Gestational Hypothyroxinemia Imprints a Switch in the Capacity of Astrocytes and Microglial Cells of the Offspring to React in Inflammation

Gestational hypothyroxinemia induces ASD-like phenotypes in behavior, proinflammatory markers, and glutamatergic protein expression in mouse offspring of both sexes

Background

The prevalence of autism spectrum disorder (ASD) has significantly risen in the past three decades, prompting researchers to explore the potential contributions of environmental factors during pregnancy to ASD development. One such factor of interest is gestational hypothyroxinemia (HTX), a frequent condition in pregnancy associated with cognitive impairments in the offspring. While retrospective human studies have linked gestational HTX to autistic traits, the cellular and molecular mechanisms underlying the development of ASD-like phenotypes remain poorly understood. This study used a mouse model of gestational HTX to evaluate ASD-like phenotypes in the offspring.

Methods

To induce gestational HTX, pregnant mice were treated with 2-mercapto-1-methylimidazole (MMI), a thyroid hormones synthesis inhibitor, in the tap-drinking water from embryonic days (E) 10 to E14. A separate group received MMI along with a daily subcutaneous injection of T4, while the control group received regular tap water during the entire pregnancy. Female and male offspring underwent assessments for repetitive, anxious, and social behaviors from postnatal day (P) 55 to P64. On P65, mice were euthanized for the evaluation of ASD-related inflammatory markers in blood, spleen, and specific brain regions. Additionally, the expression of glutamatergic proteins (NLGN3 and HOMER1) was analyzed in the prefrontal cortex and hippocampus.

Results

The HTX-offspring exhibited anxious-like behavior, a subordinate state, and impaired social interactions. Subsequently, both female and male HTX-offspring displayed elevated proinflammatory cytokines in blood, including IL-1β, IL-6, IL-17A, and TNF-α, while only males showed reduced levels of IL-10. The spleen of HTX-offspring of both sexes showed increased Th17/Treg ratio and M1-like macrophages. In the prefrontal cortex and hippocampus of male HTX-offspring, elevated levels of IL-17A and reduced IL-10 were observed, accompanied by increased expression of hippocampal NLGN3 and HOMER1. All these observations were compared to those observed in the Control-offspring. Notably, the supplementation with T4 during the MMI treatment prevents the development of the observed phenotypes. Correlation analysis revealed an association between maternal T4 levels and specific ASD-like outcomes.

Discussion

This study validates human observations, demonstrating for the first time that gestational HTX induces ASD-like phenotypes in the offspring, highlighting the need of monitoring thyroid function during pregnancy.

Transient gestational hypothyroxinemia accelerates and enhances ulcerative colitis-like disorder in the male offspring

Introduction

Gestational hypothyroxinemia (HTX) is a condition that occurs frequently at the beginning of pregnancy, and it correlates with cognitive impairment, autism, and attentional deficit in the offspring. Evidence in animal models suggests that gestational HTX can increase the susceptibility of the offspring to develop strong inflammation in immune-mediated inflammatory diseases. Ulcerative colitis (UC) is a frequent inflammatory bowel disease with unknown causes. Therefore, the intensity of ulcerative colitis-like disorder (UCLD) and the cellular and molecular factors involved in proinflammatory or anti-inflammatory responses were analyzed in the offspring gestated in HTX (HTX-offspring) and compared with the offspring gestated in euthyroidism (Control-offspring).

Methods

Gestational HTX was induced by the administration of 2-mercapto-1-methylimidazole in drinking water to pregnant mice during E10-E14. The HTX-offspring were induced with UCLD by the acute administration of dextran sodium sulfate (DSS). The score of UCLD symptomatology was registered every day, and colon histopathology, immune cells, and molecular factors involved in the inflammatory or anti-inflammatory response were analyzed on day 6 of DSS treatment.

Results

The HTX-offspring displayed earlier UCLD pathological symptoms compared with the Control-offspring. After 6 days of DSS treatment, the HTX-offspring almost doubled the score of the Control-offspring. The histopathological analyses of the colon samples showed signs of inflammation at the distal and medial colon for both the HTX-offspring and Control-offspring. However, significantly more inflammatory features were detected in the proximal colon of the HTX-offspring induced with UCLD compared with the Control-offspring induced with UCLD. Significantly reduced mRNA contents encoding for protective molecules like glutamate-cysteine ligase catalytic subunit (GCLC) and mucin-2 (MUC-2) were found in the colon of the HTX-offspring as compared with the Control-offspring. Higher percentages of Th17 lymphocytes were detected in the colon tissues of the HTX-offspring induced or not with UCLD as compared with the Control-offspring.

