Ultrasound stimulation of tendon cell proliferation and upregulation of proliferating cell nuclear antigen

Therapeutic ultrasound has been widely used in sports-related tendon injuries. However, previous research has not examined the molecular mechanism of this therapeutic effect on tendon cell proliferation. This study was designed to determine the in vitro effect of ultrasound on the proliferation of tendon cells intrinsic to rat Achilles tendon. Furthermore, the existence of a correlation between this effect and the expression of the proliferating cell nuclear antigen (PCNA) was also examined. Using cultured tendon cells, cell viability was evaluated by MTT assay. The expression of PCNA protein in cells was evaluated by immunocytochemistry. The mRNA expression of PCNA was determined by reverse transcription-polymerase chain reaction (RT-PCR). A dose-dependent increase in the cellularity of tendon cells by either pulsed or continuous mode ultrasound was demonstrated by MTT assay (p = 0.044 for the pulsed mode; p = 0.004 for the continuous mode). Ten minutes of treatment achieved maximum cellularity compared to 5 min of treatment time (p = 0.010 for pulsed ultrasound; p = 0.004 for continuous ultrasound). Immunocyto-chemical staining revealed that ultrasound treated tendon cells were stained more strongly for PCNA than were control cells. Upregulation of PCNA at the mRNA level was also confirmed by RT-PCR. In conclusion, ultrasound stimulates tendon cell proliferation in a process that is probably mediated by the upregulation of PCNA.