Cyclopropanyldehydrocostunolide LJ attenuates high glucose-induced podocyte injury by suppressing RANKL/RANK-mediated NF-κB and MAPK signaling pathways

AIMS

The aim of this research was to investigate the effects of cyclopropanyldehydrocostunolide (also named LJ), a derivative of sesquiterpene lactones (SLs), on high glucose (HG)-induced podocyte injury and the associated molecular mechanisms.

METHODS

Differentiated mouse podocytes were incubated in different treatments. The migration and albumin filtration of podocytes were examined by Transwell filters. The protein and mRNA levels of MCP-1 were measured using enzyme-linked immunosorbent assay (ELISA) and quantitative real-time PCR (q-PCR). Protein expression and phosphorylation were detected by western blot, and the nuclear translocation of NF-κB was performed with a confocal microscope. The gene expression of the receptor activator for NF-κB (RANK) was silenced by small interfering RNA (siRNA).

RESULTS

Our results showed that HG enhanced migration, albumin filtration and MCP-1 expression in podocytes. At the molecular level, HG promoted the phosphorylation of NF-κB/p65, IKKβ, IκBα, mitogen-activated protein kinase (MAPK) and the nuclear translocation of p65. LJ reversed the effects of HG in a dose-dependent manner. Furthermore, our data provided the first demonstration that the receptor activator for NF-κB ligand (RANKL) and its cognate receptor RANK were overexpressed in HG-induced podocytes and were downregulated by LJ. RANK siRNA also attenuated HG-induced podocyte injury and markedly inhibited the activation of NF-κB and MAPK signaling pathways.

CONCLUSIONS

LJ attenuates HG-induced podocyte injury by suppressing RANKL/RANK-mediated NF-κB and MAPK signaling pathways.

Monoclonal antibody targeting of fibroblast growth factor receptor 1c ameliorates obesity and glucose intolerance via central mechanisms

We have generated a novel monoclonal antibody targeting human FGFR1c (R1c mAb) that caused profound body weight and body fat loss in diet-induced obese mice due to decreased food intake (with energy expenditure unaltered), in turn improving glucose control. R1c mAb also caused weight loss in leptin-deficient ob/ob mice, leptin receptor-mutant db/db mice, and in mice lacking either the melanocortin 4 receptor or the melanin-concentrating hormone receptor 1. In addition, R1c mAb did not change hypothalamic mRNA expression levels of Agrp, Cart, Pomc, Npy, Crh, Mch, or Orexin, suggesting that R1c mAb could cause food intake inhibition and body weight loss via other mechanisms in the brain. Interestingly, peripherally administered R1c mAb accumulated in the median eminence, adjacent arcuate nucleus and in the circumventricular organs where it activated the early response gene c-Fos. As a plausible mechanism and coinciding with the initiation of food intake suppression, R1c mAb induced hypothalamic expression levels of the cytokines Monocyte chemoattractant protein 1 and 3 and ERK1/2 and p70 S6 kinase 1 activation.

Both 25-hydroxyvitamin-D3 and 1,25-dihydroxyvitamin-D3 reduces inflammatory response in human periodontal ligament cells

Periodontitis is an inflammatory disease leading to the destruction of periodontal tissue. Vitamin D3 is an important hormone involved in the preservation of serum calcium and phosphate levels, regulation of bone metabolism and inflammatory response. Recent studies suggest that vitamin D3 metabolism might play a role in the progression of periodontitis. The aim of the present study was to examine the effects of 25(OH)D3, which is stable form of vitamin D3 in blood, and biologically active form 1,25(OH)2D3 on the production of interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemotactic protein-1 (MCP-1) by cells of periodontal ligament. Commercially available human periodontal ligament fibroblasts (hPdLF) and primary human periodontal ligament cells (hPdLC) were used. Cells were stimulated with either Porphyromonas gingivalis lipopolysaccharide (LPS) or heat-killed P. ginigvalis in the presence or in the absence of 25(OH)D3 or 1,25(OH)2D3 at concentrations of 10-100 nM. Stimulation of cells with either P. gingivalis LPS or heat-killed P. gingivalis resulted in a significant increase of the expression levels of IL-6, IL-8, and MCP-1 in gene as well as in protein levels, measured by qPCR and ELISA, respectively. The production of these pro-inflammatory mediators in hPdLF was significantly inhibited by both 25(OH)D3 and 1,25(OH)2D3 in a dose-dependent manner. In primary hPdLCs, both 25(OH)D3 and 1,25(OH)2D3 inhibited the production of IL-8 and MCP-1 but have no significant effect on the IL-6 production. The effect of both 25(OH)D3 and 1,25(OH)2D3 was abolished by specific knockdown of vitamin D3 receptor by siRNA. Our data suggest that vitamin D3 might play an important role in the modulation of periodontal inflammation via regulation of cytokine production by cells of periodontal ligament. Further studies are required for better understanding of the extents of this anti-inflammatory effect and its involvement in the progression of periodontal disease.

