Requirement of zinc transporter ZIP10 for epidermal development: Implication of the ZIP10-p63 axis in epithelial homeostasis

ZIP transporters-regulated Zn2+ homeostasis: A novel determinant of human diseases

As an essential trace element for organisms, zinc participates in various physiological processes, such as RNA transcription, DNA replication, cell proliferation, and cell differentiation. The destruction of zinc homeostasis is associated with various diseases. Zinc homeostasis is controlled by the cooperative action of zinc transporter proteins that are responsible for the influx and efflux of zinc. Zinc transporter proteins are mainly categorized into two families: Zrt/Irt-like protein (SLC39A/ZIP) family and zinc transporter (SLC30A/ZNT) family. ZIP transporters contain 14 members, namely ZIP1-14, which can be further divided into four subfamilies. Currently, ZIP transporters-regulated zinc homeostasis is one of the research hotspots. Cumulative evidence suggests that ZIP transporters-regulated zinc homeostasis may cause physiological dysfunction and contribute to the onset and progression of diverse diseases, such as cancers, neurological diseases, and cardiovascular diseases. In this review, we initially discuss the structure and distribution of ZIP transporters. Furthermore, we comprehensively review the latest research progress of ZIP transporters-regulated zinc homeostasis in diseases, providing a new perspective into new therapeutic targets for treating related diseases.

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.

Structural mechanism of intracellular autoregulation of zinc uptake in ZIP transporters

Zinc is an essential micronutrient that supports all living organisms through regulating numerous biological processes. However, the mechanism of uptake regulation by intracellular Zn2+ status remains unclear. Here we report a cryo-electron microscopy structure of a ZIP-family transporter from Bordetella bronchiseptica at 3.05 Å resolution in an inward-facing, inhibited conformation. The transporter forms a homodimer, each protomer containing nine transmembrane helices and three metal ions. Two metal ions form a binuclear pore structure, and the third ion is located at an egress site facing the cytoplasm. The egress site is covered by a loop, and two histidine residues on the loop interact with the egress-site ion and regulate its release. Cell-based Zn2+ uptake and cell growth viability assays reveal a negative regulation of Zn2+ uptake through sensing intracellular Zn2+ status using a built-in sensor. These structural and biochemical analyses provide mechanistic insight into the autoregulation of zinc uptake across membranes.

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.

Fear-of-intimacy-mediated zinc transport is required for Drosophila fat body endoreplication

BACKGROUND

Endoreplication is involved in the development and function of many organs, the pathologic process of several diseases. However, the metabolic underpinnings and regulation of endoreplication have yet to be well clarified.

RESULTS

Here, we showed that a zinc transporter fear-of-intimacy (foi) is necessary for Drosophila fat body endoreplication. foi knockdown in the fat body led to fat body cell nuclei failure to attain standard size, decreased fat body size and pupal lethality. These phenotypes could be modulated by either altered expression of genes involved in zinc metabolism or intervention of dietary zinc levels. Further studies indicated that the intracellular depletion of zinc caused by foi knockdown results in oxidative stress, which activates the ROS-JNK signaling pathway, and then inhibits the expression of Myc, which is required for tissue endoreplication and larval growth in Drosophila.

CONCLUSIONS

Our results indicated that FOI is critical in coordinating fat body endoreplication and larval growth in Drosophila. Our study provides a novel insight into the relationship between zinc and endoreplication in insects and may provide a reference for relevant mammalian studies.

