Differential effects of leptin administration on feeding and HPT axis function in early-life overfed adult rats

A National Multicenter Study of Leptin and Leptin Receptor Deficiency and Systematic Review

CONTEXT

Homozygous leptin (LEP) and leptin receptor (LEPR) variants lead to childhood-onset obesity.

OBJECTIVE

To present new cases with LEP and LEPR deficiency, report the long-term follow-up of previously described patients, and to define, based on all reported cases in literature, genotype-phenotype relationships.

METHODS

Our cohort included 18 patients (LEP = 11, LEPR = 7), 8 of whom had been previously reported. A systematic literature review was conducted in July 2022. Forty-two of 47 studies on LEP/LEPR were selected.

RESULTS

Of 10 new cases, 2 novel pathogenic variants were identified in LEP (c.16delC) and LEPR (c.40 + 5G > C). Eleven patients with LEP deficiency received metreleptin, 4 of whom had been treated for over 20 years. One patient developed loss of efficacy associated with neutralizing antibody development. Of 152 patients, including 134 cases from the literature review in addition to our cases, frameshift variants were the most common (48%) in LEP and missense variants (35%) in LEPR. Patients with LEP deficiency were diagnosed at a younger age [3 (9) vs 7 (13) years, P = .02] and had a higher median body mass index (BMI) SD score [3.1 (2) vs 2.8 (1) kg/m2, P = 0.02], which was more closely associated with frameshift variants (P = .02). Patients with LEP deficiency were more likely to have hyperinsulinemia (P = .02).

CONCLUSION

Frameshift variants were more common in patients with LEP deficiency whereas missense variants were more common in LEPR deficiency. Patients with LEP deficiency were identified at younger ages, had higher BMI SD scores, and had higher rates of hyperinsulinemia than patients with LEPR deficiency. Eleven patients benefitted from long-term metreleptin, with 1 losing efficacy due to neutralizing antibodies.

Effect of exposure to endocrine disrupting chemicals in obesity and neurodevelopment: The genetic and microbiota link

Current evidence highlights the importance of the genetic component in obesity and neurodevelopmental disorders (attention-deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD) and intellectual disability (ID)), given that these diseases have reported an elevated heritability. Additionally, environmental stressors, such as endocrine disrupting chemicals (EDCs) have been classified as obesogens, neuroendocrine disruptors, and microbiota disrupting chemicals (MDCs). For this reason, the importance of this work lies in examining two possible biological mechanistic pathways linking obesity and neurodevelopmental/behavioural disorders: EDCs - gene and EDCs - microbiota interactions. First, we summarise the shared mechanisms of action of EDCs and the common genetic profile in the bidirectional link between obesity and neurodevelopment. In relation to interaction models, evidence from the reviewed studies reveals significant interactions between pesticides/heavy metals and gene polymorphisms of detoxifying and neurotransmission systems and metal homeostasis on cognitive development, ASD and ADHD symptomatology. Nonetheless, available literature about obesity is quite limited. Importantly, EDCs have been found to induce gut microbiota changes through gut-brain-microbiota axis conferring susceptibility to obesity and neurodevelopmental disorders. In view of the lack of studies assessing the impact of EDCs - gene interactions and EDCs - mediated dysbiosis jointly in obesity and neurodevelopment, we support considering genetics, EDCs exposure, and microbiota as interactive factors rather than individual contributors to the risk for developing obesity and neurodevelopmental disabilities at the same time.

Litter Size Reduction as a Model of Overfeeding during Lactation and Its Consequences for the Development of Metabolic Diseases in the Offspring

Overfeeding during lactation has a deleterious impact on the baby’s health throughout life. In humans, early overnutrition has been associated with higher susceptibility to obesity and metabolic disorders in childhood and adulthood. In rodents, using a rodent litter size reduction model (small litter) to mimic early overfeeding, the same metabolic profile has been described. Therefore, the rodent small litter model is an efficient tool to investigate the adaptive mechanisms involved in obesogenesis. Besides central and metabolic dysfunctions, studies have pointed to the contribution of the endocrine system to the small litter phenotype. Hormones, especially leptin, insulin, and adrenal hormones, have been associated with satiety, glucose homeostasis, and adipogenesis, while hypothyroidism impairs energy metabolism, favoring obesity. Behavioral modifications, hepatic metabolism changes, and reproductive dysfunctions have also been reported. In this review, we update these findings, highlighting the interaction of early nutrition and the adaptive features of the endocrine system. We also report the sex-related differences and epigenetic mechanisms. This model highlights the intense plasticity during lactation triggering many adaptive responses, which are the basis of the developmental origins of health and disease (DOHaD) concept. Our review demonstrates the complexity of the adaptive mechanisms involved in the obesity phenotype promoted by early overnutrition, reinforcing the necessity of adequate nutritional habits during lactation.

Obesity and Thyroid Axis

Development of obesity is primarily the result of imbalance between energy intake and energy expenditure. Thyroid hormones influence energy expenditure by regulating cellular respiration and thermogenesis and by determining resting metabolic rate. Triiodothyronine influences lipid turnover in adipocytes and impacts appetite regulation through the central nervous system, mainly the hypothalamus. Thyroid-stimulating hormone may also influence thermogenesis, suppress appetite and regulate lipid storage through lipolysis and lipogenesis control. Subclinical hypothyroidism may induce changes in basal metabolic rate with subsequent increase in BMI, but obesity can also affect thyroid function via several mechanisms such as lipotoxicity and changes in adipokines and inflammatory cytokine secretion. The present study investigated the complex and mutual relationships between the thyroid axis and adiposity.

Response of the thyroid axis and appetite-regulating peptides to fasting and overfeeding in goldfish (Carassius auratus)

The thyroid axis is a major regulator of metabolism and energy homeostasis in vertebrates. There is conclusive evidence in mammals for the involvement of the thyroid axis in the regulation of food intake, but in fish, this link is unclear. In order to assess the effects of nutritional status on the thyroid axis in goldfish, Carassius auratus, we examined brain and peripheral transcripts of genes associated with the thyroid axis [thyrotropin-releasing hormone (TRH), thyrotropin-releasing hormone receptors (TRH-R type 1 and 2), thyroid stimulating hormone beta (TSHβ), deiodinase enzymes (DIO2, DIO3) and UDP-glucoronsyltransferase (UGT)] and appetite regulators [neuropeptide Y (NPY), proopiomelanocortin (POMC), agouti-related peptide (AgRP) and cholecystokinin (CCK)] in fasted and overfed fish for 7 and 14 day periods. We show that the thyroid axis responds to overfeeding, with an increase of brain TRH and TSHβ mRNA expression after 14 days, suggesting that overfeeding might activate the thyroid axis. In fasted fish, hepatic DIO3 and UGT transcripts were downregulated from 7 to 14 days, suggesting a time-dependent inhibition of thyroid hormone degradation pathways. Nutritional status had no effect on circulating levels of thyroid hormone. Central appetite-regulating peptides exhibited temporal changes in mRNA expression, with decreased expression of the appetite-inhibiting peptide POMC from 7 to 14 days for both fasted and overfed fish, with no change in central NPY or AgRP, or intestinal CCK transcript expression. Compared to control fish, fasting increased AgRP mRNA expression at both 7 and 14 days, and POMC expression was higher than controls only at 7 days. Our results indicate that nutritional status time-dependently affects the thyroid axis and appetite regulators, although no clear correlation between thyroid physiology and appetite regulators could be established. Our study helps to fill a knowledge gap in current fish endocrinological research on the effects of energy balance on thyroid metabolism and function.