Thyroid hormone deficiency changes the distribution of oligodendrocyte/myelin markers during oligodendroglial differentiation in vitro

The iron maiden: Oligodendroglial metabolic dysfunction in multiple sclerosis and mitochondrial signaling

Multiple sclerosis (MS) is an autoimmune disease, governed by oligodendrocyte (OL) dystrophy and central nervous system (CNS) demyelination manifesting variable neurological impairments. Mitochondrial mechanisms may drive myelin biogenesis maintaining the axo-glial unit according to dynamic requisite demands imposed by the axons they ensheath. The promotion of OL maturation and myelination by actively transporting thyroid hormone (TH) into the CNS and thereby facilitating key transcriptional and metabolic pathways that regulate myelin biogenesis is fundamental to sustain the profound energy demands at each axo-glial interface. Deficits in regulatory functions exerted through TH for these physiological roles to be orchestrated by mature OLs, can occur in genetic and acquired myelin disorders, whereby mitochondrial efficiency and eventual dysfunction can lead to profound oligodendrocytopathy, demyelination and neurodegenerative sequelae. TH-dependent transcriptional and metabolic pathways can be dysregulated during acute and chronic MS lesion activity depriving OLs from critical acetyl-CoA biochemical mechanisms governing myelin lipid biosynthesis and at the same time altering the generation of iron metabolism that may drive ferroptotic mechanisms, leading to advancing neurodegeneration.

Thyroid hormone-dependent oligodendroglial cell lineage genomic and non-genomic signaling through integrin receptors

Multiple sclerosis (MS) is a heterogeneous autoimmune disease whereby the pathological sequelae evolve from oligodendrocytes (OLs) within the central nervous system and are targeted by the immune system, which causes widespread white matter pathology and results in neuronal dysfunction and neurological impairment. The progression of this disease is facilitated by a failure in remyelination following chronic demyelination. One mediator of remyelination is thyroid hormone (TH), whose reliance on monocarboxylate transporter 8 (MCT8) was recently defined. MCT8 facilitates the entry of THs into oligodendrocyte progenitor cell (OPC) and pre-myelinating oligodendrocytes (pre-OLs). Patients with MS may exhibit downregulated MCT8 near inflammatory lesions, which emphasizes an inhibition of TH signaling and subsequent downstream targeted pathways such as phosphoinositide 3-kinase (PI3K)-Akt. However, the role of the closely related mammalian target of rapamycin (mTOR) in pre-OLs during neuroinflammation may also be central to the remyelination process and is governed by various growth promoting signals. Recent research indicates that this may be reliant on TH-dependent signaling through β1-integrins. This review identifies genomic and non-genomic signaling that is regulated through mTOR in TH-responsive pre-OLs and mature OLs in mouse models of MS. This review critiques data that implicates non-genomic Akt and mTOR signaling in response to TH-dependent integrin receptor activation in pre-OLs. We have also examined whether this can drive remyelination in the context of neuroinflammation and associated sequelae. Importantly, we outline how novel therapeutic small molecules are being designed to target integrin receptors on oligodendroglial lineage cells and whether these are viable therapeutic options for future use in clinical trials for MS.

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.

Role of thyroid hormones in normal and abnormal central nervous system myelination in humans and rodents

Thyroid hormones (THs) are instrumental in promoting the molecular mechanisms which underlie the complex nature of neural development and function within the central nervous system (CNS) in vertebrates. The key neurodevelopmental process of myelination is conserved between humans and rodents, of which both experience peak fetal TH concentrations concomitant with onset of myelination. The importance of supplying adequate levels of THs to the myelin producing cells, the oligodendrocytes, for promoting their maturation is crucial for proper neural function. In this review we examine the key TH distributor and transport proteins, including transthyretin (TTR) and monocarboxylate transporter 8 (MCT8), essential for supporting proper oligodendrocyte and myelin health; and discuss disorders with impaired TH signalling in relation to abnormal CNS myelination in humans and rodents. Furthermore, we explore the importance of using novel TH analogues in the treatment of myelination disorders associated with abnormal TH signalling.

Hormonal Regulation of Oligodendrogenesis I: Effects across the Lifespan

The brain’s capacity to respond to changing environments via hormonal signaling is critical to fine-tuned function. An emerging body of literature highlights a role for myelin plasticity as a prominent type of experience-dependent plasticity in the adult brain. Myelin plasticity is driven by oligodendrocytes (OLs) and their precursor cells (OPCs). OPC differentiation regulates the trajectory of myelin production throughout development, and importantly, OPCs maintain the ability to proliferate and generate new OLs throughout adulthood. The process of oligodendrogenesis, the creation of new OLs, can be dramatically influenced during early development and in adulthood by internal and environmental conditions such as hormones. Here, we review the current literature describing hormonal regulation of oligodendrogenesis within physiological conditions, focusing on several classes of hormones: steroid, peptide, and thyroid hormones. We discuss hormonal regulation at each stage of oligodendrogenesis and describe mechanisms of action, where known. Overall, the majority of hormones enhance oligodendrogenesis, increasing OPC differentiation and inducing maturation and myelin production in OLs. The mechanisms underlying these processes vary for each hormone but may ultimately converge upon common signaling pathways, mediated by specific receptors expressed across the OL lineage. However, not all of the mechanisms have been fully elucidated, and here, we note the remaining gaps in the literature, including the complex interactions between hormonal systems and with the immune system. In the companion manuscript in this issue, we discuss the implications of hormonal regulation of oligodendrogenesis for neurological and psychiatric disorders characterized by white matter loss. Ultimately, a better understanding of the fundamental mechanisms of hormonal regulation of oligodendrogenesis across the entire lifespan, especially in vivo, will progress both basic and translational research.

