Manganese transporter Slc39a14 deficiency revealed its key role in maintaining manganese homeostasis in mice

ATP13A2 as a prognostic biomarker and its correlation with immune infiltration in cervical cancer: A retrospective study

While the oncogene ATP13A2 is reportedly involved in colorectal cancer, its role in cervical cancer (CC) has yet to be fully characterized. In this study, we investigated ATP13A2 as a potential prognostic biomarker of CC. To this end, we compared CC tissues with normal tissues to identify differentially expressed genes, identifying ATP13A2 as a potential marker of CC. Elevated ATP13A2 expression levels were identified in CC samples compared to noncancerous samples across various data sets, with further immunohistochemical validation. Functional enrichment analysis revealed that ATP13A2 plays an essential role in the CXCL12-activated CXCR4 signalling pathway and chemotaxis regulation, which may alter immune infiltration. Notably, increased ATP13A2 levels were associated with poor overall survival. Furthermore, multiple clinical characteristics were significantly associated with ATP13A2 expression. Additionally, tumour bacterial infiltration was assessed using weighted co-expression network analysis, revealing a relationship between ATP13A2 expression and bacteria in the CC tumour microenvironment. Our results suggest that ATP13A2 is a promising diagnostic and prognostic marker for CC. However, further large-scale studies are needed to fully elucidate the mechanisms underlying the involvement of ATP13A2 in CC.

HFE-Related Hemochromatosis May Be a Primary Kupffer Cell Disease

Iron overload can lead to increased deposition of iron and cause organ damage in the liver, the pancreas, the heart and the synovium. Iron overload disorders are due to either genetic or acquired abnormalities such as excess transfusions or chronic liver diseases. The most common genetic disease of iron deposition is classic hemochromatosis (HH) type 1, which is caused by mutations of HFE. Other rare forms of HH include type 2A with mutations at the gene hemojuvelin or type 2B with mutations in HAMP that encodes hepcidin. HH type 3, is caused by mutations of the gene that encodes transferrin receptor 2. Mutations of SLC40A1 which encodes ferroportin cause either HH type 4A or HH type 4B. In the present review, an overview of iron metabolism including absorption by enterocytes and regulation of iron by macrophages, liver sinusoidal endothelial cells (LSECs) and hepatocyte production of hepcidin is presented. Hereditary Hemochromatosis and the current pathogenetic model are analyzed. Finally, a new hypothesis based on published data was suggested. The Kupffer cell is the primary defect in HFE hemochromatosis (and possibly in types 2 and 3), while the hepcidin-relative deficiency, which is the common underlying abnormality in the three types of HH, is a secondary consequence.

Recent research progress on metal ions and metal-based nanomaterials in tumor therapy

Tumors, as a disease that seriously threatens human health, have always been a major challenge in the field of medicine. Currently, the main methods of tumor treatment include surgery, radiotherapy, chemotherapy, etc., but these traditional treatment methods often have certain limitations. In addition, tumor recurrence and metastasis are also difficult problems faced in clinical treatment. In this context, the importance of metal-based nanomaterials in tumor therapy is increasingly highlighted. Metal-based nanomaterials possess unique physical, chemical, and biological properties, providing new ideas and methods for tumor treatment. Metal-based nanomaterials can achieve targeted therapy for tumors through various mechanisms, reducing damage to normal tissues; they can also serve as drug carriers, improving the stability and bioavailability of drugs; at the same time, some metal-based nanomaterials also have photothermal, photodynamic, and other characteristics, which can be used for phototherapy of tumors. This review examines the latest advances in the application of metal-based nanomaterials in tumor therapy within past 5 years, and presents prospective insights into the future applications.

SLC39A14 promotes the development of esophageal squamous cell carcinoma through PI3K/Akt/mTOR signaling pathway

OBJECTIVES

This study aims to investigate the expression of solute carrier family 39 member 14 (SLC39A14) in esophageal squamous cell carcinoma (ESCC) tissues and its prognosis, as well as the impact of SLC39A14 expression on the biological behavior of ESCC cells and associated mechanisms.

METHODS

Bioinformatics analysis was utilized to compare the differential expression of SLC39A14 mRNA between esophageal cancer tissues and adjacent non-cancerous tissues. Immunohistochemistry was employed to evaluate SLC39A14 protein expression in human ESCC tissues and normal esophageal tissues, followed by an analysis of its association with clinicopathological parameters in esophageal cancer patients. Through cell proliferation, migration, invasion, and Western blot assays, we deeply evaluated the specific effects of SLC39A14 gene knockdown (or overexpression) on ESCC cells and explored its potential biological functions in ESCC. Subsequently, we validated the role of SLC39A14 in ESCC in a xenograft model. Furthermore, LY294002 drug intervention was used to verify the regulatory effect of SLC39A14 on PI3K/Akt/mTOR signaling pathway.

RESULTS

Both mRNA and protein levels of SLC39A14 were significantly elevated in tumor tissues from ESCC patients compared to adjacent normal tissues. Notably, higher levels of SLC39A14 expression positively correlated with ESCC tumor size (p = 0.010) and clinical T stage (p = 0.025), while exhibiting a negative correlation with overall patient survival rates (p = 0.023). In vitro experiments demonstrated that knocking down SLC39A14 significantly inhibited cell proliferation, migration and invasion. In vivo study showed that SLC39A14 facilitated progression within murine models bearing ESCC tumors. Mechanistic analyses suggested that pro-carcinogenic effects exerted by SLC39A14 are mediated through activation of the PI3K/Akt/mTOR signaling pathway.

CONCLUSIONS

Our findings suggest that SLC39A14 may serve as a potential biomarker for ESCC due to its pro-oncogenic role during ESCC progression.

Artificially Engineered Nanoprobes for Ultrasensitive Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a noninvasive and radiation-free technique used for soft tissue. However, there are some limitations of the MRI modality, such as low sensitivity and poor image resolution. Artificially engineered magnetic nanoprobes have been extensively explored as a versatile platform for ultrasensitive MRI contrast agents due to their unique physiochemical characteristics and tunable magnetic properties. In this review, the emphasis is on recent progress in MRI nanoprobes with different structures and elements, including gadolinium-, iron-, manganese-based and metal-free nanoprobes. The key influencing factors and advanced engineering strategies for modulating the relaxation ratio of MRI nanoprobes are systematically condensed. Furthermore, the widespread and noninvasive visualization applications of MRI nanoprobes for real time monitoring of major organs and accurate disease diagnosing, such as cerebrovascular, ischemia, Alzheimer's disease, liver fibrosis, whole-body tumors, inflammation, as well as multi-mode imaging applications are summarized. Finally, the challenges and prospects for the future development of MRI nanoprobes are discussed, and promising strategies are specifically emphasized for improving biocompatibility, precisely engineering of optimal size, AI-driven prediction and design, and multifunctional self-assembly to enhance diagnostics. This review will provide new inspiration for artificial engineering and nanotechnology-based molecular probes for medical diagnosis and therapy with ultrasensitive MRI.

Mammalian SLC39A13 promotes ER/Golgi iron transport and iron homeostasis in multiple compartments

Iron is a potent biochemical, and accurate homeostatic control is orchestrated by a network of interacting players at multiple levels. Although our understanding of organismal iron homeostasis has advanced, intracellular iron homeostasis is poorly understood, including coordination between organelles and iron export into the ER/Golgi. Here, we show that SLC39A13 (ZIP13), previously identified as a zinc transporter, promotes intracellular iron transport and reduces intracellular iron levels. ZIP13 loss causes an iron deficiency in the ER/Golgi and other intracellular compartments, such as lysosomes and mitochondria, as well as elevating iron in the cytosol. ZIP13 overexpression has the opposite effect, increasing iron in organellar compartments. We suggest that ZIP13 gatekeeps an iron trafficking route that shunts iron from the cytosol to the ER/Golgi hub. Zip13-knockout male mice have iron deposition in several tissues. These data demonstrate that mammalian ZIP13 is crucial for iron homeostasis and suggest a potential iron transport function.

bmp10 maintains cardiac function by regulating iron homeostasis

Heart disease remains the leading cause of death worldwide. Iron imbalance, whether deficiency or overload, contributes to heart failure. However, the molecular mechanisms governing iron homeostasis in the heart are poorly understood. Here, we demonstrate that mutation of bmp10, a heart-born morphogen crucial for embryonic heart development, results in severe anemia and cardiac hypertrophy in zebrafish. Initially, bmp10 deficiency causes cardiac iron deficiency, which later progresses to iron overload due to the dysregulated hepcidin/ferroportin axis in cardiac cells, leading to ferroptosis and heart failure. Early iron supplementation in bmp10-/- mutants rescues erythropoiesis, while iron chelation in juvenile fishes significantly alleviates cardiac hypertrophy. We further demonstrate that the interplay between HIF1α-driven hypoxic signaling and the IL6/p-STAT3 inflammatory pathways is critical for regulating cardiac iron metabolism. Our findings reveal BMP10 as a key regulator of iron homeostasis in the vertebrate heart and highlight the potential of targeting the BMP10-hepcidin-iron axis as a therapeutic strategy for iron-related cardiomyopathy.

