Maternal Subclinical Hypothyroidism Impairs Neurodevelopment in Rat Offspring by Inhibiting the CREB Signaling Pathway

HDAC1/2/3-mediated downregulation of neurogranin is involved in cognitive impairment in offspring exposed to maternal subclinical hypothyroidism

Subclinical hypothyroidism (SCH) in pregnancy is the most common form of thyroid dysfunction in pregnancy, which can affect fetal nervous system development and increase the risk of neurodevelopmental disorders after birth. However, the mechanism of the effect of maternal subclinical hypothyroidism on fetal brain development and behavioral phenotypes is still unclear and requires further study. In this study, we constructed a mouse model of maternal subclinical hypothyroidism by exposing dams to drinking water containing 50 ppm propylthiouracil (PTU) during pregnancy and found that its offspring were accompanied by severe cognitive deficits by behavioral testing. Mechanistically, gestational SCH resulted in the upregulation of protein expression and activity of HDAC1/2/3 in the hippocampus of the offspring. ChIP analysis revealed that H3K9ac on the neurogranin (Ng) promoter was reduced in the hippocampus of the offspring of SCH, with a significant reduction in Ng protein, leading to reduced expression levels of synaptic plasticity markers PSD95 (a membrane-associated protein in the postsynaptic density) and SYN (synaptophysin, a specific marker for presynaptic terminals), and impaired synaptic plasticity. In addition, administration of MS-275 (an HDAC1/2/3-specific inhibitor) to SCH offspring alleviated impaired synaptic plasticity and cognitive dysfunction in offspring. Thus, our study suggests that maternal subclinical hypothyroidism may mediate offspring cognitive dysfunction through the HDAC1/2/3-H3K9ac-Ng pathway. Our study contributes to the understanding of the signaling mechanisms underlying maternal subclinical hypothyroidism-mediated cognitive impairment in the offspring.

Impact of Maternal Environment and Inflammation on Fetal Neurodevelopment

During intrauterine life, external stimuli including maternal nutrition, lifestyle, socioeconomic conditions, anxiety, stress, and air pollution can significantly impact fetal development. The human brain structures begin to form in the early weeks of gestation and continue to grow and mature throughout pregnancy. This review aims to assess, based on the latest research, the impact of environmental factors on fetal and neonatal brain development, showing that oxidative stress and inflammation are implied as a common factor for most of the stressors. Environmental insults can induce a maternal inflammatory state and modify nutrient supply to the fetus, possibly through epigenetic mechanisms, leading to significant consequences for brain morphogenesis and neurological outcomes. These risk factors are often synergic and mutually reinforcing. Fetal growth restriction and preterm birth represent paradigms of intrauterine reduced nutrient supply and inflammation, respectively. These mechanisms can lead to an increase in free radicals and, consequently, oxidative stress, with well-known adverse effects on the offspring's neurodevelopment. Therefore, a healthy intrauterine environment is a critical factor in supporting normal fetal brain development. Hence, healthcare professionals and clinicians should implement effective interventions to prevent and reduce modifiable risk factors associated with an increased inflammatory state and decreased nutrient supply during pregnancy.

Emerging research themes in maternal hypothyroidism: a bibliometric exploration

Background

Hypothyroidism, a prevalent endocrine disorder, carries significant implications for maternal and infant health, especially in the context of maternal hypothyroidism. Despite a gradual surge in recent research, achieving a comprehensive understanding of the current state, focal points, and developmental trends in this field remains challenging. Clarifying these aspects and advancing research could notably enhance maternal-infant health outcomes. Therefore, this study employs bibliometric methods to systematically scrutinize maternal hypothyroidism research, serving as a reference for further investigations.

Objective

Through bibliometric analysis, this study seeks to unveil key research focus areas, developmental trends, and primary contributors in Maternal Hypothyroidism. The findings offer insights and recommendations to inform future research endeavors in this domain.

Methods

Literature metrics analysis was performed on data retrieved and extracted from the Web of Science Core Collection database. The analysis examined the evolution and thematic trends of literature related to Maternal Hypothyroidism. Data were collected on October 28, 2023, and bibliometric analysis was performed using VOSviewer, CiteSpace, and the Bibliometrix software package, considering specific characteristics such as publication year, country/region, institution, authorship, journals, references, and keywords.

Results

Retrieved from 1,078 journals, 4,184 articles were authored by 18,037 contributors in 4,580 institutions across 113 countries/regions on six continents. Maternal Hypothyroidism research publications surged from 44 to 310 annually, a 604.54% growth from 1991 to 2022. The USA (940 articles, 45,233 citations), China Medical University (82 articles, 2,176 citations), and Teng, Weiping (52 articles, 1,347 citations) emerged as the most productive country, institution, and author, respectively. "Thyroid" topped with 233 publications, followed by "Journal of Clinical Endocrinology & Metabolism" (202) with the most citations (18,513). "Pregnancy" was the most cited keyword, with recent high-frequency keywords such as "outcome," "gestational diabetes," "iodine intake," "preterm birth," "guideline," and "diagnosis" signaling emerging themes in Maternal Hypothyroidism.

