Induction, regulation, degradation, and biological significance of mammalian metallothioneins

ESI-MS analysis of Cu(I) binding to apo and Zn7 human metallothionein 1A, 2, and 3 identifies the formation of a similar series of metallated species with no individual isoform optimization for Cu(I)

Metallothioneins (MTs) are cysteine-rich proteins involved in metal homeostasis, heavy metal detoxification, and protection against oxidative stress. Whether the four mammalian MT isoforms exhibit different metal binding properties is not clear. In this paper, the Cu(I) binding properties of the apo MT1A, apo MT2, and apo MT3 are compared and the relative Cu(I) binding affinities are reported. In all three isoforms, Cu4, Cu6, and Cu10 species form cooperatively, and MT1A and MT2 also form a Cu13 species. The Cu(I) binding properties of Zn7-MT1A, Zn7-MT2, and Zn7-MT3 are compared systematically using isotopically pure 63Cu(I) and 68Zn(II). The species formed in each MT isoform were detected through electrospray ionization-mass spectrometry and further characterized using room temperature phosphorescence spectroscopy. The mixed metal Cu, Zn species forming in MT1A, MT2, and MT3 have similar stoichiometries and their emission spectral properties indicate that analogous clusters form in the three isoforms. Three parallel metallation pathways have been proposed through analysis of the detailed Cu, Zn speciation in MT1A, MT2, and MT3. Pathway ① results in Cu5Zn5-MT and Cu9Zn3-MT. Pathway ② involves Cu6Zn4-MT and Cu10Zn2-MT. Pathway ③ includes Cu8Zn4-MT. Speciation analysis indicates that Pathway ② is the preferred pathway for MT2. This is also evident in the phosphorescence spectra with the 750 nm emission from Cu6Zn4-MT being most prominent in MT2. We see no evidence for different MT isoforms being optimized or exhibiting preferences for certain metals. We discuss the probable stoichiometry for MTs in vivo based on the in vitro determined binding constants.

Cu(I) binds to Zn7-MT2 via two parallel pathways

Metallothionein proteins are essential for Cu(I) and Zn(II) homeostasis as well as heavy metal detoxification. The metallation properties of MT2 are of great interest due to their wide patterns of expression and correlation with multiple diseases including cancers, neurological disorders, and respiratory diseases. Use of isotopically pure 63Cu(I) and 68Zn(II) eliminates the complexity of the Cu, Zn-MT2 mass spectral peaks due to significant overlap of naturally abundant isotopes. This allows for the resolution of the precise Cu(I) and Zn(II) stoichiometries when both Cu(I) and Zn(II) are bound to MT2 at physiological pH as expected in vivo. Exact Cu: Zn ratios were determined from mass spectral simulations carried out for every point in the titration. We report that Cu(I) metallation of Zn7-MT2 can only be understood in terms of two pathways occurring in parallel with pathway ① resulting in Cu5Zn5-MT2 and Cu9Zn3-MT2. Pathway ② results in Cu6Zn4-MT2 and Cu10Zn2-MT2, which are the major products of the reaction. From the electrospray ionization (ESI)-mass spectral data we report a series of formation constants (KF) for species starting from Zn7-MT2 up to Cu11Zn2-MT2. Room temperature phosphorescence and circular dichroism (CD) spectra were measured in parallel with the ESI-mass spectrometry data allowing for the assignment of specific species to specific spectral bands. Through analysis of the CD spectral bands, we propose that Cu(I) binds to the β domain first to form a Cu5Zn1 cluster or Cu6 cluster with emission at 670 and 750 nm, respectively, leaving the Zn4 cluster in the α domain.

Metallothionein-3: 63 Cu(I) binds to human 68 Zn7 -βα MT3 with no preference for Cu4 -β cluster formation

Human metallothioneins (MTs) are involved in binding the essential elements, Cu(I) and Zn(II), and the toxic element, Cd(II), in metal-thiolate clusters using 20 reduced cysteines. The brain-specific MT3 binds a mixture of Cu(I) and Zn(II) in vivo. Its metallation properties are critically important because of potential connections between Cu, Zn and neurodegenerative diseases. We report that the use of isotopically pure 63 Cu(I) and 68 Zn(II) greatly enhances the element resolution in the ESI-mass spectral data revealing species with differing Cu:Zn ratios but the same total number of metals. Room temperature phosphorescence and circular dichroism spectral data measured in parallel with ESI-mass spectral data identified the presence of specific Cu(I)-thiolate clusters in the presence of Zn(II). A series of Cu(I)-thiolate clusters form following Cu(I) addition to apo MT3: the two main clusters that form are a Cu6 cluster in the β domain followed by a Cu4 cluster in the α domain. 63 Cu(I) addition to 68 Zn7 -MT3 results in multiple species, including clustered Cu5 Zn5 -MT3 and Cu9 Zn3 -MT3. We assign the domain location of the metals for Cu5 Zn5 -MT3 as a Cu5 Zn1 -β cluster and a Zn4 -α cluster and for Cu9 Zn3 -MT3 as a Cu6 -β cluster and a Cu3 Zn3 -α cluster. While many reports of the average MT3 metal content exist, determining the exact Cu,Zn stoichiometry has proven very difficult even with native ESI-MS. The work in this paper solves the ambiguity introduced by the overlap of the naturally abundant Cu(I) and Zn(II) isotopes. Contrary to other reports, there is no indication of a major fraction of Cu4 -β-Znn -α-MT3 forming.

Structural Characterization of Cu(I)/Zn(II)-metallothionein-3 by Ion Mobility Mass Spectrometry and Top-Down Mass Spectrometry

Mammalian zinc metallothionein-3 (Zn7MT3) plays an important role in protecting against copper toxicity by scavenging free Cu(II) ions or removing Cu(II) bound to β-amyloid and α-synuclein. While previous studies reported that Zn7MT3 reacts with Cu(II) ions to form Cu(I)4Zn(II)4MT3ox containing two disulfides (ox), the precise localization of the metal ions and disulfides remained unclear. Here, we undertook comprehensive structural characterization of the metal-protein complexes formed by the reaction between Zn7MT3 and Cu(II) ions using native ion mobility mass spectrometry (IM-MS). The complex formation mechanism was found to involve the disassembly of Zn3S9 and Zn4S11 clusters from Zn7MT3 and reassembly into Cu(I)xZn(II)yMT3ox complexes rather than simply Zn(II)-to-Cu(I) exchange. At neutral pH, the β-domain was shown to be capable of binding up to six Cu(I) ions to form Cu(I)6Zn(II)4MT3ox, although the most predominant species was the Cu(I)4Zn(II)4MT3ox complex. Under acidic conditions, four Zn(II) ions dissociate, but the Cu(I)4-thiolate cluster remains stable, highlighting the MT3 role as a Cu(II) scavenger even at lower than the cytosolic pH. IM-derived collision cross sections (CCS) reveal that Cu(I)-to-Zn(II) swap in Zn7MT3 with concomitant disulfide formation induces structural compaction and a decrease in conformational heterogeneity. Collision-induced unfolding (CIU) experiments estimated that the native-like folded Cu(I)4Zn(II)4MT3ox conformation is more stable than Zn7MT3. Native top-down MS demonstrated that the Cu(I) ions are exclusively bound to the β-domain in the Cu(I)4Zn(II)4MT3ox complex as well as the two disulfides, serving as a steric constraint for the Cu(I)4-thiolate cluster. In conclusion, this study enhances our comprehension of the structure, stability, and dynamics of Cu(I)xZn(II)yMT3ox complexes.

Arsenic binding to human metallothionein-3

Arsenic poisoning is of great concern with respect to its neurological toxicity, which is especially significant for young children. Human exposure to arsenic occurs worldwide from contaminated drinking water. In human physiology, one response to toxic metals is through coordination with the metallochaperone metallothionein (MT). Central nervous system expression of MT isoform 3 (MT3) is thought to be neuroprotective. We report for the first time on the metalation pathways of As3+ binding to apo-MT3 under physiological conditions, yielding the absolute binding constants (log Kn, n = 1-6) for each sequential As3+ binding event: 10.20, 10.02, 9.79, 9.48, 9.06, and 8.31 M-1. We report on the rate of the reaction of As3+ with apo-MT3 at pH 3.5 with rate constants (kn, n = 1-6) determined for each sequential As3+ binding event: 116.9, 101.2, 85.6, 64.0, 43.9, and 21.0 M-1 s-1. We further characterize the As3+ binding pathway to fully metalated Zn7MT3 and partially metalated Zn-MT3. As3+ binds rapidly with high binding constants under physiological conditions in a noncooperative manner, but is unable to replace the Zn2+ in fully-metalated Zn-MT3. As3+ binding to partially metalated Zn-MT3 takes place with a rearrangement of the Zn-binding profile. Our work shows that As 3+ rapidly and efficiently binds to both apo-MT3 and partially metalated Zn-MT3 at physiological pH.

