Role of the Thyroid System in Myelination and Neural Connectivity

Per-polyfluoroalkyl substances (PFAS) as thyroid disruptors: is there evidence for multi-transgenerational effects?

INTRODUCTION

The environmental spread of pollutants has led to a persistent exposure of living beings to multiple chemicals, by now become ubiquitous in the surrounding environment. Environmental exposure to these substances has been reported to cause multi- and/or transgenerational health effects. Per- and Polyfluorinated Substances (PFAS) raise great concern, given their known effects both as endocrine disruptors and potential carcinogens. The multi/trans-generational effects of different endocrine disruptors have been investigated by several studies, and harmful effects observed also for PFAS.

AREAS COVERED

This review examines the current data on the multi-trans-generational effects of PFAS, with a focus on their impact on the thyroid axis. The aim is to determine if there is evidence of potential multi-trans-generational effects of PFAS on the thyroid and/or if more research is needed.

EXPERT OPINION

PFAS exposure impacts thyroid homeostasis and can cross the placental barrier. In addition PFAS have shown multi-transgenerational effects in laboratory experiences and animal models, but thyroid disruptive effects of PFAS were also investigated only in a small number of these studies. Efforts are needed to study the adverse effects of PFAS, as not all PFAS are regulated and removal strategies are still being developed.

Early childhood exposures to phthalates in association with attention-deficit/hyperactivity disorder behaviors in middle childhood and adolescence in the ReCHARGE study

BACKGROUND

Early-life exposure to phthalates alters behaviors in animals. However, epidemiological evidence on childhood phthalate exposure and attention-deficit/hyperactivity disorder (ADHD) behaviors is limited.

METHODS

This study included 243 children from the ReCHARGE (Revisiting Childhood Autism Risks from Genetics and Environment) study, who were previously classified as having autism spectrum disorder (ASD), developmental delay, other early concerns, and typical development in the CHARGE case-control study. Twenty phthalate metabolites were measured in spot urine samples collected from children aged 2-5 years. Parents reported on children's ADHD symptoms at ages 8-18 years using Conners-3 Parent Rating Scale. Covariate-adjusted negative binomial generalized linear models were used to investigate associations between individual phthalate metabolite concentrations and raw scores. Weighted quantile sum (WQS) regression with repeated holdout validation was used to examine mixture effects of phthalate metabolites on behavioral scores. Effect modification by child sex was evaluated.

RESULTS

Among 12 phthalate metabolites detected in >75% of the samples, higher mono-2-heptyl phthalate (MHPP) was associated with higher scores on Inattentive (β per doubling = 0.05, 95% confidence interval [CI]: 0.02, 0.08) and Hyperactive/Impulsive scales (β = 0.04, 95% CI: 0.00, 0.07), especially among children with ASD. Higher mono-carboxy isooctyl phthalate (MCiOP) was associated with higher Hyperactivity/Impulsivity scores (β = 0.07, 95% CI: -0.01, 0.15), especially among typically developing children. The associations of the molar sum of high molecular weight (HMW) phthalate metabolites and a phthalate metabolite mixture with Hyperactivity/Impulsivity scores were modified by sex, showing more pronounced adverse associations among females.

CONCLUSION

Exposure to phthalates during early childhood may impact ADHD behaviors in middle childhood and adolescence, particularly among females. Although our findings may not be broadly generalizable due to the diverse diagnostic profiles within our study population, our robust findings on sex-specific associations warrant further investigations.

Low T3 syndrome is associated with the severity of myelin oligodendrocyte glycoprotein antibody-associated disease exacerbation

Background

Myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) is a rare autoimmune inflammatory disease of the central nervous system, (CNS) different from multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD). While numerous studies have delved into the involvement of thyroid antibodies (ATAbs) and thyroid function in NMOSD and MS. The objective of this study is to explore the clinical significance of thyroid dysfunction and ATAbs abnormalities in adult patients with MOGAD.

Methods

36 adult inpatients diagnosed with MOGAD and 47 sex- and age-matched healthy controls were enrolled. Patients were divided into two groups based on the presence or absence of low T3 syndrome. Demographics, clinical characteristics, and results of auxiliary examinations were compared across the subgroups. Moreover, an analysis was conducted to explore the correlations between thyroid hormone levels and Expanded Disability Status Scale (EDSS) scores.

Results

Thyroid dysfunction was notably more frequent in MOGAD patients than healthy controls (p < 0.0001), particularly low T3 syndrome (p=0.03). Furthermore, subgroup analyses revealed that the low T3 syndrome group exhibited higher EDSS scores and a higher proportion of individuals with EDSS scores > 3, in comparison to the non-low T3 syndrome group (p = 0.014, p = 0.046). However, no significant differences were observed in demographic characteristics, annual relapse rates, clinical phenotypes, laboratory and MRI results, and EEG abnormalities between the two groups. Additional Spearman's analysis showed significantly negative correlations between the TT3 and FT3 levels with EDSS scores (r = -0.367, p = 0.028; r = -0.377, p = 0.024). Typical brain lesions and paralateral ventricle lesions were significantly rare in patients with positive ATAbs compared to those with negative ATAbs (p = 0.0001, p = 0.03), although the incidence of ATAbs abnormalities did not differ significantly between MOGAD patients and healthy controls.

Conclusions

Overall, this study confirmed thyroid dysfunction, especially low T3 syndrome, is frequent in adult MOGAD patients. Patients with low T3 syndrome exhibited elevated EDSS scores and a significantly higher incidence of unfavorable condition. additionally, the correlation analysis model manifests that FT3 and TT3 levels were negatively correlated with EDSS scores. These evidences indicate that low T3 syndrome is associated with the severity of MOGAD exacerbation.

