AxisTRH-TSH-T3/T4 TRH, thyrotropin-releasing hormone Characteristics - Peptide with central effects - neuromodulation, thermoregulation - Peripheral effects Hypothalamo-hypophyseal axis - Regulation of TSH and PRL secretion (prolactinemia, galactorea) Clinical significance In the past - hyperthyroidis diagnosis (hypothalamic X hypophyseal causes) Possible role in depression treatment, spinal muscular atrophy and amyotrophic lateral sclerosis Treatment of some syndromes (West, Lannox-Gastaut, early infantile epileptic encephalopathy) Regulation of secretion Neural control Circadian rhythm (maximum between 21:00 and 5:00 and between 16:00 and 19:00, peaks in 90-180 min intervals - Temperature (cold) - higher synthesis among people from colder regions in winter - together with ANS (catecholamines) Stress - TRH synthesis and secretion inhibition (indirect negative feedback loop between glucocorticoids and effect on hippocampus) Starvation - TRH secretion decrease („saving" energy); effect of leptin - Body mass - POMC (-) and ARGP (+) system TSH, thyroid stimulating hormone Characteristics - Heterodimer - Negative feedback T3 - inhibition of a subunit transcription; dopamine (a and (3) - Positive feedback-TRH - Co-translational glycosylation and folding (- T3, + TRH) TSH I Half-life ca 30 min Pulsatile secretion (2-3 h), circadian rhythms (peak between 23:00 and 5:00) Magnitude changes - starvation, disease, surgery Leptin, ADH, GLP-1, glucocorticoids, a-adrenergic agonists, prostaglandins, TRH (+) T3/T4, dopamine, gastrin, opioids, glucocorticoids (high doses), serotonin, CCK, IL-1(3 a 6, TNF-a, somatostatin (-) Function Stimulation of thyroid hormones synthesis „Growth hormone" for thyroid gland Clinical significance - TSH deficiency (mutation in genes coding TRH and TSH receptors) - Analogues of somatostatin - ! (+) Cortisol metabolism T4 + T3M (D2) st4-*t3 y% Hypothalamus \ trh (+) u srih (-) I + T3 /^(D2) \ ^ T4-T3H / Pituitary 1 #t,l,k(D1) 1, I It, sm, cm (D2)j |tsh{+) \\^\t4(T3) 1 D1 + D2 / Thyroid Feedback mechanism! Thyroid gland Glandula thyroidea (15 - 20 g, frontal side of trachea under thyroid cartilage Two lobes connected by thyroidal isthmus, lobus pyramidalis Strong vascularization Round follicles (acini) with one layer of icles are the basic functional units of thyroid gland ^ Thyroid gland Isthmus I—-Left lobe Right lobe Follicular cell Follicle Parafollicular cell (Ccell) Colloid Blood capillary Red blood cell Figure 49-1 Structure of the thyroid gland. The thyroid gland is located anterior to the cricoid cartilage in the anterior neck. The gland comprises numerous follicles, which are filled with colloid and lined by follicular cells. These follicular cells are responsible for the trapping of iodine, which they secrete along with thyToglobulin—the major protein of the thyroid colloid—into the lumen of the follicle. Iodine and hormone secretion - general view NIS (Na+/I" symporter) PDS (pendrin) TPO (thyroidal peroxidase) TG homodimers and their iodation -MIT and DIT DUOX1 and 2 - together with TPO oxidation of iodide and transportation to TG structure TPO - connection DIT+DIT (T4) or DIT+MIT(T3) Pinocytosis and phagolysosomes Deiodation of MIT and DIT - DEHAL1 (iodotyrosine dehalogenase) Other proteins (TSHR) • Transcriptional factors (TTF-1, TTF-2, PAX8, HNF-3) Dietary iodine Recommended Daily Intake Adults 