scholarly journals Genotype-Phenotype Relationship in Patients with Mutations in Thyroid Hormone Transporter MCT8

Endocrinology ◽  
2008 ◽  
Vol 149 (5) ◽  
pp. 2184-2190 ◽  
Author(s):  
Jurgen Jansen ◽  
Edith C. H. Friesema ◽  
Monique H. A. Kester ◽  
Charles E. Schwartz ◽  
Theo J. Visser
Keyword(s):  
Plasma Membrane ◽  
Thyroid Hormone ◽  
Protein Expression ◽  
Elevated Serum ◽  
Monocarboxylate Transporter ◽  
Psychomotor Development ◽  
Substrate Affinity ◽  
Loss Of Function ◽  
Wild Type ◽  
Rt Pcr

Loss-of-function mutations in thyroid hormone transporter monocarboxylate transporter 8 (MCT8) lead to severe X-linked psychomotor retardation and elevated serum T3 levels. Most patients, for example those with mutations V235M, S448X, insI189, or delF230, cannot stand, walk, or speak. Patients with mutations L434W, L568P, and S194F, however, walk independently and/or develop some dysarthric speech. To study the relationship between mutation and phenotype, we transfected JEG3 and COS1 cells with wild-type or mutant MCT8. Expression and function of the transporter were studied by analyzing T3 and T4 uptake, T3 metabolism (by cotransfected type 3 deiodinase), Western blotting, affinity labeling with N-bromoacetyl-T3, immunocytochemistry, and quantitative RT-PCR. Wild-type MCT8 increased T3 uptake and metabolism about 5-fold compared with empty vector controls. Mutants V235M, S448X, insI189, and delF230 did not significantly increase transport. However, S194F, L568P, and L434W showed about 20, 23, and 37% of wild-type activity. RT-PCR did not show significant differences in mRNA expression between wild-type and mutant MCT8. Immunocytochemistry detected the nonfunctional mutants V235M, insI189, and delF230 mostly in the cytoplasm, whereas mutants with residual function were expressed at the plasma membrane. Mutants S194F and L434W showed high protein expression but low affinity for N-bromoacetyl-T3; L568P was detected in low amounts but showed relatively high affinity. Mutations in MCT8 cause loss of function through reduced protein expression, impaired trafficking to the plasma membrane, or reduced substrate affinity. Mutants L434W, L568P, and S194F showed significant residual transport capacity, which may underlie the more advanced psychomotor development observed in patients with these mutations.

scholarly journals The Mutational Landscape of PTK7 in Congenital Scoliosis and Adolescent Idiopathic Scoliosis

Genes ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 1791
Author(s):  
Zhe Su ◽  
Yang Yang ◽  
Shengru Wang ◽  
Sen Zhao ◽  
Hengqiang Zhao ◽  
...  
Keyword(s):  
Adolescent Idiopathic Scoliosis ◽  
Idiopathic Scoliosis ◽  
Protein Expression ◽  
Rare Variants ◽  
Congenital Scoliosis ◽  
Loss Of Function ◽  
Wild Type ◽  
Cellular Location ◽  
Mutational Landscape

Depletion of ptk7 is associated with both congenital scoliosis (CS) and adolescent idiopathic scoliosis (AIS) in zebrafish models. However, only one human variant of PTK7 has been reported previously in a patient with AIS. In this study, we systemically investigated the variant landscape of PTK7 in 583 patients with CS and 302 patients with AIS from the Deciphering Disorders Involving Scoliosis and COmorbidities (DISCO) study. We identified a total of four rare variants in CS and four variants in AIS, including one protein truncating variant (c.464_465delAC) in a patient with CS. We then explored the effects of these variants on protein expression and sub-cellular location. We confirmed that the c.464_465delAC variant causes loss-of-function (LoF) of PTK7. In addition, the c.353C>T and c.2290G>A variants identified in two patients with AIS led to reduced protein expression of PTK7 as compared to that of the wild type. In conclusion, LoF and hypomorphic variants are associated with CS and AIS, respectively.

