Zinc antagonizes iron-regulation of tyrosine hydroxylase activity and dopamine production in Drosophila melanogaster

SLC30A9: an evolutionarily conserved mitochondrial zinc transporter essential for mammalian early embryonic development

SLC30A9 (ZnT9) is a mitochondria-resident zinc transporter. Mutations in SLC30A9 have been reported in human patients with a novel cerebro-renal syndrome. Here, we show that ZnT9 is an evolutionarily highly conserved protein, with many regions extremely preserved among evolutionarily distant organisms. In Drosophila melanogaster (the fly), ZnT9 (ZnT49B) knockdown results in acutely impaired movement and drastic mitochondrial deformation. Severe Drosophila ZnT9 (dZnT9) reduction and ZnT9-null mutant flies are pupal lethal. The phenotype of dZnT9 knockdown can be partially rescued by mouse ZnT9 expression or zinc chelator TPEN, indicating the defect of dZnT9 loss is indeed a result of zinc dyshomeostasis. Interestingly, in the mouse, germline loss of Znt9 produces even more extreme phenotypes: the mutant embryos exhibit midgestational lethality with severe development abnormalities. Targeted mutagenesis of Znt9 in the mouse brain leads to serious dwarfism and physical incapacitation, followed by death shortly. Strikingly, the GH/IGF-1 signals are almost non-existent in these tissue-specific knockout mice, consistent with the medical finding in some human patients with severe mitochondrial deficiecny. ZnT9 mutations cause mitochondrial zinc dyshomeostasis, and we demonstrate mechanistically that mitochondrial zinc elevation quickly and potently inhibits the activities of respiration complexes. These results reveal the critical role of ZnT9 and mitochondrial zinc homeostasis in mammalian development. Based on our functional analyses, we finally discussed the possible nature of the so far identified human SLC30A9 mutations.

Advancing glioblastoma treatment through iron metabolism: A focus on TfR1 and Ferroptosis innovations

Glioblastoma (GBM) represents a formidable challenge in oncology, characterized by aggressive proliferation and poor prognosis. Iron metabolism plays a critical player in GBM progression, with dysregulated iron uptake and utilization contributing to tumor growth and therapeutic resistance. Iron's pivotal role in DNA synthesis, oxidative stress, and angiogenesis underscores its significance in GBM pathogenesis. Elevated expression of iron transporters, such as transferrin receptor 1 (TfR1), highlights the tumor's reliance on iron for survival. Innovative treatment strategies targeting iron dysregulation hold promise for overcoming therapeutic challenges in GBM management. Approaches such as iron chelation therapies, induction of ferroptosis to nanoparticle-based drug delivery systems exploit iron-dependent vulnerabilities, offering avenues for enhance treatment efficacy and improve patient outcomes. As research advances, understanding the complexities of iron-mediated carcinogenesis provides a foundation for developing precision medicine approaches tailored to combat GBM effectively. This review explores the intricate relationship between iron metabolism and GBM, elucidating its multifaceted implications and therapeutic opportunities. By consolidating the latest insights into iron metabolism in GBM, this review underscores its potential as a therapeutic target for improving patient care in combination with the standard of care approach.

Lead specifically declines tyrosine hydroxylase activity to induce the onset of Parkinson's disease through disrupting dopamine biosynthesis in fly models