Manganese inhibits HBV transcription and promotes HBsAg degradation at non-toxic levels

Chronic hepatitis B virus (HBV) infection continues to pose a significant global health challenge. However, therapeutic measures for a cure are lacking in clinical practice. Manganese, an essential trace element, has garnered attention due to its potential to activate innate immune pathways and its significant role in antiviral and antitumor immunity. Yet, the specific impact of manganese on chronic hepatitis B has been largely unexplored. Our research reveals that manganese substantially inhibits HBV replication in hepatocellular carcinoma cells at non-toxic levels. This suppression occurs independently of well-known anti-HBV innate immune pathways, such as the cGAS-STING pathway. Mechanistically, manganese decreases HBV transcription by diminishing the levels of liver-specific transcription factors. Furthermore, it activates the mTOR pathway, enhancing HBsAg ubiquitination through the upregulation of the ubiquitin ligase β-TrCP and increasing proteasome activity via the augmentation of its subunits, leading to a ubiquitin-dependent degradation of HBsAg. Significantly, our study also uncovers a notable clinical correlation between manganese levels and chronic hepatitis B infection. These findings position manganese as a critical element in diminishing HBV replication, offering a new direction in the management of chronic hepatitis B.

SS-31 modification alleviates ferroptosis induced by superparamagnetic iron oxide nanoparticles in hypoxia/reoxygenation cardiomyocytes

Superparamagnetic iron oxide nanoparticles (SPION) are widely used in cardiovascular applications. However, their potential to induce ferroptosis in myocardial cells post-ischemia-reperfusion hinders clinical adoption. We investigated the mechanisms behind SPION-induced cytotoxicity in myocardial cells and explored whether co-loading SPION with SS-31 (a kind of mitochondrial-targeted antioxidant peptide) could counteract this toxicity. To create SPION@SS-31, SS-31 was physically adsorbed onto SPION. To study the dose- and time-dependent cytotoxic effects and assess the influence of SS-31 on reducing SPION-induced damage, hypoxia/reoxygenation(H/R) H9C2 cells were treated with either SPION or SPION@SS-31. We examined the relationship between SPION and ferroptosis by measuring mitochondrial ROS, mitochondrial membrane potential (MMP), lipid peroxidation products, ATP, GSH, GPX4, mitochondrial structure, nonheme iron content, cellular iron regulation, and typical ferroptosis markers. The findings showed that SPION induced concentration- and time-dependent toxicity, marked by a significant cell viability loss and an increase in LDH levels. In contrast, SPION@SS-31 produced results comparable to the H/R group, implying that SS-31 can notably reduce cell damage induced by SPION. SPION disrupted cellular iron homeostasis, with FtH and FtMt expression increased and reduced levels of FPN1 and ABCB8, which led to the overload of mitochondrial iron. This iron dysregulation damaged mitochondrial function and integrity, causing ATP depletion, MMP loss, and decreased GPX4 and GSH levels, accompanied by a burst of mitochondrial lipid peroxidation, ultimately resulting in ferroptosis in H/R cardiomyocytes. Notably, SS-31 significantly alleviated SPION-induced ferroptosis by decreasing mitochondrial MDA production and maintaining GSH and GPX4 levels, indicating its possibility to reverse SPION-induced cytotoxicity. The viability of H/R cells and cells treated with SPION and Fer-1 did not differ statistically, whereas cells exposed to SPION along with inhibitors like 3-MA, zVAD, or Nec-1 showed a substantial loss in viability, implying that ferroptosis is the primary mechanism behind SPION-induced myocardial toxicity. SPION triggers mitochondrial lipid peroxidation by causing overload of iron, leading to ferroptosis in H/R H9C2 cells. Mitochondria appear to be the primary target of SPION-induced toxic effects. SS-31 demonstrates potential in inhibiting this ferroptosis by acting as a mitochondria-targeted antioxidant, suggesting that the modification of mitochondria-targeted antioxidant peptides represents an innovative and practical approach to attenuate the myocardial toxicity associated with SPION.

ZIP8 Is Upregulated in the Testis of Zip14-/- Mice

BACKGROUND/OBJECTIVES

Manganese is an essential nutrient involved in various biological processes, including reproductive health, yet the mechanisms regulating its homeostasis in the testis remain poorly understood.

METHODS AND RESULTS

In this study, we investigated the expression and regulation of key manganese transporters-ZIP8, ZIP14, and ZnT10-in mouse testes. Immunoblotting analyses revealed that ZIP8 is expressed in the testes, while ZIP14 and ZnT10 were undetectable. Using Zip14 knockout (Zip14-/-) mice, which exhibit systemic manganese overload, we discovered a significant increase in manganese levels in the testis, accompanied by an upregulation of ZIP8. Importantly, the levels of other essential metals, such as iron, zinc, and copper, remained unchanged.

CONCLUSIONS

Our findings suggest that ZIP8 plays a critical role in manganese transport in the testis, and its increased expression may contribute to manganese accumulation in the absence of ZIP14. This study advances our understanding of manganese homeostasis in the testis and its potential impact on male reproductive health.

Neuronal SLC39A8 deficiency impairs cerebellar development by altering manganese homeostasis

Solute carrier family 39, member 8 (SLC39A8), is a transmembrane transporter that mediates the cellular uptake of zinc, iron, and manganese (Mn). Human genetic studies document the involvement of SLC39A8 in Mn homeostasis, brain development, and function. However, the role and pathophysiological mechanisms of SLC39A8 in the central nervous system remain elusive. We generated Slc39a8 neuron-specific knockout (Slc39a8-NSKO) mice to study SLC39A8 function in neurons. The Slc39a8-NSKO mice displayed markedly decreased Mn levels in the whole brain and brain regions, especially the cerebellum. Radiotracer studies using 54Mn revealed that Slc39a8-NSKO mice had impaired brain uptake of Mn. Slc39a8-NSKO cerebellums exhibited morphological defects and abnormal dendritic arborization of Purkinje cells. Reduced neurogenesis and increased apoptotic cell death occurred in the cerebellar external granular layer of Slc39a8-NSKO mice. Brain Mn deficiency in Slc39a8-NSKO mice was associated with motor dysfunction. Unbiased RNA-Seq analysis revealed downregulation of key pathways relevant to neurodevelopment and synaptic plasticity, including cAMP signaling pathway genes. We further demonstrated that Slc39a8 was required for the optimal transcriptional response to the cAMP-mediated signaling pathway. In summary, our study highlighted the essential roles of SLC39A8 in brain Mn uptake and cerebellum development and functions.

Rehmanniae Radix Praeparata aqueous extract improves hepatic ischemia/reperfusion injury by restoring intracellular iron homeostasis

Hepatic ischemia/reperfusion injury (HIRI) is a common pathophysiological condition occurring during or after liver resection and transplantation, leading to hepatic viability impairment and functional deterioration. Recently, ferroptosis, a newly recognized form of programmed cell death, has been implicated in IRI. Rehmanniae Radix Praeparata (RRP), extensively used in Chinese herbal medicine for its hepatoprotective, anti-inflammatory, and antioxidant properties, presents a potential therapeutic approach. However, the mechanisms by which RRP mitigates HIRI, particularly through the regulation of ferroptosis, remain unclear. In this study, we developed a HIRI mouse model and monocrotaline (MCT)- and erastin-induced in vitro hepatocyte injury models. We conducted whole-genome transcriptome analysis to elucidate the protective effects and mechanisms of RRP on HIRI. The RRP aqueous extract was characterized by the presence of acteoside, rehmannioside D, and 5-hydroxymethylfurfural. Our results demonstrate that the RRP aqueous extract ameliorated oxidative stress, reduced intracellular iron accumulation, and attenuated HIRI-induced liver damage. Additionally, RRP significantly inhibited hepatocyte death by restoring intracellular iron homeostasis both in vivo and in vitro. Mechanistically, the RRP aqueous extract reduced intrahepatocellular iron accumulation by inhibiting ZIP14-mediated iron uptake, promoting hepcidin- and ferroportin-mediated iron efflux, and ameliorating mitochondrial iron aggregation through upregulation of Cisd1 expression. Moreover, siRNA-mediated inhibition of hamp synergistically enhanced the RRP aqueous extract's inhibitory effect on ferroptosis. In conclusion, our study elucidates the mechanisms by which RRP aqueous extracts alleviate HIRI, highlighting the restoration of iron metabolic balance. These findings position RRP as a promising candidate for clinical intervention in HIRI treatment.