150 ug During pregnancy 200 ug Children 90-120 ug Typical Iodine Daily Intakes North America (1992) 75-300 Ltg Chile (1981) <=50-150ug Belgium (1993) 50-60 ug Germany (1993) 20-70 ug Switzerland (1993) 130-160 ug Bioavailability of organic and inorganic I breast milk I" filtered with passive reabsorption 60 - 70 % loss through stool (10 - 20 jig/day) Highest daily intake in Japan (several mg) In many countries on decrease - eating habits ] Status unknown I Moderate-severe deficiency 1 Mild deficiency ] Likely deficiency | Sufficiency ] Likely sufficiency I Excess Likely excess Clinical relevance - Endemic goiter - Endemic cretinism Iodine fate in follicular cells NIS - Concentration of I in follicular cells - Transport of other ions (Tc04~, CI04~, SCN) - clinical significance - Salivary glands, mammary gland, choroid plexus, gastric mucosa, cytotrophoblast, syncytiotrophoblast - Loss of ability to concentrate I in thyroid gland tumors - TSH - (+) transcription - (+) prolonged stay in PM Pendrin also kidneys (CI~/HC03~ exchanger) and inner ear DEHAL1 -MIT and DIT, iodine recyclation IYD -iodotyrosine deiodinase -MIT (+++), DIT (+) Clinical relevance -Mutation -Thiourea derivatives - methimazole, Carbimazole, propylthiouracil (TPO) Chloride channel 5 (CICn5) Oxidation, organification of iodine and MIT/DIT synthesis - Organification = incorporation I in MIT and DIT - TPO in cooperation with DUOX1 and DUOX2 - peroxide generation - DUOX1/2 - NADPH, Ca2+-dependent oxidases - generation of l2 and l+ - DUOXA2 - maturation and DUOX2 incorporation -TSH stimulation - T3 and T4 -TPO catalysis - Tg - tyreoglobulin, 660 kDA homodimer - Tg - 134 tyrosines / 25 - 30 iodinated / only 3, resp. 4, participate in T4 and T3 -3-4 molecules of T4 in Tg (physiological conditions) -Only 1T3 in Tg lodinase l2 + HO^(\ /)—CH2— CHNH2— COOH-*- HO HO HO Tyrosine ^ CH2— CHNH2 — COOH + Monoiodotyrosine ■CH2—CHNH2—COOH Diiodotyrosine Monoiodotyrosine + Diiodotyrosine \\ // 0 \\ // CHz~CHNH2_ C ' I 3,5,3'-Triiodothyronine Diiodotyrosine + Diiodotyrosine ■ CH,—CHNH,—COOH Thyroxine T3 and T4 secretion - High supply vs low daily turnover (about 1 %) - Supply ca 5000 jig T4 - euthyroid state for ca 50 days - Macropinocytosis and micropinocytosis (apical membrane) - Endocytosis - Selective proteolysis (cathepsin D and D-like thiol proteases, active at low pH) - Release from Tg in lysosomes - T4 available to deiodases Dl and D2 - modulation of systemic conversion? - Inhibition of T4 secretion by iodide TSH and T3, T4 secretion - TSHR - TSH binding - TRAb (TSHR-stimulating antibody) - TBAb (thyroid-blocking antibodies ) - LH (+) - hCG (+) PLC + Ca2+ - iodide efflux, peroxide generation, iodation of Tg -PKA - iodide uptake - Tg transcription - transcription and generation of TPO and NIS T3 and T4 transport TBG - Glycoprotein - One binding site for iodothyronine - Half-life ca 5 days Transthyretin - Binds one T4 molecule, low affinity - Half-life ca 2 days CSF - relevance ? Albumin - Low affinity Little relevance for T3/T4 transport (max. 10 %) Other - lipoproteins (3 - 6 %) Parameter Thyroxine-Binding Globulin Transthyretin Albumin Molecular weight of hoioprotetn (kDaJ 54,000 54,000 (4 subunits) 66,000 Plasma concentrations (umol/LJ 0.27 4.6 640 T4 binding capacity as ugT^dL 21 350 50,000 Association constants of the major binding site (L/mol) 1 x 1010 7* I0T 7*105 5xl08 