Cuproptosis-a potential target for the treatment of osteoporosis

Osteoporosis is an age-related disease of bone metabolism marked by reduced bone mineral density and impaired bone strength. The disease causes the bones to weaken and break more easily. Osteoclasts participate in bone resorption more than osteoblasts participate in bone formation, disrupting bone homeostasis and leading to osteoporosis. Currently, drug therapy for osteoporosis includes calcium supplements, vitamin D, parathyroid hormone, estrogen, calcitonin, bisphosphates, and other medications. These medications are effective in treating osteoporosis but have side effects. Copper is a necessary trace element in the human body, and studies have shown that it links to the development of osteoporosis. Cuproptosis is a recently proposed new type of cell death. Copper-induced cell death regulates by lipoylated components mediated via mitochondrial ferredoxin 1; that is, copper binds directly to the lipoylated components of the tricarboxylic acid cycle, resulting in lipoylated protein accumulation and subsequent loss of iron-sulfur cluster proteins, leading to proteotoxic stress and eventually cell death. Therapeutic options for tumor disorders include targeting the intracellular toxicity of copper and cuproptosis. The hypoxic environment in bone and the metabolic pathway of glycolysis to provide energy in cells can inhibit cuproptosis, which may promote the survival and proliferation of various cells, including osteoblasts, osteoclasts, effector T cells, and macrophages, thereby mediating the osteoporosis process. As a result, our group tried to explain the relationship between the role of cuproptosis and its essential regulatory genes, as well as the pathological mechanism of osteoporosis and its effects on various cells. This study intends to investigate a new treatment approach for the clinical treatment of osteoporosis that is beneficial to the treatment of osteoporosis.

Cryotop vitrification of large batches of pig embryos simultaneously provides excellent postwarming survival rates and minimal interference with gene expression

The most commonly used technique to vitrify pig embryos is the super open pulled straw (SOPS), where a maximum of 6 embryos can be vitrified simultaneously per device without compromising the minimum volume necessary for optimal preservation. Since optimal embryo transfer (ET) demands a transfer of 20-40 embryos per recipient, the customary use of SOPS complicates embryo warming and ET in field conditions. Such complications could be avoided when using the Cryotop® (OC) system, which has been proven to be an effective option for vitrifying at least 20 porcine embryos simultaneously. This study aimed to investigate the changes in the transcriptome of blastocysts caused by vitrification using both systems. In vivo-derived blastocysts were OC- (n = 60; 20 embryos/device) and SOPS- (n = 60; 4-6 embryos/device) vitrified and cultured for 24 h after warming. Nonvitrified blastocysts (n = 60) cultured for 24 h postcollection acted as controls. At the end of culture, 48 viable embryos from each group (6 pools of 8 embryos) were selected for microarray (GeneChip® Porcine Genome Array, P/N 900624, Affymetrix) analysis of differentially expressed genes (DEGs). The survival rate of embryos vitrified with the OC and SOPS systems (>97%) was similar to that of the control embryos (100%). Microarray analysis of each vitrification system compared to the control group showed 245 DEGs (89 downregulated and 156 upregulated) for the OC system and 210 (44 downregulated and 166 upregulated) for the SOPS system. Two pathways were enriched for the DEGs specifically altered in each vitrification system compared to the control (glycolysis/gluconeogenesis and carbon metabolism pathways for the OC system and amino sugar and nucleotide sugar metabolism and lysosome pathways in the SOPS group). The OC group showed 31 downregulated and 24 upregulated genes and two enriched pathways (mineral absorption and amino sugar and nucleotide sugar metabolism pathways) when compared to the SOPS group. In summary, vitrification with the OC system altered fewer genes related to apoptosis and activated genes related to cell proliferation. We conclude that vitrification with either the OC or SOPS system has a moderate to low effect on the transcriptome of in vivo-derived porcine blastocysts. Further investigation is needed to elucidate how the differences in the transcriptome of embryos vitrified with these systems affect their subsequent developmental ability after ET.

An Assessment of MT1A (rs11076161), MT2A (rs28366003) and MT1L (rs10636) Gene Polymorphisms and MT2 Concentration in Women with Endometrial Pathologies

Several studies have indicated a relationship between metallothionein (MT) polymorphisms and the development of different pathologies, including neoplastic diseases. However, no studies thus far have been conducted on the influence of MT polymorphisms and the development of endometrial lesions, including endometrial cancer. This study included 140 patients with normal endometrial tissue, endometrial polyps, uterine myomas and endometrial cancer. The tissue MT2 concentration was determined using the ELISA method. MT1A, MT2A and MT1L polymorphisms were analyzed using TaqMan real-time PCR genotyping assays. We found no statistical difference between the tissue MT2 concentration in patients with EC vs. benign endometrium (p = 0.579). However, tissue MT2 concentration was significantly different between uterine fibromas and normal endometrial tissue samples (p = 0.019). Menopause status did not influence the tissue MT2 concentration (p = 0.282). There were no significant associations between the prevalence of MT1A, MT2A and MT1L polymorphisms and MT2 concentration. The age, menopausal status, and diabetes status of patients were identified as EC risk factors.

Vermi-cyanobacterial remediation of cadmium-contaminated soil with rice husk biochar: An eco-friendly approach

Present study is aimed to evaluate the influence of earthworm (Eisenia fetida), Cyanobacteria (Cylindrospermum stagnale), and rice husk biochar (BC) on cadmium (Cd) detoxification in artificially contaminated soil. The Cd content was kept at 10 mg/kg in factorial design I, coupled with 2% and 0% BC. E. fetida and C. stagnale un-inoculated and inoculated experiments were maintained respectively as negative and positive controls. In factorial design II, E. fetida and C. stagnale were inoculated, along with BC (0% and 2%, denoted as B), without BC (WB), along with four different Cd concentrations (Cd-0, Cd-5, Cd-10, and Cd-20 mg/kg). Results suggest a substantial amount of Cd removal in BC-assisted treatments when compared to negative control-1. Cd (mg/g) in E. fetida tissue ranged from 0.019 (WB2) to 0.0985 (B4). C. stagnale of WB4 (0.036) bioaccumulated the most Cd (mg/g), while B2 showed the least (0.018). The maximum quantity of metallothionein (5.34 μM/mg) was detected in E. fetida of B4 (factorial design - II) and the minimum was claimed in WB1 (0.48 μM/mg) at the end. Earthworm metallothionein protein is a key component in Cd removal from soil by playing an important role in detoxification process. Microbial communities and humic substances were observed in BC-assisted treatments, which aided in Cd-contaminated soil remediation. The present findings suggest that BC (2%) + earthworms + algae could be a suitable remediation strategy for Cd contaminated soil. BC + earthworm + algal-based investigation on heavy metal remediation will be a valuable platform for detoxifying harmful metals in soils.

An Assessment of Metallothionein-Cadmium Binding in Rat Uterus after Subchronic Exposure Using a Long-Term Observation Model

Cadmium (Cd) is an environmental pollutant known to pose a public health issue. The mechanism of Cd toxicity on the uterus, including the protective role of metallothionein (MT), is still not fully understood. The aim of the study was to evaluate the degree of MT-Cd binding in the uterus of rats exposed per os to Cd at daily doses of 0.09, 0.9, 1.8 and 4.5 mg Cd/kg b.w. for 90 days. To assess the permanence of the bond, the rats were observed over long observation periods: 90 and 180 days after termination of exposure. Additionally, uterine concentration of Zn, Cu, Ca, Mg was determined. Cd leads immediately after exposure to a max. 30-fold increase in the concentration of Cd in the uterus, with only small amounts being bound to MT. After 90 days following termination of exposure, and especially after 180 days, an increase in MT-Cd concentration was noted for the three highest doses; even so, the degree of Cd binding by MT was still small. Additionally, the accumulation of Cd in the uterus disturbs the homeostasis of determined essential elements, manifested by a significant increase in Cu concentration and a decrease in Zn, Mg and Ca, especially 180 days after termination of exposure. The obtained results indicate that MT has only a slight protective role in the uterus and that Cd ions may have harmful effects not related to MT: directly on the uterine tissue, and indirectly by disturbing the homeostasis of its essential elements.