Relationships between the Content of Micro- and Macroelements in Animal Samples and Diseases of Different Etiologies

Many of the micro- and macro-elements (MMEs) required by the body are found in environmental objects in concentrations different from their original concentration that can lead to dangerous animal diseases ("microelementoses"). The aim was to study the features of MME (accumulating in wild and exotic animals) in connection with particular diseases. The work using 67 mammal species from four Russian zoological institutions was completed in 2022. Studies of 820 cleaned and defatted samples (hair, fur, etc.) after "wet-acid-ashing" on an electric stove and in a muffle furnace were performed using a Kvant-2A atomic absorption spectrometer. The content of zinc, copper, iron, cadmium, lead, and arsenic was assessed. The level of MME accumulation in the animal body contributes not only to the MME status and the development of various concomitant diseases, but the condition itself can occur by intake of a number of micronutrients and/or drugs. Particular correlations between the accumulation of Zn and skin, oncological diseases, Cu-musculoskeletal, cardiovascular diseases, Fe-oncological diseases, Pb-metabolic, nervous, oncological diseases, and Cd-cardiovascular diseases were established. Therefore, monitoring of the MME status of the organism must be carried out regularly (optimally once every 6 months).

Uterine epithelial Gp130 orchestrates hormone response and epithelial remodeling for successful embryo attachment in mice

Leukemia inhibitory factor (LIF) receptor, an interleukin 6 cytokine family signal transducer (Il6st, also known as Gp130) that is expressed in the uterine epithelium and stroma, has been recognized to play an essential role in embryo implantation. However, the molecular mechanism underlying Gp130-mediated LIF signaling in the uterine epithelium during embryo implantation has not been elucidated. In this study, we generated mice with uterine epithelium specific deletion of Gp130 (Gp130 ecKO). Gp130 ecKO females were infertile due to the failure of embryo attachment and decidualization. Histomorphological observation revealed that the endometrial shape and embryo position from Gp130 ecKO were comparable to those of the control, and uterine epithelial cell proliferation, whose attenuation is essential for embryo implantation, was controlled in Gp130 ecKO. Comprehensive gene expression analysis using RNA-seq indicates that epithelial Gp130 regulates the expression of estrogen- and progesterone-responsive genes in conjunction with immune response during embryo implantation. We also found that an epithelial remodeling factor, snail family transcriptional repressor 1 (Snai1), was markedly reduced in the pre-implantation uterus from Gp130 ecKO. These results suggest that not only the suppression of uterine epithelial cell proliferation, but also Gp130-mediated epithelial remodeling is required for successful implantation in mice.

Zinc and Zinc Transporters in Dermatology

Zinc is an important trace mineral in the human body and a daily intake of zinc is required to maintain a healthy status. Over the past decades, zinc has been used in formulating topical and systemic therapies for various skin disorders owing to its wound healing and antimicrobial properties. Zinc transporters play a major role in maintaining the integrity of the integumentary system by controlling zinc homeostasis within dermal layers. Mutations and abnormal function of zinc-transporting proteins can lead to disease development, such as spondylocheirodysplastic Ehlers-Danlos syndrome (SCD-EDS) and acrodermatitis enteropathica (AE) which can be fatal if left untreated. This review discusses the layers of the skin, the importance of zinc and zinc transporters in each layer, and the various skin disorders caused by zinc deficiency, in addition to zinc-containing compounds used for treating different skin disorders and skin protection.

Role of Scl39a13/ZIP13 in cardiovascular homeostasis

Zinc plays a critical role in many physiological processes, and disruption of zinc homeostasis induces various disorders, such as growth retardation, osteopenia, immune deficiency, and inflammation. However, how the imbalance in zinc homeostasis leads to heart disease is not yet fully understood. Cardiovascular diseases are a major cause of death worldwide, and the development of novel therapeutic targets to treat it is urgently needed. We report that a zinc transporter, ZIP13, regulates cardiovascular homeostasis. We found that the expression level of Zip13 mRNA was diminished in both primary neonatal cardiomyocytes and mouse heart tissues treated with the cardiotoxic agent doxycycline. Primary neonatal cardiomyocytes from Zip13 gene-knockout (KO) mice exhibited abnormal irregular arrhythmic beating. RNA-seq analysis identified 606 differentially expressed genes in Zip13-KO mouse-derived primary neonatal cardiomyocytes and Gene ontology (GO) analysis revealed that both inflammation- and cell adhesion-related genes were significantly enriched. In addition, telemetry echocardiography analysis suggested that arrhythmias were likely to occur in Zip13-KO mice, in which elevated levels of the cardiac fibrosis marker Col1a1, vascular inflammation-related gene eNOS, and Golgi-related molecule GM130 were observed. These results indicate the physiological importance of ZIP13-it maintains cardiovascular homeostasis by resolving inflammation and stress response. Our findings suggest that optimizing ZIP13 expression and/or function may improve cardiovascular disease management.