Adipocytes from New Zealand obese mice exhibit aberrant proinflammatory reactivity to the stress signal heat shock protein 60

Adipocytes release immune mediators that contribute to diabetes-associated inflammatory processes. As the stress protein heat shock protein 60 (Hsp60) induces proinflammatory adipocyte activities, we hypothesized that adipocytes of diabetes-predisposed mice exhibit an increased proinflammatory reactivity to Hsp60. Preadipocytes and mature adipocytes from nonobese diabetic (NOD), New Zealand obese (NZO), and C57BL/6J mice were analyzed for Hsp60 binding, Hsp60-activated signaling pathways, and Hsp60-induced release of the chemokine CXCL-1 (KC), interleukin 6 (IL-6), and macrophage chemoattractant protein-1 (MCP-1). Hsp60 showed specific binding to (pre-)adipocytes of NOD, NZO, and C57BL/6J mice. Hsp60 binding involved conserved binding structure(s) and Hsp60 epitopes and was strongest to NZO mouse-derived mature adipocytes. Hsp60 exposure induced KC, IL-6, and MCP-1 release from (pre-)adipocytes of all mouse strains with a pronounced increase of IL-6 release from NZO mouse-derived adipocytes. Compared to NOD and C57BL/6J mouse derived cells, Hsp60-induced formation of IL-6, KC, and MCP-1 from NZO mouse-derived (pre-)adipocytes strongly depended on NF κ B-activation. Increased Hsp60 binding and Hsp60-induced IL-6 release by mature adipocytes of NZO mice suggest that enhanced adipocyte reactivity to the stress signal Hsp60 contributes to inflammatory processes underlying diabetes associated with obesity and insulin resistance.

Functional expression of TWEAK and the receptor Fn14 in human malignant ovarian tumors: possible implication for ovarian tumor intervention

The aim of this current study was to investigate the expression of the tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible 14 (Fn14) in human malignant ovarian tumors, and test TWEAK’s potential role on tumor progression in cell models in-vitro. Using immunohistochemistry (IHC), we found that TWEAK and its receptor Fn14 were expressed in human malignant ovarian tumors, but not in normal ovarian tissues or in borderline/benign epithelial ovarian tumors. High levels of TWEAK expression was detected in the majority of malignant tumors (36 out of 41, 87.80%). Similarly, 35 out of 41 (85.37%) malignant ovarian tumors were Fn14 positive. In these malignant ovarian tumors, however, TWEAK/Fn14 expression was not corrected with patients’ clinical subtype/stages or pathological features. In vitro, we demonstrated that TWEAK only inhibited ovarian cancer HO-8910PM cell proliferation in combination with tumor necrosis factor-α (TNF-α), whereas either TWEAK or TNF-α alone didn’t affect HO-8910PM cell growth. TWEAK promoted TNF-α production in cultured THP-1 macrophages. Meanwhile, conditioned media from TWEAK-activated macrophages inhibited cultured HO-8910PM cell proliferation and invasion. Further, TWEAK increased monocyte chemoattractant protein-1 (MCP-1) production in cultured HO-8910PM cells to possibly recruit macrophages. Our results suggest that TWEAK/Fn14, by activating macrophages, could be ovarian tumor suppressors. The unique expression of TWEAK/Fn14 in malignant tumors indicates that it might be detected as a malignant ovarian tumor marker.

CCR2 acts as scavenger for CCL2 during monocyte chemotaxis

BACKGROUND

Leukocyte migration is essential for effective host defense against invading pathogens and during immune homeostasis. A hallmark of the regulation of this process is the presentation of chemokines in gradients stimulating leukocyte chemotaxis via cognate chemokine receptors. For efficient migration, receptor responsiveness must be maintained whilst the cells crawl on cell surfaces or on matrices along the attracting gradient towards increasing concentrations of agonist. On the other hand agonist-induced desensitization and internalization is a general paradigm for chemokine receptors which is inconsistent with the prolonged migratory capacity.

METHODOLOGY/PRINCIPAL FINDINGS

Chemotaxis of monocytes was monitored in response to fluorescent CCL2-mCherry by time-lapse video microscopy. Uptake of the fluorescent agonist was used as indirect measure to follow the endogenous receptor CCR2 expressed on primary human monocytes. During chemotaxis CCL2-mCherry becomes endocytosed as cargo of CCR2, however, the internalization of CCR2 is not accompanied by reduced responsiveness of the cells due to desensitization.

CONCLUSIONS/SIGNIFICANCE

During chemotaxis CCR2 expressed on monocytes internalizes with the bound chemoattractant, but cycles rapidly back to the plasma membrane to maintain high responsiveness. Moreover, following relocation of the source of attractant, monocytes can rapidly reverse their polarization axis organizing a new leading edge along the newly formed gradient, suggesting a uniform distribution of highly receptive CCR2 on the plasma membrane. The present observations further indicate that during chemotaxis CCR2 acts as scavenger consuming the chemokine forming the attracting cue.

