Nicotinic regulation of c-fos and osteopontin expression in human-derived osteoblast-like cells and human trabecular bone organ culture

Long-term in vivo studies have highlighted smoking as a risk factor in post menopausal osteoporosis, bone fracture incidence, and increased nonunion ra tes. In contrast, there are few data postulating the effects of smoking at the cellular level in human skeletal tissue. In this study, we present nove l evidence demonstrating that the nicotinic receptor alpha4 subunit is pres ent in human primary bone cells by using reverse transcriptase-polymerase c hain reaction (RT-PCR), In addition, we demonstrate direct cellular effects of nicotine on primary human bone cells and blockage of these effects with a nicotinic receptor antagonist, D-tubocurarine. Nicotine effects on cell proliferation were biphasic with toxic, antiproliferative effects at high l evels of nicotine (>1 mmol/L) and stimulatory effects at very low levels (0 .01-10 mu mol/L) after 72 h. This nicotine-induced increase in cell prolife ration was inhibited in a dose-dependent manner by the addition of D-tubocu rarine, In addition, proliferation effects from low-level treatment correla ted with an upregulation of expression of the AP-1 transcription factor, c- fos, within 1 h, which was blocked by incubation with D-tubocurarine. To de termine in situ bone cell responses within their trabecular matrix, cores o f human bone isolated from biopsies were perfused with 0.1 mu mol/L nicotin e for 24 h. Western analysis of proteins isolated from the cores highlighte d an increase in osteopontin, a bone matrix protein implicated in regulatin g resorption, which was partially inhibited by the addition of D-tubocurari ne, To conclude, our results suggest that nicotine has a direct effect on h uman bone cells in modulating proliferation, upregulation of the c-fos tran scription factor, and the synthesis of the bone matrix protein, osteopontin , (C) 2001 by Elsevier Science Inc. All rights reserved.