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.

CXCR2 antagonism promotes oligodendrocyte precursor cell differentiation and enhances remyelination in a mouse model of multiple sclerosis

Multiple sclerosis (MS) is a chronic autoimmune demyelinating disease characterized by the autoimmune attack of oligodendrocytes, leading to demyelination and progressive functional deficits. CXC chemokine receptor 2 (CXCR2) is recently reported to orchestrate the migration, proliferation and differentiation of oligodendrocyte precursor cells (OPCs), which implies its possible involvement in the demyelinating process. Here, we used a CXCR2 antagonist, compound 2, as a tool to investigate the role of CXCR2 in demyelination and the underlying mechanism. The primary cultured oligodendrocytes and cuprizone (CPZ)-intoxicated mice were applied in the present study. The results showed that compound 2 significantly promoted OPC proliferation and differentiation. In the demyelinated lesions of CPZ-intoxicated mice, vigorous OPC proliferation and myelin repair was observed after compound 2 treatment. Subsequent investigation of the underlying mechanisms identified that upon inhibition of CXCR2, compound 2 treatment upregulated Ki67, transcription factor 2 (Olig2) and Caspr expression, activated PI3K/AKT/mTOR signaling, ultimately promoted OPCs differentiation and enhanced remyelination. In conclusion, our results demonstrated that CXCR2 antagonism efficiently promoted OPC differentiation and enhanced remyelination in CPZ-intoxicated mice, supporting CXCR2 as a promising therapeutic target for the treatment of chronic demyelinating diseases such as MS.

Rapid and Efficient Differentiation of Rodent Neural Stem Cells into Oligodendrocyte Progenitor Cells

Oligodendrocyte progenitor cells (OPCs) may have beneficial effects in cell replacement therapy of neurodegenerative disease owing to their unique capability to differentiate into myelinogenic oligodendrocytes (OLs) in response to extrinsic signals. Therefore, it is of significance to establish an effective differentiation methodology to generate highly pure OPCs and OLs from some easily accessible stem cell sources. To achieve this goal, in this study, we present a rapid and efficient protocol for oligodendroglial lineage differentiation from mouse neural stem cells (NSCs), rat NSCs, or mouse embryonic stem cell-derived neuroepithelial stem cells. In a defined culture medium containing Smoothened Agonist, basic fibroblast growth factor, and platelet-derived growth factor-AA, OPCs could be generated from the above stem cells over a time course of 4–6 days, achieving a cell purity as high as ∼90%. In particular, these derived OPCs showed high expandability and could further differentiate into myelin basic protein-positive OLs within 3 days or alternatively into glial fibrillary acidic protein-positive astrocytes within 7 days. Furthermore, transplantation of rodent NSC-derived OPCs into injured spinal cord indicated that it is a feasible strategy to treat spinal cord injury. Our results suggest a differentiation strategy for robust production of OPCs and OLs from rodent stem cells, which could provide an abundant OPC source for spinal cord injury.

Oligodendroglial Lineage Cells in Thyroid Hormone-Deprived Conditions

Oligodendrocytes are supporting glial cells that ensure the metabolism and homeostasis of neurons with specific synaptic axoglial interactions in the central nervous system. These require key myelinating glial trophic signals important for growth and metabolism. Thyroid hormone (TH) is one such trophic signal that regulates oligodendrocyte maturation, myelination, and oligodendroglial synaptic dynamics via either genomic or nongenomic pathways. The intracellular and extracellular transport of TH is facilitated by a specific transmembrane transporter known as the monocarboxylate transporter 8 (MCT8). Dysfunction of the MCT8 due to mutation, inhibition, or downregulation during brain development leads to inherited hypomyelination, which manifests as psychomotor retardation in the X-linked inherited Allan-Herndon-Dudley syndrome (AHDS). In particular, oligodendroglial-specific MCT8 deficiency may restrict the intracellular T3 availability, culminating in deficient metabolic communication between the oligodendrocytes and the neurons they ensheath, potentially promulgating neurodegenerative adult diseases such as multiple sclerosis (MS). Based on the therapeutic effects exhibited by TH in various preclinical studies, particularly related to its remyelinating potential, TH has now entered the initial stages of a clinical trial to test the therapeutic efficacy in relapsing-remitting MS patients (NCT02506751). However, TH analogs, such as DITPA or Triac, may well serve as future therapeutic options to rescue mature oligodendrocytes and/or promote oligodendrocyte precursor cell differentiation in an environment of MCT8 deficiency within the CNS. This review outlines the therapeutic strategies to overcome the differentiation blockade of oligodendrocyte precursors and maintain mature axoglial interactions in TH-deprived conditions.

Antenatal prevention of cerebral palsy and childhood disability: is the impossible possible?

This review covers our current knowledge of the causes of perinatal brain injury leading to cerebral palsy-like outcomes, and argues that much of this brain damage is preventable. We review the experimental evidence that there are treatments that can be safely administered to women in late pregnancy that decrease the likelihood and extent of perinatal brain damage that occurs because of acute and severe hypoxia that arises during some births, and the additional impact of chronic fetal hypoxia, infection, inflammation, growth restriction and preterm birth. We discuss the types of interventions required to ameliorate or even prevent apoptotic and necrotic cell death, and the vulnerability of all the major cell types in the brain (neurons, astrocytes, oligodendrocytes, microglia, cerebral vasculature) to hypoxia/ischaemia, and whether a pan-protective treatment given to the mother before birth is a realistic prospect.