Zinc transporters as potential therapeutic targets: An updated review

Zinc is an essential trace element that plays important roles in the regulation of various physiological responses in the body. Zinc deficiency is known to cause various health problems, including dysgeusia, skin disorders, and immune disorders. Therefore, the maintenance of healthy zinc content in the body is critical to our healthy life. Zinc homeostasis is tightly controlled by two of the solute carrier protein families SLC30A and SLC39A, called zinc transporters. In the last decade, research on zinc biology has made dramatic progress based on the physiological and functional analysis of zinc transporters in the fields of molecular biology, human genetics, and drug discovery. In particular, since the association between zinc transporters and human diseases was recently reported using human genetics and gene knockout mouse studies, zinc and zinc signals controlled by zinc transporters have been considered useful therapeutic targets. In this review, we introduce the importance of zinc homeostasis based on the findings of zinc transporter functions and their signals in relation to human diseases.

LGR6 promotes glioblastoma malignancy and chemoresistance by activating the Akt signaling pathway

Chemoresistance is the primary cause of the poor outcome of glioblastoma multiforme (GBM) therapy. Leucine-rich repeat-containing G-protein coupled receptor 6 (LGR6) is involved in the growth and proliferation of several types of cancer, including gastric cancer and ovarian cancer. Therefore, the aim of the present study was to investigate the role of LGR6 in GBM malignancy and chemoresistance. Cell counting kit-8 and Matrigel®-Transwell assays were conducted to assess GBM cell viability and invasion. The effect of LGR6 on cell cycle progression and activation of Akt signaling was analyzed by performing propidium iodide staining and western blotting, respectively. The results demonstrated that LGR6, a microRNA-1236-3p target candidate, promoted GBM cell viability and invasion, and mediated temozolomide sensitivity in SHG-44 and U251 GBM cells. In addition, LGR6 triggered the activation of the Akt signaling pathway during GBM progression. Collectively, the results of the present study suggested that LGR6 promoted GBM malignancy and chemoresistance, at least in part, by activating the Akt signaling pathway. The results may aid with the identification of a novel therapeutic target and strategy for GBM.

The IDIP framework for assessing protein function and its application to the prion protein

The quest to determine the function of a protein can represent a profound challenge. Although this task is the mandate of countless research groups, a general framework for how it can be approached is conspicuously lacking. Moreover, even expectations for when the function of a protein can be considered to be 'known' are not well defined. In this review, we begin by introducing concepts pertinent to the challenge of protein function assignments. We then propose a framework for inferring a protein's function from four data categories: 'inheritance', 'distribution', 'interactions' and 'phenotypes' (IDIP). We document that the functions of proteins emerge at the intersection of inferences drawn from these data categories and emphasise the benefit of considering them in an evolutionary context. We then apply this approach to the cellular prion protein (PrP^C ), well known for its central role in prion diseases, whose function continues to be considered elusive by many investigators. We document that available data converge on the conclusion that the function of the prion protein is to control a critical post-translational modification of the neural cell adhesion molecule in the context of epithelial-to-mesenchymal transition and related plasticity programmes. Finally, we argue that this proposed function of PrP^C has already passed the test of time and is concordant with the IDIP framework in a way that other functions considered for this protein fail to achieve. We anticipate that the IDIP framework and the concepts analysed herein will aid the investigation of other proteins whose primary functional assignments have thus far been intractable.