Discussion

Gestational HTX accelerates the onset and increases the intensity of UCLD in the offspring. The low expression of MUC-2 and GCLC together with high levels of Th17 Lymphocytes in the colon tissue suggests that the HTX-offspring has molecular and cellular features that favor inflammation and tissue damage. These results are important evidence to be aware of the impact of gestational HTX as a risk factor for UCLD development in offspring.

Congenital Hypothyroidism in Preterm Newborns - The Challenges of Diagnostics and Treatment: A Review

Preterm newborns are forced to adapt to harsh extrauterine conditions and endure numerous adversities despite their incomplete growth and maturity. The inadequate thyroid hormones secretion as well as the impaired regulation of hypothalamus-pituitary-thyroid axis may lead to hypothyroxinemia. Two first weeks after birth are pivotal for brain neurons development, synaptogenesis and gliogenesis. The decreased level of thyroxine regardless of cause may lead to delayed mental development. Congenital hypothyroidism (CH) is a disorder highly prevalent in premature neonates and it originates from maternal factors, perinatal and labor complications, genetic abnormalities, thyroid malformations as well as side effects of medications and therapeutic actions. Because of that, the prevention is not fully attainable. CH manifests clinically in a few distinctive forms: primary, permanent or transient, and secondary. Their etiologies and implications bear little resemblance. Therefore, the exact diagnosis and differentiation between the subtypes of CH are crucial in order to plan an effective treatment. Hypothyroxinemia of prematurity indicates dynamic changes in thyroid hormone levels dependent on neonatal postmenstrual age, which directly affects patient's maintenance and wellbeing. The basis of a successful treatment relies on an early and accurate diagnosis. Neonatal screening is a recommended method of detecting CH in preterm newborns. The preferred approach involves testing serum TSH and fT4 concentrations and assessing their levels according to the cut-off values. The possible benefits also include the evaluation of CH subtype. Nevertheless, the reference range of thyroid hormones varies all around the world and impedes the introduction of universal testing recommendations. Unification of the methodology in neonatal screening would be advantageous for prevention and management of CH. Current guidelines recommend levothyroxine treatment of CH in preterm infants only when the diagnose is confirmed. Moreover, they underline the importance of the re-evaluation among preterm born infants due to the frequency of transient forms of hypothyroidism. However, results from multiple clinical trials are mixed and depend on the newborn's gestational age at birth. Some benefits of treatment are seen especially in the preterm infants born <29 weeks' gestation. The discrepancies among trials and guidelines create an urgent need to conduct more large sample size studies that could provide further analyses and consensus. This review summarizes the current state of knowledge on congenital hypothyroidism in preterm infants. We discuss screening and treatment options and demonstrate present challenges and controversies.

Iodine as Essential Nutrient during the First 1000 Days of Life

Iodine is an essential micronutrient incorporated into thyroid hormones. Although iodine deficiency can lead to a broad spectrum of disorders throughout life, it is most critical in the early stages of development, as the foetal brain is extremely dependent on iodine supply. During the last two decades, our understanding of thyroid physiology during gestation has substantially improved. Furthermore, thyroid hormone receptors have been identified and characterised in placental and embryonic tissues, allowing us to elucidate the maternal-foetal transfer of thyroid hormones. Experimental studies have demonstrated that the cyto-architecture of the cerebral cortex can be irreversibly disturbed in iodine deficiency causing abnormal neuron migratory patterns which are associated with cognitive impairment in children. In this context, the role of iodine as key factor in the programming of foetal and infant neurodevelopment, needs to be revisited with a special focus on areas of mild to moderate iodine deficiency. The objective of this review is to summarize the available evidence from both animals and human studies, for the effect of iodine deficiency (particularly, of maternal hypothyroxinemia) on brain development and neurological or behavioural disorders, such as lower intelligence quotient (IQ) or attention deficit hyperactivity disorder (ADHD).