Pregnant Greek Women May Have a Higher Prevalence of Iodine Deficiency than the General Greek Population

BACKGROUND

Adequate dietary iodine consumption, predicted via the urinary iodine concentration (UIC), is necessary for normal thyroid function and for the neurodevelopment of fetuses and neonates. The general population of Greece is considered to be iodine sufficient, but our preliminary findings suggest that Greek pregnant women are at risk of iodine deficiency.

OBJECTIVE

Our aim was to estimate the thyroid function and UIC in a representative population of pregnant Greek women.

METHODS

UIC and thyroid function were assessed in 1,118 women from 19 representative areas of the country.

RESULTS

The median UIC was found to be 127.1 µg/l (range 7.8-2,296), which is indicative of insufficient iodine intake according to the standard of the World Health Organization (WHO) for pregnant women. The median UIC was below the minimal recommended value of 150 µg/l in 61% of the women, and below 100 or 50 µg/l in 32 and 7%, respectively. An optimal iodine intake (150-250 µg/l) was observed in 26%, and was over the cut-off of 500 µg/l in 2% of the subjects. Serum thyrotropin significantly increased between trimesters, from 1.57 ± 1.2, to 1.68 ± 1.0 and to 2.02 ± 1.2 mU/l (p < 0.001). Serum-free thyroxine decreased significantly between trimesters, from 1.22 ± 0.34, to 1.01 ± 0.21 and 0.96 ± 0.2 ng/ml (p < 0.05). Serum thyroglobulin levels remained unchanged over the trimesters and were not correlated with UIC.

CONCLUSIONS

While the general population of Greece is iodine sufficient, these findings suggest that, according to the WHO, the majority of pregnant Greek women are iodine deficient. These data strongly suggest that a proactive policy should be developed to lower iodine deficiency risk in this population of women.

Serum Thyroglobulin Concentration Is a Weak Marker of Iodine Status in a Pregnant Population with Iodine Deficiency

OBJECTIVE

To assess the reliability of thyroglobulin (Tg) as a marker of iodine status during pregnancy.

DESIGN

299 women aged 30.5 ± 4.8 years (mean ± SD) were studied.

METHODS

In every subject, we measured urinary iodine concentration (UIC), serum thyrotropin (TSH), Tg, free thyroxine (fT4), Tg autoantibodies (TgAbs) and human chorionic gonadotropin (hCG) levels. We excluded samples with increased TgAbs from the analysis.

RESULTS

According to WHO criteria, the study population was iodine deficient in every trimester. Serum Tg levels did not differ during the three trimesters of pregnancy. Serum hCG levels fell significantly as pregnancies advanced. A weak, significantly negative correlation (limited to the 3rd trimester) was found between Tg and UIC (ρ = -0.187, p = 0.039). Serum fT4 decreased as pregnancies advanced and TSH increased. Serum fT4 was negatively correlated with TSH (ρ = -0.161, p = 0.006) and positively with hCG (ρ = +0.165, p = 0.005). The multiple regression equation of Tg based on hCG, TSH, UIC and trimester of pregnancy was significant but weak (F = 4.057, p = 0.003; R(2) = 0.055), with hCG as a significant predictor Tg (p for log hCG = 0.041).

CONCLUSIONS

Tg cannot be considered as a valid marker of iodine deficiency in pregnancy, at least in a mildly iodine-deficient environment. Further studies in a larger patient cohort with differences in iodine status, as well as studies on Tg changes after improving iodine status in pregnant women, are needed in order to corroborate these results.

Myelination Delay and Allan-Herndon-Dudley Syndrome Caused by a Novel Mutation in the SLC16A2 Gene

Allan-Herndon-Dudley syndrome is an X-linked disease caused by mutations in the solute carrier family 16 member 2 (SLC16A2) gene. As SLC16A2 encodes the monocarboxylate transporter 8 (MCT8), a thyroid hormone transporter, patients with Allan-Herndon-Dudley syndrome present a specific altered thyroid hormone profile. Allan-Herndon-Dudley syndrome has been associated with myelination delay on the brain magnetic resonance imaging (MRI) of affected subjects. We report a patient with Allan-Herndon-Dudley syndrome characterized by developmental delay, hypotonia, and delayed myelination caused by a novel SLC16A2 mutation (p.L291R). The thyroid hormones profile in our patient was atypical for Allan-Herndon-Dudley syndrome. The follow-up examinations showed that the progression of the myelination was not accompanied by a clinical improvement. Our paper suggests that SLC16A2 mutations should be investigated in patients with myelination delay even when the thyroid function is not conclusively altered.

Thyroid Hormone Potentially Benefits Multiple Sclerosis via Facilitating Remyelination

Myelin destruction due to inflammatory damage of oligodendrocytes (OLs) in conjunction with axonal degeneration is one of the major histopathological hallmarks of multiple sclerosis (MS), a common autoimmune disorder affecting the central nervous system (CNS). Therapies over the last 20 years mainly focus on the immune system and, more specifically, on the modulation of immune cell behavior. It seems to be effective in MS with relapse, while it is of little benefit to progressive MS in which neurodegeneration following demyelination outweighs inflammation. Otherwise, remyelination, as a result of oligodendrocyte production from oligodendrocyte precursor cells (OPCs), is considered to be a potential target for the treatment of progressive MS. In this review, positive effects of remyelination on MS will be discussed in view of the critical role played by thyroid hormone (TH), focusing on the following points: (1) promising treatment of TH on MS that potentially targets to remyelination; (2) the active role of TH that is able to promote remyelination; (3) the regulative role of TH that works on endogenous stem and precursor cells; (4) the effect of TH on gene transcription; and (5) a working hypothesis which is developed that TH can alleviate MS by promoting remyelination, and the mechanism of which is its regulative role in gene transcription of OPCs.

