Molecular and genetic features of zinc transporters in physiology and pathogenesis

Insight into brain metallothioneins from bidirectional Zn2+ signaling in synaptic dynamics

The basal levels as the labile Zn2+ pools in the extracellular and intracellular compartments are in the range of ∼10 nM and ∼100 pM, respectively. The influx of extracellular Zn2+ is used for memory via cognitive activity and is regulated for synaptic plasticity, a cellular mechanism of memory. When Zn2+ influx into neurons excessively occurs, however, it becomes a critical trigger for cognitive decline and neurodegeneration, resulting in acute and chronic pathogenesis. Aging, a biological process, generally accelerates vulnerability to neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD). The basal level of extracellular Zn2+ is age relatedly increased in the rat hippocampus, and the influx of extracellular Zn2+ contributes to accelerating vulnerability to the AD and PD pathogenesis in experimental animals with aging. Metallothioneins (MTs) are Zn2+-binding proteins for cellular Zn2+ homeostasis and involved in not only supplying functional Zn2+ required for cognitive activity, but also capturing excess (toxic) Zn2+ involved in cognitive decline and neurodegeneration. Therefore, it is estimated that regulation of MT synthesis is involved in both neuronal activity and neuroprotection. The present report provides recent knowledge regarding the protective/preventive potential of MT synthesis against not only normal aging but also the AD and PD pathogenesis in experimental animals, focused on MT function in bidirectional Zn2+ signaling in synaptic dynamics.

Mechanism of metal ion-induced cell death in gastrointestinal cancer

Gastrointestinal (GI) cancer is one of the most severe types of cancer, with a significant impact on human health worldwide. Due to the urgent demand for more effective therapeutic strategies against GI cancers, novel research on metal ions for treating GI cancers has attracted increasing attention. Currently, with accumulating research on the relationship between metal ions and cancer therapy, several metal ions have been discovered to induce cell death. In particular, the three novel modes of cell death, including ferroptosis, cuproptosis, and calcicoptosis, have become focal points of research in the field of cancer. Meanwhile, other metal ions have also been found to trigger cell death through various mechanisms. Accordingly, this review focuses on the mechanisms of metal ion-induced cell death in GI cancers, hoping to provide theoretical support for further GI cancer therapies.

Contribution of zinc accumulation to ischemic brain injury and its mechanisms about oxidative stress, inflammation, and autophagy: an update

Ischemic stroke is a leading cause of death and disability worldwide, and presently, there is no effective neuroprotective therapy. Zinc is an essential trace element that plays important physiological roles in the central nervous system. Free zinc concentration is tightly regulated by zinc-related proteins in the brain under normal conditions. Disruption of zinc homeostasis, however, has been found to play an important role in the mechanism of brain injury following ischemic stroke. A large of free zinc releases from storage sites after cerebral ischemia, which affects the functions and survival of nerve cells, including neurons, astrocytes, and microglia, resulting in cell death. Ischemia-triggered intracellular zinc accumulation also disrupts the function of blood-brain barrier via increasing its permeability, impairing endothelial cell function, and altering tight junction levels. Oxidative stress and neuroinflammation have been reported to be as major pathological mechanisms in cerebral ischemia/reperfusion injury. Studies have showed that the accumulation of intracellular free zinc could impair mitochondrial function to result in oxidative stress, and form a positive feedback loop between zinc accumulation and reactive oxygen species production, which leads to a series of harmful reactions. Meanwhile, elevated intracellular zinc leads to neuroinflammation. Recent studies also showed that autophagy is one of the important mechanisms of zinc toxicity after ischemic injury. Interrupting the accumulation of zinc will reduce cerebral ischemia injury and improve neurological outcomes. This review summarizes the role of zinc toxicity in cellular and tissue damage following cerebral ischemia, focusing on the mechanisms about oxidative stress, inflammation, and autophagy.

Targeting ZIP8 mediated ferroptosis as a novel strategy to protect against the retinal pigment epithelial degeneration

The degeneration of retinal pigment epithelium (RPE) plays an important role in the development of age-related macular degeneration (AMD). However, the underlying mechanism remains elusive. In this study, we identified that ZIP8, a metal-ion transporter, plays a crucial role in the degeneration of RPE cells mediated by ferroptosis. ZIP8 was found to be upregulated in patients with AMD through transcriptome analysis. Upregulated ZIP8 was also observed in both oxidative-stressed RPE cells and AMD mouse model. Importantly, knockdown of ZIP8 significantly inhibited ferroptosis in RPE cells induced by sodium iodate-induced oxidative stress. Blocking ZIP8 with specific antibodies reversed RPE degeneration and restored retinal function, improving visual loss in a mouse model of NaIO3-induced. Interestingly, the modification of the N-glycosylation sites N40, N72 and N88, but not N273, was essential for the intracellular iron accumulation mediated by ZIP8, which further led to increased lipid peroxidation and RPE death. These findings highlight the critical role of ZIP8 in RPE ferroptosis and provide a potential target for the treatment of diseases associated with retinal degeneration, including AMD.

The role of metal ions in the occurrence, progression, drug resistance, and biological characteristics of gastric cancer

Metal ions exert pivotal functions within the human body, encompassing essential roles in upholding cell structure, gene expression regulation, and catalytic enzyme activity. Additionally, they significantly influence various pathways implicated in divergent mechanisms of cell death. Among the prevailing malignant tumors of the digestive tract worldwide, gastric cancer stands prominent, exhibiting persistent high mortality rates. A compelling body of evidence reveals conspicuous ion irregularities in tumor tissues, encompassing gastric cancer. Notably, metal ions have been observed to elicit distinct contributions to the progression, drug resistance, and biological attributes of gastric cancer. This review consolidates pertinent literature on the involvement of metal ions in the etiology and advancement of gastric cancer. Particular attention is directed towards metal ions, namely, Na, K, Mg, Ca, Fe, Cu, Zn, and Mn, elucidating their roles in the initiation and progression of gastric cancer, cellular demise processes, drug resistance phenomena, and therapeutic approaches.

Protection of cultured vascular endothelial cells against cadmium cytotoxicity by simultaneous treatment or pretreatment with manganese

Cadmium is a heavy metal that pollutes the environment and foods and is a risk factor for vascular disorders. We have previously demonstrated that pretreatment of vascular endothelial cells with zinc and copper protects the cells against cadmium cytotoxicity. In contrast, cadmium cytotoxicity was potentiated in cells following exposure to lead, thereby indicating that in vascular endothelial cells, cadmium cytotoxicity can be differentially modified by the co-occurrence of other heavy metals. In this study, we revealed that simultaneous treatment or pretreatment with manganese protects vascular endothelial cells against cadmium cytotoxicity. Intracellular accumulation of cadmium was observed to be reduced by simultaneous treatment with manganese, although not by pretreatment. The mRNA expression of metal transporters that regulate the uptake of both cadmium and manganese (ZIP8, ZIP14, and DMT1) remained unaffected by either simultaneous treatment or pretreatment with manganese, and simultaneous treatment with manganese suppressed the cadmium-induced expression of metallothionein but pretreatment with manganese did not exhibit such suppressive effect. Thus, the protection of vascular endothelial cells against cadmium cytotoxicity conferred by simultaneous treatment with manganese is assumed to be partially attributed to a reduction in the intracellular accumulation of cadmium, whereas the effects of pretreatment with manganese are independent of both the reduced intracellular accumulation of cadmium and the induction of metallothionein. These observations accordingly indicate that the protective effects of manganese are mediated via alternative (as yet unidentified) mechanisms.