Conclusions

This study unveils developmental trends, global collaboration patterns, foundational knowledge, and emerging frontiers in Maternal Hypothyroidism. Over 30 years, research has predominantly focused on aspects like diagnosis, treatment guidelines, thyroid function during pregnancy, and postpartum outcomes, with a central emphasis on the correlation between maternal and fetal health.

Multisensory Stimulation Improves Cognition and Behavior in Adult Male Rats Born to LT4-treated Thyroidectomized Dams

Gestational hypothyroidism can impair development, cognition, and mood. Here, we tested whether multisensory stimulation (MS) improves the phenotype of rats born to surgically thyroidectomized (Tx) dams suboptimally treated with LT4. 8-week-old female Tx Wistar rats were kept on daily LT4 (0.7 µg/100 g body weight) dosed by gavage (serum TSH and T4 levels indicated moderate hypothyroidism) and 3 weeks later placed for breeding. MS of the litter started at age 60 days and lasted for 8 weeks. It consisted of twice per week of physical, cognitive, sensorial, and food stimuli. The offspring were assessed before and after MS for standardized tests of locomotor activity, cognition, and mood. Gestational hypothyroidism resulted in reduced litter size and increased offspring mortality. The pups exhibited delayed physical development, impairment of short- and long-term memory, and anxiety- and depressive-like behaviors. Nonetheless, ambulatory activity, social memory, and social preference were not affected by gestational hypothyroidism. MS restored short-term memory and anxiety while improving depressive like-behaviors. MS did not improve long-term memory. MS also did not modify the performance of control litter born to intact dams. We conclude that cognition and mood impairments caused by moderate gestational hypothyroidism were reversed or minimized in rats through MS. Further studies should define the molecular mechanisms involved.

Developmental Hypothyroidism Influences the Development of the Entorhinal-Dentate Gyrus Pathway of Rat Offspring

BACKGROUND

Developmental hypothyroidism impairs learning and memory in offspring, which depend on extensive neuronal circuits in the entorhinal cortex, together with the hippocampus and neocortex. The entorhinal-dentate gyrus pathway is the main entrance of memory circuits. We investigated whether developmental hypothyroidism impaired the morphological development of the entorhinal-dentate gyrus pathway.

METHODS

We examined the structure and function of the entorhinal-dentate gyrus pathway in response to developmental hypothyroidism induced using 2-mercapto-1-methylimidazole.

RESULTS

1,1´-Dioctadecyl-3,3,3´,3´-tetramethylindocarbocyanine perchlorate tract tracing indicated that entorhinal axons showed delayed growth in reaching the outer molecular layer of the dentate gyrus at postnatal days 2 and 4 in hypothyroid conditions. The proportion of fibers in the outer molecular layer was significantly smaller in the hypothyroid group than in the euthyroid group at postnatal day 4. At postnatal day 10, the pathway showed a layer-specific distribution in the outer molecular layer, similar to the euthyroid group. However, the projected area of entorhinal axons was smaller in the hypothyroid group than in the euthyroid group. An electrophysiological examination showed that hypothyroidism impaired the long-term potentiation of the perforant and the cornu ammonis 3-cornu ammonis 1 pathways. Many repulsive axon guidance molecules were involved in the formation of the entorhinaldentate gyrus pathway. The hypothyroid group had higher levels of erythropoietin-producing hepatocyte ligand A3 and semaphorin 3A than the euthyroid group.

CONCLUSION

We demonstrated that developmental hypothyroidism might influence the development of the entorhinal-dentate gyrus pathway, contributing to impaired long-term potentiation. These findings improve our understanding of neural mechanisms for memory function.

Maternal Subclinical Hypothyroidism in Rats Impairs Spatial Learning and Memory in Offspring by Disrupting Balance of the TrkA/p75NTR Signal Pathway

Maternal subclinical hypothyroidism (SCH) during pregnancy can adversely affect the neurodevelopment of the offspring. The balance of nerve growth factor (NGF)-related tropomyosin receptor kinase A/p75 neurotrophin receptor (TrkA/p75^NTR) signaling in the hippocampus is important in brain development, and whether it affects cognitive function in maternal SCH’s offspring is not clear. In this study, we found that compared with the control (CON) group, expression of proliferation-related proteins [NGF, p-TrkA, phospho-extracellular signal-regulated kinase 1/2 (p-ERK1/2) and phospho-cAMP response element-binding protein (p-CREB)] decreased in the hippocampus of the offspring in the SCH group, overt hypothyroidism (OHT) group, and the group with levothyroxine (L-T₄) treatment for SCH from gestational day 17 (E17). In contrast, expression of apoptosis-related proteins [pro-NGF, p75^NTR, phospho-C-Jun N-terminal kinase (p-JNK), p53, Bax and cleaved caspase-3] was increased. The two groups with treatment with L-T₄ for SCH from E10 and E13, respectively, showed no significant difference compared with the CON group. L-T₄ treatment enhanced relative expression of NGF by increasing NGF/proNGF ratio in offspring from maternal SCH rats. In conclusion, L-T₄ treatment for SCH from early pregnancy dramatically ameliorated cognitive impairment via TrkA/p75^NTR signaling, which involved activation of the neuronal proliferation and inhibition of neuronal apoptosis in SCH rats’ offspring.

Thyroid Diseases During Pregnancy: Bibliometric Analysis of Scientific Publications

BACKGROUND

Bibliometric analysis can analyze development trends and predict research hotspots. We used these analyses to better understand pregnancy-related implications of thyroid diseases.