Iodised salt contribution to iodine nutrition status of pregnant and lactating women

Sufficient iodine intake by pregnant and lactating women is crucial to their offspring's cognitive development. The aim of the present study was to explore the impact of iodised salt intake on the iodine status of pregnant and lactating women. Thirty towns were selected from 211 towns in the rural areas of Shijiazhuang city using probability proportionate to size sampling in this cross-sectional survey. In each selected town, forty pregnant women and forty lactating women were randomly selected to contribute urine samples to determine iodine content. The median urinary iodine content (UIC) of 1200 pregnant women in all was 146 (interquartile range (IQR) 88–239) μg/l. The median UIC in the first, second and third trimesters were 166 (IQR 92–276) μg/l, 145 (IQR 83–248) μg/l and 134 (IQR 79–221) μg/l, respectively. The median UIC in the first trimester was significantly higher than that in the third trimester (P= 0·04). The median UIC of 1200 lactating women in all was 120 (IQR 66–195) μg/l. Their median UIC in every 4-week block was higher than the WHO criteria except in weeks 25–28 and weeks 33–36 of lactation. Pregnant women's median UIC did not correlate with median salt iodine (MSI) (P= 0·402); however, there was a linear correlation between MSI and the lactating women's median UIC (P= 0·007). Iodised salt failed to provide adequate iodine to pregnant women possibly due to limited intake of iodised salt during pregnancy, though it was found to provide adequate iodine to lactating women in the rural areas of Shijiazhuang city.

Glial development: the crossroads of regeneration and repair in the CNS

Given the complexities of the mammalian CNS, its regeneration is viewed as the holy grail of regenerative medicine. Extraordinary efforts have been made to understand developmental neurogenesis, with the hopes of clinically applying this knowledge. CNS regeneration also involves glia, which comprises at least 50% of the cellular constituency of the brain and is involved in all forms of injury and disease response, recovery, and regeneration. Recent developmental studies have given us unprecedented insight into the processes that regulate the generation of CNS glia. Because restorative processes often parallel those found in development, we will peer through the lens of developmental gliogenesis to gain a clearer understanding of the processes that underlie glial regeneration under pathological conditions. Specifically, this review will focus on key signaling pathways that regulate astrocyte and oligodendrocyte development and describe how these mechanisms are reutilized in these populations during regeneration and repair after CNS injury.

Genetic disorders of thyroid metabolism and brain development

Normal thyroid metabolism is essential for human development, including the formation and functioning of the central and peripheral nervous system. Disorders of thyroid metabolism are increasingly recognized within the spectrum of paediatric neurological disorders. Both hypothyroid and hyperthyroid disease states (resulting from genetic and acquired aetiologies) can lead to characteristic neurological syndromes, with cognitive delay, extrapyramidal movement disorders, neuropsychiatric symptoms, and neuromuscular manifestations. In this review, the neurological manifestations of genetic disorders of thyroid metabolism are outlined, with particular focus on Allan-Herndon-Dudley syndrome and benign hereditary chorea. We report in detail the clinical features, major neurological and neuropsychiatric manifestations, molecular genetic findings, disease mechanisms, and therapeutic strategies for these emerging genetic 'brain-thyroid' disorders.

Selective stimulatory action of olfactory ensheathing glia-conditioned medium on oligodendroglial differentiation, with additional reference to signaling mechanisms

We examined the effects of conditioned medium from olfactory ensheathing glia (OEGCM) on the differentiation of oligodendrocytes in mixed cultures of early postnatal hippocampi. Differentiation was judged from the numerical density (ND) of cells immunoreactive to 2'3' cyclic nucleotide 3'phosphodiesterase (CNPase) and O4 antibodies. NDs increased according to inverted-U dose-response curves, particularly for CNPase+ cells (9-fold at optimal dilution) and these changes were blocked by inhibitors of ERK1, p38-MAPK, and PI3K. Our results raise the possibility that OEG secreted factor(s) may counteract demyelination induced by trauma, neurodegenerative diseases, and advanced age, and should stimulate novel methods to deliver these factors and/or potentiating chemicals.

Treatment with thyroxine restores myelination and clinical recovery after intraventricular hemorrhage

Intraventricular hemorrhage (IVH) remains a major cause of white matter injury in preterm infants with no viable therapeutic strategy to restore myelination. Maturation of oligodendrocytes and myelination is influenced by thyroid hormone (TH) signaling, which is mediated by TH receptor α (TRα) and TRβ. In the brain, cellular levels of TH are regulated by deiodinases, with deiodinase-2 mediating TH activation and deiodinase-3 TH inactivation. Therefore, we hypothesized that IVH would decrease TH signaling via changes in the expression of deiodinases and/or TRs, and normalization of TH signaling would enhance maturation of oligodendrocytes and myelination in preterm infants with IVH. These hypotheses were tested using both autopsy materials from human preterm infants and a rabbit model of IVH. We found that deiodinase-2 levels were reduced, whereas deiodinase-3 levels were increased in brain samples of both humans and rabbits with IVH compared with controls without IVH. TRα expression was also increased in human infants with IVH. Importantly, treatment with TH accelerated the proliferation and maturation of oligodendrocytes, increased transcription of Olig2 and Sox10 genes, augmented myelination, and restored neurological function in pups with IVH. Consistent with these findings, the density of myelinating oligodendrocytes was almost doubled in TH-treated human preterm infants compared with controls. Thus, in infants with IVH the combined elevation in deiodinase-3 and reduction in deiodinase-2 decreases TH signaling that can be worsened by an increase in unliganded TRα. Given that TH promotes neurological recovery in IVH, TH treatment might improve the neurodevelopmental outcome of preterm infants with IVH.

