Cold exposure restores the decrease in leptin receptors (OB-Rb) caused by neonatal leptin treatment in 30-day-old rats

Paternal developmental thyrotoxicosis disrupts neonatal leptin leading to increased adiposity and altered physiology of the melanocortin system

Background

The genetic code does not fully explain individual variability and inheritance of susceptibility to endocrine conditions, suggesting the contribution of epigenetic factors acting across generations.

Methods

We used a mouse model of developmental thyrotoxicosis (Dio3-/- mouse) to analyze endocrine outcomes in the adult offspring of Dio3-/- males using standard methods for body composition, and baseline and fasting hormonal and gene expression determinations in serum and tissues of relevance to the control of energy balance.

Results

Compared to controls, adult females with an exposed father (EF females) exhibited higher body weight and fat mass, but not lean mass, a phenotype that was much milder in EF males. After fasting, both EF females and males exhibited a more pronounced decrease in body weight than controls. EF females also showed markedly elevated serum leptin, increased white adipose tissue mRNA expression of leptin and mesoderm-specific transcript but decreased expression of type 2 deiodinase. EF females exhibited decreased serum ghrelin, which showed more pronounced post-fasting changes in EF females than in control females. EF female hypothalami also revealed significant decreases in the expression of pro-opiomelanocortin, agouti-related peptide, neuropeptide Y and melanocortin receptor 4. These markers also showed larger changes in response to fasting in EF females than in control females. Adult EF females showed no abnormalities in serum thyroid hormones, but pituitary expression of thyrotropin-releasing hormone receptor 1 and thyroid gland expression of thyroid-stimulating hormone receptor, thyroid peroxidase and iodotyrosine deiodinase were increased at baseline and showed differential regulation after fasting, with no increase in Trhr1 expression and more pronounced reductions in Tshr, Tpo and Iyd. In EF males, these abnormalities were generally milder. In addition, postnatal day 14 (P14) serum leptin was markedly reduced in EF pups.

Discussion

A paternal excess of thyroid hormone during development modifies the endocrine programming and energy balance in the offspring in a sexually dimorphic manner, with baseline and dynamic range alterations in the leptin-melanocortin system and thyroid gland, and consequences for adiposity phenotypes. We conclude that thyroid hormone overexposure may have important implications for the non-genetic, inherited etiology of endocrine and metabolic pathologies.

Adverse perinatal conditions and the developmental origins of thyroid dysfunction-Lessons from Animal Models

PURPOSE

Nutritional, hormonal, and environmental status during development can predispose the individual to obesity and endocrine diseases later in life, an association known as metabolic programming. In general, weight loss or gain are seen in thyroid disorders, and thyroid function can be affected by body adiposity. In addition, hyper- and hypothyroidism can be related to metabolic programming. Our aim was to gather evidence that regardless of the type or critical window of metabolic imprinting, offspring exposed to certain adverse perinatal conditions have a higher risk of developing thyroid dysfunction.

METHODS

We reviewed literature data that relate insults occurring during pregnancy and/or lactation to short- and long-term offspring thyroid dysfunction in animal models.

RESULTS

Few studies have addressed the hypothalamic-pituitary-thyroid axis and thyroid dysfunction related to metabolic programming. The literature shows that under- and overnutrition, exposure to endocrine disruptors, early weaning, maternal thyroid disease and maternal high-fat diet can induce alterations in offspring thyroid function in a sex-dependent manner.

CONCLUSION

Based on the few available data, mainly in rodent models, we can conclude that diet, hormones, and environmental contaminants are related to the developmental origins of later thyroid dysfunction by interrupting the normal maturation of the thyroid gland.

