Increased inflammatory response in aged mice is associated with age-related zinc deficiency and zinc transporter dysregulation

Aging is a complex process associated with physiological changes in numerous organ systems. In particular, aging of the immune system is characterized by progressive dysregulation of immune responses, resulting in increased susceptibility to infectious diseases, impaired vaccination efficacy and systemic low-grade chronic inflammation. Increasing evidence suggest that intracellular zinc homeostasis, regulated by zinc transporter expression, is critically involved in the signaling and activation of immune cells. We hypothesize that epigenetic alterations and nutritional deficits associated with aging may lead to zinc transporter dysregulation, resulting in decreases in cellular zinc levels and enhanced inflammation with age. The goal of this study was to examine the contribution of age-related zinc deficiency and zinc transporter dysregulation on the inflammatory response in immune cells. The effects of zinc deficiency and age on the induction of inflammatory responses were determined using an in vitro cell culture system and an aged mouse model. We showed that zinc deficiency, particularly the reduction in intracellular zinc in immune cells, was associated with increased inflammation with age. Furthermore, reduced Zip 6 expression enhanced proinflammatory response, and age-specific Zip 6 dysregulation correlated with an increase in Zip 6 promoter methylation. Furthermore, restoring zinc status via dietary supplementation reduced aged-associated inflammation. Our data suggested that age-related epigenetic dysregulation in zinc transporter expression may influence cellular zinc levels and contribute to increased susceptibility to inflammation with age.     

Oxidative stress and aging: Learning from yeast lessons

The yeast Saccharomyces cerevisiae has played a vital role in the understanding of the molecular basis of aging and the relationship of aging process with oxidative stress (non-homeostatic accumulation of Reactive Oxygen Species, ROS). The mammalian and yeast antioxidant responses are similar and over 25 % of human-degenerative disease related genes have close homologues in yeast. The reduced genetic redundancy of yeast facilitates visualization of the effect of a deleted or mutated gene. By manipulating growth conditions, yeast cells can survive only fermenting (low ROS levels) or respiring (increased ROS levels), which facilitates the elucidation of the mechanisms involved with acquisition of tolerance to oxidative stress. Furthermore, the yeast databases are the most complete of all eukaryotic models. In this work, we highlight the value of S. cerevisiae as a model to investigate the oxidative stress response and its potential impact on aging and age-related diseases.     

Zinc depletion regulates the processing and secretion of IL-1β

Sterile inflammation contributes to many common and serious human diseases. The pro-inflammatory cytokine interleukin-1β (IL-1β) drives sterile inflammatory responses and is thus a very attractive therapeutic target. Activation of IL-1β in sterile diseases commonly requires an intracellular multi-protein complex called the NLRP3 (NACHT, LRR, and PYD domains-containing protein 3) inflammasome. A number of disease-associated danger molecules are known to activate the NLRP3 inflammasome. We show here that depletion of zinc from macrophages, a paradigm for zinc deficiency, also activates the NLRP3 inflammasome and induces IL-1β secretion. Our data suggest that zinc depletion damages the integrity of lysosomes and that this event is important for NLRP3 activation. These data provide new mechanistic insight to how zinc deficiency contributes to inflammation and further unravel the mechanisms of NLRP3 inflammasome activation.     

MTM1 plays an important role in the regulation of zinc tolerance in Saccharomyces cerevisiae

BackgroundAcquisition and distribution of zinc supports a number of biological processes. Various molecular factors are involved in zinc metabolism but not fully explored.Basic proceduresSpontaneous mutants were generated in yeast with excess zinc culture followed by whole genome DNA sequencing to discover zinc metabolism related genes by bioinformatics. An identified mutant was characterized through metallomic and molecular biology methods.Main findingsHere we reported that MTM1 knockout cells displayed much stronger zinc tolerance than wild type cells on SC medium when exposed to excess zinc. Zn accumulation of mtm1Δ cells was dramatically decreased compared to wild type cells under excessive zinc condition due to MTM1 deletion reduced zinc uptake. ZRC1 mRNA level of mtm1Δ cells was significantly higher than that in the wild-type strain leading to increased vacuolar zinc accumulations in mtm1Δ cells. The mRNA levels of ZRT1 and ZAP1 decreased in mtm1Δ cells contributing to less Zn uptake. The zrc1Δmtm1Δ double knockout strain exhibited Zn sensitivity. MTM1 knockout did not afford resistance to excess zinc through an effect mediated through an influence on levels of ROS. Superoxide dismutase 2 (Sod2p) activity in mtm1Δ cells was severely impaired and not restored through Zn supplementation. Meanwhile, additional Zn showed no significant effect on the localization and expression of Mtm1p.Principal conclusionsOur study reveals the MTM1 gene plays an important role in the regulation of zinc homeostasis in yeast cells via changing zinc uptake and distribution. This discovery provides new insights for better understanding biochemical communication between vacuole and mitochondrial in relation to zinc-metabolism.     