Iodine nutrition during pregnancy in Toronto, Canada

OBJECTIVE

To evaluate the status of iodine nutrition among pregnant women presenting for routine antenatal care in Toronto, Canada, as determined by the median urine iodine concentration (UIC) of this population.

METHODS

A cross-sectional, observational study was conducted involving 142 pregnant women recruited from four low-risk antenatal outpatient clinics in Toronto, Canada. Subjects completed a questionnaire and provided a spot urine sample for the measurement of iodine concentration.

RESULTS

Mean maternal age was 33.8 ± 4.3 years. Mean gestational age was 29.3 ± 7.8 weeks. The median UIC was 221 μg/L (interquartile range, 142 to 397 μg/L). Six women (4.2%) had urine iodine levels <50 μg/L, and 36 women (25.4%) had levels between 50 and 150 μg/L.

CONCLUSION

This cohort of primarily Caucasian, well-educated, and relatively affluent pregnant women in Toronto, Canada, are iodine sufficient, perhaps due to universal salt iodization and/or other dietary and lifestyle factors.

PPARγ agonists promote oligodendrocyte differentiation of neural stem cells by modulating stemness and differentiation genes

Neural stem cells (NSCs) are a small population of resident cells that can grow, migrate and differentiate into neuro-glial cells in the central nervous system (CNS). Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor transcription factor that regulates cell growth and differentiation. In this study we analyzed the influence of PPARγ agonists on neural stem cell growth and differentiation in culture. We found that in vitro culture of mouse NSCs in neurobasal medium with B27 in the presence of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) induced their growth and expansion as neurospheres. Addition of all-trans retinoic acid (ATRA) and PPARγ agonist ciglitazone or 15-Deoxy-Δ^12,14-Prostaglandin J₂ (15d-PGJ2) resulted in a dose-dependent inhibition of cell viability and proliferation of NSCs in culture. Interestingly, NSCs cultured with PPARγ agonists, but not ATRA, showed significant increase in oligodendrocyte precursor-specific O4 and NG2 reactivity with a reduction in NSC marker nestin, in 3–7 days. In vitro treatment with PPARγ agonists and ATRA also induced modest increase in the expression of neuronal β-III tubulin and astrocyte-specific GFAP in NSCs in 3–7 days. Further analyses showed that PPARγ agonists and ATRA induced significant alterations in the expression of many stemness and differentiation genes associated with neuro-glial differentiation in NSCs. These findings highlight the influence of PPARγ agonists in promoting neuro-glial differentiation of NSCs and its significance in the treatment of neurodegenerative diseases.

Breastmilk iodine concentrations following acute dietary iodine intake

BACKGROUND

Breastmilk iodine levels may vary temporally in response to recent changes in dietary iodine intake. We assessed the effect of and time to peak breastmilk iodine levels after potassium iodine ingestion, which has never been studied and is important toward interpretation of studies of breastmilk iodine measurements.

METHODS

Sixteen healthy lactating Boston-area women with no known thyroid disease were each given 600 μg oral potassium iodide (KI) (456 μg iodine) after an overnight fast. Iodine was measured in breastmilk and urine at baseline and hourly for 8 hours following iodine intake. All dietary iodine ingested during the study period was also measured.

RESULTS

Mean age of mothers was 30.2±4.1 (SD) years. Median (interquartile range [IQR]) baseline breastmilk and urine iodine levels were 45.5 μg/L (IQR 34.5-169.0) and 67.5 μg/L (IQR 57.5-140.0), respectively. Following 600 μg KI administration, median increase in breastmilk iodine levels above baseline was 280.5 μg/L (IQR 71.5-338.0), and median peak breastmilk iodine concentration was 354 μg/L (IQR 315-495). Median time to peak breastmilk iodine levels following KI administration was 6 hours (IQR 5-7). Dietary iodine sources provided an additional 36-685 μg iodine intake during the 8-hour study.

CONCLUSIONS

Following ingestion of 600 μg KI, there is a measurable rise in breastmilk iodine concentrations, with peak levels occurring at 6 hours. These findings strongly suggest that breastmilk iodine concentrations should be interpreted in relation to recent iodine intake.

Thyroid disorders in pregnancy

The thyroid gland is substantially challenged during pregnancy. Total T(3) and T(4) levels increase by 50% during pregnancy owing to a 50% increase in thyroxine-binding globulin levels. Serum TSH levels decrease in the first trimester and increase in the second and third trimesters; however, not to prepregnancy levels. Hypothyroidism is present in up to 3% of all pregnant women. Subclinical hypothyroidism during pregnancy is associated with an increased rate of miscarriage and preterm delivery, and a decrease in the IQ of the child. Overt hyperthyroidism is present in less than 1% of pregnant women but is linked to increased rates of miscarriage, preterm delivery and maternal congestive heart failure. In women who are euthyroid, thyroid autoantibodies are associated with an increased risk of spontaneous miscarriage and preterm delivery. Postpartum thyroiditis occurs in 5.4% of all women following pregnancy; moreover, 50% of women who are euthyroid in the first trimester of pregnancy but test positive for thyroid autoantibodies will develop postpartum thyroiditis. The need for the essential nutrient iodine increases during pregnancy and in women who are breastfeeding, and the effect of treatment of mild iodine deficiency on maternal and fetal outcomes is consequently being evaluated in a prospective study. The debate regarding the pros and cons of universal screening for thyroid disease during pregnancy is ongoing.

