ResearchPad - thyroid-hormone-action-and-signaling Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[OR01-04 Kruppel-Like Factors 9 and 13 Cooperate to Maintain Mammalian Neuronal Differentiation]]> During development of the central nervous system, neural cells respond to several external cues that influence cell proliferation, differentiation, axonal growth and synaptogenesis. Thyroid hormone plays a critical role in each of these processes. Previously, we showed that Krüppel-like factor 9 (KLF9), a zinc finger transcription factor, is strongly and directly induced by liganded thyroid hormone receptors, and it mediates the actions of thyroid hormone on neuronal differentiation during late fetal development. Here we analyzed the molecular mechanisms by which KLF9 maintains neuronal structure, and inhibits regeneration in juvenile and adult neuronal cells. We also investigated the actions of the closely related transcription factor KLF13, which is paralogous to KLF9. We engineered the adult mouse hippocampus-derived cell line HT22 to control Klf9 or Klf13 expression by addition of doxycycline. We also used CRISPR/Cas9 genome editing to generate Klf9 or Klf13 knock out (KO), and Klf9+Klf13 double KO HT22 cell lines. To induce neurite outgrowth, we treated cells with forskolin (FK)+IBMX, which increases intracellular cAMP; elevated cAMP is a hallmark of regenerative responses of neurons to injury. Our results show that FK+IBMX increased neurite length in the parent HT22 cell line, and this action was enhanced in Klf9 and Klf13 single KO cells, and was even greater in double KO cells. By contrast, the stimulatory effect of FK+IBMX on neurite outgrowth was blocked by simultaneous forced expression of Klf9 or Klf13 in parent HT22 cells. This effect on neurite outgrowth was confirmed in primary mouse hippocampal neurons, where electroporation of expression plasmids for Klf9 or Klf13 suppressed FK+IBMX-induced neurite extension compared with empty vector-transfected cells. Analysis of RNA-seq data obtained from HT22 cells following 8 hr of induced Klf9 or Klf13 expression showed that both proteins impact the cAMP signaling pathway. Using transfection-reporter assays and chromatin immunoprecipitation, we confirmed that several genes in this pathway are direct targets of both KLFs. Our findings suggest that KLF9 and KLF13 may cooperate to maintain the differentiated state of mammalian neurons and thereby block regeneration, in part, by repressing the cAMP signaling pathway.

<![CDATA[OR01-05 Long-Term Efficacy of T3 Analogue Triac in MCT8 Deficiency]]> Background: MCT8 deficiency is a severe disorder caused by mutations in the thyroid hormone transporter MCT8. MCT8 deficiency is characterized by severe intellectual and motor disability and high serum T3 concentrations that result in thyrotoxic symptoms in peripheral tissues. This predisposes to substantial morbidity and mortality. Preclinical studies showed that the T3 analogue Triac can bypass defective MCT8 at the cellular level. Recently, we reported the results of an international multicenter trial, in which biochemical and clinical outcomes improved in patients with MCT8 deficiency who were treated with Triac for 12 months (1). However, long-term follow-up data of patients with MCT8 deficiency treated with Triac are lacking, particularly in young children. Therefore, we aimed to investigate the long-term efficacy of Triac therapy in a worldwide cohort of patients with MCT8 deficiency.

Methods: We investigated the efficacy of oral Triac treatment in pediatric (n=78) and adult (n=5) patients with MCT8 deficiency in 20 countries. Triac dose was titrated according a predefined dose-escalation scheme aiming to normalize serum T3 concentrations (target 1.4-2.5 nmol/L). Thyroid function tests and biochemical markers of thyroid hormone action in peripheral tissues (SHBG, creatine kinase, creatinine) were measured at baseline and during control visits.

Findings: In total, 83 patients with a median baseline age of 5 years (range 6 months – 66 years) were treated, including 24 patients aged 0-2.5 years and 17 patients aged 2.5-5 years. They were treated with Triac during 144 patient years, of whom the follow-up time was >5 years in 9 patients and 2-5 years in 22 patients. Mean dose was 45 µg/kg/day (range 11-107 µg/kg/day). Once a stable dose was achieved, no further dose adjustments were needed.

