Recent Advances in the Role of SLC39A/ZIP Zinc Transporters In Vivo

ZnT6-mediated Zn2+ redistribution: impact on mitochondrial fission and autophagy in H9c2 cells

Cytosolic free Zn2⁺ level ([Zn2⁺]Cyt) is tightly regulated by Zn2⁺ transporters, under both physiological and pathological conditions. At the cellular level, dysregulated free Zn2⁺ levels have been linked to metabolic and cardiovascular diseases, primarily through their association with various Zn2⁺ transporters. However, the role and localization of ZnT6 in cardiomyocytes remain unclear. Previous studies have shown a significant increase in ZnT6 expression in insulin-resistant cardiomyocytes, suggesting a potential link between ZnT6 dysregulation and cardiac cell dysfunction. Therefore, here, we investigated the impact of ZnT6 overexpression (ZnT6-OE) on cellular Zn2⁺ distribution, mitochondrial dynamics, and autophagy-induced apoptosis in H9c2 cardiomyocytes. Using confocal imaging, biochemical assays, and electron microscopy, we demonstrated the mitochondrial localization of ZnT6 and its role in H9c2 cells. Our findings showed that ZnT6 overexpression led to a significant increase in mitochondrial free Zn2⁺ level ([Zn2⁺]Mit) with a significant reduction in [Zn2⁺]Cyt, which seems to be associated with enhanced numbers of mitochondria and mitochondrial fission process. Specifically, the ZnT6-OE cells exhibited increased dynamin-related protein 1 (DRP1) translocation to mitochondria which is an indication of excessive fission activity. We also determined severe mitochondrial dysfunction in ZnT6-OE cells, such as depolarization in mitochondrial membrane potential, production of excessive reactive oxygen species (ROS), reduced ATP levels, and autophagosome accumulation. Furthermore, these impairments were accompanied by elevated apoptotic markers, indicating autophagy-induced apoptosis. Our findings highlight ZnT6 as a critical regulator of mitochondrial dynamics and function in cardiomyocytes, contributing to disruption Zn2⁺ homeostasis by its overexpression, triggering excessive DRP1-mediated mitochondrial fission and leading to mitochondrial dysfunction, oxidative stress, and apoptotic cell death, suggesting an important impact of ZnT6 dysregulation on cardiomyocyte pathophysiology in metabolic disorders.

Adaptation responses to salt stress in the gut of Poecilia reticulata

Osmoregulation is essential for the survival of aquatic organisms, particularly teleost fish facing osmotic challenges in environments characterized by variable salinity. While the gills are known for ion exchange, the intestine's role in water and salt absorption is gaining attention. Here, we investigated the adaptive responses of the intestine to salinity stress in guppies (Poecilia reticulata), observing significant morphological and transcriptomic alterations. Guppies showed superior salt tolerance compared to zebrafish (Danio rerio). Increasing salinity reduced villus length and intestinal diameter in guppies, while zebrafish exhibited damage to villus structure and loss of goblet cells. Transcriptomic analysis identified key genes involved in osmoregulation, tissue remodeling, and immune modulation. Upregulated genes included the solute carrier transporters slc2al and slc3al, which facilitate ion and water transport, as well as a transcription factor AP-1 subunit and phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit beta, both of which participate in tissue repair and growth responses. In contrast, many genes related to the innate immune system (such as Tnfaip6) were downregulated, suggesting a shift toward the prioritization of osmoregulatory functions over immune responses. Interestingly, the differential expression of adaptation genes was linked to variations in epigenetic modifications and transcription factor activity. Transcription factors crucial for adapting to salt stress, such as bhlhe40, cebpd, and gata6, were progressively upregulated in guppies but remained downregulated in zebrafish. Our findings highlight the intricate mechanisms of adaptation to salinity stress in P. reticulata, providing insights into osmoregulatory mechanisms involving the intestine in aquatic organisms.

Impact of zinc on immunometabolism and its putative role on respiratory diseases

Zinc is the second most abundant trace mineral in the human body and plays a critical role in immune cell function and metabolism. Zinc deficiency impairs immune cell function and is associated with increased susceptibility to respiratory diseases, including pneumonia, influenza, and COVID-19. Zinc homeostasis, maintained by numerous zinc transporters and metal-binding proteins (ie, metallothionein), is essential for coordinating immune cell signaling, gene expression, and enzymatic activities in response to respiratory infections. This article highlights the emerging role of zinc in various aspects of immune function, particularly through its influence on cellular metabolism. Given the significant global burden of respiratory diseases, there is a need to identify effective nutritional interventions that could be readily leveraged to prevent and/or mitigate respiratory disease risk, particularly in older adults who are prone to zinc deficiency. However, the immunometabolic mechanisms underlying zinc's protective effects remain poorly characterized. Future research should focus on elucidating how micronutrients, such as zinc, can support changes in immune cell metabolism in response to infections. Such efforts will help determine how zinc metabolism and zinc intervention strategies may best be leveraged to prevent or mitigate respiratory disease.

Metal-Dependent Cell Death in Renal Fibrosis: Now and in the Future

Renal fibrosis is a common final pathway underlying nearly almost all progressive kidney diseases. Metal ions are essential trace elements in organisms and are involved in important physiological activities. However, aberrations in intracellular metal ion metabolism may disrupt homeostasis, causing cell death and increasing susceptibility to various diseases. Accumulating evidence suggests a complex association between metal-dependent cell death and renal fibrosis. In this article, we provide a comprehensive overview of the specific molecular mechanisms of metal-dependent cell death and their crosstalk, up-to-date evidence supporting their role in renal fibrosis, therapeutic targeting strategies, and research needs, aiming to offer a rationale for future clinical treatment of renal fibrosis.

Dietary Zinc Restriction and Chronic Restraint Stress Affect Mice Physiology, Immune Organ Morphology, and Liver Function

BACKGROUND

Preclinical and clinical studies suggest that zinc deficiency and chronic stress contribute to depressive symptoms. Our study explores the intricate relationship between these factors by examining their physiological and biochemical effects across various organs in C57Bl/6J mice.

METHODS

The mice were divided into four groups: control, chronic restraint stress for 3 weeks, a zinc-restricted diet (<3 mg/kg) for 4 weeks, and a combination of stress and zinc restriction. Mice spleen and thymus weights were measured, and hematoxylin-eosin staining was conducted for liver and intestinal morphometry. Moreover, metallothionein (MT-1, MT-2, and MT-3), zinc transporter (ZnT-1), oxidative stress markers (TBARS, SOD, and GSH-Px), and zinc, iron, and copper concentrations in the liver were evaluated. Immunohistochemical analysis of the jejunum for ZIP1 and ZIP4 was also performed.

CONCLUSIONS

Our findings reveal that dietary zinc restriction and chronic stress induce structural changes in the intestines and immune organs and impact metallothionein expression, oxidative stress, and liver iron and copper homeostasis.

Impact of dietary zinc on stimulated zinc secretion MRI in the healthy and malignant mouse prostate

Previous studies have shown that the zinc-responsive MRI probe, GdL1, can distinguish healthy versus malignant prostate tissues based upon differences in zinc content and secretion. In this study, mice were fed chow containing low, normal, or high zinc content for 3 weeks before imaging glucose stimulated zinc secretion (GSZS) by MRI. The distribution of zinc in prostate tissue in these three groups was imaged by synchrotron radiation X-ray fluorescence (SR-XRF). A zinc deficiency caused systemic and organ-level dysregulation, weight loss, and altered zinc bioavailability. Zinc efflux from the prostate increased in parallel to dietary zinc in healthy mice but not in TRAMP mice, consistent with a lowered capacity to store dietary zinc in malignant cells. This differential zinc efflux suggests that a dietary supplement of zinc prior to a GSZS study may enhance image contrast between healthy and malignant prostate tissue, thereby improving the accuracy of prostate cancer detection in man.

Evolution, classification, and mechanisms of transport, activity regulation, and substrate specificity of ZIP metal transporters

The Zrt/Irt-like protein (ZIP) family consists of ubiquitously expressed divalent d-block metal transporters that play central roles in the uptake, secretion, excretion, and distribution of several essential and toxic metals in living organisms. The past few years has witnessed rapid progress in the molecular basis of these membrane transport proteins. In this critical review, we summarize the research progress at the molecular level of the ZIP family and discuss the future prospects. Furthermore, an evolutionary path for the unique ZIP fold and a new classification of the ZIP family are proposed based on the presented structural and sequence analyses.

