Estrogen receptor-α expressing neurons in the ventrolateral VMH regulate glucose balance

Suppression of hypothalamic oestrogenic signal sustains hyperprolactinemia and metabolic adaptation in lactating mice

17β-oestradiol (E2) inhibits overeating and promotes brown adipose tissue (BAT) thermogenesis, whereas prolactin (PRL) does the opposite. During lactation, the simultaneous decline in E2 and surge in PRL contribute to maternal metabolic adaptations, including hyperphagia and suppressed BAT thermogenesis. However, the underlying neuroendocrine mechanisms remain unclear. Here, we find that oestrogen receptor alpha (ERα)-expressing neurons in the medial basal hypothalamus (MBH), specifically the arcuate nucleus of the hypothalamus and the ventrolateral subdivision of the ventromedial hypothalamus (vlVMH), are suppressed during lactation. Deletion of ERα from MBH neurons in virgin female mice induces metabolic phenotypes characteristic of lactation, including hyperprolactinemia, hyperphagia and suppressed BAT thermogenesis. By contrast, activation of ERαvlVMH neurons in lactating mice attenuates these phenotypes. Overall, our study reveals an inhibitory effect of E2-ERαvlVMH signalling on PRL production, which is suppressed during lactation to sustain hyperprolactinemia and metabolic adaptations.

Parkinson's disease and glucose metabolism impairment

Parkinson's disease (PD) is the second most common neurodegenerative disorder. PD patients exhibit varying degrees of abnormal glucose metabolism throughout disease stages. Abnormal glucose metabolism is closely linked to the PD pathogenesis and progression. Key glucose metabolism processes involved in PD include glucose transport, glycolysis, the tricarboxylic acid cycle, oxidative phosphorylation, the pentose phosphate pathway, and gluconeogenesis. Recent studies suggest that glucose metabolism is a potential therapeutic target for PD. In this review, we explore the connection between PD and abnormal glucose metabolism, focusing on the underlying pathophysiological mechanisms. We also summarize potential therapeutic drugs related to glucose metabolism based on results from current cellular and animal model studies.

Leptin receptor neurons in the dorsomedial hypothalamus require distinct neuronal subsets for thermogenesis and weight loss

The dorsomedial hypothalamus (DMH) receives inputs from the preoptic area (POA), where ambient temperature mediates physiological adaptations of energy expenditure and food intake. Warm-activated POA neurons suppress energy expenditure via brown adipose tissue (BAT) projecting neurons in the dorsomedial hypothalamus/dorsal hypothalamic area (dDMH/DHA). Our earlier work identified leptin receptor (Lepr)-expressing, BAT-projecting dDMH/DHA neurons that mediate metabolic leptin effects. Yet, the neurotransmitter (glutamate or GABA) used by dDMH/DHALepr neurons remains unexplored and was investigated in this study using mice. We report that dDMH/DHALepr neurons represent equally glutamatergic and GABAergic neurons. Surprisingly, chemogenetic activation of glutamatergic and/or GABAergic dDMH/DHA neurons were capable to increase energy expenditure and locomotion, but neither reproduced the beneficial metabolic effects observed after chemogenetic activation of dDMH/DHALepr neurons. We clarify that BAT-projecting dDMH/DHA neurons that innervate the raphe pallidus (RPa) are exclusively glutamatergic Lepr neurons. In contrast, projections of GABAergic or dDMH/DHALepr neurons overlapped in the ventromedial arcuate nucleus (vmARC), suggesting distinct energy expenditure pathways. Brain slice patch clamp recordings further demonstrate a considerable proportion of leptin-inhibited dDMH/DHALepr neurons, while removal of pre-synaptic (indirect) effects with synaptic blocker increased the proportion of leptin-activated dDMH/DHALepr neurons, suggesting that pre-synaptic Lepr neurons inhibit dDMH/DHALepr neurons. We conclude that stimulation of BAT-related, GABA- and glutamatergic dDMH/DHALepr neurons in combination mediate the beneficial metabolic effects. Our data support the idea that dDMH/DHALepr neurons integrate upstream Lepr neurons (e.g., originating from POA and ARC). We speculate that these neurons manage dynamic adaptations to a variety of environmental changes including ambient temperature and energy state. SIGNIFICANCE STATEMENT: Our earlier work identified leptin receptor expressing neurons in the dDMH/DHA as an important thermoregulatory site. Dorsomedial hypothalamus (DMH) Lepr neurons participate in processing and integration of environmental exteroceptive signals like ambient temperature and circadian rhythm, as well as interoceptive signals including leptin and the gut hormone glucagon-like-peptide-1 (GLP1). The present work further characterizes dDMH/DHALepr neurons as a mixed glutamatergic and GABAergic population, but with distinct axonal projection sites. Surprisingly, select activation of glutamatergic and/or GABAergic populations are all able to increase energy expenditure, but are unable to replicate the beneficial metabolic effects observed by Lepr activation. These findings highlighting dDMH/DHA Lepr neurons as a distinct subgroup of glutamatergic and GABAergic neurons that are under indirect and direct influence of the interoceptive hormone leptin and if stimulated are uniquely capable to mediate beneficial metabolic effects. Our work significantly expands our knowledge of thermoregulatory circuits and puts a spotlight onto DMH-Lepr neurons for the integration into whole body energy and body weight homeostasis.

Functionally Separate Populations of Ventromedial Hypothalamic Neurons in Obesity and Diabetes: A Report on Research Supported by Pathway to Stop Diabetes

The ventromedial hypothalamic nucleus (VMN) maintains healthy metabolic function through several important roles. Collectively, homeostasis is maintained via intermingled cells within the VMN that raise blood glucose, lower blood glucose, and stimulate energy expenditure when needed. In this article I discuss the defining factors for the VMN cell types that govern distinct functions induced by the VMN, particularly in relation to energy balance and blood glucose levels. Special attention is given to distinct features of VMN cells responsible for these processes. Finally, these topics are reviewed in the context of research funded by the American Diabetes Association Pathway to Stop Diabetes initiative, with highlighting of key findings and current unresolved questions for future investigations.

Tak1 licenses mitochondrial transfer from astrocytes to POMC neurons to maintain glucose and cholesterol homeostasis

It remains incompletely understood how the astrocytes in the mediobasal hypothalamus (MBH) regulate systemic glucose and cholesterol metabolism. Here, we show that MBH astrocytic Tak1 (transforming growth factor β [TGF-β]-activated kinase 1) controls the metabolism of glucose and cholesterol. Tak1 is expressed in MBH astrocytes and activated after a short-term nutritional excess. In chow-fed mice, astrocytic deletion of Tak1 across the brain or its suppression in the MBH impairs glucose tolerance, reduces insulin sensitivity, and results in hypercholesterolemia. Astrocytic Tak1 activation in the MBH alleviates these symptoms in mice fed a high-fat diet (HFD). We show that astrocytic Tak1 modulates the activity of proopiomelanocortin (POMC) neurons and enables the transport of mitochondria from astrocytes to POMC neurons. In astrocytic Tak1 knockout mice, supplementation of CD38, a molecule that is crucial in mitochondrial transfer, restores glucose and cholesterol homeostasis. Overall, these findings highlight an important role of MBH astrocytic Tak1 in glucose and cholesterol metabolism.

Sex-specific thermoregulatory effects of estrogen signaling in Reprimo lineage cells

Menopause affects over a million individuals annually and is characterized by variable and declining ovarian hormones. Decreasing estrogen levels impact energy homeostasis and increases the risk of metabolic disorders. Energy expenditure is largely directed towards thermoregulation, which is modulated in part by estrogen receptor (ER) α expressing neurons in the hypothalamus. Whether specific sub-populations of ERα+ neurons control the effects of estrogens on thermogenesis remains poorly understood. This study investigates the function of ERα in neurons that express Rprm (Reprimo), a gene we previously linked to thermoregulation in females. Here, we use a novel ReprimoCre mouse to selectively knock out ERα in Rprm lineage neurons (Reprimo-specific estrogen receptor α KO; RERKO) and report changes in core temperature in female mice, with no changes in body weight, body composition, or food intake. RERKO females have elevated brown adipose tissue (BAT) temperature and lower tail temperature relative to controls, suggesting increased heat production and impaired heat dissipation, respectively. Developmental expression of Rprm was detected in the brain, but not in BAT or white adipose tissue suggesting temperature changes may be mediated by the nervous system. Thus, we next ablated Rprm expressing neurons in the ventrolateral area of the ventromedial nucleus of the hypothalamus (VMHvl) and observed a reduction in core temperature and increased fat mass in ablated female mice relative to controls. Taken together, these results show that estrogen signaling in Rprm expressing cells and VMHvl Rprm neurons are critical for thermoregulation, mainly through the modulation of brown adipose tissue thermogenesis in female, but not male mice.