METHODS

Publications on thyroid diseases during pregnancy from 1926 to hitherto were retrieved based on the Web of Science database. The publications and references, the institutions and countries, the journals, the keywords and citations, were analyzed by utilizing VOSviewer, CiteSpace and CitNetExplorer.

RESULTS

A total of 3310 publications were retrieved and were cited 87913 times. The United States took the dominant position in outputs and collaborations. Harvard University had the most articles 86, which also had the highest h-index 30. Thyroid ranked first with 201 publications and Journal of Clinical Endocrinology Metabolism had the highest h-index 67. Among the 49 burst keywords, "antibody" had the longest burst period from 1991 to 2012, "thyroxine" had the strongest burst strength 16.7026, "hypothyroxinemia" appeared most recently in 2018. The most frequent keyword was "pregnancy" occurred 1324 times. All the top 98 frequent keywords were clustered into 4 clusters. The citation network visualization was grouped into 8 groups.

CONCLUSION

The research focus of thyroid diseases in pregnancy ranged from clinical thyroid dysfunction to milder thyroid dysfunction. Guidelines published by the American Thyroid Association enacted a crucial purpose in the treatment and development of thyroid diseases during pregnancy. Some randomized controlled studies of unresolved problems and long-term follow-up of offspring may be the direction of future research. In the meantime, bibliometric methods can help scholars choose journals, track research hotspots, and identify the direction or focus of future research.

Prenatal Maternal Low Selenium, High Thyrotropin, and Low Birth Weights

In consideration of the potential roles of selenoproteins in thyroid function, we aimed to evaluate the association of low selenium status with hypothyroidism during pregnancy and the association of maternal low thyroid function with infant birth size. We conducted a prospective birth cohort study in Shanghai in 2010 and investigated 1931 pregnant mothers of gestational weeks 28-36. Maternal serum selenium and thyrotropin (TSH) levels were determined and birth weights and lengths of newborns were measured. Other covariates were obtained through maternal interviews and medical records. A non-linear association was observed between maternal selenium and TSH levels. Two-piecewise multivariable linear regression models were therefore applied to assess the association of serum selenium with TSH levels, and multivariable linear regression models were applied to assess the association of TSH levels with birth weight/length. Adjusting for potential confounders, when maternal serum selenium levels < 103.7 μg/L (P25th), each unit increase in selenium levels (μg/L) was significantly associated with a decrease of 0.014 μIU/mL in TSH levels (β = - 0.014, 95%CI - 0.025, - 0.002, P = 0.023). However, when selenium levels ≥ 103.7 μg/L, there were no significant relationships between selenium and TSH (β = 0.000, 95%CI - 0.001, 0.002, P = 0.859). Maternal TSH levels were significantly inversely associated with infant birth weight (β = - 0.060, 95%CI - 0.100, - 0.010, P = 0.010). We observed a non-linear association between maternal selenium status and TSH levels. Low selenium status during pregnancy may associate with low thyroid function that was related with low birth weights. Graphical abstract .

Thyroid disrupting chemicals and developmental neurotoxicity - New tools and approaches to evaluate hormone action

It is well documented that thyroid hormone (TH) action is critical for normal brain development and is mediated by both nuclear and extranuclear pathways. Given this dependence, the impact of environmental endocrine disrupting chemicals that interfere with thyroid signaling is a major concern with direct implications for children's health. However, identifying thyroid disrupting chemicals in vivo is primarily reliant on serum thyroxine (T4) measurements within greater developmental and reproductive toxicity assessments. These studies do not examine known TH-dependent phenotypes in parallel, which complicates chemical evaluation. Additionally, there exist no recommendations regarding what degree of serum T4 dysfunction is adverse, and little consideration is given to quantifying TH action within the developing brain. This review summarizes current testing strategies in rodent models and discusses new approaches for evaluating the developmental neurotoxicity of thyroid disrupting chemicals. This includes assays to identify adverse cellular effects of the brain by both immunohistochemistry and gene expression, which would compliment serum T4 measures. While additional experiments are needed to test the full utility of these approaches, incorporation of these cellular and molecular assays could enhance chemical evaluation in the regulatory arena.

Identification of gene targets of developmental neurotoxicity focusing on DNA hypermethylation involved in irreversible disruption of hippocampal neurogenesis in rats

We have previously found that maternal exposure to 6‐propyl‐2‐thiouracil (PTU), valproic acid (VPA), or glycidol (GLY) has a sustained or late effect on hippocampal neurogenesis at the adult stage in rat offspring. Herein, we searched for genes with hypermethylated promoter region and downregulated transcript level to reveal irreversible markers of developmental neurotoxicity. The hippocampal dentate gyrus of male rat offspring exposed maternally to PTU, VPA, or GLY was subjected to Methyl‐Seq and RNA‐Seq analyses on postnatal day (PND) 21. Among the genes identified, 170 were selected for further validation analysis of gene expression on PND 21 and PND 77 by real‐time reverse transcription‐PCR. PTU and GLY downregulated many genes on PND 21, reflecting diverse effects on neurogenesis. Furthermore, genes showing sustained downregulation were found after PTU or VPA exposure, reflecting a sustained or late effect on neurogenesis by these compounds. In contrast, such genes were not observed with GLY, probably because of the reversible nature of the effects. Among the genes showing sustained downregulation, Creb, Arc, and Hes5 were concurrently downregulated by PTU, suggesting an association with neuronal mismigration, suppressed synaptic plasticity, and reduction in neural stem and progenitor cells. Epha7 and Pvalb were also concurrently downregulated by PTU, suggesting an association with the reduction in late‐stage progenitor cells. VPA induced sustained downregulation of Vgf and Dpysl4, which may be related to the aberrations in synaptic plasticity. The genes showing sustained downregulation may be irreversible markers of developmental neurotoxicity.

