Hydrostatic pressure as epigenetic modulator in chondrocyte cultures: A study on miRNA-155, miRNA-181a and miRNA-223 expression levels.

Mechanical stimuli and hydrostatic pressure (HP) play an important role in the regulation of chondrocytes metabolism. Growing evidence demonstrated the ability of mechanical loading to modulate the expression of microRNA (miRNA) involved in chondrocytes homeostasis and in the pathogenesis of osteoarthritis (OA). The expression of miR-155, miR-181a and miR-223 in normal and OA chondrocyte cultures, and their potential modifications following exposure to three hours of a cyclic HP (1-5 MPa, frequency 0.25 Hz) were investigated. Also evaluated the expression of Chuk, regulator of the NF-kB pathway activation, which is a target gene of miR-223, was evaluated. Chondrocytes were collected immediately after pressurization (T0), and following 12, 24, and 48 h. Total RNA was extracted, reverse transcribed and used for real-time PCR. At basal condition, a significant increase of miR-155 and miR-181a was observed in OA in comparison to normal cells; on the contrary, no differences in miR-223 and Chuk expression levels were detected between normal and OA chondrocytes. miR-155 and miR-181a resulted significantly downregulated immediately after pressurization (T0) in OA cells. The pressure effect on miR-155 and miR-181a levels was maintained over time. No modifications of miR-223 were observed in response to HP, while Chuk levels resulted significantly reduced at T0 and after 12 h. Pressurization did not cause any modifications in normal cells. In conclusion, HP was able to modulate the expression of miRNA associated to OA pathogenesis. The preliminary results about Chuk response to pressure raised interest in its involvement in the possible HP induced NF-kB pathway modulation.