scholarly journals Age-Dependent and Sleep/Seizure-Induced Pathomechanisms of Autosomal Dominant Sleep-Related Hypermotor Epilepsy

2020 ◽  
Vol 21 (21) ◽  
pp. 8142 ◽  
Author(s):  
Kouji Fukuyama ◽  
Motohiro Okada
Keyword(s):  
Plasma Membrane ◽  
Autosomal Dominant ◽  
Loss Of Function ◽  
Glutamatergic Transmission ◽  
Wild Type ◽  
Cx43 Expression ◽  
Nicotine Administration ◽  
Extracellular Signal ◽  
Age Dependent ◽  
Before And After

The loss-of-function S284L-mutant α4 subunit of the nicotinic acetylcholine receptor (nAChR) is considered to contribute to the pathomechanism of autosomal dominant sleep-related hypermotor epilepsy (ADSHE); however, the age-dependent and sleep-related pathomechanisms of ADSHE remain to be clarified. To explore the age-dependent and sleep-induced pathomechanism of ADSHE, the present study determined the glutamatergic transmission abnormalities associated with α4β2-nAChR and the astroglial hemichannel in the hyperdirect and corticostriatal pathways of ADSHE model transgenic rats (S286L-TG) bearing the rat S286L-mutant Chrna4 gene corresponding to the human S284L-mutant CHRNA4 gene of ADSHE, using multiprobe microdialysis and capillary immunoblotting analyses. This study could not detect glutamatergic transmission in the corticostriatal pathway from the orbitofrontal cortex (OFC) to the striatum. Before ADSHE onset (four weeks of age), functional abnormalities of glutamatergic transmission compared to the wild-type in the cortical hyperdirect pathway, from OFC to the subthalamic nucleus (STN) in S286L-TG, could not be detected. Conversely, after ADSHE onset (eight weeks of age), glutamatergic transmission in the hyperdirect pathway of S286L-TG was enhanced compared to the wild-type. Notably, enhanced glutamatergic transmission of S286L-TG was revealed by hemichannel activation in the OFC. Expression of connexin43 (Cx43) in the OFC of S286L-TG was upregulated after ADSHE onset but was almost equal to the wild-type prior to ADSHE onset. Differences in the expression of phosphorylated protein kinase B (pAkt) before ADSHE onset between the wild-type and S286L-TG were not observed; however, after ADSHE onset, pAkt was upregulated in S286L-TG. Conversely, the expression of phosphorylated extracellular signal-regulated kinase (pErk) was already upregulated before ADSHE onset compared to the wild-type. Both before and after ADSHE onset, subchronic nicotine administration decreased and did not affect the both expression of Cx43 and pErk of respective wild-type and S286L-TG, whereas the pAkt expression of both the wild-type and S286L-TG was increased by nicotine. Cx43 expression in the plasma membrane of the primary cultured astrocytes of the wild-type was increased by elevation of the extracellular K+ level (higher than 10 mM), and the increase in Cx43 expression in the plasma membrane required pErk functions. These observations indicate that a combination of functional abnormalities, GABAergic disinhibition, and upregulated pErk induced by the loss-of-function S286L-mutant α4β2-nAChR contribute to the age-dependent and sleep-induced pathomechanism of ADSHE via the upregulation/hyperactivation of the Cx43 hemichannels.

scholarly journals Effective Cellular Uptake and Efflux of Thyroid Hormone by Human Monocarboxylate Transporter 10

2008 ◽  
Vol 22 (6) ◽  
pp. 1357-1369 ◽  
Author(s):  
Edith C. H. Friesema ◽  
Jurgen Jansen ◽  
Jan-willem Jachtenberg ◽  
W. Edward Visser ◽  
Monique H. A. Kester ◽  
...  
Keyword(s):  
Amino Acids ◽  
Plasma Membrane ◽  
Thyroid Hormone ◽  
Cellular Uptake ◽  
Aromatic Amino Acids ◽  
Significant Inhibition ◽  
Monocarboxylate Transporter ◽  
Strong Increase ◽  
Type I ◽  
Hormone Binding Protein

