The involvement of leptin in humans revealed by mutations in leptin and leptin receptor genes

Molecular genetics of human obesity: A comprehensive review

Obesity and its related health complications is a major problem worldwide. Hypothalamus and their signalling molecules play a critical role in the intervening and coordination with energy balance and homeostasis. Genetic factors play a crucial role in determining an individual's predisposition to the weight gain and being obese. In the past few years, several genetic variants were identified as monogenic forms of human obesity having success over common polygenic forms. In the context of molecular genetics, genome-wide association studies (GWAS) approach and their findings signified a number of genetic variants predisposing to obesity. However, the last couple of years, it has also been noticed that alterations in the environmental and epigenetic factors are one of the key causes of obesity. Hence, this review might be helpful in the current scenario of molecular genetics of human obesity, obesity-related health complications (ORHC), and energy homeostasis. Future work based on the clinical discoveries may play a role in the molecular dissection of genetic approaches to find more obesity-susceptible gene loci.

Identification of the Long-Sought Leptin in Chicken and Duck: Expression Pattern of the Highly GC-Rich Avian leptin Fits an Autocrine/Paracrine Rather Than Endocrine Function

More than 20 years after characterization of the key regulator of mammalian energy balance, leptin, we identified the leptin (LEP) genes of chicken (Gallus gallus) and duck (Anas platyrhynchos). The extreme guanine-cytosine content (∼70%), the location in a genomic region with low-complexity repetitive and palindromic sequence elements, the relatively low sequence conservation, and low level of expression have hampered the identification of these genes until now. In vitro-expressed chicken and duck leptins specifically activated signaling through the chicken leptin receptor in cell culture. In situ hybridization demonstrated expression of LEP mRNA in granular and Purkinje cells of the cerebellum, anterior pituitary, and in embryonic limb buds, somites, and branchial arches, suggesting roles in adult brain control of energy balance and during embryonic development. The expression patterns of LEP and the leptin receptor (LEPR) were explored in chicken, duck, and quail (Coturnix japonica) using RNA-sequencing experiments available in the Short Read Archive and by quantitative RT-PCR. In adipose tissue, LEP and LEPR were scarcely transcribed, and the expression level was not correlated to adiposity. Our identification of the leptin genes in chicken and duck genomes resolves a long lasting controversy regarding the existence of leptin genes in these species. This identification was confirmed by sequence and structural similarity, conserved exon-intron boundaries, detection in numerous genomic, and transcriptomic datasets and characterization by PCR, quantitative RT-PCR, in situ hybridization, and bioassays. Our results point to an autocrine/paracrine mode of action for bird leptin instead of being a circulating hormone as in mammals.

Role of genetic susceptibility in development of treatment-related adverse outcomes in cancer survivors

Clear and unambiguous associations have been established between therapeutic exposures and specific complications. However, considerable interindividual variability is observed in the risk of developing an outcome for a given therapeutic exposure. Genetic predisposition and especially its interaction with therapeutic exposures can potentially exacerbate the toxic effect of treatment on normal tissues and organ systems, and can possibly explain the interindividual variability. This article provides a brief overview of the current knowledge about the role of genomic variation in the development of therapy-related complications. Relatively common outcomes with strong associations with therapeutic exposures, including cardiomyopathy, obesity, osteonecrosis, ototoxicity, and subsequent malignancies are discussed here. To develop a deeper understanding of the molecular underpinnings of therapy-related complications, comprehensive and near-complete collection of clinically annotated samples is critical. Methodologic issues such as study design, definition of the endpoints or phenotypes, identification of appropriate and adequately sized study population together with a reliable plan for collecting and maintaining high-quality DNA, and selection of an appropriate approach or platform for genotyping are also discussed. Understanding the etiopathogenetic pathways that lead to the morbidity is critical to developing targeted prevention and intervention strategies, optimizing risk-based health care of cancer survivors, thus minimizing chronic morbidities and improving quality of life.

