Calcium signaling pathway involving calcineurin regulates interleukin-8 gene expression through activation of NF-kappaB in human osteoblast-like cells

IL-6-induced response of human osteoblasts from patients with rheumatoid arthritis after inhibition of the signaling pathway

Interleukin (IL-) 6 is a critical factor in inflammatory processes of rheumatoid arthritis (RA). This is of high interest as the progression of RA may lead to the implantation of joint endoprostheses, which is associated with a pro-inflammatory increase in IL-6 in the periprosthetic tissue. Biological agents such as sarilumab have been developed to inhibit IL-6-mediated signaling. However, IL-6 signaling blockade should consider the inhibition of inflammatory processes and the regenerative functions of IL-6. This in vitro study investigated whether inhibiting IL-6 receptors can affect the differentiation of osteoblasts isolated from patients with RA. Since wear particles can be generated at the articular surfaces of endoprostheses leading to osteolysis and implant loosening, the potential of sarilumab to inhibit wear particle-induced pro-inflammatory processes should be investigated. Both in monocultures and indirect co-cultures with osteoclast-like cells (OLCs), human osteoblasts were stimulated with 50 ng/mL each of IL-6 + sIL-6R and in combination with sarilumab (250 nM) to characterize cell viability and osteogenic differentiation capacity. Furthermore, the influence of IL-6 + sIL-6R or sarilumab on viability, differentiation, and inflammation was evaluated in osteoblasts exposed to particles. Stimulation with IL-6 + sIL-6R and sarilumab did not affect cell viability. Except for the significant induction of RUNX2 mRNA by IL-6 + sIL-6R and a significant reduction with sarilumab, no effects on cell differentiation and mineralization could be detected. Furthermore, the different stimulations did not affect the osteogenic and osteoclastic differentiation of co-cultured cells. Compared to the osteoblastic monocultures, a decreased release of IL-8 was triggered in the co-culture. Among these, treatment with sarilumab alone resulted in the greatest reduction of IL-8. The co-culture also showed clearly increased OPN concentrations than the respective monocultures, with OPN secretion apparently triggered by the OLCs. Particle exposure demonstrated decreased osteogenic differentiation using different treatment strategies. However, sarilumab administration caused a trend toward a decrease in IL-8 production after stimulation with IL-6 + sIL-6R. The blockade of IL-6 and its pathway have no significant effect on the osteogenic and osteoclastic differentiation of bone cells derived from patients with RA. Nonetheless, observed effects on the reduced IL-8 secretion need further investigation.

UVA1 radiation inhibits calcineurin through oxidative damage mediated by photosensitization

The protein phosphatase calcineurin has been gradually revealing itself as the central controller of our immune response, although it is involved in a wide array of signaling pathways related to cellular development and cell cycle progression. As such, calcineurin is an attractive, yet delicate, therapeutic target for the prevention of allograft rejection and treatment of several inflammatory skin conditions. However, calcineurin activity is not only sensitive to immunosuppressants such as cyclosporin A and tacrolimus, but also subject to modulation by reactive oxygen species. We have recently shown, both in vivo and in vitro, that UVA1 radiation suppresses calcineurin activity. In this paper, we present evidence that this activity loss is due to singlet oxygen and superoxide generated by photosensitization and show that a closely related phosphatase, PP2A, is not affected. Furthermore, a survey of this damage reveals oxidation of several Met and Cys residues as well as an overall conformational change. These findings provide a mechanistic basis for the hypothesis that UVA1 and calcineurin inhibitors both affect the same signal transduction pathway in skin.

A novel 3-D mineralized tumor model to study breast cancer bone metastasis

Background

Metastatic bone disease is a frequent cause of morbidity in patients with advanced breast cancer, but the role of the bone mineral hydroxyapatite (HA) in this process remains unclear. We have developed a novel mineralized 3-D tumor model and have employed this culture system to systematically investigate the pro-metastatic role of HA under physiologically relevant conditions in vitro.

Methodology/Principal Findings

MDA-MB231 breast cancer cells were cultured within non-mineralized or mineralized polymeric scaffolds fabricated by a gas foaming-particulate leaching technique. Tumor cell adhesion, proliferation, and secretion of pro-osteoclastic interleukin-8 (IL-8) was increased in mineralized tumor models as compared to non-mineralized tumor models, and IL-8 secretion was more pronounced for bone-specific MDA-MB231 subpopulations relative to lung-specific breast cancer cells. These differences were pathologically significant as conditioned media collected from mineralized tumor models promoted osteoclastogenesis in an IL-8 dependent manner. Finally, drug testing and signaling studies with transforming growth factor beta (TGFβ) confirmed the clinical relevance of our culture system and revealed that breast cancer cell behavior is broadly affected by HA.