Crossing the Antarctica: Exploring the Effects of Appetite-Regulating Hormones and Indicators of Nutrition Status during a 93-Day Solo-Expedition

Future deep space astronauts must maintain adequate nutrition despite highly stressful, isolated, confined and dangerous environments. The present case-study investigated appetite regulating hormones, nutrition status, and physical and emotional stress in a space analog condition: an explorer conducting a 93-day unsupported solo crossing of Antarctica. Using the dried blood spot (DBS) method, the subject drew samples of his blood on a regular basis during the expedition. The DBSs were later analyzed for the appetite regulating hormones leptin and adiponectin. Energy intake and nutritional status were monitored by analysis of albumin and globulin (including their ratio). Interleukin-6 (IL-6) was also analyzed and used as an energy sensor. The results showed a marked reduction in levels of the appetite-reducing hormone, leptin, and the appetite stimulating hormone, adiponectin, during both extreme physical and psychological strain. Nutrition status showed a variation over the expedition, with below-normal levels during extreme psychological strain and levels abutting the lower bounds of the normal range during a phase dominated by extreme physical hardship. The IL-6 levels varied substantially, with levels above the normal range except during the recovery phase. It was concluded that a daily intake of 5058 to 5931 calories seemed to allow recovery of both appetite and nutritional status between extreme physical and psychological hardship during a long Arctic expedition. Furthermore, IL-6 may be a sensor in the muscle-liver, muscle-fat and muscle-brain crosstalk. These results may help guide nutrition planning for future astronaut crews, mountaineers and others involved in highly demanding missions.

Leptin, adiponectin, and ghrelin responses to endurance exercise in different ambient conditions

Excessive positive energy balance is a major factor leading to obesity. The ability to alter the appetite-regulating hormones leptin, adiponectin, and ghrelin may help decrease excessive energy intake. Exercise and exposure to extreme temperatures can independently affect these appetite-regulating hormones.

PURPOSE

To determine the effect of exercising in different environmental conditions on the circulating concentrations of leptin, adiponectin, and ghrelin.

METHODS

Eleven recreationally-trained male participants completed 3 separate 1 h cycling bouts at 60% W_max in hot, cold, and room temperature conditions (33°C, 7°C, 20°C), followed by a 3 h recovery at room temperature. Blood was drawn pre-exercise, post-exercise, and 3 h post-exercise. Hematocrit and hemoglobin were measured to account for change in plasma volume.

RESULTS

Leptin concentrations were lower at post and 3 h post-exercise compared with pre-exercise, with and without correction for plasma volume shifts, regardless of temperature (p < 0.05). Adiponectin was higher post-exercise compared with pre-exercise (p = 0.021) but not 3 h post-exercise (p = 0.084) without correction for plasma volume shifts. However, adiponectin concentrations were not different at any time point when plasma volume shifts were accounted for (p > 0.05). Total ghrelin and acylated ghrelin concentrations were not affected at post and 3 h post-exercise compared with pre-exercise, with and without correcting for plasma volume shifts, regardless of ambient temperature (p > 0.05). No differences in leptin, adiponectin, or ghrelin were found between trials (p > 0.05).

CONCLUSION

Temperature does not affect the circulating concentrations of appetite-regulating hormones during an acute bout of endurance exercise.

Leptin-programmed rats respond to cold exposure changing hypothalamic leptin receptor and thyroid function differently from cold-exposed controls

We showed that neonatal leptin treatment programmes for hyperleptinemia and central leptin resistance both at 30days-old and adulthood, while programmes for lower serum T3 at 30days-old, but higher thyroid hormones (TH) at adulthood. As in these animals, acute cold at 30days-old normalized leptinemia and restored the expression of hypothalamic leptin receptor (OBR), here we evaluate the effect of cold exposure on the thyroid function and OBR in adult rats programmed by neonatal hyperleptinemia. Pups were divided into 2 groups: Lep-injected with leptin (8μg/100g/BW, sc) for the first 10days of lactation, and C-injected with saline. At 150days, both groups were subdivided into: LepC and CC, which were exposed to 8°C for 12h. Serum leptin, TH, TSH, liver type I and brown adipose tissue (BAT) type II deiodinases (D1 and D2) activities, liver mitochondrial alpha-glycerol-3-phosphate dehydrogenase (mGPD) activity and adrenal catecholamine content were measured. Hypothalamic and thyroid OBR protein contents were evaluated. Differences were significant when p<0.05. Lep group had hyperleptinemia (+19%), higher T4 (+20%) and T3 (+30%) with lower TSH (-55%), higher liver D1 (1.4 fold-increase), lower BAT D2 (-44%) and liver mGPD activities (-55%), higher adrenal catecholamines (+44%), lower hypothalamic OBR (-51%) and normal thyroid OBR. Cold exposure normalized leptinemia, D1, mGPD, catecholamine and hypothalamic OBR. However, cold exposure further increased TH and decreased D2. Thus, cold exposure normalizes most of the changes programmed by neonatal hyperleptinemia, at the expense of worsening the hyperthyroidism and BAT thermogenesis.

