Compressive force promotes chondrogenic differentiation and hypertrophy inmidpalatal suture cartilage in growing rats

Midpalatal suture cartilage (MSC) is secondary cartilage located between th e bilateral maxillary bones and has been utilized in the analysis of the bi omechanical characteristics of secondary cartilage. The present study was d esigned to investigate the effects of compressive force on the differentiat ion of cartilage in midpalatal suture cartilage in rats. Forces of various magnitudes were applied to the midpalatal suture cartilage in 4-week-old ma le Wistar rats for 1, 2, 4, 7, or 14 days, mediated through the bilateral I st molars using orthodontic wires. The differentiation pathways in the MSC cells were examined by immunohistochemistry for the differentiation markers type I, type II and type X collagen, and glycosaminoglycans (GAGs), chondr oitin-4-sulfate, condroition-6-sulfate and keratan sulfate. Histologically and immunohistochemically, the midpalatal suture cartilage in control rats had the characteristic appearance of secondary cartilage. In the experiment al groups, the center of the midpalatal suture cartilage that contained ost eo-chondro progenitor cells seemed to become mature cartilage and its immun e-reaction to type II and X collagen and GAGs increased as the experiment p rogressed. This differentiation was dependent upon the magnitude and durati on of the force applied to the midpalatal suture cartilage; i.e., cartilagi nous differentiation progressed more rapidly as the applied force increased . The present results suggest that the differentiation of osteo-chondro pro genitor cells into mature and hypertrophic chondrocytes in the precartilagi nous cell layer is promoted by compressive force. Anat Rec 260:392-401, 200 0. (C) 2000 Wiley-Liss, Inc.