Parathyroid hormone (1-34)-mediated interleukin-6 induction

Physiological and Pharmacological Roles of PTH and PTHrP in Bone Using Their Shared Receptor, PTH1R

Parathyroid hormone (PTH) and the paracrine factor, PTH-related protein (PTHrP), have preserved in evolution sufficient identities in their amino-terminal domains to share equivalent actions upon a common G protein-coupled receptor, PTH1R, that predominantly uses the cyclic adenosine monophosphate-protein kinase A signaling pathway. Such a relationship between a hormone and local factor poses questions about how their common receptor mediates pharmacological and physiological actions of the two. Mouse genetic studies show that PTHrP is essential for endochondral bone lengthening in the fetus and is essential for bone remodeling. In contrast, the main postnatal function of PTH is hormonal control of calcium homeostasis, with no evidence that PTHrP contributes. Pharmacologically, amino-terminal PTH and PTHrP peptides (teriparatide and abaloparatide) promote bone formation when administered by intermittent (daily) injection. This anabolic effect is remodeling-based with a lesser contribution from modeling. The apparent lesser potency of PTHrP than PTH peptides as skeletal anabolic agents could be explained by lesser bioavailability to PTH1R. By contrast, prolongation of PTH1R stimulation by excessive dosing or infusion, converts the response to a predominantly resorptive one by stimulating osteoclast formation. Physiologically, locally generated PTHrP is better equipped than the circulating hormone to regulate bone remodeling, which occurs asynchronously at widely distributed sites throughout the skeleton where it is needed to replace old or damaged bone. While it remains possible that PTH, circulating within a narrow concentration range, could contribute in some way to remodeling and modeling, its main physiological role is in regulating calcium homeostasis.

Osteoimmunopathology in HIV/AIDS: A Translational Evidence-Based Perspective

Infection with the human immunodeficiency virus-1 (HIV) and the resulting acquired immune deficiency syndrome (AIDS) alter not only cellular immune regulation but also the bone metabolism. Since cellular immunity and bone metabolism are intimately intertwined in the osteoimmune network, it is to be expected that bone metabolism is also affected in patients with HIV/AIDS. The concerted evidence points convincingly toward impaired activity of osteoblasts and increased activity of osteoclasts in patients with HIV/AIDS, leading to a significant increase in the prevalence of osteoporosis. Research attributes these outcomes in part at least to the ART, PI, and HAART therapies endured by these patients. We review and discuss these lines of evidence from the perspective of translational clinically relevant complex systematic reviews for comparative effectiveness analysis and evidence-based intervention on a global scale.

Novel targets for myeloma bone disease

BACKGROUND

Multiple myeloma (MM) is a plasma cell malignancy in which osteolytic bone lesions develop in over 80% of patients. The increased bone destruction results from increased osteoclast formation and activity, which occurs adjacent to marrow sites involved with MM cells. This is accompanied by suppressed or absent osteoblast differentiation and activity, resulting in severely impaired bone formation and development of purely osteolytic lesions.

OBJECTIVE

The pathophysiology underlying this bone remodeling is reviewed, and potential new strategies to treat MM bone disease are discussed.

RESULTS

Recent advances in our understanding of factors involved in pathogenesis of MM bone disease have identified novel therapeutic targets. Several of these are or will be in clinical trials soon.

CONCLUSION

Agents which target the tumor and bone-destructive process, such as the immunomodulatory drugs (IMiDs) or bortezomib, in combination with novel anti-resorptives should be effective. These combinations should be in clinical trials in the next few years. It is unclear if these treatments will be able to 'heal' bone lesions in MM patients.

Primary pulmonary squamous cell carcinoma associated with elevated IL-6, leukocytosis, hypercalcemia, phagocytosis, reactive lymphadenopathy and glomerular mesangial cell proliferation via the production of PTH-rP and G-CSF

We report an autopsied case of a 74-year-old man with primary pulmonary squamous cell carcinoma (SCC) associated with leukocytosis, hypercalcemia, phagocytosis in the bone marrow, reactive lymphadenopathy and mesangial cell proliferation in the glomerulus. Laboratory examination revealed increased serum levels of parathyroid hormone-related peptide (PTH-rP), granulocyte colony stimulating factor (G-CSF), interleukin-6 (IL-6) and soluble interleukin 2 receptor (s-IL2R). An autopsy showed moderately differentiated SCC at the left lower lobe of the lung, of which tumor cells distinctly showed cytoplasmic immunoreactivity to anti-G-CSF and anti-PTH-rP antibodies. Thus, pulmonary SCC seemed to produce both G-CSF and PTH-rP, causing leukocytosis, hypercalcemia, and IL-6 production from the bone. IL-6 also might have stimulated the proliferation of SCC and glomerular mesangial cells, and induced phagocytosis, reactive lymphadenopathy and hepatosplenomegaly by interacting with the mononuclear phagocytic system.