Hippocampal dentate gyrus of rat offspring exposed maternally to PTU, VPA, or GLY was subjected to global methylation analysis on PND 21. Genes downregulated on PND 77 were examined. PTU concurrently downregulated Creb, Arc, and Hes5, suggesting an association with the diverse effects on neurogenesis. PTU also concurrently downregulated Epha7 and Pvalb, suggesting an association with progenitor cell reduction. VPA downregulated Vgf and Dpysl4, suggesting an association with the aberrant synaptic plasticity. In contrast, GLY did not induce sustained downregulation.

Universal screening for thyroid disease during pregnancy should be performed

Thyroid disease can significantly impact the pregnant woman and her child. Human and animal studies have firmly linked overt hypothyroidism and overt hyperthyroidism to miscarriage, preterm delivery and other adverse pregnancy outcomes. Overt hypothyroidism and overt hyperthyroidism affect 1% of all pregnancies. Treatment is widely available, and if detected early, results in decreased rates of adverse outcomes. Universal screening for thyroid disease in pregnancy can identify patients with thyroid disease requiring treatment, and ultimately decrease rates of complications. Universal screening is cost-effective compared to the currently accepted practice of targeted screening and may even be cost-saving in some healthcare systems. Targeted screening, which is recommended by most professional associations, fails to detect a large proportion of pregnant women with thyroid disease. In fact, an increasing number of providers are performing universal screening for thyroid disease in pregnancy, contrary to society guidelines. Limited evidence concerning the impact of untreated and treated subclinical disease and thyroid autoimmunity has distracted from the core rationale for universal screening - the beneficial impact of detecting and treating overt thyroid disease. Evidence supporting universal screening for overt disease stands independently from that of subclinical and autoimmune disease. The time to initiate universal screening is now.

Study on subclinical hypothyroidism in pregnancy: a bibliometric analysis via CiteSpace

Background: Subclinical hypothyroidism (SCH) in pregnancy has drawn an increasing amount of attention over the past two decades. However, the definition of it, including its clinical diagnosis and treatment, is still being revised. An increased risk of adverse pregnancy outcomes have been shown in most but not all studies. The objective of this study was to evaluate the origin, current trend and research hotspots on SCH in pregnancy.Methods: We obtained 630 records with 12,033 references, published between 1999 and 2018, from the online version of SCI-Expanded, Thomson Reuters Web of Science. The CiteSpace 5.3.R4 was used to perform the cooperation network analysis, key words co-occurrence and burst detection analysis, and reference cocitation analysis.Results: We identified that the number of publications on SCH in pregnancy was increasing over the past two decades. Teng WP and Shan ZY from the First Hospital of China Medical University, Shenyang, China, were found to be the most productive researchers in this field. USA was the leading country for publications. Subclinical hypothyroidism, pregnancy, hypothyroidism, dysfunction, disease, management, women, deficiency, association and hyperthyroidism were the top 10 high frequency keywords in all recruit documents. Follow up was the most strength burst key word in this field from 1999 through 2018, followed by maternal hypothyroxinemia, child, hypothyroidism complicating pregnancy, antithyroid antibody and fetal. Moreover, cocitation reference analysis revealed the top landmark articles and clusters in this field.Conclusion: This study provides the trends and frontiers in the field of SCH in pregnancy and valuable information for endocrine and/or obstetric researchers to identify new perspectives on potential collaborators and cooperative countries.

Implantation failure in rats with subclinical hypothyroidism is associated with LIF/STAT3 signaling

BACKGROUND

Pregnant women with subclinical hypothyroidism are associated with an increased risk of spontaneous abortion. This study aims to investigate the mechanisms underlying the effects of maternal subclinical hypothyroidism during early pregnancy on abortion in the uterus, focusing upon the LIF/STAT3 signaling pathway.

METHODS

One hundred five Wistar rats were randomly divided into three groups (35 rats in each group): control (CON) group, subclinical hypothyroidism (SCH) group and overt hypothyroidism (OH) group. We examined the weight of rat uteri, rat placenta and embryos. We also determined the number of implantation sites and the embryo absorption rates. The protein and mRNA expressions of TSHR, TR-α, TR-β, LIFR, gp130, JAK1, p-STAT3 and STAT3 were measured by immunohistochemical staining, real-time PCR and Western blotting.

RESULTS

The weights of rat uteri, rat placenta and embryos were significantly reduced in the SCH and OH groups. The number of implantation sites was significantly decreased in the SCH and OH groups, while embryo absorption rates were significantly increased. The mRNA and protein expressions of TSHR were upregulated in the SCH and OH groups, while TR-α and TR-β showed no difference when compared between the three groups. The expression levels of LIFR, gp130, JAK1 and p-STAT3 were significantly higher in the SCH and OH groups.

