Leptin treatment during lactation programs leptin synthesis, intermediate metabolism, and liver microsteatosis in adult rats

Early Life Nutrition and Energy Balance Disorders in Offspring in Later Life

The global pandemic of obesity and type 2 diabetes is often causally linked to changes in diet and lifestyle; namely increased intake of calorically dense foods and concomitant reductions in physical activity. Epidemiological studies in humans and controlled animal intervention studies have now shown that nutritional programming in early periods of life is a phenomenon that affects metabolic and physiological functions throughout life. This link is conceptualised as the developmental programming hypothesis whereby environmental influences during critical periods of developmental plasticity can elicit lifelong effects on the health and well-being of the offspring. The mechanisms by which early environmental insults can have long-term effects on offspring remain poorly defined. However there is evidence from intervention studies which indicate altered wiring of the hypothalamic circuits that regulate energy balance and epigenetic effects including altered DNA methylation of key adipokines including leptin. Studies that elucidate the mechanisms behind these associations will have a positive impact on the health of future populations and adopting a life course perspective will allow identification of phenotype and markers of risk earlier, with the possibility of nutritional and other lifestyle interventions that have obvious implications for prevention of non-communicable diseases.

Maternal high-fat diet induces obesity and adrenal and thyroid dysfunction in male rat offspring at weaning

Maternal nutritional status affects the future development of offspring. Both undernutrition and overnutrition in critical periods of life (gestation or lactation) may cause several hormonal changes in the pups and programme obesity in the adult offspring. We have shown that hyperleptinaemia during lactation results in central leptin resistance, higher adrenal catecholamine secretion, hyperthyroidism, and higher blood pressure and heart rate in the adult rats. Here, we evaluated the effect of a maternal isocaloric high-fat diet on breast milk composition and its impact on leptinaemia, energy metabolism, and adrenal and thyroid function of the offspring at weaning. We hypothesised that the altered source of fat in the maternal diet even under normal calorie intake would disturb the metabolism of the offspring. Female Wistar rats were fed a normal (9% fat; C group) or high-fat diet (29% fat as lard; HF group) for 8 weeks before mating and during pregnancy and lactation. HF mothers presented increased total body fat content after 8 weeks (+27%, P < 0.05) and a similar fat content at the end of lactation. In consequence, the breast milk from the HF group had higher concentration of protein (+18%, P < 0.05), cholesterol (+52%, P < 0.05) and triglycerides (+86%, P < 0.05). At weaning, HF offspring had increased body weight (+53%, P < 0.05) and adiposity (2 fold, P < 0.05), which was associated with lower β3-adrenoreceptor content in adipose tissue (-40%, P < 0.05). The offspring also presented hyperglycaemia (+30%, P < 0.05) and hyperleptinaemia (+62%, P < 0.05). In the leptin signalling pathway in the hypothalamus, we found lower p-STAT3/STAT3 (-40%, P < 0.05) and SOCS3 (-55%, P < 0.05) content in the arcuate nucleus, suggesting leptin resistance. HF offspring also had higher adrenal catecholamine content (+17%, P < 0.05), liver glycogen content (+50%, P < 0.05) and hyperactivity of the thyroid axis at weaning. Our results suggest that a high fat diet increases maternal body fat and this additional energy is transferred to the offspring during lactation, since at weaning the dams had normal fat and the pups were obese. The higher fat and protein concentrations in the breast milk seemed to induce early overnutrition in the HF offspring. In addition to storing energy as fat, the HF offspring had a larger reserve of glycogen and hyperglycaemia that may have resulted from increased gluconeogenesis. Hyperleptinaemia may stimulate both adrenal medullary and thyroid function, which may contribute to the development of cardiovascular diseases. These early changes induced by the maternal high-fat diet may contribute to development of metabolic syndrome.