A Novel Role for the Longevity-Associated Protein SLC39A11 as a Manganese Transporter

The identification of aging- and longevity-associated genes is important for promoting healthy aging. By analyzing a large cohort of Chinese centenarians, we previously found that single-nucleotide polymorphisms (SNPs) in the SLC39A11 gene (also known as ZIP11) are associated with longevity in males. However, the function of the SLC39A11 protein remains unclear. Here, we found that SLC39A11 expression is significantly reduced in patients with Hutchinson-Gilford progeria syndrome (HGPS). In addition, we found that zebrafish with a mutation in slc39a11 that significantly reduces its expression have an accelerated aging phenotype, including a shortened average lifespan, muscle atrophy and reduced swimming, impaired muscle regeneration, gut damage, and abnormal morphology in the reproductive system. Interestingly, these signs of premature aging were more pronounced in male zebrafish than in females. RNA-sequencing analysis revealed that cellular senescence may serve as a potential mechanism for driving this slc39a11 deficiency-induced phenotype in mutant zebrafish. Moreover, immunofluorescence showed significantly increased DNA damage and reactive oxygen species signaling in slc39a11 mutant zebrafish. Using inductively coupled plasma mass spectrometry (ICP-MS), we found that manganese significantly accumulates in slc39a11 mutant zebrafish, as well as in the serum of both global Slc39a11 knockout and hepatocyte-specific Slc39a11 knockout mice, suggesting that this metal transporter regulates systemic manganese levels. Finally, using cultured human fibroblasts, we found that both knocking down SLC39A11 and exposure to high extracellular manganese increased cellular senescence. These findings provide compelling evidence that SLC39A11 serves to protect against the aging process, at least in part by regulating cellular manganese homeostasis.

Genetic control of MRI contrast using the manganese transporter Zip14

PURPOSE

Gene-expression reporter systems, such as green fluorescent protein, have been instrumental to understanding biological processes in living organisms at organ system, tissue, cell, and molecular scales. More than 30 years of work on developing MRI-visible gene-expression reporter systems has resulted in a variety of clever application-specific methods. However, these techniques have not yet been widely adopted, so a general-purpose expression reporter is still required. Here, we demonstrate that the manganese ion transporter Zip14 is an in vivo MRI-visible, flexible, and robust gene-expression reporter to meet this need.

METHODS

Plasmid constructs consisting of a cell type-specific promoter, gene coding for human Zip14, and a histology-visible tag were packaged into adeno-associated viruses. These viruses were intracranially injected into the mouse brain. Serial in vivo MRI was performed using a vendor-supplied 3D-MPRAGE sequence. No additional contrast agents were administered. Animals were sacrificed after the last imaging timepoint for immunohistological validation.

RESULTS

Neuron-specific overexpression of Zip14 produced substantial and long-lasting changes in MRI contrast. Using appropriate viruses enabled both anterograde and retrograde neural tracing. Expression of Zip14 in astrocytes also enabled MRI of glia populations in the living mammalian brain.

CONCLUSIONS

The flexibility of this system as an MRI-visible gene-expression reporter will enable many applications of serial, high-resolution imaging of gene expression for basic science and therapy development.

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

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

Hepatic HIF2 is a key determinant of manganese excess and polycythemia in SLC30A10 deficiency

Manganese is an essential yet potentially toxic metal. Initially reported in 2012, mutations in SLC30A10 are the first known inherited cause of manganese excess. SLC30A10 is an apical membrane protein that exports manganese from hepatocytes into bile and from enterocytes into the lumen of the gastrointestinal tract. SLC30A10 deficiency results in impaired gastrointestinal manganese excretion, leading to manganese excess, neurologic deficits, liver cirrhosis, polycythemia, and erythropoietin excess. Neurologic and liver disease are attributed to manganese toxicity. Polycythemia is attributed to erythropoietin excess. The goal of this study was to determine the basis of erythropoietin excess in SLC30A10 deficiency. Here, we demonstrate that transcription factors hypoxia-inducible factor 1a (Hif1a) and 2a (Hif2a), key mediators of the cellular response to hypoxia, are both upregulated in livers of Slc30a10-deficient mice. Hepatic Hif2a deficiency corrected erythropoietin expression and polycythemia and attenuated aberrant hepatic gene expression in Slc30a10-deficient mice, while hepatic Hif1a deficiency had no discernible impact. Hepatic Hif2a deficiency also attenuated manganese excess, though the underlying cause of this is not clear at this time. Overall, our results indicate that hepatic HIF2 is a key determinant of pathophysiology in SLC30A10 deficiency and expand our understanding of the contribution of HIFs to human disease.

Ultrasmall Mn-doped iron oxide nanoparticles with dual hepatobiliary and renal clearances for T1 MR liver imaging

Although magnetic nanoparticles demonstrate significant potential as magnetic resonance imaging (MRI) contrast agents, their negative contrasts, liver accumulation, and limited excretion hinder their application. Herein, we developed ultrasmall Mn-doped iron oxide nanoparticles (UMIOs) with distinct advantages as T1 MRI contrast agents. Exceptionally small particle sizes (ca. 2 nm) and magnetization values (5 emu gMn+Fe-1) of UMIOs provided optimal T1 contrast effects with an ideally low r2/r1 value of ∼1. Furthermore, the use of Mn as a dopant facilitated hepatocyte uptake of the particles, allowing liver imaging. In animal studies, UMIOs exhibited significantly enhanced contrasts for sequential T1 imaging of blood vessels and the liver, distinguishing them from conventional magnetic nanoparticles. UMIOs were systematically cleared via dual hepatobiliary and renal excretion pathways, highlighting their safety profile. These characteristics imply substantial potential of UMIOs as T1 contrast agents for the accurate diagnosis of liver diseases.

Lipophilic Group-Modified Manganese(II)-Based Contrast Agents for Vascular and Hepatobiliary Magnetic Resonance Imaging

Effective vascular and hepatic enhancement and better safety are the key drivers for exploring gadolinium-free hepatobiliary contrast agents. Herein, a facile strategy proposes that the high lipophilicity may be favorable to enhancing sequentially vascular and hepatobiliary signal intensity based on the structure-activity relationship that both hepatic uptake and interaction with serum albumins partly depend on lipophilicity. Therefore, 11 newly synthesized derivatives of manganese o-phenylenediamine-N,N,N',N'-tetraacetic acid (MnLs) were evaluated as vascular and hepatobiliary agents. The maximum signal intensities of the heart, liver, and kidneys were strongly correlated with log P, a key indicator of lipophilicity. The most lipophilic agent, MnL6, showed favorable relaxivity when binding with serum albumin, good vascular enhancement, rapid excretion, and reliable hepatobiliary phases comparable to a classic hepatobiliary agent, gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) for in vivo liver tumor imaging. Inhibition experiments confirmed the hepatic targeting of MnL6 is mediated by organic anion-transporting polypeptides.

AAV-mediated hepatic expression of SLC30A10 and the Thr95Ile variant attenuates manganese excess and other phenotypes in Slc30a10-deficient mice

The manganese (Mn) export protein SLC30A10 is essential for Mn excretion via the liver and intestines. Patients with SLC30A10 deficiency develop Mn excess, dystonia, liver disease, and polycythemia. Recent genome-wide association studies revealed a link between the SLC30A10 variant T95I and markers of liver disease. The in vivo relevance of this variant has yet to be investigated. Using in vitro and in vivo models, we explore the impact of the T95I variant on SLC30A10 function. While SLC30A10 I95 expressed at lower levels than T95 in transfected cell lines, both T95 and I95 variants protected cells similarly from Mn-induced toxicity. Adeno-associated virus 8-mediated expression of T95 or I95 SLC30A10 using the liver-specific thyroxine binding globulin promoter normalized liver Mn levels in mice with hepatocyte Slc30a10 deficiency. Furthermore, Adeno-associated virus-mediated expression of T95 or I95 SLC30A10 normalized red blood cell parameters and body weights and attenuated Mn levels and differential gene expression in livers and brains of mice with whole body Slc30a10 deficiency. While our in vivo data do not indicate that the T95I variant significantly compromises SLC30A10 function, it does reinforce the notion that the liver is a key site of SLC30A10 function. It also supports the idea that restoration of hepatic SLC30A10 expression is sufficient to attenuate phenotypes in SLC30A10 deficiency.