The mitochondrial Cu+ transporter PiC2 (SLC25A3) is a target of MTF1 and contributes to the development of skeletal muscle in vitro

The loading of copper (Cu) into cytochrome c oxidase (COX) in mitochondria is essential for energy production in cells. Extensive studies have been performed to characterize mitochondrial cuproenzymes that contribute to the metallation of COX, such as Sco1, Sco2, and Cox17. However, limited information is available on the upstream mechanism of Cu transport and delivery to mitochondria, especially through Cu-impermeable membranes, in mammalian cells. The mitochondrial phosphate transporter SLC25A3, also known as PiC2, binds Cu+ and transports the ion through these membranes in eukaryotic cells, ultimately aiding in the metallation of COX. We used the well-established differentiation model of primary myoblasts derived from mouse satellite cells, wherein Cu availability is necessary for growth and maturation, and showed that PiC2 is a target of MTF1, and its expression is both induced during myogenesis and favored by Cu supplementation. PiC2 deletion using CRISPR/Cas9 showed that the transporter is required for proliferation and differentiation of primary myoblasts, as both processes are delayed upon PiC2 knock-out. The effects of PiC2 deletion were rescued by the addition of Cu to the growth medium, implying the deleterious effects of PiC2 knockout in myoblasts may be in part due to a failure to deliver sufficient Cu to the mitochondria, which can be compensated by other mitochondrial cuproproteins. Co-localization and co-immunoprecipitation of PiC2 and COX also suggest that PiC2 may participate upstream in the copper delivery chain into COX, as verified by in vitro Cu+-transfer experiments. These data indicate an important role for PiC2 in both the delivery of Cu to the mitochondria and COX, favoring the differentiation of primary myoblasts.

Comparative cisplatin reactivity towards human Zn7-metallothionein-2 and MTF-1 zinc fingers: potential implications in anticancer drug resistance

Cis-diamminedichloroplatinum(II) (cisplatin) is a widely used metal-based chemotherapeutic drug for the treatment of cancers. However, intrinsic and acquired drug resistance limit the efficacy of cisplatin-based treatments. Increased production of intracellular thiol-rich molecules, in particular metallothioneins (MTs), which form stable coordination complexes with the electrophilic cisplatin, results in cisplatin sequestration leading to pre-target resistance. MT-1/-2 are overexpressed in cancer cells, and their expression is controlled by the metal response element (MRE)-binding transcription factor-1 (MTF-1), featuring six Cys2His2-type zinc fingers which, upon zinc metalation, recognize specific MRE sequences in the promoter region of MT genes triggering their expression. Cisplatin can efficiently react with protein metal binding sites featuring nucleophilic cysteine and/or histidine residues, including MTs and zinc fingers proteins, but the preferential reactivity towards specific targets with competing binding sites cannot be easily predicted. In this work, by in vitro competition reactions, we investigated the thermodynamic and kinetic preferential reactivity of cisplatin towards human Zn7MT-2, each of the six MTF-1 zinc fingers, and the entire human MTF-1 zinc finger domain. By spectroscopic, spectrometric, and electrophoretic mobility shift assays (EMSA), we demonstrated that cisplatin preferentially reacts with Zn7MT-2 to form Cys4-Pt(II) complexes, resulting in zinc release from MT-2. Zinc transfer from MT-2 to the MTF-1 triggers MTF-1 metalation, activation, and binding to target MRE sequences, as demonstrated by EMSA with DNA oligonucleotides. The cisplatin-dependent MT-mediated MTF-1 activation leading to apo-MT overexpression potentially establishes one of the molecular mechanisms underlying the development and potentiation of MT-mediated pre-target resistance.

Metals and Metallothionein Expression in Relation to Progression of Chronic Kidney Disease of Unknown Etiology (CKDu) in Sri Lanka

Chronic kidney disease of unknown etiology was investigated for metal relations in an endemic area by a cross-sectional study with CKD stages G1, G2, G3a, G3b, G4, G5 (ESRD), and endemic and nonendemic controls (EC and NEC) as groups. Subjects with the medical diagnosis were classified into groups by eGFR (SCr, CKD-EPI) and UACR of the study. It determined 24 metals/metalloids in plasma (ICPMS) and metallothionein (MT) mRNA in blood (RT-PCR). MT1A at G3b and MT2A throughout G2−G5 showed increased transcription compared to NEC (ANOVA, p < 0.01). Both MT1A and MT2A remained metal-responsive as associations emerged between MT2A and human MT inducer Cr (in EC: r = 0.54, p < 0.05, n = 14), and between MT1A and MT2A (in EC pooled with G1−G5: r = 0.58, p < 0.001, n = 110). Human MT (hMT)-inducers, namely Zn, Cu, As, Pb, and Ni; Σ hMT-inducers; 14 more non-inducer metals; and Σ MT-binding metals remained higher (p < 0.05) in EC as compared to NEC. Declining eGFR or CKD progression increased the burden of Be, Mg, Al, V, Co, Ni, Rb, Cs, Ba, Mn, Zn, Sr, Σ hMT-inducers, and Σ MT-binding metals in plasma, suggesting an MT role in the disease. MT1A/2A mRNA followed UACR (PCA, Dendrogram: similarity, 57.7%). The study provides evidence that proteinuric chronic renal failure may increase plasma metal levels where blood MT2A could be a marker.

Sophisticated expression responses of ZNT1 and MT in response to changes in the expression of ZIPs

The zinc homeostatic proteins Zn transporter 1 (ZNT1) and metallothionein (MT) function in dampening increases in cytosolic zinc concentrations. Conversely, the expression of ZNT1 and MT is expected to be suppressed during decreases in cytosolic zinc concentrations. Thus, ZNT1/MT homeostatic responses are considered to be essential for maintaining cellular zinc homeostasis because cellular zinc concentrations are readily altered by changes in the expression of several Zrt-/Irt-like proteins (ZIPs) under both physiological and pathological conditions. However, this notion remains to be tested experimentally. Here, we investigated the aforementioned homeostatic process by analyzing ZNT1 and MT protein expression in response to ZIP expression. Overexpression of cell-surface-localized ZIPs, such as ZIP4 and ZIP5, increased the cellular zinc content, which caused an increase in the expression of cell-surface ZNT1 and cytosolic MT in the absence of zinc supplementation in the culture medium. By contrast, elimination of the overexpressed ZIP4 and ZIP5 resulted in decreased expression of ZNT1 but not MT, which suggests that differential regulation of ZNT1 and MT expression at the protein level underlies the homeostatic responses necessary for zinc metabolism under certain conditions. Moreover, increased expression of apically localized ZIP4 facilitated basolateral ZNT1 expression in polarized cells, which indicates that such a coordinated expression mechanism is crucial for vectorial transcellular transport. Our results provide novel insights into the physiological maintenance of cellular zinc homeostasis in response to alterations in cytosolic zinc concentrations caused by changes in the expression of ZIPs.

Toxicity response to benzo[α]pyrene exposure: Modulation of immune parameters of the bay scallop, Argopectenirradians

Bay scallops were exposed to four BaP concentrations (0.5, 1.0, 10 and 50 μg/L) for 72 h to elucidate their immune response. Immune parameters were evaluated by measuring nitric oxide (NO) levels in hemolymph. Additionally, we measured peptidoglycan recognition proteins (PGRP), fibrinogen-domain-containing protein (FReDC1), metallothionein (MT), and heat shock protein (HSP) 70 mRNA expression in digestive diverticula. NO as well as FReDC1 and MT expression in each BaP group increased significantly over time except for the BaP 0.5 group. The PGRP and HSP70 mRNA expression in the BaP 50 group increased in the range 6-24 h and then decreased. In situ hybridization also confirmed that there was higher MT mRNA expression in the BaP 50 group than in the control group at 72 h. Our results suggest that higher levels of BaP dampened scallop immune responses, while simultaneously reducing their ability to cope with oxidative stress and DNA damage. BaP exposure can be considered a potential immune inducer in bay scallop.

Mitochondria-Dependent Oxidative Stress Mediates ZnO Nanoparticle (ZnO NP)-Induced Mitophagy and Lipotoxicity in Freshwater Teleost Fish

Due to many special characteristics, zinc oxide nanoparticles (ZnO NPs) are widely used all over the world, leading to their wide distribution in the environment. However, the toxicities and mechanisms of environmental ZnO NP-induced changes of physiological processes and metabolism remain largely unknown. Here, we found that addition of dietary ZnO NPs disturbed hepatic Zn metabolism, increased hepatic Zn and lipid accumulation, downregulated lipolysis, induced oxidative stress, and activated mitophagy; N,N,N',N'-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN, Zn²⁺ ions chelator) alleviated high ZnO NP-induced Zn and lipid accumulation, oxidative stress, and mitophagy. Mechanistically, the suppression of mitochondrial oxidative stress attenuated ZnO NP-activated mitophagy and ZnO NP-induced lipotoxicity. Taken together, our study elucidated that mitochondrial oxidative stress mediated ZnO NP-induced mitophagy and lipotoxicity; ZnO NPs could be dissociated to free Zn²⁺ ions, which partially contributed to ZnO NP-induced changes in oxidative stress, mitophagy, and lipid metabolism. Our study provides novel insights into the impacts and mechanism of ZnO NPs as harmful substances inducing lipotoxicity of aquatic organisms, and accordingly, metabolism-relevant parameters will be useful for the risk assessment of nanoparticle materials in the environment.

