The Intensity of Low-intensity Pulsed Ultrasound Influences Chondrocyte Differentiation

Objectives: Low-intensity pulsed ultrasound (LIPUS) is used for bone healing in orthopedics. Compared to a placebo treatment, 30 mW/cm2 LIPUS could accelerate fracture repair by about 38% (Thomas K et al., J BONE JOINT SURG 1997). However, reports on the influence of LIPUS on chondrocytes have been few and far between. In this study, we investigated the effects of LIPUS intensity on the expression of extracellular matrix proteins (ECMPs) in chondrocytes.
Methods: ATDC5 cells were plated on a 6-well plate. After confluence, the cells were cultured in a differentiation medium for 14 days. They were then stimulated with a LIPUS intensity of 30 and 60 mW/cm2 for 20 min /day using OSTEOTRON D2, for a maximum of 14 days. The mRNA expression of Aggrecan, Sox9，Collagen type II (Col II), and Collagen type X (Col X) was determined using real-time PCR . ALPase activity was determined using ALP staining.
Results: After 5 days of 60 mW/cm2 LIPUS stimulation, gene expression levels of Sox9, Aggrecan, and Col II were significantly increased compared to those in the control. After 7 days of the stimulation, Aggrecan and Col X gene expression levels were significantly increased compared to those in the control. The ALPase staining increased in a LIPUS intensity-dependent manner after 14 days of stimulation.
Conclusions: These results suggest that LIPUS can promote differentiation and ECMPs in chondrocytes, and LIPUS intensity can have different effects on chondrocyte differentiation.