Metalation and activation of Zn2+ enzymes via early secretory pathway-resident ZNT proteins

Zinc (Zn2+), an essential trace element, binds to various proteins, including enzymes, transcription factors, channels, and signaling molecules and their receptors, to regulate their activities in a wide range of physiological functions. Zn2+ proteome analyses have indicated that approximately 10% of the proteins encoded by the human genome have potential Zn2+ binding sites. Zn2+ binding to the functional site of a protein (for enzymes, the active site) is termed Zn2+ metalation. In eukaryotic cells, approximately one-third of proteins are targeted to the endoplasmic reticulum; therefore, a considerable number of proteins mature by Zn2+ metalation in the early secretory pathway compartments. Failure to capture Zn2+ in these compartments results in not only the inactivation of enzymes (apo-Zn2+ enzymes), but also their elimination via degradation. This process deserves attention because many Zn2+ enzymes that mature during the secretory process are associated with disease pathogenesis. However, how Zn2+ is mobilized via Zn2+ transporters, particularly ZNTs, and incorporated in enzymes has not been fully elucidated from the cellular perspective and much less from the biophysical perspective. This review focuses on Zn2+ enzymes that are activated by Zn2+ metalation via Zn2+ transporters during the secretory process. Further, we describe the importance of Zn2+ metalation from the physiopathological perspective, helping to reveal the importance of understanding Zn2+ enzymes from a biophysical perspective.

Ligand-independent signaling and migration of breast cancer cells expressing membrane androgen receptor, ZIP9 (SLC39A9)

Zinc transporter ZIP9 is also a membrane androgen receptor that mediates androgen-dependent zinc and G-protein signaling to modulate tumorigenic responses in cancer cells. It is unclear whether unliganded ZIP9 causes similar responses. ZIP9 overexpression in MDA-MB-231 breast cancer cells (ZIP9 cells) increased zinc levels and cell migration/invasion which was mimicked with a zinc ionophore and attenuated with a zinc chelator, suggesting these tumorigenic responses are zinc-dependent. Expression of migration markers MYL9 and CYR61 was elevated in ZIP9 cells and further increased together with cell migration by forskolin treatment and blocked with H-89, indicating they are mediated through an AC/PKA pathway. Knockdown of ZIP9 expression in MDA-MB-468 cells decreased cell migration/invasion, migration markers and zinc levels, confirming similar roles of unliganded ZIP9 in another breast cancer cell line. Testosterone treatment further increased migration, biomarker expression and zinc in ZIP9 cells, suggesting it may act through similar pathways to induce tumorigenic responses.

A Potential Association of Zinc Deficiency and Tyrosine Kinase Inhibitor-Induced Hand-Foot Skin Reaction

Hand-foot skin reaction (HFSR) is a common skin-related adverse event induced by multikinase inhibitors targeting both platelet-derived growth factor receptor and vascular endothelial growth factor receptor, possibly due to inadequate repair following frictional trauma. Zinc is a trace element and essential nutrient in humans that plays critical roles in the development and differentiation of skin cells. Zinc transporters (Zrt- and Irt-like proteins and Zn transporters) and metallothioneins are involved in zinc efflux, uptake, and homeostasis and have been reported to be involved in skin differentiation. The underlying mechanism of HFSR remains unclear, and the association between HFSR and zinc has not been previously studied. However, some case reports and case series provide potential evidence to suggest that zinc deficiency may be involved in HFSR development and zinc supplementation may relieve HFSR symptoms. However, no large-scale clinical studies have been conducted to examine this role. Therefore, this review summarizes the evidence supporting a possible link between HFSR development and zinc and proposes potential mechanisms underlying this association based on current evidence.

Antiviral activity of zinc against hepatitis viruses: current status and future prospects

Viral hepatitis is a major public health concern globally. World health organization aims at eliminating viral hepatitis as a public health threat by 2030. Among the hepatitis causing viruses, hepatitis B and C are primarily transmitted via contaminated blood. Hepatitis A and E, which gets transmitted primarily via the feco-oral route, are the leading cause of acute viral hepatitis. Although vaccines are available against some of these viruses, new cases continue to be reported. There is an urgent need to devise a potent yet economical antiviral strategy against the hepatitis-causing viruses (denoted as hepatitis viruses) for achieving global elimination of viral hepatitis. Although zinc was known to mankind for a long time (since before Christ era), it was identified as an element in 1746 and its importance for human health was discovered in 1963 by the pioneering work of Dr. Ananda S. Prasad. A series of follow up studies involving zinc supplementation as a therapy demonstrated zinc as an essential element for humans, leading to establishment of a recommended dietary allowance (RDA) of 15 milligram zinc [United States RDA for zinc]. Being an essential component of many cellular enzymes and transcription factors, zinc is vital for growth and homeostasis of most living organisms, including human. Importantly, several studies indicate potent antiviral activity of zinc. Multiple studies have demonstrated antiviral activity of zinc against viruses that cause hepatitis. This article provides a comprehensive overview of the findings on antiviral activity of zinc against hepatitis viruses, discusses the mechanisms underlying the antiviral properties of zinc and summarizes the prospects of harnessing the therapeutic benefit of zinc supplementation therapy in reducing the disease burden due to viral hepatitis.

Construction of a prognostic model for colorectal adenocarcinoma based on Zn transport-related genes identified by single-cell sequencing and weighted co-expression network analysis

Background

Colorectal cancer (CRC) is one of the most prevalent malignancies and the third most lethal cancer globally. The most reported histological subtype of CRC is colon adenocarcinoma (COAD). The zinc transport pathway is critically involved in various tumors, and its anti-tumor effect may be through improving immune function. However, the Zn transport pathway in COAD has not been reported.

Methods

The determination of Zn transport-related genes in COAD was carried out through single-cell analysis of the GSE 161277 obtained from the GEO dataset. Subsequently, a weighted co-expression network analysis of the TCGA cohort was performed. Then, the prognostic model was conducted utilizing univariate Cox regression and least absolute shrinkage and selection operator (LASSO) Cox regression analysis. Functional enrichment, immune microenvironment, and survival analyses were also carried out. Consensus clustering analysis was utilized to verify the validity of the prognostic model and explore the immune microenvironment. Ultimately, cell experiments, including CCK-8,transwell and scratch assays, were performed to identify the function of LRRC59 in COAD.

Results

According to the Zn transport-related prognostic model, the individuals with COAD in TCGA and GEO databases were classified into high- and low-risk groups. The group with low risk had a comparatively more favorable prognosis. Two groups had significant variations in the immune infiltration, MHC, and the expression of genes related to the immune checkpoint. The cell experiments indicated that the proliferation, migration, and invasion of the HCT-116, DLD-1, and RKO cell lines were considerably increased after LRRC59 knockdown. It proved that LRRC59 was indeed a protective factor for COAD.

Conclusion

A prognostic model for COAD was developed using zinc transport-related genes. This model can efficiently assess the immune microenvironment and prognosis of individuals with COAD. Subsequently, the function of LRRC59 in COAD was validated via cell experiments, highlighting its potential as a biomarker.

Human genetic adaptation related to cellular zinc homeostasis

SLC30A9 encodes a ubiquitously zinc transporter (ZnT9) and has been consistently suggested as a candidate for positive selection in humans. However, no direct adaptive molecular phenotype has been demonstrated. Our results provide evidence for directional selection operating in two major complementary haplotypes in Africa and East Asia. These haplotypes are associated with differential gene expression but also differ in the Met50Val substitution (rs1047626) in ZnT9, which we show is found in homozygosis in the Denisovan genome and displays accompanying signatures suggestive of archaic introgression. Although we found no significant differences in systemic zinc content between individuals with different rs1047626 genotypes, we demonstrate that the expression of the derived isoform (ZnT9 50Val) in HEK293 cells shows a gain of function when compared with the ancestral (ZnT9 50Met) variant. Notably, the ZnT9 50Val variant was found associated with differences in zinc handling by the mitochondria and endoplasmic reticulum, with an impact on mitochondrial metabolism. Given the essential role of the mitochondria in skeletal muscle and since the derived allele at rs1047626 is known to be associated with greater susceptibility to several neuropsychiatric traits, we propose that adaptation to cold may have driven this selection event, while also impacting predisposition to neuropsychiatric disorders in modern humans.

Directed Neural Stem Cells Differentiation via Signal Communication with Ni-Zn Micromotors

Neural stem cells (NSCs), with the capability of self-renewal, differentiation, and environment modulation, are considered promising for stroke, brain injury therapy, and neuron regeneration. Activation of endogenous NSCs, is attracting increasing research enthusiasm, which avoids immune rejection and ethical issues of exogenous cell transplantation. Yet, how to induce directed growth and differentiation in situ remain a major challenge. In this study, a pure water-driven Ni-Zn micromotor via a self-established electric-chemical field is proposed. The micromotors can be magnetically guided and precisely approach target NSCs. Through the electric-chemical field, bioelectrical signal exchange and communication with endogenous NSCs are allowed, thus allowing for regulated proliferation and directed neuron differentiation in vivo. Therefore, the Ni-Zn micromotor provides a platform for controlling cell fate via a self-established electrochemical field and targeted activation of endogenous NSCs.

