Cellular zinc homeostasis modulates polarization of THP-1-derived macrophages.

PURPOSE: Polarization of macrophages by environmental stimuli leads to the characteristic of different phenotypes that exhibit distinct functions, ranging in a continuous spectrum from pro-inflammatory M1 up to immunoregulatory and wound-healing M2 macrophages. Diseases like cancer, allergic asthma or diabetes are associated with an M1/M2 imbalance. Owing to the importance of the essential trace element zinc for the immune system and its involvement in signal transduction as a second messenger, we investigated the impact of zinc on M1 and M2 polarization of macrophages in vitro. METHODS: A polarization model with human THP-1 cells was established and validated with previously described markers using quantitative real-time PCR, Western blot and flow cytometry. Intracellular free Zn2+ was determined with FluoZin-3-AM. RESULTS: Whereas pSTAT1 and HLA-DR or pSTAT6 and Dectin-1 distinguish between M1 and M2 macrophages, respectively, CD86 and CD206 failed. Depending on the used markers, both zinc supplementation in physiological dose (50 µM) and zinc deficiency promote M1 polarization of THP-1-derived macrophages. Furthermore, zinc supplementation strongly inhibits M2 polarization. CONCLUSION: For the first time, we show a modulating effect of zinc for the polarization of human macrophages. The strong inhibitory effect of zinc supplementation on M2 polarization indicates a relevance regarding M2-dominated diseases like allergic asthma or cancer. All in all, zinc achieves a great potential for modulating macrophage polarization.

Zinc deficiency leads to reduced interleukin-2 production by active gene silencing due to enhanced CREMα expression in T cells.

BACKGROUND & AIMS: The micronutrient zinc is essential for proper immune function. Consequently, zinc deficiency leads to impaired immune function, as seen in decreased secretion of interleukin (IL)-2 by T cells. Although this association has been known since the late 1980s, the underlying molecular mechanisms are still unknown. Zinc deficiency and reduced IL-2 levels are especially found in the elderly, which in turn are prone to chronic diseases. Here, we describe a new molecular link between zinc deficiency and reduced IL-2 expression in T cells. METHODS: The effects of zinc deficiency were first investigated in vitro in the human T cell lines Jurkat and Hut-78 and complemented by in vivo data from zinc-supplemented pigs. A short- and long-term model for zinc deficiency was established. Zinc levels were detected by flow cytometry and expression profiles were investigated on the mRNA and protein level. RESULTS: The expression of the transcription factor cAMP-responsive-element modulator α (CREMα) is increased during zinc deficiency in vitro, due to increased protein phosphatase 2A (PP2A) activity, resulting in decreased IL-2 production. Additionally, zinc supplementation in vivo reduced CREMα levels causing increased IL-2 expression. On epigenetic levels increased CREMα binding to the IL-2 promoter is mediated by histone deacetylase 1 (HDAC1). The HDAC1 activity is inhibited by zinc. Moreover, deacetylation of the activating histone mark H3K9 was increased under zinc deficiency, resulting in reduced IL-2 expression. CONCLUSIONS: With the transcription factor CREMα a molecular link was uncovered, connecting zinc deficiency with reduced IL-2 production due to enhanced PP2A and HDAC1 activity.

Selection of an inadequate housekeeping gene leads to misinterpretation of target gene expression in zinc deficiency and zinc supplementation models.

BACKGROUND: Numerous studies try to find the most stable housekeeping gene for a specific experimental setup. However, there is no universal housekeeping gene described so far and, therefore, new testing of housekeeping genes at the beginning of a new experiment is of high importance. METHODS: In the present study, target gene expression of mitochondrial serine/threonine-protein phosphatase (PGAM)5, nuclear factor erythroid 2-related factor (Nrf)2, dynamin related protein (Drp)1 and kelch like ECH associated protein (Keap)1 was tested in zinc-deficient and zinc-supplemented THP-1 cells and compared to control cells. Normalization of results obtained by quantitative real-time polymerase chain reaction (qRT-PCR) was performed by using the housekeeping genes porphobilinogen deaminase (PBGD), ß-actin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Additionally, this 3 housekeeping genes were tested in Jurkat cells under these conditions. RESULTS: Surprisingly, analyses of one and the same target gene revealed opposite results depending on the used housekeeping gene. This was caused by significant altered housekeeping gene expressions due to zinc availability. CONCLUSION: Therefore, this study highlights the importance of choosing adequate housekeeping genes, which might comprise the use of more than one housekeeping gene when different conditions are tested, such as zinc deficiency and zinc supplementation. Related to the herein used experimental setup, the use ofGAPDH to study gene expression upon zinc deficiency and PBGD to study gene expression after zinc supplementation is recommended.

