Zinc
What are disruptions to normal Zn Homeostasis?
- Disruptions to Normal Zn homeostasis o Genetic and non-genetic causes o Biochemical markers Serum/plasma levels of Zn or Zn levels in RBCs Enzymatic activity — lower than normal deficiency
What are some therapeutic uses of Zinc?
- Therapeutic uses of Zn o Common cold o Acute diarrhea o Treatment of WD (Wilson's Disease) o Supplements of Zn can decrease muscular degeneration
Provide an overview of zinc roles in physiology and pathogenesis.
- Zn Roles in physiology and pathogenesis — overview o Different responses at the cellular level Organismal level Changes at different systems (Endocrine, immune) Hypogonadism Growth retardation Increased risk of infections and inflammation Diabetes
When was the significance of zinc deficiency in discovered in humans?
- Zn deficiency in humans — discovery o Mandatory to include Zn in IV fluids o First case in Iran o Small testes, growth retardation, low spermatogenesis o Whole wheat flour-based diets, very low intake of animal protein (low bioavailability of Zn) o Cereal high in phytates, that inhibit Zn absorption o Refined foods are high in phytates
What are the non-genetic causes of Zn deficiency?
- Zn deficiency — non-genetic causes o Insufficient Zn intake o Unrefined cereal-based diets o IV fluid for prolonged time without Zn
What is the Spondylocheirodysplastic Ehlers-Danlos Syndrome (SCD-EDS)?
- Zn disorders: SCD-EDS o Mutations in a different ZIP o Connective tissue disorder o Increased rate of ZIP13 degradation o No treatment for this disorder
What are the non-genetic causes of Zn overload?
- Zn overload: non-genetic causes o Accidental ingestion of supplements o Overuse of some medicines can also cause overload o Zn coming off utensils o Main effect is copper deficiency o Inhalation of fumes that are Zn-based Treatments: chelating therapy — bind tightly to Zn and potentially get rid of it through urine
What are Zn recommendations?
- Zn recommendations o For different age groups and enders o RDA ~8-11 mg/day; UL = 40 mg/day (Cu deficiency) o Adults F: 11 mg, Adults M: 8 mg o Requirements change with pregnancy/lactating o Important for growth and cell differentiation o Last trimester of fetal growth Zn requirement is much higher o Mt can bind both Zn and overload of Zn can lead to Cu-deficiency activates MTF4, leading to increased Mt expression Mt will preferentially bind to Cu over Zn
Zinc Overview
1. Trace element essential for almost all living organisms 2. Second most abundant after iron 3. Content in human body: 2-3 g all organs, tissues and body fluids 4. It exists as a divalent cation (Zn2+) only not redox active (redox neutral) under physiological/normal conditions! 5. number of zinc proteins = 10% of human proteome Coordinated by nitrogen, oxygen, and sulfur atoms Extra:Differences in content and RDA (Fe, Cu and Zn) Cannot generate free radicals like Cu and Fe Many zinc proteins - more than Fe and Cu Cadmium coordinated by particular amino acids? Binds to O of cysteine, glutamic acid, aspartic acid under physiological conditions
What are some dietary enhancers that influence Cu absorption?
1.Acidic pH 2.Citric acid 3.Amino acids such as histidine and cysteine 4.Glutathione (also found in lumen of GI tract) *pH breaks down food and increases chances of releasing zinc from proteins and nucleic acids in food pH helps with release of zinc Glutathione: Solubilize zinc and increases chances of absorption Soluble + loose binding complexes easier to be bound to transporters
What is Zn deficiency presented in the elderly?
1.Nearly 30% of healthy elderly subjects may be zinc deficient in developed countries 2.Oxidative stress and chronic inflammation are important contributing factors for several chronic diseases attributed to aging - e.g. atherosclerosis and related cardiac disorders, cancer, neurodegeneration, immunologic disorders and the aging process itself! Zinc Supplementation - Protective?
Describe the cellular distribution of Zn transporters?
10 different types of ZIPs have been found and 14 ZnTs have been found depends on type of tissue Secretory granules of vesicles, they are mostly ZntS
What are the two types of Zn transporters?