SLC39A10 promotes malignant phenotypes of gastric cancer cells by activating the CK2-mediated MAPK/ERK and PI3K/AKT pathways

Solute carrier family 39 member 10 (SLC39A10) belongs to a subfamily of zinc transporters and plays a key role in B-cell development. Previous studies have reported that its upregulation promotes breast cancer metastasis by enhancing the influx of zinc ions (Zn2+); however, its role in gastric cancer remains totally unclear. Here, we found that SLC39A10 expression was frequently increased in gastric adenocarcinomas and that SLC39A10 upregulation was strongly associated with poor patient outcomes; in addition, we identified SLC39A10 as a direct target of c-Myc. Functional studies showed that ectopic expression of SLC39A10 in gastric cancer cells dramatically enhanced the proliferation, colony formation, invasiveness abilities of these gastric cancer cells and tumorigenic potential in nude mice. Conversely, SLC39A10 knockdown inhibited gastric cancer cell proliferation and colony formation. Mechanistically, SLC39A10 exerted its carcinogenic effects by increasing Zn2+ availability and subsequently enhancing the enzyme activity of CK2 (casein kinase 2). As a result, the MAPK/ERK and PI3K/AKT pathways, two major downstream effectors of CK2, were activated, while c-Myc, a downstream target of these two pathways, formed a vicious feedback loop with SLC39A10 to drive the malignant progression of gastric cancer. Taken together, our data demonstrate that SLC39A10 is a functional oncogene in gastric cancer and suggest that targeting CK2 is an alternative therapeutic strategy for gastric cancer patients with high SLC39A10 expression.

An endomembrane zinc transporter negatively regulates systemic RNAi in Caenorhabditis elegans

Double-stranded RNA (dsRNA) regulates gene expression in a sequence-dependent manner. In Caenorhabditis elegans, dsRNA spreads through the body and leads to systemic RNA silencing. Although several genes involved in systemic RNAi have been genetically identified, molecules that mediate systemic RNAi remain largely unknown. Here, we identified ZIPT-9, a C. elegans homolog of ZIP9/SLC39A9, as a broad-spectrum negative regulator of systemic RNAi. We showed that RSD-3, SID-3, and SID-5 genetically act in parallel for efficient RNAi, and that zipt-9 mutants suppress the RNAi defects of all the mutants. Analysis of a complete set of deletion mutants for SLC30 and SLC39 family genes revealed that only zipt-9 mutants showed altered RNAi activity. Based on these results and our analysis using transgenic Zn2+ reporters, we propose that ZIPT-9-dependent Zn2+ homeostasis, rather than overall cytosolic Zn2+, modulates systemic RNAi activity. Our findings reveal a previously unknown function of zinc transporters in negative RNAi regulation.

Resolving the zinc binding capacity of honey bee vitellogenin and locating its putative binding sites

The protein vitellogenin (Vg) plays a central role in lipid transportation in most egg-laying animals. High Vg levels correlate with stress resistance and lifespan potential in honey bees (Apis mellifera). Vg is the primary circulating zinc-carrying protein in honey bees. Zinc is an essential metal ion in numerous biological processes, including the function and structure of many proteins. Measurements of Zn²⁺ suggest a variable number of ions per Vg molecule in different animal species, but the molecular implications of zinc-binding by this protein are not well-understood. We used inductively coupled plasma mass spectrometry to determine that, on average, each honey bee Vg molecule binds 3 Zn²⁺ -ions. Our full-length protein structure and sequence analysis revealed seven potential zinc-binding sites. These are located in the β-barrel and α-helical subdomains of the N-terminal domain, the lipid binding site, and the cysteine-rich C-terminal region of unknown function. Interestingly, two potential zinc-binding sites in the β-barrel can support a proposed role for this structure in DNA-binding. Overall, our findings suggest that honey bee Vg bind zinc at several functional regions, indicating that Zn²⁺ -ions are important for many of the activities of this protein. In addition to being potentially relevant for other egg-laying species, these insights provide a platform for studies of metal ions in bee health, which is of global interest due to recent declines in pollinator numbers.

Zinc in Human Health and Infectious Diseases

During the last few decades, the micronutrient zinc has proven to be an important metal ion for a well-functioning immune system, and thus also for a suitable immune defense. Nowadays, it is known that the main cause of zinc deficiency is malnutrition. In particular, vulnerable populations, such as the elderly in Western countries and children in developing countries, are often affected. However, sufficient zinc intake and homeostasis is essential for a healthy life, as it is known that zinc deficiency is associated with a multitude of immune disorders such as metabolic and chronic diseases, as well as infectious diseases such as respiratory infections, malaria, HIV, or tuberculosis. Moreover, the modulation of the proinflammatory immune response and oxidative stress is well described. The anti-inflammatory and antioxidant properties of zinc have been known for a long time, but are not comprehensively researched and understood yet. Therefore, this review highlights the current molecular mechanisms underlying the development of a pro-/ and anti-inflammatory immune response as a result of zinc deficiency and zinc supplementation. Additionally, we emphasize the potential of zinc as a preventive and therapeutic agent, alone or in combination with other strategies, that could ameliorate infectious diseases.

Zinc transporter LIV1: A promising cell surface target for triple negative breast cancer

Breast cancer is one of the leading causes contributing to the global cancer burden. The triple negative breast cancer (TNBC) molecular subtype accounts for the most aggressive type. Despite progression in therapeutic options and prognosis in breast cancer treatment options, there remains a high rate of distant relapse. With advancements in understanding the role of zinc and zinc carriers in the prognosis and treatment of the disease, the scope of precision treatment/targeted therapy has been expanded. Zinc levels and zinc transporters play a vital role in maintaining cellular homeostasis, tumor surveillance, apoptosis, and immune function. This review focuses on the zinc transporter, LIV1, as an essential target for breast cancer prognosis and emerging treatment options. Previous studies give an insight into the role of LIV1 in fulfilling the most important hallmarks of cancer such as apoptosis, metastasis, invasion, and evading the immune system. Normal tissue expression of LIV1 is limited. Higher expression of LIV1 has been linked to Epithelial-Mesenchymal Transition, histological grade of cancer, and early node metastasis. LIV1 was found to be one of the attractive targets in the therapeutic hunt for TNBCs. TNBCs are an immunogenic breast cancer subtype. As zinc transporters are known to serve as the metabolic gatekeepers of immune cells, this review bridges tumor infiltrating lymphocytes, TNBC and LIV1. In addition, the suitability of LIV1 as an antibody-drug conjugate (Seattle genetics [SGN]-LIV1A) target in TNBC, represents a promising strategy for patients. Early clinical trial results reveal that this novel agent reduces tumor burden by inducing mitotic arrest, immunomodulation, and immunogenic cell death, warranting further investigation of SGN-LIV1A in combination with immuno-oncology agents. Priming the patient's immune response in combination with SGN-LIV1A could eventually change the landscape for the TNBC patient population.

First report on the burden and distribution of Cu, Zn, Pb, and Cd in the Ocellated icefish (Chionodraco rastrospinosus) of northern Antarctic Peninsula

Understanding the distribution of trace elements in Ocellated icefish (Chionodraco rastrospinosus), one of fish species with lacking hemoglobin from the family Channichthyidae and distributes in a very limited area at the south Scotia Sea, will help understand their physiological composition and conserve this vulnerable population; however, information on this topic is extremely limited. This study examines trace elements (two essential elements, copper [Cu] and zinc [Zn], and two non-essential elements, cadmium [Cd] and lead [Pb]) in C. rastrospinosus and provides for the first time baseline data on elemental distribution in four tissues of C. rastrospinosus in the northern Antarctic Peninsula (NAP). The element concentrations showed the following trends: Zn > Cu > Pb > Cd in muscle and stomach and Zn > Cu > Cd > Pb in intestine and liver. Among all tissues, muscle had the lowest element concentrations. The average Zn level is 70.81 ± 28.91 μg g^-1 dry weight (DW) in C. rastrospinosus muscle, which is higher significantly than average levels of Cu (0.56 ± 0.41 μg g^-1 DW), Pb (0.29 ± 0.33 μg g^-1 DW) and Cd (0.12 ± 0.05 μg g^-1 DW). Zn and Cd concentrations in the stomach and intestines were significantly positively correlated. C. rastrospinosus could be a useful bioindicator for monitoring variability in trace elements dynamics in NAP and the environmental variability in this region.