Neuronostatin regulates neuronal function and energetic metabolism in Alzheimer's disease in a GPR107-dependent manner

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease, which is characterized by the accumulation and aggregation of amyloid in brain. Neuronostatin (NST) is an endogenous peptide hormone that participates in many fundamental neuronal processes. However, the metabolism and function of NST in neurons of AD mice are not known. In this study, by combining the structural analyses, primary cultures, knockout cells, and various assessments, the behavior, histopathology, brain-wide expression and cellular signaling pathways in the APP/PS1 mice were investigated. It was found that NST directly bound to GPR107, which was primarily expressed in neurons. NST modulated the neuronal survivability and neurite outgrowth induced by Aβ via GPR107 in neurons. Intracerebroventricular (i.c.v.) administration of NST attenuated learning and memory abilities, reduced the synaptic protein levels of hippocampus, but improved amyloid plaques in the cortex and hippocampus of APP/PS1 mice. NST modulated glucose metabolism of hypothalamus-hippocampus-cortex axis in APP/PS1 mice and decreased ATP levels via the regulation of reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) in response to Aβ, suppressed energetic metabolism, and mitochondrial function in neurons via GPR107/protein kinase A (PKA) signaling pathway. In summary, our findings suggest that NST regulates neuronal function and brain energetic metabolism in AD mice via the GPR107/PKA signaling pathway, which can be a promising target for the treatment of AD.

Hypothalamus-sympathetic-liver axis mediates the early phase of stress-induced hyperglycemia in the male mice

Rapid glucose supply is crucial for animal survival during stress response. How the timescale of stress-induced glucose release precisely controlled by hypothalamic corticotropin-releasing hormone (CRH) neurons remains unclear. Here, we show that stress-induced hyperglycemia can be divided into at least two stages in male mice: the first fast stage is mediated by hypothalamus (paraventricular to ventromedial hypothalamus)-sympathetic (raphe pallidus nucleus to intermediolateral nucleus)-liver (HSL) axis activity; the second delayed stage is mediated by adrenal activity. Blocking the activity of HSL axis impairs predatory evoked flight responses, indicating that the HSL pathway activity is necessary for stress coping. We further reveal the intracellular signal cascade for CRH signal in the hypothalamus, which is mediated by GABAA receptor β3 subunit phosphorylation at S408/409, results in prevention of GABAA receptor membrane recruitment. Thus, we uncovered the precise timescale of glucose supply during stress which is mediated by adrenal independent HSL and adrenal dependent pathway respectively.

Identification of an ionic mechanism for ERα-mediated rapid excitation in neurons

The major female ovarian hormone, 17β-estradiol (E2), can alter neuronal excitability within milliseconds to regulate a variety of physiological processes. Estrogen receptor-α (ERα), classically known as a nuclear receptor, exists as a membrane-bound receptor to mediate this rapid action of E2, but the ionic mechanisms remain unclear. Here, we show that a membrane channel protein, chloride intracellular channel protein-1 (Clic1), can physically interact with ERα with a preference to the membrane-bound ERα. Clic1-mediated currents can be enhanced by E2 and reduced by its depletion. In addition, Clic1 currents are required to mediate the E2-induced rapid excitations in multiple brain ERα populations. Further, genetic disruption of Clic1 in hypothalamic ERα neurons blunts the regulations of E2 on female body weight balance. In conclusion, we identified the Clic1 chloride channel as a key mediator for E2-induced rapid neuronal excitation, which may have a broad impact on multiple neurobiological processes regulated by E2.

Neuronal glucose sensing mechanisms and circuits in the control of insulin and glucagon secretion

Glucose homeostasis is mainly under the control of the pancreatic islet hormones insulin and glucagon, which, respectively, stimulate glucose uptake and utilization by liver, fat, and muscle and glucose production by the liver. The balance between the secretions of these hormones is under the control of blood glucose concentrations. Indeed, pancreatic islet β-cells and α-cells can sense variations in glycemia and respond by an appropriate secretory response. However, the secretory activity of these cells is also under multiple additional metabolic, hormonal, and neuronal signals that combine to ensure the perfect control of glycemia over a lifetime. The central nervous system (CNS), which has an almost absolute requirement for glucose as a source of metabolic energy and thus a vital interest in ensuring that glycemic levels never fall below ∼5 mM, is equipped with populations of neurons responsive to changes in glucose concentrations. These neurons control pancreatic islet cell secretion activity in multiple ways: through both branches of the autonomic nervous system, through the hypothalamic-pituitary-adrenal axis, and by secreting vasopressin (AVP) in the blood at the level of the posterior pituitary. Here, we present the autonomic innervation of the pancreatic islets; the mechanisms of neuron activation by a rise or a fall in glucose concentration; how current viral tracing, chemogenetic, and optogenetic techniques allow integration of specific glucose sensing neurons in defined neuronal circuits that control endocrine pancreas function; and, finally, how genetic screens in mice can untangle the diversity of the hypothalamic mechanisms controlling the response to hypoglycemia.

Tirzepatide shows neuroprotective effects via regulating brain glucose metabolism in APP/PS1 mice

Tirzepatide (LY3298176), a GLP-1 and GIP receptor agonist, is fatty-acid-modified and 39-amino acid linear peptide, which ameliorates learning and memory impairment in diabetic rats. However, the specific molecular mechanism remains unknown. In the present study, we investigated the role of tirzepatide in the neuroprotective effects in Alzheimer's disease (AD) model mice. Tirzepatide was administrated intraperitoneal (i.p.) APP/PS1 mice for 8 weeks with at 10 nmol/kg once-weekly, it significantly decreased the levels of GLP-1R, and GFAP protein expression and amyloid plaques in the cortex, it also lowered neuronal apoptosis induced by amyloid-β (Aβ), but did not affect the anxiety and cognitive function in APP/PS1 mice. Moreover, tirzepatide reduced the blood glucose levels and increased the mRNA expression of GLP-1R, SACF1, ATF4, Glu2A, and Glu2B in the hypothalamus of APP/PS1 mice. Tirzepatide increased the mRNA expression of glucose transporter 1, hexokinase, glucose-6-phosphate dehydrogenase, and phosphofructokinase in the cortex. Lastly, tirzepatide improved the energetic metabolism by regulated reactive oxygen species production and mitochondrial membrane potential caused by Aβ, thereby decreasing mitochondrial function and ATP levels in astrocytes through GLP-1R. These results provide valuable insights into the mechanism of brain glucose metabolism and mitochondrial function of tirzepatide, presenting potential strategies for AD treatment.

27-Hydroxycholesterol acts on estrogen receptor α expressed by POMC neurons in the arcuate nucleus to modulate feeding behavior

Oxysterols are metabolites of cholesterol that regulate cholesterol homeostasis. Among these, the most abundant oxysterol is 27-hydroxycholesterol (27HC), which can cross the blood-brain barrier. Because 27HC functions as an endogenous selective estrogen receptor modulator, we hypothesize that 27HC binds to the estrogen receptor α (ERα) in the brain to regulate energy balance. Supporting this view, we found that delivering 27HC to the brain reduced food intake and activated proopiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (POMCARH) in an ERα-dependent manner. In addition, we observed that inhibiting brain ERα, deleting ERα in POMC neurons, or chemogenetic inhibition of POMCARH neurons blocked the anorexigenic effects of 27HC. Mechanistically, we further revealed that 27HC stimulates POMCARH neurons by inhibiting the small conductance of the calcium-activated potassium (SK) channel. Together, our findings suggest that 27HC, through its interaction with ERα and modulation of the SK channel, inhibits food intake as a negative feedback mechanism against a surge in circulating cholesterol.