CONCLUSIONS

Clinical and subclinical hypothyroidism during early pregnancy might cause adverse pregnancy outcomes. Implantation failure in rats with subclinical hypothyroidism was associated with abnormal LIF/STAT3 signaling.

Neurodevelopmental toxicity induced by maternal PM2.5 exposure and protective effects of quercetin and Vitamin C

Epidemiological studies show that maternal exposure to PM_2.5 affects the neurodevelopment of the offspring, especially the neurocognitive function. However, no relevant experimental researches have been published on toxic mechanism and diet intervention. We evaluated the effects of exposure to different doses of PM_2.5 on the behavioral development of offspring via a PM_2.5 exposure model established by intratracheal instillation, explored its mechanism and the protective effects of quercetin and VC intervention, and focused on the protein expression of CREB/BDNF signaling pathway. Specifically, Exposure to PM_2.5 during gestation and lactation period caused maternal oxidative stress. Maternal exposure to PM_2.5 changed postnatal open-field behaviors in both gender, impaired spatial learning and memory in the female offspring, increased the level of IL-1β, IL-6, down-regulated p-CREB/CREB, BDNF, TrkB, p-CaMKII/CaMKII, p-CaMKIV/CaMKIV, up-regulated p-Akt/Akt and p-ERK1/2/ERK1/2 in the offspring. In addition, maternal supplementation with quercetin ameliorate the maternal oxidative stress, improved progeny inflammatory response, regulated BDNF, TrkB, p-Akt/Akt, p-ERK1/2/ERK1/2 in female offspring, regulated TrkB, p-CREB/CREB and p-Akt/Akt in male offspring. Maternal supplementation with VC increased the levels of CAT in maternal mice, up-regulated BDNF in female offspring, regulated p-CREB/CREB and p-ERK1/2/ERK1/2 in male offspring. Our findings indicate that PM2.5 exposure during pregnancy and lactation could impair behavioral development of offspring. Quercetin shows more protective effects than VC. The mechanism of neurodevelopmental toxicity induced by PM_2.5 may be related to oxidative stress, inflammatory response and modulation of the CREB/BDNF signaling pathway.

Thyroid Hormone Disruption in the Fetal and Neonatal Rat: Predictive Hormone Measures and Bioindicators of Hormone Action in the Developing Cortex

Adverse neurodevelopmental consequences remain a primary concern when evaluating the effects of thyroid hormone (TH) disrupting chemicals. Though the developing brain is a known target of TH insufficiency, the relationship between THs in the serum and the central nervous system is not well characterized. To address this issue, dose response experiments were performed in pregnant rats using the goitrogen propylthiouracil (PTU) (dose range 0.1-10 ppm). THs were quantified in the serum and brain of offspring at gestational day 20 (GD20) and postnatal day 14 (PN14), two developmental stages included in OECD and EPA regulatory guideline/guidance studies. From the dose response data, the quantitative relationships between THs in the serum and brain were determined. Next, targeted gene expression analyses were performed in the fetal and neonatal cortex to test the hypothesis that TH action in the developing brain is linked to changes in TH concentrations within the tissue. Results show a significant reduction of T4/T3 in the serum and brain of the GD20 fetus in response to low doses of PTU; interestingly, very few genes were significantly different at any dose tested. In the PN14 pup significant reductions of T4/T3 in the serum and brain were also detected; however, twelve transcriptional targets were identified in the neonatal cortex that correlated well with reduced brain THs. These results show that serum T4 is a good predictor of brain THs, and offer several target genes that could serve as pragmatic readouts of T4/T3 dysfunction within the PN14 cortex.

Possible mechanism of Vitis vinifera L. flavones on neurotransmitters, synaptic transmission and related learning and memory in Alzheimer model rats

BACKGROUND

This study explored the possible mechanism of flavones from Vitis vinifera L. (VTF) on neurotransmitters, synaptic transmission and related learning and memory in rats with Alzheimer disease (AD).

METHODS

The researchers injected amyloid-β_(25-35) into the hippocampus to establish AD model rats. The Sprague-Dawley (SD) rats were divided into a control group, a donepezil group, an AD model group, a VTF low-dose group, a VTF medium-dose group and a VTF high-dose group. The researchers detected the activity of choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) according to kit instructions. The protein expression of brain-derived neurotrophic factor (BDNF), synaptotagmin-1 (SYT1) and cyclic adenosine monophosphate response element binding protein (CREB) in the rats' hippocampi was detected by immunohistochemistry and Western blot, and the gene expression of cAMP-regulated enhancer (CRE) was detected by real-time quantitative polymerase chain reaction (PCR).

RESULTS

VTF may enhance the protein expression of p-CREB, BDNF and SYT1 in rat hippocampi, depending on dose. The messenger RNA (mRNA) level of CREB was significantly higher in the VTF high-dose group than in the model group, which was consistent with the results of Western blotting. VTF may reduce the activity of AChE and increase that of ChAT in rat hippocampi. Finally, VTF effectively improved the learning and memory abilities of AD rats.