Parkinson's disease (PD) is one of the fastest-growing neurodegenerative diseases and has been linked to the exposure to numerous environmental neurotoxins. Although lead (Pb) exposure has been related to the development of PD, the molecular target of Pb to cause the onset of PD is insufficiently investigated. Herein, we explored the effects of Pb exposure on behavior, pathophysiology, and gene expression of wild-type (WT) fly (Drosophila melanogaster) by comparison with its PD model. After exposure to Pb, the WT flies showed PD-like locomotor impairments and selective loss of dopaminergic (DAergic) neurons, displaying similar phenotypes to fly PD model (PINK1). Transcriptomic analysis showed the similarity in gene expression profiles between Pb treatment WT flies and PINK1 mutant flies. Moreover, Pb exposure resulted in endogenous dopamine deficits in WT flies. Analyses of gene expression and enzyme activity confirmed that Pb exposure reduced tyrosine hydroxylase (TH) activity and led to failure of dopamine synthesis. Furthermore, molecular dynamics simulation confirmed that Pb was adsorbed by TH and subsequently inhibited the enzymatic activity. Exogenous injection of L-dopa and melatonin could partially rescue the pathological phenotypes of Pb-exposed flies and PD fly model. Antagonist injection of microRNA-133, which negatively regulated the expression of TH gene, ultimately rescued in the manifestation of PD phenotypes in flies. Involvement of TH overexpression mutants of fly strongly promoted the resistance to Pb exposure and rescued both behavior and the number of DAergic neurons. Therefore, our study elucidates the Pb molecular target in dopamine pathway and mechanism underlying the risks of Pb exposure on the occurrence of PD at environmentally-relevant concentrations.

Tyrosine Hydroxylase Inhibitors and Dopamine Receptor Agonists Combination Therapy for Parkinson's Disease

There are currently no disease-modifying therapies for Parkinson's disease (PD), a progressive neurodegenerative disorder associated with dopaminergic neuronal loss. There is increasing evidence that endogenous dopamine (DA) can be a pathological factor in neurodegeneration in PD. Tyrosine hydroxylase (TH) is the key rate-limiting enzyme for DA generation. Drugs that inhibit TH, such as alpha-methyltyrosine (α-MT), have recently been shown to protect against neurodegeneration in various PD models. DA receptor agonists can activate post-synaptic DA receptors to alleviate DA-deficiency-induced PD symptoms. However, DA receptor agonists have no therapeutic effects against neurodegeneration. Thus, a combination therapy with DA receptor agonists plus TH inhibitors may be an attractive therapeutic approach. TH inhibitors can protect and promote the survival of remaining dopaminergic neurons in PD patients' brains, whereas DA receptor agonists activate post-synaptic DA receptors to alleviate PD symptoms. Additionally, other PD drugs, such as N-acetylcysteine (NAC) and anticholinergic drugs, may be used as adjunctive medications to improve therapeutic effects. This multi-drug cocktail may represent a novel strategy to protect against progressive dopaminergic neurodegeneration and alleviate PD disease progression.

Effects of Zinc Supplementation on Metabolomic Profiles in Tanzanian Infants: A Randomized Trial

BACKGROUND

Provision of zinc supplementation to young children has been associated with reduced infectious morbidity and better growth outcomes. However, the metabolic pathways underlying these outcomes are unclear, and metabolomic data from humans undergoing zinc supplementation, particularly infants, are generally lacking.

OBJECTIVES

This study aimed to examine the effect of zinc supplementation on metabolic profiles in Tanzanian infants aged 6 wk and 6 mo.

METHODS

Blood samples were collected at age 6 wk and 6 mo from 50 Tanzanian infants who were enrolled in a randomized placebo-controlled trial of zinc supplementation (5 mg oral daily). Metabolomic analysis using an ultrahigh-performance liquid chromatography/tandem mass spectroscopy platform was performed to identify potential metabolomic profiles and biomarkers associated with zinc supplementation. Principal component analysis (PCA) was used to summarize metabolomic data from all samples. Two-way repeated measures analysis of variance with compound symmetry covariance structures were used to compare metabolome levels over time between infants in the 2 treatment arms.

RESULTS

In PCA, the samples tended to be more separated by child age (6 wk compared with 6 mo) than by zinc supplementation status. We found that zinc supplementation affected a variety of metabolites associated with amino acid, lipid, nucleotide, and xenobiotic metabolism, including indoleacetate in the tryptophan metabolism pathway; 3-methoxytrosine and 4-hydrxoyphenylphruvate in the tyrosine pathway; eicosanedioate, 2-aminooctanoate, and N-acetyl-2-aminooctanoate in the fatty acid pathway; and N6-succinyladenosine in the purine metabolism pathway. Compared to the relatively small number of metabolites associated with zinc supplements, many infant metabolites changed significantly from age 6 wk to 6 mo.