Lactococci and lactobacilli as mucosal delivery vectors for therapeutic proteins and DNA vaccines

Food-grade Lactic Acid Bacteria (LAB) have been safely consumed for centuries by humans in fermented foods. Thus, they are good candidates to develop novel oral vectors, constituting attractive alternatives to attenuated pathogens, for mucosal delivery strategies. Herein, this review summarizes our research, up until now, on the use of LAB as mucosal delivery vectors for therapeutic proteins and DNA vaccines. Most of our work has been based on the model LAB Lactococcus lactis, for which we have developed efficient genetic tools, including expression signals and host strains, for the heterologous expression of therapeutic proteins such as antigens, cytokines and enzymes. Resulting recombinant lactococci strains have been tested successfully for their prophylactic and therapeutic effects in different animal models: i) against human papillomavirus type 16 (HPV-16)-induced tumors in mice, ii) to partially prevent a bovine β-lactoglobulin (BLG)-allergic reaction in mice and iii) to regulate body weight and food consumption in obese mice. Strikingly, all of these tools have been successfully transposed to the Lactobacillus genus, in recent years, within our laboratory. Notably, anti-oxidative Lactobacillus casei strains were constructed and tested in two chemically-induced colitis models. In parallel, we also developed a strategy based on the use of L. lactis to deliver DNA at the mucosal level, and were able to show that L. lactis is able to modulate the host response through DNA delivery. Today, we consider that all of our consistent data, together with those obtained by other groups, demonstrate and reinforce the interest of using LAB, particularly lactococci and lactobacilli strains, to develop novel therapeutic protein mucosal delivery vectors which should be tested now in human clinical trials.

ENU mutagenesis identifies mice with morbid obesity and severe hyperinsulinemia caused by a novel mutation in leptin

BACKGROUND

Obesity is a multifactorial disease that arises from complex interactions between genetic predisposition and environmental factors. Leptin is central to the regulation of energy metabolism and control of body weight in mammals.

METHODOLOGY/PRINCIPAL FINDINGS

To better recapitulate the complexity of human obesity syndrome, we applied N-ethyl-N-nitrosourea (ENU) mutagenesis in combination with a set of metabolic assays in screening mice for obesity. Mapping revealed linkage to the chromosome 6 within a region containing mouse Leptin gene. Sequencing on the candidate genes identified a novel T-to-A mutation in the third exon of Leptin gene, which translates to a V145E amino acid exchange in the leptin propeptide. Homozygous Leptin(145E/145E) mutant mice exhibited morbid obesity, accompanied by adipose hypertrophy, energy imbalance, and liver steatosis. This was further associated with severe insulin resistance, hyperinsulinemia, dyslipidemia, and hyperleptinemia, characteristics of human obesity syndrome. Hypothalamic leptin actions in inhibition of orexigenic peptides NPY and AgRP and induction of SOCS1 and SOCS3 were attenuated in Leptin(145E/145E) mice. Administration of exogenous wild-type leptin attenuated hyperphagia and body weight increase in Leptin(145E/145E) mice. However, mutant V145E leptin coimmunoprecipitated with leptin receptor, suggesting that the V145E mutation does not affect the binding of leptin to its receptor. Molecular modeling predicted that the mutated residue would form hydrogen bond with the adjacent residues, potentially affecting the structure and formation of an active complex with leptin receptor within that region.

CONCLUSIONS/SIGNIFICANCE

Thus, our evolutionary, structural, and in vivo metabolic information suggests the residue 145 as of special function significance. The mouse model harboring leptin V145E mutation will provide new information on the current understanding of leptin biology and novel mouse model for the study of human obesity syndrome.

High incidence of fatty liver and insulin resistance in long-term adult survivors of childhood SCT

Overweight/obesity among adult survivors of childhood SCT has been considered to be predictive of eventual development of metabolic abnormalities. Fatty liver is increasingly recognized as a major cause of liver-related morbidity and mortality in the general population. However, the real incidence of fatty liver in adult survivors of SCT has not been fully elucidated. We determined whether adult survivors are at risk for overweight/obesity, metabolic abnormalities and fatty liver and whether these risks are associated with cranial radiotherapy (CRT) before SCT. Among the 51 patients (30 males), only two male patients were overweight/obese at the last evaluation. On the other hand, 9 male (30%) and 15 female (71%) patients were underweight. Fatty liver was diagnosed in 11 male (37%) and 10 female (48%) patients during the follow-up period, although patients who had fatty liver did not tend to be overweight/obese. Significantly more patients who received CRT before SCT developed fatty liver with insulin resistance than those who did not (P<0.05). Even patients who are not overweight/obese may develop fatty liver and metabolic abnormalities. We recommend that healthcare professionals recognize these risks and give life-long attention to detecting, preventing and treating late complications after SCT.

Changes in body composition after childhood cancer treatment: Impact on future health status—A review

PURPOSE

To describe data on changes in body composition in childhood cancer survivors. Underlying mechanisms in development of obesity are addressed, in order to discuss intervention strategies.