Programmed changes in the adult rat offspring caused by maternal protein restriction during gestation and lactation are attenuated by maternal moderate–low physical training

The effects of maternal moderate–low physical training on postnatal development, glucose homeostasis and leptin concentration in adult offspring subjected to a low-protein diet during the perinatal period were investigated. Male Wistar rats (aged 150 d old) were divided into four groups according to maternal group: untrained (NTp, n 8); trained (Tp, n 8); untrained with a low-protein diet (NT+LPp, n 8); trained with a low-protein diet (T+LPp, n 8). The trained mothers were subjected to a protocol of moderate physical training over a period of 4 weeks (treadmill, 5 d/week, 60 min/d, at 65 % VO2max) before mating. At pregnancy, the intensity and duration of exercise was progressively reduced (50–20 min/d, at 65–30 % VO2max). The low-protein diet groups received an 8 % casein diet, and their peers received a 17 % casein diet during gestation and lactation. The pups' birth weight and somatic growth were recorded weekly up to the 150th day. Fasting blood glucose, cholesterol, serum leptin concentration, glucose and insulin tolerance tests were evaluated. The Tp animals showed no changes in somatic and biochemical parameters, while the NT+LPp group showed a greater abdominal circumference, hyperglycaemia, hypercholesterolaemia, glucose intolerance and lower plasma leptin. In the T+LPp animals, all of those alterations were reversed except for plasma leptin concentration. In conclusion, the effects of a perinatal low-protein diet on growth and development, glucose homeostasis and serum leptin concentration in the offspring were attenuated in pups from trained mothers.

The Δ337T mutation on the TRβ causes alterations in growth, adiposity, and hepatic glucose homeostasis in mice

Mice bearing the genomic mutation Δ337T on the thyroid hormone receptor β (TRβ) gene present the classical signs of resistance to thyroid hormone (TH), with high serum TH and TSH. This mutant TR is unable to bind TH, remains constitutively bound to co-repressors, and has a dominant negative effect on normal TRs. In this study, we show that homozygous (TRβΔ337T) mice for this mutation have reduced body weight, length, and body fat content, despite augmented relative food intake and relative increase in serum leptin. TRβΔ337T mice exhibited normal glycemia and were more tolerant to an i.p. glucose load accompanied by reduced insulin secretion. Higher insulin sensitivity was observed after single insulin injection, when the TRβΔ337T mice developed a profound hypoglycemia. Impaired hepatic glucose production was confirmed by the reduction in glucose generation after pyruvate administration. In addition, hepatic glycogen content was lower in homozygous TRβΔ337T mice than in wild type. Collectively, the data suggest that TRβΔ337T mice have deficient hepatic glucose production, by reduced gluconeogenesis and lower glycogen deposits. Analysis of liver gluconeogenic gene expression showed a reduction in the mRNA of phosphoenolpyruvate carboxykinase, a rate-limiting enzyme, and of peroxisome proliferator-activated receptor-γ coactivator 1α, a key transcriptional factor essential to gluconeogenesis. Reduction in both gene expressions is consistent with resistance to TH action via TRβ, reproducing a hypothyroid phenotype. In conclusion, mice carrying the Δ337T-dominant negative mutation on the TRβ are leaner, exhibit impaired hepatic glucose production, and are more sensitive to hypoglycemic effects of insulin.

Knockout of the neurokinin-1 receptor reduces cholangiocyte proliferation in bile duct-ligated mice