1.4 x 107 lxlO5 Fraction of sites occupied by TA in euthyroid plasma 0.31 0.02 <0.001 Distribution volume (L) 7 5.7 7.8 Turnover rate (% day) 13 59 5 Distribution of iodothyronines [% protein) T4 68 11 20 SO 9 11 T3r triiodothyronine; T4, thyroxine. ow solubility of iodothyronines determines their reversible binding and transport by plasmatic proteins. TBG concentration and saturation is the main free-T4 determinan T4/T3 transport across PM and their cell fate Transport systems: MCT8 (monocarboxylate transporter 8) MCT10 (monocarboxylate transporter 10) - Expression in various tissues T3, T4, rT3 OATP1C1 (organic anion transporting polypeptide 1C1) ]- CNS (astrocytes) T4 (HEB) Blood-brain barrier Deiodination and (seleno-)deiodinases * Catalytic center all deiodinases require thiol presence as cofactor (glutathione (GSH), thioredoxin (TRX), glutaredoxin (GRX)) Dl - main source of plasmatic T3 D3 - most important ^deactivating" enzyme over-expressed in tumor tissue Parameter Type 1 (Outer and Inner Ring) Type 2 (Outer Ring) Type 3 (inner Ring) Physiologic role rT3 and T3S degradation, the source of plasma Ji in thyrotoxic patients Provide intracellular^ in specific tissues, a source of plasma Inactivate T3 and J, Tissue location Liver, kidney, thyroid, pituitary (?) (not CNS) CNS, pituitary, BAT, placenta thyroid, skeletal muscle, heart Placenta, CNS, hemangiomas, fetal or adult liver, skeletal muscle Subcellular location Plasma membrane Endoplasmic reticulum Plasma membrane Preferred substrates (position deiodinated) rT3(5'),T3S(5) T+, rT3 (5') T3, T4 (5) Km rT3,10 "7; T4,10"6 ID" Susceptibility to PTU High Absent Absent Response to increased T4 f t BAT, brown adipose tissue; CNS, central nervous system; Km, Michaeiis-Menten constant; PTU, 6-n-propylthiouracil; rT3, reverse triiodothyronine; T3, triiodothyronine; T3S, T3SO,,; Ti, thyroxine. Sources of intracellular T3 and T4 CO O co o c CO i— o -t—1 Q. O Ü É CO 8 - 4 - 0 □ Unoccupied receptor □ Local T3 (D2) □ T3 from plasma (D1 + D2) Total T3 receptor sites Total sites occupied i 1 Kidney Liver | Cortex BAT PIT as a source of supplementary nucleic T3 T3 supply critical for tissues: - cortex - BAT - PIT Physiological relevance: - Normal development - Thyroid gland function regulation - Cold Clinical relevance - Amiodarone (D1/D2 (-)) - Propylthiouracil (Dl (-)) Glucocorticoids (D3 (+)) Preferential plasmatic T3 utilization Physiological effects of thyroid hormones Non-nuclear receptors Interactions with adaptor proteins - Regulation of transcriptional activity cAMP MAPK Ca2+-ATPase (+) Na+/H+ antiporter (+) Cell response Normal growth and development Regulation of metabolism Organ-specific effects of thyroid hormones Bones - increase of bone turnover - regulation of activity of osteoblasts/clasts, chondrocytes - hyperthyroidism - risk of osteoporosis Cardiovascular system - Inotropic and chronotropic effect - (+) cardiac output and IVF - (-) vascular resistance - changes in transcriptional activity: -Ca2+-ATPase -Phospholamban -Myosin -(3-AR (upregulation and sensitivity) -G-proteins, AC -Na+/Ca2+ exchanger -Na+/K+-ATPase -Voltage-gated ion channels GIT - (+) resorption of monosaccharides - (+) motility Adipose tissue - (+) differentiation of adipose tissue, adipocytes proliferation - (+) lipogenic enzymes - (+) cell accumulation of lipids - (+) uncoupling proteins, uncoupling