A MicroRNA Linking Human Positive Selection and Metabolic Disorders.

Positive selection in Europeans at the 2q21.3 locus harboring the lactase gene has been attributed to selection for the ability of adults to digest milk to survive famine in ancient times. However, the 2q21.3 locus is also associated with obesity and type 2 diabetes in humans, raising the possibility that additional genetic elements in the locus may have contributed to evolutionary adaptation to famine by promoting energy storage, but which now confer susceptibility to metabolic diseases. We show here that the miR-128-1 microRNA, located at the center of the positively selected locus, represents a crucial metabolic regulator in mammals. Antisense targeting and genetic ablation of miR-128-1 in mouse metabolic disease models result in increased energy expenditure and amelioration of high-fat-diet-induced obesity and markedly improved glucose tolerance. A thrifty phenotype connected to miR-128-1-dependent energy storage may link ancient adaptation to famine and modern metabolic maladaptation associated with nutritional overabundance.

Human Semaphorin 3 Variants Link Melanocortin Circuit Development and Energy Balance.

Hypothalamic melanocortin neurons play a pivotal role in weight regulation. Here, we examined the contribution of Semaphorin 3 (SEMA3) signaling to the development of these circuits. In genetic studies, we found 40 rare variants in SEMA3A-G and their receptors (PLXNA1-4; NRP1-2) in 573 severely obese individuals; variants disrupted secretion and/or signaling through multiple molecular mechanisms. Rare variants in this set of genes were significantly enriched in 982 severely obese cases compared to 4,449 controls. In a zebrafish mutagenesis screen, deletion of 7 genes in this pathway led to increased somatic growth and/or adiposity demonstrating that disruption of Semaphorin 3 signaling perturbs energy homeostasis. In mice, deletion of the Neuropilin-2 receptor in Pro-opiomelanocortin neurons disrupted their projections from the arcuate to the paraventricular nucleus, reduced energy expenditure, and caused weight gain. Cumulatively, these studies demonstrate that SEMA3-mediated signaling drives the development of hypothalamic melanocortin circuits involved in energy homeostasis.

Leptin Mediates a Glucose-Fatty Acid Cycle to Maintain Glucose Homeostasis in Starvation.

The transition from the fed to the fasted state necessitates a shift from carbohydrate to fat metabolism that is thought to be mostly orchestrated by reductions in plasma insulin concentrations. Here, we show in awake rats that insulinopenia per se does not cause this transition but that both hypoleptinemia and insulinopenia are necessary. Furthermore, we show that hypoleptinemia mediates a glucose-fatty acid cycle through activation of the hypothalamic-pituitary-adrenal axis, resulting in increased white adipose tissue (WAT) lipolysis rates and increased hepatic acetyl-coenzyme A (CoA) content, which are essential to maintain gluconeogenesis during starvation. We also show that in prolonged starvation, substrate limitation due to reduced rates of glucose-alanine cycling lowers rates of hepatic mitochondrial anaplerosis, oxidation, and gluconeogenesis. Taken together, these data identify a leptin-mediated glucose-fatty acid cycle that integrates responses of the muscle, WAT, and liver to promote a shift from carbohydrate to fat oxidation and maintain glucose homeostasis during starvation.

A sympathetic view on fat by leptin.

Zeng et al. reveal that the lipolytic effect of the hormone leptin is mediated by sympathetic nerve fibers that directly "envelope" white adipocytes. Local activation of the sympathetic input to the fat opens new venues to circumvent central leptin resistance in obesity.

Leptin Does Not Mediate Hypertension Associated With Human Obesity.

Hypertension and obesity are known to be linked, with recent studies in mice proposing that leptin may be mediating this effect. This regulation, however, may not extend to humans, where a yet-to-be-identified factor is likely the underlying cause of hypertension.

Sympathetic neuro-adipose connections mediate leptin-driven lipolysis.

Leptin is a hormone produced by the adipose tissue that acts in the brain, stimulating white fat breakdown. We find that the lipolytic effect of leptin is mediated through the action of sympathetic nerve fibers that innervate the adipose tissue. Using intravital two-photon microscopy, we observe that sympathetic nerve fibers establish neuro-adipose junctions, directly "enveloping" adipocytes. Local optogenetic stimulation of sympathetic inputs induces a local lipolytic response and depletion of white adipose mass. Conversely, genetic ablation of sympathetic inputs onto fat pads blocks leptin-stimulated phosphorylation of hormone-sensitive lipase and consequent lipolysis, as do knockouts of dopamine ß-hydroxylase, an enzyme required for catecholamine synthesis. Thus, neuro-adipose junctions are necessary and sufficient for the induction of lipolysis in white adipose tissue and are an efferent effector of leptin action. Direct activation of sympathetic inputs to adipose tissues may represent an alternative approach to induce fat loss, circumventing central leptin resistance. PAPERCLIP.