Zinc in Dog Nutrition, Health and Disease: A Review

Simple Summary

This work compiles the current state of knowledge regarding zinc requirements of healthy dogs and biomarkers of zinc status. To ensure an adequate zinc status, it is important to know the zinc content of foods and their bioavailability to assess the need and the ideal supplementation strategy regarding levels and sources of additives in complete dog foods. As zinc is required for enzymatic, structural, and regulatory functions in the animal body, its nutritional status has been associated with several pathologies that may be due to, or exacerbated by, a deficit of dietary zinc supply.

Abstract

Zinc is an essential trace element, required for enzymatic, structural, and regulatory functions. As body reserves are scarce, an adequate zinc status relies on proper dietary supply and efficient homeostasis. Several biomarkers have been proposed that enable the detection of poor zinc status, but more sensitive and specific ones are needed to detect marginal deficiencies. The zinc content of commercial dry dog foods has great variability, with a more frequent non-compliance with the maximum authorized limit than with the nutritional requirement. The bioavailability of dietary zinc also plays a crucial role in ensuring an adequate zinc status. Despite controversial results, organic zinc sources have been considered more bioavailable than inorganic sources, albeit the zinc source effect is more evident after a restriction period of dietary zinc. Many disorders have been associated with inadequate zinc status, not being clear whether the occurrence of the disease is the consequence or the cause. This review presents data on zinc requirements and biomarkers for zinc status, that can be applied for the development of supplementation strategies of zinc in complete pet foods. Moreover, it provides an understanding of the role zinc plays in the health of dogs, and how altered zinc status affects diseases in dogs.

Role of intracellular zinc in molecular and cellular function in allergic inflammatory diseases

Zinc is an essential micronutrient in human body and a vital cofactor for the function of numerous proteins encoded by the human genome. Zinc has a critical role in maintaining many biochemical and physiological processes at the molecular, cellular, and multiple organ and systemic levels. The alteration of zinc homeostasis causes dysfunction of many organs and systems. In the immune system, zinc regulates the differentiation, proliferation and function of inflammatory cells, including T cells, eosinophils, and B cells, by modifying several signaling pathways such as NFκB signaling pathways and TCR signals. An adequate zinc level is essential for proper immune responses and decreased zinc levels were reported in many allergic inflammatory diseases, including atopic dermatitis, bronchial asthma, and chronic rhinosinusitis. Decreased zinc levels often enhance inflammatory activation. On the other hand, the inflammatory conditions alter the intracellular homeostasis of zinc, often decreasing zinc levels. These findings implied that there could be a vicious cycle between zinc deficiency and inflammatory conditions. In this review, we present recent evidence on the involvement of zinc in atopic dermatitis, bronchial asthma, and chronic rhinosinusitis, with insights into the involvement of zinc in the underlying molecular and cellular mechanisms related to these allergic inflammatory diseases.

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.

Zinc deficiency induces abnormal development of the myocardium by promoting SENP5 overexpression

Gestational zinc deficiency is a cause of congenital heart disease in the fetus, and sentrin/small ubiquitin-like modifier (SUMO)-specific proteases (SENPs) as deSUMOylation enzymes play a crucial role in the development of cardiac structures. However, current studies of the regulation and function of SENP in zinc-deficient status during heart development remain limited. In this study, SUMO1 modification was found to gradually decrease during heart development, and the level of SENP5 exhibited a similar trend to SUMO1 conjugation. In addition, zinc deficiency resulted in cardiac dysplasia, increased cell apoptosis, decreased cell viability, and differentiation inhibition of hiPSC-CMs. In order to investigate the function of SENP5 in zinc deficiency, hiPSC-CMs were transfected with SENP5 small interfering RNA. The negative effects of zinc lacking conditions were reversed with depletion of SENP5. It was confirmed that zinc deficiency induced abnormal differentiation of hiPSCs and increased apoptosis of hiPSC-CMs by promoting SENP5 overexpression, which led to cardiac dysplasia. Thus, it was concluded that SENP5 regulates the SUMO1 deconjugation during heart development and zinc deficiency may reduce conjugated SUMO by promoting SENP5 overexpression, which induces abnormal development of the myocardium.