Evaluation of the diagnosis and treatment options for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)

Viruses are non-living organisms that cause many problems for human societies annually. The outbreak of some dangerous viruses causing acute pneumonia has been the leading cause of death in the world. The epidemiological findings showed that the virus is developing different and dangerous species by creating new mutations, which makes it difficult to treat. The diagnosis and treatment of corona virus disease (COVID-19) has been one of the most important topics in the scientific community for the past 2 years. There are several diagnostic methods available for the detection of COVID-19 that are highly accurate and require less time. The use of some therapies such as remdesivir with basic therapy has shown high therapeutic effectiveness, but the therapeutic side effects such as decreased glomerular filtration rate, decreased lymphocyte count, respiratory failure, and increased blood creatinine levels in most treatments have been observed. The COVID-19 infection and the associated deaths are still very worrying, therefore, rapid diagnosis and timely management of this deadly infection and the necessary measures for eradicating COVID-19 are important.

The Assessment of Dietary Organic Zinc on Zinc Homeostasis, Antioxidant Capacity, Immune Response, Glycolysis and Intestinal Microbiota in White Shrimp (Litopenaeus vannamei Boone, 1931)

This study aimed to assess dietary organic zinc on zinc homeostasis, antioxidant capacity, immune response, glycolysis and intestinal microbiota in white shrimp (Litopenaeus vannamei Boone, 1931). Six experimental diets were formulated: Control, zinc free; S120, 120 mg·kg-1 zinc from ZnSO4·7H2O added into control diet; O30, O60, O90 and O120, 30, 60, 90 and 120 mg·kg-1 zinc from Zn-proteinate added into control diet, respectively. The results showed that organic zinc significantly promoted zinc content and gene expression of ZnT1, ZIP11 and MT in the hepatopancreas and enhanced antioxidant capacity and immunity (in terms of increased activities of T-SOD, Cu/Zn SOD, PO, LZM, decreased content of MDA, upregulated expressions of GST, G6PDH, ProPO, LZM and Hemo, and increased resistance to Vibrio parahaemolyticus). Organic zinc significantly upregulated GluT1 expression in the intestine, increased glucose content of plasma and GCK, PFK and PDH activities of hepatopancreas, and decreased pyruvate content of hepatopancreas. Organic zinc improved intestinal microbiota communities, increased the abundance of potentially beneficial bacteria and decreased the abundance of potential pathogens. Inorganic zinc (S120) also had positive effects, but organic zinc (as low as O60) could achieve better effects. Overall, organic zinc had a higher bioavailability and was a more beneficial zinc resource than inorganic zinc in shrimp feeds.

Consequences of zinc deficiency on zinc localization, taurine transport, and zinc transporters in rat retina

The colocalization of taurine and zinc transporters (TAUT, ZnTs) has not been explored in retina. Our objective is to evaluate the effect of the intracellular zinc chelator N,N,N,N-tetrakis-(2-pyridylmethyl) ethylenediamine (TPEN) on zinc localization and colocalization TAUT and ZnT-1 (of plasma membrane), 3 (vesicular), and 7 (vesicular and golgi apparatus) in layers of retina by immunohistochemistry. To mark zinc, it was used cell-permeable fluorescent Zinquin ethyl ester. Specific first and secondary antibodies, conjugated with rhodamine or fluorescein-isothiocyanate were used to mark TAUT and ZnTs. The fluorescence results were reported as integrated optical density (IOD). Zinc was detected in all layers of the retina. The treatment with TPEN produced changes in the distribution of zinc in layers of retina less in the outer nuclear layer compared with the control. TAUT was detected in all layers of retina and TPEN chelator produced decrease of IOD in all layers of retina except in the photoreceptor compared with the control. ZnT 1, 3, and 7 were distributed in all retina layers, with more intensity in ganglion cell layer (GCL) and in the layers where there is synaptic connection. For all transporters, the treatment with TPEN produced significant decrease of IOD in layers of retina least in the inner nuclear layer for ZnT1, in the photoreceptor for ZnT3 and in the GCL and outer plexiform layer for ZnT7. The distribution of zinc, TAUT, and ZnTs in the layers of retina is indicative of the interaction of taurine and zinc for the function of the retina and normal operation of said layers. HIGHLIGHTS: Taurine and zinc are two molecules highly concentrated in the retina and with relevant functions in this structure. Maintaining zinc homeostasis in this tissue is necessary for the normal function of the taurine system in the retina. The study of the taurine transporter and the different zinc transporters in the retina (responsible for maintaining adequate levels of taurine and zinc) is relevant and novel, since it is indicative of the interactions between both molecules in this structure.

Zinc in Regulating Protein Kinases and Phosphatases in Neurodegenerative Diseases

Zinc is essential for human growth and development. As a trace nutrient, zinc plays important roles in numerous signal transduction pathways involved in distinct physiologic or pathologic processes. Protein phosphorylation is a posttranslational modification which regulates protein activity, degradation, and interaction with other molecules. Protein kinases (PKs) and phosphatases (PPs), with their effects of adding phosphate to or removing phosphate from certain substrates, are master regulators in controlling the phosphorylation of proteins. In this review, we summarize the disturbance of zinc homeostasis and role of zinc disturbance in regulating protein kinases and protein phosphatases in neurodegenerative diseases, with the focus of that in Alzheimer’s disease, providing a new perspective for understanding the mechanisms of these neurologic diseases.

Understanding signatures of positive natural selection in human zinc transporter genes

Zinc is an essential micronutrient with a tightly regulated systemic and cellular homeostasis. In humans, some zinc transporter genes (ZTGs) have been previously reported as candidates for strong geographically restricted selective sweeps. However, since zinc homeostasis is maintained by the joint action of 24 ZTGs, other more subtle modes of selection could have also facilitated human adaptation to zinc availability. Here, we studied whether the complete set of ZTGs are enriched for signals of positive selection in worldwide populations and population groups from South Asia. ZTGs showed higher levels of genetic differentiation between African and non-African populations than would be randomly expected, as well as other signals of polygenic selection outside Africa. Moreover, in several South Asian population groups, ZTGs were significantly enriched for SNPs with unusually extended haplotypes and displayed SNP genotype-environmental correlations when considering zinc deficiency levels in soil in that geographical area. Our study replicated some well-characterized targets for positive selection in East Asia and sub-Saharan Africa, and proposes new candidates for follow-up in South Asia (SLC39A5) and Africa (SLC39A7). Finally, we identified candidate variants for adaptation in ZTGs that could contribute to different disease susceptibilities and zinc-related human health traits.

Zinc homeostasis and regulation: Zinc transmembrane transport through transporters

The second abundant micronutrient, zinc, is attracting more and more attention for it performs essential functions in living organisms and bears close relationships with the occurrence of diseases. However, excess zinc is toxic to cells. Ensuring a balanced zinc state for organisms is essential. Zinc transporters, including ZIPs and ZnTs, are pivotal in regulating zinc homeostasis. Benefiting from zinc transporter structures determination and their transporting dynamic revelation, the clarification of detailed mechanisms of zinc trafficking and the maintenance of zinc homeostasis by transporters in the human body are getting more and more evident. The present review gives a detailed description of the structural basis of zinc transport through ZIP and ZnT, through which the molecular mechanism of zinc binding and transport was illustrated. Then the motive force that drives zinc transmembrane transport and finally a generalization for the regulation models of zinc transporters were summarized.