Treatment of obesity with celastrol.

Despite all modern advances in medicine, an effective drug treatment of obesity has not been found yet. Discovery of leptin two decades ago created hopes for treatment of obesity. However, development of leptin resistance has been a big obstacle, mitigating a leptin-centric treatment of obesity. Here, by using in silico drug-screening methods, we discovered that Celastrol, a pentacyclic triterpene extracted from the roots of Tripterygium Wilfordi (thunder god vine) plant, is a powerful anti-obesity agent. Celastrol suppresses food intake, blocks reduction of energy expenditure, and leads to up to 45% weight loss in hyperleptinemic diet-induced obese (DIO) mice by increasing leptin sensitivity, but it is ineffective in leptin-deficient (ob/ob) and leptin receptor-deficient (db/db) mouse models. These results indicate that Celastrol is a leptin sensitizer and a promising agent for the pharmacological treatment of obesity.

Leptin and insulin act on POMC neurons to promote the browning of white fat.

The primary task of white adipose tissue (WAT) is the storage of lipids. However, "beige" adipocytes also exist in WAT. Beige adipocytes burn fat and dissipate the energy as heat, but their abundance is diminished in obesity. Stimulating beige adipocyte development, or WAT browning, increases energy expenditure and holds potential for combating metabolic disease and obesity. Here, we report that insulin and leptin act together on hypothalamic neurons to promote WAT browning and weight loss. Deletion of the phosphatases PTP1B and TCPTP enhanced insulin and leptin signaling in proopiomelanocortin neurons and prevented diet-induced obesity by increasing WAT browning and energy expenditure. The coinfusion of insulin plus leptin into the CNS or the activation of proopiomelanocortin neurons also increased WAT browning and decreased adiposity. Our findings identify a homeostatic mechanism for coordinating the status of energy stores, as relayed by insulin and leptin, with the central control of WAT browning.

Paternal microbiome perturbations impact offspring fitness.

The gut microbiota operates at the interface of host-environment interactions to influence human homoeostasis and metabolic networks1-4. Environmental factors that unbalance gut microbial ecosystems can therefore shape physiological and disease-associated responses across somatic tissues5-9. However, the systemic impact of the gut microbiome on the germline-and consequently on the F1 offspring it gives rise to-is unexplored10. Here we show that the gut microbiota act as a key interface between paternal preconception environment and intergenerational health in mice. Perturbations to the gut microbiota of prospective fathers increase the probability of their offspring presenting with low birth weight, severe growth restriction and premature mortality. Transmission of disease risk occurs via the germline and is provoked by pervasive gut microbiome perturbations, including non-absorbable antibiotics or osmotic laxatives, but is rescued by restoring the paternal microbiota before conception. This effect is linked with a dynamic response to induced dysbiosis in the male reproductive system, including impaired leptin signalling, altered testicular metabolite profiles and remapped small RNA payloads in sperm. As a result, dysbiotic fathers trigger an elevated risk of in utero placental insufficiency, revealing a placental origin of mammalian intergenerational effects. Our study defines a regulatory 'gut-germline axis' in males, which is sensitive to environmental exposures and programmes offspring fitness through impacting placenta function.

Leptin mediates the increase in blood pressure associated with obesity.

Obesity is associated with increased blood pressure (BP), which in turn increases the risk of cardiovascular diseases. We found that the increase in leptin levels seen in diet-induced obesity (DIO) drives an increase in BP in rodents, an effect that was not seen in animals deficient in leptin or leptin receptors (LepR). Furthermore, humans with loss-of-function mutations in leptin and the LepR have low BP despite severe obesity. Leptin's effects on BP are mediated by neuronal circuits in the dorsomedial hypothalamus (DMH), as blocking leptin with a specific antibody, antagonist, or inhibition of the activity of LepR-expressing neurons in the DMH caused a rapid reduction of BP in DIO mice, independent of changes in weight. Re-expression of LepRs in the DMH of DIO LepR-deficient mice caused an increase in BP. These studies demonstrate that leptin couples changes in weight to changes in BP in mammalian species.