Genistein modulates the effects of parathyroid hormone in human osteoblastic SaOS-2 cells

Genistein and parathyroid hormone (PTH) are anabolic agents that stimulate bone formation through their direct actions in osteoblastic cells. In the present study, we aimed to determinewhether genistein modulates the actions of PTH in human osteoblastic SaOS-2 cells in an oestrogen-depleted condition. The present results showed that genistein (10−8to 10−6m) induced alkaline phosphatase (ALP) activity and osteoprotegrin (OPG) expression in SaOS-2 cells in a dose-dependent manner. These effects could be completely abolished by co-treatment with oestrogen antagonist ICI 182780 (7α-[9-[(4,4,5,5,5-pentafluoropentyl)sulfonyl]nonyl]-estra-1,3,5(10)-triene-3,17β-diol). Genistein (at 1μm) could stimulate the mRNA expression of receptor activator of NF-κB ligand (RANKL). As OPG and RANKL are known to modulate osteoclastogenesis, the ability of genistein to modulate OPG and RANKL expression in SaOS-2 cells suggested that it might modulate osteoclastogenesis through its direct actions on osteoblastic cells. PTH (at 10nm) stimulated ALP activity, induced RANKL mRNA expression and suppressed OPG mRNA expression in SaOS-2 cells, confirming its bi-directional effects on osteoblastic cells. Pre-treatment of SaOS-2 cells with genistein andoestrogen not only enhanced PTH-induced ALP activity, but also attenuated PTH up regulation ofRANKL mRNA expression and PTH down regulation of OPG mRNA expression. Taken together, the present study provides the first evidence that genistein could modulate the actions of PTH in human osteoblastic SaOS-2 cells in an oestrogen-depleted condition.

Osteoimmunology

Osteoimmunology is an interdisciplinary research field combining the exciting fields of osteology and immunology. An observation that contributed enormously to the emergence of osteoimmunology was the accelerated bone loss caused by inflammatory diseases such as rheumatoid arthritis. Receptor activator of nuclear factor kappaB ligand (RANKL), which is the main regulator of osteoclastogenesis, was found to be the primary culprit responsible for the enhanced activation of osteoclasts: activated T cells directly and indirectly increased the expression of RANKL, and thereby promoted osteoclastic activity. Excessive bone loss is not only present in inflammatory diseases but also in autoimmune diseases and cancer. Furthermore, there is accumulating evidence that the very prevalent skeletal disorder osteoporosis is associated with alterations in the immune system. Meanwhile, numerous connections have been discovered in osteoimmunology beyond merely the actions of RANKL. These include the importance of osteoblasts in the maintenance of the hematopoietic stem cell niche and in lymphocyte development as well as the functions of immune cells participating in osteoblast and osteoclast development. Furthermore, research is being done investigating cytokines, chemokines, transcription factors and co-stimulatory molecules which are shared by both systems. Research in osteoimmunology promises the discovery of new strategies and the development of innovative therapeutics to cure or alleviate bone loss in inflammatory and autoimmune diseases as well as in osteoporosis. This review gives an introduction to bone remodeling and the cells governing that process and summarizes the most recent discoveries in the interdisciplinary field of osteoimmunology. Furthermore, an alternative large animal model will be discussed and the pathophysiological alterations of the immune system in osteoporosis will be highlighted.

TNFalpha and PTH utilize distinct mechanisms to induce IL-6 and RANKL expression with markedly different kinetics