ZIP9 Is a Druggable Determinant of Sex Differences in Melanoma

Melanoma and most other cancers occur more frequently and have worse prognosis in males compared with females. Although sex steroids are thought to be involved, classical androgen and estrogen receptors are not detectable in most melanomas. Here we show that testosterone promotes melanoma proliferation by activating ZIP9 (SLC39A9), a zinc transporter that is widely expressed in human melanoma but not intentionally targeted by available therapeutics. This testosterone activity required an influx of zinc, activation of MAPK, and nuclear translocation of YAP. FDA-approved inhibitors of the classical androgen receptor also inhibited ZIP9, thereby antagonizing the protumorigenic effects of testosterone in melanoma. In male mice, androgen receptor inhibitors suppressed growth of ZIP9-expressing melanomas but had no effect on isogenic melanomas lacking ZIP9 or on melanomas in females. These data suggest that ZIP9 might be effectively targeted in melanoma and other cancers by repurposing androgen receptor inhibitors that are currently approved only for prostate cancer. SIGNIFICANCE: Testosterone signaling through ZIP9 mediates some of the sex differences in melanoma, and drugs that target AR can be repurposed to block ZIP9 and inhibit melanoma in males.

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 trafficking 1. Probing the roles of proteome, metallothionein, and glutathione

The cellular trafficking pathways that conduct zinc to its sites of binding in functional proteins remain largely unspecified. In this study, the hypothesis was investigated that nonspecific proteomic binding sites serve as intermediates in zinc trafficking. Proteome from pig kidney LLC-PK1 cells contains a large concentration of such sites, displaying an average conditional stability constant of 1010-11, that are dependent on sulfhydryl ligands to achieve high-affinity binding of zinc. As a result, the proteome competes effectively with induced metallothionein for Zn2+ upon exposure of cells to extracellular Zn2+ or during in vitro direct competition. The reaction of added Zn2+ bound to proteome with apo-carbonic anhydrase was examined as a potential model for intracellular zinc trafficking. The extent of this reaction was inversely dependent upon proteome concentration and under cellular conditions thought to be negligible. The rate of reaction was strictly first order in both Zn2+ and apo-carbonic anhydrase, and also considered to be insignificant in cells. Adding the low molecular weight fraction of cell supernatant to the proteome markedly enhanced the speed of this reaction, a phenomenon dependent on the presence of glutathione (GSH). In agreement, inclusion of GSH accelerated the reaction in a concentration-dependent manner. The implications of abundant high-affinity binding sites for Zn2+ within the proteome are considered in relation to their interaction with GSH in the efficient delivery of Zn2+ to functional binding sites and in the operation of fluorescent zinc sensors as a tool to observe zinc trafficking.

Nutrition and Metabolism of Minerals in Fish

Simple Summary

Our aim is to introduce the mineral nutrition of fish and explain the complexity of determining requirements for these elements, which are absorbed and excreted by the fish into the surrounding water. To date, only the requirements for nine minerals have been investigated. The review is focused on the absorption and the dietary factors that reduce their absorption from feed ingredients of plant and animal origin. Some diseases, such as cataracts, anemia and bone deformity, have been linked to dietary deficiency of minerals.

Abstract

Aquatic animals have unique physiological mechanisms to absorb and retain minerals from their diets and water. Research and development in the area of mineral nutrition of farmed fish and crustaceans have been relatively slow and major gaps exist in the knowledge of trace element requirements, physiological functions and bioavailability from feed ingredients. Quantitative dietary requirements have been reported for three macroelements (calcium, phosphorus and magnesium) and six trace minerals (zinc, iron, copper, manganese, iodine and selenium) for selected fish species. Mineral deficiency signs in fish include reduced bone mineralization, anorexia, lens cataracts (zinc), skeletal deformities (phosphorus, magnesium, zinc), fin erosion (copper, zinc), nephrocalcinosis (magnesium deficiency, selenium toxicity), thyroid hyperplasia (iodine), muscular dystrophy (selenium) and hypochromic microcytic anemia (iron). An excessive intake of minerals from either diet or gill uptake causes toxicity and therefore a fine balance between mineral deficiency and toxicity is vital for aquatic organisms to maintain their homeostasis, either through increased absorption or excretion. Release of minerals from uneaten or undigested feed and from urinary excretion can cause eutrophication of natural waters, which requires additional consideration in feed formulation. The current knowledge in mineral nutrition of fish is briefly reviewed.

Increased expression of zinc transporter ZIP4, ZIP11, ZnT1, and ZnT6 predicts poor prognosis in pancreatic cancer

INTRODUCTION

Zinc homeostasis is regulated by SLC39A/ZIP, SLC30A/ZnT, and metallothionein (MT) families in human cells. Zinc dyshomeostasis may affect or be affected by the abnormal behavior of cancer cells. Although decreased serum zinc levels are observed in patients with pancreatic adenocarcinoma (PAAD), limited information is available regarding the expression pattern and prognostic roles of zinc homeostasis-related genes in PAAD.

OBJECTIVES

The primary objective of this study was to explore the expression pattern and prognostic roles of zinc homeostasis-related genes in PAAD.

METHODS

The expression pattern of 35 known zinc homeostasis-related genes in PAAD was systemically explored based on RNA-sequencing data from the Cancer Genome Atlas (TCGA) and the Genotype-Tissue Expression (GTEx) projects. The association between the expression levels of zinc homeostasis-related genes and survival of PAAD patients was evaluated using the Kaplan-Meier method and the log-rank test. Expressional correlation between zinc homeostasis-related genes with potential prognostic value in PAAD and normal pancreatic controls was evaluated using Pearson's correlation analysis. Functional enrichment analyses were performed to elucidate possible mechanisms for the potential prognostic and therapeutic roles of these zinc homeostasis-related genes in PAAD. Effects of ZIP11, ZnT1, or ZnT6 knockdown on the proliferation and the migration of Capan-1 pancreatic cancer cells were assessed by the CCK-8 assay and the wound healing assay respectively.

RESULTS

We demonstrated that the expression levels of ZIP1, ZIP3, ZIP4, ZIP6, ZIP7, ZIP9, ZIP10, ZIP11, ZIP13, ZnT1, ZnT5, ZnT6, ZnT7, and ZnT9 were increased, whereas the expression levels of ZIP5, ZIP14, ZnT2, MT1 G, MT1H, and MT1X were decreased in PAAD tumors compared with normal pancreatic controls. Among these differentially-expressed genes related to zinc homeostasis, higher expression of ZIP4, ZIP11, ZnT1 or ZnT6 predicted poorer prognosis with the possible involvement of several cancer-related processes and pathways in PAAD patients. We further demonstrated that knockdown of ZIP11 attenuated Capan-1 cell proliferation with decreased activation of ERK1/2 pathway; knockdown of ZnT1 attenuated Capan-1 cell proliferation with decreased activation of ERK1/2, p38 MAPK, NF-kB, and mTOR pathways; knockdown of ZnT6 attenuated Capan-1 cell proliferation with decreased activation of ERK1/2, p38 MAPK, and NF-kB pathways.

CONCLUSIONS

Higher expression of the zinc transporter ZIP4, ZIP11, ZnT1 or ZnT6 predicted poorer prognosis in patients with PAAD. These findings provide new clues for understanding the complex relationship between zinc homeostasis and pancreatic cancer.

ZIP8 exacerbates collagen-induced arthritis by increasing pathogenic T cell responses

Zinc is a trace element that is essential for immune responses. Therefore, changes in cellular zinc levels in specific immune cells may influence inflammatory autoimmune diseases, such as rheumatoid arthritis (RA). However, the regulation of zinc mobilization in immune cells and its role in the pathogenesis of RA are not fully understood. Thus, we investigated the roles of zinc transporters in RA pathogenesis. We demonstrated that ZIP8 was specifically upregulated in CD4+ T cells that infiltrated the inflamed joint and that ZIP8 deficiency in CD4+ T cells abrogated collagen-induced arthritis. ZIP8 deficiency dramatically affected zinc influx in effector T cells and profoundly reduced T cell receptor (TCR)-mediated signaling, including NF-κB and MAPK signaling, which are pathways that are involved in T helper (Th) 17 cell differentiation. Taken together, our findings suggest that ZIP8 depletion in CD4+ T cells attenuates TCR signaling due to insufficient cellular zinc, thereby reducing the function of effector CD4+ T cells, including Th17 cells. Our results also suggest that targeting ZIP8 may be a useful strategy to inhibit RA development and pathogenesis.

