Influence of mature adipocytes on osteoblast proliferation in human primary cocultures

It has been shown that the bone loss occurring with aging in spongy bone is associated with a reduced osteoblastic bone formation and an increased vol ume of marrow adipose tissue. This observation suggests a relationship betw een cells from the osteoblastic and adipogenic lineages. The purpose of the present study was to evaluate the influence of mature adipocytes on osteob lastic proliferation and activity in a model of coculture. Human primary os teoblastic (hROB) cells were derived from femoral bone explants collected i n patients undergoing orthopedic surgery. Human stromal osteoblastic (hMSOB ) cells were obtained from bone marrow samples collected by aspiration duri ng orthopedic surgery. Extramedullary and medullary mature adipocytes (hAd) showing similar functions, except for their response to insulin, hAd were isolated from mammary adipose tissue collected in women undergoing tumorect omy. Cells were cocultured, with hAd being separated from osteoblastic cell s (hBOB or hMSOB) by a porous membrane (0.4 mu m). When hBOB cells were see ded on the upper side of the insert and hAd were floating on the lower side , cell contacts between the two cell types were possible through the pores of the membrane. At the end of the experiment, proliferation of the osteobl astic cells was evaluated by [H-3]-thymidine incorporation and alkaline pho sphatase (AP) activity was measured. After 20 h of coculture, proliferation of the hBOB cells was significantly decreased when compared with control h BOB (-40 +/- 6%, p < 0.05), To establish whether or not the influence of hA d on hBOB proliferation required intercfllular communications, hAd and hBOB cells were cocultured far front the porous membrane. Six other independent experiments confirmed an inhibition of hBOB proliferation under both exper imental conditions (p < 0,05): -35 +/- 7% with possible intercellular conta cts, and -30 +/- 7% without any contact. In contrast, the proliferation of hMSOB cells was not significantly modified after coculture with hAd, In add ition, the presence of hAd did not significantly modify the AP activity of hBOB (0.163 +/- 0.143 and 0.181 +/- 0.114 nmol/min per microgram of protein in controls and after coculture, respectively), No reproducible effect of hAd-conditioned medium was noted on hBOB- and hMSOB-cell proliferation or h BOB-cell activity. In conclusion, mature adipocytes induced an inhibition o f hBOB-cells proliferation, probably mediated by a factor secreted by hAd, This effect may contribute to the age-related reduction of bone formation a nd bone loss, (C) 2000 by Elsevier Science Inc. All rights reserved.