Zn2+ efflux through lysosomal exocytosis prevents Zn2+-induced toxicity

ZnT 9 Involvement in Estradiol-Modulated Zinc Homeostasis of the Human Follicular Microenvironment

Female subfertility has been a growing concern for reproductive health. Assisted reproductive technologies make pregnancy possible, but the outcome rate is still suboptimal. Zinc is an essential factor for fertility and development. Zinc levels in follicular fluids were measured by electrochemical method, and we found that zinc in the follicular fluids was related to high-quality embryo rate (R = 0.39, p = 0.01). Basal estradiol levels and estradiol levels on the day of HCG injection were negatively correlated with zinc concentrations in the follicular fluid (R =  - 0.53, p < 0.001; R =  - 0.32, p < 0.05), and estradiol promoted ZnT 9 protein expression in cumulus granulosa cells in vitro and in vivo. When the zinc level was at 3.63-3.85 μg/mL, follicular fluid samples had the highest SOD activity. Therefore, zinc played an important role in improving oocyte development by increasing antioxidant capacity. Our results suggested that estradiol affected zinc homeostasis in follicles by controlling the expression of ZnT 9, which in turn influenced the potential of oocytes to develop into good-quality embryos. This study to provide tangible improvements to patient outcomes will make it a focus of both scientific and translational efforts in the future.

Coordination chemistry suggests that independently observed benefits of metformin and Zn2+ against COVID-19 are not independent

Independent trials indicate that either oral Zn2+ or metformin can separately improve COVID-19 outcomes by approximately 40%. Coordination chemistry predicts a mechanistic relationship and therapeutic synergy. Zn2+ deficit is a known risk factor for both COVID-19 and non-infectious inflammation. Most dietary Zn2+ is not absorbed. Metformin is a naked ligand that presumably increases intestinal Zn2+ bioavailability and active absorption by cation transporters known to transport metformin. Intracellular Zn2+ provides a natural buffer of many protease reactions; the variable "set point" is determined by Zn2+ regulation or availability. A Zn2+-interactive protease network is suggested here. The two viral cysteine proteases are therapeutic targets against COVID-19. Viral and many host proteases are submaximally inhibited by exchangeable cell Zn2+. Inhibition of cysteine proteases can improve COVID-19 outcomes and non-infectious inflammation. Metformin reportedly enhances the natural moderating effect of Zn2+ on bioassayed proteome degradation. Firstly, the dissociable metformin-Zn2+ complex could be actively transported by intestinal cation transporters; thereby creating artificial pathways of absorption and increased body Zn2+ content. Secondly, metformin Zn2+ coordination can create a non-natural protease inhibitor independent of cell Zn2+ content. Moderation of peptidolytic reactions by either or both mechanisms could slow (a) viral multiplication (b) viral invasion and (c) the pathogenic host inflammatory response. These combined actions could allow development of acquired immunity to clear the infection before life-threatening inflammation. Nirmatrelvir (Paxlovid®) opposes COVID-19 by selective inhibition the viral main protease by a Zn2+-independent mechanism. Pending safety evaluation, predictable synergistic benefits of metformin and Zn2+, and perhaps metformin/Zn2+/Paxlovid® co-administration should be investigated.

The role of Zn2+ in shaping intracellular Ca2+ dynamics in the heart

Increasing evidence suggests that Zn2+ acts as a second messenger capable of transducing extracellular stimuli into intracellular signaling events. The importance of Zn2+ as a signaling molecule in cardiovascular functioning is gaining traction. In the heart, Zn2+ plays important roles in excitation-contraction (EC) coupling, excitation-transcription coupling, and cardiac ventricular morphogenesis. Zn2+ homeostasis in cardiac tissue is tightly regulated through the action of a combination of transporters, buffers, and sensors. Zn2+ mishandling is a common feature of various cardiovascular diseases. However, the precise mechanisms controlling the intracellular distribution of Zn2+ and its variations during normal cardiac function and during pathological conditions are not fully understood. In this review, we consider the major pathways by which the concentration of intracellular Zn2+ is regulated in the heart, the role of Zn2+ in EC coupling, and discuss how Zn2+ dyshomeostasis resulting from altered expression levels and efficacy of Zn2+ regulatory proteins are key drivers in the progression of cardiac dysfunction.

Rescue of proteotoxic stress and neurodegeneration by the Zn2+ transporter ZIP7

Proteotoxic stress drives numerous degenerative diseases. In response to misfolded proteins, cells adapt by activating the unfolded protein response (UPR), including endoplasmic reticulum-associated protein degradation (ERAD). However persistent stress triggers apoptosis. Enhancing ERAD is a promising therapeutic approach for protein misfolding diseases. From plants to humans, loss of the Zn2+ transporter ZIP7 causes ER stress, however the mechanism is unknown. Here we show that ZIP7 enhances ERAD and that cytosolic Zn2+ is limiting for deubiquitination of client proteins by the Rpn11 Zn2+ metalloproteinase as they enter the proteasome in Drosophila and human cells. ZIP7 overexpression rescues defective vision caused by misfolded rhodopsin in Drosophila. Thus ZIP7 overexpression may prevent diseases caused by proteotoxic stress, and existing ZIP inhibitors may be effective against proteasome-dependent cancers.

Magnetically Driven Self-Degrading Zinc-Containing Cystine Microrobots for Treatment of Prostate Cancer

Prostate cancer is the most commonly diagnosed tumor disease in men, and its treatment is still a big challenge in standard oncology therapy. Magnetically actuated microrobots represent the most promising technology in modern nanomedicine, offering the advantage of wireless guidance, effective cell penetration, and non-invasive actuation. Here, new biodegradable magnetically actuated zinc/cystine-based microrobots for in situ treatment of prostate cancer cells are reported. The microrobots are fabricated via metal-ion-mediated self-assembly of the amino acid cystine encapsulating superparamagnetic Fe₃ O₄ nanoparticles (NPs) during the synthesis, which allows their precise manipulation by a rotating magnetic field. Inside the cells, the typical enzymatic reducing environment favors the disassembly of the aminoacidic chemical structure due to the cleavage of cystine disulfide bonds and disruption of non-covalent interactions with the metal ions, as demonstrated by in vitro experiments with reduced nicotinamide adenine dinucleotide (NADH). In this way, the cystine microrobots served for site-specific delivery of Zn²⁺ ions responsible for tumor cell killing via a "Trojan horse effect". This work presents a new concept of cell internalization exploiting robotic systems' self-degradation, proposing a step forward in non-invasive cancer therapy.

Zinc and Respiratory Viral Infections: Important Trace Element in Anti-viral Response and Immune Regulation

Influenza viruses, respiratory syncytial virus (RSV), and SARS-COV2 are among the most dangerous respiratory viruses. Zinc is one of the essential micronutrients and is very important in the immune system. The aim of this narrative review is to review the most interesting findings about the importance of zinc in the anti-viral immune response in the respiratory tract and defense against influenza, RSV, and SARS-COV2 infections. The most interesting findings on the role of zinc in regulating immunity in the respiratory tract and the relationship between zinc and acute respiratory distress syndrome (ARDS) are reviewed, as well. Besides, current findings regarding the relationship between zinc and the effectiveness of respiratory viruses' vaccines are reviewed. The results of reviewed studies have shown that zinc and some zinc-dependent proteins are involved in anti-viral defense and immune regulation in the respiratory tract. It seems that zinc can reduce the viral titer following influenza infection. Zinc may reduce RSV burden in the lungs. Zinc can be effective in reducing the duration of viral pneumonia symptoms. Zinc may enhance the effectiveness of hydroxychloroquine in reducing mortality rate in COVID-19 patients. Besides, zinc has a positive effect in preventing ARDS and ventilator-induced lung damage. The relationship between zinc levels and the effectiveness of respiratory viruses' vaccines, especially influenza vaccines, is still unclear, and the findings are somewhat contradictory. In conclusion, zinc has anti-viral properties and is important in defending against respiratory viral infections and regulating the immune response in the respiratory tract.