The Manganese-Bone Connection: Investigating the Role of Manganese in Bone Health

The complex relationship between trace elements and skeletal health has received increasing attention in the scientific community. Among these minerals, manganese (Mn) has emerged as a key element affecting bone metabolism and integrity. This review examines the multifaceted role of Mn in bone health, including its effects on bone regeneration, mineralization, and overall skeletal strength. This review article is based on a synthesis of experimental models, epidemiologic studies, and clinical trials of the mechanisms of the effect of Mn on bone metabolism. Current research data show that Mn is actively involved in the processes of bone remodeling by modulating the activity of osteoblasts and osteoclasts, as well as the main cells that regulate bone formation and resorption. Mn ions have a profound effect on bone mineralization and density by intricately regulating signaling pathways and enzymatic reactions in these cells. Additionally, Mn superoxide dismutase (MnSOD), located in bone mitochondria, plays a crucial role in osteoclast differentiation and function, protecting osteoclasts from oxidative damage. Understanding the nuances of Mn's interaction with bone is essential for optimizing bone strategies, potentially preventing and managing skeletal diseases. Key findings include the stimulation of osteoblast proliferation and differentiation, the inhibition of osteoclastogenesis, and the preservation of bone mass through the RANK/RANKL/OPG pathway. These results underscore the importance of Mn in maintaining bone health and highlight the need for further research into its therapeutic potential.

Unlocking the brain's zinc code: implications for cognitive function and disease

Zn2+ transport across neuronal membranes relies on two classes of transition metal transporters: the ZnT (SLC30) and ZIP (SLC39) families. These proteins function to decrease and increase cytosolic Zn2+ levels, respectively. Dysfunction of ZnT and ZIP transporters can alter intracellular Zn2+ levels resulting in deleterious effects. In neurons, imbalances in Zn2+ levels have been implicated as risk factors in conditions such as Alzheimer's disease and neurodegeneration, highlighting the pivotal role of Zn2+ homeostasis in neuropathologies. In addition, Zn2+ modulates the function of plasma membrane proteins, including ion channels and receptors. Changes in Zn2+ levels, on both sides of the plasma membrane, profoundly impact signaling pathways governing cell development, differentiation, and survival. This review is focused on recent developments of neuronal Zn2+ homeostasis, including the impact of Zn2+ dyshomeostasis in neurological disorders, therapeutic approaches, and the increasingly recognized role of Zn2+ as a neurotransmitter in the brain.

The effect of dietary zinc and zinc physiological status on the composition of the gut microbiome in vivo

Zinc serves critical catalytic, regulatory, and structural roles. Hosts and their resident gut microbiota both require zinc, leading to competition, where a balance must be maintained. This systematic review examined evidence on dietary zinc and physiological status (zinc deficiency or high zinc/zinc overload) effects on gut microbiota. This review was conducted according to PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) guidelines and registered in PROSPERO (CRD42021250566). PubMed, Web of Science, and Scopus databases were searched for in vivo (animal) studies, resulting in eight selected studies. Study quality limitations were evaluated using the SYRCLE risk of bias tool and according to ARRIVE guidelines. The results demonstrated that zinc deficiency led to inconsistent changes in α-diversity and short-chain fatty acid production but led to alterations in bacterial taxa with functions in carbohydrate metabolism, glycan metabolism, and intestinal mucin degradation. High dietary zinc/zinc overload generally resulted in either unchanged or decreased α-diversity, decreased short-chain fatty acid production, and increased bacterial metal resistance and antibiotic resistance genes. Additional studies in human and animal models are needed to further understand zinc physiological status effects on the intestinal microbiome and clarify the applicability of utilizing the gut microbiome as a potential zinc status biomarker.

Possible involvement of zinc transporter ZIP13 in myogenic differentiation

Ehlers-Danlos syndrome spondylodysplastic type 3 (EDSSPD3, OMIM 612350) is an inherited recessive connective tissue disorder that is caused by loss of function of SLC39A13/ZIP13, a zinc transporter belonging to the Slc39a/ZIP family. We previously reported that patients with EDSSPD3 harboring a homozygous loss of function mutation (c.221G > A, p.G64D) in ZIP13 exon 2 (ZIP13G64D) suffer from impaired development of bone and connective tissues, and muscular hypotonia. However, whether ZIP13 participates in the early differentiation of these cell types remains unclear. In the present study, we investigated the role of ZIP13 in myogenic differentiation using a murine myoblast cell line (C2C12) as well as patient-derived induced pluripotent stem cells (iPSCs). We found that ZIP13 gene expression was upregulated by myogenic stimulation in C2C12 cells, and its knockdown disrupted myotubular differentiation. Myocytes differentiated from iPSCs derived from patients with EDSSPD3 (EDSSPD3-iPSCs) also exhibited incomplete myogenic differentiation. Such phenotypic abnormalities of EDSSPD3-iPSC-derived myocytes were corrected by genomic editing of the pathogenic ZIP13G64D mutation. Collectively, our findings suggest the possible involvement of ZIP13 in myogenic differentiation, and that EDSSPD3-iPSCs established herein may be a promising tool to study the molecular basis underlying the clinical features caused by loss of ZIP13 function.

Role of zinc in health and disease

This review provides a concise overview of the cellular and clinical aspects of the role of zinc, an essential micronutrient, in human physiology and discusses zinc-related pathological states. Zinc cannot be stored in significant amounts, so regular dietary intake is essential. ZIP4 and/or ZnT5B transport dietary zinc ions from the duodenum into the enterocyte, ZnT1 transports zinc ions from the enterocyte into the circulation, and ZnT5B (bidirectional zinc transporter) facilitates endogenous zinc secretion into the intestinal lumen. Putative promoters of zinc absorption that increase its bioavailability include amino acids released from protein digestion and citrate, whereas dietary phytates, casein and calcium can reduce zinc bioavailability. In circulation, 70% of zinc is bound to albumin, and the majority in the body is found in skeletal muscle and bone. Zinc excretion is via faeces (predominantly), urine, sweat, menstrual flow and semen. Excessive zinc intake can inhibit the absorption of copper and iron, leading to copper deficiency and anaemia, respectively. Zinc toxicity can adversely affect the lipid profile and immune system, and its treatment depends on the mode of zinc acquisition. Acquired zinc deficiency usually presents later in life alongside risk factors like malabsorption syndromes, but medications like diuretics and angiotensin-receptor blockers can also cause zinc deficiency. Inherited zinc deficiency condition acrodermatitis enteropathica, which occurs due to mutation in the SLC39A4 gene (encoding ZIP4), presents from birth. Treatment involves zinc supplementation via zinc gluconate, zinc sulphate or zinc chloride. Notably, oral zinc supplementation may decrease the absorption of drugs like ciprofloxacin, doxycycline and risedronate.

Zinc homeostasis and redox alterations in obesity

Impairment of both cellular zinc and redox homeostasis is a feature of several chronic diseases, including obesity. A significant two-way interaction exists between redox metabolism and the relatively redox-inert zinc ion. Redox metabolism critically influences zinc homeostasis and controls its cellular availability for various cellular functions by regulating zinc exchange from/to zinc-binding proteins. Zinc can regulate redox metabolism and exhibits multiple pro-antioxidant properties. On the other hand, even minor disturbances in zinc status and zinc homeostasis affect systemic and cellular redox homeostasis. At the cellular level, zinc homeostasis is regulated by a multi-layered machinery consisting of zinc-binding molecules, zinc sensors, and two selective families of zinc transporters, the Zinc Transporter (ZnT) and Zrt, Irt-like protein (ZIP). In the present review, we summarize the current state of knowledge on the role of the mutual interaction between zinc and redox homeostasis in physiology and pathophysiology, pointing to the role of zinc in the alterations responsible for redox stress in obesity. Since zinc transporters primarily control zinc homeostasis, we describe how changes in the expression and activity of these zinc-regulating proteins are associated with obesity.

