Metabolic Impact of Subclinical Hypothyroidism in Obese Children and Adolescents

Effect of TSH on aromatase expression of ovarian granulosa cells in obese mice

PURPOSE

Aromatase plays an important role in ovarian development, the normal progress of the menstrual cycle, and fertility status. Elevated aromatase activity is linked to obesity. There is a bidirectional relationship between obesity and thyroid function. Few studies have investigated the relationship between TSH and ovarian aromatase in obesity. Our aim was to investigate the effect of TSH on aromatase expression of ovarian granulosa cells in obese mice.

METHODS

Female mice pups were divided into an obesity group and a control group. Obese parameters and the time of pubertal onset were recorded. At the age of 5 weeks, blood and tissues were obtained. Serum aromatase and hormone concentrations were measured using ELISA. The granulosa cells were isolated and exposed to variable concentrations (0 μM, 1 μM, 10 μM, 100 μM) of TSH. The expression of CYP19A1 mRNA and protein were assessed via RT-qPCR and western blot.

RESULTS

In female mice, body weight, Lee's obesity index, and serum levels of E2, aromatase, and TSH were significantly higher in the obesity group compared to the control group, whereas the time of pubertal onset and serum T3 and T4 concentrations were significantly lower (all P < 0.001). In granulosa cells, the expression of CYP19A1 mRNA in the obesity group was lower than that in the control group at 1 μM and 100 μM concentrations of TSH (both P < 0.001). The expression of CYP19A1 protein in the obesity group was higher than that in the control group after TSH stimulation (P = 0.014, P < 0.001, and P = 0.004, respectively). With the increase of TSH concentrations, the expression of CYP19A1 mRNA and protein in the two groups significantly increased (all P < 0.001).

CONCLUSION

Early puberty and elevated serum aromatase and TSH levels were found in obese female mice. In the granulosa cells of obese mice, TSH directly regulates aromatase expression in a dose-dependent manner.

Causal association between obesity and hypothyroidism: a two-sample bidirectional Mendelian randomization study

Introduction

Previous observational studies have reported a positive correlation between obesity and susceptibility to hypothyroidism; however, there is limited evidence from alternative methodologies to establish a causal link.

Methods

We investigated the causal relationship between obesity and hypothyroidism using a two-sample bidirectional Mendelian randomization (MR) analysis. Single-nucleotide polymorphisms (SNPs) associated with obesity-related traits were extracted from a published genome-wide association study (GWAS) of European individuals. Summarized diagnostic data of hypothyroidism were obtained from the UK Biobank. Primary analyses were conducted using the inverse variance-weighted (IVW) method with a random-effects model as well as three complementary approaches. Sensitivity analyses were performed to ascertain the correlation between obesity and hypothyroidism.

Results

MR analyses of the IVW method and the analyses of hypothyroidism/myxedema indicated that body mass index (BMI) and waist circumference (WC) were significantly associated with higher odds and risk of hypothyroidism. Reverse MR analysis demonstrated that a genetic predisposition to hypothyroidism was associated with an increased risk of elevated BMI and WC, which was not observed between WC adjusted for BMI (WCadjBMI) and hypothyroidism.

Discussion

Our current study indicates that obesity is a risk factor for hypothyroidism, suggesting that individuals with higher BMI/WC have an increased risk of developing hypothyroidism and indicating the importance of weight loss in reducing the risk of hypothyroidism.

Thyroid dysfunction in children and adolescents affected by undernourished and overnourished eating disorders

Eating disorders (ED) are one of the most prevalent chronic disorders in adolescents and young adults, with a significantly increasing prevalence in younger children, particularly in girls. Even if obesity in essence is not framed as an eating disorder and has always been considered a separate pathology, ED and obesity could be considered part of a continuum. It has become evident that one condition can lead to another, such as binge eating disorder (BED) and bulimia nervosa, and that they share the same repercussions in terms of psychosocial, metabolic, and nutritional health. This narrative review aims to investigate the hypothalamic-pituitary-thyroid axis in undernourished and overnourished patients with ED, including obesity, in order to highlight the relationship between weight control and thyroid function and its effects and to consider therapeutic and preventive strategies in children and adolescents. Literature data report that thyroid alterations occur in patients with ED, both underweight and overweight, and represent a continuum of changes depending on the severity and time course of the disease involving the endocrine system. Considering the relevant role thyroid hormones (TH) play not only in energy expenditure (EE) but also in metabolic control and cardiovascular risks related to dysmetabolism and mood regulation, continuous monitoring of thyroid homeostasis in patients with ED is mandatory to prevent severe complications and to start early treatment when necessary.