The Role of Genetics, the Environment, and Epigenetics in Atopic Dermatitis

Atopic Dermatitis (AD) is a common inflammatory disease with a genetic background. The prevalence of AD has been increasing in many countries. AD patients often have manifestations of pruritus, generalized skin dryness, and eczematous lesions. The pathogenesis of AD is complicated. The impaired skin barrier and immune imbalance play significant roles in the development of AD. Environmental factors such as allergens and pollutants are associated with the increasing prevalence. Many genetic and environmental factors induce a skin barrier deficiency, and this can lead to immune imbalance, which exacerbates the impaired skin barrier to form a vicious cycle (outside-inside-outside view). Genetic studies find many gene mutations and genetic variants, such as filaggrin mutations, which may directly induce the deficiency of the skin barrier and immune system. Epigenetic studies provide a connection between the relationship of an impaired skin barrier and immune and environmental factors, such as tobacco exposure, pollutants, microbes, and diet and nutrients. AD is a multigene disease, and thus there are many targets for regulation of expression of these genes which may contribute to the pathogenesis of AD. However, the epigenetic regulation of environmental factors in AD pathogenesis still needs to be further researched.

Zinc and Its Transporters in Epigenetics

Epigenetic events like DNA methylation and histone modification can alter heritable phenotypes. Zinc is required for the activity of various epigenetic enzymes, such as DNA methyltransferases (DNMTs), histone acetyltransferases (HATs), histone deacetylases (HDACs), and histone demethylases, which possess several zinc binding sites. Thus, the dysregulation of zinc homeostasis can lead to epigenetic alterations. Zinc homeostasis is regulated by Zinc Transporters (ZnTs), Zrt- and Irt-like proteins (ZIPs), and the zinc storage protein metallothionein (MT). Recent advances revealed that ZIPs modulate epigenetics. ZIP10 deficiency was found to result in reduced HATs, confirming its involvement in histone acetylation for rigid skin barrier formation. ZIP13 deficiency, which is associated with Spondylocheirodysplastic Ehlers-Danlos syndrome (SCD-EDS), increases DNMT activity, leading to dysgenesis of dermis via improper gene expressions. However, the precise molecular mechanisms remain to be elucidated. Future molecular studies investigating the involvement of zinc and its transporters in epigenetics are warranted.

FIH-1 engages novel binding partners to positively influence epithelial proliferation via p63

Whereas much is known about the genes regulated by ΔNp63α in keratinocytes, how ΔNp63α is regulated is less clear. During studies with the hydroxylase, factor inhibiting hypoxia-inducible factor 1 (FIH-1), we observed increases in epidermal ΔNp63α expression along with proliferative capacity in a conditional FIH-1 transgenic mouse. Conversely, loss of FIH-1 in vivo and in vitro attenuated ΔNp63α expression. To elucidate the FIH-1/p63 relationship, BioID proteomics assays identified FIH-1 binding partners that had the potential to regulate p63 expression. FIH-1 interacts with two previously unknown partners, Plectin1 and signal transducer and activator of transcription 1 (STAT1) leading to the regulation of ΔNp63α expression. Two known interactors of FIH-1, apoptosis-stimulating of P53 protein 2 (ASPP2) and histone deacetylase 1 (HDAC1), were also identified. Knockdown of ASPP2 upregulated ΔNp63α and reversed the decrease in ΔNp63α by FIH-1 depletion. Additionally, FIH-1 regulates growth arrest and DNA damage-45 alpha (GADD45α), a negative regulator of ΔNp63α by interacting with HDAC1. GADD45α knockdown rescued reduction in ΔNp63α by FIH-1 depletion. Collectively, our data reveal that FIH-1 positively regulates ΔNp63α in keratinocytes via variety of signaling partners: (a) Plectin1/STAT1, (b) ASPP2, and (c) HDAC1/GADD45α signaling pathways.