METHODS

A systematic literature search was undertaken with a number of search terms.

RESULTS

Female survivors of ALL and brain tumours, especially if treated with cranial irradiation, showed a higher prevalence of obesity compared with the general population, while survivors of other malignancies had a higher prevalence of underweight. Influences of corticosteroid treatment and cytostatics on body composition are uncertain. Diminished physical activity, early adiposity rebound (<5 years of age) and/or hypothalamic involvement of tumour or treatment, and subsequent growth hormone deficiency, may play a role in the development of obesity in childhood cancer survivors.

CONCLUSION

Longitudinal prospective studies in more extensive cohorts are necessary to estimate actual prevalence and facilitate the unravelling of the underlying mechanisms in change of body composition.

Effects of intranasal administration of a leptin-secreting Lactococcus lactis recombinant on food intake, body weight, and immune response of mice

Leptin is an adipocyte-derived pleiotropic hormone that modulates a large number of physiological functions, including control of body weight and regulation of the immune system. In this work, we show that a recombinant strain of the food-grade lactic acid bacterium Lactococcus lactis (LL-lep) can produce and efficiently secrete human leptin. The secreted leptin is a fully biologically active hormone, as demonstrated by its capacity to stimulate a STAT3 reporter gene in HEK293 cells transfected with the Ob-Rb leptin receptor. The immunomodulatory activity of leptin-secreting L. lactis was evaluated in vivo by coexpression with the human papillomavirus type 16 E7 protein. In C57BL/6 mice immunized intranasally with a recombinant L. lactis strain coproducing leptin and E7 antigen, the adaptive immune response was significantly higher than in mice immunized with recombinant L. lactis producing only E7 antigen, demonstrating adjuvanticity of leptin. We then analyzed the effects of intranasally administered LL-lep in obese ob/ob mice. We observed that daily administration of LL-lep to these mice significantly reduced body weight gain and food intake. These results demonstrate that leptin can be produced and secreted in an active form by L. lactis and that leptin-producing L. lactis regulates in vivo antigen-specific immune responses, as well as body weight and food consumption.

Genetic susceptibility and body mass in childhood cancer survivors

Childhood cancer survivors are at increased risk of many long-term treatment-related sequel such as second cancers, cardiovascular disease, and pulmonary complications. Certain treatments seem to influence the risk of becoming overweight, obese, or underweight, and abnormal body mass index (BMI) is associated with increased morbidity and mortality. Because BMI is modifiable, it is important to identify treatment and patient-related factors contributing to altered BMI. New research areas include exploring how genetic susceptibility through population polymorphism may contribute to BMI. Illuminating potential gene-environment interactions that influence obesity and underweight might be more readily accomplished in a study of high-risk individuals (i.e., childhood cancer survivors) with well-characterized exposures. The new Childhood Cancer Research Network in the Children's Oncology Group, when fully implemented, should make it less difficult in the future to recruit the large numbers of patients needed for such studies.

Genetics of human obesity

This chapter presents the current state of knowledge in the field of the genetics of human obesity. The molecular approach has proved to be powerful in defining new syndromes associated with obesity. The pivotal role of leptin and melanocortin pathways has been recognized, but only in rare cases of obesity. In the more common form of obesity a multitude of polymorphisms located in genes and candidate regions throughout the genome regulate an individual's susceptibility to weight gain in a permissive environment. The effects are often uncertain and the results not always confirmed. Combining these single nucleotide polymorphisms and defining the associated risks for obesity will be a real challenge in the future. It is now necessary to integrate data of various origins (environment, genotype, expression) to clarify this field.

Genetics of human obesity

We present the knowledge acquired in the field of the genetics of human obesity. The molecular approach proved to be powerful to define new syndromes associated to obesity. The pivotal role of leptin and melanocortin pathways were recognized but in rare obesity cases. In the commoner form of obesities, a multitude of polymorphisms located in genes and candidate regions participate in an individual susceptibility to weight gain in a permissive environment. The effects are often uncertain and the results not always confirmed. It is now necessary to integrate data of various origins (environment, genotype, expression) to clarify the domain.

Genetic Variation in the Leptin Receptor Gene and Obesity in Survivors of Childhood Acute Lymphoblastic Leukemia: A Report From the Childhood Cancer Survivor Study

Purpose

Overweight (body mass index [BMI] 25 to 29 kg/m2) and obesity (BMI ≥ 30 kg/m2) frequently follow treatment for childhood acute lymphoblastic leukemia (ALL). Recent studies suggest that risk is most apparent in females treated with cranial radiation at a younger age. Because radiation at a young age may affect the hypothalamus causing leptin receptor insensitivity, we hypothesized that a polymorphism in the leptin receptor (LEPR) gene, Gln223Arg, might influence susceptibility to obesity in survivors of childhood ALL.

