Effect of tumor necrosis factor-alpha on the expression of insulin-like growth factor I and insulin-like growth factor binding protein 4 in mouse osteoblasts.

Abstract

Tumor necrosis factor-alpha (TNF-alpha) is a cytokine produced by immune cells, which has multiple effects on bone cells and is therefore thought to mediate changes in bone metabolism occurring during inflammation. In the present study we have investigated the effect of TNF-alpha on the secretion of insulin-like growth factor I (IGF-I) and IGF binding protein 4 (IGFBP-4) by clonal mouse osteoblasts (MC3T3-E1 cells) using subconfluent in vitro cultures and serum-free conditions. The IGF-I was determined by radioimmunoassay under conditions eliminating the interference of IGFBPs. Treatment of MC3T3-E1 cultures with TNF-alpha for 24 h resulted in a dose-dependent decrease in IGF-I secretion (maximally to 34 +/- 9.7% of control with 60 pmol/l TNF-alpha; mean +/- SD). The TNF-alpha treatment also resulted in decreased messenger ribonucleic acid (mRNA) levels of IGF-I at 4 and 24 h, as detected by Northern analysis. Because basal secretion of IGFBPs is very low in MC3T3-E1 cells, effects of TNF-alpha on IGFBP secretion were studied in cultures in which IGFBP-4 expression was increased by calcitriol (1,25(OH)2D3) treatment. The presence of TNF-alpha (600 pmol/l) inhibited this calcitriol-induced stimulation of IGFBP-4 mRNA levels from 4 h onwards, with complete inhibition of the calcitriol effect occurring at 24 h. We also observed a dose-dependent inhibition of calcitriol-stimulated IGFBP-4 secretion into the culture medium (as detected by Western ligand blot), with the maximal inhibition occurring with 600 pmol/l TFN-alpha to 25 +/- 7% of control levels.(ABSTRACT TRUNCATED AT 250 WORDS)