CONCLUSIONS

Zinc supplementation, despite having overall clinical benefits, appears to induce limited metabolomic changes in blood metabolites in young infants. Future larger studies may be warranted to further examine metabolic pathways associated with zinc supplementation. The parent trial was registered at clinicaltrials.gov as NCT00421668.

Immobilization of Aspergillus oryzae tyrosine hydroxylase on ZnO nanocrystals for improved stability and catalytic efficiency towards L-dopa production

The current study focuses on the submerged fermentation of tyrosine hydroxylase (TH) from Aspergillus oryzae IIB-9 and its immobilization on zinc oxide nanocrystals (ZnO-NPs) for increased L-dopa production. The volume of Vogel's medium (75 ml), period of incubation (72 h), initial pH (5.5), and size of inoculum (1.5 ml) were optimal for maximum TH activity. The watch glass-dried (WG) and filter paper-dried (FP) ZnO-NPs were prepared and characterized using analytical techniques. The UV-Vis spectra revealed 295 and 285 nm absorption peaks for WG-ZnO-NPs and FP-ZnO-NPs dispersed in isopropanol. X-ray diffraction analysis confirmed the crystalline nature of ZnO-NPs. FTIR spectra band from 740 to 648.1/cm and 735.8/cm to 650.1/cm showed the stretching vibrations of WG-ZnO-NPs and FP-ZnO-NPs, respectively. The particle size of ZnO-NPs observed by scanning electron microscopy (SEM) images was between 130 and 170 nm. Furthermore, the stability of immobilized TH on ZnO-NPs was determined by varying the incubation period (10 min for WG-NPs and 15 min for FP-NPs) and temperature (45 °C and 30 °C for WG and FP-NPs, respectively). Incubating enzymes with various copper, iron, manganese, and zinc salts studied the catalytic efficiency of TH. Immobilization of TH on ZnO-NPs resulted in an 11.05-fold increase in TH activity, thus enhancing stability and catalytic efficiency.

Targeting dopamine transporter to ameliorate cognitive deficits in Alzheimer's disease

Alzheimer's disease (AD) is characterized by the pathologic deposition of amyloid and neurofibrillary tangles in the brain, leading to neuronal damage and defective synapses. These changes manifest as abnormalities in cognition and behavior. The functional deficits are also attributed to abnormalities in multiple neurotransmitter systems contributing to neuronal dysfunction. One such important system is the dopaminergic system. It plays a crucial role in modulating movement, cognition, and behavior while connecting various brain areas and influencing other neurotransmitter systems, making it relevant in neurodegenerative disorders like AD and Parkinson's disease (PD). Considering its significance, the dopaminergic system has emerged as a promising target for alleviating movement and cognitive deficits in PD and AD, respectively. Extensive research has been conducted on dopaminergic neurons, receptors, and dopamine levels as critical factors in cognition and memory in AD. However, the exact nature of movement abnormalities and other features of extrapyramidal symptoms are not fully understood yet in AD. Recently, a previously overlooked element of the dopaminergic system, the dopamine transporter, has shown significant promise as a more effective target for enhancing cognition while addressing dopaminergic system dysfunction in AD.