Response of biomarkers to metals, hydrocarbons and organochlorine pesticides contamination in crabs (Callinectes ornatus and C. bocourti) from two tropical estuaries (São José and São Marcos bays) of the Maranhão State (northeastern Brazil)

Response of biomarkers to chemical contamination was evaluated in crabs of the Callinectes genus (Callinectes ornatus and C. bocourti) from two tropical estuaries (São José and São Marcos bays) of the Maranhão State (northeastern Brazil). Biomarkers evaluated included hepatopancreatic metallothionein-like proteins (MTLP) and lipid peroxidation (LPO), as well as muscle acetylcholinesterase (AChE). Tissue concentrations of metals (pereiopod muscle and hepatopancreas), hydrocarbons (hepatopancreas) and organochlorine pesticides (hepatopancreas) were also evaluated. Crab samples were collected in three sites of each estuary (São Marcos Bay and São José Bay). Sampling was performed in August/2012 (dry season), January/2013 (rainy season), August/2013 (dry season), and January/2014 (rainy season). Concentrations of chemical contaminants and responses of biomarkers showed significant spatial (São Marcos Bay and São José Bay) and/or seasonal (dry and rainy seasons) and annual (2012-2014) variability. However, a general higher Zn concentration was observed in hepatopancreas of crabs from São José Bay. In turn, a general higher Cd concentration paralleled by oxidative damage (LPO) was observed in hepatopancreas of crabs from São Marcos Bay. As expected, these findings support the idea that this bay is more intensively or chronically impacted by industrial activities while the São José Bay is likely more affected by domestic activities. Interestingly, LPO level in crab hepatopancreas showed to be the most reliable and adequate biomarker to distinguish the two bays.

Bioreduction and bioremoval of hexavalent chromium by genetically engineered strains (Escherichia coli MT2A and Escherichia coli MT3)

The number of studies on the removal of hazardous metals from water using genetic engineering technologies is growing. A high rate of metal ion removal from the environment is ensured, particularly through the expression of cysteine and thiol-rich proteins such as metallothioneins in bacterial cells. In this study, we used recombinant strains created by cloning the human metallothioneins MT2A and MT3 into Escherichia coli Jm109 to assess the removal and reduction of hexavalent chromium (Cr(VI)) from aqueous solutions. MT2A was the most effective strain in both Cr(VI) removal (89% in 25 mg/L Cr(VI)) and Cr(VI) reduction (76% in 25 mg/L Cr(VI)). The amount of Cr adsorbed per dry cell by the MT2A strain was 22 mg/g. The biosorption of total Cr was consistent with the Langmuir isotherm model. Scanning electron microscope (SEM) images revealed that the morphological structures of Cr(VI)-treated cells were significantly damaged when compared to control cells. Scanning transmission electron microscope (STEM) images showed black spots in the cytoplasm of cells treated with Cr(VI). Shifts in the Fourier transform infrared spectroscopy analysis (FTIR) spectra of the cells treated with Cr(VI) showed that the groups interacting with Cr were hydroxyl, amine, amide I, amide II, phosphoryl and carbonyl. When all of the experimental data was combined, it was determined that both MT2A and MT3 were effective in removing Cr(VI) from aqueous solutions, but MT2A was more effective, indicating that MT2A may be employed as a biotechnological tool.

Resolving the immune landscape of human prostate at a single-cell level in health and cancer

The prostate gland produces prostatic fluid, high in zinc and citrate and essential for the maintenance of spermatozoa. Prostate cancer is a common condition with limited treatment efficacy in castration-resistant metastatic disease, including with immune checkpoint inhibitors. Using single-cell RNA-sequencing to perform an unbiased assessment of the cellular landscape of human prostate, we identify a subset of tumor-enriched androgen receptor-negative luminal epithelial cells with increased expression of cancer-associated genes. We also find a variety of innate and adaptive immune cells in normal prostate that were transcriptionally perturbed in prostate cancer. An exception is a prostate-specific, zinc transporter-expressing macrophage population (MAC-MT) that contributes to tissue zinc accumulation in homeostasis but shows enhanced inflammatory gene expression in tumors, including T cell-recruiting chemokines. Remarkably, enrichment of the MAC-MT signature in cancer biopsies is associated with improved disease-free survival, suggesting beneficial antitumor functions.

The Bioinorganic Chemistry of Mammalian Metallothioneins

The functions, purposes, and roles of metallothioneins have been the subject of speculations since the discovery of the protein over 60 years ago. This article guides through the history of investigations and resolves multiple contentions by providing new interpretations of the structure-stability-function relationship. It challenges the dogma that the biologically relevant structure of the mammalian proteins is only the one determined by X-ray diffraction and NMR spectroscopy. The terms metallothionein and thionein are ambiguous and insufficient to understand biological function. The proteins need to be seen in their biological context, which limits and defines the chemistry possible. They exist in multiple forms with different degrees of metalation and types of metal ions. The homoleptic thiolate coordination of mammalian metallothioneins is important for their molecular mechanism. It endows the proteins with redox activity and a specific pH dependence of their metal affinities. The proteins, therefore, also exist in different redox states of the sulfur donor ligands. Their coordination dynamics allows a vast conformational landscape for interactions with other proteins and ligands. Many fundamental signal transduction pathways regulate the expression of the dozen of human metallothionein genes. Recent advances in understanding the control of cellular zinc and copper homeostasis are the foundation for suggesting that mammalian metallothioneins provide a highly dynamic, regulated, and uniquely biological metal buffer to control the availability, fluctuations, and signaling transients of the most competitive Zn(II) and Cu(I) ions in cellular space and time.

The molecular and cellular basis of copper dysregulation and its relationship with human pathologies

Copper (Cu) is an essential micronutrient required for the activity of redox-active enzymes involved in critical metabolic reactions, signaling pathways, and biological functions. Transporters and chaperones control Cu ion levels and bioavailability to ensure proper subcellular and systemic Cu distribution. Intensive research has focused on understanding how mammalian cells maintain Cu homeostasis, and how molecular signals coordinate Cu acquisition and storage within organs. In humans, mutations of genes that regulate Cu homeostasis or facilitate interactions with Cu ions lead to numerous pathologic conditions. Malfunctions of the Cu⁺ -transporting ATPases ATP7A and ATP7B cause Menkes disease and Wilson disease, respectively. Additionally, defects in the mitochondrial and cellular distributions and homeostasis of Cu lead to severe neurodegenerative conditions, mitochondrial myopathies, and metabolic diseases. Cu has a dual nature in carcinogenesis as a promotor of tumor growth and an inducer of redox stress in cancer cells. Cu also plays role in cancer treatment as a component of drugs and a regulator of drug sensitivity and uptake. In this review, we provide an overview of the current knowledge of Cu metabolism and transport and its relation to various human pathologies.

Crambescin C1 Acts as A Possible Substrate of iNOS and eNOS Increasing Nitric Oxide Production and Inducing In Vivo Hypotensive Effect

Crambescins are guanidine alkaloids from the sponge Crambe crambe. Crambescin C1 (CC) induces metallothionein genes and nitric oxide (NO) is one of the triggers. We studied and compared the in vitro, in vivo, and in silico effects of some crambescine A and C analogs. HepG2 gene expression was analyzed using microarrays. Vasodilation was studied in rat aortic rings. In vivo hypotensive effect was directly measured in anesthetized rats. The targets of crambescines were studied in silico. CC and homo-crambescine C1 (HCC), but not crambescine A1 (CA), induced metallothioneins transcripts. CC increased NO production in HepG2 cells. In isolated rat aortic rings, CC and HCC induced an endothelium-dependent relaxation related to eNOS activation and an endothelium-independent relaxation related to iNOS activation, hence both compounds increase NO and reduce vascular tone. In silico analysis also points to eNOS and iNOS as targets of Crambescin C1 and source of NO increment. CC effect is mediated through crambescin binding to the active site of eNOS and iNOS. CC docking studies in iNOS and eNOS active site revealed hydrogen bonding of the hydroxylated chain with residues Glu377 and Glu361, involved in the substrate recognition, and explains its higher binding affinity than CA. The later interaction and the extra polar contacts with its pyrimidine moiety, absent in the endogenous substrate, explain its role as exogenous substrate of NOSs and NO production. Our results suggest that CC serve as a basis to develop new useful drugs when bioavailability of NO is perturbed.

Dysregulation of metallothionein and zinc aggravates periodontal diseases

BACKGROUND

Periodontitis (PD) is a multifaceted inflammatory disease connected to bacterial infection that results in the destruction of tooth supporting structures and eventually tooth loss. Given their involvement in infection and inflammation, both metallothionein (MT) and zinc (Zn) might play vital roles in the development and progression of PD. More specifically, both MT and Zn are heavily involved in regulating immune functions, controlling bacterial infection, balancing inflammatory responses, and reducing oxidative stress, all of which are associated with the pathogenesis of PD.