The Role of the Metabolism of Zinc and Manganese Ions in Human Cancerogenesis

Metal ion homeostasis is fundamental for life. Specifically, transition metals iron, manganese and zinc play a pivotal role in mitochondrial metabolism and energy generation, anti-oxidation defense, transcriptional regulation and the immune response. The misregulation of expression or mutations in ion carriers and the corresponding changes in Mn²⁺ and Zn²⁺ levels suggest that these ions play a pivotal role in cancer progression. Moreover, coordinated changes in Mn²⁺ and Zn²⁺ ion carriers have been detected, suggesting that particular mechanisms influenced by both ions might be required for the growth of cancer cells, metastasis and immune evasion. Here, we present a review of zinc and manganese pathophysiology suggesting that these ions might cooperatively regulate cancerogenesis. Zn and Mn effects converge on mitochondria-induced apoptosis, transcriptional regulation and the cGAS-STING signaling pathway, mediating the immune response. Both Zn and Mn influence cancer progression and impact treatment efficacy in animal models and clinical trials. We predict that novel strategies targeting the regulation of both Zn and Mn in cancer will complement current therapeutic strategies.

Lysosomal inhibition sensitizes TMEM16A-expressing cancer cells to chemotherapy

Cisplatin is the first line therapy for patients with head and neck cancer. However, resistance to cisplatin remains a major concern. High expression of the calcium-activated chloride channel TMEM16A in tumors portends poor survival in these patients, possibly because of drug resistance. Here, we show that TMEM16A drives the sequestration of cisplatin into lysosomes. Subsequently, cisplatin is expelled via the delivery of lysosomes to the cell surface. We show that TMEM16A enhances this process, thereby promoting cisplatin resistance. We also show that lysosomal inhibition synergizes with cisplatin to induce tumor cell death. Our data uncovers a new fundamental feature of both lysosomal physiology and cancer cell biology that can potentially impact the treatment of patients with head and neck cancer.

Squamous cell carcinoma of the head and neck (SCCHN) is a devastating disease that continues to have low cure rates despite the recent advances in therapies. Cisplatin is the most used chemotherapy agent, and treatment failure is largely driven by resistance to this drug. Amplification of chromosomal band 11q13 occurs in ∼30% of SCCHN tumors. This region harbors the ANO1 gene that encodes the TMEM16A ion channel, which is responsible for calcium-activated chloride transport in epithelial tissues. TMEM16A overexpression is associated with cisplatin resistance, and high TMEM16A levels correlate with decreased survival. However, the mechanistic underpinning of this effect remains unknown. Lysosomal biogenesis and exocytosis have been implicated in cancer because of their roles in the clearance of damaged organelles and exocytosis of chemotherapeutic drugs and toxins. Here, we show that TMEM16A overexpression promotes lysosomal biogenesis and exocytosis, which is consistent with the expulsion of intracellular cisplatin. Using a combination of genetic and pharmacologic approaches, we find that TMEM16A promotes lysosomal flux in a manner that requires reactive oxygen species, TRPML1, and the activation of the β-catenin–melanocyte-inducing transcription factor pathway. The lysosomal inhibitor hydroxychloroquine (HCQ) synergizes with cisplatin in killing SCCHN cells in vitro. Using a murine model of SCCHN, we show that HCQ and cisplatin retard the growth of cisplatin-resistant patient-derived xenografts in vivo. We propose that TMEM16A enables cell survival by the up-regulation of lysosomal sequestration and exocytosis of the cytotoxic drugs. These results uncover a model of treatment for resistance in cancer, its reversal, and a role for TMEM16A.

The Oxidative Balance Orchestrates the Main Keystones of the Functional Activity of Cardiomyocytes

This review is aimed at providing an overview of the key hallmarks of cardiomyocytes in physiological and pathological conditions. The main feature of cardiac tissue is the force generation through contraction. This process requires a conspicuous energy demand and therefore an active metabolism. The cardiac tissue is rich of mitochondria, the powerhouses in cells. These organelles, producing ATP, are also the main sources of ROS whose altered handling can cause their accumulation and therefore triggers detrimental effects on mitochondria themselves and other cell components thus leading to apoptosis and cardiac diseases. This review highlights the metabolic aspects of cardiomyocytes and wanders through the main systems of these cells: (a) the unique structural organization (such as different protein complexes represented by contractile, regulatory, and structural proteins); (b) the homeostasis of intracellular Ca²⁺ that represents a crucial ion for cardiac functions and E-C coupling; and (c) the balance of Zn²⁺, an ion with a crucial impact on the cardiovascular system. Although each system seems to be independent and finely controlled, the contractile proteins, intracellular Ca²⁺ homeostasis, and intracellular Zn²⁺ signals are strongly linked to each other by the intracellular ROS management in a fascinating way to form a "functional tetrad" which ensures the proper functioning of the myocardium. Nevertheless, if ROS balance is not properly handled, one or more of these components could be altered resulting in deleterious effects leading to an unbalance of this "tetrad" and promoting cardiovascular diseases. In conclusion, this "functional tetrad" is proposed as a complex network that communicates continuously in the cardiomyocytes and can drive the switch from physiological to pathological conditions in the heart.

Does roundup affect zinc functions in a bivalve mollusk in ex vivo exposure?

Roundup (Rn), a glyphosate-based formulation, is one of the most commonly used herbicides in the world. It affects non-targeted organisms in several ways, including adhesive activity towards metal ions. Zinc (Zn) plays a crucial role in a number of biochemical processes. In this study, we aim to elucidate the direct impact of Rn on Zn accumulation and Zn-dependent activities in the ex vivo system. To this end, we exposed the samples of the digestive gland of a bivalve mollusk Unio tumidus to 3 µM of Rn (calculated as 3 µM of glyphosate), Zn, Zn chelator (N,N,N',N'-Tetrakis(2-pyridylmethyl)ethylenediamine) (TPEN, Tp), and their combinations ZnTp and ZnRn for 17 h. We determined the levels of Zn in the tissue (Zn t) and metallothioneins (Zn-MT), metallothioneins (MTSH), and glutathione (GSH & GSSG), total antioxidant capacity (TAC), lysosomal membrane integrity, and caspase-3 activity. Our study demonstrated that Rn and Tp had different effects on the accumulation and functionality of Zn. Rn did not affect the accumulation of Zn (Zn t, Zn-MT) in the Zn- and ZnRn-groups. On the contrary, Tp produced effects antagonistic to Zn on caspase-3 activity, lysosomal stability, and MTSH concentration. Rn caused particular pro-oxidative effect that decreased GSH level (Rn- and ZnRn-groups) and lysosomal stability (Rn-group). The shared affected index was the GSH/GSSG ratio, which decreased by 2-8 times in each exposure. As the first experience with the application of Tp to indicate Zn activity in mollusks, the study concluded that the ex vivo approach could be useful in the study of numeral aquatic pollutants.

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

PURPOSE

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

PROCEDURE

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

RESULTS

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

CONCLUSIONS

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

Zn2+-Depletion Enhances Lysosome Fission in Cultured Rat Embryonic Cortical Neurons Revealed by a Modified Epifluorescence Microscopic Technique

Lysosomes are integration hubs for several signaling pathways, such as autophagy and endocytosis, and also crucial stores of ions, including Zn2+. Lysosomal dysfunction caused by changes in their morphology by fusion and fission processes can result in several pathological disorders. However, the role of Zn2+ in modulating the morphology of lysosomes is unclear. The resolution of conventional epifluorescence microscopy restricts accurate observation of morphological changes of subcellular fluorescence punctum. In this study, we used a modified epifluorescence microscopy to identify the center of a punctum from a series of z-stack images and calculate the morphological changes. We stained primary cultured rat embryonic cortical neurons with FluoZin3, a Zn2+-sensitive fluorescent dye, and Lysotracker, a lysosome-specific marker, to visualize the distribution of Zn2+-enriched vesicles and lysosomes, respectively. Our results revealed that treating neurons with N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine, a cell-permeable Zn2+ chelator, shrank Zn2+-enriched vesicles and lysosomes by up to 25% in an hour. Pretreating the neurons with YM201636, a blocker of lysosome fission, could suppress this shrinkage. These results demonstrate the usefulness of the modified epifluorescence microscopy for investigating the homeostasis of intracellular organelles and related disorders.