VSI: The anoctamins: Structure and function: "Intracellular" anoctamins

Plasma membrane localized anoctamin 1, 2 and 6 (TMEM16A, B, F) have been examined in great detail with respect to structure and function, but much less is known about the other seven intracellular members of this exciting family of proteins. This is probably due to their limited accessibility in intracellular membranous compartments, such as the endoplasmic reticulum (ER) or endosomes. However, these so-called intracellular anoctamins are also found in the plasma membrane (PM) which adds to the confusion regarding their cellular role. Probably all intracellular anoctamins except of ANO8 operate as intracellular phospholipid (PL) scramblases, allowing for Ca2+-activated, passive transport of phospholipids like phosphatidylserine between both membrane leaflets. Probably all of them also conduct ions, which is probably part of their physiological function. In this brief overview, we summarize key findings on the biological functions of ANO3, 4, 5, 7, 8, 9 and 10 (TMEM16C, D, E, G, H, J, K) that are gradually coming to light. Compartmentalized regulation of intracellular Ca2+ signals, tethering of the ER to specific PM contact sites, and control of intracellular vesicular trafficking appear to be some of the functions of intracellular anoctamins, while loss of function and abnormal expression are the cause for various diseases.

Unveiling the potential of estrogen: Exploring its role in neuropsychiatric disorders and exercise intervention

Neuropsychiatric disorders shorten human life spans through multiple ways and become major threats to human health. Exercise can regulate the estrogen signaling, which may be involved in depression, Alzheimer's disease (AD) and Parkinson's disease (PD), and other neuropsychiatric disorders as well in their sex differences. In nervous system, estrogen is an important regulator of cell development, synaptic development, and brain connectivity. Therefore, this review aimed to investigate the potential of estrogen system in the exercise intervention of neuropsychiatric disorders to better understand the exercise in neuropsychiatric disorders and its sex specific. Exercise can exert a protective effect in neuropsychiatric disorders through regulating the expression of estrogen and estrogen receptors, which are involved in neuroprotection, neurodevelopment, and neuronal glucose homeostasis. These processes are mediated by the downstream factors of estrogen signaling, including N-myc downstream regulatory gene 2 (Ndrg2), serotonin (5-HT), delta like canonical Notch ligand 1 (DLL1), NOD-like receptor thermal protein domain associated protein 3 (NLRP3), etc. In addition, exercise can act on the estrogen response element (ERE) fragment in the genes of estrogenic downstream factors like β-amyloid precursor protein cleavase 1 (BACE1). However, there are few studies on the relationship between exercise, the estrogen signaling pathway, and neuropsychiatric disorders. Hence, we review how the estrogen signaling mediates the mechanism of exercise intervention in neuropsychiatric disorders. We aim to provide a theoretical perspective for neuropsychiatric disorders affecting female health and provide theoretical support for the design of exercise prescriptions.

Distinct and shared genetic architectures of gestational diabetes mellitus and type 2 diabetes

Gestational diabetes mellitus (GDM) is a common metabolic disorder affecting more than 16 million pregnancies annually worldwide1,2. GDM is related to an increased lifetime risk of type 2 diabetes (T2D)1-3, with over a third of women developing T2D within 15 years of their GDM diagnosis. The diseases are hypothesized to share a genetic predisposition1-7, but few studies have sought to uncover the genetic underpinnings of GDM. Most studies have evaluated the impact of T2D loci only8-10, and the three prior genome-wide association studies of GDM11-13 have identified only five loci, limiting the power to assess to what extent variants or biological pathways are specific to GDM. We conducted the largest genome-wide association study of GDM to date in 12,332 cases and 131,109 parous female controls in the FinnGen study and identified 13 GDM-associated loci, including nine new loci. Genetic features distinct from T2D were identified both at the locus and genomic scale. Our results suggest that the genetics of GDM risk falls into the following two distinct categories: one part conventional T2D polygenic risk and one part predominantly influencing mechanisms disrupted in pregnancy. Loci with GDM-predominant effects map to genes related to islet cells, central glucose homeostasis, steroidogenesis and placental expression.

Central Channelopathies in Obesity

As obesity has raised heightening awareness, researchers have attempted to identify potential targets that can be treated for therapeutic intervention. Focusing on the central nervous system (CNS), the key organ in maintaining energy balance, a plethora of ion channels that are expressed in the CNS have been inspected and determined through manipulation in different hypothalamic neural subpopulations for their roles in fine-tuning neuronal activity on energy state alterations, possibly acting as metabolic sensors. However, a remaining gap persists between human clinical investigations and mouse studies. Despite having delineated the pathways and mechanisms of how the mouse study-identified ion channels modulate energy homeostasis, only a few targets overlap with the obesity-related risk genes extracted from human genome-wide association studies. Here, we present the most recently discovered CNS-specific metabolism-correlated ion channels using reverse and forward genetics approaches in mice and humans, respectively, in the hope of illuminating the prospects for future therapeutic development.

[Research advances in neuromodulation techniques for blood glucose regulation and diabetes intervention]

Diabetes and its complications that seriously threaten the health and life of human, has become a public health problem of global concern. Glycemic control remains a major focus in the treatment and management of patients with diabetes. The traditional lifestyle interventions, drug therapies, and surgeries have benefited many patients with diabetes. However, due to problems such as poor patient compliance, drug side effects, and limited surgical indications, there are still patients who fail to effectively control their blood glucose levels. With the development of bioelectronic medicine, neuromodulation techniques have shown great potential in the field of glycemic control and diabetes intervention with its unique advantages. This paper mainly reviewed the research advances and latest achievements of neuromodulation technologies such as peripheral nerve electrical stimulation, ultrasound neuromodulation, and optogenetics in blood glucose regulation and diabetes intervention, analyzed the existing problems and presented prospects for the future development trend to promote clinical research and application of neuromodulation technologies in the treatment of diabetes.

Ghrelin-responsive mediobasal hypothalamic neurons mediate exercise-associated food intake and exercise endurance

Previous studies have implicated the orexigenic hormone ghrelin as a mediator of exercise endurance and the feeding response postexercise. Specifically, plasma ghrelin levels nearly double in mice when they are subjected to an hour-long bout of high-intensity interval exercise (HIIE) using treadmills. Also, growth hormone secretagogue receptor-null (GHSR-null) mice exhibit decreased food intake following HIIE and diminished running distance (time until exhaustion) during a longer, stepwise exercise endurance protocol. To investigate whether ghrelin-responsive mediobasal hypothalamus (MBH) neurons mediate these effects, we stereotaxically delivered the inhibitory designer receptor exclusively activated by designer drugs virus AAV2-hSyn-DIO-hM4(Gi)-mCherry to the MBH of Ghsr-IRES-Cre mice, which express Cre recombinase directed by the Ghsr promoter. We found that chemogenetic inhibition of GHSR-expressing MBH neurons (upon delivery of clozapine-N-oxide) 1) suppressed food intake following HIIE, 2) reduced maximum running distance and raised blood glucose and blood lactate levels during an exercise endurance protocol, 3) reduced food intake following ghrelin administration, and 4) did not affect glucose tolerance. Further, HIIE increased MBH Ghsr expression. These results indicate that activation of ghrelin-responsive MBH neurons is required for the normal feeding response to HIIE and the usual amount of running exhibited during an exercise endurance protocol.

Patch-seq: Advances and Biological Applications

Multimodal analysis of gene-expression patterns, electrophysiological properties, and morphological phenotypes at the single-cell/single-nucleus level has been arduous because of the diversity and complexity of neurons. The emergence of Patch-sequencing (Patch-seq) directly links transcriptomics, morphology, and electrophysiology, taking neuroscience research to a multimodal era. In this review, we summarized the development of Patch-seq and recent applications in the cortex, hippocampus, and other nervous systems. Through generating multimodal cell type atlases, targeting specific cell populations, and correlating transcriptomic data with phenotypic information, Patch-seq has provided new insight into outstanding questions in neuroscience. We highlight the challenges and opportunities of Patch-seq in neuroscience and hope to shed new light on future neuroscience research.

Ion channels regulate energy homeostasis and the progression of metabolic disorders: Novel mechanisms and pharmacology of their modulators

The progression of metabolic diseases, featured by dysregulated metabolic signaling pathways, is orchestrated by numerous signaling networks. Among the regulators, ion channels transport ions across the membranes and trigger downstream signaling transduction. They critically regulate energy homeostasis and pathogenesis of metabolic diseases and are potential therapeutic targets for treating metabolic disorders. Ion channel blockers have been used to treat diabetes for decades by stimulating insulin secretion, yet with hypoglycemia and other adverse effects. It calls for deeper understanding of the largely elusive regulatory mechanisms, which facilitates the identification of new therapeutic targets and safe drugs against ion channels. In the article, we critically assess the two principal regulatory mechanisms, protein-channel interaction and post-translational modification on the activities of ion channels to modulate energy homeostasis and metabolic disorders through multiple novel mechanisms. Moreover, we discuss the multidisciplinary methods that provide the tools for elucidation of the regulatory mechanisms mediating metabolic disorders by ion channels. In terms of translational perspective, the mechanistic analysis of recently validated ion channels that regulate insulin resistance, body weight control, and adverse effects of current ion channel antagonists are discussed in details. Their small molecule modulators serve as promising new drug candidates to combat metabolic disorders.