Cellular zinc metabolism and zinc signaling: from biological functions to diseases and therapeutic targets

Zinc metabolism at the cellular level is critical for many biological processes in the body. A key observation is the disruption of cellular homeostasis, often coinciding with disease progression. As an essential factor in maintaining cellular equilibrium, cellular zinc has been increasingly spotlighted in the context of disease development. Extensive research suggests zinc's involvement in promoting malignancy and invasion in cancer cells, despite its low tissue concentration. This has led to a growing body of literature investigating zinc's cellular metabolism, particularly the functions of zinc transporters and storage mechanisms during cancer progression. Zinc transportation is under the control of two major transporter families: SLC30 (ZnT) for the excretion of zinc and SLC39 (ZIP) for the zinc intake. Additionally, the storage of this essential element is predominantly mediated by metallothioneins (MTs). This review consolidates knowledge on the critical functions of cellular zinc signaling and underscores potential molecular pathways linking zinc metabolism to disease progression, with a special focus on cancer. We also compile a summary of clinical trials involving zinc ions. Given the main localization of zinc transporters at the cell membrane, the potential for targeted therapies, including small molecules and monoclonal antibodies, offers promising avenues for future exploration.

Genome-Wide Association Study of Blood Mercury in European Pregnant Women and Children

Mercury has high industrial utility and is present in many products, and environmental contamination and occupational exposure are widespread. There are numerous biological systems involved in the absorption, metabolism, and excretion of Hg, and it is possible that some systems may be impacted by genetic variation. If so, genotype may affect tissue concentrations of Hg and subsequent toxic effects. Genome-wide association testing was performed on blood Hg samples from pregnant women of the Avon Longitudinal Study of Parents and Children (n = 2893) and children of the Human Early Life Exposome (n = 1042). Directly-genotyped single-nucleotide polymorphisms (SNPs) were imputed to the Haplotype Reference Consortium r1.1 panel of whole genotypes and modelled againstlog-transformed Hg. Heritability was estimated using linkage disequilibrium score regression. The heritability of Hg was estimated as 24.0% (95% CI: 16.9% to 46.4%) in pregnant women, but could not be determined in children. There were 16 SNPs associated with Hg in pregnant women above a suggestive p-value threshold (p < 1 × 10-5), and 21 for children. However, no SNP passed this threshold in both studies, and none were genome-wide significant (p < 5 × 10-8). SNP-Hg associations were highly discordant between women and children, and this may reflect differences in metabolism, a gene-age interaction, or dose-response effects. Several suggestive variants had plausible links to Hg metabolism, such as rs146099921 in metal transporter SLC39A14, and two variants (rs28618224, rs7154700) in potassium voltage-gated channel genes. The findings would benefit from external validation, as suggestive results may contain both true associations and false positives.

Hepatic and intestinal manganese excretion are both required to regulate brain manganese during elevated manganese exposure

Manganese (Mn) is essential but neurotoxic at elevated levels. Under physiological conditions, Mn is primarily excreted by the liver, with the intestines playing a secondary role. Recent analyses of tissue-specific Slc30a10 or Slc39a14 knockout mice (SLC30A10 and SLC39A14 are Mn transporters) revealed that, under physiological conditions: 1) excretion of Mn by the liver and intestines is a major pathway that regulates brain Mn; and surprisingly, 2) the intestines compensate for loss of hepatic Mn excretion in controlling brain Mn. The unexpected importance of the intestines in controlling physiological brain Mn led us to determine the role of hepatic and intestinal Mn excretion in regulating brain Mn during elevated Mn exposure. We used liver- or intestine-specific Slc30a10 knockout mice as models to inhibit hepatic or intestinal Mn excretion. Compared with littermates, both knockout strains exhibited similar increases in brain Mn after elevated Mn exposure in early or later life. Thus, unlike physiological conditions, both hepatic and intestinal Mn excretion are required to control brain Mn during elevated Mn exposure. However, brain Mn levels of littermates and both knockout strains exposed to elevated Mn only in early life were normalized in later life. Thus, hepatic and intestinal Mn excretion play compensatory roles in clearing brain Mn accumulated by early life Mn exposure. Finally, neuromotor assays provided evidence consistent with a role for hepatic and intestinal Mn excretion in functionally modulating Mn neurotoxicity during Mn exposure. Put together, these findings substantially enhance understanding of the regulation of brain Mn by excretion.NEW & NOTEWORTHY This article shows that, in contrast with expectations from prior studies and physiological conditions, excretion of manganese by the intestines and liver is equally important in controlling brain manganese during human-relevant manganese exposure. The results provide foundational insights about the interorgan mechanisms that control brain manganese homeostasis at the organism level and have important implications for the development of therapeutics to treat manganese-induced neurological disease.

Targeting Labile Iron-Mediated Ferroptosis Provides a Potential Therapeutic Strategy for Rhabdomyolysis-Induced Acute Kidney Injury

Acute kidney injury (AKI) is a global health problem that occurs in a variety of clinical settings. Despite some advances in supportive clinical care, no medicinal intervention has been demonstrated to reliably prevent AKI thus far. Therefore, it is highly necessary to investigate the pathophysiology and mechanisms involved in AKI for the discovery of therapeutics. In the current study, a robust change in the level of renal malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE) and elevated renal iron levels were observed in murine rhabdomyolysis-induced AKI (RM-AKI), which supports a pathogenic role of labile iron-mediated ferroptosis and provides a chance to utilize iron chelation for RM-AKI prevention. Given that the existing small molecule-based iron chelators did not show promising preventative effects against RM-AKI, we further designed and synthesized a new hydroxypyridinone-based iron chelator to potently inhibit labile iron-mediated ferroptosis. Lead compound AKI-02 was identified, which remarkably protected renal proximal tubular epithelial cells from ferroptosis as well as showed excellent iron chelation ability. Moreover, administration of AKI-02 led to renal function recovery, a result that was substantiated by the decreased contents of BUN and creatinine, as well as the reduced labile iron level and improved histopathology. Thus, our studies highlighted that targeting labile iron-mediated ferroptosis could provide therapeutic benefits against RM-AKI.

Physiology of Dystonia: Animal Studies

Dystonia is currently ranked as the third most prevalent motor disorder. It is typically characterized by involuntary muscle over- or co-contractions that can cause painful abnormal postures and jerky movements. Dystonia is a heterogenous disorder-across patients, dystonic symptoms vary in their severity, body distribution, temporal pattern, onset, and progression. There are also a growing number of genes that are associated with hereditary dystonia. In addition, multiple brain regions are associated with dystonic symptoms in both genetic and sporadic forms of the disease. The heterogeneity of dystonia has made it difficult to fully understand its underlying pathophysiology. However, the use of animal models has been used to uncover the complex circuit mechanisms that lead to dystonic behaviors. Here, we summarize findings from animal models harboring mutations in dystonia-associated genes and phenotypic animal models with overt dystonic motor signs resulting from spontaneous mutations, neural circuit perturbations, or pharmacological manipulations. Taken together, an emerging picture depicts dystonia as a result of brain-wide network dysfunction driven by basal ganglia and cerebellar dysfunction. In the basal ganglia, changes in dopaminergic, serotonergic, noradrenergic, and cholinergic signaling are found across different animal models. In the cerebellum, abnormal burst firing activity is observed in multiple dystonia models. We are now beginning to unveil the extent to which these structures mechanistically interact with each other. Such mechanisms inspire the use of pre-clinical animal models that will be used to design new therapies including drug treatments and brain stimulation.