2 main types but not the only one ZIP: do not know how they work, thought to be channels and not transporters, (channel = open and close VS transporter = allow efflux/influx due to [ ] differences and use energy that comes from ATP) works as channels ZnTs: zin proton exchangers and use energy associated with [ ] of H+s to transport zinc (zinc protein exchangers) Direction of flow of zinc via tube - zinc comes into cell and increase [ ] of cytosolic zinc and can be placed/found in membrane of organelles and this could be lumen of organelle but zinc allows transports zinc from lumen to cytosol Decrease of cytosolic Zn [ ] Other transporters can transport zinc (ex. voltage gated Ca channels, TRPs or glutamate receptors-NMDA, DMT1 can transport zinc - minor role)
What is the job of Zinc responsive-transcriptional regulators?
Activate gene expression (ex. MTF1)* Bolded transcription activators are eukaryotic cells increase gene expression Repressors: And MTF1 can do both
What are some dietary inhibitors of Zn?
Fe: Non-heme Fe when in huge [ ] compared to zinc, can act as inhibitor why does it have to be non-heme? Tight binding, insoluble complex Increase in heat causes AGE's (compounds that bind to Zn and are hard to degrade and zinc is not available because it decreases bioavailability of zinc) Zinc needs to be released from whatever it is bound to Production of compounds and complexes that decrease absorption of Zn Compounds that inhibits absorption - tightly binds to zinc which makes it less available for transporters decrease availability
How is Zn involved in the (ZnR/GPR39) receptors?
G alpha q: Zn binds to its receptor and activates G protein and alpha subunit activates PLC - production of IPP and second messenger increased in cell Increased Ca2+ means different kinds of kinases Binding site for Zn: histidine and aspartic acid are typical coordinating amino acids ------------ GPCR receptor is coupled to G protein (interacting with zinc receptor is G alpha q type and the one associated with activation of Ca pathway and intracellular Ca)
What are the mechanisms of maintaining systemic zinc homeostasis?
Gene expression level of ZIP4 and ZnT1 and they regulate how much is coming in and ends up in blood Storage: degraded MT in liver = source of zinc if body needs it Excretion: resorption = most zinc goes from lumen of GI tract to blood but resportion is from blood to lumen (body excretes zinc back to lumen of GI tract to get rid of excess) Control and regulate amount of zinc in fluid and provide point of control of homeostasis at whole body level ZIP5: bring zinc in from blood into cell and ZnT6: spills out zinc into lumen of GI tract
How is zinc important in the structural role of crystallization and storage of insulin?
Glucose metabolism Insulin is made and secreted in beta cells of pancreas Insulin can be stored in dense granules as hexamer 2 zinc atoms coordinated by 6 histidine side chains
What is the protein mediated intracellular Zn2+ release?
How MT can release zinc and what is signal that causes release of zinc? Oxidative NO (many radicals and molecules that have antioxidant activity) MT bound to zinc and oxidant signaling such as NO would oxidate MT what does S mean? When sulfurs gets oxidized, they release zn and form bridge but oxidizing sulfurs release zinc that initially binds atoms of zinc? Release of zinc causes changes in gene expression by binding MTF1 more MT expression (ia transcription factor MTF1 which has zinc fingers - fingers act as regulatory domains that leave [ ] of zinc in cella nd activate MTF1 which increases expression of certain genes) MTF1 as transcription factor binds to particular regions in genes and one specific for MTF1 is MRE What started that signal? Cell tries to protect itself and one of them is MT itself MT is MT once it has metal bound to it (thymine + metal = Metallothionine = MT)
What are some Zn-MTF1 regulated genes?
How does it act as an activator for certain genes and repressor for other genes? Physical inhibition - MRE (sequence that MTF can recognize - metal responsive element - DNA sequence for that gene) MRE is downstream for where polymerase binds Znt! = upstream and VS Zip10 is downstream Complexes of transcription so molecules of different proteins that polymerize and MT interact with may be different to change gene transcription of particular genes Physical inhibition/change Additional proteins involved in that transcription DONE
How does regulation of Zn take place at the cellular level?
