Integrins play an important role in cell adhesion to the extracellular matrix and other cells. Upon ligand binding, signaling is initiated and several intracellular pathways are activated. This leads to a wide variety of effects, depending on cell type. Integrin activation has been linked to proliferation, secretion of matrix-degrading enzymes, cytokine production, migration, and invasion. Dysregulated integrin expression is often found in malignant disease. Tumors use integrins to evade apoptosis or metastasize, indicating that integrin signaling has to be tightly controlled. During the course of rheumatoid arthritis, the synovial tissue is infiltrated by immune cells that secrete large amounts of cytokines. This pro-inflammatory milieu leads to an upregulation of integrin receptors and their ligands in the synovial tissue. As a consequence, integrin signaling is enhanced, leading to enhanced production of matrix-degrading enzymes and cytokines. Furthermore, in analogy to invading tumors, synovial fibroblasts start invading and degrading cartilage, thereby generating extracellular matrix debris that can further activate integrins.

Objective. The sympathetic nervous system confers a proinflammatory effect during the early phase of type II collagen-induced arthritis (CIA). These effects might be mediated by up-regulation of cytokines such as interferon-␥ (IFN␥) or chemokines such as CXCL1 (cytokine-induced neutrophil chemoattractant, or KC). This study aimed to identify the role of sympathetic neurotransmitters in splenic secretion of IFN␥ and KC shortly after the onset of CIA.Methods. At different time points during CIA, we determined the density of sympathetic nerve fibers in the spleens of mice. Spleens were removed when the mouse joints were assessed an arthritis score of 3 (at approximately day 32). Spleen slices (0.35 mm thick) were transferred to superfusion microchambers to allow observation of the effects of physiologically released sympathetic neurotransmitters on secretion of IFN␥ and KC.Results. Compared with control mice, mice with CIA demonstrated a decrease in sympathetic nerve fiber density in the spleens, which reached a minimum density shortly after the start of symptomatic arthritis (day 32). T cell depletion markedly reduced splenic secretion of IFN␥ and KC. Electrical-field stimulation of the spleen slices reduced the secretion of IFN␥, which was attenuated by an ␣ 1 -adrenergic antagonist. In addition, splenic IFN␥ secretion was stimulated by norepinephrine, via ␤-adrenergic receptors, and adenosine, via A 1 adenosine receptors. Similarly, splenic KC secretion was stimulated by norepinephrine, via ␤-adrenergic receptors.Conclusion. The results of this study demonstrate a reduction of sympathetic nerve fibers in the spleens of arthritic animals. Nevertheless, sympathetic nerves help to increase secretion of IFN␥ and KC, which, at the early stages shortly after the onset of CIA, can contribute to the proinflammatory effect of the sympathetic nervous system.

The nonstructural proteins of parvovirus exert a variety of disparate functions during viral infection ranging from promoter regulation, involvement in DNA replication, and induction of apoptosis. Our interest was focused on the possible mechanism by which the NS1 protein mediates its effects on the p6 promoter of parvovirus B19. It is known that the p6 promoter is highly active in different cell lines and interaction with the viral NS1 protein results in a further increase of the activity. The protein may function by binding directly to the viral DNA or via an indirect binding through interaction with cellular transcription factors bound to the promoter. We examined the interaction of the NS1 protein with cellular transcription factors which are involved in regulating the promoter activity. After purified baculovirus-expressed NS1 protein in gel retardation assays was added, an altered complex formation was observed, indicating that NS1 protein interacts with Sp1/Sp3 transcription factors. Enzyme-linked immunosorbent assays verified these findings. The direct interaction of NS1 protein with p6 promoter elements was analyzed by a coprecipitation assay whereby labeled oligonucleotides spanning the entire promoter region were incubated with NS1 protein followed by an immunoprecipitation with NS1-specific antibodies. An eight-nucleotide-long, almost palindromic sequence (AGGGCGGA) was found as potential NS1-binding motif. Footprint analysis with oligonucleotides containing this DNA motif confirmed this result. Thus, transcriptional regulation by the NS1 protein may involve both the interaction with Sp1/Sp3 that binds to the promoter region and direct binding of NS1 to the promoter DNA.

ABSTRACT

IntroductionThe endocannabinoid system modulates function of immune cells and mesenchymal cells such as fibroblasts, which contribute to cartilage destruction in rheumatoid arthritis (RA). The aim of the study was to determine the influence of N-acylethanolamines anandamide (AEA), palmitoylethanolamine (PEA) and oleylethanolamine (OEA) on several features of arthritic inflammation in vitro (human material) and in vivo (a mouse model).MethodsImmunofluorescence and western blotting were used to detect cannabinoid receptors and related enzymes. Cytokines and MMP-3 were measured by ELISA. Intracellular signaling proteins were detected by proteome profiling. Proliferation was quantified by CTB reagent. Adhesion was assessed by the xCELLigence system. After onset of collagen type II arthritis, mice were treated daily with the FAAH inhibitor JNJ1661010 (20 mg/kg) or vehicle.ResultsIL-6, IL-8 and MMP-3 (determined only in synovial fibroblasts (SFs)) were downregulated in primary synoviocytes and SFs of RA and OA after AEA, PEA and OEA treatment. In SFs, this was due to activation of TRPV1 and TRPA1 in a COX-2-dependent fashion. FAAH inhibition increased the efficacy of AEA in primary synoviocytes but not in SFs. The effects of OEA and PEA on SFs were diminished by FAAH inhibition. Adhesion to fibronectin was increased in a CB1-dependent manner by AEA in OASFs. Furthermore, elevation of endocannabinoids ameliorated collagen-induced arthritis in mice.ConclusionsN-acylethanolamines exert anti-inflammatory effects in SFs. A dual FAAH/COX-2 inhibitor, increasing N-acylethanolamine levels with concomitant TRP channel desensitization, might be a good candidate to inhibit the production of proinflammatory mediators of synovial cells and to reduce erosions.Electronic supplementary materialThe online version of this article (doi:10.1186/s13075-015-0845-5) contains supplementary material, which is available to authorized users.