Hypothalamic control of innate social behaviors

Sexual, parental, and aggressive behaviors are central to the reproductive success of individuals and species survival and thus are supported by hardwired neural circuits. The reproductive behavior control column (RBCC), which comprises the medial preoptic nucleus (MPN), the ventrolateral part of the ventromedial hypothalamus (VMHvl), and the ventral premammillary nucleus (PMv), is essential for all social behaviors. The RBCC integrates diverse hormonal and metabolic cues and adjusts an animal's physical activity, hence the chance of social encounters. The RBCC further engages the mesolimbic dopamine system to maintain social interest and reinforces cues and actions that are time-locked with social behaviors. We propose that the RBCC and brainstem form a dual-control system for generating moment-to-moment social actions. This Review summarizes recent progress regarding the identities of RBCC cells and their pathways that drive different aspects of social behaviors.

GHRH Neurons from the Ventromedial Hypothalamic Nucleus Provide Dynamic and Sex-Specific Input to the Brain Glucose-Regulatory Network

The ventromedial hypothalamic nucleus (VMN) controls glucose counter-regulation, including pituitary growth hormone (GH) secretion. VMN neurons that express the transcription factor steroidogenic factor-1/NR5A1 (SF-1) participate in glucose homeostasis. Research utilized in vivo gene knockdown tools to determine if VMN growth hormone-releasing hormone (Ghrh) regulates hypoglycemic patterns of glucagon, corticosterone, and GH outflow according to sex. Intra-VMN Ghrh siRNA administration blunted hypoglycemic hypercorticosteronemia in each sex, but abolished elevated GH release in males only. Single-cell multiplex qPCR showed that dorsomedial VMN (VMNdm) Ghrh neurons express mRNAs encoding Ghrh, SF-1, and protein markers for glucose-inhibitory (γ-aminobutyric acid) or -stimulatory (nitric oxide; glutamate) neurotransmitters. Hypoglycemia decreased glutamate decarboxylase67 (GAD67) transcripts in male, not female VMNdm Ghrh/SF-1 neurons, a response that was refractory to Ghrh siRNA. Ghrh gene knockdown prevented, in each sex, hypoglycemic down-regulation of Ghrh/SF-1 nerve cell GAD65 transcription. Ghrh siRNA amplified hypoglycemia-associated up-regulation of Ghrh/SF-1 neuron nitric oxide synthase mRNA in male and female, without affecting glutaminase gene expression. Ghrh gene knockdown altered Ghrh/SF-1 neuron estrogen receptor-alpha (ERα) and ER-beta transcripts in hypoglycemic male, not female rats, but up-regulated GPR81 lactate receptor mRNA in both sexes. Outcomes infer that VMNdm Ghrh/SF-1 neurons may be an effector of SF-1 control of counter-regulation, and document Ghrh modulation of hypoglycemic patterns of glucose-regulatory neurotransmitter along with estradiol and lactate receptor gene transcription in these cells. Co-transmission of glucose-inhibitory and -stimulatory neurochemicals of diverse chemical structure, spatial, and temporal profiles may enable VMNdm Ghrh neurons to provide complex dynamic, sex-specific input to the brain glucose-regulatory network.

Differential G Protein-Coupled Estrogen Receptor-1 Regulation of Counter-Regulatory Transmitter Marker and 5'-AMP-Activated Protein Kinase Expression in Ventrolateral versus Dorsomedial Ventromedial Hypothalamic Nucleus

INTRODUCTION

The ventromedial hypothalamic nucleus (VMN) is an estrogen receptor (ER)-rich structure that regulates glucostasis. The role of nuclear but not membrane G protein-coupled ER-1 (GPER) in that function has been studied.

METHODS

Gene silencing and laser-catapult microdissection/immunoblot tools were used to examine whether GPER regulates transmitter and energy sensor function in dorsomedial (VMNdm) and/or ventrolateral (VMNvl) VMN counter-regulatory nitrergic and γ-Aminobutyric acid (GABA) neurons.

RESULTS

Intra-VMN GPER siRNA administration to euglycemic animals did not affect VMNdm or -vl nitrergic neuron nitric oxide synthase (nNOS), but upregulated (VMNdm) or lacked influence on (VMNvl) GABA nerve cell glutamate decarboxylase65/67 (GAD) protein. Insulin-induced hypoglycemia (IIH) caused GPER knockdown-reversible augmentation of nNOS, 5'-AMP-activated protein kinase (AMPK), and phospho-AMPK proteins in nitrergic neurons in both divisions. IIH had dissimilar effects on VMNvl (unchanged) versus VMNdm (increased) GABAergic neuron GAD levels, yet GPER knockdown affected these profiles. GPER siRNA prevented hypoglycemic upregulation of VMNvl and -dm GABA neuron AMPK without altering pAMPK expression.

CONCLUSIONS

Outcomes infer that GPER exerts differential control of VMNdm versus -vl GABA transmission during glucostasis and is required for hypoglycemic upregulated nitrergic (VMNdm and -vl) and GABA (VMNdm) signaling. Glycogen metabolism is reported to regulate VMN nNOS and GAD proteins. Data show that GPER limits VMNvl glycogen phosphorylase (GP) protein expression and glycogen buildup during euglycemia but mediates hypoglycemic augmentation of VMNvl GP protein and glycogen content; VMNdm glycogen mass is refractory to GPER control. GPER regulation of VMNvl glycogen metabolism infers that this receptor may govern local counter-regulatory transmission in part by astrocyte metabolic coupling.

Advances in Research on Type 2 Diabetes Mellitus Targets and Therapeutic Agents

Diabetes mellitus is a chronic multifaceted disease with multiple potential complications, the treatment of which can only delay and prolong the terminal stage of the disease, i.e., type 2 diabetes mellitus (T2DM). The World Health Organization predicts that diabetes will be the seventh leading cause of death by 2030. Although many antidiabetic medicines have been successfully developed in recent years, such as GLP-1 receptor agonists and SGLT-2 inhibitors, single-target drugs are gradually failing to meet the therapeutic requirements owing to the individual variability, diversity of pathogenesis, and organismal resistance. Therefore, there remains a need to investigate the pathogenesis of T2DM in more depth, identify multiple therapeutic targets, and provide improved glycemic control solutions. This review presents an overview of the mechanisms of action and the development of the latest therapeutic agents targeting T2DM in recent years. It also discusses emerging target-based therapies and new potential therapeutic targets that have emerged within the last three years. The aim of our review is to provide a theoretical basis for further advancement in targeted therapies for T2DM.

Anoctamin 4 channel currents activate glucose-inhibited neurons in the mouse ventromedial hypothalamus during hypoglycemia

Glucose is the basic fuel essential for maintenance of viability and functionality of all cells. However, some neurons - namely, glucose-inhibited (GI) neurons - paradoxically increase their firing activity in low-glucose conditions and decrease that activity in high-glucose conditions. The ionic mechanisms mediating electric responses of GI neurons to glucose fluctuations remain unclear. Here, we showed that currents mediated by the anoctamin 4 (Ano4) channel are only detected in GI neurons in the ventromedial hypothalamic nucleus (VMH) and are functionally required for their activation in response to low glucose. Genetic disruption of the Ano4 gene in VMH neurons reduced blood glucose and impaired counterregulatory responses during hypoglycemia in mice. Activation of VMHAno4 neurons increased food intake and blood glucose, while chronic inhibition of VMHAno4 neurons ameliorated hyperglycemia in a type 1 diabetic mouse model. Finally, we showed that VMHAno4 neurons represent a unique orexigenic VMH population and transmit a positive valence, while stimulation of neurons that do not express Ano4 in the VMH (VMHnon-Ano4) suppress feeding and transmit a negative valence. Together, our results indicate that the Ano4 channel and VMHAno4 neurons are potential therapeutic targets for human diseases with abnormal feeding behavior or glucose imbalance.