From zinc homeostasis to disease progression: Unveiling the neurodegenerative puzzle

Zinc is a crucial trace element in the human body, playing a role in various physiological processes such as oxidative stress, neurotransmission, protein synthesis, and DNA repair. The zinc transporters (ZnTs) family members are responsible for exporting intracellular zinc, while Zrt- and Irt-like proteins (ZIPs) are involved in importing extracellular zinc. These processes are essential for maintaining cellular zinc homeostasis. Imbalances in zinc metabolism have been linked to the development of neurodegenerative diseases. Disruptions in zinc levels can impact the survival and activity of neurons, thereby contributing to the progression of neurodegenerative diseases through mechanisms like cell apoptosis regulation, protein phase separation, ferroptosis, oxidative stress, and neuroinflammation. Therefore, conducting a systematic review of the regulatory network of zinc and investigating the relationship between zinc dysmetabolism and neurodegenerative diseases can enhance our understanding of the pathogenesis of these diseases. Additionally, it may offer new insights and approaches for the treatment of neurodegenerative diseases.

Identification of Zip8-correlated hub genes in pulmonary hypertension by informatic analysis

Background

Pulmonary hypertension (PH) is a syndrome characterized by marked remodeling of the pulmonary vasculature and increased pulmonary vascular resistance, ultimately leading to right heart failure and even death. The localization of Zrt/Irt-like Protein 8 (ZIP8, a metal ion transporter, encoded by SLC39A8) was abundantly in microvasculature endothelium and its pivotal role in the lung has been demonstrated. However, the role of Zip8 in PH remains unclear.

Methods

Bioinformatics analysis was employed to identify SLC39A8 expression patterns and differentially expressed genes (DEGs) between PH patients and normal controls (NC), based on four datasets (GSE24988, GSE113439, GSE117261, and GSE15197) from the Biotechnology Gene Expression Omnibus (NCBI GEO) database. Gene set enrichment analysis (GSEA) was performed to analyze signaling pathways enriched for DEGs. Hub genes were identified by cytoHubba analysis in Cytoscape. Reverse transcriptase-polymerase chain reaction was used to validate SLC39A8 and its correlated metabolic DEGs expression in PH (SU5416/Hypoxia) mice.

Results

SLC39A8 expression was downregulated in PH patients, and this expression pattern was validated in PH (SU5416/Hypoxia) mouse lung tissue. SLC39A8-correlated genes were mainly enriched in the metabolic pathways. Within these SLC39A8-correlated genes, 202 SLC39A8-correlated metabolic genes were screened out, and seven genes were identified as SLC39A8-correlated metabolic hub genes. The expression patterns of hub genes were analyzed between PH patients and controls and further validated in PH mice. Finally, four genes (Fasn, Nsdhl, Acat2, and Acly) were downregulated in PH mice. However, there were no significant differences in the expression of the other three hub genes between PH mice and controls. Of the four genes, Fasn and Acly are key enzymes in fatty acids synthesis, Nsdhl is involved in cholesterol synthesis, and Acat2 is implicated in cholesterol metabolic transformation. Taken together, these results provide novel insight into the role of Zip8 in PH.

Rational engineering of an elevator-type metal transporter ZIP8 reveals a conditional selectivity filter critically involved in determining substrate specificity

Engineering of transporters to alter substrate specificity as desired holds great potential for applications, including metabolic engineering. However, the lack of knowledge on molecular mechanisms of substrate specificity hinders designing effective strategies for transporter engineering. Here, we applied an integrated approach to rationally alter the substrate preference of ZIP8, a Zrt-/Irt-like protein (ZIP) metal transporter with multiple natural substrates, and uncovered the determinants of substrate specificity. By systematically replacing the differentially conserved residues with the counterparts in the zinc transporter ZIP4, we created a zinc-preferring quadruple variant (Q180H/E343H/C310A/N357H), which exhibited largely reduced transport activities towards Cd2+, Fe2+, and Mn2+ whereas increased activity toward Zn2+. Combined mutagenesis, modeling, covariance analysis, and computational studies revealed a conditional selectivity filter which functions only when the transporter adopts the outward-facing conformation. The demonstrated approach for transporter engineering and the gained knowledge about substrate specificity will facilitate engineering and mechanistic studies of other transporters.

Adaptive Changes in Detoxification Metabolism and Transmembrane Transport of Bombyx mori Malpighian Tubules to Artificial Diet

The high adaptability of insects to food sources has contributed to their ranking among the most abundant and diverse species on Earth. However, the molecular mechanisms underlying the rapid adaptation of insects to different foods remain unclear. We explored the changes in gene expression and metabolic composition of the Malpighian tubules as an important metabolic excretion and detoxification organ in silkworms (Bombyx mori) fed mulberry leaf and artificial diets. A total of 2436 differentially expressed genes (DEGs) and 245 differential metabolites were identified between groups, with the majority of DEGs associated with metabolic detoxification, transmembrane transport, and mitochondrial function. Detoxification enzymes, such as cytochrome P450 (CYP), glutathione-S-transferase (GST), and UDP-glycosyltransferase, and ABC and SLC transporters of endogenous and exogenous solutes were more abundant in the artificial diet group. Enzyme activity assays confirmed increased CYP and GST activity in the Malpighian tubules of the artificial diet-fed group. Metabolome analysis showed increased contents of secondary metabolites, terpenoids, flavonoids, alkaloids, organic acids, lipids, and food additives in the artificial diet group. Our findings highlight the important role of the Malpighian tubules in adaptation to different foods and provide guidance for further optimization of artificial diets to improve silkworm breeding.

How fish cells responded to zinc challenges: Insights from bioimaging

Zinc ion (Zn) is an essential nutrition element and it is important to understand its regulation and distribution among different cellular organelles. Here, subcellular trafficking of Zn in rabbitfish fin cells was investigated through bioimaging, and the results showed that the toxicity and bioaccumulation of Zn were both dose- and time-dependent. Cytotoxicity of Zn only occurred when the Zn concentration reached 200-250 μM after 3 h of exposure when the cellular quota of Zn:P reached a threshold level around 0.7. Remarkably, the cells were able to maintain homeostasis at a low Zn exposure concentration or within the first 4-h exposure. Zn homeostasis was mainly regulated by the lysosomes which stored Zn within the short exposure period, during which the number and size of lysosomes as well as the lysozyme activity increased in response to incoming Zn. However, with increasing Zn concentration beyond a threshold concentration (> 200 μM) and an exposure time > 3 h, homeostasis was disrupted, leading to an Zn spillover to cytoplasm and other cellular organelles. At the same time, cell viability decreased due to the Zn damage on mitochondria which caused morphological changes (smaller and rounder dots) and over production of reactive oxygen species, indicating the dysfunction of mitochondria. By further purifying the cellular organelles, cell viability was found to be consistent with the mitochondrial Zn amount. This study suggested that the amount of mitochondrial Zn was an excellent predictor of Zn toxicity on fish cells.

Getting zinc into and out of cells

Ion channels are specialized proteins located on the plasma membrane and control the movement of ions across the membrane. Zn ion plays an indispensable role as a structural constituent of various proteins, moreover, it plays an important dynamic role in cell signaling. In this chapter, we discuss computational insights into zinc efflux and influx mechanism through YiiP (from Escherichia coli and Shewanella oneidensis) and BbZIP (Bordetella bronchiseptica) transporters, respectively. Gaining knowledge about the mechanism of zinc transport at the molecular level can aid in developing treatments for conditions such as diabetes and cancer by manipulating extracellular and intracellular levels of zinc ions.

Simple in vitro method to evaluate ZIP zinc transport ability through zinc transporter 1 and metallothionein expression measurements

Measuring the cellular zinc content and examining the alteration of zinc status are critical for investigating the cellular homeostasis and dynamics of zinc and its involvement in patho-physiological functions. Many Zrt- and Irt-related protein (ZIP) transporters uptake zinc from the extracellular space. Among Zn transporters (ZNTs), ZNT1 effluxes cytosolic zinc. As cytosolic zinc-binding proteins, metallothioneins (MTs) also contribute to the control of cellular zinc homeostasis. Systemic and cellular zinc homeostasis is considered to be maintained by balancing expression and functional activities of these proteins. The zinc transport ability of ZIPs is typically measured by evaluating cellular zinc content with various zinc-detection methods and systems. Many small-molecule fluorescent probes and fluorescence resonance energy transfer-based protein sensors have been exploited for this purpose. Although powerful analytical methods using special instruments have been developed to quantify zinc, they are often not easily accessible. Here, we present a simplified and inexpensive method to estimate the zinc transport ability of ZIP transporters using the expression responses of ZNT1 and MT. This protocol should be effective in several applications because ZNT1 and MT expression are easily evaluated by immunoblotting and immunofluorescence staining as basic biochemical techniques available in most laboratories. This method is advantageous for examining the relative zinc status or alterations mediated by expression changes of ZIPs in cells cultured in normal medium without zinc supplementation. As zinc is an essential micronutrient, extensive research is necessary to improve dietary zinc absorption to promote health. Therefore, we also propose a simple screening method of foods to improve zinc absorption as an application of measuring ZIP-mediated MT expression.