Programming of rat adrenal medulla by neonatal hyperleptinemia: adrenal morphology, catecholamine secretion, and leptin signaling pathway

Leptin serum concentration in early life is an important factor for adequate future development of the offspring. Previously, we demonstrated that hyperleptinemia on lactation programmed for hyperleptinemia, central leptin resistance with lower expression of the long form of leptin receptor at hypothalamus, and higher medullary catecholamine levels with cardiovascular consequences at adulthood. The central objective of this study was to determine the direct effect of leptin on adrenal medullary function of adult rats that were leptin treated during lactation. Adrenal morphology was also accessed. Recombinant murine leptin was injected in the pups during the first 10 days of life (group L, leptin-programmed) or at adulthood during 6 days (group LC). The controls of both experiments received saline (groups C and CC). Both treatments resulted in hyperleptinemia at 150 days old (+78% and 2-fold increase, respectively; P < 0.05). Programmed animals showed hypertrophy of adrenal and higher adrenal catecholamine content at 150 days old (3-fold increase, P < 0.05), and no changes were observed in the LC group. However, LC rats had lower adrenal content of tyrosine hydroxylase (-17%, P < 0.05). Leptin-programmed rats had a lower response to leptin in vitro stimulation (-22%, P < 0.05) and lower expression of key proteins of the leptin signaling pathway, leptin receptor and janus tyrosine kinase 2 in the medullas (-61% and -29%, respectively, P < 0.05). However, they presented higher expression of phosphorylated signal transducer and activator of transcription 3 (+2-fold, P < 0.05). Leptin treatment at adulthood did not affect these parameters. The higher catecholamine synthesis and secretion in the leptin-programmed rats observed in our previous study does not seem to be a consequence of the direct effect of leptin on the medullas. We suggest that the hyperleptinemia of the programmed animals increases adrenal medullary function through sympathetic nervous system activation. In conclusion, high leptin levels on lactation program the activity of the sympathoadrenal system at adulthood that may contribute to the development of adult chronic diseases such as hypertension.

Postnatal early overnutrition changes the leptin signalling pathway in the hypothalamic-pituitary-thyroid axis of young and adult rats

Postnatal early overnutrition (EO) is a risk factor for obesity in adult life. Rats raised in a small litter can develop hyperinsulinaemia, hyperphagia, hyperleptinaemia and hypertension as adults. Since leptin regulates the hypothalamic-pituitary-thyroid axis and the metabolism of thyroid hormones, we studied the leptin signalling pathway in pituitary and thyroid glands of the postnatal EO model. To induce EO, at the third day of lactation the litter size was reduced to three pups per litter (SL group). In control litters (NL group), the litter size was adjusted to 10 pups per litter. Body weight and food intake were monitored. Rat offspring were killed at 21 (weaning) and 180 days old (adulthood). Plasma thyroid hormones, thyroid-stimulating hormone (TSH) and leptin were measured by radioimmunoassay. Proteins of the leptin signalling pathway were analysed by Western blotting. Body weight of offspring in the SL group was higher from the seventh day of lactation (+33%, P < 0.05) until 180 days old (+18%, P < 0.05). Offspring in the SL group showed higher visceral fat mass at 21 and 180 days old (+176 and +52%, respectively, P < 0.05), but plasma leptin was higher only at 21 days (+88%, P < 0.05). The SL offspring showed higher plasma TSH, 3,5,3'-triiodothronine (T(3)) and thyroxine (T(4)) at 21 days (+60, +91 and +68%, respectively, P < 0.05), while the opposite was observed at 180 days regarding thyroid hormones (T(3), -10%; and T(4), -30%, P < 0.05), with no difference in TSH levels. In hypothalamus, no change was observed in the leptin signalling pathway at 21 days. However, lower janus thyrosine kinase 2 (JAK2) and phosphorilated-signal transducer and activator of transcription-3 (p-STAT3) content were detected in adulthood. In pituitary, the SL group presented higher leptin receptors (Ob-R), JAK2 and p-STAT3 content at 21 days and lower JAK2 and STAT3 content at 180 days old. In contrast, in thyroid, the Ob-R expression was lower in young SL rats, while the adult SL group presented higher Ob-R and JAK2 content. We showed that postnatal EO induces short- and long-term effects upon the hypothalamic-pituitary-thyroid axis. These changes may help to explain future development of metabolic and endocrine dysfunctions, such as metabolic syndrome and hypothyroidism.