Sonic hedgehog signalling pathway contributes in age-related disorders and Alzheimer's disease

Alzheimer's disease (AD) is caused by the aging process and manifested by cognitive deficits and progressive memory loss. During aging, several conditions, including hypertension, diabetes, and cholesterol, have been identified as potential causes of AD by affecting Sonic hedgehog (Shh) signalling. In addition to being essential for cell differentiation and proliferation, Shh signalling is involved in tissue repair and the prevention of neurodegeneration. Neurogenesis is dependent on Shh signalling; inhibition of this pathway results in neurodegeneration. Several protein-protein interactions that are involved in Shh signalling are implicated in the pathophysiology of AD like overexpression of the protein nexin-1 inhibits the Shh pathway in AD. A protein called Growth Arrest Specific-1 works with another protein called cysteine dioxygenase (CDO) to boost Shh signalling. CDO is involved in the development of the central nervous system (CNS). Shh signalling strengthened the blood brain barrier and therefore prevent the entry of amyloid beta and other toxins to the brain from periphery. Further, several traditional remedies used for AD and dementia, including Epigallocatechin gallate, yokukansan, Lycium barbarum polysaccharides, salvianolic acid, and baicalin, are known to stimulate the Shh pathway. In this review, we elaborated that the Shh signalling exerts a substantial influence on the pathogenesis of AD. In this article, we have tried to explore the various possible connections between the Shh signalling and various known pathologies of AD.

Brain white matter alterations in young adult male patients with childhood-onset growth hormone deficiency: a diffusion tensor imaging study

PURPOSE

This study aimed to detect white matter changes and different effects of thyroid hormone on the white matter integrity in young adult male patients with childhood-onset growth hormone deficiency (CO-GHD), compared with healthy people.

METHODS

Magnetic resonance imaging (structural imaging and diffusion tensor imaging) was performed in 17 young adult male patients with CO-GHD and 17 healthy male controls. The white matter volume, mean diffusivity (MD) values and fractional anisotropy (FA) values were quantified and compared between two groups (CO-GHD group vs. control group). We assessed the interaction effects between thyroid hormone and groups (CO-GHD group vs. control group) on white matter integrity.

RESULTS

Patients with CO-GHD exhibited similar white matter volumes compared with controls. However, compared with the controls, patients with CO-GHD showed a significant reduction in FA values in six clusters and a substantial increase in MD values in four clusters, mainly involving the corticospinal tracts, corpus callosum and so on. Moreover, after correcting for insulin-like growth factor-1 levels, the significant interaction effects between groups (CO-GHD group vs. control group) and serum free thyroxine levels on MD values were noted in three clusters, mainly involving in superior longitudinal fasciculus and sagittal stratum.

CONCLUSION

In conclusion, young males with CO-GHD showed white matter changes in multiple brain regions and different effects of thyroid hormone on the white matter integrity.

FT4-to-FT3 ratio is a novel prognostic marker in subacute combined spinal cord degeneration patients

Objectives

The FT4-to-FT3 ratio (FFR) variations in patients with subacute combined spinal cord degeneration (SCSD) as a potentially useful prognostic indicator are still unknown. This study aimed to investigate the changes of FFR as a potentially valuable prognostic predictor in patients with SCSD.

Methods

This study included 144 consecutive SCSD patients who received standard diagnostic and therapeutic procedures between January 2015 and December 2021 and were admitted to the Department of Neurology at the First Affiliated Hospital of Bengbu Medical University. At the time of admission, we gathered data on all patients' demographics, daily routines, previous chronic conditions, medication histories, and other clinical details. For the purpose of measuring FFR, blood samples were specifically taken within 48 h of admission. The degree of neurological impairment of patients was assessed using the functional disability scale at the time of admission. At 6 months following discharge, the Modified Rankin Scale (mRS) was used to evaluate the clinical prognosis. To evaluate the relationship between the FFR and the risks of a poor outcome (mRS > 2), univariate and multivariate logistic regression analysis was utilized. The significance of the FT4/FT3 ratio in predicting the clinical outcomes in SCSD patients 6 months after discharge was assessed using the area under curve-receiver operating characteristic (AUC-ROC).

Results

About 90 patients (62.5%) of the 144 patients had poor outcomes, while 54 (37.5%) had favorable outcomes. Higher FFR at admission was independently linked to higher odds of a poor outcome, according to a logistic analysis. With an optimized cutoff value of >2.843, the FFR exhibited the maximum accuracy for predicting a poor outcome, according to the AUC‒ROC curve (AUC 0.731, P < 0.001; sensitivity, 77.8%; specificity, 83.3%). FFR was identified as an independent predictor of poor outcomes by multivariate logistic regression (OR, 2.244; 95% CI, 1.74-2.90; P < 0.001).

Conclusions

We discovered that in patients who had a bad result 6 months after discharge, the FFR had dramatically increased at the time of admission, providing a unique prognostic marker in patients with SCSD.

Low levels of free triiodothyronine are associated with risk of cognitive impairment in older euthyroid adults

Accumulated evidence showed that thyroid diseases induced cognitive decline. However, the relationship between thyroid hormones (THs) and cognition in older euthyroid people is still unclear. Our study aimed to estimate the association between THs within the euthyroid range and cognition in community-dwelling older adults in China. Data were extracted from a cohort study on the health status of rural older adults from the Guizhou province in China (HSRO). Serum thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3) were measured using the electrochemiluminescence immunoassay. Cognitive function was evaluated by the Mini-Mental State Examination (MMSE). Linear regression and a binary logistic regression model were used to explore the relationship between THs and cognition in euthyroidism (TSH level of 0.27 ~ 4.20mIU/L). A total of 957 euthyroidism individuals were included in this study, with a mean (SD) age of 71.34 (6.35) years. In individuals with euthyroidism, serum TSH and FT3 levels were positively associated with cognition (TSH:β = 0.06, 95% CI  0.01 ~ 0.11, P = 0.03; FT3:β = 0.07, 95% CI  0.01 ~ 0.12, P = 0.01); and serum FT3 and TSH levels were significantly associated with cognitive domains (P < 0.05). Further, euthyroid individuals in the lowest serum FT3(OR = 1.96; 95% CI 1.27 ~ 3.03) quartile had a twofold increased risk of cognitive impairment compared to those in the highest quartile after adjusting for potential confounding factors. These findings suggested that low levels of FT3 could be an independent risk factor for cognitive impairment in older euthyroid adults. Additionally, a positive linear association exists between serum FT3 levels and cognitive domains (such as immediate memory, language, and attention). Further studies are needed to determine the underlying mechanisms and the community significance of these findings.

