Intracellular Zinc Availability Research Articles

The Leptospira interrogans proteome's response to zinc highlights the potential involvement of this metal in translational-machinery and virulence.

Leptospires, as motile Gram-negative bacteria, employ sophisticated strategies for efficient invasion and dissemination within their hosts. In response, hosts counteract pathogens through nutritional immunity, a concept involving the deprivation of essential metals such as zinc. Zinc, pivotal in modulating pathogen-host interactions, influences proteins structural, catalytic, and regulatory functions. A comprehensive understanding of how leptospires regulate intracellular zinc availability is crucial for deciphering their survival mechanisms. This study explores the proteomic profile of Leptospira interrogans sv. Copenhageni str. 10A cultivated in Ellinghausen-McCullough-Johnson-Harris medium supplemented with the zinc chelator TPA or ZnCl2. Among the 2161 proteins identified, 488 were subjected to scrutiny, revealing 102 less abundant and 81 more abundant in response to TPA. Of these 488 proteins, 164 were exclusive to the presence of TPA and 141 were exclusive to the zinc-enriched conditions. Differentially expressed proteins were classified into clusters of orthologous groups (COGs) with a distribution in metabolic functions (37.8%), information storage/processing (21.08%), cellular processes/signaling (28.04%), and poorly characterized proteins (10.65%). Differentially expressed proteins are putatively involved in processes like 1-carbon compound metabolism, folate biosynthesis, and amino acid/nucleotide synthesis. Zinc availability significantly impacted key processes putatively related to leptospires' interactions with their host, such as motility, biofilm formation, and immune escape. Under conditions of higher zinc concentration, ribosomal proteins, chaperones and components of transport systems were observed, highlighting interactions between regulatory networks responsive to zinc and iron in L. interrogans. This study not only revealed hypothetical proteins potentially related to zinc homeostasis, but also identified possible virulence mechanisms and pathogen-host adaptation strategies influenced by the availability of this metal. There is an urgent need, based on these data, for further in-depth studies aimed at detailing the role of zinc in these pathways and mechanisms, which may ultimately determine more effective therapeutic approaches to combat Leptospira infections.

The labile zinc pool in plant cells.

Zinc is the most abundant and important transition metal in plants; however, the dynamic aspects of zinc homeostasis in plant cells are poorly understood. In this study we explored the pool of labile exchangeable zinc complexes in plant cells, and the potential influence of changes in intracellular zinc availability on cellular physiology. Work was performed on cultivated cell extracts of Arabidopsis thaliana (L.) Heynh. and Thellungiella salsuginea (Pall.) O.E. Schulz grown under control (3.48 µM Zn2+), 10-fold Zn excess or Zn starvation conditions. The free and labile Zn contents in the extracts were then determined by fluorimetric titration. We observed for the first time that plant cells contain micromolar concentrations of labile zinc complexes that account for a low percentage of the total zinc content. Labile zinc is mainly protein bound. Zn starvation inhibits cell proliferation and leads to the disappearance of the labile zinc pool, whereas Zn excess drastically increases the labile zinc pool. Free Zn2+ is buffered at picomolar concentrations in the intracellular milieu, and the increase in free Zn2+ concentrations to low nanomolar values clearly modulates enzyme activity by direct reversible binding. Such increases in free Zn2+ can be achieved by the substantial influx of additional zinc or by the oxidation of zinc-binding thiols. The observed features of the labile zinc pool in plant cells suggest it has a role in intracellular zinc trafficking and zinc signalling.

Zinc sensing and regulation in yeast model systems

The Zap1 transcription factor of Saccharomyces cerevisiae and the Loz1 transcription factor of Schizosaccharomyces pombe both play a central role in zinc homeostasis by controlling the expression of genes necessary for zinc metabolism. Zap1 activates gene expression when cells are limited for zinc, while Loz1 is required for gene repression when zinc is in excess. In this review we highlight what is known about the underlying mechanisms by which these factors are regulated by zinc, and how transcriptional activation and repression in eukaryotic cells can be finely tuned according to intracellular zinc availability.

