Production of interleukin-6 in human osteoblasts and human bone marrow stromal cells: evidence that induction by interleukin-1 and tumor necrosis factor-alpha is not regulated by ovarian steroids

Abstract

Studies in murine models of osteoporosis have suggested the hypothesis that ovarian steroids may control osteoclastic bone remodeling by limiting the production of interleukin-6 (IL-6) from osteoblasts and bone marrow stromal cells. To investigate this hypothesis in a human model, we have examined 12 separate strains of normal human osteoblasts (HOB) and 11 separate strains of human bone marrow stromal cells (HBMSC) and determined whether ovarian steroids regulate the induction of IL-6 by interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha) or IL-1 + TNF. Treatment with IL-1, TNF or IL-1 + TNF resulted in the induction of IL-6 from both cell types with IL-1 + TNF inducing a synergistic induction of IL-6 in HOB (24- to 324-fold) and HBMSC (35-288 fold). Addition of 17 beta-estradiol or progesterone did not significantly alter IL-6 messenger RNA or protein levels in either HOB or HBMSC cultures stimulated with IL-1, TNF or IL-1 + TNF. Cultures incubated up to 96 h with the steroids did not affect IL-6 expression. Furthermore ovarian steroids did not affect IL-6 production in either HBMSC cultures representative of preosteoblasts or HOB cultures representative of highly differentiated osteoblasts. Specific chloramphenicol acetyl transferase assays and reverse transcriptase-polymerase chain reaction studies also demonstrated that the lack of an estrogen effect was not due to the failure of HOB to express functional estrogen receptors. Therefore, we conclude that the regulation of human osteoclastic bone remodeling by ovarian steroids does not occur through the direct regulation of IL-6 gene transcription or protein secretion in either early stages of osteoblast differentiation or the differentiated osteoblast.