Bone resorption induced by 1 alpha,25 dihydroxyvitamin D(3) in vivo is not altered by inactivation of the plasminogen activator inhibitor 1.
One of the proteolytic systems produced by bone cells is the plasminogen activator/plasmin pathway, which involves the two plasminogen activators and the type 1 plasminogen activator inhibitor (PAI-1) and results in plasmin generation. We have recently demonstrated that this pathway plays a specific role in the degradation of the nonmineralized matrix of bone in vitro. To evaluate whether PAI-1 is required during bone resorption in vivo, we studied the effects of PAI-1 inactivation on bone metabolism using systemic administration of 1alpha,25 dihydroxyvitamin D(3) [1, 25(OH)(2)D(3)] as model. PAI-1-deficient (PAI-1-/-) and wild-type (WT) mice were injected intraperitoneally with 1,25(OH)(2)D(3) (2 microg/kg) or vehicle every other day during 4 weeks and analyzed using biochemical parameters of bone turnover, histomorphometric analysis of the proximal tibial metaphysis, and pQCT analysis of the distal femoral metaphysis. PAI-1 inactivation did not affect bone metabolism in vehicle-treated mice. Treatment with 1,25(OH)(2)D(3) induced bone resorption similarly in PAI-1-/- and WT mice, as assessed by the increase in the urinary excretion of calcium (2. 2-fold and 2.3-fold, respectively) and of pyridinoline crosslinks (by 24% and 22%, respectively). In addition, a comparable reduction in bone mass was observed in PAI-1-/- and WT mice after treatment with 1,25(OH)(2)D(3), as evidenced by the decrease in the femoral calcium content (by 25% and 32%, respectively), in the trabecular bone volume (by 50% and 40%, respectively), in the trabecular mineral content (by 17% and 15%, respectively), and in the cortical mineral content (by 45% and 52%, respectively). The parameters of bone turnover also increased after 1,25(OH)(2)D(3) treatment. Serum osteocalcin was, respectively, 25% and 28% higher in PAI-1-/- and WT mice treated with 1,25(OH)(2)D(3) compared with the mice injected with vehicle. Similarly, the osteoid surface increased in 1, 25(OH)(2)D(3)-treated PAI-1-/- and WT mice by 40% and 51%, respectively, the mineral apposition rate increased by 15% and 8%, respectively, and the bone formation rate by 54% and 48%, respectively. These data indicate that PAI-1 is not critical during bone resorption induced by 1,25(OH)(2)D(3) in vivo.
Daci
E
E
Laboratorium voor Experimentele Geneeskunde en Endocrinologie, Katholieke Universiteit Leuven, Belgium.
Verstuyf
A
A
Moermans
K
K
Bouillon
R
R
Carmeliet
G
G
D000818:Animals; D016723:Bone Remodeling / Q000187:drug effects / Q000502:physiology; D001862:Bone Resorption; D002117:Calcitriol / Q000494:pharmacology*; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D017353:Gene Deletion; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D017395:Plasminogen Activator Inhibitor 1 / Q000502:physiology*
D002120:Calcium Channel Agonists; D017395:Plasminogen Activator Inhibitor 1; D002117:Calcitriol