Dynamic compression influences interleukin-1β-induced nitric oxide and prostaglandin E 2 release by articular chondrocytes via alterations in iNOS and COX-2 expression

Abstract

Interleukin-1β (IL-1β) induces the release of nitric oxide (^·NO) and prostaglandin E₂ (PGE₂) by chondrocytes and this effect can be reversed with the application of dynamic compression. Previous studies have indicated that integrins may play a role. In addition, IL-1β upregulates the expression of iNOS and COX-2 mRNA via upstream activation of p38 MAPK. The current study examines the involvement of these pathways in mediating ^·NO and PGE₂ release in IL-1β stimulated bovine chondrocytes subjected to dynamic compression.

Bovine chondrocytes were seeded in agarose constructs and cultured with 0 or 10 ng·ml⁻¹ IL-1β with or without the application of 15% dynamic compressive strain at 1 Hz. Selected inhibitors were used to interrogate the role of α5β1 integrin signalling and p38 MAPK activation in mediating the release of ^·NO and PGE₂ in response to both IL-1β and dynamic compression. The relative expression levels of iNOS and COX-2 were assessed using real-time quantitative PCR. Nitrite, a stable end product of ^·NO, was measured using the Griess assay and PGE₂ release was measured using an enzyme immunoassay.

IL-1β enhanced ^·NO and PGE₂ release and this effect was reversed by the application of dynamic compression. Co-incubation with an integrin binding peptide (GRGDSP) abolished the compression-induced effect. Real-time quantitative PCR analysis revealed that IL-1β enhanced iNOS and COX-2 mRNA levels, with the maximum expression at 6 or 12 hours. Dynamic compression reduced this effect via a p38 MAPK sensitive pathway. These results suggest that dynamic compression acts to abrogate of ^·NO and PGE₂ release by directly influencing the expression levels of iNOS and COX-2.