Redox and metal profiles in human coronary endothelial and smooth muscle cells under hyperoxia, physiological normoxia and hypoxia: Effects of NRF2 signaling on intracellular zinc

Zinc is an important component of cellular antioxidant defenses and dysregulation of zinc homeostasis is a risk factor for coronary heart disease and ischemia/reperfusion injury. Intracellular homeostasis of metals, such as zinc, iron and calcium are interrelated with cellular responses to oxidative stress. Most cells experience significantly lower oxygen levels in vivo (2-10 kPa O₂) compared to standard in vitro cell culture (18kPa O₂). We report the first evidence that total intracellular zinc content decreases significantly in human coronary artery endothelial cells (HCAEC), but not in human coronary artery smooth muscle cells (HCASMC), after lowering of O₂ levels from hyperoxia (18 kPa O₂) to physiological normoxia (5 kPa O₂) and hypoxia (1 kPa O₂). This was paralleled by O₂-dependent differences in redox phenotype based on measurements of glutathione, ATP and NRF2-targeted protein expression in HCAEC and HCASMC. NRF2-induced NQO1 expression was attenuated in both HCAEC and HCASMC under 5 kPa O₂ compared to 18 kPa O₂. Expression of the zinc efflux transporter ZnT1 increased in HCAEC under 5 kPa O₂, whilst expression of the zinc-binding protein metallothionine (MT) decreased as O₂ levels were lowered from 18 to 1 kPa O₂. Negligible changes in ZnT1 and MT expression were observed in HCASMC. Silencing NRF2 transcription reduced total intracellular zinc under 18 kPa O₂ in HCAEC with negligible changes in HCASMC, whilst NRF2 activation or overexpression increased zinc content in HCAEC, but not HCASMC, under 5 kPa O₂. This study has identified cell type specific changes in the redox phenotype and metal profile in human coronary artery cells under physiological O₂ levels. Our findings provide novel insights into the effect of NRF2 signaling on Zn content and may inform targeted therapies for cardiovascular diseases.

Capsaicin and Zinc Signalling Pathways as Promising Targets for Managing Insulin Resistance and Type 2 Diabetes

The global burden of type 2 diabetes (T2DM) has led to significant interest in finding novel and effective therapeutic targets for this chronic disorder. Bioactive food components have effectively improved abnormal glucose metabolism associated with this disease. Capsaicin and zinc are food components that have shown the potential to improve glucose metabolism by activating signalling events in the target cells. Capsaicin and zinc stimulate glucose uptake through the activation of distinct pathways (AMPK and AKT, respectively); however, calcium signal transduction seems to be the common pathway between the two. The investigation of molecular pathways that are activated by capsaicin and zinc has the potential to lead to the discovery of new therapeutic targets for T2DM. Therefore, this literature review aims to provide a summary of the main signalling pathways triggered by capsaicin and zinc in glucose metabolism.

Zinc: From Biological Functions to Therapeutic Potential

The trace element zinc (Zn) displays a wide range of biological functions. Zn ions control intercellular communication and intracellular events that maintain normal physiological processes. These effects are achieved through the modulation of several Zn-dependent proteins, including transcription factors and enzymes of key cell signaling pathways, namely those involved in proliferation, apoptosis, and antioxidant defenses. Efficient homeostatic systems carefully regulate intracellular Zn concentrations. However, perturbed Zn homeostasis has been implicated in the pathogenesis of several chronic human diseases, such as cancer, diabetes, depression, Wilson's disease, Alzheimer's disease, and other age-related diseases. This review focuses on Zn's roles in cell proliferation, survival/death, and DNA repair mechanisms, outlines some biological Zn targets, and addresses the therapeutic potential of Zn supplementation in some human diseases.

Structural informatic study of determined and AlphaFold2 predicted molecular structures of 13 human solute carrier transporters and their water-soluble QTY variants

Solute carrier transporters are integral membrane proteins, and are important for diverse cellular nutrient transports, metabolism, energy demand, and other vital biological activities. They have recently been implicated in pancreatic cancer and other cancer metastasis, angiogenesis, programmed cell death and proliferation, cell metabolism and chemo-sensitivity. Here we report the study of 13 human solute carrier membrane transporters using the highly accurate AlphaFold2 predictions of 3D protein structures. In the native structures, there are hydrophobic amino acids leucine (L), isoleucine (I), valine (V) and phenylalanine (F) in the transmembrane alpha-helices. These hydrophobic amino acids L, I, V, F are systematically replaced by hydrophilic amino acids glutamine (Q), threonine (T) and tyrosine (Y), thus the QTY code. Therefore, these QTY variant transporters become water-soluble without requiring detergents. We present the superposed structures of these native solute carrier transporters and their water-soluble QTY variants. The superposed structures show remarkable similarity with RMSD ~ 1 Å-< 3 Å despite > 46% protein sequence substitutions in transmembrane alpha-helices. We also show the differences of surface hydrophobicity between the native solute carrier transporters and their QTY variants. Our study may further stimulate designs of water-soluble transmembrane proteins and other aggregated proteins for drug discovery and biotechnological applications.

Intraamniotic Administration (Gallus gallus) of Genistein Alters Mineral Transport, Intestinal Morphology, and Gut Microbiota

Genistein is an isoflavone naturally present in numerous staple food crops, such as soybeans and chickpeas. This study utilized the Gallus gallus intraamniotic administration procedure to assess genistein administration effects on trace mineral status, brush border membrane (BBM) functionality, intestinal morphology, and intestinal microbiome in vivo. Eggs were divided into five groups with 1 mL injection of the following treatments: no-injection, DI H₂O, 5% inulin, and 1.25% and 2.5% genistein (n = 8 per group). Upon hatch, blood, cecum, small intestine, and liver were collected for assessment of hemoglobin, intestinal microflora alterations, intestinal morphometric assessment, and mRNA gene expression of relevant iron and zinc transporter proteins, respectively. This study demonstrated that intraamniotic administration of 2.5% genistein increased villus surface area, number of acidic goblet cells, and hemoglobin. Additionally, genistein exposure downregulated duodenal cytochrome B (DcytB) and upregulated hepcidin expression. Further, genistein exposure positively altered the composition and function of the intestinal microbiota. Our results suggest a physiological role for genistein administration in improving mineral status, favorably altering BBM functionality and development, positively modulating the intestinal microbiome, as well as improving physiological status.

Immunolocalization of zinc transporters and metallothioneins reveals links to microvascular morphology and functions

Zinc homeostasis is vital to immune and other organ system functions, yet over a quarter of the world’s population is zinc deficient. Abnormal zinc transport or storage protein expression has been linked to diseases, such as cancer and chronic obstructive pulmonary disorder. Although recent studies indicate a role for zinc regulation in vascular functions and diseases, detailed knowledge of the mechanisms involved remains unknown. This study aimed to assess protein expression and localization of zinc transporters of the SLC39A/ZIP family (ZIPs) and metallothioneins (MTs) in human subcutaneous microvessels and to relate them to morphological features and expression of function-related molecules in the microvasculature. Microvessels in paraffin biopsies of subcutaneous adipose tissues from 14 patients undergoing hernia reconstruction surgery were analysed for 9 ZIPs and 3 MT proteins by MQCM (multifluorescence quantitative confocal microscopy). Zinc regulation proteins detected in human microvasculature included ZIP1, ZIP2, ZIP8, ZIP10, ZIP12, ZIP14 and MT1-3, which showed differential localization among endothelial and smooth muscle cells. ZIP1, ZIP2, ZIP12 and MT3 showed significantly (p < 0.05) increased immunoreactivities, in association with increased microvascular muscularization, and upregulated ET-1, α-SMA and the active form of p38 MAPK (Thr180/Tyr182 phosphorylated, p38 MAPK-P). These findings support roles of the zinc regulation system in microvascular physiology and diseases.