OBJECTIVE

This review paper will explore the physiological functions of MT and Zn and hypothesise how dysregulation could negatively affect periodontal health, leading to PD.

FINDINGS

Bacterial lipopolysaccharide (LPS) derived from periodontal pathogens, namely P. gingivalis initiates the acute phase response, thus upregulating the expression of MT which leads to the subsequent deficiency of Zn, a hallmark of periodontal disease. This deficiency leads to ineffective NETosis, increases the permeability of the gingival epithelium, and disrupts the humoral immune response, collectively contributing to PD. In addition, the presence of LPS in Zn deficient conditions favours M1 macrophage polarisation and maturation of dendritic cells, and also inhibits the anti-inflammatory activity of regulatory T cells. Collectively, these observations could theoretically give rise to the chronic inflammation seen in PD.

CONCLUSION

A disrupted MT and Zn homeostasis is expected to exert an adverse impact on periodontal health and contribute to the development and progression of PD.

Gawky modulates MTF-1-mediated transcription activation and metal discrimination

Metal-induced genes are usually transcribed at relatively low levels under normal conditions and are rapidly activated by heavy metal stress. Many of these genes respond preferentially to specific metal-stressed conditions. However, the mechanism by which the general transcription machinery discriminates metal stress from normal conditions and the regulation of MTF-1-meditated metal discrimination are poorly characterized. Using a focused RNAi screening in Drosophila Schneider 2 (S2) cells, we identified a novel activator, the Drosophila gawky, of metal-responsive genes. Depletion of gawky has almost no effect on the basal transcription of the metallothionein (MT) genes, but impairs the metal-induced transcription by inducing the dissociation of MTF-1 from the MT promoters and the deficient nuclear import of MTF-1 under metal-stressed conditions. This suggests that gawky serves as a 'checkpoint' for metal stress and metal-induced transcription. In fact, regular mRNAs are converted into gawky-controlled transcripts if expressed under the control of a metal-responsive promoter, suggesting that whether transcription undergoes gawky-mediated regulation is encrypted therein. Additionally, lack of gawky eliminates the DNA binding bias of MTF-1 and the transcription preference of metal-specific genes. This suggests a combinatorial control of metal discrimination by gawky, MTF-1, and MTF-1 binding sites.

Purification and structure analysis of zinc-binding protein from Mizuhopecten yessoensis

Zn-binding protein was obtained after purification from scallops (Mizuhopecten yessoensis) using gel permeation and ion-exchange chromatography. Amino acid determination showed that the cysteine of the zinc-binding protein accounted for one-third of the total amino acids, which is a typical feature of metallothionein (MT). The spectra of Fourier Transform Infrared Spectroscopy (FTIR) and Circular Dichroism (CD) were analyzed to predict the secondary structure information of zinc-binding protein: the α-helix was 46.55%, the β-sheets was 27.07%, the random coil was 16.48%, and the β-turns was 9.89%. Using a commercial kit to measure its antioxidant activity in vitro, the result showed that it had good scavenging ability to 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl radical (·OH), and reducing the ability to ferrous iron ions. With the process provided by this study, zinc-binding protein can be prepared in large quantities, which is the basis for its future commercialization. PRACTICAL APPLICATIONS: According to the extraction and purification process established in this study, a large amount of zinc-bound MT from the viscera of scallops can be obtained. And the zinc-bound MT had good antioxidant activity. In addition, the yield of each purification step has been calculated. The zinc-bound MTs from scallop' viscera can be prepared in large quantities by directly using the process in this manuscript or by equal magnification of this process. In the future, large-scale production can be considered to increase the economic value of scallops' viscera.

Revisiting the metallothionein genes polymorphisms and the risk of oral squamous cell carcinoma in a Brazilian population

Background

Metallothioneins (MTs) gene polymorphisms have been associated with the ability of free radical scavenging and detoxification of heavy metals leading to cancer development. Our aim was to revisit, in a Brazilian population, single-nucleotide polymorphisms (SNPs) of the MT gene family previously associated with oral squamous cell carcinoma (OSCC).

Material and Methods

A case-control investigation with 28 OSCC patients and 45 controls was conducted, using conventional risk factors (tobacco use and alcohol consumption) as covariates. SNPs genotyping for rs8052334 (MT1B), rs964372 (MT1B), and rs1610216 (MT2A) was performed by PCR-RFLP, and SNPs for rs11076161 (MT1A) were analyzed by TaqMan assay.

Results

The only SNP associated with increased risk for OSCC was the MT-1A AA genotype (OR = 4.7; p = 0.01). We have also evidenced for the first time a significant linkage disequilibrium between the SNPs of MT-2A and MT-1A in this population with the highest frequency (30%) of the unfavorable haplotype G/A/C/T (rs1610216 / rs11076161 / rs964372 / rs8052334) of MT gene polymorphisms (OR = 6.2; p = 0.04). Interestingly, after removing the effects of conventional risk factors, we have uncovered the significance of the AA genotype of the rs11076161 with increased odds of 19-fold higher towards OSCC development.

Conclusions

This is the first demonstration that a significant linkage disequilibrium among gene polymorphisms of the MT family may affect susceptibility to oral cancer, which is conditioned by the G/A/C/T haplotype (rs1610216/rs11076161/rs964372/ rs8052334) and the MT-1A gene polymorphism has a potential clinical utility for the OSCC risk assessment.

Key words:Oral squamous cell carcinoma, polymorphism, metallothionein, oral cancer.

Metallothionein MT1M Suppresses Carcinogenesis of Esophageal Carcinoma Cells through Inhibition of the Epithelial-Mesenchymal Transition and the SOD1/PI3K Axis

Metallothionein (MT1M) belongs to a family of cysteine-rich cytosolic protein and has been reported to be a tumor suppressor gene in multiple cancers. However, its role in esophageal carcinoma carcinogenesis remains unclear. In this study, MT1M expression was correlated with tumor type, stage, drinking and smoking history, as well as patient survival. We also studied the regulation and biological function of MT1M in esophageal squamous cell carcinoma (ESCC). We have found that MT1M is significantly downregulated in ESCC tissues compared with adjacent non-cancer tissues. Furthermore, restoration of expression by treatment with the demethylation agent A + T showed that MT1M downregulation might be closely related to hypermethylation in its promoter region. Over-expression of MT1M in ESCC cells significantly altered cell morphology, induced apoptosis, and reduced colony formation, cell viability, migration and epithelial-mesenchymal transition. Moreover, based on reactive oxygen species (ROS) levels, a superoxide dismutase 1 (SOD1) activity assay and protein analysis, we verified that the tumor-suppressive function of MT1M was at least partially caused by its upregulation of ROS levels, downregulation of SOD1 activity and phosphorylation of the SOD1 downstream pathway PI3K/AKT. In conclusion, our results demonstrated that MT1M was a novel tumor-suppressor in ESCC and may be disrupted by promoter CpG methylation during esophageal carcinogenesis.

Metallothionein dependent-detoxification of heavy metals in the agricultural field soil of industrial area: Earthworm as field experimental model system

Earthworms are known to reclaim soil contamination and maintain soil health. In the present study, the concentration of DTPA extractable heavy metals, Cd, Cu, Cr, Pb, and Zn in vermicasts and tissues of the earthworms (anecic: Lampito mauritii; epigeic: Drawida sulcata) collected from the soils of four different industrial sites, Site-I (Sago industry), Site-II (Chemplast industry), Site-III (Dairy industry) and Site-IV (Dye industry) have been studied. The heavy metals in industrial soils recorded were 0.01-326.42 mg kg^-1 with higher Cu, Cr, and Zn contents while the vermicasts showed lower heavy metal loads with improved physicochemical properties and elevated humic substances. The higher humic substances dramatically decreased the heavy metals in the soil. The bioaccumulation factors of heavy metals (mg kg^-1) are in the order: Zn (54.50) > Cu (17.43) > Cr (4.54) > Pb (2.24) > Cd (2.12). The greatest amount of metallothionein protein (nmol g^-1) was recorded in earthworms from Site-IV (386.76) followed by Site-III (322.14), Site-II (245.82), and Site-I (232.21). Drawida sulcata can produce a considerable amount of metallothionein protein than Lampito mauritii as the metallothionein production is dependent upon the presence of pollutants. The molecular docking analysis indicates a binding score of 980 for Cd, Cr and Cu, and 372 for Zn. Pb may bind with a non-metallothionein protein of earthworms and bio-accumulated in the internal chloragogenous tissues. Metallothionein neutralizes the metal toxicity and controls the ingestion of essential elements.