Abstract Cellular entry of thyroid hormone is mediated by plasma membrane transporters, among others a T-type (aromatic) amino acid transporter. Monocarboxylate transporter 10 (MCT10) has been reported to transport aromatic amino acids but not iodothyronines. Within the MCT family, MCT10 is most homologous to MCT8, which is a very important iodothyronine transporter but does not transport amino acids. In view of this paradox, we decided to reinvestigate the possible transport of thyroid hormone by human (h) MCT10 in comparison with hMCT8. Transfection of COS1 cells with hMCT10 cDNA resulted in 1) the production of an approximately 55 kDa protein located to the plasma membrane as shown by immunoblotting and confocal microscopy, 2) a strong increase in the affinity labeling of intracellular type I deiodinase by N-bromoacetyl-[125I]T3, 3) a marked stimulation of cellular T4 and, particularly, T3 uptake, 4) a significant inhibition of T3 uptake by phenylalanine, tyrosine, and tryptophan of 12.5%, 22.2%, and 51.4%, respectively, and 5) a marked increase in the intracellular deiodination of T4 and T3 by different deiodinases. Cotransfection studies using the cytosolic thyroid hormone-binding protein μ-crystallin (CRYM) indicated that hMCT10 facilitates both cellular uptake and efflux of T4 and T3. In the absence of CRYM, hMCT10 and hMCT8 increased T3 uptake after 5 min incubation up to 4.0- and 1.9-fold, and in the presence of CRYM up to 6.9- and 5.8-fold, respectively. hMCT10 was less active toward T4 than hMCT8. These findings establish that hMCT10 is at least as active a thyroid hormone transporter as hMCT8, and that both transporters facilitate iodothyronine uptake as well as efflux.

scholarly journals Calcium Signaling Regulates Trafficking of Familial Hypocalciuric Hypercalcemia (FHH) Mutants of the Calcium Sensing Receptor

2012 ◽  
Vol 26 (12) ◽  
pp. 2081-2091 ◽  
Author(s):  
Michael P. Grant ◽  
Ann Stepanchick ◽  
Gerda E. Breitwieser
Keyword(s):  
Plasma Membrane ◽  
Steady State ◽  
State Level ◽  
Membrane Targeting ◽  
Familial Hypocalciuric Hypercalcemia ◽  
Loss Of Function ◽  
Wild Type ◽  
Calcium Sensing Receptor ◽  
Dynamic Changes ◽  
Calcium Sensing

Abstract Calcium-sensing receptors (CaSRs) regulate systemic Ca2+ homeostasis. Loss-of-function mutations cause familial benign hypocalciuric hypercalcemia (FHH) or neonatal severe hyperparathyroidism (NSHPT). FHH/NSHPT mutations can reduce trafficking of CaSRs to the plasma membrane. CaSR signaling is potentiated by agonist-driven anterograde CaSR trafficking, leading to a new steady state level of plasma membrane CaSR, which is maintained, with minimal functional desensitization, as long as extracellular Ca2+ is elevated. This requirement for CaSR signaling to drive CaSR trafficking to the plasma membrane led us to reconsider the mechanism(s) contributing to dysregulated trafficking of FHH/NSHPT mutants. We simultaneously monitored dynamic changes in plasma membrane levels of CaSR and intracellular Ca2+, using a chimeric CaSR construct, which allowed explicit tracking of plasma membrane levels of mutant or wild-type CaSRs in the presence of nonchimeric partners. Expression of mutants alone revealed severe defects in plasma membrane targeting and Ca2+ signaling, which were substantially rescued by coexpression with wild-type CaSR. Biasing toward heterodimerization of wild-type and FHH/NSHPT mutants revealed that intracellular Ca2+ oscillations were insufficient to rescue plasma membrane targeting. Coexpression of the nonfunctional mutant E297K with the truncation CaSRΔ868 robustly rescued trafficking and Ca2+ signaling, whereas coexpression of distinct FHH/NSHPT mutants rescued neither trafficking nor signaling. Our study suggests that rescue of FHH/NSHPT mutants requires a steady state intracellular Ca2+ response when extracellular Ca2+ is elevated and argues that Ca2+ signaling by wild-type CaSRs rescues FHH mutant trafficking to the plasma membrane.