Neurometals in the Pathogenesis of Prion Diseases

Prion diseases are progressive and transmissive neurodegenerative diseases. The conformational conversion of normal cellular prion protein (PrP^C) into abnormal pathogenic prion protein (PrP^Sc) is critical for its infection and pathogenesis. PrP^C possesses the ability to bind to various neurometals, including copper, zinc, iron, and manganese. Moreover, increasing evidence suggests that PrP^C plays essential roles in the maintenance of homeostasis of these neurometals in the synapse. In addition, trace metals are critical determinants of the conformational change and toxicity of PrP^C. Here, we review our studies and other new findings that inform the current understanding of the links between trace elements and physiological functions of PrP^C and the neurotoxicity of PrP^Sc.

The response of zinc transporter gene expression of selected tissues in a pig model of subclinical zinc deficiency

This study compared the relative mRNA expression of all mammal zinc (Zn) transporter genes in selected tissues of weaned piglets challenged with short-term subclinical Zn deficiency (SZD). The dietary model involved restrictive feeding (450 g/animal*day^-1) of a high-phytate diet (9 g/kg) supplemented with varying amounts of zinc from ZnSO₄*7H₂O ranging from deficient to sufficient supply levels (total diet Zn: 28.1, 33.6, 38.8, 42.7, 47.5, 58.2, 67.8, 88.0 mg Zn/kg). Total RNA preparations comprised jejunal and colonic mucosa as well as hepatic and nephric tissue. Statistical modelling involved broken-line regression (P≤.05). ZIP10 and ZIP12 mRNAs were not detected in any tissue and ZnT3 mRNA was only identified in the kidney. All other genes were expressed in all tissues but only a few gene expression patterns allowed a significant (P<.0001) fitting of broken-line regression models, indicating homeostatic regulation under the present experimental conditions. Interestingly, these genes could be subcategorized by showing significant turnarounds in their response patterns, either at ~40 or ~60 mg Zn/kg diet (P<.0001). In conclusion, the present study showed clear differences in Zn transporter gene expression in response to SZD compared to the present literature on clinical models. We recognized that certain Zn transporter genes were regulated under the present experimental conditions by two distinct homeostatic networks. For the best of our knowledge, this represents the first comprehensive screening of Zn transporter gene expression in a highly translational model to human physiology.

The clinical characteristics, biochemical parameters and insulin response to oral glucose tolerance test (OGTT) in 25 transfusion dependent β-thalassemia (TDT) patients recently diagnosed with diabetes mellitus (DM)

BACKGROUND

Patients with transfusion dependent β-thalassemia (TDT) are at high risk for developing, over the time, a form of diabetes distinct from type 1 and type 2 diabetes, but with similarities to both.

AIMS OF STUDY

The aim of this study is to describe the clinical and laboratory data, and the insulin secretion and sensitivity, in TDT patients , recently diagnosed with diabetes mellitus (DM).

MATERIALS AND METHODS

The medical records of 25 TDT patients with DM, diagnosed by standardized oral glucose tolerance test (OGTT) and insulin secretion, were analysed; data were compared to TDT patients without diabetes and to a group of healthy subjects. Natural history of glucometabolic status before the diagnosis of DM was also reviewed.

RESULTS

On average, the TDT patients with DM were younger compared to TDT patients without diabetes. The mean age at diagnosis of  DM in female and male TDT patients was 24.0 ± 7.1 years and 31.9 ± 5.6 years, respectively (P: 0.007). Serum alanine aminotransferase values, basal insulin levels and prevalence of hypogonadism were consistently higher in TDT patients with DM compared to those without diabetes. Decreased insulin secretion and increased insulin resistance was observed in patients with DM.

CONCLUSION

The natural history of glucometabolic status in TDT patients is characterized by a deterioration of glucose tolerance over time. Iron overload and liver dysfuction are the main factors responsible for glucose disturbances (GD) in TDT patients. The therapeutic approach must be individualized and followed by a multidisciplinary team.

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.

The Role of Zinc in Male Fertility

Several studies proposed the importance of zinc ion in male fertility. Here, we describe the properties, roles and cellular mechanisms of action of Zn²⁺ in spermatozoa, focusing on its involvement in sperm motility, capacitation and acrosomal exocytosis, three functions that are crucial for successful fertilization. The impact of zinc supplementation on assisted fertilization techniques is also described. The impact of zinc on sperm motility has been investigated in many vertebrate and invertebrate species. It has been reported that Zn²⁺ in human seminal plasma decreases sperm motility and that Zn²⁺ removal enhances motility. Reduction in the intracellular concentration of Zn²⁺ during epididymal transit allows the development of progressive motility and the subsequent hyper activated motility during sperm capacitation. Extracellular Zn²⁺ affects intracellular signaling pathways through its interaction with the Zn²⁺ sensing receptor (ZnR), also named GPR39. This receptor was found in the sperm tail and the acrosome, suggesting the possible involvement of Zn²⁺ in sperm motility and acrosomal exocytosis. Our studies showed that Zn²⁺ stimulates bovine sperm acrosomal exocytosis, as well as human sperm hyper-activated motility, were both mediated by GPR39. Zn²⁺ binds and activates GPR39, which activates the trans-membrane-adenylyl-cyclase (tmAC) to catalyze cAMP production. The NHE (Na⁺/H⁺-exchanger) is activated by cAMP, leading in increased pHi and activation of the sperm-specific Ca²⁺ channel CatSper, resulting in an increase in [Ca²⁺]_i, which, together with HCO₃⁻, activates the soluble adenylyl-cyclase (sAC). The increase in [cAMP]_i activates protein kinase A (PKA), followed by activation of the Src-epidermal growth factor receptor-Pphospholipase C (Src-EGFR-PLC) cascade, resulting in inositol-triphosphate (IP₃) production, which mobilizes Ca²⁺ from the acrosome, causing a further increase in [Ca²⁺]_i and the development of hyper-activated motility. PKA also activates phospholipase D1 (PLD1), leading to F-actin formation during capacitation. Prior to the acrosomal exocytosis, PLC induces phosphadidylinositol-4,5-bisphosphate (PIP₂) hydrolysis, leading to the release of the actin-severing protein gelsolin to the cytosol, which is activated by Ca²⁺, resulting in F-actin breakdown and the occurrence of acrosomal exocytosis.

Androgens regulate follicle stage-dependent pro- and anti-apoptosis in teleost ovaries through ZIP9 activation of different G proteins†

Androgens mediate a number of processes in mammalian and teleost ovaries in a follicle-stage dependent manner, including follicle growth, survival, and apoptosis. We recently reported that the membrane androgen receptor ZIP9 mediates apoptosis in Atlantic croaker granulosa/theca (G/T) cells from mature ovarian follicles, but the effects of androgens on early stage G/T cells in this model remains unknown. Here we show that testosterone mediates pro- and anti-apoptotic responses in a follicle stage-dependent manner in croaker ovarian follicle cells. Testosterone treatment decreased the incidence of apoptosis in G/T cells from early stage follicles (diameter <300 μm) but increased apoptosis in G/T cells from late stage follicles (diameter >400 μm). Small interfering RNA targeting ZIP9, but not the nuclear androgen receptor, blocked the anti-apoptotic response, indicating ZIP9 mediates anti-apoptotic in addition to pro-apoptotic responses. Testosterone treatment of early stage G/T cells resulted in opposite signaling outcomes from those previously characterized for the ZIP9-mediated apoptotic response including decreased cAMP and intracellular free zinc levels, and downregulation of pro-apoptotic member mRNA expression. While ZIP9-mediated apoptosis involves activation of a stimulatory G protein (Gs), activators of Gs signaling antagonized the anti-apoptotic response. Proximity ligation and G protein activation assays indicated that in G/T cells from early stage follicles ZIP9 is in close proximity and activates an inhibitory G protein, while in G/T cells from late stage follicles ZIP9 is in close proximity and activates Gs. This study demonstrates that ZIP9 mediates opposite survival responses of croaker G/T cells by activating different G proteins in a follicle stage-dependent manner.