Increase expression of ZIPs Znts decrease proteins that will bind to zinc (ex. MT) And excess Zn in cytosol cell increases proteins that capture zinc (ex. MT) and decrease transporters that bring zinc out of organelles and cell Changing expression of transporters ensures that cell regulates amount and [ ] of zinc inside cell because [ ] gives a message to cell
How does Zn act as 2nd messenger:the Ca2+ of the 21st century?
Left: Ligand and have receptor Ligand acts on its own receptor and initiates downstream signaling cascade and there is different outcomes Cascade stimulates release of zinc from intracellular stores (ex. ER) - causes temporary increase of intracellular zinc in cytosol (similar to Ca) downstream target proteins that sense increase causes a cellular response Binding of ligand to receptor changes activity of transporters of zinc (increase or decrease transport of zinc from outside of cell) causes increase or decrease of intracellular zinc causes cellular response by means of [zinc] activating particular target proteins Activation of receptor may cause release of zinc from MT (methallothione - can bind to Cu and Zn but it prefers to bind to Cu but it is possible for MT to bind to Zn) signaling cascade can cause release of Zn from MT causes increase in cytosolic zinc causes cellular response Zinc wave = transient increase in cytosolic zinc due to transient increase in Ca Ca increase causes increase in zinc How to change activity of protein quickly without changing expression or transcription? Phosphorylation Right: Different receptor bound to ligand causes signaling cascade and transfer message to nucleus - changes in gene transcription Genes that code for zinc transporters (positively or negatively) express more or less transporters at plasma membrane causes particular cellular response Homeostatic zinc signals change [ ] of transporters and can increase or decrease expression (at transcriptional level and causes changes in membrane expression) Different between 2? Any response that involves gene transcription changes is considered a slower response
What are some the zinc responsive-bfs and regulated genes?
Mammalian: Sense [ ] of zinc and KLF4 is a transcription factor that has zinc fingers KLF4 stimulates expression of ZIP4 Low zinc levels: need cell to express more ZIP4 to absorb more zinc in intestine Do not bring more zinc inside cell(ZIP10) ZMT1 - allows for export of zinc outside of cell = increased expression when zinc is high inside of cell Diagrams are very general
Provide an overview of zinc distribution in cells.
Nanomolar range allows zinc to work as signaling molecule If cells want to use zinc as signaling molecule in cytosol. Then [zinc] in cytosol has to be low in resting state in order for cell to detect changing [ ] to see it as a message to the cell Cytosol = fluid of cytoplasm VS cytoplasm = anything inside of cell (ex. organelles) Zinc can be stored in vesicles (feature of zinc compared to Fe and Cu) Intestinal cells (paneth cells) are able to store zinc in vesicles, zinc is also found in mitochondria ZIP can be expressed at plasma membrane and vesicles and different organelles brings zinc into cytosol and increase [zinc] ZnTs: found at plasma membrane and in vesicles andin organelles take away zinc from cytosol decrease [ ] of zinc in cytosol
How is zinc absorbed and handled by enterocytes?
Proteases and nucleases release zinc bound to nucleic acids and proteins and zinc is free and mainly at leel of intestine, is taken up of ZIP4 (main transporter) Zinc can be transported by other carriers (ex. DMT1, amino acid transporters - histamine have zinc bound to it and whole complex is brought in) but main pathway is through ZIP4 Zinc can also be a source of paracellular way goes in between cells secondary absorption mechanisms for when carriers are saturated (due to high Zn in food and once ZIP is saturated) Cell store zinc in organelles (7 for golgi), ZIP allows for efflux of xinc depending on requirements of cell, in certain vesicles or released into circulation by ZnT1 Once in circulation, albumin is main carrier for zinc but there are other proteins that can bind to zinc
What are the dietary zinc food sources?
Seafood and liver chicken and beef Bound to proteins found in sources and to nucleic acids Grains and cereals: whole wheat VS white bread zinc is higher for whole wheat BUT due to [ ] of phytates acids in grains, phytates are higher in [ ] in whole wheat bread (phytates and inhibitors of absorption of Zn) but bioavailability of zinc is lower Whole wheat: lower bioavailability but higher zinc content compared to white bread (less Zn but more bioavailable because it has less phytates)
How is Zn able to regulate insulin secretion and clearance?