Maternal Thyroid Function During Pregnancy and Offspring White Matter Microstructure in Early Adulthood: A Prospective Birth Cohort Study

Background: The fetus is fully dependent on maternal thyroid hormones until mid-gestation and suboptimal maternal thyroid function has been associated with alterations in the neurodevelopment of the offspring. We used maternal free thyroxine (fT4) and thyrotropin (TSH) levels in early gestation to study the association of maternal thyroid function during early pregnancy and offspring brain white matter (WM) integrity in early adulthood. Methods: Our study population consisted of a total of 292 mother-child pairs. Maternal fT4 and TSH were used as predictors and offspring multimodal imaging measures of fractional anisotropy, mean diffusivity, and magnetization transfer ratio (FA, MD, and MTR) as dependent variables. First, as Global analysis, all analyzed 14 WM tracts were studied simultaneously using linear-mixed effect models. Second, if a global effect was detected, a post hoc Tract-wise analysis was carried out using linear models individually in each WM tract. Study population was stratified by sex. Results: We found a positive association between maternal fT4 and offspring Global FA in males when adjusted for all maternal and offspring covariates (n = 114; β = 0.154; confidence interval = 0.045-0.263; p = 0.006). The finding was observed to be driven by multiple WM tracts, of which three projection fiber tracts and the forceps minor survived correcting for multiple comparisons in Tract-wise analysis. Conclusions: Maternal thyroid function in early pregnancy was observed to be associated with WM microstructure in male offspring in early adulthood. Our results suggest that maternal fT4 levels in early pregnancy may modulate axonal characteristics, with a long-term effect on offspring WM development.

Thyroid hormone levels paradox in acute ischemic stroke

Objective

Accumulating evidence has suggested that thyroid hormone levels affect the prognosis of acute ischemic stroke (AIS), but the results have been inconsistent.

Methods

Basic data, neural scale scores, thyroid hormone levels, and other laboratory examination data of AIS patients were collected. The patients were divided into excellent and poor prognosis group at discharge and 90 days after discharge. Logistic regression models were applied to evaluate the relationship between thyroid hormone levels and prognosis. A subgroup analysis was performed based on stroke severity.

Results

A number of 441 AIS patients were included in this study. Those in the poor prognosis group were older, with higher blood sugar levels, higher free thyroxine (FT4) levels, and severe stroke (all p < 0.05) at baseline. Free thyroxine (FT4) showed a predictive value (all p < 0.05) for prognosis in the model adjusted for age, gender, systolic pressure, and glucose level. However, after adjustment for types and severity of stroke, FT4 showed insignificant associations. In the severe subgroup at discharge, the change in FT4 was statistically significant (p = 0.015), odds ratio (95% confidence interval) = 1.394 (1.068-1.820) but not in the other subgroups.

Conclusions

High-normal FT4 serum levels in patients with severe stroke receiving conservative medical treatment at admission may indicate a worse short-term prognosis.

Neuroprotection and neuroregeneration: roles for the white matter

Efficient strategies for neuroprotection and repair are still an unmet medical need for neurodegenerative diseases and lesions of the central nervous system. Over the last few decades, a great deal of attention has been focused on white matter as a potential therapeutic target, mainly due to the discovery of the oligodendrocyte precursor cells in the adult central nervous system, a cell type able to fully repair myelin damage, and to the development of advanced imaging techniques to visualize and measure white matter lesions. The combination of these two events has greatly increased the body of research into white matter alterations in central nervous system lesions and neurodegenerative diseases and has identified the oligodendrocyte precursor cell as a putative target for white matter lesion repair, thus indirectly contributing to neuroprotection. This review aims to discuss the potential of white matter as a therapeutic target for neuroprotection in lesions and diseases of the central nervous system. Pivot conditions are discussed, specifically multiple sclerosis as a white matter disease; spinal cord injury, the acute lesion of a central nervous system component where white matter prevails over the gray matter, and Alzheimer's disease, where the white matter was considered an ancillary component until recently. We first describe oligodendrocyte precursor cell biology and developmental myelination, and its regulation by thyroid hormones, then briefly describe white matter imaging techniques, which are providing information on white matter involvement in central nervous system lesions and degenerative diseases. Finally, we discuss pathological mechanisms which interfere with myelin repair in adulthood.

A novel frameshift mutation in Allan-Herndon-Dudley syndrome

Allan-Herndon-Dudley syndrome (AHDS) is a very rare, X-linked psychomotor disability syndrome with delayed myelination, almost exclusively affecting boys. We present a case of a 4-year-old boy with AHDS who was found cyanotic, with intermittent vomiting and paroxysmal convulsions about 4 h after his parents went out, and was then taken to the hospital, where he eventually died the next day. The autopsy revealed foreign bodies in the tiny bronchi and alveoli of the deceased, congestion, and punctate hemorrhage in multiple organs, consistent with the diagnosis of asphyxia. Compared with a normally developing 4-year-old boy, the deceased showed cerebral atrophy and cerebral edema, and Luxol Fast Blue (LFB) stain indicated delayed cerebellar, hippocampal, and basal ganglia development and myelination. A novel frameshift mutation c.584delG in the SLC16A2 gene was detected. Family lineage investigation showed that the mutation was also detected in the deceased's 8-year-old brother and biological mother. The present work enriches the profile mutations in SLC16A2 related to AHDS and emphasizes the importance of autopsy and postmortem genetic analysis in such cases.

When pharmaceutical drugs become environmental pollutants: Potential neural effects and underlying mechanisms

Pharmaceutical drugs have become consumer products, with a daily use for some of them. The volume of production and consumption of drugs is such that they have become environmental pollutants. Their transfer to wastewater through urine, feces or rinsing in case of skin use, associated with partial elimination by wastewater treatment plants generalize pollution in the hydrosphere, including drinking water, sediments, soils, the food chain and plants. Here, we review the potential effects of environmental exposure to three classes of pharmaceutical drugs, i.e. antibiotics, antidepressants and non-steroidal anti-inflammatory drugs, on neurodevelopment. Experimental studies analyzing their underlying modes of action including those related to endocrine disruption, and molecular mechanisms including epigenetic modifications are presented. In addition, the contribution of brain imaging to the assessment of adverse effects of these three classes of pharmaceuticals is approached.