Environmental perchlorate and thiocyanate exposures and infant serum thyroid function

BACKGROUND

Breastfed infants rely on maternal iodine for thyroid hormone production required for neurodevelopment. Dietary iodine among women of childbearing age in the United States may be insufficient. Perchlorate (competitive inhibitor of the sodium/iodide symporter [NIS]) exposure is ubiquitous. Thiocyanate, from cigarettes and diet, is a weaker NIS inhibitor. Environmental perchlorate and thiocyanate exposures could decrease breast milk iodine by competitively inhibiting NIS in lactating breasts (thus impairing infants' iodine availability), and/or infants' thyroidal NIS to directly decrease infant thyroid function. The current study assessed the relationships between environmental perchlorate and thiocyanate exposures and infant serum thyroid function.

METHODS

Iodine, perchlorate, and thiocyanate in breast milk, maternal and infant urine, and infant serum thyroid function tests were cross-sectionally measured in Boston-area women and their 1-3 month-old breastfed infants. Univariate and multivariable analyses assessed relationships between iodine, perchlorate, thiocyanate, thyroid-stimulating hormone (TSH), and free thyroxine (FT4) levels.

RESULTS

In 64 mothers and infants, median (range) iodine levels were 45.6 μg/L (4.3-1080) in breast milk, 101.9 μg/L (27-570) in maternal urine, and 197.5 μg/L (40-785) in infant urine. Median perchlorate concentrations were 4.4 μg/L (0.5-29.5) in breast milk, 3.1 μg/L (0.2-22.4) in maternal urine, and 4.7 μg/L (0.3-25.3) in infant urine. There were no correlations between infant TSH or FT4 and iodine, perchlorate, and thiocyanate levels in breast milk, maternal urine, and infant urine. In multivariable analyses, perchlorate and thiocyanate levels in breast milk, maternal urine, and infant urine were not significant predictors of infant TSH or FT4.

CONCLUSIONS

Boston-area mothers and their breastfed infants are generally iodine sufficient. Although environmental perchlorate and thiocyanate are ubiquitous, these results do not support the concern that maternal and infant environmental perchlorate and thiocyanate exposures affect infant thyroid function.

Effects of iodine deficiency in pregnancy

Dietary iodine requirements are increased in pregnancy due to increased thyroid hormone production, increased renal iodine losses, and fetal iodine requirements. Adverse effects of iodine deficiency in pregnancy include maternal and fetal goiter, cretinism, intellectual impairments, neonatal hypothyroidism, and increased pregnancy loss and infant. Dietary iodine requirements remain increased in lactation due to the concentration of iodine in breast milk. Iodine deficiency remains a significant global public health problem. Excess iodine ingestion in pregnancy, while a relatively uncommon problem, may also have adverse fetal effects. However, the safe upper limit for chronic iodine ingestion in pregnancy and lactation is not currently well defined.

In vitro differentiation of bone marrow stromal cells into oligodendrocyte-like cells using triiodothyronine as inducer

An in vitro technique was devised to induced autologous adult stem cells into oligodendrocyte-like cells. In this study, a protocol was developed for the induction of bone marrow stromal cells (BMSCs) into oligodendrocyte-like cells. BMSCs were incubated in one of these three pre-inducers: dimethyl sulfoxide (DMSO), β-mercaptoethanol (βME) or biotylated hydroxyanisol (BHA), each followed by retinoic acid (RA) treatment. The percentage of viable cells in BHA-RA preinduced cells was significantly lower than the others. The results showed that the preinduced cells were immunoreactive for nestin and NF-68; among the mentioned protocols, the immunoreactivity yielded by following the DMSO-RA protocol was significantly higher than the others. Moreover, no significant immunoreactivity was observed for preinduced cells to O4, O1, MBP (myelin basic protein), S100, and GFAP (glial fibrillary acidic protein). The cells were immunoreactive to oligo-2. Two phases of induction were done: the first was a combination of basic fibroblast growth factor (bFGF), platelet-derived growth factor (PDGF) and heregulin (HRG), followed by either triiodothyronine (T3) or Forskolin (FSK) as the second phase. The conclusion is that the trans-differentiation of BMSCs by DMSO followed by RA (preinduction stage) then bFGF-PDGF-HRG followed by T3 (10 ng/ml) (induction stage) can be a potential source for oligodendrocyte-like cells preparation.

Iodine nutrition in pregnancy and lactation

Adequate iodine intake is required for the synthesis of thyroid hormones that are important for normal fetal and infant neurodevelopment. In this review, we discuss iodine physiology during pregnancy and lactation, methods to assess iodine sufficiency, the importance of adequate iodine nutrition, studies of iodine supplementation during pregnancy and lactation, the consequences of hypothyroidism during pregnancy, the current status of iodine nutrition in the United States, the global efforts toward achieving universal iodine sufficiency, and substances that may interfere with iodine use.

Iodine and pregnancy

Iodine is a necessary element for the production of thyroid hormone. We will review the impact of dietary iodine status on thyroid function in pregnancy. We will discuss iodine metabolism, homeostasis, and nutritional recommendations for pregnancy. We will also discuss the possible effects of environmental contaminants on iodine utilization in pregnant women.

Severe impairment of cerebellum development in mice expressing a dominant-negative mutation inactivating thyroid hormone receptor alpha1 isoform

Thyroid hormone deficiency is known to deeply affect cerebellum post-natal development. We present here a detailed analysis of the phenotype of a recently generated mouse model, expressing a dominant-negative TRα1 mutation. Although hormonal level is not affected, the cerebellum of these mice displays profound alterations in neuronal and glial differentiation, which are reminiscent of congenital hypothyroidism, indicating a predominant function of this receptor isoform in normal cerebellum development. Some of the observed effects might result from the cell autonomous action of the mutation, while others are more likely to result from a reduction in neurotrophic factor production.