Identification of a GABAergic neural circuit governing leptin signaling deficiency-induced obesity

The hormone leptin is known to robustly suppress food intake by acting upon the leptin receptor (LepR) signaling system residing within the agouti-related protein (AgRP) neurons of the hypothalamus. However, clinical studies indicate that leptin is undesirable as a therapeutic regiment for obesity, which is at least partly attributed to the poorly understood complex secondary structure and key signaling mechanism of the leptin-responsive neural circuit. Here, we show that the LepR-expressing portal neurons send GABAergic projections to a cohort of α3-GABAA receptor expressing neurons within the dorsomedial hypothalamic nucleus (DMH) for the control of leptin-mediated obesity phenotype. We identified the DMH as a key brain region that contributes to the regulation of leptin-mediated feeding. Acute activation of the GABAergic AgRP-DMH circuit promoted food intake and glucose intolerance, while activation of post-synaptic MC4R neurons in the DMH elicited exactly opposite phenotypes. Rapid deletion of LepR from AgRP neurons caused an obesity phenotype which can be rescued by blockage of GABAA receptor in the DMH. Consistent with behavioral results, these DMH neurons displayed suppressed neural activities in response to hunger or hyperglycemia. Furthermore, we identified that α3-GABAA receptor signaling within the DMH exerts potent bi-directional regulation of the central effects of leptin on feeding and body weight. Together, our results demonstrate a novel GABAergic neural circuit governing leptin-mediated feeding and energy balance via a unique α3-GABAA signaling within the secondary leptin-responsive neural circuit, constituting a new avenue for therapeutic interventions in the treatment of obesity and associated comorbidities.

A Microelectrode Array Modified by PtNPs/PB Nanocomposites Used for the Detection and Analysis of Glucose-Sensitive Neurons under Different Blood Glucose States

Hypoglycemia state damages the organism, and glucose-excited and glucose-inhibited neurons from the ventral medial hypothalamus can regulate this state. Therefore, it is crucial to understand the functional mechanism between blood glucose and electrophysiology of glucose-excited and glucose-inhibited neurons. To better detect and analyze this mechanism, a PtNPs/PB nanomaterials modified 32-channel microelectrode array with low impedance (21.91 ± 6.80 kΩ), slight phase delay (-12.7° ± 2.7°), high double layer capacitance (0.606 μF), and biocompatibility was developed to realize in vivo real-time detection of the electrophysiology activities of glucose-excited and glucose-inhibited neurons. The phase-locking level of some glucose-inhibited neurons elevated during fasting (low blood glucose state) and showed theta rhythms after glucose injection (high blood glucose state). With an independent oscillating ability, glucose-inhibited neurons can provide an essential indicator to prevent severe hypoglycemia. The results reveal a mechanism for glucose-sensitive neurons to respond to blood glucose. Some glucose-inhibited neurons can integrate glucose information input and convert it into theta oscillating or phase lock output. It helps in enhancing the interaction between neurons and glucose. Therefore, the research can provide a basis for further controlling blood glucose by modulating the characteristics of neuronal electrophysiology. This helps reduce the damage of organisms under energy-limiting conditions, such as prolonged manned spaceflight or metabolic disorders.

Distinct and shared genetic architectures of Gestational diabetes mellitus and Type 2 Diabetes Mellitus

Gestational diabetes mellitus (GDM) affects more than 16 million pregnancies annually worldwide and is related to an increased lifetime risk of Type 2 diabetes (T2D). The diseases are hypothesized to share a genetic predisposition, but there are few GWAS studies of GDM and none of them is sufficiently powered to assess whether any variants or biological pathways are specific to GDM. We conducted the largest genome-wide association study of GDM to date in 12,332 cases and 131,109 parous female controls in the FinnGen Study and identified 13 GDM-associated loci including 8 novel loci. Genetic features distinct from T2D were identified both at the locus and genomic scale. Our results suggest that the genetics of GDM risk falls into two distinct categories - one part conventional T2D polygenic risk and one part predominantly influencing mechanisms disrupted in pregnancy. Loci with GDM-predominant effects map to genes related to islet cells, central glucose homeostasis, steroidogenesis, and placental expression. These results pave the way for an improved biological understanding of GDM pathophysiology and its role in the development and course of T2D.

Asprosin promotes feeding through SK channel-dependent activation of AgRP neurons

Asprosin, a recently identified adipokine, activates agouti-related peptide (AgRP) neurons in the arcuate nucleus of the hypothalamus (ARH) via binding to protein tyrosine phosphatase receptor δ (Ptprd) to increase food intake. However, the intracellular mechanisms responsible for asprosin/Ptprd-mediated activation of AgRPARH neurons remain unknown. Here, we demonstrate that the small-conductance calcium-activated potassium (SK) channel is required for the stimulatory effects of asprosin/Ptprd on AgRPARH neurons. Specifically, we found that deficiency or elevation of circulating asprosin increased or decreased the SK current in AgRPARH neurons, respectively. AgRPARH-specific deletion of SK3 (an SK channel subtype highly expressed in AgRPARH neurons) blocked asprosin-induced AgRPARH activation and overeating. Furthermore, pharmacological blockade, genetic knockdown, or knockout of Ptprd abolished asprosin's effects on the SK current and AgRPARH neuronal activity. Therefore, our results demonstrated an essential asprosin-Ptprd-SK3 mechanism in asprosin-induced AgRPARH activation and hyperphagia, which is a potential therapeutic target for the treatment of obesity.

Brain nuclear receptors and cardiovascular function

Brain-heart interaction has raised up increasing attentions. Nuclear receptors (NRs) are abundantly expressed in the brain, and emerging evidence indicates that a number of these brain NRs regulate multiple aspects of cardiovascular diseases (CVDs), including hypertension, heart failure, atherosclerosis, etc. In this review, we will elaborate recent findings that have established the physiological relevance of brain NRs in the context of cardiovascular function. In addition, we will discuss the currently available evidence regarding the distinct neuronal populations that respond to brain NRs in the cardiovascular control. These findings suggest connections between cardiac control and brain dynamics through NR signaling, which may lead to novel tools for the treatment of pathological changes in the CVDs.

Hypothalamic Grb10 enhances leptin signalling and promotes weight loss

Leptin acts on hypothalamic neurons expressing agouti-related protein (AgRP) or pro-opiomelanocortin (POMC) to suppress appetite and increase energy expenditure, but the intracellular mechanisms that modulate central leptin signalling are not fully understood. Here we show that growth factor receptor-bound protein 10 (Grb10), an adaptor protein that binds to the insulin receptor and negatively regulates its signalling pathway, can interact with the leptin receptor and enhance leptin signalling. Ablation of Grb10 in AgRP neurons promotes weight gain, while overexpression of Grb10 in AgRP neurons reduces body weight in male and female mice. In parallel, deletion or overexpression of Grb10 in POMC neurons exacerbates or attenuates diet-induced obesity, respectively. Consistent with its role in leptin signalling, Grb10 in AgRP and POMC neurons enhances the anorexic and weight-reducing actions of leptin. Grb10 also exaggerates the inhibitory effects of leptin on AgRP neurons via ATP-sensitive potassium channel-mediated currents while facilitating the excitatory drive of leptin on POMC neurons through transient receptor potential channels. Our study identifies Grb10 as a potent leptin sensitizer that contributes to the maintenance of energy homeostasis by enhancing the response of AgRP and POMC neurons to leptin.

