Effects of Low Intensity Ultrasound on the Chondrogenic Differentiation of Adult Stem Cells From Adipose Tissue

Background Adult stem cells from adipose tissue can be used in tissue engineering because of their capacity to differentiate into chondrocytes. Low intensity ultrasound (LIUS) as a physical chondrogenic inducer differentiates adipose stem cells (ASC) into chondrocyte the same as transforming growth factor-β (TGFβ). However the stage of differentiation and hypertrophy of chondrocytes by LIUS have not yet been studied. Objectives The aim of this study was to determine the effect of LIUS on hypertrophic states of differentiated chondrocytes. Materials and Methods In this experimental study, ASCs were cultured in chondrogenic differentiation medium (10 ng/mL of TGFβ) with or without LIUS stimulation for two weeks. The ultrasound signal was applied at an intensity of 200 mW/cm² for 10 min/day. For evaluation, the mRNA expression of collagen type X, alkaline phosphatase, Runx2 and Runx2II, were studied using quantitative gene expression method. Histologic and immunohistochemistry evaluations were performed. The data were analyzed by one way ANOVA (Tukey’s). Results The mRNA expression of collagen type X, and alkaline phosphatase, Runx2 and Runx2II were decreased markedly by the LIUS stimulation, whereas the expression of these genes drastically increased when TGFβ applied alone or with LIUS. LIUS containing cultures showed lower hypertrophic protein expression (alkaline phosphatase and Indian hedgehog) as compared with the controls. Conclusions Our results showed that LIUS suppresses hypertrophic chondrocyte formation and that LIUS induced chondrocytes are more suitable than TGFβ induced ones due to low expression of hyperthrophic markers in cartilage tissue engineering for clinical applications.