CATECHOLAMINES STIMULATE THE PROLIFERATION AND ALKALINE-PHOSPHATASE ACTIVITY OF MC3T3-E1 OSTEOBLAST-LIKE CELLS

A number of factors have been shown to influence osteoblastic prolifer ation, including fluoride, Recent observations suggest that heterotrim eric G proteins are probably involved in the mitogenic response induce d by this agent, further suggesting a role of guanosine 5'-triphosphat e (GTP)-binding protein-coupled receptors (GPCR) in the regulation of osteoblastic cell growth. We therefore explored what mitogenic factors known to activate GPCR can influence the replication of mouse osteobl ast-like MC3T3-E1 cells, Among several candidates, epinephrine was fou nd to be a potent mitogen for these cells, and its effect on the growt h and differentiation of these cells was further investigated. Deoxyri bonucleic acid (DNA) synthesis was dose dependently enhanced by this c atecholamine in the concentration range of 1 nmol/L-10 mu mol/L. Stimu lation of DNA synthesis by catecholamines was in the order of epinephr ine > norepinephrine >> isoproterenol, indicating that a adrenergic re ceptors mediated this cellular response. Further analysis with specifi c adrenergic receptor agonists and antagonists suggested that the mito genic response induced by epinephrine in MC3T3-E1 cells is mediated by cr, adrenergic receptors, In addition to its effect on cell replicati on, epinephrine also enhanced alkaline phosphatase (ALP) activity in t hese cells but had little effect on collagen synthesis and osteocalcin production. As for the mitogenic response, the change in ALP activity was found to be mediated by rw, adrenergic receptors, Both effects of epinephrine on cell replication and ALP activity were markedly reduce d by pretreatment of the cells with pertussis toxin (PTX), suggesting a role of Gi proteins. These effects were also completely blocked by p retreatment of the cells with 50 mu mol/L genistein, a nonselective in hibitor of tyrosine kinase, In conclusion, the results indicate that e pinephrine enhances replication and ALP activity of MC3T3-E1 osteoblas t-like cells via alpha(1) adrenergic receptors coupled to Gi proteins, The signaling mechanism probably involves a tyrosine phosphorylation mechanism. These observations suggest that PTX-sensitive G proteins ar e potent mediators of cell proliferation and ALP activity of osteoblas t-like cells in response to factors acting through G protein-coupled r eceptors, (Bone 23: 197-203; 1998) (C) 1998 by Elsevier Science Inc. A ll rights reserved.