CONCLUSIONS

VTF can promote synaptic plasticity and indirectly affect the expression of cholinergic neurotransmitters, which may be one mechanism of VTF protection in AD rats.

The Association Between Maternal Subclinical Hypothyroidism and Growth, Development, and Childhood Intelligence: A Meta-analysis

OBJECTIVE

To explore the association between maternal subclinical hypothyroidism (SCH) in pregnancy and the somatic and intellectual development of their offspring.

METHODS

Using RevMan 5.3 software, a meta-analysis of cohort studies published from inception to May 2017, focusing on the association between maternal SCH in pregnancy and childhood growth, development and intelligence, was performed. Sources included the Cochrane Library, Pub-Med, Web of Science, China National Knowledge Infrastructure and Wan Fang Data.

RESULTS

Analysis of a total of 15 cohort studies involving 1.896 pregnant women with SCH revealed that SCH in pregnancy was significantly associated with the intelligence (p=0.0007) and motor development (p<0.00001) of the offspring. SCH was also significantly associated with the child’s weight in four studies involving 222 women (p=0.02). Maternal SCH in pregnancy was identified as a risk factor for fetal growth restriction with a combined relative risk (RR) value of 2.4 [95% confidence interval (CI): 1.56, 3.7]. Meta-analysis of 10 studies that provided numbers of preterm infants revealed a significant association between maternal SCH in pregnancy and premature delivery, with a combined RR of 1.96 (95% CI: 1.34, 2.88). There was a significant effect of maternal SCH in pregnancy on fetal distress in utero (p=0.003).

CONCLUSION

Maternal SCH in pregnancy is associated with increased risk of adverse neonatal outcomes, including delayed intellectual and motor development, low birth weight, premature delivery, fetal distress and fetal growth restriction.

Subclinical hypothyroidism in pregnant rats impaired learning and memory of their offspring by promoting the p75NTR signal pathway

OBJECTIVE

Maternal hypothyroidism during pregnancy can affect the neurodevelopment of their offspring. This study aimed to investigate the effects of maternal subclinical hypothyroidism (SCH) on spatial learning and memory, and its relationship with the apoptotic factors in cerebral cortex of the offspring.

METHODS

Female adult Wistar rats were randomly divided into three groups (n = 15 per group): control (CON) group, SCH group and overt hypothyroidism (OH) group. Spatial learning and memory in the offspring were evaluated by long-term potentiation (LTP) and Morris water-maze (MWM) test. The protein expression of the p75 neurotrophin receptor (p75^NTR), phospho-c-Jun N-terminal kinase (p-JNK), the pro-apoptotic protein p53 and Bax were detected by Western blotting.

RESULTS

The Pups in the SCH and OH groups showed longer escape latencies in the MWM and decreased field-excitatory post synaptic potentials in LTP tests compared with those in the CON group. p75^NTR, p-JNK, p53 and Bax expression levels in the cerebral cortex increased in pups in the SCH and OH groups compared with those in the CON group.

CONCLUSIONS

Maternal SCH during pregnancy may impair spatial learning and memory in the offspring and may be associated with the increased apoptosis in the cerebral cortex.

Mild Maternal Hypothyroxinemia During Pregnancy Induces Persistent DNA Hypermethylation in the Hippocampal Brain-Derived Neurotrophic Factor Gene in Mouse Offspring

BACKGROUND

Thyroid hormones are essential for normal development of the central nervous system (CNS). Experimental rodents have shown that even a subtle thyroid hormone insufficiency in circulating maternal thyroid hormones during pregnancy may adversely affect neurodevelopment in offspring, resulting in irreversible cognitive deficits. This may be due to the persistent reduced expression of the hippocampal brain-derived neurotrophic factor gene Bdnf, which plays a crucial role in CNS development. However, the underlying molecular mechanisms remain unclear.

METHODS

Thiamazole (MMI; 0.025% [w/v]) was administered to dams from two weeks prior to conception until delivery, which succeeded in inducing mild maternal hypothyroxinemia during pregnancy. Serum thyroid hormone and thyrotropin levels of the offspring derived from dams with mild maternal hypothyroxinemia (M offspring) and the control offspring (C offspring) were measured. At 70 days after birth, several behavior tests were performed on the offspring. Gene expression and DNA methylation status were also evaluated in the promoter region of Bdnf exon IV, which is largely responsible for neural activity-dependent Bdnf gene expression, in the hippocampus of the offspring at day 28 and day 70.

RESULTS

No significant differences in serum thyroid hormone or thyrotropin levels were found between M and C offspring at day 28 and day 70. M offspring showed an impaired learning capacity in the behavior tests. Hippocampal steady-state Bdnf exon IV expression was significantly weaker in M offspring than it was in C offspring at day 28. At day 70, hippocampal Bdnf exon IV expression at the basal level was comparable between M and C offspring. However, it was significantly weaker in M offspring than in C offspring after the behavior tests. Persistent DNA hypermethylation was also found in the promoter region of Bdnf exon IV in the hippocampus of M offspring compared to that of C offspring, which may cause the attenuation of Bdnf exon IV expression in M offspring.

CONCLUSIONS

Mild maternal hypothyroxinemia induces persistent DNA hypermethylation in Bdnf exon IV in offspring as epigenetic memory, which may result in long-term cognitive disorders.