The Function and Regulation of Zinc in the Brain

Nearly sixty years ago Fredrich Timm developed a histochemical technique that revealed a rich reserve of free zinc in distinct regions of the brain. Subsequent electron microscopy studies in Timm- stained brain tissue found that this "labile" pool of cellular zinc was highly concentrated at synaptic boutons, hinting a possible role for the metal in synaptic transmission. Although evidence for activity-dependent synaptic release of zinc would not be reported for another twenty years, these initial findings spurred decades of research into zinc's role in neuronal function and revealed a diverse array of signaling cascades triggered or regulated by the metal. Here, we delve into our current understanding of the many roles zinc plays in the brain, from influencing neurotransmission and sensory processing, to activating both pro-survival and pro-death neuronal signaling pathways. Moreover, we detail the many mechanisms that tightly regulate cellular zinc levels, including metal binding proteins and a large array of zinc transporters.

Acute Increases in Intracellular Zinc Lead to an Increased Lysosomal and Mitochondrial Autophagy and Subsequent Cell Demise in Malignant Melanoma

Changes in zinc content and dysregulated zinc homeostatic mechanisms have been recognized in several solid malignancies such as prostate cancer, breast cancer, or pancreatic cancer. Moreover, it has been shown that zinc serum and/or tissue levels are altered in melanoma with varying effects on melanoma development and biology. This study was conducted to explore the effects of acute increases of intracellular zinc in a set of melanoma tissue explants obtained from clinical samples. Measurements of their zinc content showed an extant heterogeneity in total and free intracellular zinc pools associated with varying biological behavior of individual cells, e.g., autophagy levels and propensity to cell death. Use of zinc pyrithione elevated intracellular zinc in a short time frame which resulted in marked changes in mitochondrial activity and lysosomes. These alterations were accompanied by significantly enhanced autophagy flux and subsequent cell demise in the absence of typical apoptotic cell death markers. The present results show for the first time that acutely increased intracellular zinc in melanoma cells specifically enhances their autophagic activity via mitochondria and lysosomes which leads to autophagic cell death. While biologically relevant, this discovery may contribute to our understanding and exploration of zinc in relation to autophagy as a means of controlling melanoma growth and survival.

Lysosomal Exocytosis: The Extracellular Role of an Intracellular Organelle

Lysosomes are acidic cell compartments containing a large set of hydrolytic enzymes. These lysosomal hydrolases degrade proteins, lipids, polysaccharides, and nucleic acids into their constituents. Materials to be degraded can reach lysosomes either from inside the cell, by autophagy, or from outside the cell, by different forms of endocytosis. In addition to their degradative functions, lysosomes are also able to extracellularly release their contents by lysosomal exocytosis. These organelles move from the perinuclear region along microtubules towards the proximity of the plasma membrane, then the lysosomal and plasma membrane fuse together via a Ca²⁺-dependent process. The fusion of the lysosomal membrane with plasma membrane plays an important role in plasma membrane repair, while the secretion of lysosomal content is relevant for the remodelling of extracellular matrix and release of functional substrates. Lysosomal storage disorders (LSDs) and age-related neurodegenerative disorders, such as Parkinson’s and Alzheimer’s diseases, share as a pathological feature the accumulation of undigested material within organelles of the endolysosomal system. Recent studies suggest that lysosomal exocytosis stimulation may have beneficial effects on the accumulation of these unprocessed aggregates, leading to their extracellular elimination. However, many details of the molecular machinery required for lysosomal exocytosis are only beginning to be unravelled. Here, we are going to review the current literature on molecular mechanisms and biological functions underlying lysosomal exocytosis, to shed light on the potential of lysosomal exocytosis stimulation as a therapeutic approach.

Characterization of T-DM1-resistant breast cancer cells

The development of targeted therapies has drastically improved the outcome of patients with different types of cancer. T-DM1 (trastuzumab-emtansine) is an antibody-drug conjugate used for the treatment of HER2-positive breast cancer combining the FDA approved mAb (monoclonal antibody) trastuzumab and the microtubule cytotoxic agent DM1 (emtansine). Despite clinical successes achieved by targeted therapies, a large number of patients develop resistance during treatment. To explore mechanisms of resistance to T-DM1, the MDA-MB-361 HER2-positive breast cancer cell line was exposed in vitro to T-DM1 in the absence or presence of ciclosporin A. Previously reported mechanisms of resistance such as trastuzumab-binding alterations, MDR1 upregulation, and SLC46A3 downregulation were not observed in these models. Despite a decrease in HER2 expression at the cell surface, both resistant cell lines remained sensitive to HER2 targeted therapies such as mAbs and tyrosine kinase inhibitors. In addition, sensitivity to DNA damaging agents and topoisomerase inhibitors were unchanged. Conversely resistance to anti-tubulin agents increased. Resistant cells displayed a decreased content of polymerized tubulin and a decreased content of βIII tubulin although the downregulation of βIII tubulin by siRNA in the parental cell line did not modified the sensitivity to T-DM1. Both cell lines resistant to T-DM1 also presented giant aneuploid cells. Several SLC (solute carrier) transporters were found to be differentially expressed in the resistant cells in comparison to parental cells. These results suggest that some characteristics such as increased baseline aneuploidy and altered intracellular drug trafficking might be involved in resistance to T-DM1.

Drug Sequestration in Lysosomes as One of the Mechanisms of Chemoresistance of Cancer Cells and the Possibilities of Its Inhibition

Resistance to chemotherapeutics and targeted drugs is one of the main problems in successful cancer therapy. Various mechanisms have been identified to contribute to drug resistance. One of those mechanisms is lysosome-mediated drug resistance. Lysosomes have been shown to trap certain hydrophobic weak base chemotherapeutics, as well as some tyrosine kinase inhibitors, thereby being sequestered away from their intracellular target site. Lysosomal sequestration is in most cases followed by the release of their content from the cell by exocytosis. Lysosomal accumulation of anticancer drugs is caused mainly by ion-trapping, but active transport of certain drugs into lysosomes was also described. Lysosomal low pH, which is necessary for ion-trapping is achieved by the activity of the V-ATPase. This sequestration can be successfully inhibited by lysosomotropic agents and V-ATPase inhibitors in experimental conditions. Clinical trials have been performed only with lysosomotropic drug chloroquine and their results were less successful. The aim of this review is to give an overview of lysosomal sequestration and expression of acidifying enzymes as yet not well known mechanism of cancer cell chemoresistance and about possibilities how to overcome this form of resistance.

A common genetic variant in zinc transporter ZnT2 (Thr288Ser) is present in women with low milk volume and alters lysosome function and cell energetics

Suboptimal lactation is a common, yet underappreciated cause for early cessation of breastfeeding. Molecular regulation of mammary gland function is critical to the process lactation; however, physiological factors underlying insufficient milk production are poorly understood. The zinc (Zn) transporter ZnT2 is critical for regulation of mammary gland development and maturation during puberty, lactation, and postlactation gland remodeling. Numerous genetic variants in the gene encoding ZnT2 (SLC30A2) are associated with low milk Zn concentration and result in severe Zn deficiency in exclusively breastfed infants. However, the functional impacts of genetic variation in ZnT2 on key mammary epithelial cell functions have not yet been systematically explored at the cellular level. Here we determined a common mutation in SLC30A2/ZnT2 substituting serine for threonine at amino acid 288 (Thr288Ser) was found in 20% of women producing low milk volume (n = 2/10) but was not identified in women producing normal volume. Exploration of cellular consequences in vitro using phosphomimetics showed the serine substitution promoted preferential phosphorylation of ZnT2, driving localization to the lysosome and increasing lysosome biogenesis and acidification. While the substitution did not initiate lysosome-mediated cell death, cellular ATP levels were significantly reduced. Our findings demonstrate the Thr288Ser mutation in SLC30A2/ZnT2 impairs critical functions of mammary epithelial cells and suggest a role for genetic variation in the regulation of milk production and lactation performance.