Nano-ZnO leads to tubulin macrotube assembly and actin bundling, triggering cytoskeletal catastrophe and cell necrosis.

Zinc is a crucial element in biology that plays chief catalytic, structural and protein regulatory roles. Excess cytoplasmic zinc is toxic to cells so there are cell-entry and intracellular buffering mechanisms that control intracellular zinc availability. Tubulin and actin are two zinc-scavenging proteins that are essential components of the cellular cytoskeleton implicated in cell division, migration and cellular architecture maintenance. Here we demonstrate how exposure to different ZnO nanostructures, namely ZnO commercial nanoparticles and custom-made ZnO nanowires, produce acute cytotoxic effects in human keratinocytes (HaCat) and epithelial cells (HeLa) triggering a dose-dependent cell retraction and collapse. We show how engulfed ZnO nanoparticles dissolve intracellularly, triggering actin filament bundling and structural changes in microtubules, transforming these highly dynamic 25 nm diameter polymers into rigid macrotubes of tubulin, severely affecting cell proliferation and survival. Our results demonstrate that nano-ZnO causes acute cytoskeletal collapse that triggers necrosis, followed by a late reactive oxygen species (ROS)-dependent apoptotic process.

Zinc transporter Slc39a14 regulates inflammatory signaling associated with hypertrophic adiposity.

Zinc is a signaling molecule in numerous metabolic pathways, the coordination of which occurs through activity of zinc transporters. The expression of zinc transporter Zip14 (Slc39a14), a zinc importer of the solute carrier 39 family, is stimulated under proinflammatory conditions. Adipose tissue upregulates Zip14 during lipopolysaccharide-induced endotoxemia. A null mutation of Zip14 (KO) revealed that phenotypic changes in adipose include increased cytokine production, increased plasma leptin, hypertrophied adipocytes, and dampened insulin signaling. Adipose tissue from KO mice had increased levels of preadipocyte markers, lower expression of the differentiation marker (PPARγ), and activation of NF-κB and STAT3 pathways. Our overall hypothesis was that ZIP14 would play a role in adipocyte differentiation and inflammatory obesity. Global Zip14 KO causes systemic endotoxemia. The observed metabolic changes in adipose metabolism were reversed when oral antibiotics were administrated, indicating that circulating levels of endotoxin were in part responsible for the adipose phenotype. To evaluate a mechanism, 3T3-L1 cells were differentiated into adipocytes and treated with siRNA to knock down Zip14. These cells had an impaired ability to mobilize zinc, which caused dysregulation of inflammatory pathways (JAK2/STAT3 and NF-κB). The Zip14 deletion may limit the availability of intracellular zinc, yielding the unique phenotype of inflammation coupled with hypertrophy. Taken together, these results suggest that aberrant zinc distribution observed with Zip14 ablation impacts adipose cytokine production and metabolism, ultimately increasing fat deposition when exposed to endotoxin. To our knowledge, this is the first investigation into the mechanistic role of ZIP14 in adipose tissue regulation and metabolism.

Indomethacin preconditioning induces ischemic tolerance by modifying zinc availability in the brain

Intracellular zinc overload causes neuronal injury during the course of neurological disorders, whereas mild levels of zinc are beneficial to neurons. Previous reports indicated that non-steroidal anti-inflammatory drugs, including indomethacin and aspirin, can reduce the risk of ischemic stroke. This study found that chronic pretreatment of rats with indomethacin, a non-selective cyclooxygenase inhibitor, provided tolerance to ischemic injuries in an animal model of stroke by eliciting moderate zinc elevation in neurons. Consecutive intraperitoneal injection of indomethacin (3mg/kg/day for 28days) led to modest increases in intraneuronal zinc as well as synaptic zinc content, with no significant stimulation of neuronal death. Furthermore, indomethacin induced the expressions of intracellular zinc homeostatic and neuroprotective proteins, rendering the brain resistant against ischemic damages and improving neurological outcomes. However, administration of a zinc-chelator, N,N,N′,N′-tetra(2-picolyl)ethylenediamine (TPEN; 15mg/kg/day), immediately after indomethacin administration eliminated the beneficial actions of the drug. Therefore, indomethacin preconditioning can modulate intracellular zinc availability, contributing to ischemic tolerance in the brain after stroke.

