S13.3 TLR2 DOWNREGULATION AS A POTENTIAL THERAPEUTIC TARGET IN GRAM(+) SEPTIC ARTHRITIS

Abstract

Septic arthritis induced by Staphylococcus aureus causes a rapid destruction of joint cartilage and periarticular bone. The mechanisms behind this phenomenon are not fully understood. Toll-like receptors (TLRs) are essential in host defense against pathogens by virtue of their capacity to detect microbes and initiate the immune response. TLR2 is seen as the most important receptor for gram-positive bacteria. TLR2 signaling can lead to the activation of NF-kB through myeloid differentiation factor 88 (MyD88) dependent pathway. The purpose of this study was to examine the catabolic role of TLR2 mediated by the NF-kB pathway in human septic arthritic chondrocytes.

Septic arthritic (SA) chondrocytes (n=7) and fibroblast-like synoviocytes (n=7) infected by gram-positive bacteria, mainly Staphylococcus aureus, as well as chondrocytes from healthy individuals (n=5) were used for this study.

The expression of TLR2 in septic articular cartilage and normal cartilage was analyzed by real time reverse transcription polymerase chain reaction as well western blot analysis. Production of matrix metalloproteinase MMP- 13 and IL-1b was evaluated by enzyme-linked immunosorbent assay. MyD88 protein expression levels and NF-kB activation were evalutated by western blot analysis. Downregulation of TLR2 expression was achieved after transfection with specific siRNA against TLR2 using liposomes.

We observed that TLR2 mRNA and protein expression was significantly up-regulated in septic arthritic cartilage. Also MMP-13 and IL-1b production were significantly increased in septic arthritic chondrocytes compared to normal. Blocking TLR2 in septic chondrocytes resulted in significant reduction of MyD88 and NF-kB protein levels as well as reduction in MMP-13 and IL-1b expression.

It could be suggested that stimulation of TLRs by microbial components may represent the initial signal promoting a pro-inflammatory environment that will enhance degeneration of articular cartilage and the surrounding synovial cells. Targeting NF-kB signalling pathway through TLR2 gene silencing may be of potential therapeutic value in treatment of joint diseases.