Ultrasound stimulation of types I and III collagen expression of tendon cell and upregulation of transforming growth factor β

Traumatic tendon injuries are commonly treated with ultrasound. However, previous research has not examined the molecular mechanism of this therapeutic effect on collagen synthesis of tendon cells. This study was designed to determine the effect of ultrasound on the expression of type I and type III collagen of tendon cells intrinsic to rat Achilles tendon. Whether a correlation exits between this effect and the expression of transforming growth factor β (TGF-β), which enhances collagen synthesis, was also investigated. Tendon cells after ultrasound treatment and protein expression of types I and III collagen were determined by immunocytochemistry. The mRNA expressions of α1(I) procollagen, α1(III) procollagen, and TGF-β were determined by reverse transcription-polymerase chain reaction (RT-PCR). Furthermore, the concentration of TGF-β in conditioned medium was evaluated by enzyme-linked immunosorbent assay (ELISA). Immunocytochemical staining revealed that ultrasound-treated tendon cells were stained more strongly for types I and III collagen than were control cells. Upregulation of procollagen α1(I) gene, procollagen α1(III) gene, and TGF-β at the mRNA level was confirmed by RT-PCR. A dose-dependent increase in the concentration of TGF-β in conditioned medium obtained from cells treated with ultrasound was demonstrated by ELISA assay (p = 0.043). In conclusion, ultrasound stimulates the expression of type I and type III collagen in a process that is likely mediated by the upregulation of TGF-β.