Transmembrane 163 (TMEM163) protein effluxes zinc

Recent investigations of rodent Tmem163 suggest that it binds to and transports zinc as a dimer, and that alanine mutagenesis of its two species-conserved aspartate (D123A/D127A) residues proposed to bind zinc, perturbs protein function. Direct corroboration, however, is lacking whether it is an influx or efflux transporter in cells. We hypothesized that human TMEM163 is a zinc effluxer based on its predicted protein characteristics. We used cultured human cell lines that either stably or transiently expressed TMEM163, and pre-loaded the cells with zinc to determine transport activity. We found that TMEM163-expressing cells exhibited significant reduction of intracellular zinc levels as evidenced by two zinc-specific fluorescent dyes and radionuclide zinc-65. The specificity of the fluorescence signal was confirmed upon treatment with TPEN, a high-affinity zinc chelator. Multiple sequence alignment and phylogenetic analyses showed that TMEM163 is related to distinct members of the cation diffusion facilitator (CDF) protein family. To further characterize the efflux function of TMEM163, we substituted alanine in two homologous aspartate residues (D124A/D128A) and performed site-directed mutagenesis of several conserved amino acid residues identified as non-synonymous single nucleotide polymorphism (S61R, S95C, S193P, and E286K). We found a significant reduction of zinc efflux upon cellular expression of D124A/D128A or E286K protein variant when compared with wild-type, suggesting that these particular amino acids are important for normal protein function. Taken together, our findings demonstrate that TMEM163 effluxes zinc, and it should now be designated ZNT11 as a new member of the mammalian CDF family of zinc efflux transporters.

Solving the secretory acid sphingomyelinase puzzle: Insights from lysosome-mediated parasite invasion and plasma membrane repair

Acid sphingomyelinase (ASM) is a lysosomal enzyme that cleaves the phosphorylcholine head group of sphingomyelin, generating ceramide. Recessive mutations in SMPD1, the gene encoding ASM, cause Niemann-Pick Disease Types A and B. These disorders are attributed not only to lipid accumulation inside lysosomes but also to changes on the outer leaflet of the plasma membrane, highlighting an extracellular role for ASM. Secretion of ASM occurs under physiological conditions, and earlier studies proposed two forms of the enzyme, one resident in lysosomes and another form that would be diverted to the secretory pathway. Such differential intracellular trafficking has been difficult to explain because there is only one SMPD1 transcript that generates an active enzyme, found primarily inside lysosomes. Unexpectedly, studies of cell invasion by the protozoan parasite Trypanosoma cruzi revealed that conventional lysosomes can fuse with the plasma membrane in response to elevations in intracellular Ca²⁺ , releasing their contents extracellularly. ASM exocytosed from lysosomes remodels the outer leaflet of the plasma membrane, promoting parasite invasion and wound repair. Here, we discuss the possibility that ASM release during lysosomal exocytosis, in response to various forms of stress, may represent a major source of the secretory form of this enzyme.

Key Role of Microtubule and Its Acetylation in a Zinc Oxide Nanoparticle-Mediated Lysosome-Autophagy System

Autophagy is a biological process that has attracted considerable attention as a target for novel therapeutics. Recently, nanomaterials (NMs) have been reported to modulate autophagy, which makes them potential agents for the treatment of autophagy-related diseases. In this study, zinc oxide nanoparticles (ZNPs) are utilized to evaluate NM-induced autophagy and debate the mechanisms involved. It is found that ZNPs undergo pH-dependent ion shedding and that intracellular zinc ions (Zn²⁺ ) play a crucial role in autophagy. Autophagy is activated with ZNPs treatment, which is inhibited after Zn²⁺ sequestration via ethylenediamine tetra-acetic acid. Lysosome-based autophagic degradation is halted after ZNPs treatment for more than 3 h and is accompanied by blockage of lysophagy, which renews impaired lysosomes. Furthermore, the microtubule (MT) system participates in ZNP-induced lysosome-autophagy system changes, especially in the fusion between autophagosomes and lysosomes. MT acetylation is helpful for protecting from ZNP-induced MT disruption, and it promotes the autophagic degradation process. In conclusion, this study provides valuable information on NM-induced lysosome-autophagy system changes, particularly with respect to the role of lysophagy and the MT system, which point to some attractive targets for the design of engineered nanoparticles.

Biguanide is a modifiable pharmacophore for recruitment of endogenous Zn2+ to inhibit cysteinyl cathepsins: review and implications

Excessive activities of cysteinyl cathepsins (CysCts) contribute to the progress of many diseases; however, therapeutic inhibition has been problematic. Zn²⁺ is a natural inhibitor of proteases with CysHis dyads or CysHis(Xaa) triads. Biguanide forms bidentate metal complexes through the two imino nitrogens. Here, it is discussed that phenformin (phenylethyl biguanide) is a model for recruitment of endogenous Zn²⁺ to inhibit CysHis/CysHis(X) peptidolysis. Phenformin is a Zn²⁺-interactive, anti-proteolytic agent in bioassay of living tissue. Benzoyl-L-arginine amide (BAA) is a classical substrate of papain-like proteases; the amide bond is scissile. In this review, the structures of BAA and the phenformin-Zn²⁺ complex were compared in silico. Their chemistry and dimensions are discussed in light of the active sites of papain-like proteases. The phenyl moieties of both structures bind to the "S2" substrate-binding site that is typical of many proteases. When the phenyl moiety of BAA binds to S2, then the scissile amide bond is directed to the position of the thiolate-imidazolium ion pair, and is then hydrolyzed. However, when the phenyl moiety of phenformin binds to S2, then the coordinated Zn²⁺ is directed to the identical position; and catalysis is inhibited. Phenformin stabilizes a "Zn²⁺ sandwich" between the drug and protease active site. Hundreds of biguanide derivatives have been synthesized at the 1 and 5 nitrogen positions; many more are conceivable. Various substituent moieties can register with various arrays of substrate-binding sites so as to align coordinated Zn²⁺ with catalytic partners of diverse proteases. Biguanide is identified here as a modifiable pharmacophore for synthesis of therapeutic CysCt inhibitors with a wide range of potencies and specificities. Phenformin-Zn²⁺ Complex.

Structural Basis of Lysosomal Phospholipase A2 Inhibition by Zn2

Lysosomal phospholipase A₂ (LPLA₂/PLA2G15) is a key enzyme involved in lipid homeostasis and is characterized by both phospholipase A2 and transacylase activity and by an acidic pH optimum. Divalent cations such as Ca²⁺ and Mg²⁺ have previously been shown to have little effect on the activity of LPLA₂, but the discovery of a novel crystal form of LPLA₂ with Zn²⁺ bound in the active site suggested a role for this divalent cation in regulating enzyme activity. In this complex, the cation directly coordinates the serine and histidine of the α/β-hydrolase triad and stabilizes a closed conformation. This closed conformation is characterized by an inward shift of the lid loop, which extends over the active site and effectively blocks access to one of its lipid acyl chain binding tracks. Therefore, we hypothesized that Zn²⁺ would inhibit LPLA₂ activity at a neutral but not acidic pH because histidine would be positively charged at lower pH. Indeed, Zn²⁺ was found to inhibit the esterase activity of LPLA₂ in a noncompetitive manner exclusively at a neutral pH (between 6.5 and 8.0). Because lysosomes are reservoirs of Zn²⁺ in cells, the pH optimum of LPLA₂ might allow it to catalyze acyl transfer unimpeded within the organelle. We conjecture that Zn²⁺ inhibition of LPLA₂ at higher pH maintains a lower activity of the esterase in environments where its activity is not typically required.