Conclusions/Significance

Our results indicate that HA promotes features associated with the neoplastic and metastatic growth of breast carcinoma cells in bone and that IL-8 may play an important role in this process. The developed mineralized tumor models may help to reveal the underlying cellular and molecular mechanisms that may ultimately enable more efficacious therapy of patients with advanced breast cancer.

Expression and activities of N-myristoyltransferase and calcineurin in normal and inflamed lungs

The role of N-myristoyltransferase and calcineurin is well established in signaling pathways. However, there are no data on their expression and activities in normal and inflamed lungs. The mechanisms of lung inflammation induced following administration of lipopolysaccharides (LPS) or exposure to swine barn air remain unclear. Therefore, we examined expression and activities of N-myristoyltransferase and calcineurin in normal and inflamed lungs of rats. Histopathology showed acute inflammation in the lungs of rats exposed to barn air or LPS but not of control rats. There was no difference in the activities of N-myristoyltransferase and calcineurin among the control, barn-exposed, and LPS-treated rat lungs. Although N-myristoyltransferase and calcineurin were localized in airway epithelium, blood vessel walls, alveolar macrophages, and septa in the lungs of rats from all the groups, the staining intensity was increased in the lungs from rats exposed to intravenous LPS or barn air. Densitometric analyses of Western blots of 55- and 60-kDa polypeptide bands corresponding to N-myristoyltransferase and calcineurin, respectively, in the lung homogenates revealed no differences among the groups. These results show that expression of myristoyltransferase and calcineurin in lung epithelium and endothelium and a cell-specific increase in immunohistochemical expression.

iNOS in cardiac myocytes plays a critical role in death in a murine model of hypertrophy induced by calcineurin

Transgenic overexpression of calcineurin (CN/Tg) in mouse cardiac myocytes results in hypertrophy followed by dilation, dysfunction, and sudden death. Nitric oxide (NO) produced via inducible NO synthase (iNOS) has been implicated in cardiac injury. Since calcineurin regulates iNOS expression, and since phenotypes of mice overexpressing iNOS are similar to CN/Tg, we hypothesized that iNOS is pathogenically involved in cardiac phenotypes of CN/Tg mice. CN/Tg mice had increased serum and cardiac iNOS levels. When CN/Tg-iNOS−/− and CN/Tg mice were compared, some phenotypes were similar: extent of hypertrophy and fibrosis. However, CN/Tg-iNOS−/− mice had improved systolic performance ( P < 0.001) and less heart block ( P < 0.0001); larger sodium current density and lower serum TNF-α levels ( P < 0.03); and less apoptosis ( P < 0.01) resulting in improved survival ( P < 0.0003). To define tissue origins of iNOS production, chimeric lines were generated. Bone marrow (BM) from wild-type or iNOS−/− mice was transplanted into CN/Tg mice. iNOS deficiency restricted to BM-derived cells was not protective. Calcineurin activates the local production of NO by iNOS in cardiac myocytes, which significantly contributes to sudden death, heart block, left ventricular dilation, and impaired systolic performance in this murine model of cardiac hypertrophy induced by the overexpression of calcineurin.

Acidic pH stimulates the production of the angiogenic CXC chemokine, CXCL8 (interleukin-8), in human adult mesenchymal stem cells via the extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, and NF-kappaB pathways

Blood vessel injury results in limited oxygen tension and diffusion leading to hypoxia, increased anaerobic metabolism, and elevated production of acidic metabolites that cannot be easily removed due to the reduced blood flow. Therefore, an acidic extracellular pH occurs in the local microenvironment of disrupted bone. The potential role of acidic pH and glu-leu-arg (ELR(+)) CXC chemokines in early events in bone repair was studied in human mesenchymal stem cells (hMSCs) treated with medium of decreasing pH (7.4, 7.0, 6.7, and 6.4). The cells showed a reciprocal increase in CXCL8 (interleukin-8, IL-8) mRNA levels as extracellular pH decreased. At pH 6.4, CXCL8 mRNA was induced >60x in comparison to levels at pH 7.4. hMSCs treated with osteogenic medium (OGM) also showed an increase in CXCL8 mRNA with decreasing pH; although, at a lower level than that seen in cells grown in non-OGM. CXCL8 protein was secreted into the medium at all pHs with maximal induction at pH 6.7. Inhibition of the G-protein-coupled receptor alpha, G(alphai), suppressed CXCL8 levels in response to acidic pH; whereas phospholipase C inhibition had no effect on CXCL8. The use of specific mitogen-activated protein kinase (MAPK) signal transduction inhibitors indicated that the pH-dependent increase in CXCL8 mRNA is due to activation of ERK and p38 pathways. The JNK pathway was not involved. NF-kappaB inhibition resulted in a decrease in CXCL8 levels in hMSCs grown in non-OGM. However, OGM-differentiated hMSCs showed an increase in CXCL8 levels when treated with the NF-kappaB inhibitor PDTC, a pyrrolidine derivative of dithiocarbamate.