Parathyroid hormone (PTH) and tumor necrosis factoralpha (TNFalpha) are bone resorptive agents that upregulate interleukin-6 (IL-6) and RANKL production by osteoblasts. IL-6 mRNA expression induced by PTH is rapid and transient in osteoblasts both in vitro and in vivo. This study found that IL-6 secretion induced by PTH is also rapid and transient. The induction of RANKL mRNA by PTH is also rapid and transient although with an extended time course compared to that of IL-6 mRNA. In contrast, the effects of TNFalpha are biphasic. During the first 2 h of stimulation with TNFalpha, the responses are similar to those induced by PTH. This is followed by a period of relatively low IL-6 and RANKL mRNA levels and little IL-6 secretion. A late phase of increased IL-6 and RANKL mRNA expression occurs 12-24 h after stimulation with TNFalpha leading to a significant increase in IL-6 secretion. A similar biphasic pattern of activation of p38 MAP kinase is induced by TNFalpha. p38alpha/beta activation is required for the increased RANKL mRNA during the early phase of stimulation by TNFalpha but not in the late phase. In contrast, p38alpha/beta activation is not required for increased IL-6 mRNA or IL-6 protein secretion in either the early or late phases of stimulation by TNFalpha. Blocking the increases in IL-6 transcription completely eliminates IL-6 secretion induced during the early phases of stimulation by either PTH or TNFalpha. Consistent with the dependence on transcription, IL-6 mRNA is rapidly degraded with half-lives of 10-14 min following stimulation with either PTH or TNFalpha. In contrast to IL-6, RANKL mRNA is substantially more stable with half-lives of 40-60 min. Taken together, our results show that TNFalpha and PTH utilize distinct mechanisms to induce IL-6 and RANKL expression with markedly different kinetics. The more extensive effect of TNFalpha likely reflects that TNFalpha stimulates IL-6 production and bone resorption in pathological situations. In contrast, the less extensive effect of PTH likely reflects that it acts in physiological situations where it is important to minimize the potential adverse effects of high levels of IL-6 on bone and/or surrounding tissues.

Secondary hyperparathyroidism promotes the acute phase response – a rationale for supplemental Vitamin D in prevention of vascular events in the elderly

Parathyroid hormone (PTH) promotes IL-6 secretion by osteoblasts, and may also up-regulate IL-6 production in the liver and adipose tissue; this may explain why serum IL-6 is markedly elevated in primary hyperparathyroidism, and low in hypoparathyroidism. IL-6 is the chief stimulus to hepatic production of many acute phase reactants, notably fibrinogen and C-reactive protein (CRP). Mild secondary hyperparathyroidism is common in elderly people, particularly at high latitudes during the winter, owing to poor vitamin D status. This may rationalize evidence that acute phase proteins show seasonal variations and are typically elevated in the elderly, whereas leisure physical activity is associated with a reduction in these proteins. In a recent clinical trial targeting elderly chronically ill patients, administration of vitamin D reduced serum levels of both CRP and IL-6; further such studies should assess the impact of physiologically meaningful doses of vitamin D on acute phase reactants in elderly subjects likely to have poor vitamin D status. Since elevations of CRP and fibrinogen may increase risk for thromboembolic vascular events, these considerations may help to explain the excess of coronary mortality observed during winter months, and suggest a role for supplemental vitamin D in preservation of vascular health. Moderate alcohol intake is associated with reduced serum PTH as well as decreased levels of CRP and fibrinogen; conceivably, modulation of PTH mediates, at least in part, the favorable impact of moderate drinking on the acute phase reactants.

Impact of the mitogen-activated protein kinase pathway on parathyroid hormone-related protein actions in osteoblasts

Parathyroid hormone-related protein (PTHrP) regulates proliferation and differentiation of osteoblastic cells via binding to the parathyroid hormone receptor (PTH-1R). The cAMP-dependent protein kinase A pathway governs the majority of these effects, but recent evidence also implicates the MAPK pathway. MC3T3-E1 subclone 4 cells (MC4) were treated with the MAPK inhibitor U0126 and PTHrP. In differentiated MC4 cells, osteocalcin and bone sialoprotein gene expression were both down-regulated by PTHrP and also by inhibition of the MAPK pathway. PTHrP-mediated down-regulation of PTH-1R mRNA and up-regulation of c-fos mRNA were MAPK-independent, whereas PTHrP stimulation of fra-2 and interleukin-6 (IL-6) mRNA was MAPK-dependent. Luciferase promoter assays revealed that regulation of IL-6 involved the cAMP-dependent protein kinase A and MAPK pathways with a potential minor role of the protein kinase C pathway, and a promoter region containing an activator protein-1 site was necessary for PTHrP-induced IL-6 gene transcription. An alternative pathway, through cAMP/Epac/Rap1/MAPK, mediated ERK phosphorylation but was not sufficient for IL-6 promoter activation. Phosphorylation of the transcription factor CREB was also necessary but not sufficient for PTHrP-mediated IL-6 promoter activity. Most interesting, a bidirectional effect was found with PTHrP increasing phosphorylated ERK in undifferentiated MC4 cells but decreasing phosphorylated ERK in differentiated cells. These data indicate that inactivation of the MAPK pathway shows differential regulation of PTHrP-stimulated activator protein-1 members, blocks PTHrP-stimulated IL-6, and synergistically down-regulates certain osteoblastic markers associated with differentiation. These novel findings indicate that the MAPK pathway plays a selective but important role in the actions of PTHrP.

