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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.

Ehlers–Danlos syndrome spondylodysplastic type 3 (EDSSPD3, OMIM 612350) is an inherited recessive connective tissues disease caused by loss of function of SLC39A13/ZIP13, a zinc transporter belonging to the Slc39a/ZIP family. Patients with EDSSPD3 suffer from impaired development of bone and connective tissues, and muscular hypotonia, or myopathy. However, whether ZIP13 participates in the early differentiation process of these cell types remains unclear. In this study, we investigated the role of ZIP13 in myogenic differentiation using murine myoblast cell line (C2C12) as well as human patient-derived induced pluripotent stem cells (iPSCs). We found that ZIP13 expression was upregulated by myogenic stimulation in C2C12 cells, and its knockdown disrupted myotubular differentiation. Myocytes differentiated from iPSCs of patients with EDSSPD3 (EDSSPD3-iPSCs) exhibited incomplete myogenic differentiation. Moreover, the phenotypic abnormalities of EDSSPD3-iPSC-derived myocytes were corrected by genomic editing of the pathogenic ZIP13 mutation, suggesting the indispensable role of ZIP13 in myogenic differentiation. These results clearly indicate that ZIP13 is required for proper myogenic differentiation and that the study of EDSSPD3-iPSCs may help shed light on the molecular basis underlying various clinical features caused by the loss of ZIP13.

Magnetic resonance imaging (MRI) was used to observe growth of the mandibular condyle, mandibular fossa, and articular disc as a single unit. Changes in each component's relative position and size were observed using 7-tesla MRI. Mandibular condyle chondrocytes' growth was evaluated with immunohistochemistry, using the expression of zinc transporter ZIP13. Three-dimensional T1-weighted (T1w) MRI was used to obtain images of the TMJ of Sprague Dawley rats at 4-78 days old (P4-78) with a voxel resolution of 65 μm. Two-dimensional T1w MR images were acquired after a subcutaneous injection of the contrast reagent gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA). The T1w MR images showed that the mandibular condyle was located posterior to the mandibular fossa until P20; however, it then moved to a location underneath the mandibular fossa. In the Gd-DTPA enhanced images, the articular disc was identified as a region with lower signal intensity from P20. The number of ZIP13-positive chondrocytes at P6 was larger than the number at P24. In conclusion, the mandibular condyle with cartilage and disc grows on the posterior side of the mandibular fossa until P20, which was the weaning age. Then, the condyle fit into the mandibular fossa and completed the functional unit.

Background The skin is the first organ that manifests changes in response to zinc deficiency. However, the molecular mechanism underlying how zinc is involved in skin homeostasis, especially its epigenetic regulation, is largely unknown. Objectives In this study we demonstrate the importance of zinc levels and the zinc transporter ZIP10 in the epigenetic maintenance of human epidermal homeostasis. Methods Adult human skin, including skin appendages, were stained with anti-ZIP10 antibody. Histone acetyltransferase (HAT) activity was assessed after treating human keratinocytes with ZIP10 small interfering (si)RNAs or the zinc chelator TPEN. ZIP10- or HAT-regulated genes were analysed based on limma bioinformatics analysis for keratinocytes treated with ZIP10 siRNAs or a HAT inhibitor, or using a public database for transcription factors. A reconstituted human skin model was used to validate the role of ZIP10 in epidermal differentiation and the functional association between ZIP10 and HAT. Results ZIP10 is predominantly expressed in the interfollicular epidermis, epidermal appendages and hair follicles. ZIP10 depletion resulted in epidermal malformations in a reconstituted human skin model via downregulation of the activity of the epigenetic enzyme HAT. This decreased HAT activity, resulting from either ZIP10 depletion or treatment with the zinc chelator TPEN, was readily restored by zinc supplementation. Through bioinformatics analysis for gene sets regulated by knockdown of SLC39A10 (encoding ZIP10) and HAT inhibition, we demonstrated that ZIP10 and HATs were closely linked with the regulation of genes related to epidermal homeostasis, particularly filaggrin and metallothionein. Conclusions Our study suggests that ZIP10-mediated zinc distribution is crucial for epidermal homeostasis via HATs. Therefore, zinc-dependent epigenetic regulation could provide alternatives to maintaining healthy skin or alleviating disorders with skin barrier defects.

