Endocrine Abstracts

Vascular calcification is a regulated process with similarities to osteogenesis, however, the precise mechanism underlying this process is poorly understood. Pericytes are pluripotential microvascular cells which have been shown to differentiate along an osteogenic lineage. Glucocorticoids are widely prescribed drugs but have adverse side-effects including both vascular lesion formation and bone loss. The mechanism underpinning the contrasting effects of dexamethasone (dex) on the formation and loss of bone by vascular and bone cells, respectively, remains to be determined. We investigated the effects of dex on mineralisation of vascular pericytes in vitro to test the hypothesis that a loss in inhibitory molecules would be accompanied by an enhanced rate of mineralisation. Dex treatment of pericytes for 3 weeks showed no change in their proliferation pattern within the first week, but an enhanced rate of differentiation and mineralisation. After 3 weeks of dex treatment results show i), a 3.4 fold increase in the number of nodule-forming cells, ii), a 2.6 fold increase in alkaline phosphatase activity and iii), a 10.2 fold increase in calcium deposition in dex-treated cells vs untreated cells. We have previously isolated a novel gene C15 and shown high expression in both mineralised cells in vitro and ethically approved calcified tissue sections, suggesting its involvement in the mineralisation process. Using slot- and Northern blot analysis, we investigated the expression of C15 together with two other genes, Matrix Gla protein (MGP) and osteopontin which are also associated with vascular calcification. Although all three mRNA transcripts are up-regulated when pericytes differentiate in vitro, dex treatment down regulates the expression of MGP and osteopontin, but has little effect on C15. These results suggest that the dex-stimulation of pericyte osteogenic differentiation occurs by down-regulating MGP and osteopontin, which are proposed inhibitors of vascular mineralisation.