Patients and Methods

We genotyped 600 non-Hispanic white adult ALL survivors enrolled onto the Childhood Cancer Survivor Study. BMI was compared between those with two copies of the Arg allele to those who had at least one copy of the Gln allele.

Results

Female survivors with BMI ≥ 25 kg/m2were more likely Arg homozygous than those with BMI less than 25 kg/m2(24% v 12%; P = .007). This difference was not observed in males. Moreover, among females treated with ≥ 20 Gy cranial radiation, Arg/Arg individuals had six times higher odds of having BMI ≥ 25 kg/m2(95% CI, 2.1 to 22.0) than those with a Gln allele (P = .04 for interaction).

Conclusion

LEPR polymorphism may influence obesity in female survivors of childhood ALL, particularly those exposed to cranial radiation. Because obesity is associated with increased morbidity and mortality in later life, identification of children at high risk might allow for early targeted interventions.

Gamma-aminobutyric acid neurons integrate and rapidly transmit permissive and inhibitory metabolic cues to gonadotropin-releasing hormone neurons

Negative energy balance inhibits fertility by decreasing GnRH release; however, the mechanisms are not well understood. GnRH neurons can be excited by activation of gamma-aminobutyric acid (GABA)(A) receptors, and GABAergic neurons provide a major synaptic input. We hypothesized that permissive metabolic signals mediated by leptin and inhibitory signals conveyed by neuropeptide Y (NPY) and opiates rapidly alter GABA(A) receptor-mediated drive to GnRH neurons. In fed and fasted female mice, GABAergic postsynaptic currents (PSCs) were recorded from GnRH neurons before and after in vitro treatment with leptin, NPY, or met-enkephalin. Leptin increased PSC frequency in fed and fasted mice, indicating that it increased presynaptic activity. Leptin also increased PSC size. Inhibiting leptin receptor signaling pathways within GnRH neurons abolished the latter effect, indicating a direct action on these cells. In fed, but not fasted, mice, NPY and met-enkephalin decreased PSC frequency in an antagonist-reversible manner, but did not alter PSC size. NPY-1 receptor antagonists alone increased frequency in fed and fasted mice, as did opiate receptor blockade in fasted animals, suggesting that endogenous NPY and opiates modulate GABAergic drive to GnRH neurons. These data suggest that GABAergic afferents integrate metabolic signals for delivery to GnRH neurons. Decreased sensitivity to NPY and opiates in fasted mice indicate that these peptides send physiologically relevant signals regarding energy balance to GnRH neurons.

Metabolic regulation of fertility through presynaptic and postsynaptic signaling to gonadotropin-releasing hormone neurons

Gonadotropin-releasing hormone (GnRH) neurons form the final common pathway for the central regulation of reproduction and are inhibited by negative energy balance. In normal adults, these neurons maintain elevated intracellular chloride so that GABA(A) receptor activation is excitatory. We hypothesized that fasting alters homeostatic mechanisms to eliminate excitatory responses to GABA but rejected this hypothesis when brief, local GABA application elicited action currents in GnRH neurons from fed and fasted mice. This response was specific to GABA(A) receptors, because glycine elicited no response. We next found that fasting reduced the frequency of spontaneous GABAergic postsynaptic currents (PSCs) and that this was reversed by in vivo treatment with leptin during the fast. In the presence of tetrodotoxin to minimize presynaptic actions, leptin also potentiated the postsynaptic response of these cells to GABA(A) receptor activation. Postsynaptic effects of leptin on GABAergic miniature PSCs were eliminated by inhibiting JAK2/3 (Janus kinase), the tyrosine kinase through which leptin receptors signal. In all experiments, elimination of PSCs at ECl or by treatment with the GABAA receptor antagonist bicuculline confirmed that PSCs were specifically mediated by GABA(A) receptor chloride channels. These data demonstrate that fasting and leptin act presynaptically and postsynaptically to alter GABAergic drive to GnRH neurons, providing evidence for GABAergic communication of metabolic cues to GnRH neurons, and suggest the possibility for functional leptin receptors on GnRH neurons. They further demonstrate cytokine modulation of the postsynaptic response to GABA in mammals, which may be important to central neural regulation in both healthy and diseased states.