Activation of the zinc-sensing receptor GPR39 promotes T-cell reconstitution after hematopoietic cell transplant in mice

Prolonged lymphopenia represents a major clinical problem after cytoreductive therapies such as chemotherapy and the conditioning required for hematopoietic stem cell transplant (HCT), contributing to the risk of infections and malignant relapse. Restoration of T-cell immunity depends on tissue regeneration in the thymus, the primary site of T-cell development, although the capacity of the thymus to repair itself diminishes over its lifespan. However, although boosting thymic function and T-cell reconstitution is of considerable clinical importance, there are currently no approved therapies for treating lymphopenia. Here we found that zinc (Zn) is critically important for both normal T-cell development and repair after acute damage. Accumulated Zn in thymocytes during development was released into the extracellular milieu after HCT conditioning, where it triggered regeneration by stimulating endothelial cell production of BMP4 via the cell surface receptor GPR39. Dietary supplementation of Zn was sufficient to promote thymic function in a mouse model of allogeneic HCT, including enhancing the number of recent thymic emigrants in circulation although direct targeting of GPR39 with a small molecule agonist enhanced thymic function without the need for prior Zn accumulation in thymocytes. Together, these findings not only define an important pathway underlying tissue regeneration but also offer an innovative preclinical approach to treat lymphopenia in HCT recipients.

Interference with zinc homeostasis and oxidative stress induction as probable mechanisms for cadmium-induced embryo-toxicity in zebrafish

The present study was conducted to provide new insights into the mechanisms that may be responsible for cadmium (Cd)-induced toxicity in zebrafish larvae as well as the role of the trace element zinc (Zn) in reversing Cd harmful effects. For this purpose, zebrafish eggs were exposed to Cd or/and Zn for 96 h. The effects on morphological aspect; mortality rate; Cd, Zn, and metallothionein (MT) levels; oxidative stress biomarkers; as well as molecular expression of some genes involved in Zn metabolism (Zn-MT, ZIP10, and ZnT1) and in antioxidant defense system (Cu/Zn-SOD, CAT and GPx) were examined. Our results showed that Cd toxicity was exerted, initially, by an interference with Zn metabolism. Thus, Cd was able to modify the expression of the corresponding genes so as to ensure its intracellular accumulation at the expense of Zn, causing its depletion. An oxidative stress was then generated, representing the second mode of Cd action which resulted in developmental anomalies and subsequently mortality. Interestingly, significant corrections have been noted following Zn supplementation based, essentially, on its ability to interact with the toxic metal. The increases of Zn bioavailability, the improvement of the oxidative status, as well as changes in Zn transporter expression profile are part of the protection mechanisms. The decrease of Cd-induced MTs after Zn supplement, both at the protein and the mRNA level, suggests that the protection provided by Zn is ensured through mechanisms not involving MT expression but which rather depend on the oxidative status.

G, Kathryn M. T. The importance of targeting signalling mechanisms of the SLC39A family of zinc transporters to inhibit endocrine resistant breast cancer

Aim:

Zinc is a key secondary messenger that can regulate multiple signalling pathways within cancer cells, thus its levels need to be strictly controlled. The Zrt, Irt-like protein (ZIP, SLC39A) family of zinc transporters increase cytosolic zinc from either extracellular or intracellular stores. This study examines the relevance of zinc transporters ZIP7 and ZIP6 as therapeutic targets in tamoxifen resistant (TAMR) breast cancer.

Methods:

A series of in vitro assays, including immunohistochemistry, immunofluorescence, flow cytometry, and western blotting were used to evaluate levels and activity of ZIP7 and ZIP6 in models of TAMR and sensitive (MCF-7) breast cancer. Analyses of these transporters in the clinical setting were performed using publicly available online resources: Gene Expression Profiling Interactive Analysis (GEPIA)2 and Kaplan-Meier Plotter (KmPlot).

Results:

Both total and activated levels of ZIP7 were significantly elevated in TAMR cells versus responsive MCF-7 cells. This was accompanied by an associated increase in free cytoplasmic zinc leading to amplification of downstream signals. Consistent with our proposed model, activated ZIP6 levels correlated with mitotic cells, which could be efficiently inhibited through use of our anti-ZIP6 monoclonal antibody. Mitotic inhibition translated to impaired proliferation in both models, with TAMR cells displaying increased sensitivity. Analysis of matched tumour and normal breast samples from patients revealed significant increases in both ZIP7 and ZIP6 in tumours, as well as family member ZIP4. Kaplan-Meier analysis revealed that high ZIP7 levels correlated with decreased overall and relapse-free survival (RFS) of patients, including patient groups who had received systemic endocrine therapy or tamoxifen only. In contrast, high ZIP6 levels were significantly linked to improved overall and RFS in all patients, as well as RFS in patients that received systemic endocrine therapy.

Conclusions:

TAMR cells displayed increased activity of both ZIP7 and ZIP6 transporters compared to anti-hormone responsive cells, suggesting their potential as novel therapeutic targets following development of resistant disease.

Mechanism of Zinc Transport through the Zinc Transporter YiiP

Zinc is an essential transition metal ion that plays as a structural, functional (catalytic), and a signaling molecule regulating cellular function. Unbalanced levels of zinc in cells can result in various pathological conditions. In the current work, all-atom molecular dynamics simulations were used to study the structure-function correlation between different YiiP states embedded in a lipid bilayer. This study enabled us to develop a hypothesis on the zinc efflux mechanism of YiiP. We have created six different models of YiiP representing the stages of the ion-transport process. We found that zinc ion plays a crucial role in restraining the transmembrane domains (TMDs) of the protein. In addition, H153, located in the TMD, has been proposed to guide the zinc ion toward the ZnA site of the YiiP transporter. Understanding the molecular-level Zn²⁺-transport process sheds light on the strategies affecting intracellular transition-metal ion concentrations in order to treat diseases like diabetes and cancer.

ZIP10 is a negative determinant for anti-tumor effect of mannose in thyroid cancer by activating phosphate mannose isomerase

BACKGROUND

Mannose, a natural hexose existing in daily food, has been demonstrated to preferentially inhibit the progression of tumors with low expression of phosphate mannose isomerase (PMI). However, its function in thyroid cancer still remains elusive.

METHODS

MTT, colony formation and flow cytometry assays were performed to determine the response of thyroid cancer cells to mannose. Meanwhile, mouse models of subcutaneous xenograft and primary papillary thyroid cancer were established to determine in vivo anti-tumor activity of mannose. The underlying mechanism of mannose selectively killing thyroid cancer cells was clarified by a series of molecular and biochemical experiments.

RESULTS

Our data demonstrated that mannose selectively suppressed the growth of thyroid cancer cells, and found that enzyme activity of PMI rather than its protein expression was negatively associated with the response of thyroid cancer cells to mannose. Besides, our data showed that zinc ion (Zn2+) chelator TPEN clearly increased the response of mannose-insensitive cells to mannose by inhibiting enzyme activity of PMI, while Zn2+ supplement could effectively reverse this effect. Further studies found that the expression of zinc transport protein ZIP10, which transport Zn2+ from extracellular area into cells, was negatively related to the response of thyroid cancer cells to mannose. Knocking down ZIP10 in mannose-insensitive cells significantly inhibited in vitro and in vivo growth of these cells by decreasing intracellular Zn2+ concentration and enzyme activity of PMI. Moreover, ectopic expression of ZIP10 in mannose-sensitive cells decrease their cellular response to mannose. Mechanistically, mannose exerted its anti-tumor effect by inhibiting cellular glycolysis; however, this effect was highly dependent on expression status of ZIP10.

CONCLUSION

The present study demonstrate that mannose selectively kills thyroid cancer cells dependent on enzyme activity of PMI rather than its expression, and provide a mechanistic rationale for exploring clinical use of mannose in thyroid cancer therapy.

Metal transporter Slc30a1 controls pharyngeal neural crest differentiation via the zinc-Snai2-Jag1 cascade

The pharyngeal arch (PA) is a neural crest (NC)-derived organ that is transiently developed during embryogenesis and is required for the subsequent development of various tissues. However, the role of zinc during PA differentiation from NC progenitor cells is unknown. Here, we found that the metal transporters Slc30a1a and Slc30a1b mediate zinc homeostasis during PA differentiation. Slc30a1-deficient zebrafish develop zinc accumulation in NC cells, with increased expression of stemness markers and PA dorsal genes, and SMART-seq analyses revealed that the genes snai2 and jag1b may serve as downstream targets. Furthermore, functional studies showed that knocking down either snai2 or jag1b rescues PA development in Slc30a1-deficient zebrafish. Notably, we identified the double zinc-finger domain in the transcription factor Snai2 as a zinc-responsive element that regulates jag1b expression. Our findings indicate that the Slc30a1/zinc-snai2-jag1b axis is an essential regulatory network controlling PA differentiation, shedding new light on the function of zinc homeostasis in maintaining NC cell stemness and multipotency in vertebrates.

