Rap1 in the VMH regulates glucose homeostasis

The hypothalamus is a critical regulator of glucose metabolism and is capable of correcting diabetes conditions independently of an effect on energy balance. The small GTPase Rap1 in the forebrain is implicated in high-fat diet (HFD)-induced obesity and glucose imbalance. Here, we report that increasing Rap1 activity selectively in the medial hypothalamus elevated blood glucose without increasing the body weight of HFD-fed mice. In contrast, decreasing hypothalamic Rap1 activity protected mice from diet-induced hyperglycemia but did not prevent weight gain. The remarkable glycemic effect of Rap1 was reproduced when Rap1 was specifically deleted in SF1-positive neurons in the ventromedial hypothalamic nucleus (VMH) known to regulate glucose metabolism. While having no effect on body weight regardless of sex, diet, and age, Rap1 deficiency in the VMH SF1 neurons markedly lowered blood glucose and insulin levels, improved glucose and insulin tolerance, and protected mice against HFD-induced neural leptin resistance and peripheral insulin resistance at the cellular and whole-body levels. Lastly, acute pharmacological inhibition of brain Epac2, a direct activator of Rap1, corrected glucose imbalance in obese mouse models. Our findings uncover the primary role of VMH Rap1 in glycemic control and implicate Rap1 signaling as a potential target for therapeutic intervention in diabetes

Unsilencing of native leptin receptors (LepR) in hypothalamic SF1 neurons does not rescue obese phenotype in LepR-deficient mice

Leptin receptor (LepR) signaling in neurons of the ventromedial nucleus of the hypothalamus (VMH), specifically those expressing steroidogenic factor-1 (SF1), have been proposed to play a key role in controlling energy balance. By crossing LepR-silenced (LepR) mice to those expressing SF1-Cre, we unsilenced native LepR specifically in the VMH and tested whether SF1 neurons in the VMH are critical mediators of leptin's effect on energy homeostasis. LepR x SF1-Cre (KO/Tg+) mice were metabolically phenotyped and compared to littermate controls that either expressed or were deficient in LepR. Leptin-induced pSTAT3 was present in the VMH of KO/Tg+ mice and absent in other hypothalamic nuclei. VMH leptin signaling did not ameliorate obesity resulting from LepR-deficiency in chow-fed mice. There was no change in food intake or energy expenditure when comparing complete LepR-null mice to KO/Tg+ mice, nor did KO/Tg+ show improved glucose tolerance. The presence of functional LepR in the VMH mildly enhanced sensitivity to the pancreatic hormone amylin. When maintained on high fat diet (HFD), there was no reduction in diet-induced obesity in KO/Tg+ mice, but KO/Tg+ mice had improved glucose tolerance after 7 weeks on HFD compared to LepR-null mice. We conclude that LepR signaling in the VMH alone is not sufficient to correct metabolic dysfunction observed in LepR-null mice

Distinct Hypothalamic Neurons Mediate Estrogenic Effects on Energy Homeostasis and Reproduction

SummaryEstrogens regulate body weight and reproduction primarily through actions on estrogen receptor-α (ERα). However, ERα-expressing cells mediating these effects are not identified. We demonstrate that brain-specific deletion of ERα in female mice causes abdominal obesity stemming from both hyperphagia and hypometabolism. Hypometabolism and abdominal obesity, but not hyperphagia, are recapitulated in female mice lacking ERα in hypothalamic steroidogenic factor-1 (SF1) neurons. In contrast, deletion of ERα in hypothalamic pro-opiomelanocortin (POMC) neurons leads to hyperphagia, without directly influencing energy expenditure or fat distribution. Further, simultaneous deletion of ERα from both SF1 and POMC neurons causes hypometabolism, hyperphagia, and increased visceral adiposity. Additionally, female mice lacking ERα in SF1 neurons develop anovulation and infertility, while POMC-specific deletion of ERα inhibits negative feedback regulation of estrogens and impairs fertility in females. These results indicate that estrogens act on distinct hypothalamic ERα neurons to regulate different aspects of energy homeostasis and reproduction

