Mechanical compression afffects proteoglycan synthesis by growthplate chondrocytes

Objectives: Longitudinal growth of the appendicular skeletons such as the mandibular condyle is achieved by the transformation termed as endochondral bone formation of growth plate. It is well known that mechanical stimulus is a principal factor regulating longitudinal endochondral bone growth. In orthopedic treatment mandibular condyle is subjected to various types of mechanical forces. In our previous study, cyclic mechanical tensile stress with a frequency of 30 cycles/min (loading and relaxation for every alternate second) enhanced the proliferate rate of growth plate chondrocytes and the synthesis of cartilage matrix in monolayer cultures. This study was thus conducted to examine the effects of mechanical compression stress on the proliferation and proteoglycan synthesis of growth plate chondrocytes in 3-dimensional cultures. Methods: Chondrocytes were isolated from rib growth plate of 4-week-old Wistar strain male rats, and embedded in type I collagen 3-D gels. Then a 3 kPa static (constant force magnitude) or cyclic (30 cycles/min) compression stress was applied by FX-4000C at the matrix forming stage for 0, 12 and 24 hours. The number of chondrocytes was measured by total DNA quantity. The rate of proteoglycan synthesis was determined by measuring the incorporation of [35S]sulfate. Results: Proteoglycan synthesis was enhanced by cyclic compression stress but suppressed by the static one time-dependently. Conclusions: These findings suggest that mechanical compression stress exerts a certain anabolic action for proteoglycan synthesis of growth plate chondrocytes, and the effect is more prominent with cyclic stress than with static one.