Objective: Intra-articular injection of hyaluronan (HA) has been suggested to have disease-modifying effect in osteoarthritis, but little is known about the possible mechanisms. The present study was undertaken to investigate the effects of HA with different molecular weight including 800 kDa (HA800) and 2700 kDa (HA2700) on the expression of aggrecanases, i.e. ADAMTS species, that play a key role in aggrecan degradation.
Methods: Effects of HA species on the expression of ADAMTS1, 4, 5, 8, 9 and 15 in interleukin-1α (IL-1α)-stimulated osteoarthritic chondrocytes were studied by RT-PCR and real-time PCR. Expression of ADAMTS4 protein and aggrecanase activity and signal transduction pathways of IL-1, CD44 and ICAM-1 were examined by immunoblotting.
Results: IL-1α treatment of chondrocytes induced ADAMTS4, and HA800 and HA2700 significantly decreased the mRNA and protein expression levels of IL-1α-induced ADAMTS4. IL-1α-stimulated aggrecanase activity in osteoarthritic chondrocytes was reduced by treatment with HA2700 or transfection of siRNA for ADAMTS4. A similar finding was obtained by adding HA2700 to explant cultures of osteoarthritic cartilage. HA2700 neither directly inhibited nor did it bind to ADAMTS4. Down-regulation of ADAMTS4 expression with HA2700 was attenuated by treatment of IL-1α-treated chondrocytes with anti-CD44 antibody and/or anti-ICAM-1 antibody. Increased phosphorylation of IL-1 receptor-associated kinase-1 (IRAK-1) and ERK1/2 by the IL-1α treatment was down-regulated by enhanced IRAK-M expression after HA2700 treatment.
Conclusion: These data suggest that HA2700 suppresses the aggrecan degradation by down-regulation of the IL-1α-induced ADAMTS4 expression through the CD44 and ICAM-1 signaling pathways in osteoarthritic chondrocytes.