Zinc deficiency drives Th17 polarization and promotes loss of Treg cell function.

A high number of illnesses and disorders are connected to zinc deficiency. Equally, T cell polarization and a balance between different T helper (Th) cell subsets are essential. Therefore, in this study, the influence of zinc deficiency on T cell polarization and on respective signaling pathways was investigated. We uncovered a significantly increased number of regulatory T cells (Treg) and Th17 cells in expanded T cells during zinc deficiency after 3 days of combined treatment with IL-2 and TGF-ß1 (Treg) or IL-6 and TGF-ß1 (Th17). No difference in Th1 and Th2 cell polarization between zinc-deficient and zinc-adequate status was prominent. On the molecular level, Smad signaling was significantly enhanced by stimulation with TGF-ß1/IL-6 during zinc deficiency compared to adequate zinc condition. This represents an explanation for the elevated Th17 cell numbers associated with autoimmune disease especially during zinc deficiency. Moreover, Treg cell numbers are increased during zinc deficiency as well. However, those cells might be nonfunctional since a lower expression of miR-146a was uncovered compared to normal zinc concentrations. In summary, an adequate zinc homeostasis is fundamental to slow down or probably stop the progression of autoimmune diseases and infections. Therefore, supplementing zinc might be a therapeutic approach to dampen autoimmune diseases connected to Th17 cells.

B cell activation and proliferation increase intracellular zinc levels.

Zinc ions serve as second messengers in major cellular pathways, including the regulation pathways of proliferation and their proper regulation is necessary for homeostasis and a healthy organism. Accordingly, expression of zinc transporters can be altered in various cancer cell lines and is often involved in producing elevated intracellular zinc levels. In this study, human B cells were infected with Epstein-Barr virus (EBV) to generate immortalized cells, which revealed traits of tumor cells, such as high proliferation rates and an extended lifespan. These cells showed differentially altered zinc transporter expression with ZIP7 RNA and protein expression being especially increased as well as a corresponding increased phosphorylation of ZIP7 in EBV-transformed B cells. Accordingly, free zinc levels were elevated within these cells. To prove whether the observed changes resulted from immortalization or rather high proliferation, free zinc levels in in vitro activated B cells and in freshly isolated B cells expressing the activation marker CD69 were determined. Here, comparatively increased zinc levels were found, suggesting that activation and proliferation, but not immortalization, act as crucial factors for the elevation of intracellular free zinc.

The human allicin-proteome: S-thioallylation of proteins by the garlic defence substance allicin and its biological effects.

A single clove of edible garlic (Allium sativum L.) of about 10 g produces up to 5 mg of allicin (diallylthiosulfinate), a thiol-reactive sulfur-containing defence substance that gives injured garlic tissue its characteristic smell. Allicin induces apoptosis or necrosis in a dose-dependent manner but biocompatible doses influence cellular metabolism and signalling cascades. Oxidation of protein thiols and depletion of the glutathione pool are thought to be responsible for allicin's physiological effects. Here, we studied the effect of allicin on post-translational thiol-modification in human Jurkat T-cells using shotgun LC-MS/MS analyses. We identified 332 proteins that were modified by S-thioallylation in the Jurkat cell proteome which causes a mass shift of 72 Da on cysteines. Many S-thioallylated proteins are highly abundant proteins, including cytoskeletal proteins tubulin, actin, cofilin, filamin and plastin-2, the heat shock chaperones HSP90 and HSPA4, the glycolytic enzymes GAPDH, ALDOA, PKM as well the protein translation factor EEF2. Allicin disrupted the actin cytoskeleton in murine L929 fibroblasts. Allicin stimulated the immune response by causing Zn2+ release from proteins and increasing the Zn2+-dependent IL-1-triggered production of IL-2 in murine EL-4 T-cells. Furthermore, allicin caused inhibition of enolase activity, an enzyme considered a cancer therapy target. In conclusion, our study revealed the widespread extent of S-thioallylation in the human Jurkat cell proteome and showed effects of allicin exposure on essential cellular functions of selected targets, many of which are targets for cancer therapy.

Influence of zinc supplementation on immune parameters in weaned pigs.