Iron is essential for erythropoiesis and other biological processes, but is toxic in excess. Dietary absorption of iron is a highly regulated process and is a major determinant of body iron levels. Iron excretion, however, is considered a passive, unregulated process, and the underlying pathways are unknown. Here we investigated the role of metal transporters SLC39A14 and SLC30A10 in biliary iron excretion. While SLC39A14 imports manganese into the liver and other organs under physiological conditions, it imports iron under conditions of iron excess. SLC30A10 exports manganese from hepatocytes into the bile. We hypothesized that biliary excretion of excess iron would be impaired by SLC39A14 and SLC30A10 deficiency. We therefore analyzed biliary iron excretion in Slc39a14-and Slc30a10-deficient mice raised on iron-sufficient and -rich diets. Bile was collected surgically from the mice, then analyzed with nonheme iron assays, mass spectrometry, ELISAs, and an electrophoretic assay for iron-loaded ferritin. Our results support a model in which biliary excretion of excess iron requires iron import into hepatocytes by SLC39A14, followed by iron export into the bile predominantly as ferritin, with iron export occurring independently of SLC30A10. To our knowledge, this is the first report of a molecular determinant of mammalian iron excretion and can serve as basis for future investigations into mechanisms of iron excretion and relevance to iron homeostasis.

Manganese (Mn), an essential metal, can be toxic at elevated levels. In 2012, the first inherited cause of Mn excess was reported in patients with mutations in SLC30A10, a Mn efflux transporter. To explore the function of SLC30A10 in vitro, the current study used CRISPR/Cas9 gene editing to develop a stable SLC30A10 mutant Hep3B hepatoma cell line and collagenase perfusion in live mice to isolate primary hepatocytes deficient in Slc30a10. We also compared phenotypes of primary vs. non-primary cell lines to determine if they both serve as reliable in vitro models for the known physiological roles of SLC30A10. Mutant SLC30A10 Hep3B cells had increased Mn levels and decreased viability when exposed to excess Mn. Transport studies indicated a reduction of (54)Mn import and export in mutant cells. While impaired (54)Mn export was hypothesized given the essential role for SLC30A10 in cellular Mn export, impaired (54)Mn import was unexpected. Whole genome sequencing did not identify any additional mutations in known Mn transporters in the mutant Hep3B mutant cell line. We then evaluated (54)Mn transport in primary hepatocytes cultures isolated from genetically altered mice with varying liver Mn levels. Based on results from these experiments, we suggest that the effects of SLC30A10 deficiency on Mn homeostasis can be interrogated in vitro but only in specific types of cell lines.

Zinc is one of the essential trace elements required by humans, and its deficiency impairs zinc homeostasis, thereby affecting growth, the skin barrier, and the immune response. It also serves as a cofactor for many transcription factors and enzymes, and its levels are precisely regulated by zinc mediators, such as transporters. Zinc transporters control extracellular and intracellular zinc levels by influx and efflux via ZIP and ZnT family members, respectively. Recent investigations clearly indicate that zinc transporters are involved in a number of physiological events and disease statuses. Zinc ions act as a signaling factor, producing a “zinc signal,” and alterations in zinc signaling may result in “zinc stress” in cells. Here, we provide an overview of the relevance of zinc signaling and zinc stress to biological processes, and review the progress of zinc transporter-related studies and disorders of dermis and epidermis of the skin.

Organoids generated from pluripotent stem cells are used in the development of organ replacement regenerative therapy by recapitulating the process of organogenesis. These processes are strictly regulated by morphogen signalling and transcriptional networks. However, the precise transcription factors involved in the organogenesis of exocrine glands, including salivary glands, remain unknown. Here, we identify a specific combination of two transcription factors (Sox9 and Foxc1) responsible for the differentiation of mouse embryonic stem cell-derived oral ectoderm into the salivary gland rudiment in an organoid culture system. Following orthotopic transplantation into mice whose salivary glands had been removed, the induced salivary gland rudiment not only showed a similar morphology and gene expression profile to those of the embryonic salivary gland rudiment of normal mice but also exhibited characteristics of mature salivary glands, including saliva secretion. This study suggests that exocrine glands can be induced from pluripotent stem cells for organ replacement regenerative therapy., Functional salivary glands have not been generated from embryonic stem cells (mESCs) to date. Here the authors demonstrate directed in vitro differentiation of mESCs to oral ectoderm and salivary gland rudiments that form mature, functional salivary glands after orthotopic transplantation.