Loss of the dermis zinc transporter ZIP13 promotes the mildness of fibrosarcoma by inhibiting autophagy

Fibrosarcoma is a skin tumor that is frequently observed in humans, dogs, and cats. Despite unsightly appearance, studies on fibrosarcoma have not significantly progressed, due to a relatively mild tumor severity and a lower incidence than that of other epithelial tumors. Here, we focused on the role of a recently-found dermis zinc transporter, ZIP13, in fibrosarcoma progression. We generated two transformed cell lines from wild-type and ZIP13-KO mice-derived dermal fibroblasts by stably expressing the Simian Virus (SV) 40-T antigen. The ZIP13^−/− cell line exhibited an impairment in autophagy, followed by hypersensitivity to nutrient deficiency. The autophagy impairment in the ZIP13^−/− cell line was due to the low expression of LC3 gene and protein, and was restored by the DNA demethylating agent, 5-aza-2’-deoxycytidine (5-aza) treatment. Moreover, the DNA methyltransferase activity was significantly increased in the ZIP13^−/− cell line, indicating the disturbance of epigenetic regulations. Autophagy inhibitors effectively inhibited the growth of fibrosarcoma with relatively minor damages to normal cells in xenograft assay. Our data show that proper control over autophagy and zinc homeostasis could allow for the development of a new therapeutic strategy to treat fibrosarcoma.

Maintenance of Intestinal Epithelial Homeostasis by Zinc Transporters

Zinc is an essential micronutrient for normal organ function, and dysregulation of zinc metabolism has been implicated in a wide range of diseases. Emerging evidence has revealed that zinc transporters play diverse roles in cellular homeostasis and function by regulating zinc trafficking via organelles or the plasma membrane. In the gastrointestinal tract, zinc deficiency leads to diarrhea and dysfunction of intestinal epithelial cells. Studies also showed that zinc transporters are very important in intestinal epithelial homeostasis. In this review, we describe the physiological roles of zinc transporters in intestinal epithelial functions and relevance of zinc transporters in gastrointestinal diseases.

Different Actions of Intracellular Zinc Transporters ZIP7 and ZIP13 Are Essential for Dermal Development

Two mesenchymal zinc transporters, ZIP7 and ZIP13, play critical roles in dermal development. ZIP7 and ZIP13 are the closest among the conserved mammalian zinc transporters. However, whether their functions are complementary remains a controversial issue. In the present study, we found that the expression of ZIP13, but not ZIP7, is elevated by transforming growth factor beta (TGF-β) treatment, indicating that TGF-β-mediated ZIP13 amplification is crucial for collagen production during dermal development. Genome-wide gene expression analysis revealed that ~26% of genes are dependent on either ZIP7 or ZIP13, which is greater than the ~17% of genes dependent on both of them. ZIP7 depletion induces endoplasmic reticulum (ER) stress in mesenchymal stem cells, resulting in significant inhibition of fibrogenic differentiation. However, ZIP13 depletion does not induce ER stress. Though both ZIP7 and ZIP13 contain traditional ER signal peptides for their intracellular localization, their distributions are distinct. When ZIP7 and ZIP13 are coexpressed, their localizations are distinct; ZIP7 is located on the ER, but ZIP13 is located on both the ER and Golgi, indicating that only ZIP13 is a zinc gatekeeper on the Golgi. Our data illustrate that the different actions of ZIP7 and ZIP13 are crucial for dermal development.

A Brief Overview from the Physiological and Detrimental Roles of Zinc Homeostasis via Zinc Transporters in the Heart

