To examine the in situ distributions of vitamin D receptors (VDR) and matrix metalloproteinases (MMPs) in osteoarthritic cartilage for comparison with non-arthritic, normal cartilage; and to assess the in vitro effects of 1alpha,25 dihydroxyvitaminD(3)(1alpha,25(OH)(2)D(3)) on MMPs-1, -3 and -9 and prostaglandin E(2)(PGE(2)) production by cultures of human articular chondrocytes (HAC) shown to be VDR-positive.
Using immunohistochemistry VDR expression in different specimens of osteoarthritic cartilage (N=11) was compared to that in normal cartilage (N=6), along with the immunodetection of MMPs-1, -3 and -9. The effects of 1alpha25(OH)(2)D(3)on MMP and PGE(2)production by HAC in vitro, with and without stimulation by TNFalpha or phorbol myristate acetate (PMA), was evaluated using ELISA methodology.
VDR was demonstrated in HAC of all specimens of osteoarthritic cartilage, especially the superficial zone, whereas only two of five normal cartilage specimens were VDR(+)for a minor proportion of HAC. Immunolocalization of MMPs-1, -3 and -9 was often seen in areas where chondrocytes were VDR(+), and dual immunolocalization has demonstrated individual chondrocytes positive for both VDR and MMP-3 in situ. In vitro, 1alpha25(OH)(2)D(3)alone had no effect on MMP-1, -9 and PGE(2)production by HAC, but MMP-3 production was up-regulated by 1alpha25(OH)(2)D(3)either with or without stimulation with TNFalpha or PMA. By contrast the increased production of MMP-9 and PGE(2)induced by PMA was significantly suppressed by concomitant treatment with 1alpha25(OH)(2)D(3).
The demonstration of VDR expression by HAC in osteoarthritic cartilage was often associated with sites where MMP expression was prevalent, observations in contrast to their virtual absence in normal age-matched cartilage. Together with HAC in vitro studies, the data suggests that 1alpha25(OH)(2)D(3)contributes to the regulation of MMP and PGE(2)production by HAC in osteoarthritic cartilage.