scholarly journals Evidence for a Homodimeric Structure of Human Monocarboxylate Transporter 8

Endocrinology ◽  
2009 ◽  
Vol 150 (11) ◽  
pp. 5163-5170 ◽  
Author(s):  
W. Edward Visser ◽  
Nancy J. Philp ◽  
Thamar B. van Dijk ◽  
Wim Klootwijk ◽  
Edith C. H. Friesema ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Psychomotor Retardation ◽  
Monocarboxylate Transporter ◽  
Membrane Association ◽  
Transport Function ◽  
Wild Type ◽  
Transfected Cells ◽  
Physiological Relevance ◽  
Dimerization Process

The human monocarboxylate transporter 8 (hMCT8) protein mediates transport of thyroid hormone across the plasma membrane. Association of hMCT8 mutations with severe psychomotor retardation and disturbed thyroid hormone levels has established its physiological relevance, but little is still known about the basic properties of hMCT8. In this study we present evidence that hMCT8 does not form heterodimers with the ancillary proteins basigin, embigin, or neuroplastin, unlike other MCTs. In contrast, it is suggested that MCT8 exists as monomer and homodimer in transiently and stably transfected cells. Apparently hMCT8 forms stable dimers because the complex is resistant to denaturing conditions and dithiothreitol. Cotransfection of wild-type hMCT8 with a mutant lacking amino acids 267–360 resulted in formation of homo-and heterodimers of the variants, indicating that transmembrane domains 4–6 are not involved in the dimerization process. Furthermore, we explored the structural and functional role of the 10 Cys residues in hMCT8. All possible Cys>Ala mutants did not behave differently from wild-type hMCT8 in protein expression, cross-linking experiments with HgCl2 and transport function. Our findings indicate that individual Cys residues are not important for the function of hMCT8 or suggest that hMCT8 has other yet-undiscovered functions in which cysteines play an essential role.

scholarly journals Hyperactivity and Learning Deficits in Transgenic Mice Bearing a Human Mutant Thyroid Hormone β1 Receptor Gene

1998 ◽  
Vol 5 (4) ◽  
pp. 289-301 ◽  
Author(s):  
Michael P. McDonald ◽  
Rosemary Wong ◽  
Gregory Goldstein ◽  
Bruce Weintraub ◽  
Sheue-yann Cheng ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Transgenic Mice ◽  
Sustained Attention ◽  
Receptor Gene ◽  
Operant Chamber ◽  
Elevated Serum ◽  
Vigilance Task ◽  
Serum Levels ◽  
Wild Type ◽  
Wild Type Littermate

Resistance to thyroid hormone (RTH) is a human syndrome mapped to the thyroid receptor β(TRβ) gene on chromosome 3, representing a mutation of the ligandbinding domain of the TRβ gene. The syndrome is characterized by reduced tissue responsiveness to thyroid hormone and elevated serum levels of thyroid hormones. A common behavioral phenotype associated with RTH is attention deficit hyperactivity disorder (ADHD). To test the hypothesis that RTH produces attention deficits and/or hyperactivity, transgenic mice expressing a mutant TRβ gene were generated. The present experiment tested RTH transgenic mice from the PV kindred on behavioral tasks relevant to the primary features of ADHD: hyperactivity, sustained attention (vigilance), learning, and impulsivity. Male transgenic mice showed elevated locomotor activity in an open field compared to male wild-type littermate controls. Both male and female transgenic mice exhibited impaired learning of an autoshaping task, compared to wild-type controls. On a vigilance task in an operant chamber, there were no differences between transgenics and controls on the proportion of hits, response latency, or duration of stimulus tolerated. On an operant go/no-go task measuring sustained attention and impulsivity, there were no differences between controls and transgenics. These results indicate that transgenic mice bearing a mutant human TRβ gene demonstrate several behavioral characteristics of ADHD and may serve a valuable heuristic role in elucidating possible candidate genes in converging pathways for other causes of ADHD.