Mitofusin 2 in POMC neurons connects ER stress with leptin resistance and energy imbalance.

Mitofusin 2 (MFN2) plays critical roles in both mitochondrial fusion and the establishment of mitochondria-endoplasmic reticulum (ER) interactions. Hypothalamic ER stress has emerged as a causative factor for the development of leptin resistance, but the underlying mechanisms are largely unknown. Here, we show that mitochondria-ER contacts in anorexigenic pro-opiomelanocortin (POMC) neurons in the hypothalamus are decreased in diet-induced obesity. POMC-specific ablation of Mfn2 resulted in loss of mitochondria-ER contacts, defective POMC processing, ER stress-induced leptin resistance, hyperphagia, reduced energy expenditure, and obesity. Pharmacological relieve of hypothalamic ER stress reversed these metabolic alterations. Our data establish MFN2 in POMC neurons as an essential regulator of systemic energy balance by fine-tuning the mitochondrial-ER axis homeostasis and function. This previously unrecognized role for MFN2 argues for a crucial involvement in mediating ER stress-induced leptin resistance.

A monocyte-leptin-angiogenesis pathway critical for repair post-infection.

During infection, inflammatory monocytes are thought to be key for bacterial eradication, but this is hard to reconcile with the large numbers of neutrophils that are recruited for each monocyte that migrates to the afflicted tissue, and the much more robust microbicidal functions of the neutrophils. However, unlike neutrophils, monocytes have the capacity to convert to situationally specific macrophages that may have critical functions beyond infection control1,2. Here, using a foreign body coated with Staphylococcus aureus and imaging over time from cutaneous infection to wound resolution, we show that monocytes and neutrophils are recruited in similar numbers with low-dose infection but not with high-dose infection, and form a localization pattern in which monocytes surround the infection site, whereas neutrophils infiltrate it. Monocytes did not contribute to bacterial clearance but converted to macrophages that persisted for weeks after infection, regulating hypodermal adipocyte expansion and production of the adipokine hormone leptin. In infected monocyte-deficient mice there was increased persistent hypodermis thickening and an elevated leptin level, which drove overgrowth of dysfunctional blood vasculature and delayed healing, with a thickened scar. Ghrelin, which opposes leptin function3, was produced locally by monocytes, and reduced vascular overgrowth and improved healing post-infection. In sum, we find that monocytes function as a cellular rheostat by regulating leptin levels and revascularization during wound repair.

Ras drives malignancy through stem cell crosstalk with the microenvironment.

Squamous cell carcinomas are triggered by marked elevation of RAS-MAPK signalling and progression from benign papilloma to invasive malignancy1-4. At tumour-stromal interfaces, a subset of tumour-initiating progenitors, the cancer stem cells, obtain increased resistance to chemotherapy and immunotherapy along this pathway5,6. The distribution and changes in cancer stem cells during progression from a benign state to invasive squamous cell carcinoma remain unclear. Here we show in mice that, after oncogenic RAS activation, cancer stem cells rewire their gene expression program and trigger self-propelling, aberrant signalling crosstalk with their tissue microenvironment that drives their malignant progression. The non-genetic, dynamic cascade of intercellular exchanges involves downstream pathways that are often mutated in advanced metastatic squamous cell carcinomas with high mutational burden7. Coupling our clonal skin HRASG12V mouse model with single-cell transcriptomics, chromatin landscaping, lentiviral reporters and lineage tracing, we show that aberrant crosstalk between cancer stem cells and their microenvironment triggers angiogenesis and TGFß signalling, creating conditions that are conducive for hijacking leptin and leptin receptor signalling, which in turn launches downstream phosphoinositide 3-kinase (PI3K)-AKT-mTOR signalling during the benign-to-malignant transition. By functionally examining each step in this pathway, we reveal how dynamic temporal crosstalk with the microenvironment orchestrated by the stem cells profoundly fuels this path to malignancy. These insights suggest broad implications for cancer therapeutics.

Drosophila cytokine unpaired 2 regulates physiological homeostasis by remotely controlling insulin secretion.