Zinc (Zn) is one of the essential trace elements required for human developments and it plays an important role in the maintenance of numerous tissue homeostasis. The amount of Zn levels was below the constant level which induced the various harmful health effects such as impaired growth, hair loss, taste disturbance, anorexia. Maintenance of Zn homeostasis in body mainly depends on two families of Zn transporters; Zrt- and Irt-like proteins (ZIPs), and Zinc transporters (ZnTs). Some studies based on the gene knock-out mice and human genetic analysis have been reported the relationship between zinc transporters and human diseases. Recent studies have shown that Zn transporter-mediated Zn ion behaves as a signaling factor, called Zn signal, that exerts a multiple function in cellular events. In this review article we describe important physiological roles of Zn transporters and their contribution at the molecular, biochemical, and genetic levels underlying the mechanisms of human diseases.

Objectives: Details of the histogenesis of salivary gland tumors are largely unknown. The oncogenic role of PLAG1 in the salivary gland has been demonstrated in vivo. Herein, we demonstrate the roles of PLAG1 in the acinar and ductal cells of normal human salivary glands in an attempt to clarify the early events that occur during the histogenesis of salivary gland tumors. Methods: Normal salivary gland cells with acinar- (NS-SV-AC) and ductal- (NS-SV-DC) phenotypes were transfected with PLAG1 plasmid DNA. Subsequently, the PLAG1 overexpressed and mock cells were examined by cell proliferation, transwell migration, and salisphere formation assays. The expression levels of salivary and pluripotent stem cell markers and differentiation markers were evaluated by quantitative real-time polymerase chain reaction and immunofluorescence. Alterations in transcriptional expressions were investigated via cap analysis of gene expression with gene-enrichment and functional annotation analysis. Results: PLAG1 promoted cell proliferation and transwell migration in the acinar and ductal cells, and markedly enhanced the stemness profiles and luminal cell-like profiles in acinar cells; the stemness profiles were partially increased in the ductal cells. Conclusion: PLAG1 enhanced the stemness profiles in the acinar cells of normal human salivary glands in a cell type-specific manner. Thus, it may be involved in salivary gland tumorigenesis by increasing the stemness character of the normal salivary gland cells.

Patients with metastatic cancer experience a severe loss of skeletal muscle mass and function known as cachexia. Cachexia is associated with poor prognosis and accelerated death in patients with cancer, yet its underlying mechanisms remain poorly understood. Here, we identify the metal-ion transporter ZRT- and IRT-like protein 14 (ZIP14) as a critical mediator of cancer-induced cachexia. ZIP14 is upregulated in cachectic muscles of mice and in patients with metastatic cancer and can be induced by TNF-α and TGF-β cytokines. Strikingly, germline ablation or muscle-specific depletion of Zip14 markedly reduces muscle atrophy in metastatic cancer models. We find that ZIP14-mediated zinc uptake in muscle progenitor cells represses the expression of MyoD and Mef2c and blocks muscle-cell differentiation. Importantly, ZIP14-mediated zinc accumulation in differentiated muscle cells induces myosin heavy chain loss. These results highlight a previously unrecognized role for altered zinc homeostasis in metastatic cancer-induced muscle wasting and implicate ZIP14 as a therapeutic target for its treatment.

Ehlers-Danlos syndrome (EDS) is a group of hereditary diseases caused by mutation of extracellular matrix-related genes. Recently, spondylodysplastic EDS-Zip13 (spEDS-Zip13: OMIM 612350) was recognized as a new EDS type. This current study could reveal various morphometric differences of collagenous population in the proper substance of cornea between the wild type and spEDS-Zip13-knockout (Zip13-KO) mice. Blockade of Smad-signaling pathway might initiate these alterations. Predilected dissimilarity in level of transcriptional activity probably dictated morphology of keratocyte and shape and electron density of its nucleus. In addition, the imbalance of proteoglycans and glycosaminoglycans would also affect the diameter and arrangement of collagen fibrils. These findings would be considered as vulnerable characteristics of corneal stroma of the Zip13-KO mice.

Despite the known importance of zinc for human immunity, molecular insights into its roles have remained limited. Here we report a novel autosomal recessive disease characterized by absent B cells, agammaglobulinemia and early-onset infections in five unrelated families. The immunodeficiency results from hypomorphic mutations of SLC39A7, which encodes the endoplasmic reticulum–to–cytoplasm zinc transporter ZIP7. Using CRISPR-Cas9 mutagenesis we have precisely modelled ZIP7 deficiency in mice. Homozygosity for a null allele caused embryonic death, but hypomorphic alleles reproduced the block in B cell development seen in patients. B cells from mutant mice exhibited a diminished concentration of cytoplasmic free zinc, increased phosphatase activity and decreased phosphorylation of signalling molecules downstream of the pre-B cell and B cell receptors. Our findings highlight a specific role for cytosolic Zn(2+) in modulating B cell receptor signal strength and positive selection.

