title: Leukemia inhibitory factor inhibits osteogenic differentiation in rat calvaria cell cultures.
abstract: Leukemia inhibitory factor (LIF) is a pleiotropic cytokine with both anabolic and catabolic effects on bone tissue. To investigate the effect of LIF on bone formation in the absence of a resorption cycle, we used fetal rat calvaria cell cultures and quantified bone nodule production, which provides a colony assay to analyze the effects of factors on osteoprogenitor differentiation and bone formation. In these cultures, dexamethasone (Dex) stimulates bone nodule formation. In dose-response experiments, LIF inhibited bone nodule formation by cells cultured with (+Dex; ID50 = 250 U/ml) or without (-Dex; ID50 = 30 U/ml) 10(-8) M Dex. Residual nodules were small and poorly mineralized. Continuous exposure to LIF (500 U/ml) up to day 25 did not affect either the growth rate or saturation density of the cultures, but decreased alkaline phosphatase activity and bone nodule production, with greater inhibition in -Dex cultures. Exposure to LIF (500 U/ml) for 3 days early during nodule formation (about day 10) reduced bone nodule numbers to the same extent as continuous treatment in -Dex cultures and significantly, but less markedly, in +Dex cultures; earlier and later pulses had no effect. Northern blot analysis of expression of messenger RNAs of bone related proteins in cultures pulsed (-Dex) at various stages of development showed marked inhibition of alkaline phosphatase, bone sialoprotein, and osteocalcin; slight inhibition of type I collagen; early stimulation of osteopontin; and no effect on Secreted Protein, Acidic and Rich in Cysteine/osteonectin. These results suggest that LIF is an inhibitor of bone nodule formation in these cultures, acting at a stage when late osteoprogenitors and/or early osteoblasts are present, and that Dex may modulate the effects of LIF by shifting effective doses to higher concentrations.
authors.affiliation: Medical Research Council Group in Periodontal Physiology, University of Toronto, Ontario, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Malaval
authors.forename: A K
authors.initials: AK
authors.lastname: Gupta
authors.forename: J E
authors.initials: JE
authors.lastname: Aubin
mesh_terms: D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015152:Blotting, Northern; D001842:Bone and Bones / Q000166:cytology* / Q000196:embryology; D002454:Cell Differentiation; D002478:Cells, Cultured; D003094:Collagen / Q000235:genetics; D015870:Gene Expression; D006131:Growth Inhibitors / Q000494:pharmacology*; D015850:Interleukin-6; D007700:Kinetics; D053605:Leukemia Inhibitory Factor; D008222:Lymphokines / Q000494:pharmacology*; D015675:Osteocalcin / Q000235:genetics; D010012:Osteogenesis; D053495:Osteopontin; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D012795:Sialoglycoproteins / Q000235:genetics
chemical_list: D006131:Growth Inhibitors; D015850:Interleukin-6; D053605:Leukemia Inhibitory Factor; D008222:Lymphokines; D012333:RNA, Messenger; D012795:Sialoglycoproteins; C506897:Spp1 protein, rat; D015675:Osteocalcin; D053495:Osteopontin; D003094:Collagen; D000469:Alkaline Phosphatase