Zinc is an essential trace element, highly important for a well functioning immune system. In case of zinc deficiency, proper immune functions are not ensured thus leading to various diseases. Weaning of pigs from the sow causes stress, increasing susceptibility to infections. Moreover, low feed intake during the first two weeks post-weaning, accompanied by low zinc intake, results in temporary zinc deficiency. Therefore, supporting the immune system by zinc supplementation might improve its function and thereby the pigs' health and well-being. In this study, the immune status of weaned pigs was analyzed under different conditions of zinc supplementation. More precisely, the daily porcine diet was either left unsupplemented (0 ppm), or was supplemented with low (100 ppm), or high (2500 ppm) amounts of additional zinc in the form of zinc oxide (ZnO) (Zn0, Zn100, and Zn2500, respectively). Porcine innate and adaptive immune cells of the different dietary groups were analyzed. Results revealed an improved innate immune capacity, represented by increased phagocytosis and slightly increased oxidative burst in cells from the Zn2500 pigs and Zn100 pigs, respectively. Apart from that, zinc supplementation improved adaptive immunity, as seen by increased numbers of CD3+ T cells as well as increased numbers of CD3+CD4+Foxp3+ regulatory T cells, elevated interleukin (IL)-2 production and decreased IL-10 production. Although not significant, supplementing 2500 ppm zinc slightly decreased killing activity of natural killer (NK) cells. Thus, the optimal concentration for zinc supplementation of weaned pigs two weeks post-weaning needs to be further studied, presumably establishing an optimal concentration between 100 ppm and 2500 ppm zinc. Genome comparisons indicate that the porcine genome is more closely related to the human genome than the murine genome is related to the human genome. Therefore, the pig seems to be a suitable organism to study human immunity and diseases. Results obtained in the current study might therefore be transferable to the human immune system.

Zinc as a micronutrient and its preventive role of oxidative damage in cells.

Zinc is an essential trace element with special importance in the immune system. Deficiencies of zinc are seen in the course of ageing and in various diseases, such as diabetes mellitus or rheumathoid arthritis. The trace element is essential for a variety of basic cellular functions and especially important for various enzymes participating in the production and neutralization of reactive oxygen species (ROS) which are normally produced by the cell. Under normal conditions ROS are neutralized and are not able to harm the cell, but in case of ROS elevation, oxidative damage within the cell is the result. Interestingly, zinc deficiency is directly associated with oxidative stress. Thus, control and regulation of the intracellular zinc content is essential with participation of various transporter and zinc-binding proteins, such as metallothionein. Oxidative stress is mainly caused by elevated ROS production and a decrease of antioxidant mechanisms. Zinc partly functions as an antioxidant although it is redox inert. Zinc supplementation is associated with decreased ROS formation exhibiting beneficial effects especially in ageing and diabetes mellitus. This review summarizes current findings concerning zinc as a micronutrient and its actions as a pro-antioxidant, and the association between zinc and oxidative stress under various conditions is highlighted.

BDNF is associated with SFRP1 expression in luminal and basal-like breast cancer cell lines and primary breast cancer tissues: a novel role in tumor suppression?

Secreted frizzled related protein 1 (SFRP1) functions as an important inhibitor of the Wnt pathway and is a known tumor suppressor gene, which is epigenetically silenced in a variety of tumors e.g. in breast cancer. However, it is still unclear how SFRP1 exactly affects the Wnt pathway. Our aim was to decipher SFRP1 involvement in biochemical signaling in dependency of different breast cancer subtypes and to identify novel SFRP1-regulated genes. We generated SFRP1 over-expressing in vitro breast cancer models, reflecting the two major subtypes by using basal-like BT20 and luminal-like HER2-positive SKBR3 cells. DNA microarray expression profiling of these models revealed that SFRP1 expression potentially modulates Bone morphogenetic protein- and Smoothened signaling (p<0.01), in addition to the known impact on Wnt signaling. Importantly, further statistical analysis revealed that in dependency of the cancer subtype model SFRP1 may affect the canonical and non-canonical Wnt pathway (p<0.01), respectively. While SFRP1 re-expression generally mediated distinct patterns of transcriptionally induced or repressed genes in BT20 and SKBR3 cells, brain derived neurotrophic factor (BDNF) was identified as a SFRP1 induced gene in both cell lines. Although BDNF has been postulated as a putative oncogene, the co-regulation with SFRP1 indicates a potential suppressive function in breast cancer. Indeed, a positive correlation between SFRP1 and BDNF protein expression could be shown (p<0.001) in primary breast cancer samples. Moreover, TCGA dataset based analysis clearly underscores that BDNF mRNA is down-regulated in primary breast cancer samples predicting a poor prognosis of these patients. In line, we functionally provide evidence that stable BDNF re-expression in basal-like BT20 breast cancer cells blocks tumor cell proliferation. Hence, our results suggest that BDNF might rather mediate suppressive than promoting function in human breast cancer whose mode of action should be addressed in future studies.