Slc39a2-Mediated Zinc Homeostasis Modulates Innate Immune Signaling in Phenylephrine-Induced Cardiomyocyte Hypertrophy

Zinc dyshomeostasis has been involved in the pathogenesis of cardiac hypertrophy; however, the dynamic regulation of intracellular zinc and its downstream signaling in cardiac hypertrophy remain largely unknown. Using Zincpyr1 staining, we found a significant decrease of intracellular Zinc concentration in phenylephrine (PE)-induced hypertrophy of neonatal rat ventricular myocytes (NRVMs). We then screened SLC39 family members responsible for zinc uptake and identified Slc39a2 as the only one altered by PE treatment. Slc39a2 knockdown in NRVMs reduced the intracellular Zinc level, and exacerbated the hypertrophic responses to PE treatment. In contrast, adenovirus-mediated Slc39a2 overexpression enhanced zinc uptake and suppressed PE-induced Nppb expression. RNA sequencing analysis showed a pro-hypertrophic transcriptome reprogramming after Slc39a2 knockdown. Interestingly, the innate immune signaling pathways, including NOD signaling, TOLL-like receptor, NFκB, and IRFs, were remarkably enriched in the Slc39a2-regulated genes. Slc39a2 deficiency enhanced the phosphorylation of P65 NFκB and STAT3, and reduced the expression of IκBα. Finally, the expression of IRF7 was significantly increased by Slc39a2 knockdown, which was in turn suppressed by IRF7 knockdown. Our data demonstrate that zinc homeostasis mediated by a Slc39a2/IRF7 regulatory circuit contributes to the alteration of innate immune signaling in cardiomyocyte hypertrophy.

Zinc Status Index (ZSI) for Quantification of Zinc Physiological Status

Zinc (Zn) deficiency is estimated to affect over one billion (17%) of the world’s population. Zn plays a key role in various cellular processes such as differentiation, apoptosis, and proliferation, and is used for vital biochemical and structural processes in the body. Widely used biomarkers of Zn status include plasma, whole blood, and urine Zn, which decrease in severe Zn deficiency; however, accurate assessment of Zn status, especially in mild to moderate deficiency, is difficult, as studies with these biomarkers are often contradictory and inconsistent. Thus, sensitive and specific biological markers of Zn physiological status are still needed. In this communication, we provide the Zn status index (ZSI) concept, which consists of a three-pillar formula: (1) the LA:DGLA ratio, (2) mRNA gene expression of Zn-related proteins, and (3) gut microbiome profiling to provide a clear assessment of Zn physiological status and degree of Zn deficiency with respect to assessing dietary Zn manipulation. Analysis of five selected studies found that with lower dietary Zn intake, erythrocyte LA:DGLA ratio increased, mRNA gene expression of Zn-related proteins in duodenal and liver tissues was altered, and gut microbiota populations differed, where the ZSI, a statistical model trained on data from these studies, was built to give an accurate estimation of Zn physiological status. However, the ZSI needs to be tested and refined further to determine its full potential.

Formation of the Metal-Binding Core of the ZRT/IRT-like Protein (ZIP) Family Zinc Transporter

Zinc homeostasis in mammals is constantly and precisely maintained by sophisticated regulatory proteins. Among them, the Zrt/Irt-like protein (ZIP) regulates the influx of zinc into the cytoplasm. In this work, we have employed all-atom molecular dynamics simulations to investigate the Zn²⁺ transport mechanism in prokaryotic ZIP obtained from Bordetella bronchiseptica (BbZIP) in a membrane bilayer. Additionally, the structural and dynamical transformations of BbZIP during this process have been analyzed. This study allowed us to develop a hypothesis for the zinc influx mechanism and formation of the metal-binding site. We have created a model for the outward-facing form of BbZIP (experimentally only the inward-facing form has been characterized) that has allowed us, for the first time, to observe the Zn²⁺ ion entering the channel and binding to the negatively charged M2 site. It is thought that the M2 site is less favored than the M1 site, which then leads to metal ion egress; however, we have not observed the M1 site being occupied in our simulations. Furthermore, removing both Zn²⁺ ions from this complex resulted in the collapse of the metal-binding site, illustrating the "structural role" of metal ions in maintaining the binding site and holding the proteins together. Finally, due to the long Cd²⁺-residue bond distances observed in the X-ray structures, we have proposed the existence of an H₃O⁺ ion at the M2 site that plays an important role in protein stability in the absence of the metal ion.

Dietary Phytochemicals in Zinc Homeostasis: A Strategy for Prostate Cancer Management

Studies have suggested an important role of the trace element zinc (Zn) in prostate biology and functions. Zn has been shown to exist in very high concentrations in the healthy prostate and is important for several prostatic functions. In prostate cancer (PCa), Zn levels are significantly decreased and inversely correlated with disease progression. Ideally, restoration of adequate Zn levels in premalignant/malignant prostate cells could abort prostate malignancy. However, studies have shown that Zn supplementation is not an efficient way to significantly increase Zn concentrations in PCa. Based on a limited number of investigations, the reason for the lower levels of Zn in PCa is believed to be the dysregulation of Zn transporters (especially ZIP and ZnT family of proteins), metallothioneins (for storing and releasing Zn), and their regulators (e.g., Zn finger transcription factor RREB1). Interestingly, the level of Zn in cells has been shown to be modulated by naturally occurring dietary phytochemicals. In this review, we discussed the effect of selected phytochemicals (quercetin, resveratrol, epigallocatechin-3-gallate and curcumin) on Zn functioning and proposes that Zn in combination with specific dietary phytochemicals may lead to enhanced Zn bioaccumulation in the prostate, and therefore, may inhibit PCa.

Molecular Basis of Zinc-Dependent Endocytosis of Human ZIP4 Transceptor

Nutrient transporters can be rapidly removed from the cell surface via substrate-stimulated endocytosis as a way to control nutrient influx, but the molecular underpinnings are not well understood. In this work, we focus on zinc-dependent endocytosis of human ZIP4 (hZIP4), a zinc transporter that is essential for dietary zinc uptake. Structure-guided mutagenesis and internalization assay reveal that hZIP4 per se acts as the exclusive zinc sensor, with the transport site’s being responsible for zinc sensing. In an effort of seeking sorting signal, a scan of the longest cytosolic loop (L2) leads to identification of a conserved Leu-Gln-Leu motif that is essential for endocytosis. Partial proteolysis of purified hZIP4 demonstrates a structural coupling between the transport site and the L2 upon zinc binding, which supports a working model of how zinc ions at physiological concentration trigger a conformation-dependent endocytosis of the zinc transporter. This work provides a paradigm on post-translational regulation of nutrient transporters.

Cell surface expression of ZIP4, a transporter for intestinal zinc uptake, is regulated by zinc availability. Zhang et al. report that human ZIP4 acts as the exclusive zinc sensor in initiating the zinc-dependent endocytosis, and a cytosolic motif is essential for sorting signal formation, indicating that ZIP4 is a transceptor.