Pycnogenol Reduces Toll-Like Receptor 4 Signaling Pathway-Mediated Atherosclerosis Formation in Apolipoprotein E-Deficient Mice

Pycnogenol (PYC) is an extract from French maritime pine bark. Its antioxidative and anti-inflammatory effects have been shown to be beneficial for atherosclerosis. Here, we tested whether PYC could suppress high cholesterol and fat diet (HCD)-induced atherosclerosis formation in apolipoprotein E (apoE)-deficient mice. In our study, PYC suppressed oxidized low-density lipoprotein (ox-LDL)-induced lipid accumulation in peritoneal macrophages. Apolipoprotein E-deficient mice were orally administered PYC or a control solvent for ten weeks, and these mice were fed a standard diet or high cholesterol and fat diet during the latter eight weeks. Pycnogenol markedly decreased the size of atherosclerotic lesions induced by high cholesterol and fat diet compared with the nontreated controls. In addition, TLR4 expression in aortic sinus was stimulated by high cholesterol and fat diet feeding and was significantly reduced by PYC. A mechanistic analysis indicated that lipopolysaccharide (LPS) significantly increased expression of fatty acid binding protein (aP2) and macrophage scavenger receptor class A (SR-A), which were blocked by a JNK inhibitor. Furthermore, PYC inhibited the lipopolysaccharide-induced upregulation of aP2 and scavenger receptor class A via the JNK pathway. In conclusion, PYC administration effectively attenuates atherosclerosis through the TLR4-JNK pathway. Our results suggest that PYC could be a potential prophylaxis or treatment for atherosclerosis in humans.

Critical role of TRPC1 in thyroid hormone-dependent dopaminergic neuron development

Thyroid hormones play a crucial role in midbrain dopaminergic (DA) neuron development. However, the underlying molecular mechanisms remain largely unknown. In this study, we revealed that thyroid hormone treatment evokes significant calcium entry through canonical transient receptor potential (TRPC) channels in ventral midbrain neural stem cells and this calcium signaling is essential for thyroid hormone-dependent DA neuronal differentiation. We also found that TRPC1 is the dominant TRPC channel expressed in ventral midbrain neural stem cells which responds to thyroid hormone. In addition, thyroid hormone increases TRPC1 expression through its receptor alpha 1 during DA neuron differentiation, and, importantly, produces calcium signals by activating TRPC1 channels. In vivo and in vitro gene silencing experiments indicate that TRPC1-mediated calcium signaling is required for thyroid hormone-dependent DA neuronal differentiation. Finally, we confirmed that the activation of OTX2, a determinant of DA neuron development and the expression of which is induced by thyroid hormone, is dependent on TRPC1-mediated calcium signaling. These data revealed the molecular mechanisms of how thyroid hormone regulates DA neuron development from ventral midbrain neural stem cells, particularly endowing a novel physiological relevance to TRPC1 channels.

Elevated Thyroid Peroxidase Antibody Increases Risk of Post-partum Depression by Decreasing Prefrontal Cortex BDNF and 5-HT Levels in Mice

Post-partum depression (PPD) is a common mental disease in the perinatal period that profoundly affects mothers and their offspring. Some clinical studies have found that PPD is related to thyroid peroxidase antibodies (TPOAbs); however, the mechanism underlying this relationship is unclear. Female C57BL/6 mice immunized with adenovirus encoding the cDNA of the full-length mTPO (mTPO-Ad) were used to establish the isolated TPOAb-positive mouse model in the present study. Maternal depressive-like behaviors were assessed using the forced swimming test (FST), sucrose preference test (SPT), and tail suspension test (TST) post-partum. The serum TPOAb titer was measured by enzyme-linked immunosorbent assay (ELISA) before pregnancy and post-partum. Furthermore, in the prefrontal cortex, the mRNA and protein expression levels of brain-derived neurotrophic factor (BDNF) were measured, serotonin (5-HT) levels were measured by ultra-high-performance liquid chromatography–tandem mass-spectrometry (UHPLC–MS/MS), and total thyroxine (TT4) levels were determined by ELISA. Compared with the controls, the mice immunized with mTPO-Ad displayed depressive behaviors, with a significantly lower sucrose preference (SP) at the 12-h time point and a longer immobility time in the FST and TST, which were accompanied by a lower expression of BDNF and 5-HT but no change in the TT4 concentration in the prefrontal cortex. Together, these findings suggest that elevated TPOAb may increase the risk of subsequent PPD and decrease the concentration of BDNF and 5-HT in the prefrontal cortex.