A hepatocyte-targeting nanoparticle for enhanced hepatobiliary magnetic resonance imaging

Hepatobiliary magnetic resonance imaging (MRI) can inform the diagnosis of liver tumours in patients with liver cirrhosis and hepatitis. However, its clinical utility has been hampered by the lack of sensitive and specific contrast agents, partly because hepatocyte-specific nanoparticles, regardless of their surface ligands, are readily sequestered by Kupffer cells. Here we show, in rabbits, pigs and macaques, that the performance of hepatobiliary MRI can be enhanced by an ultrasmall nanoparticle composed of a manganese ferrite core (3 nm in diameter) and poly(ethylene glycol)-ethoxy-benzyl surface ligands binding to hepatocyte-specific transmembrane metal and anion transporters. The nanoparticle facilitated faster, more sensitive and higher-resolution hepatobiliary MRI than the clinically used contrast agent gadoxetate disodium, a substantial enhancement in the detection rate (92% versus 48%) of early-stage liver tumours in rabbits, and a more accurate assessment of biliary obstruction in macaques. The nanoparticle's performance and biocompatibility support the further translational development of liver-specific MRI contrast agents.

The Impact of Zinc on Manganese Bioavailability and Cytotoxicity in HepG2 Cells

SCOPE

Despite their essentiality, several studies have shown that either manganese (Mn) or zinc (Zn) overexposure may lead to detrimental health effects. Although Mn is transported by some of the SLC family transporters that translocate Zn, the role of Zn in hepatocellular Mn transport and Mn-induced toxicity have yet to be fully characterized.

METHODS AND RESULTS

The human hepatoma cell line, HepG2, is utilized. Total cellular Mn and Zn amounts are determined after cells are treated with Zn 2 or 24 h prior to Mn incubation for additional 24 h with inductively coupled plasma-based spectrometry and labile Zn is assessed with the fluorescent probe FluoZin-3. Furthermore, mRNA expression of genes involved in metal homeostasis, and mechanistic endpoints associated with Mn-induced cytotoxicity are addressed. These results suggest that Zn protects against Mn-induced cytotoxicity and impacts Mn bioavailability to a great extent when cells are preincubated with higher Zn concentrations for longer duration as characterized by decreased activation of caspase-3 as well as lactate dehydrogenase (LDH) release.

CONCLUSIONS

Zn protects against Mn-induced cytotoxicity in HepG2 cells possibly due to decreased Mn bioavailability. Additionally, mRNA expression of metal homeostasis-related genes indicates possible underlying pathways that should to be addressed in future studies.

Hypoxia-inducible factor 2 is a key determinant of manganese excess and polycythemia in SLC30A10 deficiency

Manganese is an essential yet potentially toxic metal. Initially reported in 2012, mutations in SLC30A10 are the first known inherited cause of manganese excess. SLC30A10 is an apical membrane transport protein that exports manganese from hepatocytes into bile and from enterocytes into the lumen of the gastrointestinal tract. SLC30A10 deficiency results in impaired gastrointestinal manganese excretion, leading to severe manganese excess, neurologic deficits, liver cirrhosis, polycythemia, and erythropoietin excess. Neurologic and liver disease are attributed to manganese toxicity. Polycythemia is attributed to erythropoietin excess, but the basis of erythropoietin excess in SLC30A10 deficiency has yet to be established. Here we demonstrate that erythropoietin expression is increased in liver but decreased in kidneys in Slc30a10-deficient mice. Using pharmacologic and genetic approaches, we show that liver expression of hypoxia-inducible factor 2 (Hif2), a transcription factor that mediates the cellular response to hypoxia, is essential for erythropoietin excess and polycythemia in Slc30a10-deficient mice, while hypoxia-inducible factor 1 (HIF1) plays no discernible role. RNA-seq analysis determined that Slc30a10-deficient livers exhibit aberrant expression of a large number of genes, most of which align with cell cycle and metabolic processes, while hepatic Hif2 deficiency attenuates differential expression of half of these genes in mutant mice. One such gene downregulated in Slc30a10-deficient mice in a Hif2-dependent manner is hepcidin, a hormonal inhibitor of dietary iron absorption. Our analyses indicate that hepcidin downregulation serves to increase iron absorption to meet the demands of erythropoiesis driven by erythropoietin excess. Finally, we also observed that hepatic Hif2 deficiency attenuates tissue manganese excess, although the underlying cause of this observation is not clear at this time. Overall, our results indicate that HIF2 is a key determinant of pathophysiology in SLC30A10 deficiency.

Recent progress toward understanding the role of ZIP14 in regulating systemic manganese homeostasis

ZIP14 is a metal transporter essential for the regulation of body manganese homeostasis. The physiological functions of ZIP14 have been uncovered mainly through two lines of in vivo studies that examined the phenotypes of ZIP14 loss, including studies of humans with ZIP14 mutations and animals with ZIP14 deficiency. This mini review aims at presenting an updated view of the important advances made towards understanding the genetic and pathological mechanisms of brain manganese overload caused by ZIP14 deficiency.

The cGAS-STING-autophagy pathway: Novel perspectives in neurotoxicity induced by manganese exposure

Chronic high-level heavy metal exposure increases the risk of developing different neurodegenerative diseases. Chronic excessive manganese (Mn) exposure is known to lead to neurodegenerative diseases. In addition, some evidence suggests that autophagy dysfunction plays an important role in the pathogenesis of various neurodegenerative diseases. Over the past decade, the DNA-sensing receptor cyclic GMP-AMP synthase (cGAS) and its downstream signal-efficient interferon gene stimulator (STING), as well as the molecular composition and regulatory mechanisms of this pathway have been well understood. The cGAS-STING pathway has emerged as a crucial mechanism to induce effective innate immune responses by inducing type I interferons in mammalian cells. Moreover, recent studies have found that Mn²⁺ is the second activator of the cGAS-STING pathway besides dsDNA, and inducing autophagy is a primitive function for the activation of the cGAS-STING pathway. However, overactivation of the immune response can lead to tissue damage. This review discusses the mechanism of neurotoxicity induced by Mn exposure from the cGAS-STING-autophagy pathway. Future work exploiting the cGAS-STING-autophagy pathway may provide a novel perspective for manganese neurotoxicity.

Hereditary Disorders of Manganese Metabolism: Pathophysiology of Childhood-Onset Dystonia-Parkinsonism in SLC39A14 Mutation Carriers and Genetic Animal Models

Over the last decade, several clinical reports have outlined cases of childhood-onset manganese (Mn)-induced dystonia-parkinsonism, resulting from loss-of-function mutations in the Mn influx transporter gene SLC39A14. These clinical cases have provided a wealth of knowledge on Mn toxicity and homeostasis. However, our current understanding of the underlying neuropathophysiology is severely lacking. The recent availability of Slc39a14 knockout (KO) murine and zebrafish animal models provide a powerful platform to investigate the neurological effects of elevated blood and brain Mn concentrations in vivo. As such, the objective of this review was to organize and summarize the current clinical literature and studies utilizing Slc39a14-KO animal models and assess the validity of the animal models based on the clinical presentation of the disease in human mutation carriers.

Clinical Profile and Treatment Outcomes of Hypermanganesemia with Dystonia 1 and 2 among 27 Indian Children

Background

Hypermanganesemia with dystonia 1 and 2 (HMNDYT1 and 2) are rare, inherited disorders of manganese transport.

Objectives

We aimed to describe clinical, laboratory features, and outcomes among children with HMNDYT.

Methods

We conducted a retrospective multicenter study involving tertiary centers across India. We enrolled children between 1 month to 18 years of age with genetically confirmed/clinically probable HMNDYT. Clinical, laboratory profile, genetic testing, treatment details, and outcomes scored by treating physicians on a Likert scale were recorded.

Results

We enrolled 27 children (19 girls). Fourteen harbored SLC30A10 mutations; nine had SLC39A14 mutations. The SLC39A14 cohort had lower median age at onset (1.3 [interquartile range (IQR), 0.7-5.5] years) versus SLC30A10 cohort (2.0 [IQR, 1.5-5.1] years). The most frequent neurological features were dystonia (100%; n = 27), gait abnormality (77.7%; n = 21), falls (66.7%; n = 18), and parkinsonism (59.3%; n = 16). Median serum manganese (Mn) levels among SLC39A14 (44.9 [IQR, 27.3-147.7] mcg/L) cohort were higher than SLC30A10 (29.4 [17.1-42.0] mcg/L); median hemoglobin was higher in SLC30A10 (16.3 [IQR, 15.2-17.5] g/dL) versus SLC39A14 cohort (12.5 [8.8-13.2] g/dL). Hepatic involvement and polycythaemia were observed exclusively in SLC30A10 variants. A total of 26/27 children underwent chelation with disodium calcium edetate. Nine demonstrated some improvement, three stabilized, two had marked improvement, and one had normalization. Children with SLC39A14 mutations had poorer response. Two children died and nine were lost to follow-up.