scholarly journals The Protein Translocation Defect of MCT8L291R Is Rescued by Sodium Phenylbutyrate

2020 ◽  
Vol 9 (5) ◽  
pp. 269-280
Author(s):  
Doreen Braun ◽  
Ulrich Schweizer
Keyword(s):  
Plasma Membrane ◽  
Protein Function ◽  
Monocarboxylate Transporter ◽  
Cell Surface Expression ◽  
Mrna Levels ◽  
Wild Type ◽  
Chemical Chaperone ◽  
Mct8 Deficiency ◽  
Sodium Phenylbutyrate

Introduction: The monocarboxylate transporter 8 (MCT8; SLC16A2) is a specific transporter for thyroid hormones. MCT8 deficiency, formerly known as the Allan-Herndon-Dudley syndrome, is a rare genetic disease that leads to neurological impairments and muscle weakness. Current experimental treatment options rely on thyromimetic agonists that do not depend on MCT8 for cellular uptake. Another approach comes from studies with the chemical chaperone sodium phenylbutyrate (NaPB), which was able to stabilize MCT8 mutants having protein folding defects in vitro. In addition, NaPB is known as a compound that assists with plasma membrane translocation. Objective: The pathogenic MCT8L291R leads to the same severe neurological impairments found for other MCT8-deficient patients but, unexpectedly, lacks alterations in plasma 3,3′,5-triiodothyronine (T3) levels. Here we tried to unravel the underlying mechanism of MCT8 deficiency and tested whether the pathogenic MCT8L291R mutant responds to NaPB treatment. Therefore, we overexpressed the mutant in Madin-Darby canine kidney cells in the human choriocarcinoma cell line JEG1 and in COS7 cells of African green monkey origin. Results: In our recent study we describe that the MCT8L291R mutation most likely leads to a translocation defect. The pathogenic mutant is not located at the plasma membrane, but shows overlapping expression with a marker protein of the lysosome. Mutation of the corresponding amino acid in murine Mct8 (Mct8L223R) displays a similar effect on cell surface expression and transport function as seen before for MCT8L291R. NaPB was able to correct the translocation defect of MCT8L291R/Mct8L223R and restored protein function by increasing T3 transport activity. Furthermore, we detected enhanced mRNA levels of wild-type and mutant MCT8/Mct8 after NaPB treatment. The increase in mRNA levels could be an explanation for the positive effect on protein expression and function detected for wild-type MCT8. Conclusion: NaPB is not only suitable for the treatment of mutations leading to misfolding and protein degradation, but also for a mutant wrongly sorted inside a cell which is otherwise functional.

scholarly journals Molecular aspects of thyroid hormone transporters, including MCT8, MCT10, and OATPs, and the effects of genetic variation in these transporters

2009 ◽  
Vol 44 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Wendy M van der Deure ◽  
Robin P Peeters ◽  
Theo J Visser
Keyword(s):  
Genetic Variation ◽  
Thyroid Hormone ◽  
Organic Anion ◽  
Elevated Serum ◽  
Tissue Level ◽  
Psychomotor Retardation ◽  
Monocarboxylate Transporter ◽  
Organic Anion Transporting Polypeptides ◽  
The Central Nervous System ◽  
Molecular Aspects

Thyroid hormone is a pleiotropic hormone with widespread biological actions. For instance, adequate levels of thyroid hormone are critical for the development of different tissues such as the central nervous system, but are also essential for the regulation of metabolic processes throughout life. The biological activity of thyroid hormone depends not only on serum thyroid hormone levels, but is also regulated at the tissue level by the expression and activity of deiodinases, which activate thyroid hormone or mediate its degradation. In addition, thyroid hormone transporters are necessary for the uptake of thyroid hormone into target tissues. With the discovery of monocarboxylate transporter 8 (MCT8) as a specific thyroid hormone transporter and the finding that mutations in this transporter lead to a syndrome of severe psychomotor retardation and elevated serum 3,3′,5-tri-iodothyronine levels known as the Allan–Herndon–Dudley syndrome, the interest in this area of research has greatly increased. In this review, we will focus on the molecular aspects of thyroid hormone transporters, including MCT8, MCT10, organic anion transporting polypeptides, and the effects of genetic variation in these transporters.