G protein-coupled lactate receptor GPR81 control of ventrolateral ventromedial hypothalamic nucleus glucoregulatory neurotransmitter and 5'-AMP-activated protein kinase expression

Astrocytes store glycogen as energy and promote neurometabolic stability through supply of oxidizable l-lactate. Whether lactate regulates ventromedial hypothalamic nucleus (VMN) glucostatic function as a metabolic volume transmitter is unknown. Current research investigated whether G protein-coupled lactate receptor GPR81 controls astrocyte glycogen metabolism and glucose-regulatory neurotransmission in the ventrolateral VMN (VMNvl), where glucose-regulatory neurons reside. Female rats were pretreated by intra-VMN GPR81 or scramble siRNA infusion before insulin or vehicle injection. VMNvl cell or tissue samples were acquired by laser-catapult- or micropunch microdissection for Western blot protein or uHPLC-electrospray ionization-mass spectrometric glycogen analyses. Data show that GPR81 regulates eu- and/or hypoglycemic patterns of VMNvl astrocyte glycogen metabolic enzyme and 5'-AMP-activated protein kinase (AMPK) protein expression according to VMNvl segment. GPR81 stimulates baseline rostral and caudal VMNvl glycogen accumulation but mediates glycogen breakdown in the former site during hypoglycemia. During euglycemia, GPR81 suppresses the transmitter marker neuronal nitric oxide synthase (nNOS) in rostral and caudal VMNvl nitrergic neurons, but stimulates (rostral VMNvl) or inhibits (caudal VMNvl) GABAergic neuron glutamate decarboxylase65/67 (GAD)protein. During hypoglycemia, GPR81 regulates AMPK activation in nitrergic and GABAergic neurons located in the rostral, but not caudal VMNvl. VMN GPR81 knockdown amplified hypoglycemic hypercorticosteronemia, but not hyperglucagonemia. Results provide novel evidence that VMNvl astrocyte and glucose-regulatory neurons express GPR81 protein. Data identify neuroanatomical subpopulations of VMNvl astrocytes and glucose-regulatory neurons that exhibit differential reactivity to GPR81 input. Heterogeneous GPR81 effects during eu- versus hypoglycemia infer that energy state may affect cellular sensitivity to or postreceptor processing of lactate transmitter signaling.

SK3 in POMC neurons plays a sexually dimorphic role in energy and glucose homeostasis

BACKGROUND

Pro-opiomelanocortin (POMC) neurons play a sexually dimorphic role in body weight and glucose balance. However, the mechanisms for the sex differences in POMC neuron functions are not fully understood.

RESULTS

We detected small conductance calcium-activated potassium (SK) current in POMC neurons. Secondary analysis of published single-cell RNA-Seq data showed that POMC neurons abundantly express SK3, one SK channel subunit. To test whether SK3 in POMC neurons regulates POMC neuron functions on energy and glucose homeostasis, we used a Cre-loxP strategy to delete SK3 specifically from mature POMC neurons. POMC-specific deletion of SK3 did not affect body weight in either male or female mice. Interestingly, male mutant mice showed not only decreased food intake but also decreased physical activity, resulting in unchanged body weight. Further, POMC-specific SK3 deficiency impaired glucose balance specifically in female mice but not in male mice. Finally, no sex differences were detected in the expression of SK3 and SK current in total POMC neurons. However, we found higher SK current but lower SK3 positive neuron population in male POMC neurons co-expressing estrogen receptor α (ERα) compared to that in females.

CONCLUSION

These results revealed a sexually dimorphic role of SK3 in POMC neurons in both energy and glucose homeostasis independent of body weight control, which was associated with the sex difference of SK current in a subpopulation of POMC + ERα + neurons.

Single-cell multiplex qPCR evidence for sex-dimorphic glutamate decarboxylase, estrogen receptor, and 5'-AMP-activated protein kinase alpha subunit mRNA expression by ventromedial hypothalamic nucleus GABAergic neurons

The inhibitory amino acid transmitter γ-aminobutryic acid (GABA) acts within the ventromedial hypothalamus to regulate systemic glucose homeostasis, but the issue of whether this neurochemical signal originates locally or is supplied by afferent innervation remains controversial. Here, combinatory in situ immunocytochemistry/laser-catapult microdissection/single-cell multiplex qPCR techniques were used to investigate the premise that ventromedial hypothalamic nucleus ventrolateral (VMNvl) and/or dorsomedial (VMNdm) division neurons contain mRNAs that encode glutamate decarboxylase (GAD)65 or GAD67 and metabolic-sensory biomarkers, and that expression of these genes is sex-dimorphic. In male and female rats, GAD65 mRNA was elevated in VMNvl versus VMNdm GAD65/67-immunopositive (-ir) neurons, yet the female exhibited higher GAD67 transcript content in VMNdm versus VMNvl GABAergic nerve cells. Estrogen receptor (ER)-alpha transcripts were lower in female versus male GABA neurons from either VMN division; ER-beta and G-protein-coupled ER-1 mRNA expression profiles were also comparatively reduced in cells from female versus male VMNvl. VMNvl and VMNdm GAD65/67-ir-positive neurons showed equivalent levels of glucokinase and sulfonylurea receptor-1 mRNA between sexes. 5'-AMP-activated protein kinase-alpha 1 (AMPKα1) and -alpha 2 (AMPKα2) transcripts were lower in female versus male VMNdm GABAergic neurons, yet AMPKα2 mRNA levels were higher in cells acquired from female versus male VMNvl. Current studies document GAD65 and -67 gene expression in VMNvl and VMNdm GAD65/67-ir-positive neurons in each sex. Results infer that GABAergic neurons in each division may exhibit sex differences in receptiveness to estradiol. Outcomes also support the prospect that energy sensory function by this neurotransmitter cell type may predominate in the VMNvl in female versus VMNdm in the male.

Linking transcriptomes with morphological and functional phenotypes in mammalian retinal ganglion cells

Retinal ganglion cells (RGCs) are the brain's gateway to the visual world. They can be classified into different types on the basis of their electrophysiological, transcriptomic, or morphological characteristics. Here, we characterize the transcriptomic, morphological, and functional features of 472 high-quality RGCs using Patch sequencing (Patch-seq), providing functional and morphological annotation of many transcriptomic-defined cell types of a previously established RGC atlas. We show a convergence of different modalities in defining the RGC identity and reveal the degree of correspondence for well-characterized cell types across multimodal data. Moreover, we complement some RGC types with detailed morphological and functional properties. We also identify differentially expressed genes among ON, OFF, and ON-OFF RGCs such as Vat1l, Slitrk6, and Lmo7, providing candidate marker genes for functional studies. Our research suggests that the molecularly distinct clusters may also differ in their roles of encoding visual information.

Ventromedial hypothalamic OGT drives adipose tissue lipolysis and curbs obesity

The ventromedial hypothalamus (VMH) is known to regulate body weight and counterregulatory response. However, how VMH neurons regulate lipid metabolism and energy balance remains unknown. O-linked β-d-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation), catalyzed by O-GlcNAc transferase (OGT), is considered a cellular sensor of nutrients and hormones. Here, we report that genetic ablation of OGT in VMH neurons inhibits neuronal excitability. Mice with VMH neuron-specific OGT deletion show rapid weight gain, increased adiposity, and reduced energy expenditure, without significant changes in food intake or physical activity. The obesity phenotype is associated with adipocyte hypertrophy and reduced lipolysis of white adipose tissues. In addition, OGT deletion in VMH neurons down-regulates the sympathetic activity and impairs the sympathetic innervation of white adipose tissues. These findings identify OGT in the VMH as a homeostatic set point that controls body weight and underscore the importance of the VMH in regulating lipid metabolism through white adipose tissue-specific innervation.

Gabra5 plays a sexually dimorphic role in POMC neuron activity and glucose balance

Pro-opiomelanocortin (POMC) neurons are important for the regulation of body weight and glucose balance. The inhibitory tone to POMC neurons is mediated primarily by the GABA receptors. However, the detailed mechanisms and functions of GABA receptors are not well understood. The α5 subunit of GABAA receptor, Gabra5, is reported to regulate feeding, and we found that Gabra5 is highly expressed in POMC neurons. To explore the function of Gabra5 in POMC neurons, we knocked down Gabra5 specifically from mature hypothalamic POMC neurons using the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 strategy. This POMC-specific knock-down of Gabra5 did not affect body weight or food intake in either male or female mice. Interestingly, the loss of Gabra5 caused significant increases in the firing frequency and resting membrane potential, and a decrease in the amplitude of the miniature inhibitory postsynaptic current (mIPSC) in male POMC neurons. However, the loss of Gabra5 only modestly decreased the frequency of mIPSC in female POMC neurons. Consistently, POMC-specific knock-down of Gabra5 significantly improved glucose tolerance in male mice but not in female mice. These results revealed a sexually dimorphic role of Gabra5 in POMC neuron activity and glucose balance, independent of body weight control.