Conclusions

We found female predominance. Children with SLC39A14 mutations presented at younger age and responded less favorably to chelation compared to SLC30A10 mutations. There is emerging need to better define management strategies, especially in low resource settings.

Pathophysiological studies of aging Slc39a14 knockout mice to assess the progression of manganese-induced dystonia-parkinsonism

Over the last decade, several clinical reports have outlined cases of early-onset manganese (Mn)-induced dystonia-parkinsonism, resulting from loss of function mutations of the Mn transporter gene SLC39A14. Previously, we have performed characterization of the behavioral, neurochemical, and neuropathological changes in 60-day old (PN60) Slc39a14-knockout (KO) murine model of the human disease. Here, we extend our studies to aging Slc39a14-KO mice to assess the progression of the disease. Our results indicate that 365-day old (PN365) Slc39a14-KO mice present with markedly elevated blood and brain Mn levels, similar to those found in the PN60 mice and representative of the human cases of the disease. Furthermore, aging Slc39a14-KO mice consistently manifest a hypoactive and dystonic behavioral deficits, similar to the PN60 animals, suggesting that the behavioral changes are established early in life without further age-associated deterioration. Neurochemical, neuropathological, and functional assessment of the dopaminergic system of the basal ganglia revealed absence of neurodegenerative changes of dopamine (DA) neurons in the substantia nigra pars compacta (SNc), with no changes in DA or metabolite concentrations in the striatum of Slc39a14-KO mice relative to wildtype (WT). Similar to the PN60 animals, aging Slc39a14-KO mice expressed a marked inhibition of potassium-stimulated DA release in the striatum. Together our findings indicate that the pathophysiological changes observed in the basal ganglia of aging Slc39a14-KO animals are similar to those at PN60 and aging does not have a significant effect on these parameters.

Mn(II)-Mediated Self-Assembly of Tea Polysaccharide Nanoparticles and Their Functional Role in Mice with Type 2 Diabetes

Tea polysaccharide (TPS) is a bioactive compound that has attracted increasing attention for its health effect on regulating the metabolism of glucose and lipid. Moreover, due to their good biocompatibility and biodegradability, TPS-based nanoparticles have emerged as effective nanocarriers for the delivery of bioactive molecules. In this study, we developed a TPS-based biocarrier system for the orally targeted administration of Mn(II) ions and investigated their antidiabetic effects in C57BL/6 mice with HFD/streptozotocin (STZ)-induced T2DM. Mn(II)-loaded TPS-based nanoparticles (MTNPs) were synthesized, in which negatively charged functional groups in protein and uronic acid in TPS conjugates would act as binding sites for Mn(II) ions, which is responsible for the cross-linking reaction of MTNP. The resulting MTNP had a spherical shape and a mean particle size of around 30 nm with a Mn(II) ion content of 2.24 ± 0.13 mg/g. In T2DM mice, we discovered that MTNP treatment significantly lowered blood glucose levels and improved glucose intolerance. Furthermore, the impact of MTNP on the recovery of FINS, the homeostatic index of insulin resistance (HOMA-IR), and the homeostatic index of β-cell (HOMA β-cell) levels was significantly larger (p < 0.05) than TPS alone, demonstrating that Mn(II) ions can enhance TPS's ability to repair HFD/STZ-induced β-cell damage. Mn(II) ions in MTNP not only acted as cofactors to increase the exocytosis of insulin secretory cells by upregulating the expression of Ca(II)/calmodulin-dependent protein kinase II (CaMK II) but also promoted TPS's lipid-lowering effect in T2DM mice by inhibiting glucogenesis and regulating the lipid metabolism. Our findings suggest that Mn(II) ions can be used not only as cross-linkers in the formation of nanoparticulated TPS but also as cofactors in improving the functional role of TPS in regulating the glucose and lipid metabolism, which will provide insights into the development of TPS-based drug delivery systems for the prevention of type 2 diabetes.

Use of Circular RNAs in Diagnosis, Prognosis and Therapeutics of Renal Cell Carcinoma

Renal cell carcinoma is the most common type of kidney cancer, representing 90% of kidney cancer diagnoses, and the deadliest urological cancer. While the incidence and mortality rates by renal cell carcinoma are higher in men compared to women, in both sexes the clinical characteristics are the same, and usually unspecific, thereby hindering and delaying the diagnostic process and increasing the metastatic potential. Regarding treatment, surgical resection remains the main therapeutic strategy. However, even after radical nephrectomy, metastasis may still occur in some patients, with most metastatic renal cell carcinomas being resistant to chemotherapy and radiotherapy. Therefore, the identification of new biomarkers to help clinicians in the early detection, and treatment of renal cell carcinoma is essential. In this review, we describe circRNAs related to renal cell carcinoma processes reported to date and propose the use of some in therapeutic strategies for renal cell carcinoma treatment.

The Combined Inactivation of Intestinal and Hepatic ZIP14 Exacerbates Manganese Overload in Mice

ZIP14 is a newly identified manganese transporter with high levels of expression in the small intestine and the liver. Loss-of-function mutations in ZIP14 can lead to systemic manganese overload, which primarily affects the central nervous system, causing neurological disorders. To elucidate the roles of intestinal ZIP14 and hepatic ZIP14 in maintaining systemic manganese homeostasis, we generated mice with single-tissue or two-tissue Zip14 knockout, including intestine-specific (Zip14-In-KO), liver-specific (Zip14-L-KO), and double (intestine and liver) Zip14-knockout (Zip14-DKO) mice. Zip14^flox/flox mice were used as the control. Tissue manganese contents in these mice were compared using inductively coupled plasma mass spectrometry (ICP-MS) analysis. We discovered that although the deletion of intestinal ZIP14 only moderately increased systemic manganese loading, the deletion of both intestinal and hepatic ZIP14 greatly exacerbated the body's manganese burden. Our results provide new knowledge to further the understanding of manganese metabolism, and offer important insights into the mechanisms underlying systemic manganese overload caused by the loss of ZIP14.

Role of excretion in manganese homeostasis and neurotoxicity: a historical perspective

The essential metal manganese (Mn) induces incurable neurotoxicity at elevated levels that manifests as parkinsonism in adults and fine motor and executive function deficits in children. Studies on Mn neurotoxicity have largely focused on the role and mechanisms of disease induced by elevated Mn exposure from occupational or environmental sources. In contrast, the critical role of excretion in regulating Mn homeostasis and neurotoxicity has received less attention although 1) studies on Mn excretion date back to the 1920s; 2) elegant radiotracer Mn excretion assays in the 1940s to 1960s established the routes of Mn excretion; and 3) studies on patients with liver cirrhosis in the 1990s to 2000s identified an association between decreased Mn excretion and the risk of developing Mn-induced parkinsonism in the absence of elevated Mn exposure. Notably, the last few years have seen renewed interest in Mn excretion largely driven by the discovery that hereditary Mn neurotoxicity due to mutations in SLC30A10 or SLC39A14 is caused, at least in part, by deficits in Mn excretion. Quite remarkably, some of the recent results on SLC30A10 and SLC39A14 provide explanations for observations made ∼40-50 years ago. The goal of the current review is to integrate the historic studies on Mn excretion with more contemporary recent work and provide a comprehensive state-of-the-art overview of Mn excretion and its role in regulating Mn homeostasis and neurotoxicity. A related goal is to discuss the significance of some of the foundational studies on Mn excretion so that these highly consequential earlier studies remain influential in the field.

A novel homozygous SLC39A14 variant in an infant with hypermanganesemia and a review of the literature

BACKGROUND

Manganese (Mn) is an essential trace metal necessary for good health; however, excessive amounts in the body are neurotoxic. To date, three genes (SLC30A10, SLC39A8, and SLC39A14) have been discovered to cause inborn errors in Mn metabolism in humans. As very rare diseases, the clinical features require further clarification.

METHODS

A male Chinese patient who mainly presented with hypermanganesemia and progressive parkinsonism-dystonia was recruited for this study. We collected and analyzed clinical information, performed whole-exome sequencing (WES), and reviewed the relevant literature.