In Drosophila, the fat body (FB), a functional analog of the vertebrate adipose tissue, is the nutrient sensor that conveys the nutrient status to the insulin-producing cells (IPCs) in the fly brain to release Drosophila insulin-like peptides (Dilps). Dilp secretion in turn regulates energy balance and promotes systemic growth. We identify Unpaired 2 (Upd2), a protein with similarities to type I cytokines, as a secreted factor produced by the FB in the fed state. When upd2 function is perturbed specifically in the FB, it results in a systemic reduction in growth and alters energy metabolism. Upd2 activates JAK/STAT signaling in a population of GABAergic neurons that project onto the IPCs. This activation relieves the inhibitory tone of the GABAergic neurons on the IPCs, resulting in the secretion of Dilps. Strikingly, we find that human Leptin can rescue the upd2 mutant phenotypes, suggesting that Upd2 is the functional homolog of Leptin.

FoxO1 target Gpr17 activates AgRP neurons to regulate food intake.

Hypothalamic neurons expressing Agouti-related peptide (AgRP) are critical for initiating food intake, but druggable biochemical pathways that control this response remain elusive. Thus, genetic ablation of insulin or leptin signaling in AgRP neurons is predicted to reduce satiety but fails to do so. FoxO1 is a shared mediator of both pathways, and its inhibition is required to induce satiety. Accordingly, FoxO1 ablation in AgRP neurons of mice results in reduced food intake, leanness, improved glucose homeostasis, and increased sensitivity to insulin and leptin. Expression profiling of flow-sorted FoxO1-deficient AgRP neurons identifies G-protein-coupled receptor Gpr17 as a FoxO1 target whose expression is regulated by nutritional status. Intracerebroventricular injection of Gpr17 agonists induces food intake, whereas Gpr17 antagonist cangrelor curtails it. These effects are absent in Agrp-Foxo1 knockouts, suggesting that pharmacological modulation of this pathway has therapeutic potential to treat obesity.

GABAergic RIP-Cre neurons in the arcuate nucleus selectively regulate energy expenditure.

Neural regulation of energy expenditure is incompletely understood. By genetically disrupting GABAergic transmission in a cell-specific fashion, and by combining this with selective pharmacogenetic activation and optogenetic mapping techniques, we have uncovered an arcuate-based circuit that selectively drives energy expenditure. Specifically, mice lacking synaptic GABA release from RIP-Cre neurons have reduced energy expenditure, become obese and are extremely sensitive to high-fat diet-induced obesity, the latter due to defective diet-induced thermogenesis. Leptin's ability to stimulate thermogenesis, but not to reduce feeding, is markedly attenuated. Acute, selective activation of arcuate GABAergic RIP-Cre neurons, which monosynaptically innervate PVH neurons projecting to the NTS, rapidly stimulates brown fat and increases energy expenditure but does not affect feeding. Importantly, this response is dependent upon GABA release from RIP-Cre neurons. Thus, GABAergic RIP-Cre neurons in the arcuate selectively drive energy expenditure, contribute to leptin's stimulatory effect on thermogenesis, and protect against diet-induced obesity.

A leptin-BDNF pathway regulating sympathetic innervation of adipose tissue.

Mutations in the leptin gene (ob) result in a metabolic disorder that includes severe obesity1, and defects in thermogenesis2 and lipolysis3, both of which are adipose tissue functions regulated by the sympathetic nervous system. However, the basis of these sympathetic-associated abnormalities remains unclear. Furthermore, chronic leptin administration reverses these abnormalities in adipose tissue, but the underlying mechanism remains to be discovered. Here we report that ob/ob mice, as well as leptin-resistant diet-induced obese mice, show significant reductions of sympathetic innervation of subcutaneous white and brown adipose tissue. Chronic leptin treatment of ob/ob mice restores adipose tissue sympathetic innervation, which in turn is necessary to correct the associated functional defects. The effects of leptin on innervation are mediated via agouti-related peptide and pro-opiomelanocortin neurons in the hypothalamic arcuate nucleus. Deletion of the gene encoding the leptin receptor in either population leads to reduced innervation in fat. These agouti-related peptide and pro-opiomelanocortin neurons act via brain-derived neurotropic factor-expressing neurons in the paraventricular nucleus of the hypothalamus (BDNFPVH). Deletion of BDNFPVH blunts the effects of leptin on innervation. These data show that leptin signalling regulates the plasticity of sympathetic architecture of adipose tissue via a top-down neural pathway that is crucial for energy homeostasis.

Conditional Deletion of ß-Catenin in the Mediobasal Hypothalamus Impairs Adaptive Energy Expenditure in Response to High-Fat Diet and Exacerbates Diet-Induced Obesity.