Termination of immediate-early gene expression after stimulation by parathyroid hormone or isoproterenol

cAMP/PKA signaling transiently stimulates mRNA expression of immediate-early genes, including IL-6 and c-fos. We confirmed that these mRNAs are transiently stimulated by parathyroid hormone (PTH) in ROS 17/2.8 osteoblastic cells. Consistent with the role for cAMP/PKA signaling in this response, PTH induces transient cAMP elevation, PKA activation, and cAMP-responsive element-binding protein (CREB) phosphorylation. Our goal was to determine whether termination of immediate-early gene expression is due to receptor desensitization or cAMP degradation. The approaches used were 1) inhibition of PTH receptor desensitization with G protein-coupled receptor kinase 2 (GRK2) antisense oligonucleotides or antisense plasmids, 2) sustained activation of adenyl cyclase with forskolin, and 3) inhibition of cAMP degradation with 3-isobutyl-1-methylxanthine. These experiments show that mechanisms downstream of receptor desensitization and cAMP degradation are primarily responsible for termination of PKA activity, CREB phosphorylation, and immediate-early gene expression. Similar conclusions were also obtained in response to PTH in a second osteoblastic cell line (MC3T3-E1) and in response to isoproterenol in NIH3T3 fibroblasts. This conclusion may therefore reflect a general mechanism for termination of immediate-early gene expression after induction by cAMP/PKA.

Both N- and C-terminal domains of parathyroid hormone-related protein increase interleukin-6 by nuclear factor-kappa B activation in osteoblastic cells

Parathyroid hormone (PTH)-related protein (PTHrP) seems to affect bone resorption by interaction with bone cytokines, among them interleukin-6 (IL-6). Recent studies suggest that nuclear factor (NF)-kappaB activation has an important role in bone resorption. We assessed whether the N-terminal fragment of PTHrP, and its C-terminal region, unrelated to PTH, can activate NF-kappaB, and its relationship with IL-6 gene induction in different rat and human osteoblastic cell preparations. Here we present molecular data demonstrating that both PTHrP (1-36) and PTHrP (107-139) activate NF-kappaB, leading to an increase in IL-6 mRNA, in these cells. Using anti-p65 and anti-p50 antibodies, we detected the presence of both proteins in the activated NF-kappaB complex. This effect induced by either the N- or C-terminal PTHrP domain in osteoblastic cells appears to occur by different intracellular mechanisms, involving protein kinase A or intracellular Ca(2+)/protein kinase C activation, respectively. However, the effect of each peptide alone did not increase further when added together. Our findings lend support to the hypothesis that the C-terminal domain of PTHrP, in a manner similar to its N-terminal fragment, might stimulate bone resorption. These studies also provide further insights into the putative role of PTHrP as a modulator of bone remodeling.

Mechanisms balancing skeletal matrix synthesis and degradation

Bone is regulated by evolutionarily conserved signals that balance continuous differentiation of bone matrix-producing cells against apoptosis and matrix removal. This is continued from embryogenesis, where the skeleton differentiates as a solid mass and is shaped into separate bones by cell death and proteolysis. The two major tissues of the skeleton are avascular cartilage, with an extracellular matrix based on type II collagen and hydrophilic proteoglycans, and bone, a stronger and lighter material based on oriented type I collagen and hydroxyapatite. Both differentiate from the same mesenchymal stem cells. This differentiation is regulated by a family of related signals centred on bone morphogenic proteins. Fibroblast growth factors, Indian hedgehog and parathyroid hormone-related protein are important in determining the type of matrix and the relation of skeletal and non-skeletal structures. Removal of mineralized matrix involves apoptosis of matrix cells and differentiation of acid-secreting cells (osteoclasts) from macrophage precursors. Key regulators of matrix removal are signals in the tumour-necrosis-factor family. Osteoclasts dissolve bone by isolating a region of the matrix and secreting HCl and proteinases at that site. Successive cycles of removal and replacement allow growth, repair and remodelling. The signals for bone turnover are predominantly cell-membrane-associated, allowing very specific spatial regulation. In addition to its support function, bone is a reservoir of Ca2+, PO3-(4) and OH-. Secondary modulation of mineral secretion and bone degradation are mediated by humoral signals, including parathyroid hormone and vitamin D, as well as the cytokines that also regulate the underlying cell differentiation.