of oxidative phosphorylation - Hyperthyroidism (+) lipolysis - (+) ß-AR - (-) phosphodiesterase activity (+) activity HSL -(+) cAMP - Hypothyroidism (-) lipolysis Liver - regulation of triglyceride, lipoprotein and cholesterol metabolism - (+) fatty acids metabolism - (+) gluconeogenesis - (+) mitochondrial respiration CNS - expression of genes related myelination, cell differentiation, migration and signaling - Axonal growth and further development Metabolie effects of thyroid hormones Saccharides Lipids increased glucose resorption Increased utilization of Glu in tissues Increased liver gluconeogenesis Increased glycolysis hyperthyroidism = postprandial hyperglycaemia hypothyroidism = inbalances in glycaemia Proteins increased activity of lipoprotein lipase Increased synthesis of LDL receptor in hepatocytes increased synthesis of fatty acids (nonesterified) increased beta-oxidation hypothyreosis = proatherogenic changes! - Proteoanabolic effect (mainly during intrauterine development and the first year after birth - brain) - hyperthyroidism = protein catabolism! Thyroid hormones and iodide deficit and excess Deficit - Rapid T4 decrease, TSH increase - No change in T3 - Increased synthesis of NIS, TPO, Tg, organification of iodide and Tg turnover - Increase D2 in CNS, hypothalamus and hypophysis - Stimulation of follicular cells (TSH) - Long-term deficit - decreased D3 - Decrease supplementation under 75 u.g/day (China, India, Indonesia, Africa) - hypothyroidismus Excess - At first increase, then decrease of iodide organification (Wolff-Chaikoff effect) - Long-term high iodide supplementation = hypothyroidism and goitre - decreased NIS generation - Immediate inhibition of thyroid hormones secretion Functions of thyroid gland in fetus and newborn Physiologic Change Thyroid-Related Consequences ■r Serum thyroxine-bindlng globulin t TotalT4 and T3; ^ T4 production ^ Plasma volume f T4 and T3 pool size; * JA production; f cardiac output D3 expression [n placenta and (?) uterus * TA production First trimester f in hCG ^FreeT4; 4- basal thyrotropin; ? T4 production ^ Renal 1" clearance t Iodine requirements f T4 production; fetal T< synthesis during second and third trimesters t Oxygen consumption by fetoplacental unit, gravid uterus, and mother t Basai metabolic rate; t cardiac output D3, type 3 iodothyronine deiodmase; 1", plasma iodide;. hCG, human chorionic gonadotropin; TJt triiodothyronine; T„, thyroxine. Mother 20 Week of pregnancy 40 Thyroid gland and development stages Fetal thyroid gland - qualitative and quantitative differences - 10-fold higher T4 production - Dl (-), D3 (+; liver, skin, tracheobronchial system, urothelial system, GIT epithelium) - T3(-), rT3 (+) - D2 - generation of T3 in tissues - Start at the beginning of the 3rd trimester - TSH during whole development higher than in mother - Almost no interaction with mother (exception placental transport of T4), high expression of D3 in uterus and placenta Thyroid gland in newborns - qualitative and quantitative differences - Increased TBG level - Lower T4 levels compared to mother - Low T3 level in serum, increased levels of rT3 and T3S04 - Rapid increase TSH 2-4 hours after birth, decrease in 48 hours - Rapid increase T4, T3, Tg - 24 hours (+D1 a D2, adrenergic stimulation of D2 in BAT) Thyroid gland and aging - Normal T4 level, decreased T3 level - TSH