Superiority of SpiroZin2 Versus FluoZin-3 for monitoring vesicular Zn2+ allows tracking of lysosomal Zn2+ pools

Small-molecule fluorescent probes are powerful and ubiquitous tools for measuring the concentration and distribution of analytes in living cells. However, accurate characterization of these analytes requires rigorous evaluation of cell-to-cell heterogeneity in fluorescence intensities and intracellular distribution of probes. In this study, we perform a parallel and systematic comparison of two small-molecule fluorescent vesicular Zn²⁺ probes, FluoZin-3 AM and SpiroZin2, to evaluate each probe for measurement of vesicular Zn²⁺ pools. Our results reveal that SpiroZin2 is a specific lysosomal vesicular Zn²⁺ probe and affords uniform measurement of resting Zn²⁺ levels at the single cell level with proper calibration. In contrast, FluoZin-3 AM produces highly variable fluorescence intensities and non-specifically localizes in the cytosol and multiple vesicular compartments. We further applied SpiroZin2 to lactating mouse mammary epithelial cells and detected a transient increase of lysosomal free Zn²⁺ at 24-hour after lactation hormone treatment, which implies that lysosomes play a role in the regulation of Zn²⁺ homeostasis during lactation. This study demonstrates the need for critical characterization of small-molecule fluorescent probes to define the concentration and localization of analytes in different cell populations, and reveals SpiroZin2 to be capable of reporting diverse perturbations to lysosomal Zn²⁺.

The Effect of Different Levels of Cu, Zn and Mn Nanoparticles in Hen Turkey Diet on the Activity of Aminopeptidases

The aim of the study was to estimate the influence of the different levels of Cu, Zn, and Mn nanoparticles on the activity of aminopeptidases in turkey. An experiment was carried out on 144 turkey hen Hybrid Converter. The birds were divided into groups given standard- and nanoparticle-supplementation of different level of copper (Cu 20, 10, 2 mg/kg), zinc (Zn 100, 50, 10 ppm), and manganese (Mn 100, 50, 10 ppm), covering respectively 100%, 50%, and 10% of the physiological demands for those minerals in the diet. The activity of aminopeptidases (alanyl: AlaAP, leucyl: LeuAP and arginyl: ArgAP) after supplementation of minerals was determined in the breast and thigh turkey muscle. The strongest effect of interaction among minerals supplementation form and dose on the activity levels of the aminopeptidases in thigh muscle was observed for nano-Cu already at the lowest dose of 2 mg/kg. In this dose (covering 10% of the birds’ demand) nano form of supplementation significantly increased the activity of Ala-, Leu-, and ArgAP (877, 201, and 719, respectively), compared to standard form of supplementation (461, 90.5, and 576, respectively). In turn, in breast muscle, after supplementation covering 10% of the demand with the nano-Cu, nano-Zn, and nano-Mn compared to the standard form, we did not observe any significant difference in the activity levels of any of the investigated aminopeptidases, except for AlaAP under Zn supplementation. Supplementation with the 20 mg/kg of Nano-Cu (100% of demand) and with 10 mg/kg of Nano-Cu (50% of demand) inhibited the activity of all of the three aminopeptidases in thigh muscle. Supplementation of the minerals in nano form into the diet, especially of Cu and Zn in the dose covering 10% of the demand is relevant to maintain homeostasis in turkey muscles, as indicated by the activity of the aminopeptidases.

Critical Role of Zinc as Either an Antioxidant or a Prooxidant in Cellular Systems

Zinc is recognized as an essential trace metal required for human health; its deficiency is strongly associated with neuronal and immune system defects. Although zinc is a redox-inert metal, it functions as an antioxidant through the catalytic action of copper/zinc-superoxide dismutase, stabilization of membrane structure, protection of the protein sulfhydryl groups, and upregulation of the expression of metallothionein, which possesses a metal-binding capacity and also exhibits antioxidant functions. In addition, zinc suppresses anti-inflammatory responses that would otherwise augment oxidative stress. The actions of zinc are not straightforward owing to its numerous roles in biological systems. It has been shown that zinc deficiency and zinc excess cause cellular oxidative stress. To gain insights into the dual action of zinc, as either an antioxidant or a prooxidant, and the conditions under which each role is performed, the oxidative stresses that occur in zinc deficiency and zinc overload in conjunction with the intracellular regulation of free zinc are summarized. Additionally, the regulatory role of zinc in mitochondrial homeostasis and its impact on oxidative stress are briefly addressed.

Lysosomal Ca2+ Signaling Regulates High Glucose-Mediated Interleukin-1β Secretion via Transcription Factor EB in Human Monocytic Cells

Aberrant activation of the innate immune system, including NOD-like receptor pyrin domain containing 3 (NLRP3) inflammasome-dependent interleukin-1β (IL-1β) secretion, has been implicated in the pathogenesis of type 2 diabetes mellitus (T2DM) and its complication. Our previous study demonstrated that hyperglycemia, a hallmark characteristic of T2DM, induced NLRP3 inflammasome-dependent caspase-1 activation and IL-1β maturation in human monocytic cells. In this study, we examined the underlying mechanisms of secreting IL-1β during hyperglycemia, with a focus on the alteration of Ca²⁺ homeostasis and lysosomal exocytosis. We found that high glucose (HG; 30 mM glucose for 48 h) altered Ca²⁺ homeostasis by reducing lysosomal Ca²⁺ concentration that appeared to be resulted from Ca²⁺ moving out of lysosomes into cytosol in human monocytic cell lines, U937 and THP-1 cells. Moreover, HG-induced lysosomal Ca²⁺-dependent mature IL-1β release was strongly correlated with the activation and upregulation of two lysosomal marker proteins, cathepsin D and lysosomal-associated membrane protein-1 (LAMP-1). This involved calcineurin/transcription factor EB (TFEB) pathway and its target genes, cathepsin B, cathepsin D, and LAMP-1, to mediate lysosomal exocytosis. Therefore in this study, we revealed a novel mechanism of HG-induced lysosomal exocytosis which was regulated by lysosomal Ca²⁺ signals through calcineurin/TFEB pathway, thus contributing to IL-1β secretion in human monocytic cells.

High glucose-induced ROS activates TRPM2 to trigger lysosomal membrane permeabilization and Zn2+-mediated mitochondrial fission

Diabetic stress increases the production of reactive oxygen species (ROS), leading to mitochondrial fragmentation and dysfunction. We hypothesized that ROS-sensitive TRPM2 channels mediated diabetic stress-induced mitochondrial fragmentation. We found that chemical inhibitors, RNAi silencing, and genetic knockout of TRPM2 channels abolished the ability of high glucose to cause mitochondrial fission in endothelial cells, a cell type that is particularly vulnerable to diabetic stress. Similar to high glucose, increasing ROS in endothelial cells by applying H₂O₂ induced mitochondrial fission. Ca²⁺ that entered through TRPM2 induced lysosomal membrane permeabilization, which led to the release of lysosomal Zn²⁺ and a subsequent increase in mitochondrial Zn²⁺ Zn²⁺ promoted the recruitment of the fission factor Drp-1 to mitochondria to trigger their fission. This signaling pathway may operate in aging-associated illnesses in which excessive mitochondrial fragmentation plays a central role.