Parathyroid hormone induces RGS-2 expression by a cyclic adenosine 3',5'-monophosphate-mediated pathway in primary neonatal murine osteoblasts

Parathyroid hormone (PTH) is a promising anabolic agent for the treatment of osteoporosis. However, PTH is also potently catabolic. To help delineate the molecular mediators of PTH's opposing effects on skeletal metabolism, we have examined PTH-induced regulator of G-protein signaling-2 (RGS-2) expression and function in murine osteoblasts. RGS proteins are GTPase-activating proteins (GAPs) that regulate GTP-binding protein-coupled receptor (GPCR) signaling by enhancing the intrinsic GTPase activity of Galpha subunits. We found that 10 nmol/L PTH maximally induced RGS-2 mRNA in murine MC3T3-E1 cells, rat Py1a and ROS-17/2.8 cells, primary mouse osteoblasts (MOB cells), and mouse calvariae organ culture at 1-2 h posttreatment. PTH signaling through its receptor, PTHR1, is coupled to cAMP-protein kinase A (PKA), protein kinase C (PKC), and calcium signaling pathways. We examined the effect of selective signaling agonists and antagonists on RGS-2 expression in MOB cells to determine which pathway(s) mediates PTH-induced RGS-2 expression. Although selective activation of all three pathways led to RGS-2 expression, cAMP-PKA activation with 10 nmol/L PTH and 10 micromol/L forskolin elicited the strongest induction. Similarly, RGS-2 mRNA expression was most strongly inhibited by the PKA inhibitor, H89 (10-30 micromol/L). The phorbol ester, PMA (1 micromol/L), which activates the PKC pathway, and ionomycin (1 micromol/L), which activates the calcium pathway, produced small but detectable elevations in RGS-2 mRNA levels. Overnight treatment with 1 micromol/L PMA to deplete PKC did not affect subsequent RGS-2 induction by PTH, but significantly inhibited PMA-induced RGS-2 expression. Treatment with 1-100 nmol/L PTH(3-34), which does not activate cAMP-PKA signaling, did not induce RGS-2 expression. MOB cells pretreated with 3 microg/mL cycloheximide produced sustained RGS-2 mRNA levels 2 h after 10 nmol/L PTH treatment. Actinomycin D (5 microg/mL) completely blocked 10 nmol/L PTH-induced RGS-2 expression. Finally, we tested the effect of RGS-2 overexpression on PTH- and fluprostenol-induced interleukin (IL)-6 promoter activity in MOB cells. PTH induces IL-6 through PKA activation, whereas fluprostenol induces IL-6 through PKC activation. We found that RGS-2 overexpression significantly inhibited IL-6 promoter activity following fluprostenol treatment, but not following PTH treatment. We conclude that RGS-2 is a PTH-induced primary response gene in murine osteoblasts that is induced mainly through the cAMP-PKA pathway and specifically inhibits Galphaq-coupled receptors.

Involvement of PKC-beta in PTH, TNF-alpha, and IL-1 beta effects on IL-6 promoter in osteoblastic cells and on PTH-stimulated bone resorption

Protein kinase C (PKC) has been shown to be activated by parathyroid hormone (PTH) in osteoblasts. Prior evidence suggests that this activation mediates responses leading to bone resorption, including production of the osteoclastogenic cytokine interleukin-6 (IL-6). However, the importance of specific PKC isozymes in this process has not been investigated. A selective antagonist of PKC-beta, LY379196, was used to determine the role of the PKC-beta isozyme in the expression of IL-6 in UMR-106 rat osteoblastic cells and in bone resorption in fetal rat limb bone organ cultures. PTH, tumor necrosis factor-alpha (TNF-alpha), and interleukin-1 beta (IL-1 beta) induced translocation of PKC-alpha and -beta(I) to the plasma membrane in UMR-106 cells within 5 min. The stimulation of PKC-beta(I) translocation by PTH, TNF-alpha or IL-1 beta was inhibited by LY379196. In contrast, LY379196 did not affect PTH, TNF-alpha-, or IL-1 beta-stimulated translocation of PKC-alpha. PTH, TNF-alpha, and IL-1 beta increased luciferase expression in UMR-106 cells transiently transfected with a -224/+11 bp IL-6 promoter-driven reporter construct. The IL-6 responses were also attenuated by treatment with LY379196. Furthermore, LY379196 inhibited bone resorption elicited by PTH in fetal rat bone organ cultures. These results indicate that PKC-beta(I) is a component of the signaling pathway that mediates PTH-, TNF-alpha-, and IL-1 beta-stimulated IL-6 expression and PTH-stimulated bone resorption.