Agonist-specific regulation of monocyte chemoattractant protein-1 expression by cyclooxygenase metabolites in hepatic stellate cells

Activated hepatic stellate cells (HSC) regulate the liver "wound-healing" response through expression of chemokines, including monocyte chemoattractant protein-1 (MCP-1), which participate in the formation of the inflammatory infiltrate during liver injury. Cyclooxygenase (COX) catalyzes the conversion of arachidonic acid into prostaglandins, which may contribute to the inflammatory response. In this study, we investigated the effects of COX inhibitors on the expression of MCP-1 in cultured HSC. Pretreatment of HSC with nonspecific COX inhibitors such as indomethacin or ibuprofen markedly reduced the expression of MCP-1 caused by exposure to tumor necrosis factor alpha (TNF-alpha) or interleukin-1alpha (IL-1alpha). NS-398, a specific COX-2 inhibitor, also resulted in a dose-dependent inhibition of MCP-1 gene and protein expression. These effects were dependent on reduced MCP-1 transcription, as established using a reporter plasmid. In contrast, the up-regulation of MCP-1 expression caused by interferon gamma (IFN-gamma) was not sensitive to COX inhibitors. Quiescent HSC did not show detectable expression of COX-2, which became evident after activation in culture, and while TNF-alpha and IL-1alpha markedly increased the expression of COX-2, IFN-gamma did not have any effects. Pretreatment of HSC with the stable cyclic adenosine monophosphate (cAMP) analog, 8-bromo cAMP, reverted the effects of the COX-2 inhibitor, but not of a nuclear factor-kappaB (NF-kappaB) inhibitor, demonstrating that prostaglandins modulate MCP-1 expression via production of cAMP. On the other hand, the action of NF-kappaB inhibitors was negligible in IFN-gamma-stimulated cells. These findings indicate that cross-talk between cytokines and a prostaglandin-cAMP pathway differentially regulates the proinflammatory potential of HSC, contributing to the modulation of liver tissue inflammation.

Enhanced pulmonary allergic responses to Aspergillus in CCR2-/- mice

Allergic responses to Aspergillus species exacerbate asthma and cystic fibrosis. The natural defense against live Aspergillus fumigatus spores or conidia depends on the recruitment and activation of mononuclear and polymorphonuclear leukocytes, events that are dependent on chemotactic cytokines. In this study, we explored the relative contribution of the monocyte chemoattractant protein-1 receptor, CCR2, in the pulmonary response to A. fumigatus conidia. Following sensitization to soluble A. fumigatus Ags, mice lacking CCR2 due to targeted deletion were markedly more susceptible to the injurious effects of an intrapulmonary challenge with live conidia compared with mice that expressed CCR2 or CCR2+/+. CCR2-/- mice exhibited a major defect in the recruitment of polymorphonuclear cells, but these mice also had significantly more eosinophils and lymphocytes in bronchoalveolar lavage samples. CCR2-/- mice also had significant increases in serum levels of total IgE and whole lung levels of IL-5, IL-13, eotaxin, and RANTES compared with CCR2+/+ mice. Airway inflammation, hyper-responsiveness to spasmogens, and subepithelial fibrosis were significantly enhanced in CCR2-/- mice compared with CCR2+/+ mice after the conidia challenge. Thus, these findings demonstrate that CCR2 plays an important role in the immune response against A. fumigatus, thereby limiting the allergic airway inflammatory and remodeling responses to this fungus.

Identification of surface residues of the monocyte chemotactic protein 1 that affect signaling through the receptor CCR2

The CC chemokine, monocyte chemotactic protein, 1 (MCP-1) functions as a major chemoattractant for T-cells and monocytes by interacting with the seven-transmembrane G protein-coupled receptor CCR2. To identify which residues of MCP-1 contribute to signaling though CCR2, we mutated all the surface-exposed residues to alanine and other amino acids and made some selective large changes at the amino terminus. We then characterized the impact of these mutations on three postreceptor pathways involving inhibition of cAMP synthesis, stimulation of cytosolic calcium influx, and chemotaxis. The results highlight several important features of the signaling process and the correlation between binding and signaling: The amino terminus of MCP-1 is essential as truncation of residues 2-8 ([1+9-76]hMCP-1) results in a protein that cannot stimulate chemotaxis. However, the exact peptide sequence may be unimportant as individual alanine mutations or simultaneous replacement of residues 3-6 with alanine had little effect. Y13 is also important and must be a large nonpolar residue for chemotaxis to occur. Interestingly, both Y13 and [1+9-76]hMCP-1 are high-affinity binders and thus affinity of these mutants is not correlated with ability to promote chemotaxis. For the other surface residues there is a strong correlation between binding affinity and agonist potency in all three signaling pathways. Perhaps the most interesting observation is that although Y13A and [1+9-76]hMCP are antagonists of chemotaxis, they are agonists of pathways involving inhibition of cAMP synthesis and, in the case of Y13A, calcium influx. These results demonstrate that these two well-known signaling events are not sufficient to drive chemotaxis. Furthermore, it suggests that specific molecular features of MCP-1 induce different conformations in CCR2 that are coupled to separate postreceptor pathways. Therefore, by judicious design of antagonists, it should be possible to trap CCR2 in conformational states that are unable to stimulate all of the pathways required for chemotaxis.