Detoxification gene expression, genotoxicity, and hepatorenal damage induced by subacute exposure to the new pyrethroid, imiprothrin, in rats

The pyrethroid imiprothrin is widely used worldwide for control of insects in the agriculture and public health sectors. No sufficient information is however available concerning detoxification gene expression, i.e., cytochrome P450 1A2 (CYP1A2) and metallothionein 1a gene, oxidative stress, lipid peroxidation, DNA damage, cytotoxicity, genotoxicity, and organ injury induced by imiprothrin in mammals. This study is designed to explain the mechanism of imiprothrin induced detoxification gene expression, DNA damage, cytotoxicity, genotoxicity, and organ toxicity in male rats. The benchmark dose (BMD) was calculated to find the best sensitive markers to imiprothrin toxicity. Imiprothrin was injected intraperitoneally (i.p.) into male rats once a day for 5 days with doses of 19, 38, and 75 mg/kg body weight (b.wt.). Imiprothrin caused a significant increase in lipid peroxidation and changes in oxidative stress biomarkers in treated rats. Significant dose-dependent changes in the liver and kidney biomarkers were observed. Histopathological alterations were seen in the liver and kidney tissue of male rats. Imiprothrin also significantly increased chromosomal aberrations (CA) and micronuclei in bone-marrow cells, and induced lipid peroxidation, oxidative stress, cytotoxicity, and liver and kidney dysfunction, and damage. Imiprothrin induced DNA damage and over detoxification gene expression of CYP1A2 and metallothionein 1a gene in hepatocytes of male rats. Imiprothrin thus shows clastogenic and genotoxic potential. The mechanism for hepatorenal toxicity and injury, genotoxicity/cytotoxicity of imiprothrin might be due to enhanced lipid peroxidation, and oxidative stress associated with overproduction of free radicals, especially reactive oxygen species, and an imbalance in redox status. From the BMD models, aspartate aminotransferase (AST), total protein, uric acid, superoxide dismutase (SOD), and micronuclei (MPEs) were very sensitive markers to imiprothrin toxicity.

Metallothionein 1 Overexpression Does Not Protect Against Mitochondrial Disease Pathology in Ndufs4 Knockout Mice

Mitochondrial diseases (MD), such as Leigh syndrome (LS), present with severe neurological and muscular phenotypes in patients, but have no known cure and limited treatment options. Based on their neuroprotective effects against other neurodegenerative diseases in vivo and their positive impact as an antioxidant against complex I deficiency in vitro, we investigated the potential protective effect of metallothioneins (MTs) in an Ndufs4 knockout mouse model (with a very similar phenotype to LS) crossed with an Mt1 overexpressing mouse model (TgMt1). Despite subtle reductions in the expression of neuroinflammatory markers GFAP and IBA1 in the vestibular nucleus and hippocampus, we found no improvement in survival, growth, locomotor activity, balance, or motor coordination in the Mt1 overexpressing Ndufs4-/- mice. Furthermore, at a cellular level, no differences were detected in the metabolomics profile or gene expression of selected one-carbon metabolism and oxidative stress genes, performed in the brain and quadriceps, nor in the ROS levels of macrophages derived from these mice. Considering these outcomes, we conclude that MT1, in general, does not protect against the impaired motor activity or improve survival in these complex I-deficient mice. The unexpected absence of increased oxidative stress and metabolic redox imbalance in this MD model may explain these observations. However, tissue-specific observations such as the mildly reduced inflammation in the hippocampus and vestibular nucleus, as well as differential MT1 expression in these tissues, may yet reveal a tissue- or cell-specific role for MTs in these mice.

Identification of novel activators of the metal responsive transcription factor (MTF-1) using a gene expression biomarker in a microarray compendium

Environmental exposure to metals is known to cause a number of human toxicities including cancer. Metal-responsive transcription factor 1 (MTF-1) is an important component of metal regulation systems in mammalian cells. Here, we describe a novel method to identify chemicals that activate MTF-1 based on microarray profiling data. MTF-1 biomarker genes were identified that exhibited consistent, robust expression across 10 microarray comparisons examining the effects of metals (zinc, nickel, lead, arsenic, mercury, and silver) on gene expression in human cells. A subset of the resulting 81 biomarker genes was shown to be altered by knockdown of the MTF1 gene including metallothionein family members and a zinc transporter. The ability to correctly identify treatment conditions that activate MTF-1 was determined by comparing the biomarker to microarray comparisons from cells exposed to reference metal activators of MTF-1 using the rank-based Running Fisher algorithm. The balanced accuracy for prediction was 93%. The biomarker was then used to identify organic chemicals that activate MTF-1 from a compendium of 11 725 human gene expression comparisons representing 2582 chemicals. There were 700 chemicals identified that included those known to interact with cellular metals, such as clioquinol and disulfiram, as well as a set of novel chemicals. All nine of the novel chemicals selected for validation were confirmed to activate MTF-1 biomarker genes in MCF-7 cells and to lesser extents in MTF1-null cells by qPCR and targeted RNA-Seq. Overall, our work demonstrates that the biomarker for MTF-1 coupled with the Running Fisher test is a reliable strategy to identify novel chemical modulators of metal homeostasis using gene expression profiling.

MicroRNA-101 inhibits cadmium-induced angiogenesis by targeting cyclooxygenase-2 in primary human umbilical vein endothelial cells

Exposure to toxic metal contaminants, such as cadmium compounds (Cd²⁺), has been shown to induce adverse effects on various organs and tissues. In particular, blood vessels are severely impacted by Cd²⁺ exposure, which may lead to cardiovascular diseases (CVDs). According to previous studies, CVDs are associated with increased cyclooxygenase 2 (COX-2) levels. However, the mechanisms by which CdCl₂-induced COX-2 overexpression leads to cardiovascular dysfunction remain unclear. Herein, we show that the relative gene expressions of VEGF and PTGS2 (COX-2 encoding gene) are positively correlated in CVDs patients. Moreover, we demonstrate that the in vitro administration of CdCl₂ induces cytotoxicity and endoplasmic reticulum (ER) stress in primary human umbilical vein endothelial cells (HUVECs). The induction of ER stress and the overexpression of COX-2 in CdCl₂-treated cells alters the protein level of vascular endothelial growth factor (VEGF), resulting in abnormal angiogenesis and increased cytotoxicity. At the pre-transcription level, the inhibition of ER stress by siGRP78 (a key mediator of ER stress) can restore normal angiogenesis in the CdCl₂-exposed cells. Meanwhile, at the transcription level, the adverse effects of CdCl₂ exposure may be reversed via genetic modification with siRNA (siPTGS2) or by using phytochemical inhibitors (parthenolide, PN) of COX-2. Finally, at the post-transcription level, COX-2 expression may be restricted by the binding of microRNA-101 (miR-101) to the 3'-UTR of PTGS2 mRNA. The use of mimic miR-101 (mi101) to induce the expression of miR-101 eventually leads to reduced COX-2 protein levels, relieved ER stress, and less abnormal angiogenesis and cytotoxicity of CdCl₂-exposed primary HUVECs. Overall, our results suggest that CdCl₂-induced abnormal angiogenesis is mediated by miR-101/COX-2/VEGF-axis-dependent ER stress, and that cardiovascular dysfunction may be controlled by manipulating COX-2 at the pre-transcription, transcription, and post-transcription levels.

Copper-induced oxidative stress and biomarkers in the postlarvae of Penaeus indicus

The objective of the present research is to study the levels of reactive oxygen species (ROS) and protein carbonyl (PC) and the functional protein levels of metallothioneins (MT) in Penaeus indicus postlarvae (PL) upon sublethal copper exposure and to determine the biomarkers. The PL were exposed to sublethal copper of 0.164 ppm. The experiments were carried out in the laboratory over a period of 30 days with sampling intervals of 24, 48, and 96 h and 10, 20, and 30 days. The present study confirms that high oxidative stress can be induced from 24 h onwards upon sublethal exposure to copper in P. indicus PL. This is evident from the increasing levels of ROS in the exposed PL during both short-term and long-term exposures to sublethal copper. Since variability in metallothionein levels from 24 h through 30 days of experimental period was observed, metallothioneins cannot be regarded as a good biomarker as far as copper toxicity with respect to P. indicus PL is concerned. The effect of copper on protein carbonyl seems to be very rapid and consistent. The results suggest that protein carbonyl in P. indicus PL is significantly induced in a time-dependent manner upon copper exposure even at sublethal dose, and it seems reasonable to support that protein carbonyl could be used as a biomarker to copper toxicity.

