage, rat, type I collagen, type II collagen