Zinc (mostly as free/labile Zn²⁺) is an essential structural constituent of many proteins, including enzymes in cellular signaling pathways via functioning as an important signaling molecule in mammalian cells. In cardiomyocytes at resting condition, intracellular labile Zn²⁺ concentration ([Zn²⁺]_i) is in the nanomolar range, whereas it can increase dramatically under pathological conditions, including hyperglycemia, but the mechanisms that affect its subcellular redistribution is not clear. Therefore, overall, very little is known about the precise mechanisms controlling the intracellular distribution of labile Zn²⁺, particularly via Zn²⁺ transporters during cardiac function under both physiological and pathophysiological conditions. Literature data demonstrated that [Zn²⁺]_i homeostasis in mammalian cells is primarily coordinated by Zn²⁺ transporters classified as ZnTs (SLC30A) and ZIPs (SLC39A). To identify the molecular mechanisms of diverse functions of labile Zn²⁺ in the heart, the recent studies focused on the discovery of subcellular localization of these Zn²⁺ transporters in parallel to the discovery of novel physiological functions of [Zn²⁺]_i in cardiomyocytes. The present review summarizes the current understanding of the role of [Zn²⁺]_i changes in cardiomyocytes under pathological conditions, and under high [Zn²⁺]_i and how Zn²⁺ transporters are important for its subcellular redistribution. The emerging importance and the promise of some Zn²⁺ transporters for targeted cardiac therapy against pathological stimuli are also provided. Taken together, the review clearly outlines cellular control of cytosolic Zn²⁺ signaling by Zn²⁺ transporters, the role of Zn²⁺ transporters in heart function under hyperglycemia, the role of Zn²⁺ under increased oxidative stress and ER stress, and their roles in cancer are discussed.

Zinc in Keratinocytes and Langerhans Cells: Relevance to the Epidermal Homeostasis

In the skin, the epidermis is continuously exposed to various kinds of external substances and stimuli. Therefore, epidermal barriers are crucial for providing protection, safeguarding health, and regulating water balance by maintaining skin homeostasis. Disruption of the epidermal barrier allows external substances and stimuli to invade or stimulate the epidermal cells, leading to the elicitation of skin inflammation. The major components of the epidermal barrier are the stratum corneum (SC) and tight junctions (TJs). The presence of zinc in the epidermis promotes epidermal homeostasis; hence, this study reviewed the role of zinc in the formation and function of the SC and TJs. Langerhans cells (LCs) are one of the antigen-presenting cells found in the epidermis. They form TJs with adjacent keratinocytes (KCs), capture external antigens, and induce antigen-specific immune reactions. Thus, the function of zinc in LCs was examined in this review. We also summarized the general knowledge of zinc and zinc transporters in the epidermis with updated findings.

Function, Structure, and Transport Aspects of ZIP and ZnT Zinc Transporters in Immune Cells

Zinc is an important trace metal in immune systems, and zinc transporters are involved in many immune responses. Recent advances have revealed the structural and biochemical bases for zinc transport across the cell membrane, with clinical implications for the regulation of zinc homeostasis in immune cells like dendritic cells, T cells, B cells, and mast cells. In this review, we discuss the function, structure, and transport aspects of two major mammalian zinc transporter types, importers and exporters. First, Zrt-/Irt-like proteins (ZIPs) mediate the zinc influx from the extracellular or luminal side into the cytoplasm. There are 14 ZIP family members in humans. They form a homo- or heterodimer with 8 transmembrane domains and extra-/intracellular domains of various lengths. Several ZIP members show specific extracellular domains composed of two subdomains, a helix-rich domain and proline-alanine-leucine (PAL) motif-containing domain. Second, ZnT (zinc transporter) was initially identified in early studies of zinc biology; it mediates zinc efflux as a counterpart of ZIPs in zinc homeostasis. Ten family members have been identified. They show a unique architecture characterized by a Y-shaped conformation and a large cytoplasmic domain. A precise, comprehensive understanding of the structures and transport mechanisms of ZIP and ZnT in combination with mice experiments would provide promising drug targets as well as a basis for identifying other transporters with therapeutic potential.