Estrogen modulates parathyroid hormone-induced interleukin-6 production in vivo and in vitro

Interleukin (IL)-6 promotes osteoclastogenesis and is thought to play a role in the bone loss that follows estrogen withdrawal. In vitro studies have demonstrated that IL-6 is produced in response to PTH by cells in the osteoblast lineage and that PTH-induced bone resorption is inhibited by a neutralizing antibody to the IL-6 receptor. In addition, we have recently reported that IL-6 plays a role in PTH-induced bone resorption in humans with chronic PTH excess and in experimental animals during the short-term infusion of PTH. In the current study, we examined whether estrogen withdrawal augments PTH-induced IL-6 production. When cultured in the absence of estrogen, human osteosarcoma cells (Saos-2) treated with PTH demonstrated significantly greater release of IL-6 than cells grown under estrogen-replete conditions, 30-fold vs. 15-fold (P = 0.005). A similar effect but of lesser magnitude was seen with primary human osteoblasts. In vivo, PTH induced IL-6 production was also increased in the estrogen-deficient state (ovx) such that at the end of a 5-day PTH infusion, the mean circulating level of IL-6 was significantly higher in ovx vs. sham/ovx mice (60.1 vs. 16.9 pg/ml; P < 0.0001). The greater increase in circulating levels of IL-6 in PTH-treated ovx mice was paralleled by a greater rise in bone resorption markers with the mean level of urine collagen cross-links in the PTH-treated ovx group being more than 2.5-fold higher than in the PTH-treated sham/ovx animals (236 vs. 88.5 microg/mmol creatinine, P < 0.0001). Mean serum collagen cross-link values were 17.4 microg/liter in PTH-treated ovx vs. 7.4 microg/liter in PTH-treated sham/ovx animals (P < 0.0001). Treatment of animals with estrogen prevented the exaggerated response to PTH infusion such that the increase in both circulating levels of IL-6 and bone turnover markers in estrogen-treated animals were similar to those observed in sham/ovx animals and significantly lower than those in PTH-treated ovx animals. These findings may help to explain the increased skeletal sensitivity to the resorbing effects of PTH seen in the estrogen-deficient state.

Protein kinase C involvement in interleukin-6 production by parathyroid hormone and tumor necrosis factor-alpha in UMR-106 osteoblastic cells

The cytokine interleukin-6 (IL-6) is increased in bone and bone cells by several resorptive stimuli, including parathyroid hormone (PTH), IL-1beta, and tumor necrosis factor-alpha (TNF-alpha). The current studies were designed to determine the contribution of the protein kinase C (PKC) signaling pathway to the effects of these three agents to increase IL-6 in UMR-106 rat osteoblastic cells. Cells were pretreated with vehicle (dimethylsulfoxide [DMSO]) or the phorbol ester, phorbol 12,13-dibutyrate (PDB; 300 nM) for 48 h to down-regulate phorbol-sensitive PKC isozymes. Either PTH (0.1-10 nM), IL-1beta (0.1-10 nM), or TNF-alpha (5 nM and 10 nM) was then added for 24 h in the continued presence of vehicle or PDB. PKC isozymes were visualized by Western immunoblotting and IL-6 was determined by bioassay. PDB pretreatment caused a partial down-regulation of the conventional alpha-PKC and betaI-PKC isozymes and complete down-regulation of the novel delta-isoenzyme and epsilon-isozymes but it had no effect on the atypical zeta-PKC isozyme. PDB pretreatment reduced IL-6 responses to 5 nM and 10 nM PTH by 61% and 33%, respectively, reduced IL-6 responses to 5nM and 10 nM TNF-a by 54% and 42%, respectively, and failed to inhibit the IL-6 responses to 0.1-10 nM IL-1beta. The PDB pretreatment protocol significantly enhanced PTH-stimulated cyclic adenosine monophosphate (cAMP) production. The PKC inhibitor calphostin C also decreased IL-6 responses to PTH. Thus, in this osteoblast cell line, the PKC pathway is an important component of the signaling pathway for the IL-6 production stimulated by PTH and TNF-alpha but not that from IL-1beta.

