Effect of IL‐1β, PGE₂, and TGF‐β1 on the expression of OPG and RANKL in normal and osteoporotic primary human osteoblasts

Abstract

The RANKL/RANK/OPG pathway is essential for bone remodeling regulation. Many hormones and cytokines are involved in regulating gene expression in most of the pathway components. Moreover, any deregulation of this pathway can alter bone metabolism, resulting in loss or gain of bone mass. Whether osteoblasts from osteoporotic and nonosteoporotic patients respond differently to cytokines is unknown. The aim of this study was to compare the effect of interleukin (IL)-1beta, proftaglandin E(2) (PGE(2)), and transforming growth factor-beta1 (TGF-beta1) treatments on OPG and RANKL gene expression in normal (n = 11) and osteoporotic (n = 8) primary osteoblasts. OPG and RANKL mRNA levels of primary human osteoblastic (hOB) cell cultures were assessed by real-time PCR. In all cultures, OPG mRNA increased significantly in response to IL-1beta treatment and decreased in response to TGF-beta1 whereas PGE(2) treatment had no effect. RANKL mRNA levels were significantly increased by all treatments. Differences in OPG and RANKL responses were observed between osteoporotic and nonosteoporotic hOB: in osteoporotic hOB, the OPG response to IL-1beta treatment was up to three times lower (P = 0.009), whereas that of RANKL response to TGF-beta1 was five times higher (P = 0.002) after 8 h of treatment, as compared with those in nonosteoporotic hOBs. In conclusion, osteoporotic hOB cells showed an anomalous response under cytokine stimulation, consistent with an enhanced osteoclastogenesis resulting in high levels of bone resorption.

Engineering of a functional bone organ through endochondral ossification

“…Quantification of cytokines retained in the samples after 5 wk of in vitro culture also showed an increase of M-CSF (56-fold), MCP-1 (26-fold), receptor activator of nuclear factor kappa-B ligand (RANKL) (29-fold), MMP-13 (12-fold), and osteoprotegerin (OPG) (sixfold) compared with untreated controls. In particular, the establishment of an environment prone to remodeling was confirmed by a 4.3-fold increase in the RANKL/OPG ratio (17).…”

Wybrane cytokiny prozapalne, metabolizm kostny, osteoprotegeryna i ligand receptora aktywatora czynnika jądrowego-kB u dziewcząt z jadłowstrętem psychicznym

“…However, both OPG and RANKL, and OPG in particular, are regulated not only by 17β-estradiol, but also by other hormones and cytokines (maybe also pro-inflammatory cytokines), whose effect might be similar or opposite to that of 17β-estradiol [27]. It has been demonstrated that pro-inflammatory cytokines influence the bone tissue directly and/or indirectly, via the RANKL/RANK/OPG system [27][28][29][30][31][32][33][34][35][36][37][38][39]. Since it has been documented that IL-1β, IL-6, and TNF-α stimulate bone resorption both in vitro and in vivo [27][28][29][30], it seems reasonable to presume that any potential disturbances in the production of these cytokines in patients with AN might play a role in the development of osteoporosis.…”

“…The above data suggest that cytokines may regulate osteoclastogenesis not only directly, but also indirectly via the RANKL/ /RANK/OPG system [27][28][29][30][31][32][33][34][35][36][37][38][39]. Through an increase in the expression of RANKL and/or a decrease in OPG expression, IL-1β, IL-6, or TNF-α may suppress the OPG/RANKL ratio resulting in enhanced bone resorption [27][28][29][30][31][32][33][34][35][36][37][38][39].…”

“…Previous in vitro investigations revealed that, depending on its local concentration, IL-1β may stimulate or inhibit osteoblasts through specific receptors [27]. It also stimulates bone resorption via the RANKL/RANK/OPG system [31][32][33]. In vitro investigations demonstrated that IL-1β enhanced the expression of the RANKL gene in osteoblasts and marrow stromal cells leading to a shift in the OPG/sRANKL ratio toward a functional excess of sRANKL, and, consequently, increased bone resorption [31][32][33].…”

“…It activates mature osteoclasts and stimulates the recruitment and differentiation of precursor cells [27]. IL-1-induced stimulation of osteoclastogenesis occurs indirectly via enhanced expression of receptor activator of nuclear factor-kB ligand (RANKL) in osteoblasts and marrow stromal cells [31][32][33]. Interleukin-6 is a protein synthesised by lymphocytes and other cell types including osteoblasts and osteoclasts.…”