Cross-Talk between Metabolism and Reproduction: The Role of POMC and SF1 Neurons

Energy homeostasis and reproduction require tight coordination, but the mechanisms underlying their interaction are not fully understood. Two sets of hypothalamic neurons, namely pro-opiomelanocortin (POMC) neurons in the arcuate nucleus and steroidogenic factor-1 (SF1) neurons in the ventromedial hypothalamic nucleus, are emerging as critical nodes where metabolic and reproductive signals communicate. This view is supported by recent genetic studies showing that disruption of metabolic signals (e.g., leptin and insulin) or reproductive signals (e.g., estradiol) in these neurons leads to impaired regulation of both energy homeostasis and fertility. In this review, we will examine the potential mechanisms of neuronal communication between POMC, SF1, and gonadotropin-releasing hormone neurons in the regulation of metabolism and reproduction

The Role of Neuronal DNA Methyltransferase 1 in Energy Homeostasis and Obesity

Obesity is a grave disease that is increasing in global prevalence. Aberrant neuronal DNA methylation patterns have been implicated in the promotion of obesity development, but the role of neuronal DNA methyltransferases (Dnmts; enzymes that catalyze DNA methylation) in energy balance remains poorly understood. We investigated the role of neuronal Dnmt1 in normal energy regulation and obesity development using a novel Dnmt1 knockout mouse model, Dnmt1fl/fl Synapsin1Cre (ND1KO), which specifically deletes Dnmt1 in neurons. ND1KO and fl/fl control littermates were fedeither a standard chow diet or a high fat diet (HFD). We conducted a deep analysis to characterize both peripheral and central aspects of the ND1KO phenotype. We found that neuronal Dnmt1 deficiency reduced adiposity in chow-fed mice and attenuated obesity in HFD-fed male mice. ND1KO male mice had reduced food intake and increased energy expenditure on the HFD. Furthermore, these mice had improved insulin sensitivity as measured by an insulin tolerance test. HFD-fed ND1KO mice had smaller fat pads and an upregulation of thermogenic genes in brown adipose tissue. These data suggest that neuronal Dnmt1 deletion increased diet-induced thermogenesis, which may explain the lean phenotype in HFD-fed ND1KO mice. Interestingly, we found that ND1KO male mice had elevated estrogen receptor-α gene expression in the hypothalamus, which previously has been shown to control body weight. Immunohistochemistry experiments revealed that estrogen receptor-α (ERα) protein expression was upregulated in the dorsomedial region of the VMH (VMHdm), a region which may mediate the central effect of leptin. Finally, we tested whether ND1KO mice had reduced methylation of the ERα gene promoter, which might explain the ERα upregulation. Neuronal Dnmt1 deficiency decreased methylation at two CpG sites on Exon A in chow-fed mice. Collectively, these data suggest that neuronal Dnmt1 regulates energy homeostasis through pathways controlling food intake and energy expenditure, and that ERα in the VMHdm may mediate these effects

Specific Subpopulations of Hypothalamic Leptin Receptor-Expressing Neurons Mediate the Effects of Early Developmental Leptin Receptor Deletion on Energy Balance

ACKNOWLEDGEMENTS We thank MedImmune, Inc. and James Trevaskis, PhD and Christopher Rhodes, PhD for the gift of leptin. We thank members of the Myers and Olson labs for helpful discussions. Research support was provided by the Michigan Diabetes Research Center (NIH P3 0 DK020572, including the Molecular Genetics, Animal Phenotyping, and Clinical Cores), the American Diabetes Association (MGM), the Marilyn H. Vincent Foundation (MGM), the NIH (MGM: D K05673 1; ACR:DK071212; MBA: DK097861), the BBSRC (LKH: BB/NO17838/1) and WellcomeTrust (LKH: 098012).Peer reviewedPublisher PD