Influence of +1245 A/G MT1A polymorphism on advanced glycation end-products (AGEs) in elderly: effect of zinc supplementation.

Advanced glycation end-products (AGEs) stimulate reactive oxygen species (ROS) generation and represent a risk factor for atherosclerosis, while their formation seems to be prevented by zinc. Metallothioneins (MT), zinc-binding proteins exert an antioxidant function by regulating intracellular zinc availability and protecting cells from ROS damages. +1245 A/G MT1A polymorphism was implicated in type 2 diabetes and in cardiovascular disease development as well as in the modulation of antioxidant response. The purpose of this study was to investigate the influence of +1245 A/G MT1A polymorphism on AGEs and ROS production and to verify the effect of zinc supplementation on plasma AGEs, zinc status parameters and antioxidant enzyme activity in relation to this SNP. One hundred and ten healthy subjects (72±6years) from the ZincAge study were supplied with zinc aspartate (10mg/day for 7weeks) and screened for +1245 MT1A polymorphism. +1245 MT1A G+ (Arginine) genotype showed higher plasma AGEs and ROS production in peripheral blood mononuclear cells (PBMCs) than G- (Lysine) one at the baseline. No significant changes after zinc supplementation were observed for AGEs, ROS and MT levels as well as for enzyme antioxidant activity in relation to the genotype. Among zinc status parameters, major increases were observed for the intracellular labile zinc (iZnL) and the NO-induced release of zinc in PBMCs, in G+ genotype as compared to G- one. In summary, +1245 G+ carriers showed increased plasma AGEs and ROS production in PBMCs at baseline and a higher improvement in iZnL after zinc intervention with respect to G- individuals.

Zinc supplementation boosts the stress response in the elderly: Hsp70 status is linked to zinc availability in peripheral lymphocytes

Chaperones and zinc are indispensable for proper immune function. All the zinc status, the immune function and the stress response decline during aging. Here we studied the effect of nutritional zinc and zinc homeostasis on the stress response in healthy old subjects recruited during the ZincAge European Union project that either underwent or not a 48-day zinc supplementation. Inducible Hsp70 levels were determined at basal conditions as well as after heat shock in the CD3+ and CD3− subset of lymphocytes by a two-color FACS analysis. Short term zinc supplementation resulted in a marked increase in both basal as well as stress-induced Hsp70 levels in lymphocytes from healthy elderly donors with a higher impact on CD3+ cells. Heat inducibility showed a strong correlation with basal Hsp70 level, and both basal as well as stress-induced Hsp70 highly correlated with intracellular zinc availability. In conclusion, short term oral supplementation with zinc safely and efficiently induces the stress response in lymphocytes of old donors. The stress response may be a candidate pathway connecting zinc deficiency with aging and immunosenescence. Thus, proper dietary zinc intake may emerge as a chaperone inducer and an anti-aging mechanism in the immune system.

The +838 C/G MT2A polymorphism, metals, and the inflammatory/immune response in carotid artery stenosis in elderly people.