Deficient thyroid hormone transport to the brain leads to impairments in axonal caliber and oligodendroglial development

Mutations in the thyroid hormone transporter monocarboxylate transporter 8 (MCT8) lead to profound brain alterations, including myelination impairments, in humans. We aimed to further explore the pathophysiological mechanisms underlying the MCT8 deficiency-associated myelination impairments to unravel new biomarkers and therapeutic targets. We have performed brain histological analysis on an MCT8-deficient subject and histological, ultrastructural, and magnetic resonance imaging (MRI) analysis in the brain of a mouse model of the syndrome, lacking MCT8 and enzyme deiodinase type 2 (DIO2, Mct8/Dio2 KO). We have found that the MCT8-deficient subject presents severely reduced myelin lipid and protein staining and increased proportion of small-caliber myelinated axons in detriment of large-caliber ones. Mct8/Dio2 KO mice present myelination impairments and abnormal oligodendroglial development. We conclude that the greater proportion of small-caliber axons and impairments in the oligodendroglia lineage progression arise as potential mechanisms underlying the permanent myelination defects in MCT8-deficiency. Moreover, we present the Mct8/Dio2 KO mouse model, and MRI as a non-invasive biomarker, as highly valuable tools for preclinical studies involving MCT8 deficiency. These findings contribute to the understanding of the pathological mechanisms in MCT8 deficiency and suggest new biomarkers and therapeutic targets to consider therapeutic options for the neurological defects in patients.

Positive antithyroid antibody predicts severity of neuromyelitis optica spectrum disorder in children

BACKGROUND

Neuromyelitis optica spectrum disease (NMOSD) is a rare autoimmune disease, which can coexist with autoimmune thyroid diseases (AITDS). There has been no report on the clinical characteristics of NMOSD in children with positive anti-thyroid antibodies (ATAbs). The aim of this study is to evaluate thyroid function and detect the difference between ATAbs seropositive and seronegative NMOSD children.

METHODS

108 children with a confirmed diagnosis of NMOSD who were admitted to Shengjing Hospital of China Medical University from January 2015 to September 2020 were enrolled and their thyroid functions were evaluated. They were divided into two groups by ATAbs abnormalities. Their demographic characteristics, clinical symptoms, laboratory and MRI scan results of the brain and spinal cord were assessed.

RESULTS

ATAbs positive rate was higher in children with NMOSD when compared with healthy controls (P < 0.05). Most NMOSD children with positive ATAbs were female (P < 0.01). The expanded disability status scale (EDSS) score was significantly higher in the ATAbs positive group (P < 0.01). There were statistically significant differences for the incidence of bulbar area postrema symptoms, spinal cord symptoms, and fever of unknown origin of the first onset between the ATAbs positive and negative group (P < 0.05). The ANA and MOG antibody positive rate, longitudinally extensive transverse myelitis (LETM), and electroencephalogram (EEG) were significantly higher in ATAbs positive group (P < 0.05).

CONCLUSION

MOG antibody-positive is a unique marker of aggravation of neurological dysfunction in ATAbs-positive NMOSD children. Monitoring ATAbs may play an important role in predicting the prognosis of NMOSD.

Thyroid hormone deficiency during zebrafish development impairs central nervous system myelination

Thyroid hormones are messengers that bind to specific nuclear receptors and regulate a wide range of physiological processes in the early stages of vertebrate embryonic development, including neurodevelopment and myelogenesis. We here tested the effects of reduced T3 availability upon the myelination process by treating zebrafish embryos with low concentrations of iopanoic acid (IOP) to block T4 to T3 conversion. Black Gold II staining showed that T3 deficiency reduced the myelin density in the forebrain, midbrain, hindbrain and the spinal cord at 3 and 7 dpf. These observations were confirmed in 3 dpf mbp:egfp transgenic zebrafish, showing that the administration of IOP reduced the fluorescent signal in the brain. T3 rescue treatment restored brain myelination and reversed the changes in myelin-related gene expression induced by IOP exposure. NG2 immunostaining revealed that T3 deficiency reduced the amount of oligodendrocyte precursor cells in 3 dpf IOP-treated larvae. Altogether, the present results show that inhibition of T4 to T3 conversion results in hypomyelination, suggesting that THs are part of the key signaling molecules that control the timing of oligodendrocyte differentiation and myelin synthesis from very early stages of brain development.

Design and In Vitro Study of a Dual Drug-Loaded Delivery System Produced by Electrospinning for the Treatment of Acute Injuries of the Central Nervous System

Vascular and traumatic injuries of the central nervous system are recognized as global health priorities. A polypharmacology approach that is able to simultaneously target several injury factors by the combination of agents having synergistic effects appears to be promising. Herein, we designed a polymeric delivery system loaded with two drugs, ibuprofen (Ibu) and thyroid hormone triiodothyronine (T3) to in vitro release the suitable amount of the anti-inflammation and the remyelination drug. As a production method, electrospinning technology was used. First, Ibu-loaded micro (diameter circa 0.95–1.20 µm) and nano (diameter circa 0.70 µm) fibers were produced using poly(l-lactide) PLLA and PLGA with different lactide/glycolide ratios (50:50, 75:25, and 85:15) to select the most suitable polymer and fiber diameter. Based on the in vitro release results and in-house knowledge, PLLA nanofibers (mean diameter = 580 ± 120 nm) loaded with both Ibu and T3 were then successfully produced by a co-axial electrospinning technique. The in vitro release studies demonstrated that the final Ibu/T3 PLLA system extended the release of both drugs for 14 days, providing the target sustained release. Finally, studies in cell cultures (RAW macrophages and neural stem cell-derived oligodendrocyte precursor cells—OPCs) demonstrated the anti-inflammatory and promyelinating efficacy of the dual drug-loaded delivery platform.

