Modulation of osteoblast-like cell behavior by activation of protease-activated receptor-1.
In addition to playing a central role in thrombosis and hemostasis, the serine protease thrombin is a specific agonist for a variety of functional responses in cells including osteoblast-like cells. Many of the cellular responses to thrombin are mediated by protease-activated receptor-1 (PAR-1). Since osteoblasts express PAR-1 in vivo during development, the effect of PAR-1 activation on proliferation and differentiation in primary rat osteoblast-like cells was investigated. Thrombin or the rat PAR-1-activating peptide SFFLRNPSENTFELVPL (SFFL) stimulated cell proliferation (as assessed by 3H- thymidine incorporation) of primary osteoblast-like cells derived from long bone or calvaria, and treatment with antibodies to PAR-1 abolished the proliferative response to thrombin. Activation of PAR-1 by thrombin or SFFL inhibited endogenous alkaline phosphatase (ALP) activity and caused a transient elevation of intracellular calcium in the osteoblast-like cells. Calcium mobilization was not, however, required for thrombin's effect on proliferation or ALP activity. The ability of a number of growth factors and hormones to regulate expression of PAR-1 in osteoblast-like cells was investigated. Expression of PAR-1 transcript and protein by osteoblast-like cells in vitro was markedly increased by treatment with transforming growth factor-beta (TGF-beta), and the proliferative response to thrombin was enhanced by TGF-beta pretreatment. Platelet-derived growth factor-BB caused a slight but significant down-regulation of PAR-1 mRNA expression. Thrombin caused a transient increase in PAR-1 expression, whereas neither parathyroid hormone-related peptide nor 1, 25-dihydroxyvitamin D3 had any effect. The observations described here suggest that PAR-1 mediates thrombin-induced osteoblast proliferation, which in turn may contribute to responses of osteoblasts to osteogenic growth factors.
Abraham
L A
LA
School of Veterinary Science, University of Melbourne, Parkville, Victoria, Australia.
MacKie
E J
EJ
D000469:Alkaline Phosphatase / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D008969:Molecular Sequence Data; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology*; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin / Q000235:genetics*
D012333:RNA, Messenger; D044463:Receptor, PAR-1; D018179:Receptors, Thrombin; D000469:Alkaline Phosphatase; D002118:Calcium