VITAMIN-D METABOLITES REGULATE MATRIX VESICLE METALLOPROTEINASE CONTENT IN A CELL MATURATION-DEPENDENT MANNER

Matrix vesicles are extracellular organelles produced by cells that mi neralize their matrix. They contain enzymes that are associated with c alcification and are regulated by vitamin D metabolites in a cell matu ration-dependent manner. Matrix vesicles also contain metalloproteinas es that degrade proteoglycans, macromolecules known to inhibit calcifi cation in vitro, as well as plasminogen activator, a proteinase postul ated to play a role in activation of latent TGF-beta. In the present s tudy, we examined whether matrix vesicle metalloproteinase and plasmin ogen activator are regulated by 1,25(OH)(2)D-3 and 24,25(OH)(2)D-3. Ma trix vesicles and plasma membranes were isolated from fourth passage c ultures of resting zone chondrocytes that had been incubated with 10(- 10)-10(-7) M24,25(OH)(2)D-3 or growth zone chondrocytes incubated with 10(-11)-10(-8) M 1,25(OH)(2)D-3, and their alkaline phosphatase, acti ve and total neutral metalloproteinase, and plasminogen activator acti vities determined. 24,25(OH)(2)D-3 increased alkaline phosphatase by 3 5-60%, decreased active and total metalloproteinase by 75%, and increa sed plasminogen activator by fivefold in matrix vesicles from resting zone chondrocyte cultures. No effect of vitamin D treatment was observ ed in plasma membranes isolated from these cultures. In contrast, 1,25 (OH)(2)D-3 increased alkaline phosphatase by 35-60%, but increased act ive and total metalloproteinase three- to fivefold and decreased plasm inogen activator by as much as 75% in matrix vesicles isolated from gr owth zone chondrocyte cultures. Vitamin D treatment had no effect on p lasma membrane alkaline phosphatase or metalloproteinase, but decrease d plasminogen activator activity. The results demonstrate that neutral metalloproteinase and plasminogen activator activity in matrix vesicl es are regulated by vitamin D metabolites in a cell maturation-specifi c manner. In addition, they support the hypothesis that 1,25(OH)(2)D-3 regulation of matrix vesicle function facilitates calcification by in creasing alkaline phosphatase and phospholipase A(2) specific activiti es as well as metalloproteinases which degrade proteoglycans.