Estrogen’s bone-protective effects may involve differential IL-1 receptor regulation in human osteoclast-like cells
Teresa Sunyer, … , Patricia Collin-Osdoby, Philip Osdoby
Teresa Sunyer, … , Patricia Collin-Osdoby, Philip Osdoby
Published May 15, 1999
Citation Information: J Clin Invest. 1999;103(10):1409-1418. https://doi.org/10.1172/JCI4682.
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Article

Estrogen’s bone-protective effects may involve differential IL-1 receptor regulation in human osteoclast-like cells

Abstract

Declining estrogen levels during the first postmenopausal decade lead to rapid bone loss and increased fracture risk that can be reversed by estrogen replacement therapy. The bone-protective effects of estrogen may involve suppression of inflammatory cytokines that promote osteoclastogenesis and bone resorption, such as IL-1, TNF-α, and IL-6. We investigated whether estrogen modulates IL-1 actions on human osteoclasts (OCs) and other bone cell types. Isolated human OCs and primary bone marrow–derived OC-like cells expressed both the signaling (IL-1RI) and decoy (IL-1RII) IL-1 receptors, whereas only IL-1RI was detected in osteoblasts. IL-1RII/IL-1RI mRNA ratios and release of soluble IL-1RII (sIL-1RII) were lower in OC-like cells derived from women in the late postmenopausal period compared with younger women, but were unrelated to male donor age, suggesting that estrogen might play a role in regulating IL-1 receptor levels in vivo. Estrogen directly reduced in vitro OC-like cell IL-1RI mRNA levels while increasing IL-1RII mRNA levels and sIL-1RII release. These estrogenic events were associated with inhibited IL-1–mediated cytokine (IL-8) mRNA induction and cell survival, i.e., increased apoptosis. In contrast, estrogen did not alter IL-1R levels or IL-1 responsiveness in primary human osteoblasts or bone marrow stromal cells. We conclude that one novel mechanism by which estrogen exerts bone-protective effects may include a selective modulation of IL-1R isoform levels in OC or OC-like cells, thereby reducing their IL-1 responsiveness and cell survival. Conversely, this restraint on IL-1 actions may be lost as estrogen levels decline in aging women, contributing to an enhanced OC-mediated postmenopausal bone loss.

Authors

Teresa Sunyer, Jennifer Lewis, Patricia Collin-Osdoby, Philip Osdoby

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hOC and hOCL cells express mRNA for both the type I and type II IL-1 rec...
hOC and hOCL cells express mRNA for both the type I and type II IL-1 receptors. (a) Schematic representation of the human IL-1 receptor genes. Hatched bars represent the extracellular regions of the proteins; filled bars represent the transmembrane domains; and open bars represent the intracellular tails. Arrowheads indicate the location of primers used in RT-PCR. (b) RT-PCR of IL-1RI (I) and IL-1RII (II) from hOCs directly isolated from a femoral head of a 76-year-old woman undergoing hip replacement surgery, and from hOCL and hOBL cells generated from a single bone marrow mononuclear preparation derived from a 58-year-old woman. Amplicons were separated in 1.5% agarose gels and viewed with ethidium bromide. Similar results were obtained by RT-PCR analysis for IL-1RI and IL-1RII in hOCs directly isolated from osteopenic bone specimens obtained from 6 patients (4 women of 71, 76, 78, and 78 years of age; and 2 men of 56 and 78 years of age) undergoing hip replacement surgery, and a patient with implant osteolysis (a 71-year-old man). St., molecular weight standards.