Showing papers by "Lothar Rink published in 2013"

Zinc deficiency induces production of the proinflammatory cytokines IL-1β and TNFα in promyeloid cells via epigenetic and redox-dependent mechanisms

Abstract: The deprivation of zinc, caused by malnutrition or as a consequence of aging or disease, strongly affects immune cell functions, causing higher frequency of infections. Among other effects, an increased production of reactive oxygen species (ROS) and proinflammatory cytokines has been observed in zinc-deficient patients, but the underlying mechanisms were unknown. The aim of the current study was to define mechanisms explaining the increase in proinflammatory cytokine production during zinc deficiency, focusing on the role of epigenetic and redox-mediated mechanisms. Interleukin (IL)-1β and tumor necrosis factor (TNF)α production was increased in HL-60 cells under zinc deficiency. Analyses of the chromatin structure demonstrated that the elevated cytokine production was due to increased accessibilities of IL-1β and TNFα promoters in zinc-deficient cells. Moreover, the level of nicotinamide adenine dinucleotide phosphate-oxidase (NADPH) oxidase-produced ROS was elevated under zinc deficiency, subsequently leading to p38 mitogen-activated protein kinase (MAPK) phosphorylation. The increased activation of p38 MAPK appeared to be necessary for posttranscriptional processes in IL-1β and TNFα synthesis. These data demonstrate that IL-1β and TNFα expression under zinc deficiency is regulated via epigenetic and redox-mediated mechanisms. Assuming an important role of zinc in proinflammatory cytokine regulation, this should encourage research in the use of zinc supplementation for treatment of inflammatory diseases.

Differential Regulation of TLR-Dependent MyD88 and TRIF Signaling Pathways by Free Zinc Ions

Abstract: Zinc signals are utilized by several immune cell receptors. One is TLR4, which causes an increase of free zinc ions (Zn2+) that is required for the MyD88-dependent expression of inflammatory cytokines. This study investigates the role of Zn2+ on Toll/IL-1R domain–containing adapter inducing IFN-β (TRIF)–dependent signals, the other major intracellular pathway activated by TLR4. Chelation of Zn2+ with the membrane-permeable chelator N,N,N’,N’-Tetrakis(2-pyridylmethyl)ethylenediamine augmented TLR4-mediated production of IFN-β and subsequent synthesis of inducible NO synthase and production of NO. The effect is based on Zn2+ acting as a negative regulator of the TRIF pathway via reducing IFN regulatory factor 3 activation. This was also observed with TLR3, the only TLR that signals exclusively via TRIF, but not MyD88, and does not trigger a zinc signal. In contrast, IFN-γ–induced NO production was unaffected by N,N,N’,N’-Tetrakis(2-pyridylmethyl)ethylenediamine. Taken together, Zn2+ is specifically involved in TLR signaling, where it differentially regulates MyD88 and TRIF signaling via a zinc signal or via basal Zn2+ levels, respectively.

Zinc signals in neutrophil granulocytes are required for the formation of neutrophil extracellular traps

Abstract: Zinc signals, i.e. changes in the free intracellular Zn(2+)concentration, are an integral component of signal transduction in several immune cells. The aim of the present study was to investigate if this is also the case in neutrophil granulocytes. One neutrophil function is NETosis, the release of a matrix composed of DNA, chromatin and granule proteins to capture extracellular bacteria within so-called neutrophil extracellular traps (NET). NETosis can be induced by the protein kinase C (PKC) activator 12-myristate 13-acetate (PMA). PMA treatment led to a zinc signal in neutrophil granulocytes. NETosis was inhibited when the zinc signal was sequestered by the membrane permeable high affinity chelator N,N,N',N',-tetrakis (2-pyridylmethyl)ethylenediamine (TPEN). PKC-mediated NET formation depends on the production of reactive oxygen species (ROS) by NADPH oxidase. Inhibition of NADPH oxidase with diphenyleneiodonium chloride blocked ROS formation and NETosis, as well as the zinc signal. TPEN, however, had no effect on PKC activity and ROS production, indicating that Zn(2+) is not required for activation of PKC, but for signals downstream of ROS production. In conclusion, zinc signals are an essential component of the ROS-dependent signal transduction leading to NETosis.

Zinc deficiency adversely influences interleukin-4 and interleukin-6 signaling.

Abstract: Zinc deficiency is accompanied by a severe impairment of the immune system, causing a high risk for infections and autoimmune diseases due to altered functionality of B- and T- cells. The influence of zinc deficiency on T- and B- cells via alteration of cytokine expression is well established. The aim of this study was to examine potential direct effects of zinc deficiency on the reactivity of B- and T- cells. Zinc deficient B- and T- cells revealed divergent reaction patterns compared to zinc sufficienT-cells. This was manifested by a stronger proliferative response following IL-6 and IL-2 stimulation on the one hand, but less proliferation following IL-4 stimulation on the other hand. Moreover, these results were supported by the finding that the B- and T-cell signaling cascades activated by IL-4 or IL-6, respectively, were affected directly by zinc deficiency, resulting in reduced Stat6 phosphorylation and increased Stat3 phosphorylation. Whereas the transcription factor Stat6 is involved in IL-4 signaling, Stat3 is activated by IL-6 signaling. Consequently, these results show opposing effects of zinc deficiency on IL-4 and IL-6/IL-2 signaling pathways, thus underlying the importance of zinc for proper immune function.

Impact of lead and mercuric ions on the interleukin-2-dependent proliferation and survival of T cells.