The Role of Fe, Zn, and Cu in Pregnancy

Iron (Fe), copper (Cu), and zinc (Zn) are microelements essential for the proper functioning of living organisms. These elements participatein many processes, including cellular metabolism and antioxidant and anti-inflammatory defenses, and also influence enzyme activity, regulate gene expression, and take part in protein synthesis. Fe, Cu, and Zn have a significant impact on the health of pregnant women and in the development of the fetus, as well as on the health of the newborn. A proper concentration of these elements in the body of women during pregnancy reduces the risk of complications such as anemia, induced hypertension, low birth weight, preeclampsia, and postnatal complications. The interactions between Fe, Cu, and Zn influence their availability due to their similar physicochemical properties. This most often occurs during intestinal absorption, where metal ions compete for binding sites with transport compounds. Additionally, the relationships between these ions have a great influence on the course of reactions in the tissues, as well as on their excretion, which can be stimulated or delayed. This review aims to summarize reports on the influence of Fe, Cu, and Zn on the course of single and multiple pregnancies, and to discuss the interdependencies and mechanisms occurring between Fe, Cu, and Zn.

Why and how to investigate the role of protein phosphorylation in ZIP and ZnT zinc transporter activity and regulation

Zinc is required for the regulation of proliferation, metabolism, and cell signaling. It is an intracellular second messenger, and the cellular level of ionic, mobile zinc is strictly controlled by zinc transporters. In mammals, zinc homeostasis is primarily regulated by ZIP and ZnT zinc transporters. The importance of these transporters is underscored by the list of diseases resulting from changes in transporter expression and activity. However, despite numerous structural studies of the transporters revealing both zinc binding sites and motifs important for transporter function, the exact molecular mechanisms regulating ZIP and ZnT activities are still not clear. For example, protein phosphorylation was found to regulate ZIP7 activity resulting in the release of Zn2+ from intracellular stores leading to phosphorylation of tyrosine kinases and activation of signaling pathways. In addition, sequence analyses predict all 24 human zinc transporters to be phosphorylated suggesting that protein phosphorylation is important for regulation of transporter function. This review describes how zinc transporters are implicated in a number of important human diseases. It summarizes the current knowledge regarding ZIP and ZnT transporter structures and points to how protein phosphorylation seems to be important for the regulation of zinc transporter activity. The review addresses the need to investigate the role of protein phosphorylation in zinc transporter function and regulation, and argues for a pressing need to introduce quantitative phosphoproteomics to specifically target zinc transporters and proteins involved in zinc signaling. Finally, different quantitative phosphoproteomic strategies are suggested.

Zinc Deficiency Activates the IL-23/Th17 Axis to Aggravate Experimental Colitis in Mice

BACKGROUND AND AIMS

Patients with inflammatory bowel disease [IBD], especially Crohn's disease, often develop zinc deficiency. However, the precise mechanisms by which zinc deficiency affects IBD pathology, particularly intestinal macrophage function, remain unclear. We studied the effects of zinc deficiency on the development and progression of colitis in mice.

METHODS

To induce colitis, mice were treated with 2,4,6-trinitrobenzene sulphonic acid. Rag1-/- mice were then given injections of naïve CD4+CD62L+ T cells. The respective degrees of mucosal injury of mice that had received a zinc chelator (TPEN; N,N,N',N'-tetrakis [2-pyridylmethyl]ethylenediamine) and of control mice were subsequently compared. Colonic lamina propria mononuclear cells were isolated by enzymatic digestion and were examined using flow cytometry. To generate mouse bone marrow-derived macrophages [BMDMs], bone marrow cells were stimulated with mouse macrophage-colony stimulating factor.

RESULTS

Zinc deficiency aggravates colonic inflammation through the activation of type 17 helper T [Th17] cells in mice. Flow cytometric analysis revealed that zinc deficiency significantly increases the proportion of pro-inflammatory [M1] macrophages in colonic lamina propria mononuclear cells obtained from inflamed colon. Interferon-γ plus lipopolysaccharide-mediated M1 skewing alters the expression of zinc transporters in BMDMs and thereby decreases the intracellular free zinc. TPEN treatment mimicking the effects of the M1 skewing up-regulates IL-23p19 expression, which is strongly related to Th17 development. Furthermore, the nuclear accumulation of interferon-regulatory factor 5 is closely involved in IL-23p19 induction in zinc-deficient macrophages.

CONCLUSIONS

Zinc deficiency aggravates colonic inflammation through activation of the IL-23/Th17 axis. This activation is controlled by subcellular distribution of interferon-regulatory factor 5.

Structure/Function Analysis of human ZnT8 (SLC30A8): A Diabetes Risk Factor and Zinc Transporter

The human zinc transporter ZnT8 (SLC30A8) is expressed primarily in pancreatic β-cells and plays a key function in maintaining the concentration of blood glucose through its role in insulin storage, maturation and secretion. ZnT8 is an autoantigen for Type 1 diabetes (T1D) and is associated with Type 2 diabetes (T2D) through its risk allele that encodes a major non-synonymous single nucleotide polymorphism (SNP) at Arg325. Loss of function mutations improve insulin secretion and are protective against diabetes. Despite its role in diabetes and concomitant potential as a drug target, little is known about the structure or mechanism of ZnT8. To this end, we expressed ZnT8 in Pichia pastoris yeast and Sf9 insect cells. Guided by a rational screen of 96 detergents, we developed a method to solubilize and purify recombinant ZnT8. An in vivo transport assay in Pichia and a liposome-based uptake assay for insect-cell derived ZnT8 showed that the protein is functionally active in both systems. No significant difference in activity was observed between full-length ZnT8 (ZnT8A) and the amino-terminally truncated ZnT8B isoform. A fluorescence-based in vitro transport assay using proteoliposomes indicated that human ZnT8 functions as a Zn2+/H+ antiporter. We also purified E. coli-expressed amino- and carboxy-terminal cytoplasmic domains of ZnT8A. Circular dichroism spectrometry suggested that the amino-terminal domain contains predominantly α-helical structure, and indicated that the carboxy-terminal domain has a mixed α/β structure. Negative-stain electron microscopy and single-particle image analysis yielded a density map of ZnT8B at 20 Å resolution, which revealed that ZnT8 forms a dimer in detergent micelles. Two prominent lobes are ascribed to the transmembrane domains, and the molecular envelope recapitulates that of the bacterial zinc transporter YiiP. These results provide a foundation for higher resolution structural studies and screening experiments to identify compounds that modulate ZnT8 activity.

Molecular characterization of ten zinc (Zn) transporter genes and their regulation to Zn metabolism in freshwater teleost yellow catfish Pelteobagrus fulvidraco

BACKGROUND

Zn is an essential trace element for vertebrates, and Zn uptake and transport is related with the ZIP family of Zn transporters. Meantime, Zn also influenced the expression of ZIP family members.

METHODS

We cloned and characterized the full-length cDNA sequences of ten Zn transport-relevant genes (ZIP1, ZIP3, ZIP6, ZIP7, ZIP8, ZIP9, ZIP10, ZIP11, ZIP13 and ZIP14) from yellow catfish Pelteobagrus fulvidraco, investigated their mRNA tissue expression. These ZIP mRNA expression was also assessed in the primary hepatocytes and intestinal epithelial cells of yellow catfish in response to three Zn levels (0, 30 μM and 60 μM, respectively).

RESULTS

All these genes shared the similar domains with the corresponding members in mammals. The mRNA expression of the ten ZIP genes was detected in nine-tested tissues, but variable among these tissues. Flow cytometry analysis and confocal microscopy observation indicated that intracellular free Zn²⁺ concentration in hepatocytes and intestinal epithelial cells increased with increasing Zn incubation concentration at both 24 h and 48 h. Zn incubation differentially influenced mRNA levels of ZIP transporters in the hepatocytes and intestinal epithelial cells, in a time- and cells-dependent manners. In the hepatocytes, at 24 h, compared to the control, Zn addition down-regulated mRNA levels of ZIP1, ZIP3, ZIP6, ZIP7, ZIP8, ZIP9, ZIP11 and ZIP14; however, ZIP10 mRNA levels were lower in 60 μM Zn group than those in the control and 30 μM Zn group. At 48 h, mRNA levels of ZIP1, ZIP6, ZIP7, ZIP9, ZIP10 and ZIP14 declined with increasing Zn incubation concentrations; ZIP3 mRNA levels were the lowest in 60 μM Zn group and showed no significant differences between the control and 30 μM Zn group. In the intestinal epithelial cells, at 24 h, Zn addition down-regulated mRNA levels of ZIP1, ZIP6, ZIP7, ZIP8, ZIP9, ZIP10, ZIP11, ZIP13 and ZIP14; ZIP3 mRNA levels were lower in 60 μM Zn group than those in the control and 30 μM Zn group. At 48 h, Zn addition up-regulated mRNA levels of ZIP6 and ZIP9, but down-regulated mRNA levels of ZIP8, ZIP10 and ZIP13. ZIP7, ZIP11 and ZIP14 mRNA abundances were the lowest in 60 μM Zn group and showed no significant differences between the control and 30 μM Zn group.