Angiogenic CXC chemokine expression during differentiation of human mesenchymal stem cells towards the osteoblastic lineage

The potential role of ELR(+) CXC chemokines in early events in bone repair was studied using human mesenchymal stem cells (hMSCs). Inflammation, which occurs in the initial phase of tissue healing in general, is critical to bone repair. Release of cytokines from infiltrating immune cells and injured bone can lead to recruitment of MSCs to the region of repair. CXC chemokines bearing the Glu-Leu-Arg (ELR) motif are also released by inflammatory cells and serve as angiogenic factors stimulating chemotaxis and proliferation of endothelial cells. hMSCs, induced to differentiate with osteogenic medium (OGM) containing ascorbate, beta-glycerophosphate (beta-GP), and dexamethasone (DEX), showed an increase in mRNA and protein secretion of the ELR(+) CXC chemokines CXCL8 and CXCL1. CXCL8 mRNA half-life studies reveal an increase in mRNA stability upon OGM stimulation. Increased expression and secretion is a result of DEX in OGM and is dose-dependent. Inhibition of the glucocorticoid receptor with mifepristone only partially inhibits DEX-stimulated CXCL8 expression indicating both glucocorticoid receptor dependent and independent pathways. Treatment with signal transduction inhibitors demonstrate that this expression is due to activation of the ERK and p38 mitogen-activated protein kinase (MAPK) pathways and is mediated through the G(alphai)-coupled receptors. Angiogenesis assays demonstrate that OGM-stimulated conditioned media containing secreted CXCL8 and CXCL1 can induce angiogenesis of human microvascular endothelial cells in an in vitro Matrigel assay.

Enhanced IL-1beta-induced IL-8 production in cystic fibrosis lung epithelial cells is dependent of both mitogen-activated protein kinases and NF-kappaB signaling

Transcription nuclear factor-kappaB (NF-kappaB) is hyperactivated in cystic fibrosis (CF) lung epithelial cells, and participates in exaggerated IL-8 production in the CF lung. We recently found that rapid activation of NF-kappaB occurred in a CF lung epithelial IB3-1 cell line (CF cells) upon IL-1beta stimulation, which was not observed in its CFTR-corrected lung epithelial S9 cell line (corrected cells). To test whether other signaling pathways such as that of mitogen-activated protein kinases (MAPKs) could be involved in IL-1beta-induced IL-8 production of CF cells, we investigated ERK1/2, JNK, and p38MAP signaling compared to NF-kappaB. Within 30min, exposure to IL-1beta caused high activation of NF-kappaB, ERK1/2, p38MAP but not JNK in CF cells compared to corrected cells. Treatment of IL-1beta-stimulated CF cells with a series of chemical inhibitors of NF-kappaB, ERK1/2, and p38MAP, when used separately, reduced slightly IL-8 production. However, when used together, these inhibitors caused a blockade in IL-1beta-induced IL-8 production in CF cells. Understanding of the cross-talk between NF-kappaB and MAPKs signaling in CF lung epithelial cells may help in developing new therapeutics to reduce lung inflammation in patients with CF.

Mechanically induced intracellular calcium waves in osteoblasts demonstrate calcium fingerprints in bone cell mechanotransduction

An early response to mechanical stimulation of bone cells in vitro is an increase in intracellular calcium concentration ([Ca (2+)](i)). This study analyzed the [Ca (2+)](i) wave area, magnitude, duration, rise time, fall time, and time to onset in individual osteoblasts for two identical bouts of mechanical stimulation separated by a 30-min rest period. The area under the [Ca (2+)](i) wave increased in the second loading bout compared to the first. This suggests that rest periods may potentiate mechanically induced intracellular calcium signals. Furthermore, many of the [Ca (2+)](i) wave parameters were strongly, positively correlated between the two bouts of mechanical stimulation. For example, in individual primary osteoblasts, if a cell had a large [Ca (2+)](i) wave area in the first bout it was likely to have a large [Ca (2+)](i) wave area in the second bout (r (2) = 0.933). These findings support the idea that individual bone cells have "calcium fingerprints" (i.e., a unique [Ca (2+)](i) wave profile that is reproducible for repeated exposure to a given stimulus).