Role of dopamine in the pathophysiology of Parkinson's disease

A pathological feature of Parkinson's disease (PD) is the progressive loss of dopaminergic neurons and decreased dopamine (DA) content in the substantia nigra pars compacta in PD brains. DA is the neurotransmitter of dopaminergic neurons. Accumulating evidence suggests that DA interacts with environmental and genetic factors to contribute to PD pathophysiology. Disturbances of DA synthesis, storage, transportation and metabolism have been shown to promote neurodegeneration of dopaminergic neurons in various PD models. DA is unstable and can undergo oxidation and metabolism to produce multiple reactive and toxic by-products, including reactive oxygen species, DA quinones, and 3,4-dihydroxyphenylacetaldehyde. Here we summarize and highlight recent discoveries on DA-linked pathophysiologic pathways, and discuss the potential protective and therapeutic strategies to mitigate the complications associated with DA.

The expression of Catsup in escort cells affects Drosophila ovarian stem cell niche establishment and germline stem cells self-renewal via Notch signaling

Stem cell niche provides extrinsic signals to maintain stem cell renewal or initiate cell differentiation. Drosophila niche is composed of somatic terminal filament cells, cap cells and escort cells. However, the underlying mechanism for the development of stem cell niche remains largely unclear. Here we found that the expression of a zinc transporter Catsup is essential for ovary morphogenesis. Catsup knockdown in escort cells results in defects of niche establishment and germline stem cells self-renewal. These defects could be modified by altered expression of genes involved in zinc metabolism or intervention of dietary zinc levels. Further studies indicated that Catsup RNAi affected adult ovary morphogenesis by suppressing Notch signaling. Lastly, we demonstrated that the defects of Catsup RNAi could be restored by overexpression of heat shock cognate protein 70 (Hsc70). These findings expand our understanding of the mechanisms controlling adult oogenesis and niche establishment in Drosophila.

Metal ions in the physiology of insects

The 2022 Molecular Physiology volume of Current Opinion in Insect Science offers an overview of transition-metal ion (iron, copper, manganese, and zinc) biology and nonessential heavy metal ion (cadmium, lead, and methylmercury) toxicology in the model organism Drosophila melanogaster and in other insect species. An article on ticks serves as an informative evolutionary comparator for iron and heme physiology. The complex interface between environmental exposure to metals, symbiotic or pathogenic microbes, and insect behavior and reproduction is considered.

Palliative effect of Moringa olifera-mediated zinc oxide nanoparticles against acrylamide-induced neurotoxicity in rats

Repeated acrylamide (ACR) exposure in experimental animals and humans causes variable degrees of neuronal damage. Because of its unique features, several green synthesized nanomaterials are explored for neuromodulatory activity. Hence, this study investigated the effect of green synthesized zinc oxide nanoparticles using Moriga olifera leaves extract (MO-ZnONP) against acrylamide (ACR)-induced neurobehavioral and neurotoxic impacts in rat. Forty male Sprague Dawley rats were distributed into four groups orally given distilled water, MO-ZnONP (10 mg/kg b.wt), ACR (20 mg/kg b.wt), or MO-ZnONP + ACR for 60 days. Gait quality and muscular, motor, and sensory function were assessed. Acetylcholinesterase (AChE), dopamine, catalase, malondialdehyde (MDA), and Zn brain contents were determined. Brain histopathology and immunohistochemical localization of the amyloid-β protein and abnormal Tau were performed. The results revealed that MO-ZnONP significantly reduced ACR-induced sensory dysfunctions, hind limb abnormality, and motor deficits. Additionally, the ACR-induced increase in dopamine and AChE were significantly supressed by MO-ZnONP. Besides, MO-ZnONP significantly restored catalase and Zn content but reduced increased MDA brain content resulting from ACR. Furthermore, the ACR-induced neurodegenerative changes and increased amyloid-β and phosphorylated Tau immunoexpression was significantly abolished by MO-ZnONP. Conclusively, MO-ZnONP could be used as a biologically effective compound for mitigating ACR's neurotoxic and neurobehavioral effects.