scholarly journals Monocarboxylate Transporter 8 Deficiency: From Pathophysiological Understanding to Therapy Development

2021 ◽  
Vol 12 ◽  
Author(s):  
Ferdy S. van Geest ◽  
Nilhan Gunhanlar ◽  
Stefan Groeneweg ◽  
W. Edward Visser
Keyword(s):  
Thyroid Hormone ◽  
Clinical Stage ◽  
Treatment Options ◽  
Elevated Serum ◽  
Physiological Role ◽  
Monocarboxylate Transporter ◽  
Peripheral Tissues ◽  
Motor Disability ◽  
Serum T3 ◽  
Mct8 Deficiency

Genetic defects in the thyroid hormone transporter monocarboxylate transporter 8 (MCT8) result in MCT8 deficiency. This disorder is characterized by a combination of severe intellectual and motor disability, caused by decreased cerebral thyroid hormone signalling, and a chronic thyrotoxic state in peripheral tissues, caused by exposure to elevated serum T3 concentrations. In particular, MCT8 plays a crucial role in the transport of thyroid hormone across the blood-brain-barrier. The life expectancy of patients with MCT8 deficiency is strongly impaired. Absence of head control and being underweight at a young age, which are considered proxies of the severity of the neurocognitive and peripheral phenotype, respectively, are associated with higher mortality rate. The thyroid hormone analogue triiodothyroacetic acid is able to effectively and safely ameliorate the peripheral thyrotoxicosis; its effect on the neurocognitive phenotype is currently under investigation. Other possible therapies are at a pre-clinical stage. This review provides an overview of the current understanding of the physiological role of MCT8 and the pathophysiology, key clinical characteristics and developing treatment options for MCT8 deficiency.

scholarly journals Pathophysiological Importance of Thyroid Hormone Transporters

Endocrinology ◽  
2009 ◽  
Vol 150 (3) ◽  
pp. 1078-1083 ◽  
Author(s):  
Heike Heuer ◽  
Theo J. Visser
Keyword(s):  
Thyroid Hormone ◽  
Organic Anion ◽  
Elevated Serum ◽  
Psychomotor Retardation ◽  
Monocarboxylate Transporter ◽  
Tissue Specific ◽  
Thyroid Hormone Metabolism ◽  
Serum T3 ◽  
Specific Regulation ◽  
Near Future

Thyroid hormone metabolism and action are largely intracellular events that require transport of iodothyronines across the plasma membrane. It has been assumed for a long time that this occurs by passive diffusion, but it has become increasingly clear that cellular uptake and efflux of thyroid hormone is mediated by transporter proteins. Recently, several active and specific thyroid hormone transporters have been identified, including monocarboxylate transporter 8 (MCT8), MCT10, and organic anion transporting polypeptide 1C1 (OATP1C1). The latter is expressed predominantly in brain capillaries and transports preferentially T4, whereas MCT8 and MCT10 are expressed in multiple tissues and are capable of transporting different iodothyronines. The pathophysiological importance of thyroid hormone transporters has been established by the demonstration of MCT8 mutations in patients with severe psychomotor retardation and elevated serum T3 levels. MCT8 appears to play an important role in the transport of thyroid hormone in the brain, which is essential for the crucial action of the hormone during brain development. It is expected that more specific thyroid hormone transporters will be discovered in the near future, which will lead to a better understanding of the tissue-specific regulation of thyroid hormone bioavailability. Specific thyroid hormone transporters may be discovered in the near future, leading to a better understanding of the tissue-specific regulation of thyroid hormone bioavailability.

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