Nuclear receptors and differentiation of oligodendrocyte precursor cells

Oligodendrocytes are the cells responsible for myelin formation during development and in adulthood, both for normal myelin turnover and myelin repair. These highly specialized cells derive from the oligodendrocyte precursor cells (OPCs), through a complex differentiation process involving genetic and epigenetic regulation mechanisms, which switch the phenotype from a migratory and replicative precursor to a mature post-mitotic cell. The process is regulated by a plethora of molecules, involving neurotransmitters, growth factors, hormones and other small molecules, and is mainly driven by nuclear receptors (NRs). NRs are transcription factors with heterogeneous ligand-dependent and independent actions which differ for the cell target, the responsive gene and the formation of NR homo- or heterodimers. This chapter highlights the role of NRs in regulating OPC differentiation, also in view of drug discovery strategies aimed at targeting pathological conditions which interfere with both developmental myelination and remyelination in adulthood.

Thyroid Hormone Signaling in Embryonic Stem Cells: Crosstalk with the Retinoic Acid Pathway

While the role of thyroid hormones (THs) during fetal and postnatal life is well-established, their role at preimplantation and during blastocyst development remains unclear. In this study, we used an embryonic stem cell line isolated from rat (RESC) to study the effects of THs and retinoic acid (RA) on early embryonic development during the pre-implantation stage. The results showed that THs play an important role in the differentiation/maturation processes of cells obtained from embryoid bodies (EB), with thyroid hormone nuclear receptors (TR) (TRα and TRβ), metabolic enzymes (deiodinases 1, 2, 3) and membrane transporters (Monocarboxylate transporters -MCT- 8 and 10) being expressed throughout in vitro differentiation until the Embryoid body (EB) stage. Moreover, thyroid hormone receptor antagonist TR (1-850) impaired RA-induced neuroectodermal lineage specification. This effect was significantly higher when cells were treated with retinoic acid (RA) to induce neuroectodermal lineage, studied through the gene and protein expression of nestin, an undifferentiated progenitor marker from the neuroectoderm lineage, as established by nestin mRNA and protein regulation. These results demonstrate the contribution of the two nuclear receptors, TR and RA, to the process of neuroectoderm maturation of the in vitro model embryonic stem cells obtained from rat.

Altered thyroid hormone profile in patients with Alzheimer's disease

BACKGROUND

Epidemiological studies have linked higher levels of thyroid hormones (THs) to increased risk of Alzheimer's disease (AD), whereas in advanced AD, THs have been unchanged or even decreased. In early AD dementia, little is known whether THs are related to AD neuropathology or brain morphology.

METHODS

This was a cross-sectional study of 36 euthyroid AD patients and 34 healthy controls recruited at a single memory clinic. Levels of THs were measured in serum and cerebrospinal fluid (CSF). In addition, we determined AD biomarkers (amyloid-β_1-42, total tau and phosphorylated tau) in CSF and hippocampal and amygdalar volumes using magnetic resonance imaging.

RESULTS

Serum free thyroxine (FT4) levels were elevated, whereas serum free triiodothyronine (FT3)/FT4 and total T3 (TT3)/total T4 (TT4) ratios were decreased, in AD patients compared to controls. In addition, serum TT4 was marginally higher in AD (p = 0.05 vs. the controls). Other TH levels in serum as well as CSF concentrations of THs were similar in both groups, and there were no correlations between THs and CSF AD biomarkers. However, serum FT3 correlated positively with left amygdalar volume in AD patients and serum TT3 correlated positively with left and right hippocampal volume in controls.

CONCLUSIONS

Thyroid hormones were moderately altered in mild AD dementia with increased serum FT4, and in addition, the reduced T3/T4 ratios may suggest decreased peripheral conversion of T4 to T3. Furthermore, serum T3 levels were related to brain structures involved in AD development.

Improved Functional Recovery in Rat Spinal Cord Injury Induced by a Drug Combination Administered with an Implantable Polymeric Delivery System

Spinal cord injury (SCI) is an incurable condition, in which a cascade of cellular and molecular events triggered by inflammation and excitotoxicity impairs endogenous regeneration, namely remyelination and axonal outgrowth. We designed a treatment solution based on an implantable biomaterial (electrospun poly (l-lactic acid) [PLLA]) loaded with ibuprofen and triiodothyronine (T3) to counteract inflammation, thus improving endogenous regeneration. In vivo efficacy was tested by implanting the drug-loaded PLLA in the rat model of T8 contusion SCI. We observed the expected recovery of locomotion beginning on day 7. In PLLA-implanted rats (i.e., controls), the recovery stabilized at 21 days post-lesion (DPL), after which no further improvement was observed. On the contrary, in PLLA + ibuprofen (Ibu) + T3 (PLLA-Ibu-T3) rats a further recovery and a significant treatment effect were observed, also confirmed by the gait analysis on 49 DPL. Glutamate release at 24 h and 8 DPL was reduced in PLLA-Ibu-T3- compared to PLLA-implanted rats, such as the estimated lesion volume at 60 DPL. The myelin- and 200-neurofilament-positive area fraction was higher in PLLA-Ibu-T3-implanted rats, where the percentage of astrocytes was significantly reduced. The implant of a PLLA electrospun scaffold loaded with Ibu and T3 significantly improves the endogenous regeneration, leading to an improvement of functional locomotion outcome in the SCI.

