Sustained inhibition of NPY/AgRP neuronal activity by FGF1.

In rodent models of type 2 diabetes (T2D), central administration of FGF1 normalizes elevated blood glucose levels in a manner that is sustained for weeks or months. Increased activity of NPY/AgRP neurons in the hypothalamic arcuate nucleus (ARC) is implicated in the pathogenesis of hyperglycemia in these animals, and the ARC is a key brain area for the antidiabetic action of FGF1. We therefore sought to determine whether FGF1 inhibits NPY/AgRP neurons and, if so, whether this inhibitory effect is sufficiently durable to offer a feasible explanation for sustained diabetes remission induced by central administration of FGF1. Here, we show that FGF1 inhibited ARC NPY/AgRP neuron activity, both after intracerebroventricular injection in vivo and when applied ex vivo in a slice preparation; we also showed that the underlying mechanism involved increased input from presynaptic GABAergic neurons. Following central administration, the inhibitory effect of FGF1 on NPY/AgRP neurons was also highly durable, lasting for at least 2 weeks. To our knowledge, no precedent for such a prolonged inhibitory effect exists. Future studies are warranted to determine whether NPY/AgRP neuron inhibition contributes to the sustained antidiabetic action elicited by intracerebroventricular FGF1 injection in rodent models of T2D.

Evaluation of VGF peptides as potential anti-obesity candidates in pre-clinical animal models.

VGF is a peptide precursor expressed in neuroendocrine cells that is suggested to play a role in the regulation of energy homeostasis. VGF is proteolytically cleaved to yield multiple bioactive peptides. However, the specific actions of VGF-derived peptides on energy homeostasis remain unclear. The aim of the present work was to investigate the role of VGF-derived peptides in energy homeostasis and explore the pharmacological actions of VGF-derived peptides on body weight in preclinical animal models. VGF-derived peptides (NERP-1, NERP-2, PGH-NH2, PGH-OH, NERP-4, TLQP-21, TLQP-30, TLQP-62, HHPD-41, AQEE-30, and LQEQ-19) were synthesized and screened for their ability to affect neuronal activity in vitro on hypothalamic brain slices and modulate food intake and energy expenditure after acute central administration in vivo. In addition, the effects of NERP-1, NERP-2, PGH-NH2, TLQP-21, TLQP-62, and HHPD-41 on energy homeostasis were studied after chronic central infusion. NERP-1, PGH-NH2, HHPD-41, and TLQP-62 increased the functional activity of hypothalamic neuronal networks. However, none of the peptides altered energy homeostasis after either acute or chronic ICV administration. The present data do not support the potential use of the tested VGF-derived peptides as novel anti-obesity drug candidates.

Transcriptomic analysis links diverse hypothalamic cell types to fibroblast growth factor 1-induced sustained diabetes remission.

In rodent models of type 2 diabetes (T2D), sustained remission of hyperglycemia can be induced by a single intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF1), and the mediobasal hypothalamus (MBH) was recently implicated as the brain area responsible for this effect. To better understand the cellular response to FGF1 in the MBH, we sequenced >79,000 single-cell transcriptomes from the hypothalamus of diabetic Lepob/ob mice obtained on Days 1 and 5 after icv injection of either FGF1 or vehicle. A wide range of transcriptional responses to FGF1 was observed across diverse hypothalamic cell types, with glial cell types responding much more robustly than neurons at both time points. Tanycytes and ependymal cells were the most FGF1-responsive cell type at Day 1, but astrocytes and oligodendrocyte lineage cells subsequently became more responsive. Based on histochemical and ultrastructural evidence of enhanced cell-cell interactions between astrocytes and Agrp neurons (key components of the melanocortin system), we performed a series of studies showing that intact melanocortin signaling is required for the sustained antidiabetic action of FGF1. These data collectively suggest that hypothalamic glial cells are leading targets for the effects of FGF1 and that sustained diabetes remission is dependent on intact melanocortin signaling.

Reelin is modulated by diet-induced obesity and has direct actions on arcuate proopiomelanocortin neurons.

OBJECTIVE: Reelin (RELN) is a large glycoprotein involved in synapse maturation and neuronal organization throughout development. Deficits in RELN signaling contribute to multiple psychological disorders, such as autism spectrum disorder, schizophrenia, and bipolar disorder. Nutritional stress alters RELN expression in brain regions associated with these disorders; however, the involvement of RELN in the neural circuits involved in energy metabolism is unknown. The RELN receptors apolipoprotein E receptor 2 (ApoER2) and very low-density lipoprotein receptor (VLDLR) are involved in lipid metabolism and expressed in the hypothalamus. Here we explored the involvement of RELN in hypothalamic signaling and the impact of diet-induced obesity (DIO) on this system. METHODS: Adult male mice were fed a chow diet or maintained on a high-fat diet (HFD) for 12-16 weeks. HFD-fed DIO mice exhibited decreased ApoER2 and VLDLR expression and increased RELN protein in the hypothalamus. Electrophysiology was used to determine the mechanism by which the central fragment of RELN (CF-RELN) acts on arcuate nucleus (ARH) satiety-promoting proopiomelanocortin (POMC) neurons and the impact of DIO on this circuitry. RESULTS: CF-RELN exhibited heterogeneous presynaptic actions on inhibitory inputs onto ARH-POMC-EGFP neurons and consistent postsynaptic actions. Additionally, central administration of CF-RELN caused a significant increase in ARH c-Fos expression and an acute decrease in food intake and body weight. CONCLUSIONS: We conclude that RELN signaling is modulated by diet, that RELN is involved in synaptic signaling onto ARH-POMC neurons, and that altering central CF-RELN levels can impact food intake and body weight.