Accumulation of different metals in oyster Crassostrea gigas: Significance and specificity of SLC39A (ZIP) and SLC30A (ZnT) gene families and polymorphism variation

The Zrt/Irt-like proteins (ZIP, SLC39A) and zinc transporters (ZnT, SLC30A) are the two major gene families responsible for the import/export of Zn and other metals. In this study, the mRNA expression levels and genetic variations of eight ZnTs and 14 ZIPs were identified in Crassostrea gigas after exposure to Zn, Cd, Cu, Hg, and Pb. Metal exposure induced reactive oxygen species (ROS) and malondialdehyde (MDA) accumulation and antioxidant enzyme expression. The expanded gene numbers of superoxide dismutase (SOD) in the oysters exhibited diverse expression under exposure to the five metals, and the contrasting expressions of both ZnTs and ZIPs under different metal exposures were observed, revealing their ion-specific responses. Zn and Cu have similar transporters and induce high expression levels of ZnT1, 2, 7, and 9 and ZIP1, 3, 6, 9, 10, 11, and 14. Pb induced high expression levels of ZIP7, and 13 and ZnT5, 6, and 7, which are mainly expressed in the endoplasmic reticulum (ER). Cd induced high expression levels of ZnT1, 2, and 7 and ZIP1, 6, 9, 10, 11, and 13. Hg exposure was found to have little effect on the ZIP and ZnT expression levels. Based on 3784 single nucleotide polymorphisms (SNPs) within the ZnTs and ZIPs, genetic association analysis for Zn accumulation was conducted on 427 oyster samples. The 38 SNPs, which were located within 12 genes, were identified to be associated with Zn content (p < 0.01), explaining the phenotypic variation from 1.61% to 3.37%. One nonsynonymous mutation and related haplotypes were identified within ZIP1, explaining 1.69% of the variation in Zn. Its high expression under Zn exposure revealed its important role in Zn transportation. To the best of our knowledge, this study is the first comprehensive investigation of the transportation mechanisms of ZIPs and ZnTs under different metal exposures and the genetic effect of Zn accumulation in oysters, and provides valuable biomarkers and genetic resources to evaluate environmental metal pollution.

The Multifaceted Roles of Zinc in Neuronal Mitochondrial Dysfunction

Zinc is a highly abundant cation in the brain, essential for cellular functions, including transcription, enzymatic activity, and cell signaling. However, zinc can also trigger injurious cascades in neurons, contributing to the pathology of neurodegenerative diseases. Mitochondria, critical for meeting the high energy demands of the central nervous system (CNS), are a principal target of the deleterious actions of zinc. An increasing body of work suggests that intracellular zinc can, under certain circumstances, contribute to neuronal damage by inhibiting mitochondrial energy processes, including dissipation of the mitochondrial membrane potential (MMP), leading to ATP depletion. Additional consequences of zinc-mediated mitochondrial damage include reactive oxygen species (ROS) generation, mitochondrial permeability transition, and excitotoxic calcium deregulation. Zinc can also induce mitochondrial fission, resulting in mitochondrial fragmentation, as well as inhibition of mitochondrial motility. Here, we review the known mechanisms responsible for the deleterious actions of zinc on the organelle, within the context of neuronal injury associated with neurodegenerative processes. Elucidating the critical contributions of zinc-induced mitochondrial defects to neurotoxicity and neurodegeneration may provide insight into novel therapeutic targets in the clinical setting.

The Roles of ZnT1 and ZnT4 in Glucose-Stimulated Zinc Secretion in Prostate Epithelial Cells

PURPOSE

We have previously demonstrated by MRI that high glucose stimulates efflux of zinc ions from the prostate. To our knowledge, this phenomena had not been reported previously and the mechanism remains unknown. Here, we report some initial observations that provide new insights into zinc processing during glucose-stimulated zinc secretion (GSZS) in the immortalized human prostate epithelial cell line, PNT1A. Additionally, we identified the subtypes of zinc-containing cells in human benign prostatic hyperplasia (BPH) tissue to further identify which cell types are likely responsible for zinc release in vivo.

PROCEDURE

An intracellular fluorescence marker, FluoZin-1-AM, was used to assess the different roles of ZnT1 and ZnT4 in zinc homeostasis in wild type (WT) and mRNA knockdown PNT1A cell lines. Additionally, Bafilomycin A1 (Baf) was used to disrupt lysosomes and assess the role of lysosomal storage during GSZS. ZIMIR, an extracellular zinc-responsive fluorescent marker, was used to assess dynamic zinc efflux of WT and ZnT1 mRNA knockdown cells exposed to high glucose. Electron microscopy was used to assess intracellular zinc storage in response to high glucose and evaluate how Bafilomycin A1 affects zinc trafficking. BPH cells were harvested from transurtheral prostatectomy tissue and stained with fluorescent zinc granule indicator (ZIGIR), an intracellular zinc-responsive fluorescent marker, before being sorted for cell types using flow cytometry.

RESULTS

Fluorescent studies demonstrate that ZnT1 is the major zinc efflux transporter in prostate epithelial cells and that loss of ZnT1 via mRNA knockdown combined with lysosomal storage disruption results in a nearly 4-fold increase in cytosolic zinc. Knockdown of ZnT1 dramatically reduces zinc efflux during GSZS. Electron microscopy (EM) reveals that glucose stimulation significantly increases lysosomal storage of zinc; disruption of lysosomes via Baf or ZnT4 mRNA knockdown increases multi-vesicular body (MVB) formation and cytosolic zinc levels. In human BPH tissue, only the luminal epithelial cells contained significant amounts of zinc storage granules.

CONCLUSIONS

Exposure of prostate epithelial cells to high glucose alters zinc homeostasis by inducing efflux of zinc ions via ZnT1 channels and increasing lysosomal storage via ZnT4. Given that prostate cancer cells undergo profound metabolic changes that result in reduced levels of total zinc, understanding the complex interplay between glucose exposure and zinc homeostasis in the prostate may provide new insights into the development of prostate carcinogenesis.

Emerging roles of the solute carrier family in pancreatic cancer

Pancreatic cancer is a gastrointestinal tumor with a high mortality rate, and advances in surgical procedures have only resulted in limited improvements in the prognosis of patients. Solute carriers (SLCs), which rank second among membrane transport proteins in terms of abundance, regulate cellular functions, including tumor biology. An increasing number of studies focusing on the role of SLCs in tumor biology have indicated their relationship with pancreatic cancer. The mechanism of SLC transporters in tumorigenesis has been explored to identify more effective therapies and improve survival outcomes. These transporters are significant biomarkers for pancreatic cancer, the functions of which include mainly proliferative signaling, cell death, angiogenesis, tumor invasion and metastasis, energy metabolism, chemotherapy sensitivity and other functions in tumor biology. In this review, we summarize the different roles of SLCs and explain their potential applications in pancreatic cancer treatment.

Toward unzipping the ZIP metal transporters: structure, evolution, and implications on drug discovery against cancer

The Zrt-/Irt-like protein (ZIP) family consists of divalent metal transporters, ubiquitous in all kingdoms of life. Since the discovery of the first ZIPs in the 1990s, the ZIP family has been expanding to contain tens of thousands of members playing key roles in uptake and homeostasis of life-essential trace elements, primarily zinc, iron and manganese. Some family members are also responsible for toxic metal (particularly cadmium) absorption and distribution. Their central roles in trace element biology, and implications in many human diseases, including cancers, have elicited interest across multiple disciplines for potential applications in biomedicine, agriculture and environmental protection. In this review and perspective, selected areas under rapid progress in the last several years, including structural biology, evolution, and drug discovery against cancers, are summarised and commented. Future research to address the most prominent issues associated with transport and regulation mechanisms are also discussed.

Downregulation of the zinc transporter SLC39A13 (ZIP13) is responsible for the activation of CaMKII at reperfusion and leads to myocardial ischemia/reperfusion injury in mouse hearts

While Zn²⁺ dyshomeostasis is known to contribute to ischemia/reperfusion (I/R) injury, the roles of zinc transporters that are responsible for Zn²⁺ homeostasis in the pathogenesis of I/R injury remain to be addressed. This study reports that ZIP13 (SLC39A13), a zinc transporter, plays a role in myocardial I/R injury by modulating the Ca²⁺ signaling pathway rather than by regulating Zn²⁺ transport. ZIP13 is downregulated upon reperfusion in mouse hearts or in H9c2 cells at reoxygenation. Ca²⁺ but not Zn²⁺ was responsible for ZIP13 downregulation, implying that ZIP13 may play a role in I/R injury through the Ca²⁺ signaling pathway. In line with our assumption, knockout of ZIP13 resulted in phosphorylation (Thr²⁸⁷) of Ca²⁺-calmodulin-dependent protein kinase (CaMKII), indicating that downregulation of ZIP13 leads to CaMKII activation. Further studies showed that the heart-specific knockout of ZIP13 enhanced I/R-induced CaMKII phosphorylation in mouse hearts. In contrast, overexpression of ZIP13 suppressed I/R-induced CaMKII phosphorylation. Moreover, the heart-specific knockout of ZIP13 exacerbated myocardial infarction in mouse hearts subjected to I/R, whereas overexpression of ZIP13 reduced infarct size. In addition, knockout of ZIP13 induced increases of mitochondrial Ca²⁺, ROS, mitochondrial swelling, decrease in the mitochondrial respiration control rate (RCR), and dissipation of mitochondrial membrane potential (ΔΨm) in a CaMKII-dependent manner. These data suggest that downregulation of ZIP13 at reperfusion contributes to myocardial I/R injury through activation of CaMKII and the mitochondrial death pathway.