TRPML1: The Ca(2+)retaker of the lysosome

Efficient functioning of lysosome is necessary to ensure the correct performance of a variety of intracellular processes such as degradation of cargoes coming from the endocytic and autophagic pathways, recycling of organelles, and signaling mechanisms involved in cellular adaptation to nutrient availability. Mutations in lysosomal genes lead to more than 50 lysosomal storage disorders (LSDs). Among them, mutations in the gene encoding TRPML1 (MCOLN1) cause Mucolipidosis type IV (MLIV), a recessive LSD characterized by neurodegeneration, psychomotor retardation, ophthalmologic defects and achlorhydria. At the cellular level, MLIV patient fibroblasts show enlargement and engulfment of the late endo-lysosomal compartment, autophagy impairment, and accumulation of lipids and glycosaminoglycans. TRPML1 is the most extensively studied member of a small family of genes that also includes TRPML2 and TRPML3, and it has been found to participate in vesicular trafficking, lipid and ion homeostasis, and autophagy. In this review we will provide an update on the latest and more novel findings related to the functions of TRPMLs, with particular focus on the emerging role of TRPML1 and lysosomal calcium signaling in autophagy. Moreover, we will also discuss new potential therapeutic approaches for MLIV and LSDs based on the modulation of TRPML1-mediated signaling.

The mucolipin-1 (TRPML1) ion channel, transmembrane-163 (TMEM163) protein, and lysosomal zinc handling

Lysosomes are emerging as important players in cellular zinc ion (Zn²⁺) homeostasis. The series of work on Zn2+ accumulation in the neuronal lysosomes and the mounting evidence on the role of lysosomal Zn²⁺ in cell death during mammary gland involution set a biological precedent for the central role of the lysosomes in cellular Zn²⁺ handling. Such a role appears to involve cytoprotection on the one hand, and cell death on the other. The recent series of work began to identify the molecular determinants of the lysosomal Zn²⁺ handling. In addition to zinc transporters (ZnT) of the solute-carrier family type 30A (SLC30A), the lysosomal ion channel TRPML1 and the poorly understood novel transporter TMEM163 have been shown to play a role in the Zn²⁺ uptake by the lysosomes. In this review, we summarize the current knowledge on molecular determinants of the lysosomal Zn²⁺ handling, uptake, and release pathways, as well as discuss their possible roles in health and disease.

Disorders of lysosomal acidification-The emerging role of v-ATPase in aging and neurodegenerative disease

Autophagy and endocytosis deliver unneeded cellular materials to lysosomes for degradation. Beyond processing cellular waste, lysosomes release metabolites and ions that serve signaling and nutrient sensing roles, linking the functions of the lysosome to various pathways for intracellular metabolism and nutrient homeostasis. Each of these lysosomal behaviors is influenced by the intraluminal pH of the lysosome, which is maintained in the low acidic range by a proton pump, the vacuolar ATPase (v-ATPase). New reports implicate altered v-ATPase activity and lysosomal pH dysregulation in cellular aging, longevity, and adult-onset neurodegenerative diseases, including forms of Parkinson disease and Alzheimer disease. Genetic defects of subunits composing the v-ATPase or v-ATPase-related proteins occur in an increasingly recognized group of familial neurodegenerative diseases. Here, we review the expanding roles of the v-ATPase complex as a platform regulating lysosomal hydrolysis and cellular homeostasis. We discuss the unique vulnerability of neurons to persistent low level lysosomal dysfunction and review recent clinical and experimental studies that link dysfunction of the v-ATPase complex to neurodegenerative diseases across the age spectrum.

Metal homeostasis disruption and mitochondrial dysfunction in hepatocytes exposed to sub-toxic doses of zinc oxide nanoparticles

Increased production and use of zinc oxide nanoparticles (ZnO-NPs) in consumer products has prompted the scientific community to investigate their potential toxicity, and understand their impact on the environment and organisms. Molecular mechanisms involved in ZnO-NP toxicity are still under debate and focus essentially on high dose expositions. In our study, we chose to evaluate the effect of sub-toxic doses of ZnO-NPs on human hepatocytes (HepG2) with a focus on metal homeostasis and redox balance disruptions. We showed massive dissolution of ZnO-NPs outside the cell, transport and accumulation of zinc ions inside the cell but no evidence of nanoparticle entry, even when analysed by high resolution TEM microscopy coupled with EDX. Gene expression analysis highlighted zinc homeostasis disruptions as shown by metallothionein 1X and zinc transporter 1 and 2 (ZnT1, ZnT2) over-expression. Major oxidative stress response genes, such as superoxide dismutase 1, 2 and catalase were not induced. Phase 2 enzymes in term of antioxidant response, such as heme oxygenase 1 (HMOX1) and the regulating subunit of the glutamate-cysteine ligase (GCLM) were slightly upregulated, but these observations may be linked solely to metal homeostasis disruptions, as these actors are involved in both metal and ROS responses. Finally, we observed abnormal mitochondria morphologies and autophagy vesicles in response to ZnO-NPs, indicating a potential role of mitochondria in storing and protecting cells from zinc excess but ultimately causing cell death at higher doses.

Biphasic regulation of lysosomal exocytosis by oxidative stress

Oxidative stress drives cell death in a number of diseases including ischemic stroke and neurodegenerative diseases. A better understanding of how cells recover from oxidative stress is likely to lead to better treatments for stroke and other diseases. The recent evidence obtained in several models ties the process of lysosomal exocytosis to the clearance of protein aggregates and toxic metals. The mechanisms that regulate lysosomal exocytosis, under normal or pathological conditions, are only beginning to emerge. Here we provide evidence for the biphasic effect of oxidative stress on lysosomal exocytosis. Lysosomal exocytosis was measured using the extracellular levels of the lysosomal enzyme beta-hexosaminidase (ß-hex). Low levels or oxidative stress stimulated lysosomal exocytosis, but inhibited it at high levels. Deletion of the lysosomal ion channel TRPML1 eliminated the stimulatory effect of low levels of oxidative stress. The inhibitory effects of oxidative stress appear to target the component of lysosomal exocytosis that is driven by extracellular Ca²⁺. We propose that while moderate oxidative stress promotes cellular repair by stimulating lysosomal exocytosis, at high levels oxidative stress has a dual pathological effect: it directly causes cell damage and impairs damage repair by inhibiting lysosomal exocytosis. Harnessing these adaptive mechanisms may point to pharmacological interventions for diseases involving oxidative proteotoxicity or metal toxicity.

Pinus radiata bark extract induces caspase-independent apoptosis-like cell death in MCF-7 human breast cancer cells

In the present study, we investigated the anticancer activity of Pinus radiata bark extract (PRE) against MCF-7 human breast cancer cells. First, we observed that PRE induces potent cytotoxic effects in MCF-7 cells. The cell death had features of cytoplasmic vacuolation, plasma membrane permeabilization, chromatin condensation, phosphatidylserine externalization, absence of executioner caspase activation, insensitivity to z-VAD-fmk (caspase inhibitor), increased accumulation of autophagic markers, and lysosomal membrane permeabilization (LMP). Both the inhibition of early stage autophagy flux and lysosomal cathepsins did not improve cell viability. The antioxidant, n-acetylcysteine, and the iron chelator, deferoxamine, failed to restore the lysosomal integrity indicating that PRE-induced LMP is independent of oxidative stress. This was corroborated with the absence of enhanced ROS production in PRE-treated cells. Chelation of both intracellular calcium and zinc promotes PRE-induced LMP. Geranylgeranylacetone, an inducer of Hsp70 expression, also had no significant protective effect on PRE-induced LMP. Moreover, we found that PRE induces endoplasmic reticulum (ER) stress and mitochondrial membrane depolarization in MCF-7 cells. The ER stress inhibitor, 4-PBA, did not restore the mitochondrial membrane integrity, whereas cathepsin inhibitors demonstrated significant protective effects. Collectively, our results suggest that PRE induces an autophagic block, LMP, ER stress, and mitochondrial dysfunction in MCF-7 cells. However, further studies are clearly warranted to explore the exact mechanism behind the anticancer activity of PRE in MCF-7 human breast cancer cells.