Functional analysis of MTF-1 and MT promoters and their transcriptional response to zinc (Zn) and copper (Cu) in yellow catfish Pelteobagrus fulvidraco

Metal-responsive transcription factor-1 (MTF-1) and metallothionein (MT) expression are involved in metal homeostasis and detoxification. Here, we characterized the structure and functions of mtf-1 and mt promoters in yellow catfish Pelteobagrus fulvidraco. Many important binding sites of transcriptional factors, such as heat shock promoter element (HSE) and metal responsive element (MRE), were predicted on their promoter regions. Cu did not significantly influence the activity of mtf-1 promoter, but Zn increased its promoter activity. Cu and Zn induced the increase of mt promoter activity. HSE site of mtf-1 promoter was the functional binding locus responsible for Zn-induced mtf-1 transcriptional activation. Zn and Cu induced transcriptional activation of mt gene through the MTF-1- and MRE-dependent pathway. Using primary hepatocytes of yellow catfish, we found that Cu and Zn induced the mt expression; Cu did not significantly influence the mRNA and total protein levels of MTF-1, but Zn up-regulated its mRNA and total protein expression. Both Zn and Cu treatment also up-regulated MTF-1 nuclear protein expression, which in turn increased the mt expression. Taken together, these findings delineated the transcriptional regulation of MT and MTF-1 under Zn or Cu treatments, and provided some mechanisms for the regulation of Cu and Zn homeostasis in vertebrates.

Metallothionein isoforms as double agents - Their roles in carcinogenesis, cancer progression and chemoresistance

Metallothioneins (MTs) are small cysteine-rich intracellular proteins with four major isoforms identified in mammals, designated MT-1 through MT-4. The best known biological functions of MTs are their ability to bind and sequester metal ions as well as their active role in redox homeostasis. Despite these protective roles, numerous studies have demonstrated that changes in MT expression could be associated with the process of carcinogenesis and participation in cell differentiation, proliferation, migration, and angiogenesis. Hence, MTs have the role of double agents, i.e., working with and against cancer. In view of their rich biochemical properties, it is not surprising that MTs participate in the emergence of chemoresistance in tumor cells. Many studies have demonstrated that MT overexpression is involved in the acquisition of resistance to anticancer drugs including cisplatin, anthracyclines, tyrosine kinase inhibitors and mitomycin. The evidence is gradually increasing for a cellular switch in MT functions, showing that they indeed have two faces: protector and saboteur. Initially, MTs display anti-oncogenic and protective roles; however, once the oncogenic process was launched, MTs are utilized by cancer cells for progression, survival, and contribution to chemoresistance. The duality of MTs can serve as a potential prognostic/diagnostic biomarker and can therefore pave the way towards the development of new cancer treatment strategies. Herein, we review and discuss MTs as tumor disease markers and describe their role in chemoresistance to distinct anticancer drugs.

Metallothionein 2A gene polymorphisms in relation to diseases and trace element levels in humans

Human metallothioneins are a superfamily of low molecular weight intracellular proteins, whose synthesis can be induced by essential elements (primarily Zn and Cu), toxic elements and chemical agents, and stress-producing conditions. Of the four known isoforms in the human body MT2 is the most common. The expression of metallothioneins is encoded by a multigene family of linked genes and can be influenced by single nucleotide polymorphisms (SNPs) in these genes. To date, 24 SNPs in the MT2A gene have been identified with the incidence of about 1 % in various population groups, and three of them were shown to affect physiological and pathophysiological processes. This review summarises current knowledge about these three SNPs in the MT2A gene and their associations with element concentrations in the body of healthy and diseased persons. The most investigated SNP is rs28366003 (MT2A -5 A/G). Reports associate it with longevity, cancer (breast, prostate, laryngeal, and in paranasal sinuses), and chronic renal disease. The second most investigated SNP, rs10636 (MT2A +838G/C), is associated with breast cancer, cardiovascular disease, and type 2 diabetes. Both are also associated with several metal/metalloid concentrations in the organism. The third SNP, rs1610216 (MT2A -209A/G), has been studied for association with type 2 diabetes, cardiomyopathy, hyperglycaemia, and Zn concentrations. Metallothionein concentrations and MT2A polymorphisms have a potential to be used as biomarkers of metal exposure and clinical markers of a number of chronic diseases. This potential needs to be studied and verified in a large number of well-defined groups of participants (several hundreds and thousands) with a focus on particular physiological or pathological condition and taking into consideration other contributing factors, such as environmental exposure and individual genetic and epigenetic makeup.

The classic metal-sensing transcription factor MTF1 promotes myogenesis in response to copper

Metal-regulatory transcription factor 1 (MTF1) is a conserved metal-binding transcription factor in eukaryotes that binds to conserved DNA sequence motifs, termed metal response elements. MTF1 responds to both metal excess and deprivation, protects cells from oxidative and hypoxic stresses, and is required for embryonic development in vertebrates. To examine the role for MTF1 in cell differentiation, we use multiple experimental strategies [including gene knockdown (KD) mediated by small hairpin RNA and clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9), immunofluorescence, chromatin immunopreciptation sequencing, subcellular fractionation, and atomic absorbance spectroscopy] and report a previously unappreciated role for MTF1 and copper (Cu) in cell differentiation. Upon initiation of myogenesis from primary myoblasts, both MTF1 expression and nuclear localization increased. Mtf1 KD impaired differentiation, whereas addition of nontoxic concentrations of Cu+-enhanced MTF1 expression and promoted myogenesis. Furthermore, we observed that Cu+ binds stoichiometrically to a C terminus tetra-cysteine of MTF1. MTF1 bound to chromatin at the promoter regions of myogenic genes, and Cu addition stimulated this binding. Of note, MTF1 formed a complex with myogenic differentiation (MYOD)1, the master transcriptional regulator of the myogenic lineage, at myogenic promoters. These findings uncover unexpected mechanisms by which Cu and MTF1 regulate gene expression during myoblast differentiation.-Tavera-Montañez, C., Hainer, S. J., Cangussu, D., Gordon, S. J. V., Xiao, Y., Reyes-Gutierrez, P., Imbalzano, A. N., Navea, J. G., Fazzio, T. G., Padilla-Benavides, T. The classic metal-sensing transcription factor MTF1 promotes myogenesis in response to copper.

Promoter activity of earthworm metallothionein in mouse embryonic fibroblasts

The regulation of metallothionein (MT) gene expression as important part of the detoxification machinery is only scarcely known in invertebrates. In vertebrates, MT gene activation is mediated by the metal-transcription factor 1 (MTF-1) binding to metal response elements (MREs). In invertebrates, the mechanisms of MT gene activation seems to be more diverse. In some invertebrate species, MTF-1 orthologues as well as their ability to activate MT genes via MREs have been uncovered. Although earthworm MTs have been well studied, a MTF-1 orthologue has not yet been described and MT gene activation mechanisms are largely unknown. Analyses of the earthworm wMT2 promoter by reporter gene assays have been performed. We could show that the wMT2 promoter was active in mouse embryonic fibroblasts (NIH/3T3) as well as in mouse MTF-1-/-cells (DKO7). The presence of mouse MTF-1 (mMTF1) led to a significant increase in reporter gene activity. We observed that cadmium as well as zinc had an effect on promoter activity. In the presence of zinc, promoter activity doubled in NIH cells, however, we did not observe a significant effect in the DKO7 cell line. Cadmium decreased promoter activity in DKO7 cells, but this effect could be reversed by providing mMTF1 in a co-transfection experiment. We suggest that MT gene expression in the earthworm is not entirely dependent on a MRE binding protein. Interestingly, the shortest promoter fragment including MRE1 showed the highest promoter activity under control conditions.

Effects of Marine Toxin Domoic Acid on Innate Immune Responses in Bay Scallop Argopecten irradians

Domoic acid (DA) is an amnesic shellfish poisoning toxin produced by some species of the genera Pseudo-nitzschia and Nitzschia. This toxin has harmful effects on various species, especially scallops. This study aimed to investigate the effects of DA exposure on the immune and physical responses of bay scallop, Argopecten irradians. Various immunological and physical parameters were assessed (acid phosphatase (ACP), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), lipid peroxide (LPO), nitric oxide (NO), and the total protein content) in the haemolymph of scallops at 3, 6, 12, 24, and 48 h post-exposure to DA at different concentrations (10, 50, and 100 ng/mL). Moreover, the expression of immune-related genes (CLT-6, FREP, HSP90, MT, PGRP, and PrxV) was assessed. The activities of ACP, ALP, and LDH and the total protein content and LPO increased upon exposure to DA at different concentrations, while NO levels were decreased. Furthermore, immune-related genes were assessed upon DA exposure. Our results showed that exposure to DA negatively impacts immune function and disrupts physiological activities in bay scallops.