The role of labile Zn2+ and Zn2+-transporters in the pathophysiology of mitochondria dysfunction in cardiomyocytes

An important energy supplier of cardiomyocytes is mitochondria, similar to other mammalian cells. Studies have demonstrated that any defect in the normal processes controlled by mitochondria can lead to abnormal ROS production, thereby high oxidative stress as well as lack of ATP. Taken into consideration, the relationship between mitochondrial dysfunction and overproduction of ROS as well as the relation between increased ROS and high-level release of intracellular labile Zn²⁺, those bring into consideration the importance of the events related with those stimuli in cardiomyocytes responsible from cellular Zn²⁺-homeostasis and responsible Zn²⁺-transporters associated with the Zn²⁺-homeostasis and Zn²⁺-signaling. Zn²⁺-signaling, controlled by cellular Zn²⁺-homeostatic mechanisms, is regulated with intracellular labile Zn²⁺ levels, which are controlled, especially, with the two Zn²⁺-transporter families; ZIPs and ZnTs. Our experimental studies in mammalian cardiomyocytes and human heart tissue showed that Zn²⁺-transporters localizes to mitochondria besides sarco(endo)plasmic reticulum and Golgi under physiological condition. The protein levels as well as functions of those transporters can re-distribute under pathological conditions, therefore, they can interplay among organelles in cardiomyocytes to adjust a proper intracellular labile Zn²⁺ level. In the present review, we aimed to summarize the already known Zn²⁺-transporters localize to mitochondria and function to stabilize not only the cellular Zn²⁺ level but also cellular oxidative stress status. In conclusion, one can propose that a detailed understanding of cellular Zn²⁺-homeostasis and Zn²⁺-signaling through mitochondria may emphasize the importance of new mitochondria-targeting agents for prevention and/or therapy of cardiovascular dysfunction in humans.

Slc39a5-mediated zinc homeostasis plays an essential role in venous angiogenesis in zebrafish

Angiogenesis is a precise process mediated by a variety of signals and the environmental niche. Although the essential trace element zinc and its homeostasis are essential for maintaining proper cellular functions, whether zinc plays a role in angiogenesis is currently unknown. Using zebrafish embryos as a model system, we found that zinc treatment significantly increased the expression of the slc39a5 gene, which encodes the zinc transporter Slc39a5. Moreover, knocking down slc39a5 expression using either a morpholino or CRISPR/Cas9-mediated gene editing led to cardiac ischaemia and an accumulation of red blood cells in the caudal vein plexus (CVP), as well as delayed venous sprouting and fewer vascular loops in the CVP region during early development. Further analysis revealed significantly reduced proliferation and delayed cell migration in the caudal vein of slc39a5 morphants. At the mechanistic level, we found increased levels of systemic zinc in slc39a5-deficient embryos, and chelating zinc restored CVP development. In addition, we found that zinc overload in wild-type embryos leads to impaired CVP formation. Taken together, these results indicate that Slc39a5 plays a critical role in endothelial sprouting and migration in venous angiogenesis by regulating zinc homeostasis.

Zinc: Roles in pancreatic physiology and disease

Zinc is an essential trace element. Deficiencies are frequently seen with gastrointestinal diseases, including chronic pancreatitis, nutritional deficiency, and reduced intestinal absorption. Additionally, reduced zinc levels have been linked to cellular changes associated with acute pancreatitis such as enhanced inflammation with increased macrophage activation and production of inflammatory cytokines such as IL-1β, impaired autophagy, and modulation of calcium homeostasis. Preliminary data suggest that zinc deficiency may lead to pancreatic injury in animal models. The purpose of this review is to explore the biologic effects of zinc deficiency that could impact pancreatic disease. MESH KEYWORDS: Malnutrition, inflammation, trace element.

Participation of Zip3, a ZIP domain-containing protein, in stress response and virulence in Cryptococcus gattii

Cryptococcus gattii is an etiologic agent of cryptococcosis, a potentially fatal disease that affects humans and animals. The successful infection of mammalian hosts by cryptococcal cells relies on their ability to infect and survive in macrophages. Such phagocytic cells present a hostile environment to intracellular pathogens via the production of reactive nitrogen and oxygen species, as well as low pH and reduced nutrient bioavailability. To overcome the low-metal environment found during infection, fungal pathogens express high-affinity transporters, including members of the ZIP family. Previously, we determined that functional zinc uptake driven by Zip1 and Zip2 is necessary for full C.gattiivirulence. Here, we characterized the ZIP3 gene of C. gattii, an ortholog of the Saccharomyces cerevisiae ATX2, which codes a manganese transporter localized to the membrane of the Golgi apparatus. Cryptococcal cells lacking Zip3 were tolerant to toxic concentrations of manganese and had imbalanced expression of intracellular metal transporters, such as the vacuolar Pmc1 and Vcx1, as well as the Golgi Pmr1. Moreover, null mutants of the ZIP3 gene displayed higher sensitivity to reactive oxygen species (ROS) and substantial alteration in the expression of ROS-detoxifying enzyme-coding genes. In line with these phenotypes, cryptococcal cells displayed decreased virulence in a non-vertebrate model of cryptococcosis. Furthermore, we found that the ZIP3 null mutant strain displayed decreased melanization and secretion of the major capsular component glucuronoxylomannan, as well as an altered extracellular vesicle dimensions profile. Collectively, our data suggest that Zip3 activity impacts the physiology, and consequently, several virulence traits of C. gattii.

Biometals and glycosylation in humans: Congenital disorders of glycosylation shed lights into the crucial role of Golgi manganese homeostasis

About half of the eukaryotic proteins bind biometals that participate in their structure and functions in virtually all physiological processes, including glycosylation. After reviewing the biological roles and transport mechanisms of calcium, magnesium, manganese, zinc and cobalt acting as cofactors of the metalloproteins involved in sugar metabolism and/or glycosylation, the paper will outline the pathologies resulting from a dysregulation of these metals homeostasis and more particularly Congenital Disorders of Glycosylation (CDGs) caused by ion transporter defects. Highlighting of CDGs due to defects in SLC39A8 (ZIP8) and TMEM165, two proteins transporting manganese from the extracellular space to cytosol and from cytosol to the Golgi lumen, respectively, has emphasized the importance of manganese homeostasis for glycosylation. Based on our current knowledge of TMEM165 structure and functions, this review will draw a picture of known and putative mechanisms regulating manganese homeostasis in the secretory pathway.

Hatching gland development and hatching in zebrafish embryos: A role for zinc and its transporters Zip10 and Znt1a

Zinc transporters of the ZIP (Slc39, importers) and ZnT (Slc30, exporters) protein families have evolutionary conserved roles in biology. The aim of the present study was to explore the role of zinc, and zinc transporters Zip10 and Znt1a in zebrafish hatching gland development and larval hatching. In the study, knockdown of genes for Zip10 and Znt1a in zebrafish embryos was achieved using morpholino-modified oligonucleotides. A partial loss-of-function Znt1a mutant (Znt1a^sa17) allowed comparison with the Znt1a morphant. Free Zn²⁺ in embryos and apoptosis were investigated using fluorescent dyes whereas gene expression was investigated by whole-mount in situ hybridization (WISH). The results showed high levels of free Zn²⁺ in the hatching gland cells (HGC) along with abundant expression of zip10 and znt1a in normal embryo. Knockdown of zip10 reduced free Zn²⁺ in HGC, ceased their normal developmental apoptosis, and resulted in displacement and later disappearance of hatching glands and hatching enzymes he1a and catL1b, and inability to hatch. Conversely, knockdown of znt1a or the Znt1a^sa17 mutation accelerated hatching and coincided with high expression of hatching enzymes and free Zn²⁺ in the HGC. Thus, Zip10 and free Zn²⁺ in the HGC are required both for their development and function. This study also demonstrated the opposite functions of the two zinc transporters, ZIP10 and ZnT1 as well as shedding light on the role of Zn²⁺ in regulation of the human hatching enzyme homologue, ovastacin, which is activated by zinc and cleaves the zona pellucida protein, ZP2, to prevent polyspermy.