Metabolic effects of vitamin D active metabolites in monolayer and micromass cultures of nucleus pulposus and annulus fibrosus cells isolated from human intervertebral disc

Abstract Intragenic polymorphisms in the vitamin D receptor gene are linked to disc degeneration features, suggesting that alterations in the vitamer-mediated signalling could be involved in the pathophysiology of the disc and that interaction of disc cells with vitamin D metabolites may be critical for disc health. The vitamer-mediated modulation of disc cells proliferation, metabolic activity, extracellular matrix (ECM) genes expression and proteins production was investigated. It was stated that disc cells express vitamin D receptor and are very sensitive to metabolic stimuli. In monolayer cultures, 1,25(OH) 2 D 3 , but not 24,25(OH) 2 D 3 , determined an inhibition of the proliferation and regulated also the ECM genes expression in nucleus pulposus and annulus fibrosus cells. Micromass cultures induced a more physiologic expression pattern of extracellular matrix genes. Cells Treatment with vitamin D metabolites did not result in relevant modifications of glycosaminoglycans production, except for annulus cells, whose production was reduced after 1,25(OH) 2 D 3 treatment. Moreover, a reduced glycosaminoglycans staining in both cell types and a significant reduced aggrecan gene expression in annulus cells treated with 1,25(OH) 2 D 3 were observed. A reduction of collagen I and II staining in annulus cells 1,25(OH) 2 D 3 treated, in accordance with a downregulation of collagen genes expression, was also registered. Finally, the vitamin D receptor gene expression did not show significant metabolite-mediated modification in monolayer or micromass cultures. These findings could enhance new insights on the biochemical mechanisms regulated by vitamin D in disc cartilage and possibly involved in the development of physiological/pathological modifications of the disc.