Introduction: Zinc (Zn) is an essential trace element required for normal skin homeostasis. Therefore, cutaneous changes are often observed in Zn-deficient patients. Acrodermatitis enteropathica (A...

Skin is the first area that manifests zinc deficiency. However, the molecular mechanisms by which zinc homeostasis affects skin development remain largely unknown. Here, we show that zinc-regulation transporter-/iron-regulation transporter-like protein 7 (ZIP7) localized to the endoplasmic reticulum plays critical roles in connective tissue development. Mice lacking the Slc39a7/Zip7 gene in collagen 1-expressing tissue exhibited dermal dysplasia. Ablation of ZIP7 in mesenchymal stem cells inhibited cell proliferation thereby preventing proper dermis formation, indicating that ZIP7 is required for dermal development. We also found that mesenchymal stem cells lacking ZIP7 accumulated zinc in the endoplasmic reticulum, which triggered zinc-dependent aggregation and inhibition of protein disulfide isomerase, leading to endoplasmic reticulum dysfunction. These results suggest that ZIP7 is necessary for endoplasmic reticulum function in mesenchymal stem cells and, as such, is essential for dermal development.

Acrodermatitis enteropathica is an autosomal recessive disorder characterized by scaly eczematous dermatosis accompanied by alopecia and diarrhea. Various mutations in the SLC39A4 gene (ZIP4), which encodes a zinc transporter, are responsible for this disorder. However, the molecular mechanism underlying the involvement of ZIP4 in the pathogenesis of this condition has yet to be established. In this study, we report the role of ZIP4 in human epidermis. ZIP4 is predominantly expressed in human keratinocytes, and its expression is dramatically reduced on epidermal differentiation. ZIP4 knockdown in human keratinocytes down-regulates zinc (Zn) levels and the transcriptional activity of a key epidermal Zn-binding protein, ΔNp63, and dysregulates epidermal differentiation in a reconstituted human skin model, resulting in the appearance of proliferating keratinocytes even in the uppermost layers of the skin. We verified that, among the amino acid residues in its Zn-binding motif, Cys205 is critical for the processing and nuclear distribution of ΔNp63 and, therefore, Zn-dependent transcriptional activity. Our results suggest that ZIP4 is essential for maintaining human epidermal homeostasis through the regulation of Zn-dependent ΔNp63 activity and can provide insight into the molecular mechanisms responsible for the cutaneous symptoms observed in Acrodermatitis enteropathica patients.

Zinc (Zn) is an essential trace mineral that regulates the expression and activation of biological molecules such as transcription factors, enzymes, adapters, channels, and growth factors, along with their receptors. Zn deficiency or excessive Zn absorption disrupts Zn homeostasis and affects growth, morphogenesis, and immune response, as well as neurosensory and endocrine functions. Zn levels must be adjusted properly to maintain the cellular processes and biological responses necessary for life. Zn transporters regulate Zn levels by controlling Zn influx and efflux between extracellular and intracellular compartments, thus, modulating the Zn concentration and distribution. Although the physiological functions of the Zn transporters remain to be clarified, there is growing evidence that Zn transporters are related to human diseases, and that Zn transporter-mediated Zn ion acts as a signaling factor, called "Zinc signal". Here we describe critical roles of Zn transporters in the body and their contribution at the molecular, biochemical, and genetic levels, and review recently reported disease-related mutations in the Zn transporter genes.

The skin is the first body region to manifest zinc deficiency. Recent studies have revealed that the zinc transporters, especially zinc importers belonging to the Zrt-Irt-like (ZIP) family, play crucial roles in skin homeostasis. Fourteen ZIP members have been identified in humans, with at least 6 members being related to skin development and maintenance. ZIP1, ZIP2, ZIP4, and ZIP10 are associated with epidermal morphogenesis and disorders, whereas ZIP7 and ZIP13 are essential for dermis formation and collagen metabolism. Mouse models in combination with clinical data have shown the molecular pathogenic mechanisms involving ZIP members. Although other family members have not been well studied with respect to their role in the skin, their direct or indirect associations are also considerable and they are believed to be drug targets for skin diseases. Therefore, precise analysis and understanding of ZIP family members are indispensable for the care and treatment of skin disorders.

