Cyclic tensile stretch load and oxidized low density lipoprotein synergistically induce lectin-like oxidized LDL receptor-1 in cultured bovine chondrocytes, resulting in decreased cell viability and proteoglycan synthesis

Mechanical stimulation is known to be an essential factor in the regulation of cartilage metabolism. We tested the hypothesis that expression of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) can be modulated by cyclic tensile stretch load in chondrocytes. Cyclic loading of repeated stretch stress at 10 cycles per minute with 10 kPa of stress for 6 h induced expression of LOX-1 to 2.6 times control in cultured bovine articular chondrocytes, equivalent to the addition of 10 mu g/mL oxidized low density lipoprotein (ox-LDL) (2.4 times control). Application of the cyclic load to the chondrocytes along with 10 mu g/mL ox-LDL resulted in synergistically increased LOX-1 expression to 6.3 times control. Individual application of cyclic loading and 10 mu g/mL ox-LDL significantly suppressed chondrocytes viability (84.6% 3.4% and 80.9% 3.2% of control at 24 h, respectively; n = 3; p < 0.05) and proteoglycan synthesis [81.0% 7.1% and 85.7% 5.2% of control at 24 h, respectively; p < 0.05 when compared with 94.6% 4.6% for native-LDL (n = 3)]. Cyclic loading and 10 mu g/mL ox-LDL synergistically affected cell viability and proteoglycan synthesis, which were significantly suppressed to 45.6% 4.9% and 48.7% 6.7% of control at 24 h, respectively (n 3; p < 0.01 when compared with individual application of cyclic loading or 10 mu g/mL ox-LDL). In this study, we demonstrated synergistic effects of cyclic tensile stretch load and ox-LDL on cell viability and proteoglycan synthesis in chondrocytes, which may be mediated through enhanced expression of LOX-1 and which has important implications in the progression of cartilage degeneration in osteoarthritis. (c) 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.