Hypothalamic Actions of SIRT1 and SIRT6 on Energy Balance

Sirtuins are NAD+ dependent deacetylases that regulate a large number of physiological processes. These enzymes are highly conserved and act as energy sensors to coordinate different metabolic responses in a controlled manner. At present, seven mammalian sirtuins (SIRT 1-7) have been identified, with SIRT1 and SIRT6 shown to exert their metabolic actions in the hypothalamus, both with crucial roles in eliciting responses to dampen metabolic complications associated with obesity. Therefore, our aim is to compile the current understanding on the role of SIRT1 and SIRT6 in the hypothalamus, especially highlighting their actions on the control of energy balanceThis work is supported by grants of Xunta de Galicia (MQ:2018-PG013). Centro de Investigación Biomédica en Red (CIBER) de Fisiopatología de la Obesidad y Nutrición (CIBERobn). CIBERobn is an initiative of the Instituto de Salud Carlos III (ISCIII) of Spain which is supported by FEDER funds. Western Norway Regional Health Authority (Helse Vest RHF).M.Q. is a recipient of a Postdoctoral contract from Galician Government (Xunta de Galicia ED481B2018/004). O.A.M. was funded by a research contract Miguel Servet (CP20/00146) from the ISCIIIS

Insulin regulates Energy Homeostasis and Hypoglycemia in the Ventromedial Hypothalamus

Growing evidence from the last decades intimately links obesity with insulin resistance and type 2 diabetes mellitus as a consequence. Thus, the role of the central nervous system and especially the hypothalamus in the control of energy homeostasis are intensively investigated. The melanocortin system has been identified as a pivotal neurocircuit in this homeostatic process, but many other neuronal populations are similarly involved. Furthermore, the role of insulin as adiposity signal in the control of energy homeostasis has to be further clarified. In particular, steroidogenic factor 1 (SF-1)-expressing neurons of the ventromedial hypothalamus (VMH) control energy homeostasis, but the role of insulin action in these cells remains undefined. This study shows that insulin activates phosphatidylinositol-3-kinase (PI3K) signaling in SF-1 neurons and reduces firing frequency in these cells by the activation of ATP-dependent potassium (KATP) channels. These effects were abrogated in mice with Cre-mediated insulin receptor deficiency restricted to SF-1 neurons (SF-1∆IR mice). Whereas body weight and glucose homeosta- sis remained the same in SF-1∆IR mice as in controls on a normal chow diet, they were protected from diet-induced leptin resistance, weight gain, adiposity and impaired glucose tolerance. High-fat feeding activated PI3K signaling in SF-1 neurons of control mice, and this response was attenuated in the VMH of SF-1∆IR mice. Mimicking diet- induced overactivation of PI3K signaling by disruption of the phosphatidylinositol-3,4,5- trisphosphate phosphatase PTEN led to increased body weight and hyperphagia under normal chow diet conditions. Collectively, this study reveals that high-fat diet–induced, insulin-dependent PI3K activation in VMH neurons contributes to obesity development. Additionally, insulin was identified as a necessary signal in SF-1 VMH neurons involved in the induction of the counter-regulatory response to hypoglycemia, one of the major limitations for insulin treatment in diabetic patients

The Nutritional Induction of COUP-TFII Gene Expression in Ventromedial Hypothalamic Neurons Is Mediated by the Melanocortin Pathway

BACKGROUND: The nuclear receptor chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is an important coordinator of glucose homeostasis. We report, for the first time, a unique differential regulation of its expression by the nutritional status in the mouse hypothalamus compared to peripheral tissues. METHODOLOGY/PRINCIPAL FINDINGS: Using hyperinsulinemic-euglycemic clamps and insulinopenic mice, we show that insulin upregulates its expression in the hypothalamus. Immunofluorescence studies demonstrate that COUP-TFII gene expression is restricted to a subpopulation of ventromedial hypothalamic neurons expressing the melanocortin receptor. In GT1-7 hypothalamic cells, the MC4-R agonist MTII leads to a dose dependant increase of COUP-TFII gene expression secondarily to a local increase in cAMP concentrations. Transfection experiments, using a COUP-TFII promoter containing a functional cAMP responsive element, suggest a direct transcriptional activation by cAMP. Finally, we show that the fed state or intracerebroventricular injections of MTII in mice induce an increased hypothalamic COUP-TFII expression associated with a decreased hepatic and pancreatic COUP-TFII expression. CONCLUSIONS/SIGNIFICANCE: These observations strongly suggest that hypothalamic COUP-TFII gene expression could be a central integrator of insulin and melanocortin signaling pathway within the ventromedial hypothalamus. COUP-TFII could play a crucial role in brain integration of circulating signal of hunger and satiety involved in energy balance regulation