A Feedback Loop Involving Exosomal miR-146a and NG2 to Propel the Development and Progression of Hypothyroidism

Background: Thyrotropin receptor (TSHR) plays a central role in maintaining thyroid function and TSHR impairment causes hypothyroidism, which is often associated with metabolic disarrangement. The most common type of hypothyroidism is autoimmune disease-related and the mechanism, particularly with respect to the role of microRNAs (miRNAs), has not been delineated. Methods: Serum from 30 patients with subclinical hypothyroidism (SCH) and 30 healthy individuals were collected and exosomal miR-146a (exo-miR-146a) was examined, followed by extensive mechanistic investigation using various molecular and cellular experimental approaches and genetic-knockout mouse models. Results: Our clinical investigation showed that exo-miR-146a was systemically elevated in the serum of patients with SCH (p = 0.04) compared with healthy individuals, prompting us to investigate the biological effects of miR-146a in cells. We found that miR-146a could target and down-regulate neuron-glial antigen 2 (Ng2), with consequent down-regulation of TSHR. We next generated a thyroid-specific Ng2 knockout (Thy-Ng2-/-) mouse model and found a significant down-regulation of TSHR in Thy-Ng2-/- mice, accompanied by the development of hypothyroidism and metabolic disorders. We further found that a decrease in NG2 resulted in decreased receptor tyrosine kinase-linked downstream signaling and down-regulation of c-Myc, consequently resulting in up-regulation of miR-142 and miR-146a in thyroid cells. Up-regulated miR-142 targeted the 3'-untranslated region (UTR) of TSHR messenger RNA (mRNA) and post-transcriptionally down-regulated TSHR, explaining the development of hypothyroidism above. Local up-regulation of miR-146a in thyroid cells augments the earlier cited processes initiated by systemically elevated miR-146a, thereby forming a feedback loop to propel the development and progression of hypothyroidism. Conclusions: This study has uncovered a self-augmenting molecular loop initiated by elevated exo-miR-146a to suppress TSHR through targeting and down-regulating NG2, thereby initiating and propelling the development and progression of hypothyroidism.

Association of high BMI with subclinical hypothyroidism in young, first-episode and drug-naïve patients with major depressive disorder: a large-scale cross-sectional study

Thyroid dysfunction is known to be associated with obesity, but the reliability of this relationship is easily affected by drug treatment, age, and subclinical hypothyroidism (SCH) with no apparent symptoms. Our research aims to compare obese and overweight BMI ranges with SCH and without SCH in a large sample of young, first-episode and drug-naïve (FEDN) patients with major depressive disorder (MDD), which has received little systemic investigation. A total of 1289 FEDN MDD young outpatients were recruited for this study. Serum thyroid function and lipid level parameters were measured; HAMD and PANSS scales were used to assess patients' depression and positive symptoms. A self-administered questionnaire collected other clinical and demographic data. The prevalence of SCH in FEDN MDD young patients was 58.26%. Compared to patients without SCH, the patients with SCH had a more prolonged illness duration, higher BMI levels, increased prevalence of overweight and obesity, higher HAMD score and PANSS-positive symptom scores, higher levels of TG, TC, LDL-C, and lower levels of HDL-C. Further logistic regression indicated that overweight BMI, obese BMI, illness duration, HAMD score, HDL-C, and TC were significantly associated with SCH. Our results indicate that obesity and overweight may be associated with SCH in young, FEDN MDD patients. The importance of regular thyroid function assessment in young FEDN MDD patients with high BMI should be taken into account.