according to iodide supplementation - Benefit of decreased thyroid hormones - longevity Thyroid gland functions during disease and starvation Starvation - Decreased plasmatic T3, increased rT3, T4 no change - Upregulation of D3 - Decreased oxygen consumption - Slower heart rate - More positive nitrogen balance = mechanisms to save energy and proteins - Chronic malnutrition - decreased plasmatic T3 Disease - Changes in T4 to T3 D2) conversion - TSH binding - IL-6 - Increased intra-/extracellular ros = changes in deiodinase activity - decreased T4 to T3 conversion BUT! no change in D3 - potential therapy - infusion of TSH + GHRP2 - Bipolar disorder - (+) TSH, (-) T4 - Severe depression - (-) TSH, (+) T4 Severity of Illness Free T3 Free JA Reverse T3 TSH Probable Cause Mild N t N ^ D2, Dl Moderate 4^D2,D1,?* D3 Severe ♦ 4^D2,D1,*D3 Recovery f 7 Dl through D3T iodothyronine deiodinases; N,no change; 13, triiodothyronine; l4l thyroxine; TSH, thyroid-stimulating hormone (thyrotropin). Hormones and thyroid gland Glucocorticoids - Decreased pulsatile secretion of TSH and TRH secretion - Increased activity (expression) of D3 Sex steroids - Estrogens - increased TBG - TSH (+ 15 - 20 %) - Androgen - decreased TBG Glucocorticoids Excess Decrease TSH, TBG, TTR (high-dose) Decrease serum T3/T4 and increase rT3/T4 ratios Increase rT3 production (? ■r D3) Decrease T4and T3 secretion in Graves disease Deficiency Increase TSH Estrogen Increase TBG sialylation and half-life in serum Increase TSH in postmenopausal women Increase T4 requirement in hypothyroid patients Androgen Decrease TBG Decrease T4turnover in women and reduce T4 requirements in hypothyroid patients Growth Hormone Decrease D3 activity 03, type 3 deiodinase; rT3, reverse T3; T3, triiodothyronine; T4, thyroxine; TBG, thyroxine-binding globulin; TSH, thyrotropin; TTR, transthyretin. Hypothyroidism Disruptions of HYP-ADH-TG axis including mutations Goitrogens and treatment Primary versus secondary Cold sensitivity Dry cold skin Slower movements Slow quiet speech Bradycardia Water retention - Psychomotoric retardation (children) - Myxedema (accumulation of protein complexes, polysaccharides, hyaluronic acid and chondroitin sulfuric acid in skin) - Hypothyroidism since birth = cretinism Hypothyroidism Graves disease, diffusion toxic goiter, toxic nodular goiter, inappropriate pharmacotherapy, excessive iodide intake, thyroiditidis, follicular carcinoma, tumors producing TSH increased BMR Changes in catecholamines reactivity Exophthalmos - infiltration of lymphocytes and periocular fibroblasts into extraocular muscles and tissue - unrest Tachycardia - Hyperventilation Hypo- versus hyperthyroidismus Parameter Hypothyroidism Hyperthyroidism BMR (-) (+) Carbohydrate metabolism Gluconeogenesis (-) Glycogenolysis (-) Glycemia (N) Gluconeogenesis (+) Glycogenolysis (+) Glycemia (N) Protein metabolism Proteosynthesis (-) Proteolysis (-) Proteosynthesis (+) Proteolysis (+) Muscle mass (-) Lipid metabolism Lipogenesis (-) Lipolysis (-) Serum cholesterol (+) Lipogenesis (+) Lipolysis (+) Serum cholesterol (-) Thermogenesis Autonomic nervous system Plasmatic catecholamines (N) Increased reactivity - (3-AR (+) Plasmatic catecholamines (-) Examination of hypothalamus -adenohypophysis-thyroid gland axis TSH - immumometric methods Overall T3 and T4 - immunochemical methods (immunoassays) Free T3 and T4