Graves' Disease and Toxic Nodular Goiter, Aggravated by Duration of Hyperthyroidism, Are Associated with Alzheimer's and Vascular Dementia: A Registry-Based Long-Term Follow-Up of Two Large Cohorts

Background: Dementia is an increasing burden to the health care system. It is currently debated whether hyperthyroidism is associated with a risk of dementia. Our aim was to determine the risk of dementia in hyperthyroid individuals and whether this was associated with duration of hyperthyroidism. Methods: Risk of dementia in hyperthyroid individuals was evaluated in two cohorts and matched reference populations. The Danish National Patient Registry (DNPR) cohort is a registry-based Danish nationwide cohort followed for a median of 7.2 years (from 1995 to 2013), whereas the OPENTHYRO registry cohort comprises 235,547 individuals who had at least one serum thyrotropin (TSH) measurement in the period from 1995 to 2011 and was followed for a median of 7.3 years. Each hyperthyroid case was matched with four controls according to age and sex using density sampling. Hyperthyroidism was defined as either an International Classification of Diseases Version 10 (ICD-10) diagnosis of toxic nodular goiter (TNG) or Graves' disease (GD), or two measurements of a TSH below 0.3 mU/L in the DNPR and OPENTHYRO registry cohort, respectively. The primary outcome was all-cause dementia, defined as either an ICD-10 code of dementia or prescription of medicine for dementia, with subgroup analyses of vascular dementia and Alzheimer's disease. Results: The DNPR cohort had 56,128 patients with hyperthyroidism, 2689 of whom were registered with dementia. The reference population had 224,512 individuals, of whom 10,199 had dementia (hazard ratio 1.17; 95% confidence interval [CI]: 1.12-1.23). Risk of dementia, whether Alzheimer's or vascular, was higher in both GD and TNG. The OPENTHYRO registry cohort constituted 2688 hyperthyroid individuals and 10,752 euthyroid control individuals of whom 190 and 473 individuals, respectively, were subsequently diagnosed with dementia (HR 1.06; 95% CI: 0.89-1.26). For each 6 months of decreased TSH, the risk of all-cause dementia was significantly higher (HR 1.16; 95% CI: 1.12-1.22). Conclusions: Using large-scale registry-based data, we found increased risk of dementia in hyperthyroid individuals. Every 6 months of decreased TSH was associated with increased risk of dementia by 16%, compared with individuals with normal TSH. Our data support early diagnosis and intervention in patients with hyperthyroidism.

No Dataset Left Behind: Mechanistic Insights into Thyroid Receptor Signaling Through Transcriptomic Consensome Meta-Analysis

Background: Discovery-scale omics datasets relevant to thyroid receptors (TRs) and their physiological and synthetic bioactive small-molecule ligands allow for genome-wide interrogation of TR-regulated genes. These datasets have considerable collective value as a reference resource to allow researchers to routinely generate hypotheses addressing the mechanisms underlying the cell biology and physiology of TR signaling in normal and disease states. Methods: Here, we searched the Gene Expression Omnibus database to identify a population of publicly archived transcriptomic datasets involving genetic or pharmacological manipulation of either TR isoform in a mouse tissue or cell line. After initial quality control, samples were organized into contrasts (experiments), and transcript differential expression values and associated measures of significance were generated and committed to a consensome (for consensus omics) meta-analysis pipeline. To gain insight into tissue-selective functions of TRs, we generated liver- and central nervous system (CNS)-specific consensomes and identified evidence for genes that were selectively responsive to TR signaling in each organ. Results: The TR transcriptomic consensome ranks genes based on the frequency of their significant differential expression over the entire group of experiments. The TR consensome assigns elevated rankings both to known TR-regulated genes and to genes previously uncharacterized as TR-regulated, which shed mechanistic light on known cellular and physiological roles of TR signaling in different organs. We identify evidence for unreported genomic targets of TR signaling for which it exhibits strikingly distinct regulatory preferences in the liver and CNS. Moreover, the intersection of the TR consensome with consensomes for other cellular receptors sheds light on transcripts potentially mediating crosstalk between TRs and these other signaling paradigms. Conclusions: The mouse TR datasets and consensomes are freely available in the Signaling Pathways Project website for hypothesis generation, data validation, and modeling of novel mechanisms of TR regulation of gene expression. Our results demonstrate the insights into the mechanistic basis of thyroid hormone action that can arise from an ongoing commitment on the part of the research community to the deposition of discovery-scale datasets.

Neurodevelopmental effects of low dose ionizing radiation exposure: A systematic review of the epidemiological evidence

BACKGROUND

The neurodevelopmental effects of high doses of ionizing radiation (IR) in children are well established. To what extent such effects exist at low-to-moderate doses is unclear. Considering the increasing exposure of the general population to low-to-moderate levels of IR, predominantly from diagnostic procedures, the study of these effects has become a priority for radiation protection.

OBJECTIVES

We conducted a systematic review of the current evidence for possible effects of low-to-moderate IR doses received during gestation, childhood and adolescence on different domains of neurodevelopment.

DATA SOURCES

Searches were performed in PubMed, Scopus, EMBASE and Psychinfo on the 6th of June 2017 and repeated in December 2018.

STUDY ELIGIBILITY CRITERIA

We included studies evaluating the association between low-to-moderate IR doses received during gestation, childhood and adolescence, and neurodevelopmental functions.

STUDY APPRAISAL AND SYNTHESIS METHODS

Studies were evaluated using the Cochrane Collaboration's risk of bias tool adapted to environmental sciences. A qualitative synthesis was performed.

RESULTS

A total of 26 manuscripts were finally selected. Populations analyzed in these publications were exposed to the following sources of IR: atomic bomb (Hiroshima and Nagasaki), diagnostic/therapeutic radiation, and Chernobyl and nuclear weapon testing fallout. There was limited evidence for an association between low-to-moderate doses of IR and a decrease in general cognition and language abilities, that is, a causal interpretation is credible, but chance or confounding cannot not be ruled out with reasonable confidence. Evidence for a possible stronger effect when exposure occurred early in life, in particular, during the fetal period, was inadequate. Evidence for an association between IR and other specific domains, including attention, executive function, memory, processing speed, visual-spatial abilities, motor and socio-emotional development, was inadequate, due to the very limited number of studies found.

LIMITATIONS, CONCLUSIONS, AND IMPLICATIONS OF KEY FINDINGS

Overall, depending on the domain, there was limited to inadequate evidence for an effect of low-to-moderate IR doses on neurodevelopment. Heterogeneity across studies in terms of outcome and exposure assessment hampered any quantitative synthesis and any stronger conclusion. Future research with adequate dosimetry and covering a range of specific neurodevelopmental outcomes would likely contribute to improve the body of evidence.

SYSTEMATIC REVIEW REGISTRATION NUMBER

The systematic review protocol was registered in PROSPERO (registration number CRD42018091902).

Monocarboxylate Transporter 8 Deficiency: Delayed or Permanent Hypomyelination?