Profiling of zinc-altered gene expression in human prostate normal vs. cancer cells: a time course study

We have demonstrated that zinc exposure induces apoptosis in human prostate cancer cells (PC-3) and benign hyperplasia cells (BPH), but not in normal prostate cells (HPR-1). However, the mechanisms underlying the effects of zinc on prostate cancer cell growth and zinc homeostasis remain unclear.To explore the zinc effect on gene expression profiles in normal (HPR-1) and malignant prostate cells (PC-3), we conducted a time course study of Zn treatment with microarray analysis. Microarray data were evaluated and profiled using computational approach for the primary and secondary data analyses. Final analyses were focused on the genes (1) highly sensitive to zinc; (2) associated with zinc homeostasis, i.e., metallothioneins (MTs), solute zinc carriers (ZIPs) and zinc exporters (ZnTs); (3) relevant to several oncogenic pathways. Zinc-mediated mRNA levels of MT isotypes were further validated by semi-quantitative RT-PCR.Results showed that zinc effect on genome-wide expression patterns was cell-type specific, and zinc appeared to have mainly down-regulatory effects on thousands of genes (1953 in HPR-1; 3534 in PC-3) with a threshold of ±2.5-fold, while fewer genes were up-regulated (872 in HPR-1; 571 in PC-3). The patterns of zinc effect on functional MT genes' expression provided evidence for the cell type-dependent zinc accumulation and zinc-induced apoptosis in prostate cells. In PC-3 cells, zinc significantly up-regulated the expression of MT-1 isotypes MT-1J and MT-1M, denoted previously as “nonfunctional” MT genes, and now a depictive molecular structure of MT-1J was proposed. Examination of genes involved in oncogenic pathways indicated that certain genes, e.g., Fos, Akt1, Jak3 and PI3K, were highly regulated by zinc with cell-type specificity.This work provided an extensive database on zinc-related prostate cancer research. The strategy of data analysis was devoted to finding genes highly sensitive to Zn, and the genes associated with zinc accumulation and zinc-induced apoptosis. The results indicate that zinc regulation of gene expression is cell-type specific, and MT genes play important roles in prostate malignancy.     

Zinc-regulated genes in Saccharomyces cerevisiae revealed by transposon tagging

The biochemistry of human nutritional zinc deficiency remains poorly defined. To characterize in genetic terms how cells respond to zinc deprivation, zinc-regulated genes (ZRG's) were identified in yeast. Gene expression was probed using random lacZ reporter gene fusions, integrated by transposon tagging into a diploid genome as previously described. About half of the genome was examined. Cells exhibiting differences in lacZ expression on low or moderate ( approximately 0. 1 vs. 10 microm) zinc media were isolated and the gene fusions were sequenced. Ribonuclease protection assays demonstrated four- to eightfold increases for the RNAs of the ZAP1, ZRG17 (YNR039c), DPP1, ADH4, MCD4, and YEF3B genes in zinc-deficient cells. All but YEF3B were shown through reporter gene assays to be controlled by a master regulator of zinc homeostasis now known to be encoded by ZAP1. ZAP1 mutants lacked the flocculence and distended vacuoles characteristic of zinc-deficient cells, suggesting that flocculation and vacuolation serve homeostatic functions in zinc-deficient cells. ZRG17 mutants required extra zinc supplementation to repress these phenotypes, suggesting that ZRG17 functions in zinc uptake. These findings illustrate the utility of transposon tagging as an approach for studying regulated gene expression in yeast.     

硫酸锌添加对酿酒酵母乙酸胁迫条件下全局基因转录的影响

【目的】利用转录组测序研究硫酸锌添加提高絮凝酿酒酵母SPSC01乙酸胁迫耐性的分子机理。【方法】在10.0 g/L乙酸胁迫条件下,添加0.03 g/L硫酸锌,取对数期酿酒酵母细胞,与不添加硫酸锌的对照组细胞进行比较转录组分析。【结果】添加硫酸锌的实验组与对照组相比较,50个基因转录水平上调,162个基因转录水平下调,这些转录水平变化明显的基因涉及糖代谢、甲硫氨酸合成、维生素合成等多条代谢途径,此外,转录水平变化的基因还包括抗氧化酶基因等关键胁迫响应基因。【结论】硫酸锌添加可改变酿酒酵母全局基因转录水平,提高抗氧化酶及其他胁迫耐性相关基因的表达,影响细胞氧化还原平衡和能量代谢,通过对多基因转录的调控提高酿酒酵母乙酸耐受性。     

Zinc homeostasis in the secretory pathway in yeast

It is estimated that up to 10% of proteins in eukaryotes require zinc for their function. Although the majority of these proteins are located in the nucleus and cytosol, a small subset is secreted from cells or is located within an intracellular compartment. As many of these compartmentalized metalloproteins fold to their native state and bind their zinc cofactor inside an organelle, cells require mechanisms to maintain supply of zinc to these compartments even under conditions of zinc deficiency. At the same time, intracellular compartments can also be the site for storing zinc ions, which then can be mobilized when needed. In this review, we highlight insight that has been obtained from yeast models about how zinc homeostasis is maintained in the secretory pathway and vacuole.     

Transition metal homeostasis: from yeast to human disease

Transition metal ions are essential nutrients to all forms of life. Iron, copper, zinc, manganese, cobalt and nickel all have unique chemical and physical properties that make them attractive molecules for use in biological systems. Many of these same properties that allow these metals to provide essential biochemical activities and structural motifs to a multitude of proteins including enzymes and other cellular constituents also lead to a potential for cytotoxicity. Organisms have been required to evolve a number of systems for the efficient uptake, intracellular transport, protein loading and storage of metal ions to ensure that the needs of the cells can be met while minimizing the associated toxic effects. Disruptions in the cellular systems for handling transition metals are observed as a number of diseases ranging from hemochromatosis and anemias to neurodegenerative disorders including Alzheimer??s and Parkinson??s disease. The yeast Saccharomyces cerevisiae has proved useful as a model organism for the investigation of these processes and many of the genes and biological systems that function in yeast metal homeostasis are conserved throughout eukaryotes to humans. This review focuses on the biological roles of iron, copper, zinc, manganese, nickel and cobalt, the homeostatic mechanisms that function in S. cerevisiae and the human diseases in which these metals have been implicated.