Mean serum T3 concentrations decreased from 5.02 to 1.94 nmol/L (normal 1.4 – 2.5 nmol/L). SHBG concentrations improved from 238 to 204 nmol/L (normal 40-140 nmol/L). Mean creatine kinase and creatinine concentrations improved from 113 to 140 U/L (normal <230 U/L) and from 32 to 38 µmol/L (normal 31-68 μmol/L), respectively. No drug-related severe adverse events were reported.

Interpretation: Triac is a safe treatment that results in sustainable improvements of the severe thyrotoxic state in pediatric and adult patients with MCT8 deficiency.

References: 1. Groeneweg S, Peeters RP, Moran C, Stoupa A, Auriol F, Tonduti D, et al. Effectiveness and safety of the tri-iodothyronine analogue Triac in children and adults with MCT8 deficiency: an international, single-arm, open-label, phase 2 trial. Lancet Diabetes Endocrinol. 2019;7(9):695-706.

<![CDATA[OR01-06 Resistance to Thyroid Hormone Beta Is Associated with an Increase in Hepatic Fat Measured by Transient Elastography (Fibroscan®) with Controlled Attenuation Parameter (CAP)]]> 0.05 and r=0.21;P>0.05. The lipid profile was not significant difference between the two group regarding total cholesterol (165±27 and 175±30 mg/dl), LDL cholesterol (103±16 and 113±29 mg/dl) and tryglicerides (115±45 and 108±43mg/dl). However, the HDL cholesterol was significantly lower in RTHβ patients (40±8 and 52±10 mg/dl; P<0.006). Glycemia, insulin levels and HOMA-IR (Homeostatic Model Assessment of Insulin Resistance) were within the normal range and showed no significant differences between the two groups.In conclusion, RTHβ was associated with hepatic steatosis indicating that the TRβ dependent signaling of thyroid hormone plays an important role in lipid homeostasis. This finding further emphasizes the rational for the development of thyroid hormone analogues selective for TRβ which may offer alternatives for treatment of lipid-associated hepatic disorders without generating cardiac toxicity or accelerated bone loss. ]]> <![CDATA[OR01-03 Thyroid Receptor Alpha Interacts with COUP-TFII in the Regulation of Postnatal Skeletal Muscle Regeneration]]> <![CDATA[OR01-01 Human Type 1 Iodothyronine Deiodinase (DIO1) Mutations Cause Abnormal Thyroid Hormone Metabolism]]> A:p.N94K; N-linker) was identified in four family members with relatively higher serum rT3, T4, and free T4 than unaffected relatives, and normal TSH. We identified a second heterozygous pathogenic mutation in the DIO1 (c.603G>A:p.M201I; thioredoxin-fold) in a second family. Two affected individuals presented slightly elevated TSH, higher serum rT3, normal T4 levels, while the T3/T4 ratio was lower compared to unaffected members. To assess the functional activity of the mutant D1 protein, human embryonic kidney epithelial cells (HEK293) were transiently co-transfected with pcDNA3 plasmids expressing pD1-WT, pD1-N94K or pD1-M201I, and pGFP as transfection control. In assays performed with 1μM 125I-T4, the catalytic activities of pD1-N94K and pD1-M201I were 44.7% and 54.1% lower as compared to pD1-WT, respectively. To study the enzyme kinetics, the D1 assay was repeated in the presence of increasing 125I-T4 concentrations (0.1-20μM). The enzymatic activity assays revealed similar Vmax for pD1-N94K and pD1-M201I mutants compared to pD1-WT (VmaxpD1-N94K=53.7 vs VmaxpD1-WT=40.9 and VmaxpD1-M201I=58.8 vs VmaxpD1-WT=42), but higher Michaelis constant (Km) than pD1-WT (KmpD1-N94K=16.4 vs KmpD1-WT=6 and KmpD1-M201I=21.4 vs KmpD1-WT=6.9), which demonstrates a reduced affinity for T4. In conclusion, we report the first DIO1 mutations in humans with serum thyroid tests suggestive of TH metabolism defects. These mutations affect the catalytic activity of the D1, demonstrating impaired functional activity of the mutant enzymes and consequently altering TH metabolism. ]]>