Automatic microscopic detection of mycobacteria in sputum: a proof-of-concept

The laboratory diagnosis of lung mycobacterioses including tuberculosis comprises the microscopic examination of sputum smear after appropriate staining such as Ziehl-Neelsen staining to observe acid-fast bacilli. This standard procedure is operator-dependant and its sensitivity depends on the duration of observation. We developed and evaluated an operator-independent microscopic examination of sputum smears for the automated detection and enumeration of acid-fast bacilli using a ZEISS Axio Scan.Z1 microscope. The sensitivity, specificity, positive predictive value, negative predictive values and accuracy were calculated using standard formulations by comparison with standard microscopic examination. After in-house parameterization of the automatic microscope and counting software, the limit of detection evaluated by seeding negative sputa with Mycobacterium bovis BCG or Mycobacterium tuberculosis H37Rv (10⁰–10⁵ bacilli/mL) was of 10² bacilli/mL of sputum with a 100% positivity rate. Then, the evaluation of 93 sputum specimens including 34 smear-positive and 59 smear-negative specimens yielded a sensitivity of 97.06% [84.67–99.93%], a specificity of 86.44% [73.01–92.78%]. Up to 100 smear slides could be stocked for reading in the microscope magazine and results are exportable into the laboratory information system. Based on these preliminary results, we are implanting this automatic protocol in the routine workflow so that only smears detected positive by automatic microscopy are confirmed by standard microscopic examination.

The Role of the Slc39a Family of Zinc Transporters in Zinc Homeostasis in Skin

The first manifestations that appear under zinc deficiency are skin defects such as dermatitis, alopecia, acne, eczema, dry, and scaling skin. Several genetic disorders including acrodermatitis enteropathica (also known as Danbolt-Closs syndrome) and Brandt's syndrome are highly related to zinc deficiency. However, the zinc-related molecular mechanisms underlying normal skin development and homeostasis, as well as the mechanism by which disturbed zinc homeostasis causes such skin disorders, are unknown. Recent genomic approaches have revealed the physiological importance of zinc transporters in skin formation and clarified their functional impairment in cutaneous pathogenesis. In this review, we provide an overview of the relationships between zinc deficiency and skin disorders, focusing on the roles of zinc transporters in the skin. We also discuss therapeutic outlooks and advantages of controlling zinc levels via zinc transporters to prevent cutaneous disorganization.

Zinc and Skin Disorders

The skin is the third most zinc (Zn)-abundant tissue in the body. The skin consists of the epidermis, dermis, and subcutaneous tissue, and each fraction is composed of various types of cells. Firstly, we review the physiological functions of Zn and Zn transporters in these cells. Several human disorders accompanied with skin manifestations are caused by mutations or dysregulation in Zn transporters; acrodermatitis enteropathica (Zrt-, Irt-like protein (ZIP)4 in the intestinal epithelium and possibly epidermal basal keratinocytes), the spondylocheiro dysplastic form of Ehlers-Danlos syndrome (ZIP13 in the dermal fibroblasts), transient neonatal Zn deficiency (Zn transporter (ZnT)2 in the secretory vesicles of mammary glands), and epidermodysplasia verruciformis (ZnT1 in the epidermal keratinocytes). Additionally, acquired Zn deficiency is deeply involved in the development of some diseases related to nutritional deficiencies (acquired acrodermatitis enteropathica, necrolytic migratory erythema, pellagra, and biotin deficiency), alopecia, and delayed wound healing. Therefore, it is important to associate the existence of mutations or dysregulation in Zn transporters and Zn deficiency with skin manifestations.

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

Zinc (Zn), which is an essential trace element, is involved in numerous mammalian physiological events; therefore, either a deficiency or excess of Zn impairs cellular machineries and influences physiological events, such as systemic growth, bone homeostasis, skin formation, immune responses, endocrine function, and neuronal function. Zn transporters are thought to mainly contribute to Zn homeostasis within cells and in the whole body. Recent genetic, cellular, and molecular studies of Zn transporters highlight the dynamic role of Zn as a signaling mediator linking several cellular events and signaling pathways. Dysfunction in Zn transporters causes various diseases. This review aims to provide an update of Zn transporters and Zn signaling studies and discusses the remaining questions and future directions by focusing on recent progress in determining the roles of SLC39A/ZIP family members in vivo.