Local iron deficiency in the substantia nigra directly contributes to hyperlocomotion phenotypes

Brain iron is precisely regulated, and disrupted brain iron homeostasis is implicated in neuropsychological disease. Mounting evidence connects the iron status of the substantia nigra (SN) with locomotion-related neural symptomatology. Researchers in this field have long speculated that iron deficiency in the SN directly causes the high-locomotion symptoms observed in neuropsychiatric disorders. However, no direct experimental evidence of a causal relationship has been presented. To explore the relationship between iron deficiency in the SN and locomotion-related phenotypes, we stereotaxically injected the well-documented iron chelator, deferiprone (DFP) into the SN of mice to induce regional brain iron deprivation and subsequently performed behavioral tests. Altered expression of iron metabolism-related molecules was detected in the brain regions with interventions, and behavioral changes were observed. Targeted iron chelation effectively decreased the local iron content of the SN. Among the brain regions examined, only DFP injected into the SN resulted in the hyperlocomotion phenotype. Upon SN iron chelation, transferrin receptor (Tfr) expression was found to be upregulated. Conversely, viral vector-mediated SN-Tfr knockdown was sufficient to induce SN iron deficiency and mimic the hyperlocomotion phenotype. All locomotion changes had a significant negative correlation with iron alteration in the SN. Furthermore, SN iron disturbance also contributed to poor sleep efficiency. Thus, SN iron deficiency directly contributed to triggering both hyperlocomotion and sleep disturbances. This study offers a promising research and therapeutic direction for iron-linked neuropsychiatric diseases.

Identification and characterization of a heme exporter from the MRP family in Drosophila melanogaster

BACKGROUND

The heme group constitutes a major functional form of iron, which plays vital roles in various biological processes including oxygen transport and mitochondrial respiration. Heme is an essential nutrient, but its pro-oxidant nature may have toxic cellular effects if present at high levels, and its synthesis is therefore tightly regulated. Deficiency and excess of heme both lead to pathological processes; however, our current understanding of metazoan heme transport is largely limited to work in mammals and the worm Caenorhabditis elegans, while functional analyses of heme transport in the genetically amenable Drosophila melanogaster and other arthropods have not been explored.

RESULTS

We implemented a functional screening in Schneider 2 (S2) cells to identify putative heme transporters of D. melanogaster. A few multidrug resistance-associated protein (MRP) members were found to be induced by hemin and/or involved in heme export. Between the two plasma membrane-resident heme exporters CG4562 and CG7627, the former is responsible for heme transit across the intestinal epithelium. CG4562 knockdown resulted in heme accumulation in the intestine and lethality that could be alleviated by heme synthesis inhibition, human MRP5 (hMRP5) expression, heme oxygenase (HO) expression, or zinc supplement. CG4562 is mainly expressed in the gastric caeca and the anterior part of the midgut, suggesting this is the major site of heme absorption. It thus appears that CG4562 is the functional counterpart of mammalian MRP5. Mutation analyses in the transmembrane and nucleotide binding domains of CG4562 characterized some potential binding sites and conservative ATP binding pockets for the heme transport process. Furthermore, some homologs in Aedes aegypti, including that of CG4562, have also been characterized as heme exporters.

CONCLUSIONS

Together, our findings suggest a conserved heme homeostasis mechanism within insects, and between insects and mammals. We propose the fly model may be a good complement to the existing platforms of heme studies.

Molecular physiology of zinc in Drosophila melanogaster

New research in Drosophila melanogaster has revealed the molecular mechanisms of zinc involvement in many biological processes. A newly discovered Metallothionein is predicted to have a higher zinc specificity than the other isoforms. Zinc negatively regulates tyrosine hydroxylase activity by antagonizing iron binding, thus rendering the enzyme ineffective or non-functional. The identification of a new chaperone of the protein disulfide isomerase family provided mechanistic insight into the protein trafficking defects caused by zinc dyshomeostasis in the secretory pathway. Insect models of tumor pathogenesis indicate that zinc regulates the structural stabilization of cells by transcriptionally regulating matrix metalloproteinases while zinc dyshomeostasis in the secretory pathway modulates cell signaling through endoplastic recticulum stress.