Identification of three single nucleotide polymorphisms in the chicken insulin-like growth factor 1 and 2 genes and their associations with growth and feeding traits

The chicken insulin-like growth factor (IGF)1 and IGF2 genes have been partially sequenced in six individuals of each of two chicken strains of the Black Penedesenca breed (PN and MN). These two strains are genetically diverse for growth traits. Sequence alignment revealed the existence of three single nucleotide polymorphisms (SNP) (IGF1-SNP1, IGF2-SNP2, and IGF2-SNP3). These three SNP and a fourth IGF1 polymorphism (IGF1-SNP4) were typed in 60 individuals from each strain by using PCR-RFLP or primer extension analysis. No significant associations among these four SNP, growth traits, and plasma IGF1 concentration were identified. In contrast, suggestive associations (P < or = 0.05) were found between IGF1-SNP1 and average daily gain at 107 d and feed efficiency at 44, 73, and 107 d. However, these associations were not simultaneously found in both strains suggesting that they might have been produced by linkage disequilibrium with another mutation located in the IGF1 locus or another linked gene. Since the PN and MN strains differ very markedly on their feed intake, the chicken leptin gene was included in the sequence analysis. Unfortunately, attempts to amplify several regions of this gene were unsuccessful. Even when primers complementary to highly conserved regions were used, the PCR consistently failed. Other authors have reported similar problems when trying to amplify avian leptin sequences.

Serum leptin activity in obese and lean patients

Blood levels of the satiety hormone leptin are directly correlated to fat stores in obese and lean people. Therefore, leptin resistance is the logical explanation for the phenomenon of common obesity. However, the important question of whether or not the intrinsic leptin activity could differ between obese and lean people has not been examined before. In the present study, serum leptin activity was measured by an in vitro assay of leptin signaling in a modified culture of HEK-293 cells. The system is based on activation of a luciferase reporter gene through a leptin receptor-dependent activation of the signal transducer and activator of transcription (STAT3). Serum samples from 20 obese and 20 non-obese individuals with leptin levels ranging from 3 to 75 ng/ml, as determined by radioimmunoassay (RIA), were used. A high correlation was observed for each serum sample between leptin RIA values and leptin activity in the bioassay. The results indicate that obesity in the 20 obese patients among the 40 individuals examined cannot be accounted for by alterations in leptin activity in our assay. The assay system provides a tool to screen for possible rare cases exhibiting alteration in leptin activity either due to a change in leptin itself or through interaction with other serum factors.

Heritability of fearful-anxious endophenotypes in infant rhesus macaques: a preliminary report

BACKGROUND

Research efforts to discover the genetic underpinnings of anxiety and depression is challenging because of the etiologic heterogeneity inherent to these disorders. These efforts might be aided by the study of related behavioral phenotypes in model organisms, such as monkeys.

METHODS

Eighty-five rhesus monkeys (Macaca mulatta) from the Oregon National Primate Research Center were drawn from a standard matriarchal colony and tested for behavioral response in four testing paradigms designed to elicit fearful-anxious reactions. Heritabilities were estimated using variance component-based quantitative genetic analyses with much of the genetic information arising from paternal half-sibs.

RESULTS

Individual behaviors reflecting increased distress responses (e.g., vocalizations and teeth grinding) and behavioral inhibition (e.g., latency to leave mother, latency to inspect novel fruit) showed significant heritability, even though a small number of monkeys were assessed. Exploratory factor analyses identified seven clusters of behaviors across tests, some of which were found to be heritable.

CONCLUSIONS

These results indicate that several specific fearful-anxious behaviors in infant rhesus monkeys are heritable within this colony. Accordingly, these phenotypes, which are believed to represent the genetic liability for anxiety and depression, are good candidates for further genetic investigation in this population.

Analysis of paradoxical observations on the association between leptin and insulin resistance

Obesity is commonly associated with the development of insulin resistance and diabetes in humans and rodents. Insulin resistance and diabetes are observed in lipoatrophic individuals or rodent models of lipoatrophy. Here we focus on the role of leptin, the product of the obesity (ob) gene, in the development of insulin resistance and diabetes associated with obesity and lipoatrophy. We review the reported effects of leptin on whole body glucose metabolism and compare and contrast these with direct effects on skeletal muscle, fat and liver. This summary of paradoxical observations on the effects of leptin on glucose homeostasis and the ability of leptin to induce or improve insulin resistance suggests that a complex interplay exists between direct peripheral and centrally mediated effects of the hormone. Evidence suggesting that leptin acts as a mediator of insulin release from pancreatic beta cells is reviewed. Finally, intracellular signaling mechanisms stimulated by both leptin and insulin are discussed, with potential points of cross-talk suggested.