Monocarboxylate transporter 8 (MCT8) deficiency or the Allan-Herndon-Dudley Syndrome (AHDS) is an X-linked psychomotor disability syndrome with around 320 clinical cases described worldwide. SLC16A2 gene mutations, encoding the thyroid hormone (TH) transporter MCT8, result in intellectual disability due to impaired TH uptake in the developing brain. MCT8 deficiency is a multi-organ affecting disease with a predominant neuronal cell-based pathology, with the glial component inadequately investigated. However, deficiency in myelin, a key component of white matter (WM) enabling fast nerve conduction, is a TH-dependent hallmark of the disease. Nevertheless, analysis of the myelin status in AHDS patients has led to conflicting interpretations. The majority of individual case studies reported delayed myelination, that was restored later in life. In contrast, post-mortem studies and high-resolution MRIs detected WM (micro-) abnormalities throughout adolescence, suggesting permanent hypomyelination. Thus, interpretations vary depending on methodology to investigate WM microstructure. Further, it is unknown whether the mutation within the MCT8 is linked to the severity of the myelin deficiency. Consequently, terminology is inconsistent among reports, and AHDS is occasionally misdiagnosed as another WM disorder. The evolutionary conserved TH signaling pathway that promotes the generation of myelinating oligodendrocytes enabled deciphering how the lack of MCT8 might affect myelinogenesis. Linking patient findings on myelination to those obtained from models of MCT8 deficiency revealed underlying pathophysiological mechanisms, but knowledge gaps remain, notably how myelination progresses both spatially and temporally in MCT8 deficiency. This limits predicting how myelin integrity might benefit therapeutically, and when to initiate. A recurrent observation in clinical trials is the absence of neurological improvement. Testing MCT8-independent thyromimetics in models, and evaluating treatments used in other demyelinating diseases, despite different etiologies, is crucial to propose new therapeutic strategies combatting this devastating disease.

Coordinated transcriptional regulation by thyroid hormone and glucocorticoid interaction in adult mouse hippocampus-derived neuronal cells

The hippocampus is a well-known target of thyroid hormone (TH; e.g., 3,5,3’-triiodothyronine—T₃) and glucocorticoid (GC; e.g., corticosterone—CORT) action. Despite evidence that TH and GC play critical roles in neural development and function, few studies have identified genes and patterns of gene regulation influenced by the interaction of these hormones at a genome-wide scale. In this study we investigated gene regulation by T₃, CORT, and T₃ + CORT in the mouse hippocampus-derived cell line HT-22. We treated cells with T₃, CORT, or T₃ + CORT for 4 hr before cell harvest and RNA isolation for microarray analysis. We identified 9 genes regulated by T₃, 432 genes by CORT, and 412 genes by T₃ + CORT. Among the 432 CORT-regulated genes, there were 203 genes that exhibited an altered CORT response in the presence of T₃, suggesting that T₃ plays a significant role in modulating CORT-regulated genes. We also found 80 genes synergistically induced, and 73 genes synergistically repressed by T₃ + CORT treatment. We performed in silico analysis using publicly available mouse neuronal chromatin immunoprecipitation-sequencing datasets and identified a considerable number of synergistically regulated genes with TH receptor and GC receptor peaks mapping within 1 kb of chromatin marks indicative of hormone-responsive enhancer regions. Functional annotation clustering of synergistically regulated genes reveal the relevance of proteasomal-dependent degradation, neuroprotective effect of growth hormones, and neuroinflammatory responses as key pathways to how TH and GC may coordinately influence learning and memory. Taken together, our transcriptome data represents a promising exploratory dataset for further study of common molecular mechanisms behind synergistic TH and GC gene regulation, and identify specific genes and their role in processes mediated by cross-talk between the thyroid and stress axes in a mammalian hippocampal model system.

Low Tri-iodothyronine Syndrome Is Associated With Cognitive Impairment in Patients With Acute Ischemic Stroke: A Prospective Cohort Study

OBJECTIVE

Low tri-iodothyronine (T3) syndrome is a predictor of poor prognosis in patients with stroke. Poststroke cognitive impairment (PSCI) is a common and important complication after stroke. The association between low T3 syndrome and PSCI is unclear. We aimed to explore the potential relationship between low T3 syndrome and PSCI in the acute phase of ischemic stroke at a 1-month follow-up visit.

METHODS

In total, 314 ischemic stroke patients were consecutively enrolled in the study and followed up at 1 month. Thyroid hormones were measured within 24 hours after admission. Cognitive function was evaluated by the Mini-Mental State Exam (MMSE) 1 month after acute ischemic stroke. Cognitive impairment was defined as an MMSE score of less than 27. Cognitive impairment severity was categorized as severe, mild, or none (MMSE score <23, 23-26, or ≥27, respectively).

RESULTS

According to the MMSE score, 182 participants (58.0%) had cognitive impairment 1 month after stroke. Patients with low T3 syndrome were more prone to have cognitive impairment than patients with normal levels of T3 (p < 0.001). After adjusting for potential confounders in our logistic model, low T3 syndrome was independently associated with PSCI (odds ratio 4.319, 95% confidence interval 1.553-12.013, p = 0.005).

CONCLUSION

Low T3 syndrome in the acute phase of ischemic stroke was associated with a higher prevalence of 1-month PSCI, independently of established risk factors.

Do Defective Immune System-Mediated Myelination Processes Increase Postpartum Psychosis Risk?

Postpartum (or puerperal) psychosis (PP) is a rare, severe psychiatric disorder that affects women shortly after childbirth; risk is particularly high in individuals with a history of bipolar disorder or PP, but the underlying pathophysiology remains poorly understood. Emerging evidence suggests that immune system (dys)function plays an important role in disorder onset. On the basis of new findings from clinical and animal model studies, we hypothesise that the abundance and/or activity of regulatory T cells, and the efficacy of consequent (re)myelination processes in the brain mediated by CCN proteins, is perturbed in PP; this pathway may be modulated by risk and protective/treatment factors for the disorder, and identifying abnormalities within it could signpost novel predictive biomarkers and therapeutic targets.