CONCLUSION

For the first time, our study characterized ten ZIP family members in yellow catfish, explored their mRNA tissue expression. Their regulation to Zn addition were also investigated in the hepatocytes and intestinal epithelial cells of yellow catfish. Our study revealed the mechanism of cells exposed to Zn addition and provided novel insights for the regulatory mechanism of Zn homeostasis.

Amyloids: Regulators of Metal Homeostasis in the Synapse

Conformational changes in amyloidogenic proteins, such as β-amyloid protein, prion proteins, and α-synuclein, play a critical role in the pathogenesis of numerous neurodegenerative diseases, including Alzheimer’s disease, prion disease, and Lewy body disease. The disease-associated proteins possess several common characteristics, including the ability to form amyloid oligomers with β-pleated sheet structure, as well as cytotoxicity, although they differ in amino acid sequence. Interestingly, these amyloidogenic proteins all possess the ability to bind trace metals, can regulate metal homeostasis, and are co-localized at the synapse, where metals are abundantly present. In this review, we discuss the physiological roles of these amyloidogenic proteins in metal homeostasis, and we propose hypothetical models of their pathogenetic role in the neurodegenerative process as the loss of normal metal regulatory functions of amyloidogenic proteins. Notably, these amyloidogenic proteins have the capacity to form Ca²⁺-permeable pores in membranes, suggestive of a toxic gain of function. Therefore, we focus on their potential role in the disruption of Ca²⁺ homeostasis in amyloid-associated neurodegenerative diseases.

A Guide to Human Zinc Absorption: General Overview and Recent Advances of In Vitro Intestinal Models

Zinc absorption in the small intestine is one of the main mechanisms regulating the systemic homeostasis of this essential trace element. This review summarizes the key aspects of human zinc homeostasis and distribution. In particular, current knowledge on human intestinal zinc absorption and the influence of diet-derived factors on bioaccessibility and bioavailability as well as intrinsic luminal and basolateral factors with an impact on zinc uptake are discussed. Their investigation is increasingly performed using in vitro cellular intestinal models, which are continually being refined and keep gaining importance for studying zinc uptake and transport via the human intestinal epithelium. The vast majority of these models is based on the human intestinal cell line Caco-2 in combination with other relevant components of the intestinal epithelium, such as mucin-secreting goblet cells and in vitro digestion models, and applying improved compositions of apical and basolateral media to mimic the in vivo situation as closely as possible. Particular emphasis is placed on summarizing previous applications as well as key results of these models, comparing their results to data obtained in humans, and discussing their advantages and limitations.

C-Terminal Domain of the Human Zinc Transporter hZnT8 Is Structurally Indistinguishable from Its Disease Risk Variant (R325W)

The human zinc transporter 8 (hZnT8) plays important roles in the storage of insulin in the secretory vesicles of pancreatic β cells. hZnT8 consists of a transmembrane domain, with its N- and C-termini protruding into the cytoplasm. Interestingly, the exchange of arginine to tryptophan at position 325 in the C-terminal domain (CTD) increases the risk of developing type 2 diabetes mellitus (T2D). In the present study, the CTDs of hZnT8 (the wild-type (WT) and its disease risk variant (R325W)) were expressed, purified, and characterized in their native forms by biophysical techniques. The data reveal that the CTDs form tetramers which are stabilized by zinc binding, and exhibit negligible differences in their secondary structure content and zinc-binding affinities in solution. These findings provide the basis for conducting further structural studies aimed at unravelling the molecular mechanism underlying the increased susceptibility to develop T2D, which is modulated by the disease risk variant.

Zinc dysregulation in cancers and its potential as a therapeutic target

Zinc is an essential element and serves as a structural or catalytic component in many proteins. Two families of transporters are involved in maintaining cellular zinc homeostasis: the ZIP (SLC39A) family that facilitates zinc influx into the cytoplasm, and the ZnT (SLC30A) family that facilitates zinc efflux from the cytoplasm. Zinc dyshomeostasis caused by the dysfunction of zinc transporters can contribute to the initiation or progression of various cancers, including prostate cancer, breast cancer, and pancreatic cancer. In addition, intracellular zinc fluctuations lead to the disturbance of certain signaling pathways involved in the malignant properties of cancer cells. This review briefly summarizes our current understanding of zinc dyshomeostasis in cancer, and discusses the potential roles of zinc or zinc transporters in cancer therapy.

Age-Dependent Modification of Intracellular Zn2+ Buffering in the Hippocampus and Its Impact

The basal concentrations of extracellular Zn²⁺ and intracellular Zn²⁺, which are approximately 10 nM and 100 pM, respectively, in the brain, are markedly lower than those of extracellular Ca²⁺ (1.3 mM) and intracellular Ca²⁺ (100 nM), respectively, resulting in much less attention paid to Zn²⁺ than to Ca²⁺. However, intracellular Zn²⁺ dysregulation, which is closely linked with glutamate- and amyloid β-mediated extracellular Zn²⁺ influx, is more critical for cognitive decline and neurodegeneration than intracellular Ca²⁺ dysregulation. It is estimated that the age-dependent increase in the basal concentration of extracellular Zn²⁺ in the hippocampus plays a key role in cognitive decline and neurodegeneration. The characteristics of extracellular Zn²⁺ influx in the hippocampus may be modified age-dependently, probably followed by modification of intracellular Zn²⁺ buffering that is closely linked with age-related cognitive decline and neurodegeneration. Reduction of intracellular Zn²⁺-buffering capacity may be linked with the pathophysiology of progressive neurodegeneration such as Alzheimer's disease. This paper deals with age-dependent modification of intracellular Zn²⁺ buffering in the hippocampus and its impact. On the basis of the estimated impact, we propose a potential defense strategy against Zn²⁺-mediated neurodegeneration, i.e., metallothionein induction in the hippocampus.

Metalloimmunology: The metal ion-controlled immunity

Metals are essential components in all forms of life required for the function of nearly half of all enzymes and are critically involved in virtually all fundamental biological processes. Especially, the transition metals iron (Fe), zinc (Zn), manganese (Mn), nickel (Ni), copper (Cu) and cobalt (Co) are crucial micronutrients known to play vital roles in metabolism as well due to their unique redox properties. Metals carry out three major functions within metalloproteins: to provide structural support, to serve as enzymatic cofactors, and to mediate electron transportation. Metal ions are also involved in the immune system from metal allergies to nutritional immunity. Within the past decade, much attention has been drawn to the roles of metal ions in the immune system, since increasing evidence has mounted to suggest that metals are critically implicated in regulating both the innate immune sensing of and the host defense against invading pathogens. The importance of ions in immunity is also evidenced by the identification of various immunodeficiencies in patients with mutations in ion channels and transporters. In addition, cancer immunotherapy has recently been conclusively demonstrated to be effective and important for future tumor treatment, although only a small percentage of cancer patients respond to immunotherapy because of inadequate immune activation. Importantly, metal ion-activated immunotherapy is becoming an effective and potential way in tumor therapy for better clinical application. Nevertheless, we are still in a primary stage of discovering the diverse immunological functions of ions and mechanistically understanding the roles of these ions in immune regulation. This review summarizes recent advances in the understanding of metal-controlled immunity. Particular emphasis is put on the mechanisms of innate immune stimulation and T cell activation by the essential metal ions like calcium (Ca²⁺), zinc (Zn²⁺), manganese (Mn²⁺), iron (Fe²⁺/Fe³⁺), and potassium (K⁺), followed by a few unessential metals, in order to draw a general diagram of metalloimmunology.