ß-Catenin is a bifunctional molecule that is an effector of the wingless-related integration site (Wnt) signaling to control gene expression and contributes to the regulation of cytoskeleton and neurotransmitter vesicle trafficking. In its former role, ß-catenin binds transcription factor 7-like 2 (TCF7L2), which shows strong genetic associations with the pathogenesis of obesity and type-2 diabetes. Here, we sought to determine whether ß-catenin plays a role in the neuroendocrine regulation of body weight and glucose homeostasis. Bilateral injections of adeno-associated virus type-2 (AAV2)-mCherry-Cre were placed into the arcuate nucleus of adult male and female ß-catenin flox mice, to specifically delete ß-catenin expression in the mediobasal hypothalamus (MBH-ß-cat KO). Metabolic parameters were then monitored under conditions of low-fat (LFD) and high-fat diet (HFD). On LFD, MBH-ß-cat KO mice showed minimal metabolic disturbances, but on HFD, despite having only a small difference in weekly caloric intake, the MBH-ß-cat KO mice were significantly heavier than the control mice in both sexes (p < 0.05). This deficit seemed to be due to a failure to show an adaptive increase in energy expenditure seen in controls, which served to offset the increased calories by HFD. Both male and female MBH-ß-cat KO mice were highly glucose intolerant when on HFD and displayed a significant reduction in both leptin and insulin sensitivity compared with controls. This study highlights a critical role for ß-catenin in the hypothalamic circuits regulating body weight and glucose homeostasis and reveals potential mechanisms by which genetic variation in this pathway could impact on development of metabolic disease.

Leptin signaling promotes blood vessel formation in the Xenopus tail during the embryo-larval transition.

The signals that regulate peripheral blood vessel formation during development are still under investigation. The hormone leptin promotes blood vessel formation, adipose tissue establishment and expansion, tumor growth, and wound healing, but the underlying mechanisms for these actions are currently unknown. We investigated whether leptin promotes angiogenesis in the developing tail fin using embryonic transgenic xflk-1:GFP Xenopus laevis, which express a green fluorescent protein on vascular endothelial cells to mark blood vessels. We found that leptin protein is expressed in endothelial cells of developing blood vessels and that leptin treatment via injection increased phosphorylated STAT3 signaling, which is indicative of leptin activation of its receptor, in blood vessels of the larval tail fin. Leptin administration via media increased vessel length, branching, and reconnection with the cardinal vein, while decreased leptin signaling via immunoneutralization had an opposing effect on vessel development. We also observed disorganization of major vessels and microvessels of the tail fin and muscle when leptin signaling was decreased. Reduced leptin signaling lowered mRNA expression of cenpk, gpx1, and mmp9, markers for cell proliferation, antioxidation, and extracellular matrix remodeling/cell migration, respectively, in the developing tail, providing insight into three possible mechanisms underlying leptin's promotion of angiogenesis. Together these results illustrate that leptin levels are correlated with embryonic angiogenesis and that leptin coordinates multiple aspects of blood vessel growth and development, showing that leptin is an important morphogen during embryonic development.

A quantitative pipeline to assess secretion of human leptin coding variants reveals mechanisms underlying leptin deficiencies.

The hormone leptin, primarily secreted by adipocytes, plays a crucial role in regulating whole-body energy homeostasis. Homozygous loss-of-function mutations in the leptin gene (LEP) cause hyperphagia and severe obesity, primarily through alterations in leptin's affinity for its receptor or changes in serum leptin concentrations. Although serum concentrations are influenced by various factors (e.g., gene expression, protein synthesis, stability in the serum), proper delivery of leptin from its site of synthesis in the endoplasmic reticulum via the secretory pathway to the extracellular serum is a critical step. However, the regulatory mechanisms and specific machinery involved in this trafficking route, particularly in the context of human LEP mutations, remain largely unexplored. We have employed the Retention Using Selective Hooks system to elucidate the secretory pathway of leptin. We have refined this system into a medium-throughput assay for examining the pathophysiology of a range of obesity-associated LEP variants. Our results reveal that leptin follows the default secretory pathway, with no additional regulatory steps identified prior to secretion. Through screening of leptin variants, we identified three mutations that lead to proteasomal degradation of leptin and one variant that significantly decreased leptin secretion, likely through aberrant disulfide bond formation. These observations have identified novel pathogenic effects of leptin variants, which can be informative for therapeutics and diagnostics. Finally, our novel quantitative screening platform can be adapted for other secreted proteins.