RESULTS

The motor-developmental milestones of the patient were delayed at the age of 4 months, followed by rapidly progressive dystonia. The patient displayed elevated Mn concentrations in blood and urine, and brain magnetic resonance imaging (MRI) showed symmetrical hyperintensity on T1-weighted images and hypointensity on T2-weighted images in multiple regions. A novel homozygous variant of the SLC39A14 gene (c.1058T > G, p.L353R) was identified. The patient was treated with disodium calcium edetate chelation (Na₂CaEDTA). Three months later, mild improvement in clinical manifestation, blood Mn levels, and brain MRI was observed. To date, 15 patients from 10 families have been reported with homozygous mutations of SLC39A14, with a mean age of onset of 14.9 months. The common initial symptom is motor regression or developmental milestone delay, with a disease course for nearly all patients involving development of progressive generalized dystonia and loss of ambulation before treatment. Additionally, hypermanganesemia manifests as Mn values ranging from 4- to 25-fold higher than normal baseline levels, along with brain MRI results similar to those observed in the recruited patient. Nine SLC39A14 variants have been identified. Seven patients have been treated with Na₂CaEDTA, and only one patient achieved obvious clinical improvement.

CONCLUSION

We identified a novel SLC39A14 mutation related to autosomal recessive hypermanganesemia with dystonia-2, which is a very rare disease. Patients present motor regression or delay of developmental milestones and develop progressive generalized dystonia. Chelation therapy with Na₂CaEDTA appears to effectively chelate Mn and increase urinary Mn excretion in some cases; however, clinical response varies. The outcome of the disease was unsatisfactory. This study expands the genetic spectrum of this disease.

Manganese transport in mammals by zinc transporter family proteins, ZNT and ZIP

Manganese (Mn) is an essential trace element required for various biological processes. However, excess Mn causes serious side effects in humans, including parkinsonism. Thus, elucidation of Mn homeostasis at the systemic, cellular, and molecular levels is important. Many metal transporters and channels can be involved in the transport and homeostasis of Mn, and an increasing body of evidence shows that several zinc (Zn) transporters belonging to the ZIP and ZNT families, specifically, ZNT10, ZIP8, and ZIP14, play pivotal roles in Mn metabolism. Mutations in the genes encoding these transporter proteins are associated with congenital disorders related to dysregulated Mn homeostasis in humans. Moreover, single nucleotide polymorphisms of ZIP8 are associated with multiple clinical phenotypes. In this review, we discuss the recent literature on the structural and biochemical features of ZNT10, ZIP8, and ZIP14, including transport mechanisms, regulation of expression, and pathophysiological functions. Because a disturbance in Mn homeostasis is closely associated with a variety of phenotypes and risk of human diseases, these transporters constitute a significant target for drug development. An understanding of the roles of these key transporters in Mn metabolism should provide new insights into pharmacological applications of their inhibitors and enhancers in human diseases.

Up-regulation of the manganese transporter SLC30A10 by hypoxia-inducible factors defines a homeostatic response to manganese toxicity

Manganese (Mn) is an essential metal that induces incurable parkinsonism at elevated levels. However, unlike other essential metals, mechanisms that regulate mammalian Mn homeostasis are poorly understood, which has limited therapeutic development. Here, we discovered that the exposure of mice to a translationally relevant oral Mn regimen up-regulated expression of SLC30A10, a critical Mn efflux transporter, in the liver and intestines. Mechanistic studies in cell culture, including primary human hepatocytes, revealed that 1) elevated Mn transcriptionally up-regulated SLC30A10, 2) a hypoxia response element in the SLC30A10 promoter was necessary, 3) the transcriptional activities of hypoxia-inducible factor (HIF) 1 or HIF2 were required and sufficient for the SLC30A10 response, 4) elevated Mn activated HIF1/HIF2 by blocking the prolyl hydroxylation of HIF proteins necessary for their degradation, and 5) blocking the Mn-induced up-regulation of SLC30A10 increased intracellular Mn levels and enhanced Mn toxicity. Finally, prolyl hydroxylase inhibitors that stabilize HIF proteins and are in advanced clinical trials for other diseases reduced intracellular Mn levels and afforded cellular protection against Mn toxicity and also ameliorated the in vivo Mn-induced neuromotor deficits in mice. These findings define a fundamental homeostatic protective response to Mn toxicity-elevated Mn levels activate HIF1 and HIF2 to up-regulate SLC30A10, which in turn reduces cellular and organismal Mn levels, and further indicate that it may be possible to repurpose prolyl hydroxylase inhibitors for the management of Mn neurotoxicity.

Gestational Cd Exposure in the CD-1 Mouse Induces Sex-Specific Hepatic Insulin Insensitivity, Obesity, and Metabolic Syndrome in Adult Female Offspring

There is compelling evidence that developmental exposure to toxic metals increases risk for obesity and obesity-related morbidity including cardiovascular disease and type 2 diabetes. To explore the hypothesis that developmental Cd exposure increases risk of obesity later in life, male, and female CD-1 mice were maternally exposed to 500 ppb CdCl2 in drinking water during a human gestational equivalent period (gestational day 0-postnatal day 10 [GD0-PND10]). Hallmark indicators of metabolic disruption, hepatic steatosis, and metabolic syndrome were evaluated prior to birth through adulthood. Maternal blood Cd levels were similar to those observed in human pregnancy cohorts, and Cd was undetected in adult offspring. There were no observed impacts of exposure on dams or pregnancy-related outcomes. Results of glucose and insulin tolerance testing revealed that Cd exposure impaired offspring glucose homeostasis on PND42. Exposure-related increases in circulating triglycerides and hepatic steatosis were apparent only in females. By PND120, Cd-exposed females were 30% heavier with 700% more perigonadal fat than unexposed control females. There was no evidence of dyslipidemia, steatosis, increased weight gain, nor increased adiposity in Cd-exposed male offspring. Hepatic transcriptome analysis on PND1, PND21, and PND42 revealed evidence for female-specific increases in oxidative stress and mitochondrial dysfunction with significant early disruption of retinoic acid signaling and altered insulin receptor signaling consistent with hepatic insulin sensitivity in adult females. The observed steatosis and metabolic syndrome-like phenotypes resulting from exposure to 500 ppb CdCl2 during the pre- and perinatal period of development equivalent to human gestation indicate that Cd acts developmentally as a sex-specific delayed obesogen.

Behavioral and neurochemical studies of inherited manganese-induced dystonia-parkinsonism in Slc39a14-knockout mice

Inherited autosomal recessive mutations of the manganese (Mn) transporter gene SLC39A14 in humans, results in elevated blood and brain Mn concentrations and childhood-onset dystonia-parkinsonism. The pathophysiology of this disease is unknown, but the nigrostriatal dopaminergic system of the basal ganglia has been implicated. Here, we describe pathophysiological studies in Slc39a14-knockout (KO) mice as a preclinical model of dystonia-parkinsonism in SLC39A14 mutation carriers. Blood and brain metal concentrations in Slc39a14-KO mice exhibited a pattern similar to the human disease with highly elevated Mn concentrations. We observed an early-onset backward-walking behavior at postnatal day (PN) 21 which was also noted in PN60 Slc39a14-KO mice as well as dystonia-like movements. Locomotor activity and motor coordination were also impaired in Slc39a14-KO relative to wildtype (WT) mice. From a neurochemical perspective, striatal dopamine (DA) and metabolite concentrations and their ratio in Slc39a14-KO mice did not differ from WT. Striatal tyrosine hydroxylase (TH) immunohistochemistry did not change in Slc39a14-KO mice relative to WT. Unbiased stereological cell quantification of TH-positive and Nissl-stained estimated neuron number, neuron density, and soma volume in the substantia nigra pars compacta (SNc) was the same in Slc39a14-KO mice as in WT. However, we measured a marked inhibition (85-90%) of potassium-stimulated DA release in the striatum of Slc39a14-KO mice relative to WT. Our findings indicate that the dystonia-parkinsonism observed in this genetic animal model of the human disease is associated with a dysfunctional but structurally intact nigrostriatal dopaminergic system. The presynaptic deficit in DA release is unlikely to explain the totality of the behavioral phenotype and points to the involvement of other neuronal systems and brain regions in the pathophysiology of the disease.