Structural roe of zin is in storage of insulin and have endocrine, autocrine and paracrine effects in liver and pancreas Zinc is stored with insulin - allows for creation of exomere (found in beta cells - stores insulin with zinc) Zinc can act on same cells and affect farther secretion of insulin (autocrine) Paracrine: zinc affects neighbouring cells in pancreas (ex. alpha cells) - affect secretion of other hormones of other cells Endocrine: zinc ends up in portal system (in circulation) that connects pancreas with liver and can affect function of liver in different ways (ex. decreases or inhibits clearance of insulin by liver) Liver chops many protein hormones and insulin is one of them Many protein hormones get cleaved and degraded when they go by liver (ex. insulin) Zinc as signaling molecule (message of slide) and is released into extracellular space
What are the major zinc flows and metabolism in humans?
Zinc distribution in humans - total content is higher than CU but less than Fe Most of body zinc is found in skeletal muscle (different from Cu and Fe) Blood in zinc: includes cellular components + serum + plasma most is found in cellular components (RBCs - 80%) and serum but bound to proteins which is albumin (20%) Total content of zinc in body is found in serum 2nd organ is bone and then pancreas, kidney, liver Excretion: via feces (80%) + urine or skin or semen (zinc is lost during ejaculation)
How is Zn important in forming zinc finger motifs used in RNA & DNA binding proteins?
Zinc fingers: domains/motifs of specific proteins that can interact with DNA RNA binding proteins that also bind to zinc via motifs Zinc fingers can be classified in different ways. Cys (C) or His (H) residues + zinc atom C2H2 zinc finger (e.g. MTF-1) C4 zinc finger C6 zinc finger
how is zinc important in cellular signalling?
Zinc has become 21st century-type of messenger (similar to Ca2+) Zn is involved in cellular signalling (ex. extracellular signaling - Zn can bind to specific membrane receptors in allosteric way in the case of nervous system - NMDA receptor and negatively impact activity of receptor) Receptors that use Zn as a ligand (first messenger) receptor that binds to Zn (GPR receptor) causes signaling cascade associated with G protein ----------- Zinc can act as allosteric regulator on receptor found in plasma membrane of neighbouring cell and allosteric regulation changes downstream signaling cascade of that receptor or combine its own receptor Zinc is ligand that activates receptor______
What are biological roles of some of the zinc-binding proteins?
Zinc is a cofactor - crucial for activity of enzyme Zinc is required for many proteins and enzymes to acquire final 3D conformation (associated with function) zinc can affect function of protein via being a cofactor Heme synthesis: Requires zinc as cofactor for 2nd stage of synthesis Zinc binds to tubulin Zinc roles: Catalytic (as a cofactor) Structural
Illustrate zinc's catalytic role in the body as co-factor of many enzymes?
Zinc is also bind to dismutase (SOD) Different isoforms found in mito, cytosol or extracellular (SOD1,2,3) Group of SOD that bind to both Cu and Zn (cytosolic SOD) - Cu works as a cofactor , Zn does not work as cofactor Cu is used as donor or recipient due to differences in redox but not Zn Zn is redox neutral - doesn't change charges (usually 2+) Only structural (bring amino acids together) Sturtcure dictates activity/function role of Zn in SOD is not only structural but can play a role in an indirect way - potentially affects redox potential of Cu Whether Zn is there or not, chance of Cu to work as cofactor or becomes reduced/oxidized changes based on presence/absence of Zn Zn has indirect functionality role due to its effect on Cu's redox state Role of Zn in SOD1 may not just be structural but also vital part in its catalytic activity
How does Zn help regulate glucose homeostasis?
Zinc is believed to have insulin-type of effect (stimulates insulin pathway by inhibiting inhibitors of insulin pathway - ex. phosphatases)
What is the significance of fertilization induced zinc sparks?
Zinc sparks = seen during fertilization of mammalian eggs and caused by release of zinc to extracellular space (found within cortex of egg and when fertilization occurs, release of zinc to extracellular space) Zinc sparks seen after fertilization and appear to be a good indication of successful fertilization Link between zinc release and mitotic sample (egg is rested in mitotic division and successful fertilization allows for finalization of meiosis but for embryo to develop, they need to divide so mitosis has to occur Mitosis may be zinc-dependent due to zinc sparks released out into extracellular space decrease [ ] of zinc of cell and important for hardening of zona pellucida (layer surrounding egg that prevents polyspermy - release of zinc may be important for hardening of layer and therefore for prevention of polyspermy)
How is Zn deficiency and diabetes related?