In Vivo Photometry Reveals Insulin and 2-Deoxyglucose Maintain Prolonged Inhibition of VMH Vglut2 Neurons in Male Mice

The ventromedial hypothalamic (VMH) nucleus is a well-established hub for energy and glucose homeostasis. In particular, VMH neurons are thought to be important for initiating the counterregulatory response to hypoglycemia, and ex vivo electrophysiology and immunohistochemistry data indicate a clear role for VMH neurons in sensing glucose concentration. However, the temporal response of VMH neurons to physiologically relevant changes in glucose availability in vivo has been hampered by a lack of available tools for measuring neuronal activity over time. Since the majority of neurons within the VMH are glutamatergic and can be targeted using the vesicular glutamate transporter Vglut2, we expressed cre-dependent GCaMP7s in Vglut2 cre mice and examined the response profile of VMH to intraperitoneal injections of glucose, insulin, and 2-deoxyglucose (2DG). We show that reduced available glucose via insulin-induced hypoglycemia and 2DG-induced glucoprivation, but not hyperglycemia induced by glucose injection, inhibits VMH Vglut2 neuronal population activity in vivo. Surprisingly, this inhibition was maintained for at least 45 minutes despite prolonged hypoglycemia and initiation of a counterregulatory response. Thus, although VMH stimulation, via pharmacological, electrical, or optogenetic approaches, is sufficient to drive a counterregulatory response, our data suggest VMH Vglut2 neurons are not the main drivers required to do so, since VMH Vglut2 neuronal population activity remains suppressed during hypoglycemia and glucoprivation.

Hypothalamic Irak4 is a genetically controlled regulator of hypoglycemia-induced glucagon secretion

OBJECTIVES

Glucagon secretion to stimulate hepatic glucose production is the first line of defense against hypoglycemia. This response is triggered by so far incompletely characterized central hypoglycemia-sensing mechanisms, which control autonomous nervous activity and hormone secretion. The objective of this study was to identify novel hypothalamic genes controlling insulin-induced glucagon secretion.

METHODS

To obtain new information on the mechanisms of hypothalamic hypoglycemia sensing, we combined genetic and transcriptomic analysis of glucagon response to insulin-induced hypoglycemia in a panel of BXD recombinant inbred mice.

RESULTS

We identified two QTLs on chromosome 8 and chromosome 15. We further investigated the role of Irak4 and Cpne8, both located in the QTL on chromosome 15, in C57BL/6J and DBA/2J mice, the BXD mouse parental strains. We found that the poor glucagon response of DBA/2J mice was associated with higher hypothalamic expression of Irak4, which encodes a kinase acting downstream of the interleukin-1 receptor (Il-1R), and of Il-ß when compared with C57BL/6J mice. We showed that intracerebroventricular administration of an Il-1R antagonist in DBA/2J mice restored insulin-induced glucagon secretion; this was associated with increased c-fos expression in the arcuate and paraventricular nuclei of the hypothalamus and with higher activation of both branches of the autonomous nervous system. Whole body inactivation of Cpne8, which encodes a Ca++-dependent regulator of membrane trafficking and exocytosis, however, had no impact on insulin-induced glucagon secretion.

CONCLUSIONS

Collectively, our data identify Irak4 as a genetically controlled regulator of hypoglycemia-activated hypothalamic neurons and glucagon secretion.

Glucose-sensing glucagon-like peptide-1 receptor neurons in the dorsomedial hypothalamus regulate glucose metabolism

Glucagon-like peptide-1 (GLP-1) regulates energy homeostasis via activation of the GLP-1 receptors (GLP-1Rs) in the central nervous system. However, the mechanism by which the central GLP-1 signal controls blood glucose levels, especially in different nutrient states, remains unclear. Here, we defined a population of glucose-sensing GLP-1R neurons in the dorsomedial hypothalamic nucleus (DMH), by which endogenous GLP-1 decreases glucose levels via the cross-talk between the hypothalamus and pancreas. Specifically, we illustrated the sufficiency and necessity of DMHGLP-1R in glucose regulation. The activation of the DMHGLP-1R neurons is mediated by a cAMP-PKA-dependent inhibition of a delayed rectifier potassium current. We also dissected a descending control of DMHGLP-1R -dorsal motor nucleus of the vagus nerve (DMV)-pancreas activity that can regulate glucose levels by increasing insulin release. Thus, our results illustrate how central GLP-1 action in the DMH can induce a nutrient state-dependent reduction in blood glucose level.

Hypothalamic Estrogen Signaling and Adipose Tissue Metabolism in Energy Homeostasis

Obesity has become a global epidemic, and it is a major risk factor for other metabolic disorders such as type 2 diabetes and cardiometabolic disease. Accumulating evidence indicates that there is sex-specific metabolic protection and disease susceptibility. For instance, in both clinical and experimental studies, males are more likely to develop obesity, insulin resistance, and diabetes. In line with this, males tend to have more visceral white adipose tissue (WAT) and less brown adipose tissue (BAT) thermogenic activity, both leading to an increased incidence of metabolic disorders. This female-specific fat distribution is partially mediated by sex hormone estrogens. Specifically, hypothalamic estrogen signaling plays a vital role in regulating WAT distribution, WAT beiging, and BAT thermogenesis. These regulatory effects on adipose tissue metabolism are primarily mediated by the activation of estrogen receptor alpha (ERα) in neurons, which interacts with hormones and adipokines such as leptin, ghrelin, and insulin. This review discusses the contribution of adipose tissue dysfunction to obesity and the role of hypothalamic estrogen signaling in preventing metabolic diseases with a particular focus on the VMH, the central regulator of energy expenditure and glucose homeostasis.

Recent advances in understanding hypothalamic control of defensive responses to hypoglycaemia

Maintenance of normal blood glucose is important for survival. In particular, brain function is dependent on circulating glucose. In health, a series of powerful counterregulatory defences operate to prevent/limit hypoglycaemia. These defences are altered to varying degrees in diabetes and in particular, a subset of people with diabetes can develop profound deficits in these defences placing them at increased risk of suffering episodes of severe hypoglycaemia. Brain is an important controller of glucose homeostasis and developments in molecular techniques have allowed the neurocircuitry of a number of important centrally-controlled homeostatic processes such as energy balance, thirst and thermoregulation to be defined. This review describes how some of these advances have allowed a better understanding of the neuronal/brain ensembles which help protect against hypoglycaemia.

The ventromedial hypothalamic nucleus: watchdog of whole-body glucose homeostasis

The brain, particularly the ventromedial hypothalamic nucleus (VMH), has been long known for its involvement in glucose sensing and whole-body glucose homeostasis. However, it is still not fully understood how the brain detects and responds to the changes in the circulating glucose levels, as well as brain-body coordinated control of glucose homeostasis. In this review, we address the growing evidence implicating the brain in glucose homeostasis, especially in the contexts of hypoglycemia and diabetes. In addition to neurons, we emphasize the potential roles played by non-neuronal cells, as well as extracellular matrix in the hypothalamus in whole-body glucose homeostasis. Further, we review the ionic mechanisms by which glucose-sensing neurons sense fluctuations of ambient glucose levels. We also introduce the significant implications of heterogeneous neurons in the VMH upon glucose sensing and whole-body glucose homeostasis, in which sex difference is also addressed. Meanwhile, research gaps have also been identified, which necessities further mechanistic studies in future.

Estrogenic Action in Stress-Induced Neuroendocrine Regulation of Energy Homeostasis

Estrogens are among important contributing factors to many sex differences in neuroendocrine regulation of energy homeostasis induced by stress. Research in this field is warranted since chronic stress-related psychiatric and metabolic disturbances continue to be top health concerns, and sex differences are witnessed in these aspects. For example, chronic stress disrupts energy homeostasis, leading to negative consequences in the regulation of emotion and metabolism. Females are known to be more vulnerable to the psychological consequences of stress, such as depression and anxiety, whereas males are more vulnerable to the metabolic consequences of stress. Sex differences that exist in the susceptibility to various stress-induced disorders have led researchers to hypothesize that gonadal hormones are regulatory factors that should be considered in stress studies. Further, estrogens are heavily recognized for their protective effects on metabolic dysregulation, such as anti-obesogenic and glucose-sensing effects. Perturbations to energy homeostasis using laboratory rodents, such as physiological stress or over-/under- feeding dietary regimen prevalent in today’s society, offer hints to the underlying mechanisms of estrogenic actions. Metabolic effects of estrogens primarily work through estrogen receptor α (ERα), which is differentially expressed between the sexes in hypothalamic nuclei regulating energy metabolism and in extrahypothalamic limbic regions that are not typically associated with energy homeostasis. In this review, we discuss estrogenic actions implicated in stress-induced sex-distinct metabolic disorders.

