Stimulation of the Gene and Protein Expression of Chondrocytes Seeded in Chitosan Scaffolds by Ultrasound

In this study, a low-intensity diffuse ultrasound (LIDUS) signals at 5.0 MHz (0.14 mW cm³) was employed to stimulate bovine chondrocytes seeded in 3D chitosan-based matrices. While the duration of application was constant at 51 sec, US was applied 1-time, 2-times, 4-times and 8-times per day, and the impact of US on the biosynthetic activity of chondrocytes and the expression of chondrocyte-specific genes were evaluated. When stimulated with continuous US for predetermined time intervals, chondro-
cytes had higher levels of type-II collagen, aggrecan, L-Sox5, and Sox9 mRNA expression when compared to controls, however, under the same conditions, the expression of MMP-3 was down regulated. Interestingly, both Sox5 and Sox9 genes coordinately responded to changes in US stimulation and generally mirrored the response of collagen type-II transcript to changes in US stimulation. RT-PCR analysis revealed that US stimulation increased the gene expression of cell-surface integrins a5 and B1. The expression of integrins a2 was down regulated by US treatment, suggesting that multiple integrin subunits may be involved in the regulation of chondrocytic function in response to US stimuli. The enhancement in the abundance of the mRNA transcripts upon US stimulation was observed to correlate with the protein expression of collagen type-I, collagen type-II, and integrins as and B1. In conclusion, US stimulation regimen employed was shown to modulate the proliferative capacity, biosynthetic activity, and integrin mRNA expression of articular chondrocytes maintained in 3D matrices.