Mitogen-activated protein kinase-activated protein kinase 2 (MK2) modulates key biological pathways associated with OA disease pathology

Abstract

Objective: To examine the role of mitogen-activated protein kinase-activated protein kinase 2 (MK2) in mediating the cellular response to pro-inflammatory cytokines in human primary osteoarthritis (OA) chondrocytes.

Methods: Delivery of a dominant negative MK2 was achieved in HeLa cells by adenoviral infection. Cellular heat shock protein (HSP27) activity was determined using a Bioplex assay. Primary OA chondrocytes were isolated by collagenase digestion of human articular cartilage. Phosphorylated MK2 was detected by immunoblotting and immunohistology. Transfection of primary chondrocytes with siRNA was achieved using cationic lipid and gene expression determined by real-time polymerase chain reaction. Production of prostaglandin E2 (PGE2) and matrixmetalloproteases (MMPs) was measured by enzyme-linked immunosorbent assay.

Results: Over-expression of a dominant negative MK2 inhibited HSP27 phosphorylation and significantly reduced both interleukin 1 (IL-1)beta and tumour necrosis factor (TNF)-alpha mediated release of PGE2 in HeLa cells over a 24h period. Phosphorylated MK2 was detected in OA articular cartilage and in isolated primary OA chondrocytes, where it was induced by IL-1beta. Transfection of OA chondrocytes with MK2 siRNA antisense significantly reduced both basal and IL-1beta induced PGE2 release. siRNA mediated MK2 knockdown also significantly reduced both basal and IL-1beta induced MMP13 expression and MMP13 and MMP3 protein release but had no effect on MMP1.

Conclusions: Our data reveal that MK2 is active in OA human articular cartilage and in isolated primary human chondrocytes and that MK2 mediates the release of PGE2, MMP3 and MMP13. These findings suggest a role for MK2 in contributing to OA algesia and OA joint structural deterioration by mediating the downstream effects of p38 activation on PGE2 release and the expression and release of catabolic proteases.