Almost half a decade has passed since the publication of the first edition of Zinc Signaling, entitled “Zinc Signals in Cellular Functions and Disorders”, which was the first exclusive book dedicated to “zinc signaling” at that time. Since then, a number of novel findings have been reported, which have updated our knowledge of zinc-related biology and provided new insights into many cellular functions, physiology, and pathophysiology associated with zinc. This book, Zinc Signaling, 2nd Edition has been planned to be published with a primary goal of updating the available information about the role of zinc signaling in biological processes at both molecular and physiological levels, as well as highlighting the new achievements in the field in the last 5 years after the publication of the first edition. This book will certainly assist in addressing the questions underlying this unique phenomenon and discerning its future direction, and would help in knowing what is new and what remains to be solved in the next era.

Skin homeostasis is maintained by the continuous proliferation and differentiation of epidermal cells. The skin forms a strong but flexible barrier against microorganisms as well as physical and chemical insults; however, the physiological mechanisms that maintain this barrier are not fully understood. Here, we have described a mutant mouse that spontaneously develops pruritic dermatitis as the result of an initial defect in skin homeostasis that is followed by induction of a Th2-biased immune response. These mice harbor a mutation that results in a single aa substitution in the JAK1 tyrosine kinase that results in hyperactivation, thereby leading to skin serine protease overexpression and disruption of skin barrier function. Accordingly, treatment with an ointment to maintain normal skin barrier function protected mutant mice from dermatitis onset. Pharmacological inhibition of JAK1 also delayed disease onset. Together, these findings indicate that JAK1-mediated signaling cascades in skin regulate the expression of proteases associated with the maintenance of skin barrier function and demonstrate that perturbation of these pathways can lead to the development of spontaneous pruritic dermatitis.

Ehlers-Danlos syndrome (EDS) is a collection of inheritable diseases involving the musculoskeletal, integumentary and visual systems. Spondylodysplastic EDS-ZIP13 (spEDS-ZIP13: OMIM 612350) was recently defined as a new form of EDS. Although vasculitis has been found in many spEDS-ZIP13 patients, vascular pathology has not been included as a pathognomonic lesion of this type of EDS. We investigate the morphometry of the thoracic aorta in wild-type and Zip13-knockout (Zip13-KO) mice. Our assessment found abnormalities in the number and morphology of elastic and cellular components in the aortic wall, especially the tunica media, of Zip13-KO mice, indicating aortic fragility. Accordingly, our major findings (vascular smooth muscle cells with small nuclei, small percentage of elastic membrane area per tunica media, many large elastic flaps) should be considered vulnerable characteristics indicating fragility of the aorta in patients with spEDS-ZIP13.

Solute carrier family 39, member 14 (SLC39A14) is a transmembrane transporter that can mediate the cellular uptake of zinc, iron, and manganese (Mn). Studies of Slc39a14 knockout (Slc39a14-/-) mice have documented that SLC39A14 is required for systemic growth, hepatic zinc uptake during inflammation, and iron loading of the liver in iron overload. The normal physiological roles of SLC39A14, however, remain incompletely characterized. Here, we report that Slc39a14-/- mice spontaneously display dramatic alterations in tissue Mn concentrations, suggesting that Mn is a main physiological substrate for SLC39A14. Specifically, Slc39a14-/- mice have abnormally low Mn levels in the liver coupled with markedly elevated Mn concentrations in blood and most other organs, especially the brain and bone. Radiotracer studies using 54Mn reveal that Slc39a14-/- mice have impaired Mn uptake by the liver and pancreas and reduced gastrointestinal Mn excretion. In the brain of Slc39a14-/- mice, Mn accumulated in the pons and basal ganglia, including the globus pallidus, a region susceptible to Mn-related neurotoxicity. Brain Mn accumulation in Slc39a14-/- mice was associated with locomotor impairments, as assessed by various behavioral tests. Although a low-Mn diet started at weaning was able to reverse brain Mn accumulation in Slc39a14-/- mice, it did not correct their motor deficits. We conclude that SLC39A14 is essential for efficient Mn uptake by the liver and pancreas, and its deficiency results in impaired Mn excretion and accumulation of the metal in other tissues. The inability of Mn depletion to correct the motor deficits in Slc39a14-/- mice suggests that the motor impairments represent lasting effects of early-life Mn exposure.

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.