Pharmacotherapy of obesity: targets and perspectives

The search for anti-obesity agents has become one of the most exciting areas in drug discovery. Subsequent to an enormous increase in the number of possible molecular targets, the focus has shifted from target identification to target validation. Because important biological functions such as the regulation of energy intake and expenditure are controlled by complex systems, an improved understanding of pathophysiology is a prerequisite for the selection of successful development candidates for the treatment of obesity. Although most of the information on the regulation of energy balance has been obtained from rodents, various monogenic forms of human obesity provide clinical proof of concept for some of these mechanisms. However, it is still not known which are the most promising clinical approaches to lowering body weight and subsequently reducing morbidity and mortality.

Hypothalamic neuropeptide mechanisms for regulating energy balance: from rodent models to human obesity

In small rodents there is compelling evidence of a lipostatic system of body mass regulation in which peripheral signals of energy storage are decoded in the hypothalamus. The ability of small mammals to defend an appropriate mass against imposed energy imbalance has implicated hypothalamic neuroendocrine systems in body mass regulation. The effect of the neuropeptide systems involved in this regulation is primarily compensatory. However, small mammals can also effect changes in the level of body mass that they will defend, as exemplified by seasonal species. Regulatory control over fat mass may be relatively loose in humans; the sizes of long-term storage depots may not themselves be regulated, but rather may be a consequence of temporal variations in the matching of supply and demand. Whether food intake is regulated to match energy demand, or to match demand and to regulate storage, it is clear that physiological defects or genetic variation in hypothalamic and peripheral feedback systems will have profound implications for fat storage. Study of mechanisms implicated in energy homeostasis in laboratory rodents is likely to continue to identify targets for pharmacological manipulation in the management of human obesity.

Secretory, endocrine and autocrine/paracrine function of the adipocyte

Obesity is a major public health problem in Western countries, and >55% of adult Americans are overweight or obese. A major contributor to the epidemic of obesity is the current environment, which is characterized by increased availability of high energy foods and decreased physical activity. Several studies also demonstrated that genetic susceptibility contributes to obesity in some populations. Obesity research has focused primarily on the role of the hypothalamus in neuroendocrine regulation of food intake. However, a growing number of studies support a potential contribution of adipose tissue, via its newly discovered secretory function, to the pathogenesis of obesity and co-morbid conditions including cardiovascular disease, diabetes and hypertension. This paper will review the role of four factors secreted by adipose tissue (leptin, agouti, angiotensin II and prostaglandins) and their functions in the regulation of energy balance and whole-body homeostasis. Several other peptide and nonpeptide substances are secreted from adipose tissue; their function and regulation have been documented extensively.

Transgenic study of energy homeostasis equation: implications and confounding influences

Recently novel molecular mediators and regulatory pathways for feeding and body weight regulation have been identified in the brain and the periphery. Mice lacking or overexpressing these mediators or receptors have been produced by molecular genetic techniques, and observations on mutant mice have shed new light on the role of each element in the homeostatic loop of body weight regulation. However, the interpretation of the phenotype is under the potential influence of developmental compensation and other genetic and environmental confounds. Specific alterations of the mediators and the consequences of the altered expression patterns are reviewed here and discussed in the context of their functions as suggested from conventional pharmacological studies. Advanced gene targeting strategies in which genes can be turned on or off at desired tissues and times would undoubtedly lead to a better understanding of the highly integrated and redundant systems for energy homeostasis equation.

Leptin signaling in human peripheral blood mononuclear cells, activation of p38 and p42/44 mitogen-activated protein (MAP) kinase and p70 S6 kinase

The adipocyte-derived hormone leptin plays an important role as a relayer of nutritional status to several organ systems. Evidence is accumulating that leptin plays an important role in the adequate functioning and maintenance of the immune system. Here we show that leptin induces sustained phosphorylation of p38 MAP kinase in human peripheral blood mononuclear cells (PBMCs). We show furthermore that leptin induces two routes to phosphorylation of the 40S ribosomal protein S6, one is activation of the p90 ribosomal S6 kinase (RSK) via the MEK/p42/p44 MAP kinase pathway, the other is via activation of p70 S6 kinase. Thus, these results give new insight in the mechanism that underlies the immunomodulatory effects of leptin.