One Year of Enzyme Replacement Therapy Reduces Globotriaosylceramide Inclusions in Podocytes in Male Adult Patients with Fabry Disease

Fabry nephropathy is associated with progressive accumulation of globotriaosylceramide (GL3) in podocytes. Reducing this GL3 burden may reduce podocyte injury. Sensitive methods to quantify podocyte GL3 content may determine whether a given strategy can benefit podocytes in Fabry disease. We developed an unbiased electron microscopic stereological method to estimate the average volume of podocytes and their GL3 inclusions in 6 paired pre- and post-enzyme replacement therapy (ERT) biopsies from 5 men with Fabry disease. Podocyte GL3 content was regularly reduced (average 73%) after 11-12 months of ERT. This was not detectable using a semi-quantitative approach. Parallel to GL3 reduction, podocytes became remarkably smaller (average 63%). These reductions in podocyte GL3 content or size were not significantly correlated with changes in foot process width (FPW). However, FPW after ERT was significantly correlated with the magnitude of the decrease in podocyte GL3 content from baseline to 11-12 months of ERT. Also podocytes exocytosed GL3 inclusions, a phenomenon correlated with their reduction in their GL3 content. Demonstrable after11-12 months, reduction in podocyte GL3 content allows for early assessment of treatment efficacy and shorter clinical trials in Fabry disease.

Reciprocal regulation of actin cytoskeleton remodelling and cell migration by Ca2+ and Zn2+: role of TRPM2 channels

Cell migration is a fundamental feature of tumour metastasis and angiogenesis. It is regulated by a variety of signalling molecules including H2O2 and Ca(2+) Here, we asked whether the H2O2-sensitive transient receptor potential melastatin 2 (TRPM2) Ca(2+) channel serves as a molecular link between H2O2 and Ca(2+) H2O2-mediated activation of TRPM2 channels induced filopodia formation, loss of actin stress fibres and disassembly of focal adhesions, leading to increased migration of HeLa and prostate cancer (PC)-3 cells. Activation of TRPM2 channels, however, caused intracellular release of not only Ca(2+) but also of Zn(2+) Intriguingly, elevation of intracellular Zn(2+) faithfully reproduced all of the effects of H2O2, whereas Ca(2+) showed opposite effects. Interestingly, H2O2 caused increased trafficking of Zn(2+)-enriched lysosomes to the leading edge of migrating cells, presumably to impart polarisation of Zn(2+) location. Thus, our results indicate that a reciprocal interplay between Ca(2+) and Zn(2+) regulates actin remodelling and cell migration; they call for a revision of the current notion that implicates an exclusive role for Ca(2+) in cell migration.

ROS and intracellular ion channels

Oxidative stress is a well-known driver of numerous pathological processes involving protein and lipid peroxidation and DNA damage. The resulting increase of pro-apoptotic pressure drives tissue damage in a host of conditions, including ischemic stroke and reperfusion injury, diabetes, death in acute pancreatitis and neurodegenerative diseases. Somewhat less frequently discussed, but arguably as important, is the signaling function of oxidative stress stemming from the ability of oxidative stress to modulate ion channel activity. The evidence for the modulation of the intracellular ion channels and transporters by oxidative stress is constantly emerging and such evidence suggests new regulatory and pathological circuits that can be explored towards new treatments for diseases in which oxidative stress is an issue. In this review we summarize the current knowledge on the effects of oxidative stress on the intracellular ion channels and transporters and their role in cell function.

Exome Sequencing of SLC30A2 Identifies Novel Loss- and Gain-of-Function Variants Associated with Breast Cell Dysfunction

The zinc (Zn) transporter ZnT2 (SLC30A2) is expressed in specialized secretory cells including breast, pancreas and prostate, and imports Zn into mitochondria and vesicles. Mutations in SLC30A2 substantially reduce milk Zn concentration ([Zn]) and cause severe Zn deficiency in exclusively breastfed infants. Recent studies show that ZnT2-null mice have low milk [Zn], in addition to profound defects in mammary gland function during lactation. Here, we used breast milk [Zn] to identify novel non-synonymous ZnT2 variants in a population of lactating women. We also asked whether specific variants induce disturbances in intracellular Zn management or cause cellular dysfunction in mammary epithelial cells. Healthy, breastfeeding women were stratified into quartiles by milk [Zn] and exonic sequencing of SLC30A2 was performed. We found that 36% of women tested carried non-synonymous ZnT2 variants, all of whom had milk Zn levels that were distinctly above or below those in women without variants. We identified 12 novel heterozygous variants. Two variants (D(103)E and T(288)S) were identified with high frequency (9 and 16%, respectively) and expression of T(288)S was associated with a known hallmark of breast dysfunction (elevated milk sodium/potassium ratio). Select variants (A(28)D, K(66)N, Q(71)H, D(103)E, A(105)P, Q(137)H, T(288)S and T(312)K) were characterized in vitro. Compared with wild-type ZnT2, these variants were inappropriately localized, and most resulted in either 'loss-of-function' or 'gain-of-function', and altered sub-cellular Zn pools, Zn secretion, and cell cycle check-points. Our study indicates that SLC30A2 variants are common in this population, dysregulate Zn management and can lead to breast cell dysfunction. This suggests that genetic variation in ZnT2 could be an important modifier of infant growth/development and reproductive health/disease. Importantly, milk [Zn] level may serve as a bio-reporter of breast function during lactation.

The secret life of extracellular vesicles in metal homeostasis and neurodegeneration

Biologically active metals such as copper, zinc and iron are fundamental for sustaining life in different organisms with the regulation of cellular metal homeostasis tightly controlled through proteins that coordinate metal uptake, efflux and detoxification. Many of the proteins involved in either uptake or efflux of metals are localised and function on the plasma membrane, traffic between intracellular compartments depending upon the cellular metal environment and can undergo recycling via the endosomal pathway. The biogenesis of exosomes also occurs within the endosomal system, with several major neurodegenerative disease proteins shown to be released in association with these vesicles, including the amyloid-β (Aβ) peptide in Alzheimer's disease and the infectious prion protein involved in Prion diseases. Aβ peptide and the prion protein also bind biologically active metals and are postulated to play important roles in metal homeostasis. In this review, we will discuss the role of extracellular vesicles in Alzheimer's and Prion diseases and explore their potential contribution to metal homeostasis.

Transition metals activate TFEB in overexpressing cells

Exposure of cells to micromolar Cu activates recombinant transcription factor EB (TFEB), leading to expression of the lysosomal network genes. Whereas TFEB overexpression has a cytoprotective effect under moderate Cu exposure, it enhances oxidative stress and mitochondrial damage caused by high levels of Cu.

Transition metal toxicity is an important factor in the pathogenesis of numerous human disorders, including neurodegenerative diseases. Lysosomes have emerged as important factors in transition metal toxicity because they handle transition metals via endocytosis, autophagy, absorption from the cytoplasm and exocytosis. Transcription factor EB (TFEB) regulates lysosomal biogenesis and the expression of lysosomal proteins in response to lysosomal and/or metabolic stresses. Since transition metals cause lysosomal dysfunction, we proposed that TFEB may be activated to drive gene expression in response to transition metal exposure and that such activation may influence transition metal toxicity. We found that transition metals copper (Cu) and iron (Fe) activate recombinant TFEB and stimulate the expression of TFEB-dependent genes in TFEB-overexpressing cells. In cells that show robust lysosomal exocytosis, TFEB was cytoprotective at moderate levels of Cu exposure, decreasing oxidative stress as reported by the expression of heme oxygenase-1 (HMOX1) gene. However, at high levels of Cu exposure, particularly in cells with low levels of lysosomal exocytosis, activation of overexpressed TFEB was toxic, increasing oxidative stress and mitochondrial damage. Based on these data, we conclude that TFEB-driven gene network is a component of the cellular response to transition metals. These data suggest limitations and disadvantages of TFEB overexpression as a therapeutic approach.