Implications of the thyroid hormone on neuronal development with special emphasis on the calmodulin-kinase IV pathway

Thyroid hormones influence brain development through regulation of gene expression. This is especially true for Ca²⁺-dependent regulation since a major pathway is controlled by the Ca²⁺/calmodulin-dependent protein kinase IV (CaMKIV) which in turn is induced by the thyroid hormone T₃. In addition, CaMKIV is involved in regulation of alternative splicing of a number of protein isoforms, among them PMCA1a, the neuronal specific isoform of the plasma membrane calcium pump. On the other hand, hypothyroidism or CaMKIV deficiency can have a severe influence on brain development. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Effect of Thyrotropin on Osteopontin, Integrin αvβ3, and VCAM-1 in the Endothelium via Activation of Akt

Numerous epidemiological studies have shown that subclinical hypothyroidism (SCH) can impair endothelial function and cause dyslipidemia. Studies have evaluated the effects of thyroid stimulating hormone (TSH) on endothelial cells, but the mechanism underlying the proatherosclerotic effect of increased TSH levels remains unclear. In the present study, SCH rat models were established in thyroidectomized Wistar rats that were given l-T₄ daily. The results showed that in vivo, the expression of osteopontin (OPN) vascular cell adhesion molecule (VCAM-1), and levels of integrin α_vβ₃ in the aortic tissue in SCH and Hypothyroidism (CH) groups was higher than in the control group. However, the effect in the SCH group was higher than in the CH group. In vitro, results showed that different concentration and time gradients of TSH stimulation could increase the expression of OPN, VCAM-1, and integrin α_vβ₃, and this was accompanied by extracellular signal regulated kinase 1/2 (Erk1/2) and Akt activation in human umbilical vein endothelial cells (HUVECs). TSH induced elevation of these proatherosclerotic factors was partially suppressed by a specific Akt inhibitor but not by a specific Erk inhibitor. Findings suggested that the endothelial dysfunction caused by SCH was related to increased proatherosclerotic factors induced by TSH via Akt activation.

Evolution of Plasticity: Mechanistic Link between Development and Reversible Acclimation

Phenotypic characteristics of animals can change independently from changes in the genetic code. These plastic phenotypic responses are important for population persistence in changing environments. Plasticity can be induced during early development, with persistent effects on adult phenotypes, and it can occur reversibly throughout life (acclimation). These manifestations of plasticity have been viewed as separate processes. Here we argue that developmental conditions not only change mean trait values but also modify the capacity for acclimation. Acclimation counteracts the potentially negative effects of phenotype-environment mismatches resulting from epigenetic modifications during early development. Developmental plasticity is therefore also beneficial when environmental conditions change within generations. Hence, the evolution of reversible acclimation can no longer be viewed as independent from developmental processes.

Effects of isolated positive maternal thyroglobulin antibodies on brain development of offspring in an experimental autoimmune thyroiditis model

BACKGROUND

Autoimmune thyroiditis (AIT) is a very common endocrine disorder in pregnancy. However, the effect of maternal positive thyroglobulin antibodies (TgAb) on brain development of offspring remains unclear. This study used an experimental autoimmune thyroiditis model in CBA/J mice and determined whether isolated positive maternal TgAb directly affected learning and memory abilities of offspring.

METHODS

An experimental autoimmune thyroiditis model was established in CBA/J mice through immunization with murine thyroglobulin (mTg). Measuring thyroid function and serum TgAb titer confirmed the presence of isolated positive maternal TgAb. Offspring serum TgAb titer, MCT8, Reelin, RC3, and BNDF mRNA expression in the brain, and brain histology were measured on postnatal days 0, 10, and 40 (PND0, PND10, PND40), and nerve cell migration (BrdU labeling) at PND40. Morris water maze, long-term potentiation (LTP), and LTP-related factor ERK1/2 levels were measured at PND40 to determine offspring spatial learning and memory development.

RESULTS

Maternal serum TgAb titers increased and remained elevated through pregnancy compared to controls. Thyrotropin and thyroid hormone levels were normal. The T group offspring (Tg immunized) had higher TgAb titers than the control (C) group. However, antibody titers time-dependently decreased. MCT8, Reelin, RC3, and BDNF mRNA expression in the whole brain were similar in the T and C groups on PND0, PND10, and PND40. Neuronal distribution and BrdU from the cerebral cortex and hippocampus were similar in the T and C group offspring. Morris water maze tests, excitatory postsynaptic field potentials, and ERK1/2 levels were also similar between the T and C groups.

CONCLUSIONS

Isolated positive maternal TgAb did not clearly influence the learning ability and memory of offspring, or nerve cell migration, despite a transient increase in TgAb in immunized mice.

Hypothyroidism and brain developmental players

Most of our knowledge on the mechanisms of thyroid hormone (TH) dependent brain development is based on clinical observations and animal studies of maternal/fetal hypothyroidism. THs play an essential role in brain development and hormone deficiency during critical phases in fetal life may lead to severe and permanent brain damage. Maternal hypothyroidism is considered the most common cause of fetal TH deficiency, but the problem may also arise in the fetus. In the case of congenital hypothyroidism due to defects in fetal thyroid gland development or hormone synthesis, clinical symptoms at birth are often mild as a result of compensatory maternal TH supply. TH transporters (THTs) and deiodinases (Ds) are important regulators of intracellular triiodothyronine (T3) availability and therefore contribute to the control of thyroid receptors (TRs)-dependent CNS development and early embryonic life. Defects in fetal THTs or Ds may have more impact on fetal brain since they can result in intracellular T3 deficiency despite sufficient maternal TH supply. One clear example is the recent discovery of mutations in the TH transporter (monocarboxylate transporter 8; MCT8) that could be linked to a syndrome of severe and non reversible psychomotor retardation. Even mild and transient changes in maternal TH levels can directly affect and alter the gene expression profile, and thus disturb fetal brain development. Animal studies are needed to increase our understanding of the exact role of THTs and Ds in prenatal brain development.