Parathyroid hormone regulation of the rat collagenase-3 promoter by protein kinase A-dependent transactivation of core binding factor alpha1

Previously we showed that the activator protein-1 site and the runt domain binding site in the collagenase-3 promoter act cooperatively in response to parathyroid hormone (PTH) in the rat osteoblastic osteosarcoma cell line, UMR 106-01. Our results of the expression pattern of core binding factor alpha1 (Cbfa1), which binds to the runt domain site, indicated that there is no change in the levels of Cbfa1 protein or RNA under either control conditions or after PTH treatment. The importance of posttranslational modification of Cbfa1 in the signaling pathway for PTH-induced collagenase-3 promoter activity was analyzed. PTH stimulation of collagenase-3 promoter activity was completely abrogated by protein kinase A (PKA) inhibition. To determine the role of PKA activity with respect to Cbfa1 activation (in addition to its known activity of phosphorylating cAMP-response element-binding protein to enhance c-fos promoter activity), we utilized the heterologous Gal4 transcription system. PTH stimulated the transactivation of activation domain-3 in Cbfa1 through the PKA site. In vitro phosphorylation studies indicated that the PKA site in the wild type activation domain-3 is a substrate for phosphorylation by PKA. Thus, we demonstrate that PTH induces a PKA-dependent transactivation of Cbfa1, and this transactivation is required for collagenase-3 promoter activity in UMR cells.

Correlation of estradiol, parathyroid hormone, interleukin-6, and soluble interleukin-6 receptor during the normal menstrual cycle

Rodent models suggest that estradiol deficiency promotes bone loss through increasing interleukin-6 (IL-6) activity. However, it is controversial as to whether these findings are applicable to humans. To evaluate estradiol-mediated modulation of IL-6 activity in relation to bone metabolism in humans, we measured serum IL-6, soluble interleukin-6 receptor (sIL-6R), estradiol (E2), progesterone, luteinizing hormone, follicle-stimulating hormone, intact parathyroid hormone (PTH), serum and urine Ca, and bone biochemical markers (serum bone-specific alkaline phosphatase, osteocalcin, and serum and urine deoxypyridinoline [Dpd]) across one menstrual cycle for 211 women. Neither IL-6 nor sIL-6R levels differed between the follicular phase (FP) and the luteal phases (LP). However, IL-6 was negatively correlated with E2 during the FP (p =0.003). Furthermore, IL-6 correlated positively with serum Ca over the entire cycle (p = 0.0091. Serum Ca correlated positively with serum (p = 0.040) and urine (p = 0.006) Dpd. PTH was significantly higher during the FP than in the LP (p = 0.004). PTH was negatively related to E2 (p = 0.002), serum Ca (p < 0.001), and urine Ca (p = 0.036), whereas it was positively correlated with IL-6 (p = 0.027). These data demonstrate that IL-6 and PTH fluctuate with E2, and serum II-6 is associated with PTH levels during the menstrual cycle. However, the role of 11-6 in bone remodeling during the normal menstrual cycle remains to be determined.

Molecular mechanisms of actions of interleukin-6 on the brain, with special reference to serotonin and the hypothalamo-pituitary-adrenocortical axis

Biological activities of the multifunctional cytokine, interleukin-6 (IL-6) include stimulation of B cell proliferation, immunoglobulin production, and initiation of the acute-phase response. IL-6 affects the CNS in that it activates the hypothalamo-pituitary-adrenocortical (HPA) axis and increases brain tryptophan and serotonin metabolism. IL-6 has been proposed as an important mediator of interaction between the neuroendocrine and immune systems. The peripheral and central effects of IL-6 are presumably mediated through its membrane receptor (IL-6R). IL-6, IL-6R and their respective mRNAs have been detected in several brain regions. Although the functions of cytokines overlap considerably, each displays its own characteristic properties. Expression of IL-6 in the brain has been observed in several CNS disorders, some of which have been associated with disorders of serotonin metabolism. It is proposed that interactions between IL-6 and brain serotonin is a complex process which involves corticotropin-releasing factor (CRF) and opioid peptides. It is likely that the molecular mechanisms underlying the actions of IL-6 on the HPA axis and its other brain functions involve the integrated effects of glutamate, Ca2+, 3',5'-cyclic AMP, protein kinase C, and other metabolic pathways.

Parathyroid hormone-related protein (107-139) stimulates interleukin-6 expression in human osteoblastic cells