Abstract: Mercury and lead are widespread in the environment, causing chronic exposure of a large population to low concentrations of these metals. While several studies demonstrated that low levels of both metals affect the immune system, little is known about underlying molecular mechanisms. The objective of this study was to investigate the impact of mercuric (Hg2+) and lead (Pb2+) ions on T cells. Up to 100 μM Pb(NO3)2 had no effect on cellular viability and proliferation. In contrast, HgCl2 caused a concentration-dependent decline of viable leukocytes and especially of activated T cells. Additionally, Hg2+ induced reactive oxygen species (ROS) generation accompanied by the loss of mitochondrial transmembrane potential, measured by Dihydrorhodamine and Rhodamine-123, respectively. The antioxidant N-acetylcysteine partially reversed the toxic effects of Hg2+, pointing to an involvement of ROS. The major cytokine controlling T-cell survival and proliferation is interleukin (IL)-2. Hg2+ had no effect on the secretion of IL-2, but on IL-2 mediated signal transduction pathways, reducing phosphorylation of the downstream kinases ERK1/2 and AKT. Moreover, Hg2+ led to an arrest of the cells in the S phase of the cell cycle. Taken together, these data fit a model in which Hg2+ disrupts mitochondria, and the resulting release of ROS inhibits IL-2-dependent signal transduction, reducing proliferation and survival of T cells.

Application of Zinpyr-1 for the investigation of zinc signals in Escherichia coli

Abstract: Changes of the pico- to nanomolar concentration of free intracellular Zn2+ are part of the signal transduction in mammalian cells. These zinc signals regulate the enzymatic activity of target proteins such as protein tyrosine phosphatases. For Escherichia coli, previous studies have reported diverging concentrations from femto- to picomolar, raising the question if Zn2+ could also have a function in bacterial signaling. This manuscript explores the use of the low molecular weight fluorescent probe Zinpyr-1 in E. coli. The probe detects free Zn2+ in these bacteria. Comparable to mammalian cells, other metal ions, especially Hg2+ and Cd2+, interfere with the detection of Zn2+. Moreover, experiments in E. coli were particularly prone to artifacts based on cellular autofluorescence, necessitating corrections that are not required in mammalian cells. Based on measurements in lysates of E. coli and the mammalian cell line Jurkat, similar values between 0.1 and 0.2 nM free Zn2+ were found. For E. coli, this corresponds to less than one free zinc ion per cell. Moreover, phosphatase inhibition by Zn2+ was only observed in Jurkat, but not E. coli. This excludes a function for zinc signals as a regulator of bacterial phosphatases. Still, changes in the free Zn2+ concentration were observed in response to elevated extracellular Zn2+ and pH, or to addition of the detergent NP-40, suggesting that other processes could be controlled by the free intracellular Zn2+ concentration.

The role of zinc in immunity and inflammation

Abstract: : Zinc plays a diverse role in human health. It is an essential trace element for all life forms due to its role in cell proliferation, transcription and enzyme activity. Since the immune system is the organ system with the highest proliferation rate, zinc is crucial for maintaining an intact immune system and affects virtually all of its components. The chapter first gives an overview of zinc nutrition and the role of zinc in human health. The role of zinc in the modulation of cellular processes is discussed on the basis of the altered molecular mechanisms. The influence of zinc on the immune system is reported in more detail. Finally therapeutic uses and future options of zinc supplementation are critically analysed.

Effects of human Toll-like receptor 1 polymorphisms on ageing

Abstract: Advanced age results in crucial alterations of the innate and adaptive immune system leading to functional defects resulting in infection and chronic diseases. Toll-like receptors (TLR) recognize pathogenic structures and are important in the immune response to infections and vaccination. However, the role of TLR single nucleotide polymorphisms (SNP) is poorly understood in the setting of human ageing. This study investigated the impact of the TLR1 SNPs A743G and T1805G on ageing in different age groups from two European populations. The TLR1 genotypes 743AA/1805GG (TLR1neg) are associated with a TLR1 negative phenotype, impaired function and susceptibility to tuberculosis. Carriers of heterozygous 743AG/1805TG and homozygous 743GG/1805TT genotypes (TLR1pos) have a TLR1 positive phenotype. By comparing healthy young and old German donors, the old group showed a tendency to carry more TLR1neg and less homozygous TLR1pos genotypes. Anti-inflammatory Interleukin (IL)-1 receptor antagonist (Ra) was significantly elevated in supernatants of mononuclear cells from old German subjects with a TLR1pos genotype in contrast to those with the 743AA genotype. Healthy old individuals and nonagenarians from Italy displayed significantly higher frequencies of TLR1pos genotypes than the old group from Germany. The data show that tumor-necrosis-factor (TNF)α, CXCL8 and CCL2 levels were higher in old donors from Germany than in plasma levels from old Italian donors. TNFα and CCL2 levels were significantly raised in old German individuals compared to Italian nonagenarians. German and Italian donors with the TLR1neg genotype basically produced more CCL2 than older European donors with TLR1pos genotypes. The higher frequency of the TLR1pos genotype in elderly Italian subjects may result from different ethnic populations. Lower inflammatory mediator release of aged Italian individuals is probably due to different background in nutrition, diet, genetics and to psychological aspects. Elderly donors carrying TLR1pos genotypes basically release more anti-inflammatory IL-1Ra and less inflammatory CCL2 suggesting a decline of the pro-inflammatory status found in ageing and, therefore, this may define an anti-inflammatory phenotype. Future studies are needed to elucidate the association of a TLRpos genotype with decreased susceptibility to infections and reduced risk to develop artherosclerosis.