Deciphering the oligodendrogenic program of neural progenitors: cell intrinsic and extrinsic regulators

In the developing and adult CNS, neural stem/progenitor cells (NSPCs) and oligodendroglial progenitor cells (OPCs) follow an oligodendrogenic process with the aim of myelinating axons. This process is to a high degree regulated by an oligodendrogenic program (OPr) composed of intrinsic and extrinsic factors that modulate the different steps required for NSPCs to differentiate into myelinating oligodendrocytes. Even though NSPCs and OPCs are present in the diseased CNS and have the capacity to generate oligodendrocytes, sparse remyelination of axons constitutes a major constraint in therapies toward multiple sclerosis (MS) and spinal cord injury (SCI). Lack of pro-oligodendrogenic factors and presence of anti-oligodendrogenic activities are thought to be the main reasons for this limitation. Thus, molecular and cellular strategies aiming at remyelination and at targeting such pro- and anti-oligodendrogenic mechanisms are currently under investigation. The present review summarizes the current knowledge on the OPr; it implements our own findings on mesenchymal stem cell-derived pro-oligodendroglial factors and on the role of p57/kip2 in oligodendroglial differentiation. Moreover, it describes molecular and cellular approaches for the development of future therapies toward remyelination.

White matter abnormalities and dystonic motor disorder associated with mutations in the SLC16A2 gene

AIM

Mutations in the SLC16A2 gene have been implicated in Allan-Herndon-Dudley syndrome (AHDS), an X-linked learning disability* syndrome associated with thyroid function test (TFT) abnormalities. Delayed myelination is a non-specific finding in individuals with learning disability whose genetic basis is often uncertain. The aim of this study was to describe neuroimaging findings and neurological features in males with SLC16A2 gene mutations.

METHOD

We reviewed brain magnetic resonance imaging (MRI) findings and neurological features in a cohort of five males aged between 1 year 6 months and 6 years (median 4y) from four families harbouring SLC16A2 gene mutations.

RESULTS

The participants presented aged between 4 and 9 months with initial hypotonia and subsequent spastic paraparesis with dystonic posturing and superimposed paroxysmal dyskinesias. Dystonic cerebral palsy was the most common initial clinical diagnosis, and AHDS was suspected only retrospectively, considering the characteristically abnormal thyroid function tests, with high serum tri-iodothyronine (T(3)), as the most consistent finding. Brain MRI showed absent or markedly delayed myelination in all five participants, prompting the suspicion of Pelizaeus-Merzbacher disease in one patient.

INTERPRETATION

Our findings indicate a consistent association between defective neuronal T(3) uptake and delayed myelination. SLC16A2 involvement should be considered in males with learning disability, an associated motor or movement disorder, and evidence of delayed myelination on brain MRI. Although dysmorphic features suggestive of AHDS are not always present, T(3) measurement is a reliable screening test.

A role for the MAPK/ERK pathway in oligodendroglial differentiation in vitro: stage specific effects on cell branching

The mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway is important for both long-term survival and timing of the progression of oligodendrocyte differentiation. Oligodendroglial cells treated with MEK inhibitor were distinguished by using stage specific markers: NG2 proteoglycan, A2B5, 2'3'nucleotide-cyclic 3'phosphodiesterase (CNPase) and myelin basic protein (MBP), and classified according to their morphology into different developmental stages. Treatment significantly increased the number of cells with more immature morphologies and decreased the number of mature cells. Furthermore, it increased the number of rounded cells that could not be classified into any of the oligodendroglial developmental stages. The strongest effects were usually observed shortly after treatment. Rounded cells were CNPase/MBP positive and they were not stained by anti-NG2 or A2B5, indicating that they were mature cells unable either to extend and/or to maintain their processes. These data showed an effect of the MAPK/ERK pathway on oligodendroglial branching, with possible consequences for the formation of the myelin sheath.

Thyroid hormone induces glial lineage of primary neurospheres derived from non-pathological and pathological rat brain: implications for remyelination-enhancing therapies

Thyroid hormone exerts a critical role in developmental myelination, acting on the production and maturation of oligodendrocyte, and on the expression of genes encoding for myelin protein. Since remyelination is considered a recapitulation of cellular and molecular events occurring during development, we tested the possibility of stimulating the oligodendroglial lineage and maturation in neurospheres derived from the subventricular zone of adult rats using 3,5,3'-L-triiodothyronine (T3). Both non-pathological and pathological brains derived from rats affected by the inflammatory-demyelinating disease experimental allergic encephalomyelitis (EAE) were included in the study. We investigated the effect of in vitro T3 exposure on: (i) the expression of nuclear thyroid hormone receptors; (ii) proliferation rate; (iii) differentiation into neurons, astrocytes and oligodendrocytes, focusing our attention on oligodendrocyte maturation. T3 reduced the proliferation rate of neurospheres when cultured in the presence of mitogens, shifting towards oligodendroglial lineage as indicated by increased expression of olig-1, and also favoring oligodendrocyte maturation, as indicated by the expression of antigens associated with different maturation stages. Neurospheres derived from EAE rats show a strong limitation in oligodendrocyte generation, which is completely restored by T3 treatment. These results indicate that T3 is a key factor in regulating neurosphere biology, when derived either from non-pathological or pathological adult brains, suggesting that T3 might be an important factor in favoring remyelination in demyelinating disorders.