Zn deficiency and diabetes o Linked to diabetes o Focused on diabetes 1 and 2 o Diabetes 1 complete insulin deficiency o Diabetes 2 cells become insensitive to insulin Insulin is there but cells can't respond to it o Phosphatases that negatively control the cascade of insulin Downregulated But Zn inhibits these phosphatases, and therefore activates the pathways Deficiency of Zn will mean that the phosphatases will be active and pathway will be downregulated even if insulin is present
What are the mechanisms for Zn deficiency in the elderly?
Zn deficiency in the Elderly o Zn deficiency related to age-related disorders o Protective therapy Life Sciences 3N03 Dr. Rodriguez C-01 2 Antioxidants that inhibit enzymes that generate ROS Synthesis of MT important for antioxidant response o The Zn supplementation has antioxidant and anti-inflammatory effects Protection against two things: inflammation and ROS o Two types of immunity Adaptive carried out by T-cells and B-lymphocytes that secrete antibodies T-helper cells have different types With aging, increased Th2 cells and decreased Th1 cells Th1 carries out the cell-mediated IR Th2 antibody-based IR With age, more Th2, more humoral response o Zn tends to counteract the effects of aging Zn deficiency however would make the symptoms worse o Zn deficiency enzymes requiring Zn for T-cell production won't function Less T-cells Increased pro-inflammatory cytokines o With aging, there is more Th2 and less Th1 With Zn deficiency, this is even more pronounced More humoral immunity
What is Acrodermatitis Enteropathica (AE)?
Zn disorders: AE o Both alleles mutated o Treatment: oral intake of Zn Other carriers in the intestine (other than ZIP4) Paracellular pathway: between cells and do not require a carrier; this pathway plays a major role when transporters are saturated or nonfunctional
Provide a summary of zinc features and its biological roles?
Zn does not have redox activity like Cu and Zn has Zn fingers motifs are found in what proteins? Transcription factor zinc has structural role which allows formation of particular structure that required for transcription factor to bind to DNA Zinc has become Ca2+ of 21st century inter - and intracellular important signalling molecule ------------- Zinc is extracellular signaling molecule that allosetrically affects other moelcules or binds to its receptor or changes in [cytosolic zinc] due to influx from outside of cell or stores of zinc or uptake of proteins such as MT
What is the general Zn metabolism in the body?
Zn inside of cell Can become part of different pathways Bind to metal proteins (ex. MTF1 or temporarily stored in MT)
How is Zn involved in signalling in the CNS?
Zn is released as a vesicle NMDA is one type of glutamate receptor in brain and nervous system EPR39: receptor for Zn and Zn is acting as 1st messenger Zinc is binding to NMDA receptor (glutamate receptor) and modifies activity of receptor in allosteric way Zn can also be transported inside cell by other channels/transporters (ex. nervoussystem - voltage gated Ca2+ channels - input of Ca and Zn) Zn in nervous system modulates synaptic transmission by changing activity of NT receptors in allosteric way or directly by binding to its own receptor ---------- Zn can be released to extracellular space/ synaptic cleft in nervous tissue Release of glutamate (NT) to extracellular space and zinc can bind to receptor OR it can affect allosterically post synaptic receptor (ex. NMDA - glutamate receptor-negative type of regulation) Ca can transport Zinc (ex. voltage gated Ca channels can take both Ca and zinc) Zinc is found in vesicles in presynaptic neuron cells can concentrate zinc in vesicles (zincosomes) Zinc modulates transmission by affecting activity of specific receptors
What are some of the Zn-related inherited disorders?
Zn-related inherited disorders o Mutations of ZIP and ZnTs o Know the ones in the red boxes
What are the clinical manifestations of Zn deficiency?
mild: increased risk of infections, skin lesions, poor wound healing Severe: immune dysfunction, stunted/retarded growth, alopecia, neural dysfunction (sensory: taste); hypogonadism and delayed sexual maturation