Carotid artery stenosis (CS) is a well-established risk factor for stroke. Increased proinflammatory chemokines, enhanced metallothionein (MT), and altered metal homeostasis may play roles in atherosclerosis progression and plaque destabilization. MT may sequester zinc during chronic inflammation, provoke zinc deficiency, and modulate NK cell cytotoxicity. A recent investigation of older patients with diabetes and atherosclerosis showed an association between the -209 A/G MT2A polymorphism, CS, and zinc status. In this study, we evaluated the relationship between two MT2A polymorphisms (-209 and + 838 locus), metal status, and inflammatory/immune response in older patients with CS only (the CS1 group) or with CS and previous cerebrovascular episodes (transient ischemic attack or stroke) (the CS2 group). A total of 506 individuals (188 CS1, 100 CS2, and 218 healthy controls) were studied. Atherosclerotic patients (CS1 and CS2) showed increased levels of MT, MCP-1, and RANTES, reduced NK cell cytotoxicity, and altered trace element concentrations (zinc, copper, magnesium, iron). The +838 C/G MT2A polymorphism was differently distributed in CS1 and CS2 patients, who displayed the GG genotype (C-) with significantly higher frequency than elderly controls. C- carriers showed increased MCP-1 and decreased NK cell cytotoxicity, CD56+ cells, and intracellular zinc availability along with decreased zinc, copper, and magnesium content in erythrocytes and increased iron in plasma. C- carriers also showed a major incidence of soft carotid plaques. In conclusion, the +838 C/G MT2A polymorphism seems to influence inflammatory markers, zinc availability, NK cell cytotoxicity, and trace element status, all of which may promote CS development.

The +838 C/G MT2A Polymorphism, Metals, and the Inflammatory/Immune Response in Carotid Artery Stenosis in Elderly People

Carotid artery stenosis (CS) is a well-established risk factor for stroke. Increased proinflammatory chemokines, enhanced metallothionein (MT), and altered metal homeostasis may play roles in atherosclerosis progression and plaque destabilization. MT may sequester zinc during chronic inflammation, provoke zinc deficiency, and modulate NK cell cytotoxicity. A recent investigation of older patients with diabetes and atherosclerosis showed an association between the -209 A/G MT2A polymorphism, CS, and zinc status. In this study, we evaluated the relationship between two MT2A polymorphisms (-209 and + 838 locus), metal status, and inflammatory/immune response in older patients with CS only (the CS1 group) or with CS and previous cerebrovascular episodes (transient ischemic attack or stroke) (the CS2 group). A total of 506 individuals (188 CS1, 100 CS2, and 218 healthy controls) were studied. Atherosclerotic patients (CS1 and CS2) showed increased levels of MT, MCP-1, and RANTES, reduced NK cell cytotoxicity, and altered trace element concentrations (zinc, copper, magnesium, iron). The +838 C/G MT2A polymorphism was differently distributed in CS1 and CS2 patients, who displayed the GG genotype (C-) with significantly higher frequency than elderly controls. C- carriers showed increased MCP-1 and decreased NK cell cytotoxicity, CD56+ cells, and intracellular zinc availability along with decreased zinc, copper, and magnesium content in erythrocytes and increased iron in plasma. C- carriers also showed a major incidence of soft carotid plaques. In conclusion, the +838 C/G MT2A polymorphism seems to influence inflammatory markers, zinc availability, NK cell cytotoxicity, and trace element status, all of which may promote CS development.

Mammalian zinc transporters.

New insights into mammalian zinc metabolism have been acquired through the identification and characterization of zinc transporters. These proteins all have transmembrane domains, and are encoded by two solute-linked carrier (SLC) gene families: ZnT (SLC30) and Zip (SLC39). There are at least 9 ZnT and 15 Zip transporters in human cells. They appear to have opposite roles in cellular zinc homeostasis. ZnT transporters reduce intracellular zinc availability by promoting zinc efflux from cells or into intracellular vesicles, while Zip transporters increase intracellular zinc availability by promoting extracellular zinc uptake and, perhaps, vesicular zinc release into the cytoplasm. Both the ZnT and Zip transporter families exhibit unique tissue-specific expression, differential responsiveness to dietary zinc deficiency and excess, and differential responsiveness to physiologic stimuli via hormones and cytokines.