Paving the axonal highway: from stem cells to myelin repair

Multiple sclerosis (MS), a demyelinating disorder of the central nervous system (CNS), remains among the most prominent and devastating diseases in contemporary neurology. Despite remarkable advances in anti-inflammatory therapies, the inefficiency or failure of myelin-forming oligodendrocytes to remyelinate axons and preserve axonal integrity remains a major impediment for the repair of MS lesions. To this end, the enhancement of remyelination through endogenous and exogenous repair mechanisms and the prevention of axonal degeneration are critical objectives for myelin repair therapies. Thus, recent advances in uncovering myelinating cell sources and the intrinsic and extrinsic factors that govern neural progenitor differentiation and myelination may pave a way to novel strategies for myelin regeneration. The scope of this review is to discuss the potential sources of stem/progenitor cells for CNS remyelination and the molecular mechanisms underlying oligodendrocyte myelination.

Cerebellar granule cells cultured from adolescent rats express functional NMDA receptors: an in vitro model for studying the developing cerebellum

In the developing rat cerebellum functional NMDA receptors (NMDARs) expressing the NR2C subunit have been identified on or after postnatal day 19. We obtained primary cultured cells from 19- to 35-day-old rat cerebellum that expressed few oligodendrocytes or astrocytes. Cultured cells were immunoreactive for neuron-specific proteins thus indicating a neuronal population. The primary neuron present was the granule cell as indicated by immunofluorescence for the GABA(A) alpha 6 subunit. Whole-cell patch-clamp experiments indicated that functional NMDARs were present. Functional characteristics of NMDARs expressed in cerebellar granule cells (CGCs) obtained from adolescent animals were similar to those previously reported for NMDARs expressed in CGCs obtained from neonatal rats. Cultured CGCs obtained from older animals contained NMDARs that were inhibited by EtOH and were less sensitive to the NR2B subunit-specific antagonist Ro 25-6981. Furthermore, NMDA-induced currents were smaller than those observed in CGCs. Western blot analysis indicated the presence of the NMDA NR2A and NR2C subunits, but not the NR2B in cultures obtained from the adolescent rats. CGCs obtained from adolescent rats express functional NMDARs consistent with a developmental profile observed in vivo.

Thyroid hormones promote differentiation of oligodendrocyte progenitor cells and improve remyelination after cuprizone-induced demyelination

In the present work we analyzed the capacity of thyroid hormones (THs) to improve remyelination using a rat model of cuprizone-induced demyelination previously described in our laboratories. Twenty one days old Wistar rats were fed a diet containing 0.6% cuprizone for two weeks to induce demyelination. After cuprizone withdrawal, rats were injected with triiodothyronine (T3). Histological studies carried out in these animals revealed that remyelination in the corpus callosum (CC) of T3-treated rats improved markedly when compared to saline treated animals. The cellular events occurring in the CC and in the subventricular zone (SVZ) during the first week of remyelination were analyzed using specific oligodendroglial cell (OLGc) markers. In the CC of saline treated demyelinated animals, mature OLGcs decreased and oligodendroglial precursor cells (OPCs) increased after one week of spontaneous remyelination. Furthermore, the SVZ of these animals showed an increase in early progenitor cell numbers, dispersion of OPCs and inhibition of Olig and Shh expression compared to non-demyelinated animals. The changes triggered by demyelination were reverted after T3 administration, suggesting that THs could be regulating the emergence of remyelinating oligodendrocytes from the pool of proliferating cells residing in the SVZ. Our results also suggest that THs receptor beta mediates T3 effects on remyelination. These results support a potential role for THs in the remyelination process that could be used to develop new therapeutic approaches for demyelinating diseases.

Hormonal influences in multiple sclerosis

The function of hormones has expanded to include immunomodulation and neuroprotection in addition to their classic roles. The story of how hormones influence inflammation and neuron and glial function is being slowly unraveled. There is increasing evidence that estrogen, progesterone, and testosterone contain immune responses and influence damage repair in the nervous system. Hormones such as prolactin and vitamin D are being explored as immunomodulators and may influence diseases such as multiple sclerosis (MS) or may be used therapeutically to modulate the immune response. More recently identified hormones, such as leptin and gherlin, may also influence the course of disease. This chapter reviews some of the evidence that supports a role for hormones in MS.

Ultrastructural identification of oligodendrocyte/myelin proteins in corpus callosum of hypothyroid animals

Thyroid hormone (T3) deficiency impairs the development of the CNS, particularly myelination. We have previously described an increase in the frequency of morphological abnormalities in the central myelin sheath in a hypothyroidism model, which reinforced the hypothesis of a role for T3 in myelin compaction. However, there are no data concerning the cellular distribution of myelin proteins in hypothyroid animals. In the present work, we describe the distribution of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), myelin basic protein (MBP) and proteolipid protein (PLP) throughout the central myelin sheath of a hypothyroidism model. We used euthyroid and hypothyroid adult rats at 90 days of age. In order to induce hypothyroid status, animals received 0.02% methimazol from the 19th gestation day onwards. After perfusion with a fixative mixture, small pieces of corpus callosum were obtained, dehydrated and embedded in LR White resin. Ultrathin sections were immunoreacted, using specific antibodies revealed by a secondary antibody coupled to colloidal gold particles of 10nm. Gold particle density per region of myelin sheath for each one of these proteins was obtained. In normal animals, CNPase, PLP and MBP were identified in sites that had already been described in previous studies. In hypothyroid animals, CNPase was identified in the region corresponding to compact lamellae, which normally does not contain this protein, while, in this same region, PLP and MBP immunolabeling were decreased. These results suggest that thyroid hormone deficiency impairs the distribution of the major oligodendrocyte/myelin markers. This effect may justify the reduction in myelin sheath compaction previously demonstrated in a similar model of hypothyroidism.