Early overnutrition alters synaptic signaling and induces leptin resistance in arcuate proopiomelanocortin neurons.

Early overnutrition disrupts leptin sensitivity and the development of hypothalamic pathways involved in the regulation of metabolism and feeding behavior. While previous studies have largely focused on the development of neuronal projections, few studies have examined the impact of early nutrition on hypothalamic synaptic physiology. In this study we characterized the synaptic development of proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARH), their sensitivity to leptin, and the impact of early overnutrition on the development of these neurons. Electrophysiology recordings were performed in mouse ARH brain slices containing POMC-EGFP neurons from postnatal age (P) 7-9 through adulthood. We determined that pre- and postsynaptic components of inhibitory inputs increased throughout the first 3 weeks of the postnatal period, which coincided with a decreased membrane potential in POMC neurons. We then examined whether chronic postnatal overnutrition (CPO) altered these synaptic connections. CPO mice exhibited increased body weight and circulating leptin levels, as described previously. POMC neurons in CPO mice had an increase in post-synaptic inhibitory currents compared to controls at 2 weeks of age, but this effect reversed by the third week. In control mice we observed heterogenous effects of leptin on POMC neurons in early life that transitioned to predominantly stimulatory actions in adulthood. However, postnatal overfeeding resulted in POMC neurons becoming leptin-resistant which persisted into adulthood. These studies suggest that postnatal overfeeding alters the postsynaptic development of POMC neurons and induces long-lasting leptin resistance in ARH-POMC neurons.

GLP-1R Signaling Directly Activates Arcuate Nucleus Kisspeptin Action in Brain Slices but Does not Rescue Luteinizing Hormone Inhibition in Ovariectomized Mice During Negative Energy Balance.

Kisspeptin (Kiss1) neurons in the hypothalamic arcuate nucleus (ARC) are key components of the hypothalamic-pituitary-gonadal axis, as they regulate the basal pulsatile release of gonadotropin releasing hormone (GnRH). ARC Kiss1 action is dependent on energy status, and unmasking metabolic factors responsible for modulating ARC Kiss1 neurons is of great importance. One possible factor is glucagon-like peptide 1 (GLP-1), an anorexigenic neuropeptide produced by brainstem preproglucagon neurons. Because GLP fiber projections and the GLP-1 receptor (GLP-1R) are abundant in the ARC, we hypothesized that GLP-1R signaling could modulate ARC Kiss1 action. Using ovariectomized mice, we found that GLP-producing fibers come in close apposition with ARC Kiss1 neurons; these neurons also contain Glp1r mRNA. Electrophysiological recordings revealed that liraglutide (a long-acting GLP-1R agonist) increased action potential firing and caused a direct membrane depolarization of ARC Kiss1 cells in brain slices. We determined that brainstem preproglucagon mRNA is decreased after a 48-h fast in mice, a negative energy state in which ARC Kiss1 expression and downstream GnRH/luteinizing hormone (LH) release are potently suppressed. However, activation of GLP-1R signaling in fasted mice with liraglutide was not sufficient to prevent LH inhibition. Furthermore, chronic central infusions of the GLP-1R antagonist, exendin(9-39), in ad libitum-fed mice did not alter ARC Kiss1 mRNA or plasma LH. As a whole, these data identify a novel interaction of the GLP-1 system with ARC Kiss1 neurons but indicate that CNS GLP-1R signaling alone is not critical for the maintenance of LH during fasting or normal feeding.

Postnatal undernutrition delays a key step in the maturation of hypothalamic feeding circuits.

OBJECTIVE: Humans and animals exposed to undernutrition (UN) during development often experience accelerated "catch-up" growth when food supplies are plentiful. Little is known about the mechanisms regulating early growth rates. We previously reported that actions of leptin and presynaptic inputs to orexigenic NPY/AgRP/GABA (NAG) neurons in the arcuate nucleus of the hypothalamus are almost exclusively excitatory during the lactation period, since neuronal and humoral inhibitory systems do not develop until after weaning. Moreover, we identified a critical step that regulates the maturation of electrophysiological responses of NAG neurons at weaning - the onset of genes encoding ATP-dependent potassium (KATP) channel subunits. We explored the possibility that UN promotes subsequent catch-up growth, in part, by delaying the maturation of negative feedback systems to neuronal circuits driving food intake. METHODS: We used the large litter (LL) size model to study the impacts of postnatal UN followed by catch-up growth. We evaluated the maturation of presynaptic and postsynaptic inhibitory systems in NAG neurons using a combination of electrophysiological and molecular criteria, in conjunction with leptin's ability to suppress fasting-induced hyperphagia. RESULTS: The onset of KATP channel subunit expression and function, the switch in leptin's effect on NAG neurons, the ingrowth of inhibitory inputs to NAG neurons, and the development of homeostatic feedback to feeding circuits were delayed in LL offspring relative to controls. The development of functional KATP channels and the establishment of leptin-mediated suppression of food intake in the peri-weaning period were tightly linked and were not initiated until growth and adiposity of LL offspring caught up to controls. CONCLUSIONS: Our data support the idea that initiation of KATP channel subunit expression in NAG neurons serves as a molecular gatekeeper for the maturation of homeostatic feeding circuits.