An estrogen-sensitive hypothalamus-midbrain neural circuit controls thermogenesis and physical activity

Estrogen receptor–α (ERα) expressed by neurons in the ventrolateral subdivision of the ventromedial hypothalamic nucleus (ERαvlVMH) regulates body weight in females, but the downstream neural circuits mediating this biology remain largely unknown. Here we identified a neural circuit mediating the metabolic effects of ERαvlVMH neurons. We found that selective activation of ERαvlVMH neurons stimulated brown adipose tissue (BAT) thermogenesis, physical activity, and core temperature and that ERαvlVMH neurons provide monosynaptic glutamatergic inputs to 5-hydroxytryptamine (5-HT) neurons in the dorsal raphe nucleus (DRN). Notably, the ERαvlVMH → DRN circuit responds to changes in ambient temperature and nutritional states. We further showed that 5-HTDRN neurons mediate the stimulatory effects of ERαvlVMH neurons on BAT thermogenesis and physical activity and that ERα expressed by DRN-projecting ERαvlVMH neurons is required for the maintenance of energy balance. Together, these findings support a model that ERαvlVMH neurons activate BAT thermogenesis and physical activity through stimulating 5-HTDRN neurons.

Neuronal regulation of glucagon secretion and gluconeogenesis

Hypoglycemia almost never develops in healthy individuals because multiple hypoglycemia sensing systems, located in the periphery and in the central nervous system trigger a coordinated counterregulatory hormonal response to restore normoglycemia. This involves not only the secretion of glucagon but also of epinephrine, norepinephrine, cortisol and growth hormone. Increased hepatic glucose production is also stimulated by direct autonomous nervous connections to the liver that stimulate glycogenolysis and gluconeogenesis. This counterregulatory response, however, becomes deregulated in a significant fraction of diabetic patients that receive insulin therapy. This leads to risk of developing hypoglycemic episodes, of increasing severity, which negatively impact the quality of life of the patients. How hypoglycemia is detected by the central nervous system is being actively investigated. Recent studies using novel molecular biological, optogenetic and chemogenetic techniques, allow the characterization of glucose sensing neurons, the mechanisms of hypoglycemia detection, the neuronal circuits in which they are integrated and the physiological responses they control. This review will discuss recent studies aimed at identifying central hypoglycemia sensing neuronal circuits, how neurons are activated by hypoglycemia, and how they restore normoglycemia.

Hypothalamic steroid receptor coactivator-2 regulates adaptations to fasting and overnutrition

The neuroendocrine system coordinates metabolic and behavioral adaptations to fasting, including reducing energy expenditure, promoting counterregulation, and suppressing satiation and anxiety to engage refeeding. Here, we show that steroid receptor coactivator-2 (SRC-2) in pro-opiomelanocortin (POMC) neurons is a key regulator of all these responses to fasting. POMC-specific deletion of SRC-2 enhances the basal excitability of POMC neurons; mutant mice fail to efficiently suppress energy expenditure during food deprivation. SRC-2 deficiency blunts electric responses of POMC neurons to glucose fluctuations, causing impaired counterregulation. When food becomes available, these mutant mice show insufficient refeeding associated with enhanced satiation and discoordination of anxiety and food-seeking behavior. SRC-2 coactivates Forkhead box protein O1 (FoxO1) to suppress POMC gene expression. POMC-specific deletion of SRC-2 protects mice from weight gain induced by an obesogenic diet feeding and/or FoxO1 overexpression. Collectively, we identify SRC-2 as a key molecule that coordinates multifaceted adaptive responses to food shortage.

Targeting the T-type calcium channel Cav3.2 in GABAergic arcuate nucleus neurons to treat obesity

OBJECTIVE

Cav3.2, a T-type low voltage-activated calcium channel widely expressed throughout the central nervous system, plays a vital role in neuronal excitability and various physiological functions. However, the effects of Cav3.2 on energy homeostasis remain unclear. Here, we examined the role of Cav3.2 expressed by hypothalamic GABAergic neurons in the regulation of food intake and body weight in mice and explored the underlying mechanisms.

METHODS

Male congenital Cana1h (the gene coding for Cav3.2) global knockout (Cav3.2KO) mice and their wild type (WT) littermates were first used for metabolic phenotyping studies. By using the CRISPR-Cas9 technique, Cav3.2 was selectively deleted from GABAergic neurons in the arcuate nucleus of the hypothalamus (ARH) by specifically overexpressing Cas9 protein and Cav3.2-targeting sgRNAs in ARH Vgat (VgatARH) neurons. These male mutants (Cav3.2KO-VgatARH) were used to determine whether Cav3.2 expressed by VgatARH neurons is required for the proper regulation of energy balance. Subsequently, we used an electrophysiological patch-clamp recording in ex vivo brain slices to explore the impact of Cav3.2KO on the cellular excitability of VgatARH neurons.

RESULTS

Male Cav3.2KO mice had significantly lower food intake than their WT littermate controls when fed with either a normal chow diet (NCD) or a high-fat diet (HFD). This hypophagia phenotype was associated with increased energy expenditure and decreased fat mass, lean mass, and total body weight. Selective deletion of Cav3.2 in VgatARH neurons resulted in similar feeding inhibition and lean phenotype without changing energy expenditure. These data provides an intrinsic mechanism to support the previous finding on ARH non-AgRP GABA neurons in regulating diet-induced obesity. Lastly, we found that naringenin extract, a predominant flavanone found in various fruits and herbs and known to act on Cav3.2, decreased the firing activity of VgatARH neurons and reduced food intake and body weight. These naringenin-induced inhibitions were fully blocked in Cav3.2KO-VgatARH mice.

CONCLUSION

Our results identified Cav3.2 expressed by VgatARH neurons as an essential intrinsic modulator for food intake and energy homeostasis, which is a potential therapeutic target in the treatment of obesity.

Ventromedial Nucleus of the Hypothalamus Neurons Under the Magnifying Glass

The ventromedial nucleus of the hypothalamus (VMH) is a complex brain structure that is integral to many neuroendocrine functions, including glucose regulation, thermogenesis, and appetitive, social, and sexual behaviors. As such, it is of little surprise that the nucleus is under intensive investigation to decipher the mechanisms which underlie these diverse roles. Developments in genetic and investigative tools, for example the targeting of steroidogenic factor-1-expressing neurons, have allowed us to take a closer look at the VMH, its connections, and how it affects competing behaviors. In the current review, we aim to integrate recent findings into the literature and contemplate the conclusions that can be drawn.

Barbadin Potentiates Long-Term Effects of Lorcaserin on POMC Neurons and Weight Loss

Obesity is a serious global health problem because of its increasing prevalence and comorbidities, but its treatments are limited. The serotonin 2C receptor (5-HT2CR), a G-protein-coupled receptor, activates proopiomelanocortin (POMC) neurons in the arcuate nucleus of hypothalamus (ARH) to reduce appetite and weight gain. However, several 5-HT analogs targeting this receptor, e.g., lorcaserin (Lor), suffer from diminished efficacy to reduce weight after prolonged administration. Here, we show that barbadin (Bar), a novel β-arrestin/β2-adaptin inhibitor, can prevent 5-HT2CR internalization in cells and potentiate long-term effects of Lor to reduce appetite and body weight in male mice. Mechanistically, we demonstrate that Bar co-treatment can effectively maintain the sensitivity of the 5-HT2CR in POMCARH neurons, despite prolonged Lor exposure, thereby allowing these neurons to be activated through opening the transient receptor potential cation (TRPC) channels. Thus, our results prove the concept that inhibition of 5-HT2CR desensitization can be a valid strategy to improve the long-term weight loss effects of Lor or other 5-HT2CR agonists, and also provide an intellectual framework to develop effective long-term management of weight by targeting 5-HT2CR desensitization.SIGNIFICANCE STATEMENT By demonstrating that the combination of barbadin (Bar) with a G-protein-coupled receptor (GPCR) agonist can provide prolonged weight-lowering benefits in a preclinical setting, our work should call for additional efforts to validate Bar as a safe and effective medicine or to use Bar as a lead compound to develop more suitable compounds for obesity treatment. These results prove the concept that inhibition of serotonin 2C receptor (5-HT2CR) desensitization can be a valid strategy to improve the long-term weight loss effects of lorcaserin (Lor) or other 5-HT2CR agonists. Since GPCRs represent a major category as therapeutic targets for various human diseases and desensitization of GPCRs is a common issue, our work may provide a conceptual framework to enhance effects of a broad range of GPCR medicines.