Zn Supplement-Antagonized Cadmium-Induced Cytotoxicity in Macrophages In Vitro: Involvement of Cadmium Bioaccumulation and Metallothioneins Regulation

Cadmium (Cd) is a toxic metal leading to multiple forms of organ damage. Zinc (Zn) was reported as a potential antagonist against Cd toxicity. The present study investigates the antagonistic effect of Zn (20 μM) on Cd (20 or 50 μM) cytotoxicity in macrophages in vitro. The results shows that Cd exposure caused dose-dependent morphologic and ultrastructural alterations in RAW 264.7 macrophages. Zn supplement significantly inhibited Cd cytotoxicity in RAW 264.7 or HD-11 macrophages by mitigating cell apoptosis, excessive ROS output, and mitochondrial membrane depolarization. Notably, Zn supplement for 12 h remarkably prevented intracellular Cd2+ accumulation in 20 μM (95.99 ± 9.93 vs 29.64 ± 5.08 ng/106 cells; P = 0.0008) or 50 μM Cd (179.78 ± 28.66 vs 141.62 ± 22.15 ng/106 cells; P = 0.003) exposed RAW 264.7 cells. Further investigation found that Cd promoted metallothioneins (MTs) and metal regulatory transcription factor 1 (MTF-1) expression in RAW 264.7 macrophages. Twenty μM Zn supplement dramatically enhanced MTs and MTF-1 levels in Cd-exposed RAW 264.7 macrophages. Intracellular Zn2+ chelation or MTF-1 gene silencing inhibited MTs synthesis in Cd-exposed RAW 264.7 macrophages, which was accompanied by the declined expression of MTF-1, indicating that regulation of Zn on MTs was partially achieved by MTF-1 mobilization. In conclusion, this study demonstrates the antagonism of Zn against Cd cytotoxicity in macrophages and reveals its antagonistic mechanism by preventing Cd2+ bioaccumulation and promoting MTs expression.

Hypoxia tolerance in the Norrin-deficient retina and the chronically hypoxic brain studied at single-cell resolution

The mammalian CNS is capable of tolerating chronic hypoxia, but cell type-specific responses to this stress have not been systematically characterized. In the Norrin KO (Ndp ^KO ) mouse, a model of familial exudative vitreoretinopathy (FEVR), developmental hypovascularization of the retina produces chronic hypoxia of inner nuclear-layer (INL) neurons and Muller glia. We used single-cell RNA sequencing, untargeted metabolomics, and metabolite labeling from ¹³C-glucose to compare WT and Ndp ^KO retinas. In Ndp ^KO retinas, we observe gene expression responses consistent with hypoxia in Muller glia and retinal neurons, and we find a metabolic shift that combines reduced flux through the TCA cycle with increased synthesis of serine, glycine, and glutathione. We also used single-cell RNA sequencing to compare the responses of individual cell types in Ndp ^KO retinas with those in the hypoxic cerebral cortex of mice that were housed for 1 week in a reduced oxygen environment (7.5% oxygen). In the hypoxic cerebral cortex, glial transcriptome responses most closely resemble the response of Muller glia in the Ndp ^KO retina. In both retina and brain, vascular endothelial cells activate a previously dormant tip cell gene expression program, which likely underlies the adaptive neoangiogenic response to chronic hypoxia. These analyses of retina and brain transcriptomes at single-cell resolution reveal both shared and cell type-specific changes in gene expression in response to chronic hypoxia, implying both shared and distinct cell type-specific physiologic responses.

Specificity of the Metallothionein-1 Response by Cadmium-Exposed Normal Human Urothelial Cells

Occupational and environmental exposure to cadmium is associated with the development of urothelial cancer. The metallothionein (MT) family of genes encodes proteins that sequester metal ions and modulate physiological processes, including zinc homeostasis. Little is known about the selectivity of expression of the different MT isoforms. Here, we examined the effect of cadmium exposure on MT gene and isoform expression by normal human urothelial (NHU) cell cultures. Baseline and cadmium-induced MT gene expression was characterized by next-generation sequencing and RT-PCR; protein expression was assessed by Western blotting using isoform-specific antibodies. Expression of the zinc transporter-1 (SLC30A1) gene was also assessed. NHU cells displayed transcription of MT-2A, but neither MT-3 nor MT-4 genes. Most striking was a highly inducer-specific expression of MT-1 genes, with cadmium inducing transcription of MT-1A, MT-1G, MT-1H, and MT-1M. Whereas MT-1G was also induced by zinc and nickel ions and MT-1H by iron, both MT-1A and MT-1M were highly cadmium-specific, which was confirmed for protein using isoform-specific antibodies. Protein but not transcript endured post-exposure, probably reflecting sequestration. SLC30A1 transcription was also affected by cadmium ion exposure, potentially reflecting perturbation of intracellular zinc homeostasis. We conclude that human urothelium displays a highly inductive profile of MT-1 gene expression, with two isoforms identified as highly specific to cadmium, providing candidate transcript and long-lived protein biomarkers of cadmium exposure.

Is the presence of Central European strains of Raphidiopsis (Cylindrospermopsis) raciborskii a threat to a freshwater fish? An in vitro toxicological study in common carp cells

As yet European strains of Raphidiopsis raciborskii (previously Cylindrospermopsis raciborskii) have not been found to produce known cyanotoxins although their extracts have caused adverse effects in mammals, as shown using in vitro and in vivo experimental models. The present study investigated whether R. raciborskii isolated from Western Poland and Ukraine can affect fish cells using in vitro exposures of hepatocytes and red blood cells (RBC), and brain homogenates obtained from common carp (Cyprinus carpio) to 1.0% and 0.1% extracts of 7 strains. The studied extracts evoked different responses of catalase activity in hepatocytes with both increase and decrease observed under low and high concentrations. The cellular thiol pool was also altered with most extracts inducing a decrease in the activity of glutathione-S-transferase, and Ukrainian strains leading to an increase in glutathione level and a decrease in metallothionein content. All the studied extracts induced comparable reactive oxygen species formation, lipid peroxidation, protein carbonylation and DNA fragmentation in hepatocytes, and all but one increased the activity of caspase-3. Only one extract caused lysosomal membrane destabilization as measured by neutral red retention in RBC. In contrast to extracts of Ukrainian isolates, exposure of brain homogenates to extracts of Polish strains induced an increase in acetylcholinesterase activity suggesting the neurotoxic action of their exudates. The results indicate that both Polish and Ukrainian strains of R. raciborskii may pose a toxicological risk to freshwater fish, and further, that Polish strains may produce compound(s) evoking neurotoxic effects.

Characterization analysis and heavy metal-binding properties of CsMTL3 in Escherichia coli

Members of the metallothionein (MT) superfamily are involved in coordinating transition metal ions. In plants, MT family members are characterized by their arrangement of Cys residues. In this study, one member of the MT superfamily, CsMTL3, was characterized from a complementary DNA (cDNA) library from young cucumber fruit; CsMTL3 is predicted to encode a 64 amino acid protein with a predicted molecular mass of 6.751 kDa. Phylogenetic analysis identified it as a type 3 family member as the arrangement of N-terminal Cys residues was different from that of MT-like 2. Heterologous expression of CsMTL3 in Escherichia coli improved their heavy metal tolerance, particularly to Cd2+ and Cu2+, and led to increased uptake of Cd2+ and Cu2+; increased uptake was also observed for cells expressing Arabidopsis thaliana metallothionein 3 (AtMT3) and phytochelatin-like (PCL), with greatest uptake in PCL-expressing cells. These findings demonstrate that CsMTL3 can improve metal tolerance, especially for Cd2+ ions, when heterologously expressed in E. coli, and suggest that the composition and arrangement of N-terminal Cys residues are associated with binding capacity and preference for different metal ions.

AP-1 (bZIP) Transcription Factors as Potential Regulators of Metallothionein Gene Expression in Tetrahymena thermophila

Metallothioneins (MT) are multi-stress proteins mainly involved in metal detoxification. MT gene expression is normally induced by a broad variety of stimulus and its gene expression regulation mainly occurs at a transcriptional level. Conserved motifs in the Tetrahymena thermophila MT promoters have been described. These motifs show a consensus sequence very similar to AP-1 sites, and bZIP type transcription factors might participate in the MT gene expression regulation. In this research work, we characterize four AP-1 transcription factors in each of four different analyzed Tetrahymena species, detecting a high conservation among them. Each AP-1 molecule has its counterpart in the other three Tetrahymena species. A comparative qRT-PCR analysis of these AP-1 genes have been carried out in different T. thermophila strains (including metal-adapted, knockout and/or knockdown strains among others), and under different metal-stress conditions (1 or 24 h Cd²⁺, Cu²⁺, or Pb²⁺ treatments). The possible interaction of these transcription factors with the conserved AP-1 motifs present in MT promoters has been corroborated by protein-DNA interaction experiments. Certain connection between the expression patterns of the bZIP and MT genes seems to exist. For the first time, and based on our findings, a possible gene expression regulation model including both AP-1 transcription factors and MT genes from the ciliate T. thermophila has been elaborated.