Affiliations: Department of Anatomy, Institute of Biomedicine, University of Kuopio, Kuopio, Finland | Department of Physics, University of Kuopio, Kuopio, Finland | Department of Clinical Neurophysiology, Kuopio University Hospital and University of Kuopio, Kuopio, Finland | Department of Clinical Physiology and Nuclear Medicine, Kuopio University Hospital and University of Kuopio, Kuopio, Finland
Note: [] Equal contribution to the work.
Note: [] Equal contribution to the work.
Note: [] Address for correspondence: Mikko Lammi, Department of Anatomy, Institute of Biomedicine, University of Kuopio, PO Box 1627, 70211 Kuopio, Finland. Fax: +358 17 163032; E-mail: mikko.lammi@uku.fi.
Abstract: Mechanical forces can stimulate the production of extracellular matrix molecules. We tested the efficacy of ultrasound to increase proteoglycan synthesis in bovine primary chondrocytes. The ultrasound-induced temperature rise was measured and its contribution to the synthesis was investigated using bare heat stimulus. Chondrocytes from five cellular isolations were exposed in triplicate to ultrasound (1 MHz, duty cycle 20%, pulse repetition frequency 1 kHz) at average intensity of 580 mW/cm2 for 10 minutes daily for 1–5 days. Temperature evolution was recorded during the sonication and corresponding temperature history was created using a controllable water bath. This exposure profile was used in 10-minute-long heat treatments of chondrocytes. Heat shock protein 70 (Hsp70) levels after one-time treatment to ultrasound and heat was analyzed by Western blotting, and proteoglycan synthesis was evaluated by 35S-sulfate incorporation. Ultrasound treatment did not induce Hsp70, while heat treatment caused a slight heat stress response. Proteoglycan synthesis was increased approximately 2-fold after 3–4 daily ultrasound stimulations, and remained at that level until day 5 in responsive cell isolates. However, chondrocytes from one donor cell isolation out of five remained non-responsive. Heat treatment alone did not increase proteoglycan synthesis. In conclusion, our study confirms that pulsed ultrasound stimulation can induce proteoglycan synthesis in chondrocytes.
