Edinburgh Napier University

  NMDA receptors (NMDAR) are expressed by chondrocytes in
articular cartilage although their function is yet to be fully
understood. NMDAR are ionotropic glutamate receptors which
when excessively stimulated in neurones induce cell death and
neuronal degeneration. In osteoarthritis (OA) chondrocyte death
is recognised to be important and associated with matrix loss and
cartilage degeneration. The aim of this study was to identify if
activation of chondrocyte NMDAR influences cell survival and
influences matrix production or breakdown.
Materials and Methods
Rat femoral heads. normal and OA human articular chondrocytes
(HACs) were used. Femoral heads treated with NMDA (50µM
and/or 1mM) for 72 hours, were fixed and stained to assess cell
death (live/dead and TUNEL assays) and proteoglycan content
(toluidine blue). HACs were cultured in monolayer before
treatment with 50µM NMDA for up to 24 hours, RNA extracted
and cartilage matrix and protease gene expression analysed by
RT-PCR.
Results
Excessive stimulation of NMDAR led to an increase in cell death
and loss of proteoglycan in rat femoral heads. Stimulation of
HACs with NMDA resulted in changes in gene expression. In
normal chondrocytes the expression of MMP-3 was reduced,
TIMP-1 was increased and aggrecan, collagen II, and MMP-13
were unaffected. In OA chondrocytes collagen II, MMP-13, and
TIMP-1 were reduced while aggrecan and MMP-3 gene
expression were unaffected.
Discussion
The results in this study indicate that stimulation of NMDAR in
chondrocytes has the potential to modify cartilage structure.
Excessive stimulation of normal cartilage was able to induce cell
death and reduction of proteoglycan expression. Analysis of
matrix molecule gene expression in human chondrocytes after
NMDAR stimulation from both normal and OA cartilage indicates
that there is a shift from a more anabolic (↓ MMP-3, ↑ TIMP-1) to
a more catabolic (↓ collagen, TIMP-1) gene expression profile in
OA chondrocytes.