The N-terminal region of both parathyroid hormone (PTH) and PTH-related protein (PTHrP) binds to the same PTH/PTHrP receptor in osteoblasts. However, C-terminal PTHrP (107-139) inhibits growth and various functions of osteoblasts and osteoclasts apparently through PTHrP-specific receptors. PTH (1-34) and PTHrP (1-34) rapidly induce interleukin-6 (IL-6) expression by osteoblasts. The aim of the present study was to assess the effects of PTHrP (107-139) on IL-6 gene expression and secretion by osteoblastic cells from human trabecular bone (hOB). Using reverse transcription followed by PCR, it was found that IL-6 mRNA was twofold maximally increased by either PTHrP (1-34) or PTHrP (107-139), at 10 nM, over basal within 1 to 2 h in hOB cells. This effect of PTHrP (107-139), and that of PTHrP (1-34), were abolished by the transcription inhibitor actinomycin D. Meanwhile, puromycin, a protein synthesis inhibitor, superinduced IL-6 expression in the presence or absence of each PTHrP peptide. Both PTHrP (1-34) and PTHrP (107-139), but not PTHrP (38-64), stimulated IL-6 secretion to the hOB cell-conditioned medium at 24 h, dose dependently. In addition, this maximal stimulatory effect (twofold over basal) was similar with each PTHrP peptide alone, and not additive when added together. PTHrP (107-139) stimulation of mRNA and protein in hOB cells was abolished by bisindolylmaleimide I, a protein kinase C inhibitor, but not by either adenosine 3',5'-cyclic monophosphorothioate, Rp-isomer (Rp-cAMPS), or N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H89), two protein kinase A inhibitors. These results indicate that C-terminal PTHrP, like its N-terminal domain, induces IL-6 production by human osteoblastic cells. This effect of both PTHrP regions could provide a mechanism to modulate bone turnover.

Parathyroid hormone induces interleukin-6 heterogeneous nuclear and messenger RNA expression in murine calvarial organ cultures

The cytokine, interleukin-6 (IL-6), is produced by osteoblasts and may in part mediate parathyroid hormone (PTH)-stimulated bone resorption. The goals of the present study were: (1) to examine PTH induction of IL-6 expression in 7-day-old mouse calvarial organ cultures; (2) to assess the role of intracellular signaling pathways in this model; and (3) to determine whether PTH regulates IL-6 expression by a transcriptional mechanism. Northern blot analysis of calvarial RNA showed that PTH(1-34) at 0.1-100 nmol/L induced IL-6 mRNA at 0.5 h with a peak at 2 h. Forskolin at 10 micromol/L and 8-bromocyclic-AMP at 3 mmol/L also induced IL-6 mRNA with a peak at 2 h. Phorbol myristate acetate induced IL-6 expression, whereas ionomycin and PTH(3-34) amide, an N-terminal-truncated PTH analog that has reduced ability to activate the cAMP-PKA pathway, were much less effective. PMA pretreatment of calvariae greatly blocked IL-6 mRNA induction by a subsequent dose of PMA and decreased induction by PTH and forskolin to a much lesser extent. A reverse-transcriptase polymerase chain reaction (RT-PCR) assay was used to measure IL-6 heterogeneous nuclear RNA (hnRNA) and mRNA. A 5' primer spanning exons 1 and 2 and a 3' primer complementary to exon 5 of the murine IL-6 gene were used to detect IL-6 mRNA as a 638 bp product. A 5' primer corresponding to intron 4 of the murine IL-6 gene and the 3' primer were used to detect IL-6 hnRNA as a 370 bp product. RT-PCR of total calvarial RNA showed that the induction of IL-6 hnRNA by PTH and other agonists was similar to their induction of IL-6 mRNA. These data support the conclusion that PTH transcriptionally induces IL-6 gene expression in murine calvarial organ cultures mainly through the cAMP-PKA signaling pathway.

Brown adipose tissue. More than an effector of thermogenesis?

Brown adipose tissue (BAT) produces heat by oxidation of fatty acids. This takes place when the tissue is stimulated by norepinephrine; the molecular background for the ability of BAT to produce heat is the tissue-specific mitochondrial protein UCP1. In the classic view of BAT with respect to fever, BAT is an effector organ, producing heat especially during the onset phase of the fever. There is good evidence that BAT thermogenesis is stimulated via a lipopolysaccharide (LPS), interleukin (IL)-1 beta, IL-6, prostaglandin E cascade. Under physiologic conditions of constantly stimulated activity, BAT is expected to be recruited, but in fevers this is only evident in thyroxine fever. However, BAT may be more than merely an effector. There are indications of a correlation between the amount of BAT and the intensity of fevers, and brown adipocytes can indeed produce IL-1 alpha and IL-6. Furthermore, brown adipocytes are directly sensitive to LPS; this LPS sensitivity is augmented in brown adipocytes from IL-1 beta-deficient mice. Thus, BAT may also have a controlling role in thermoregulation. The existence of transgenic mice with ablations of proteins central in fever and in BAT thermogenesis opens up possibilities for identification and elucidation of this putative new role for brown adipose tissue as an endocrine organ involved in the control of fever.