The Effects of De-Whiskering and Congenital Hypothyroidism on The Development of Nitrergic Neurons in Rat Primary Somatosensory and Motor Cortices

Objective

The aim of the present study is to investigate the effects of chronic whisker deprivation on possible alterations to the development of nitrergic neurons in the whisker part of the somatosensory (wS1) and motor (wM1) cortices in offspring with congenital hypothyroidism (CH).

Materials and Methods

In the experimental study, CH was induced by adding propylthiouracil to the rats drinking water from embryonic day 16 to postnatal day (PND) 60. In whisker-deprived (WD) pups, all the whiskers were trimmed from PND 1 to 60. Nitrergic interneurons in the wS1/M1 cortices were detected by NADPH-diaphorase histochemistry staining technique in the control (Ctl), Ctl+WD, Hypo and Hypo+WD groups.

Results

In both wS1 and wM1 cortices the number of nitrergic neurons was significantly reduced in the Hypo and Hypo+WD groups compared to Ctl and Ctl+WD groups, respectively (P<0.05) while bilateral whisker deprivation had no remarkable effect. The mean soma diameter size of NADPH-d labeled neurons in the Ctl+WD and Hypo+WD groups was decreased compared to the Ctl and Hypo groups, respectively. A similar patterns of decreased NADPH-d labeled neurons in the wS1/M1 cortices occur in the processes of nitrergic neurons in both congenital hypothyroidism and whisker deprivation.

Conclusion

Our results suggest that both congenital hypothyroidism and whisker deprivation may disturb normal development of the wS1 and wM1 cortical circuits in which nitrergic neurons are involved.

Prognostic value of thyroid hormones in acute ischemic stroke - a meta analysis

Previous studies on the association between thyroid hormones and prognosis of acute ischemic stroke (AIS) reported conflicting results. We conducted a meta-analysis to assess the prognostic value of thyroid hormones in AIS. The PubMed, EMBASE, and Cochrane library databases were searched through May 12, 2017 to identify eligible studies on this subject. Out of 2,181 studies retrieved, 11 studies were finally included with a total number of 3,936 acute stroke patients for analysis. Odds ratio (OR) for predicting poor outcome or standardized mean difference (SMD) of thyroid hormone levels with 95% confidence intervals (95% CI) obtained from the studies were pooled using Review Manager 5.3. From the results, in AIS, patients with a poor outcome had lower levels of triiodothyronine (T3) and higher thyroxine (T4). Pooled OR confirmed the same association. Our study provides statistical evidence supporting the utility of thyroid hormone levels in prognosis of acute stroke.

De novo triiodothyronine formation from thyrocytes activated by thyroid-stimulating hormone

The thyroid gland secretes primarily tetraiodothyronine (T₄), and some triiodothyronine (T₃). Under normal physiological circumstances, only one-fifth of circulating T₃ is directly released by the thyroid, but in states of hyperactivation of thyroid-stimulating hormone receptors (TSHRs), patients develop a syndrome of relative T₃ toxicosis. Thyroidal T₄ production results from iodination of thyroglobulin (TG) at residues Tyr⁵ and Tyr¹³⁰, whereas thyroidal T₃ production may originate in several different ways. In this study, the data demonstrate that within the carboxyl-terminal portion of mouse TG, T₃ is formed de novo independently of deiodination from T₄ We found that upon iodination in vitro, de novo T₃ formation in TG was decreased in mice lacking TSHRs. Conversely, de novo T₃ that can be formed upon iodination of TG secreted from PCCL3 (rat thyrocyte) cells was augmented from cells previously exposed to increased TSH, a TSHR agonist, a cAMP analog, or a TSHR-stimulating antibody. We present data suggesting that TSH-stimulated TG phosphorylation contributes to enhanced de novo T₃ formation. These effects were reversed within a few days after removal of the hyperstimulating conditions. Indeed, direct exposure of PCCL3 cells to human serum from two patients with Graves' disease, but not control sera, led to secretion of TG with an increased intrinsic ability to form T₃ upon in vitro iodination. Furthermore, TG secreted from human thyrocyte cultures hyperstimulated with TSH also showed an increased intrinsic ability to form T₃ Our data support the hypothesis that TG processing in the secretory pathway of TSHR-hyperstimulated thyrocytes alters the structure of the iodination substrate in a way that enhances de novo T₃ formation, contributing to the relative T₃ toxicosis of Graves' disease.

Inflammation severely alters thyroid hormone signaling in the central nervous system during experimental allergic encephalomyelitis in rat: Direct impact on OPCs differentiation failure

Differentiation of oligodendrocyte precursor cells (OPCs) into myelinating oligodendrocytes is severely impaired by inflammatory cytokines and this could lead to remyelination failure in inflammatory/demyelinating diseases. Due to the role of thyroid hormone in the maturation of OPCs and developmental myelination, in this study we investigated (i) the possible occurrence of dysregulation of thyroid hormone signaling in the CNS tissue during experimental neuroinflammation; (ii) the possible impact of inflammatory cytokines on thyroid hormone signaling and OPCs differentiation in vitro. The disease model is the experimental allergic encephalomyelitis in female Dark-Agouti rats, whereas in vitro experiments were carried out in OPCs derived from neural stem cells. The main results are the following: (i) a strong upregulation of cytokine mRNA expression level was found in the spinal cord during experimental allergic encephalomyelitis; (ii) thyroid hormone signaling in the spinal cord (thyroid hormone receptors; deiodinase; thyroid hormone membrane transporter) is substantially downregulated, due to the upregulation of the thyroid hormone inactivating enzyme deiodinase 3 and the downregulation of thyroid hormone receptors, as investigated at mRNA expression level; (iii) when exposed to inflammatory cytokines, deiodinase 3 is upregulated in OPCs as well, and OPCs differentiation is blocked; (iv) deiodinase 3 inhibition by iopanoic acid recovers OPCs differentiation in the presence on inflammatory cytokines. These data suggest that cellular hypothyroidism occurs during experimental allergic encephalomyelitis, possibly impacting on thyroid hormone-dependent cellular processes, including maturation of OPCs into myelinating oligodendrocytes. GLIA 2016;64:1573-1589.