In bile duct-ligated (BDL) rats, cholangiocyte proliferation is regulated by neuroendocrine factors such as α-calcitonin gene-related peptide (α-CGRP). There is no evidence that the sensory neuropeptide substance P (SP) regulates cholangiocyte hyperplasia. Wild-type (WT, (+/+)) and NK-1 receptor (NK-1R) knockout (NK-1R(-/-)) mice underwent sham or BDL for 1 wk. Then we evaluated 1) NK-1R expression, transaminases, and bilirubin serum levels; 2) necrosis, hepatocyte apoptosis and steatosis, and the number of cholangiocytes positive by CK-19 and terminal deoxynucleotidyl transferase biotin-dUTP nick-end labeling in liver sections; 3) mRNA expression for collagen 1α and α-smooth muscle (α-SMA) actin in total liver samples; and 4) PCNA expression and PKA phosphorylation in cholangiocytes. In cholangiocyte lines, we determined the effects of SP on cAMP and D-myo-inositol 1,4,5-trisphosphate levels, proliferation, and PKA phosphorylation. Cholangiocytes express NK-1R with expression being upregulated following BDL. In normal NK-1R(-/-) mice, there was higher hepatocyte apoptosis and scattered hepatocyte steatosis compared with controls. In NK-1R (-)/(-) BDL mice, there was a decrease in serum transaminases and bilirubin levels and the number of CK-19-positive cholangiocytes and enhanced biliary apoptosis compared with controls. In total liver samples, the expression of collagen 1α and α-SMA increased in BDL compared with normal mice and decreased in BDL NK-1R(-/-) compared with BDL mice. In cholangiocytes from BDL NK-1R (-)/(-) mice there was decreased PCNA expression and PKA phosphorylation. In vitro, SP increased cAMP levels, proliferation, and PKA phosphorylation of cholangiocytes. Targeting of NK-1R may be important in the inhibition of biliary hyperplasia in cholangiopathies.

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.

Neonatal exposure to leptin reduces glucose tolerance in adult mice

AIM

The aim of this study was to evaluate the effect of leptin treatment in mouse neonates on glucose metabolism in adulthood.

METHODS

Leptin was administered subcutaneously to normally nourished neonates, from 5.5 to 10.5 days of age, to mimic the premature surge observed in neonates undernourished in utero. At 15-16 weeks of age, we measured blood glucose or insulin levels after the intraperitoneal administration of glucose or insulin.

RESULTS

After the intraperitoneal administration of glucose, the levels of blood glucose, but not insulin, in adult mice that received the neonatal leptin treatment were significantly higher than that of those which received vehicle control. After the intraperitoneal administration of insulin, the levels of blood glucose in adult mice that underwent neonatal leptin treatment were significantly higher than that of those which received vehicle control.

CONCLUSION

These findings suggest that the premature leptin surge plays an essential role, as a programming signal during the early neonatal period, as well as in the developmental origins of impaired insulin sensitivity.

Litter size variation in hypothalamic gene expression determines adult metabolic phenotype in Brandt's voles (Lasiopodomys brandtii)

Background

Early postnatal environments may have long-term and potentially irreversible consequences on hypothalamic neurons involved in energy homeostasis. Litter size is an important life history trait and negatively correlated with milk intake in small mammals, and thus has been regarded as a naturally varying feature of the early developmental environment. Here we investigated the long-term effects of litter size on metabolic phenotype and hypothalamic neuropeptide mRNA expression involved in the regulation of energy homeostasis, using the offspring reared from large (10–12) and small (3–4) litter sizes, of Brandt's voles (Lasiopodomys brandtii), a rodent species from Inner Mongolia grassland in China.

Methodology/Principal Findings

Hypothalamic leptin signaling and neuropeptides were measured by Real-Time PCR. We showed that offspring reared from small litters were heavier at weaning and also in adulthood than offspring from large litters, accompanied by increased food intake during development. There were no significant differences in serum leptin levels or leptin receptor (OB-Rb) mRNA in the hypothalamus at weaning or in adulthood, however, hypothalamic suppressor of cytokine signaling 3 (SOCS3) mRNA in adulthood increased in small litters compared to that in large litters. As a result, the agouti-related peptide (AgRP) mRNA increased in the offspring from small litters.

Conclusions/Significance

These findings support our hypothesis that natural litter size has a permanent effect on offspring metabolic phenotype and hypothalamic neuropeptide expression, and suggest central leptin resistance and the resultant increase in AgRP expression may be a fundamental mechanism underlying hyperphagia and the increased risk of overweight in pups of small litters. Thus, we conclude that litter size may be an important and central determinant of metabolic fitness in adulthood.