Heterodimerization, altered subcellular localization, and function of multiple zinc transporters in viable cells using bimolecular fluorescence complementation

Zinc plays a crucial role in numerous key physiological functions. Zinc transporters (ZnTs) mediate zinc efflux and compartmentalization in intracellular organelles; thus, ZnTs play a central role in zinc homeostasis. We have recently shown the in situ dimerization and function of multiple normal and mutant ZnTs using bimolecular fluorescence complementation (BiFC). Prompted by these findings, we here uncovered the heterodimerization, altered subcellular localization, and function of multiple ZnTs in live cells using this sensitive BiFC technique. We show that ZnT1, -2, -3, and -4 form stable heterodimers at distinct intracellular compartments, some of which are completely different from their homodimer localization. Specifically, unlike the plasma membrane (PM) localization of ZnT1 homodimers, ZnT1-ZnT3 heterodimers localized at intracellular vesicles. Furthermore, upon heterodimerization with ZnT1, the zinc transporters ZnT2 and ZnT4 surprisingly localized at the PM, as opposed to their vesicular homodimer localization. We further demonstrate the deleterious effect that the G87R-ZnT2 mutation, associated with transient neonatal zinc deficiency, has on ZnT1, ZnT3, and ZnT4 upon heterodimerization. The functionality of the various ZnTs was assessed by the dual BiFC-Zinquin assay. We also undertook a novel transfection competition assay with ZnT cDNAs to confirm that the driving force for heterodimer formation is the core structure of ZnTs and not the BiFC tags. These findings uncover a novel network of homo- and heterodimers of ZnTs with distinct subcellular localizations and function, hence highlighting their possible role in zinc homeostasis under physiological and pathological conditions.

Brief exposure to copper activates lysosomal exocytosis

Copper (Cu) is essential mineral, but its toxicity necessitates existence of powerful machinery responsible for the extraction of excess Cu from the cell. Cu exposure was recently shown to induce the translocation of Cu pump ATP7B to the lysosomes followed by lysosomal exocytosis. Here we sought to investigate the mechanisms underlying the effect of Cu on lysosomal exocytosis. We found that brief exposure to Cu activates lysosomal exocytosis, which was measured as a release of the lysosomal digestive enzyme β-hexosaminidase (β-hex) into the extracellular medium and by the presence lysosomal protein LAMP1 at the plasma membrane. Such release depends on calcium (Ca) and on the lysosomal SNARE VAMP7. ATP7B knockdown using RNAi suppressed the basal lysosomal exocytosis, but did not affect the ability of Cu to activate it. ATP7B knockdown was associated with sustained oxidative stress. The removal of Ca from the extracellular medium suppressed the Cu-dependent component of the lysosomal exocytosis. We propose that Cu promotes lysosomal exocytosis by facilitating a Ca-dependent step of the lysosomal exocytosis.

Compartmentalized zinc deficiency and toxicities caused by ZnT and Zip gene over expression result in specific phenotypes in Drosophila

Movement of zinc ions across cellular membranes is achieved mainly by two families of zinc transport genes encoding multi-transmembrane domain proteins. Members of the Zip family generally transport zinc into the cytosol, either from outside the cell or from the lumen of subcellular organelles such as the endoplasmic reticulum, Golgi, endosomes or storage vacuoles. ZnT proteins move zinc in the opposite direction, resulting in efflux from the cell or uptake into organelles. Zinc homeostasis at both the cellular and systemic level is achieved by the coordinated action of numerous Zip and ZnT proteins, twenty-four in mammals and seventeen in the vinegar fly Drosophila melanogaster. Previously, we have identified a zinc toxicity phenotype in the Drosophila eye, caused by targeted over expression of dZip42C.1 (dZip1) combined with knockdown of dZnT63C (dZnT1). In general, this phenotype was rescued by increased zinc efflux or decreased uptake and was exacerbated by decreased efflux or increased uptake. Now we have identified three additional zinc dyshomeostasis phenotypes caused by over expression of dZnT86D, dZnT86D(eGFP) and dZip71B(FLAG). Genetic and dietary manipulation experiments showed that these three phenotypes all differ both from each other and from our original zinc toxicity phenotype. Based on these data and the approximate subcellular localization of each zinc transport protein, we propose that each phenotype represents a different redistribution of zinc within these cells, resulting in a Golgi zinc toxicity, a Golgi zinc deficiency and a combined Golgi/other organelle zinc toxicity respectively. We are able to group the remaining Drosophila Zip and ZnT genes into several functional categories based on their interaction with the three novel zinc dyshomeostasis phenotypes, allowing the role of each zinc transport protein to be defined in greater detail. This research highlights the differential effects that redistribution of zinc can have within a particular tissue and identifies the Golgi as being particularly sensitive to both excess and insufficient zinc.

Disulfiram-induced cytotoxicity and endo-lysosomal sequestration of zinc in breast cancer cells

Disulfiram, a clinically used alcohol-deterrent has gained prominence as a potential anti-cancer agent due to its impact on copper-dependent processes. Few studies have investigated zinc effects on disulfiram action, despite it having high affinity for this metal. Here we studied the cytotoxic effects of disulfiram in breast cancer cells, and its relationship with both intra and extracellular zinc. MCF-7 and BT474 cancer cell lines gave a striking time-dependent biphasic cytotoxic response between 0.01 and 10 μM disulfiram. Co-incubation of disulfiram with low-level zinc removed this effect, suggesting that availability of extracellular zinc significantly influences disulfiram efficacy. Live-cell confocal microscopy using fluorescent endocytic probes and the zinc dye Fluozin-3 revealed that disulfiram selectively and rapidly increased zinc levels in endo-lysosomes. Disulfiram also caused spatial disorganization of late endosomes and lysosomes, suggesting they are novel targets for this drug. This relationship between disulfiram toxicity and ionophore activity was consolidated via synthesis of a new disulfiram analog and overall we demonstrate a novel mechanism of disulfiram-cytotoxicity with significant clinical implications for future use as a cancer therapeutic.

Cellular zinc levels are modulated by TRPML1-TMEM163 interaction

Mucolipidosis type IV (MLIV) is caused by loss of function mutations in the TRPML1 ion channel. We previously reported that tissue zinc levels in MLIV were abnormally elevated; however, the mechanism behind this pathologic accumulation remains unknown. Here, we identify transmembrane (TMEM)-163 protein, a putative zinc transporter, as a novel interacting partner for TRPML1. Evidence from yeast two-hybrid, tissue expression pattern, co-immunoprecipitation, mass spectrometry and confocal microscopy studies confirmed the physical association of TMEM163 with TRPML1. This interaction is disrupted when a part of TMEM163's N-terminus was deleted. Further studies to define the relevance of their interaction revealed that the plasma membrane (PM) levels of TMEM163 significantly decrease when TRPML1 is co-expressed in HEK-293 cells, while it mostly localizes within the PM when co-expressed with a mutant TRPML1 that distributes mostly in the PM. Meanwhile, co-expression of TMEM163 does not alter TRPML1 channel activity, but its expression levels in MLIV patient fibroblasts are reduced, which correlate with marked accumulation of zinc in lysosomes when these cells are acutely exposed to exogenous zinc (100 μM). When TMEM163 is knocked down or when TMEM163 and TRPML1 are co-knocked down in HEK-293 cells treated overnight with 100 nm zinc, the cells have significantly higher intracellular zinc levels than untreated control. Overall, these findings suggest that TMEM163 and TRPML1 proteins play a critical role in cellular zinc homeostasis, and thus possibly explain a novel mechanism for the pathological overload of zinc in MLIV disease.