The impact of environmental and occupational exposures of manganese on pulmonary, hepatic, and renal functions

Manganese (Mn) is an essential trace element for humans, but long-term environmental or occupational exposures can lead to numerous health problems. Although many studies have identified an association between Mn exposures and neurological abnormalities, emerging data suggest that occupationally and environmentally relevant levels of Mn may also be linked to multiple organ dysfunction in the general population. In this regard, many experimental and clinical studies provide support for a causal link between Mn exposure and structural and functional changes that are responsible for organ dysfunction in major organs like lung, liver, and kidney. The underlying mechanisms suggested to Mn toxicity include altered activities of the components of intracellular signaling cascades, oxidative stress, apoptosis, affected cell cycle regulation, autophagy, angiogenesis, and an inflammatory response. We further discussed the sources and possible mechanisms of Mn absorption and distribution in different organs. Finally, treatment strategies available for treating Mn toxicity as well as directions for future studies were discussed.

Biliary excretion of excess iron in mice requires hepatocyte iron import by Slc39a14

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.

Insight into Crosstalk between Ferroptosis and Necroptosis: Novel Therapeutics in Ischemic Stroke

Ferroptosis is a nonapoptotic form of cell death characterized by iron-dependent accumulation of lipid hydroperoxides to lethal levels. Necroptosis, an alternative form of programmed necrosis, is regulated by receptor-interacting protein (RIP) 1 activation and by RIP3 and mixed-lineage kinase domain-like (MLKL) phosphorylation. Ferroptosis and necroptosis both play important roles in the pathological progress in ischemic stroke, which is a complex brain disease regulated by several cell death pathways. In the past few years, increasing evidence has suggested that the crosstalk occurs between necroptosis and ferroptosis in ischemic stroke. However, the potential links between ferroptosis and necroptosis in ischemic stroke have not been elucidated yet. Hence, in this review, we overview and analyze the mechanism underlying the crosstalk between necroptosis and ferroptosis in ischemic stroke. And we find that iron overload, one mechanism of ferroptosis, leads to mitochondrial permeability transition pore (MPTP) opening, which aggravates RIP1 phosphorylation and contributes to necroptosis. In addition, heat shock protein 90 (HSP90) induces necroptosis and ferroptosis by promoting RIP1 phosphorylation and suppressing glutathione peroxidase 4 (GPX4) activation. In this work, we try to deliver a new perspective in the exploration of novel therapeutic targets for the treatment of ischemic stroke.

Restriction of Manganese Intake Prevents the Onset of Brain Manganese Overload in Zip14-/- Mice

As a newly identified manganese transport protein, ZIP14 is highly expressed in the small intestine and liver, which are the two principal organs involved in regulating systemic manganese homeostasis. Loss of ZIP14 function leads to manganese overload in both humans and mice. Excess manganese in the body primarily affects the central nervous system, resulting in irreversible neurological disorders. Therefore, to prevent the onset of brain manganese accumulation becomes critical. In this study, we used Zip14^−/− mice as a model for ZIP14 deficiency and discovered that these mice were born without manganese loading in the brain, but started to hyper-accumulate manganese within 3 weeks after birth. We demonstrated that decreasing manganese intake in Zip14^−/− mice was effective in preventing manganese overload that typically occurs in these animals. Our results provide important insight into future studies that are targeted to reduce the onset of manganese accumulation associated with ZIP14 dysfunction in humans.

A hierarchy of manganese competition and entry in organotypic hippocampal slice cultures

Contrast agents improve clinical and basic research MRI. The manganese ion (Mn²⁺ ) is an essential, endogenous metal found in cells and it enhances MRI contrast because of its paramagnetic properties. Manganese-enhanced MRI (MEMRI) has been widely used to image healthy and diseased states of the body and the brain in a variety of animal models. There has also been some work in translating the useful properties of MEMRI to humans. Mn²⁺ accumulates in brain regions with high neural activity and enters cells via voltage-dependent channels that flux calcium (Ca²⁺ ). In addition, metal transporters for zinc (Zn²⁺ ) and iron (Fe²⁺ ) can also transport Mn²⁺ . There is also transfer through channels specific for Mn²⁺ . Although Mn²⁺ accumulates in many tissues including brain, the mechanisms and preferences of its mode of entry into cells are not well characterized. The current study used MRI on living organotypic hippocampal slice cultures to detect which transport mechanisms are preferentially used by Mn²⁺ to enter cells. The use of slice culture overcomes the presence of the blood brain barrier, which limits inferences made with studies of the intact brain in vivo. A range of Mn²⁺ concentrations were used and their effects on neural activity were assessed to avoid using interfering doses of Mn²⁺ . Zn²⁺ and Fe²⁺ were the most efficient competitors for Mn²⁺ uptake into the cultured slices, while the presence of Ca²⁺ or Ca²⁺ channel antagonists had a more moderate effect. Reducing slice activity via excitatory receptor antagonists was also effective at lowering Mn²⁺ uptake. In conclusion, a hierarchy of those agents which influence Mn²⁺ uptake was established to enhance understanding of how Mn²⁺ enters cells in a cultured slice preparation.

Characterization of in vitro models of SLC30A10 deficiency

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 ⁵⁴Mn import and export in mutant cells. While impaired ⁵⁴Mn export was hypothesized given the essential role for SLC30A10 in cellular Mn export, impaired ⁵⁴Mn 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 ⁵⁴Mn 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.

Inherited Manganese Disorders and the Brain: What Neurologists Need to Know

Although acquired manganese neurotoxicity has been widely reported since its first description in 1837 and is popularly referred to as "manganism," inherited disorders of manganese homeostasis have received the first genetic signature as recently as 2012. These disorders, predominantly described in children and adolescents, involve mutations in three manganese transporter genes, i.e., SLC30A10 and SLC39A14 which lead to manganese overload, and SLC39A8, which leads to manganese deficiency. Both disorders of inherited hypermanganesemia typically exhibit dystonia and parkinsonism with relatively preserved cognition and are differentiated by the occurrence of polycythemia and liver involvement in the SLC30A10-associated condition. Mutations in SLC39A8 lead to a congenital disorder of glycosylation which presents with developmental delay, failure to thrive, intellectual impairment, and seizures due to manganese deficiency. Chelation with iron supplementation is the treatment of choice in inherited hypermanganesemia. In this review, we highlight the pathognomonic clinical, laboratory, imaging features and treatment modalities for these rare disorders.

Nanoparticle-induced ferroptosis: detection methods, mechanisms and applications

Although ferroptosis is an iron-dependent cell death mechanism involved in the development of some severe diseases (e.g., Parkinsonian syndrome, stroke and tumours), the combination of nanotechnology with ferroptosis for the treatment of these diseases has attracted substantial research interest. However, it is challenging to differentiate nanoparticle-induced ferroptosis from other types of cell deaths (e.g., apoptosis, pyroptosis, and necrosis), elucidate the detailed mechanisms and identify the key property of nanoparticles responsible for ferroptotic cell deaths. Therefore, a summary of these aspects from current research on nano-ferroptosis is important and timely. In this review, we endeavour to summarize some convincing techniques that can be employed to specifically examine ferroptotic cell deaths. Then, we discuss the molecular initiating events of nanosized ferroptosis inducers and the cascade signals in cells, and therefore elaborate the ferroptosis mechanisms. Besides, the key physicochemical properties of nano-inducers are also discussed to acquire a fundamental understanding of nano-structure-activity relationships (nano-SARs) involved in ferroptosis, which may facilitate the design of nanomaterials to deliberately tune ferroptosis. Finally, future perspectives on the fundamental understanding of nanoparticle-induced ferroptosis and its applications are provided.

Manganese homeostasis at the host-pathogen interface and in the host immune system

Manganese serves as an indispensable catalytic center and the structural core of various enzymes that participate in a plethora of biological processes, including oxidative phosphorylation, glycosylation, and signal transduction. In pathogenic microorganisms, manganese is required for survival by maintaining basic biochemical activity and virulence; in contrast, the host utilizes a process known as nutritional immunity to sequester manganese from invading pathogens. Recent epidemiological and animal studies have shown that manganese increases the immune response in a wide range of vertebrates, including humans, rodents, birds, and fish. On the other hand, excess manganese can cause neurotoxicity and other detrimental effects. Here, we review recent data illustrating the essential role of manganese homeostasis at the host-pathogen interface and in the host immune system. We also discuss the accumulating body of evidence that manganese modulates various signaling pathways in immune processes. Finally, we discuss the key molecular players involved in manganese's immune regulatory function, as well as the clinical implications with respect to cancer immunotherapy.