Neonatal hyperleptinaemia programmes anxiety-like and novelty seeking behaviours but not memory/learning in adult rats

Leptin treatment during lactation programmes for leptin resistance at adulthood, evidenced by hyperleptinaemia, hyperphagia and overweight. Since leptin is known to affect stress response, emotional behaviour and memory/learning performance, the objective of the present study was to evaluate whether neonatal hyperleptinaemia programmes anxiety-like and novelty-seeking behaviours as well as memory/learning in adult male rats. During the first 10 days of lactation (from PN1 to PN10), pups were s.c. injected once per day with either 50 microL of saline (SAL) or murine leptin (LEP - 8 microg/100 g of body mass, saline diluted). Serum leptin was assessed at PN10 and at PN150. Two separate experiments were carried out: 1) experiment one: at PN137, 29 SAL and 30 LEP rats were tested in the elevated plus-maze (EPM) and, at PN142, their behaviour was assessed in the hole board (HB) arena; 2) experiment two: at PN140, a different group of rats consisting of 53 SAL and 56 LEP animals were tested in the radial arm water maze (RAWM). Serum leptin concentration was higher in the LEP group at PN10 and at PN150. LEP animals spent significantly less time in the open arms of the EPM. Furthermore, the number of nose-pokes in the HB arena was higher in LEP rats. There were no differences between groups regarding latency to find the hidden platform in the RAWM. Our results suggests that a central mechanism of leptin resistance at adulthood, caused by neonatal hyperleptinaemia, is associated with an increased level of anxiety and also that it intensifies novelty seeking-behaviour.

Role of neonatal hyperleptinaemia on serum adiponectin and suppressor of cytokine signalling-3 expression in young rats

Previously we had shown that neonatal leptin treatment programmes for both hyperleptinaemia and hyperinsulinaemia, which lead to leptin resistance and low expression of the hypothalamic leptin receptor (OB-Rb) of rats aged 150 d. Here we investigated in young post-weaned rats (age 30 d) if leptin treatment during lactation induces leptin and insulin resistance and if those changes are accompanied by changes in the suppressor of cytokine signalling-3 (SOCS-3) expression and serum adiponectin concentration. After delivery, the pups were divided into two groups: (1) a leptin group (Lep) that were injected with leptin daily (8 microg/100 g body weight subcutaneously) for the first 10 d of lactation; (2) a control (C) group, receiving saline. After weaning (day 21), body weight was monitored until the animals were age 30 d. They were tested for food intake in response to either leptin (0.5 mg/kg body weight intraperitoneally) (CL, LepL) or saline (CSal, LepSal) when they were aged 30 d. The CL group showed lower food intake, but no response was observed in the LepL group, suggesting leptin resistance. The Lep group had hyperleptinaemia (five-fold), hyperinsulinaemia (+42.5%) and lower levels of serum adiponectin (-43.2%). The hypothalamic expression of OB-Rb was lower (-22%) and SOCS-3 was higher (+52.8%) in the Lep group. We conclude that neonatal leptin treatment programmes for leptin resistance as soon as 30 d and suggests that SOCS-3 appears to be of particular importance in this event. In the Lep group, the lower serum adiponectin levels were accompanied by higher serum insulin, indicating a probable insulin resistance.