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Abstract: Low-intensity pulsed ultrasound (LIPUS) has been shown to accelerate fracture healing, but the precise mechanism is still unknown. We used aggregate chondrocyte culture system to analyze LIPUS-induced effects on chondrocytes. First, Northern analyses revealed that LIPUS maintained higher expression levels of type II collagen and aggrecan mRNA and delayed the appearance of type X collagen mRNA expression. We also showed that DNA content was increased and that alkaline phosphatase activity was maintained low by daily treatment. Moreover, LIPUS significantly promoted transforming growth factor (TGF)-β1 mRNA expression and the protein production at 2 h and 12 h after the treatment, respectively. Furthermore, recombinant TGF-β1 protein mimicked the LIPUS effect and anti-TGF-β1 neutralizing antibody reversed all these changes induced by the LIPUS treatment. These results indicate that LIPUS promotes the proliferation and retains the differentiation state of chondrocytes in the aggregate culture and that TGF-β1 plays an important role in mediating the LIPUS effects in chondrocytes. (E-mail: smukai@kyotolan.hosp.go.jp) [Copyright &y& Elsevier]