Agouti-related Protein Research Articles

A normative framework dissociates need and motivation in hypothalamic neurons.

Physiological needs evoke motivational drives that produce natural behaviors for survival. In previous studies, the temporally intertwined dynamics of need and motivation have made it challenging to differentiate these two components. On the basis of classic homeostatic theories, we established a normative framework to derive computational models for need-encoding and motivation-encoding neurons. By combining the model-based predictions and naturalistic experimental paradigms, we demonstrated that agouti-related peptide (AgRP) and lateral hypothalamic leptin receptor (LHLepR) neuronal activities encode need and motivation, respectively. Our model further explains the difference in the dynamics of appetitive behaviors induced by optogenetic stimulation of AgRP or LHLepR neurons. Our study provides a normative modeling framework that explains how hypothalamic neurons separately encode need and motivation in the mammalian brain.

Leptin-activated hypothalamic BNC2 neurons acutely suppress food intake.

Leptin is an adipose tissue hormone that maintains homeostatic control of adipose tissue mass by regulating the activity of specific neural populations controlling appetite and metabolism1. Leptin regulates food intake by inhibiting orexigenic agouti-related protein (AGRP) neurons and activating anorexigenic pro-opiomelanocortin (POMC) neurons2. However, whereas AGRP neurons regulate food intake on a rapid time scale, acute activation of POMC neurons has only a minimal effect3-5. This has raised the possibility that there is a heretofore unidentified leptin-regulated neural population that rapidly suppresses appetite. Here we report the discovery of a new population of leptin-target neurons expressing basonuclin 2 (Bnc2) in the arcuate nucleus that acutely suppress appetite by directly inhibiting AGRP neurons. Opposite to the effect of AGRP activation, BNC2 neuronal activation elicited a place preference indicative of positive valence in hungry but not fed mice. The activity of BNC2 neurons is modulated by leptin, sensory food cues and nutritional status. Finally, deleting leptin receptors in BNC2 neurons caused marked hyperphagia and obesity, similar to that observed in a leptin receptor knockout in AGRP neurons. These data indicate that BNC2-expressing neurons are a key component of the neural circuit that maintains energy balance, thus filling an important gap in our understanding of the regulation of food intake and leptin action.

Early perturbations to fluid homeostasis alter development of hypothalamic feeding circuits with context-specific changes in ingestive behavior.

Drinking and feeding are tightly coordinated homeostatic events and the paraventricular nucleus of the hypothalamus (PVH) represents a possible node of neural integration for signals related to energy and fluid homeostasis. We used TRAP2;Ai14 and Fos labeling to visualize neurons in the PVH and median preoptic nucleus (MEPO) responding to both water deprivation and hunger. Moreover, we determined that structural and functional development of dehydration-sensitive inputs to the PVH from the MEPO precedes those of agouti-related peptide (AgRP) neurons, which convey hunger signals and are known to be developmentally programmed by nutrition. We also determined that osmotic hyperstimulation of neonatal mice led to enhanced AgRP inputs to the PVH in adulthood, as well as disruptions to ingestive behaviors during high-fat diet feeding and dehydration-anorexia. Thus, development of feeding circuits is impacted not only by nutritional signals, but also by early perturbations to fluid homeostasis with context-specific consequences for coordination of ingestive behavior.

A subcortical feeding circuit linking an interoceptive node to jaw movement.

The brain processes an array of stimuli, enabling the selection of appropriate behavioural responses, but the neural pathways linking interoceptive inputs to outputs for feeding are poorly understood1-3. Here we delineate a subcortical circuit in which brain-derived neurotrophic factor (BDNF)-expressing neurons in the ventromedial hypothalamus (VMH) directly connect interoceptive inputs to motor centres, controlling food consumption and jaw movements. VMHBDNF neuron inhibition increases food intake by gating motor sequences of feeding through projections to premotor areas of the jaw. When food is unavailable, VMHBDNF inhibition elicits consummatory behaviours directed at inanimate objects such as wooden blocks, and inhibition of perimesencephalic trigeminal area (pMe5) projections evokes rhythmic jaw movements. The activity of these neurons is decreased during food consumption and increases when food is in proximity but not consumed. Activity is also increased in obese animals and after leptin treatment. VMHBDNF neurons receive monosynaptic inputs from both agouti-related peptide (AgRP) and proopiomelanocortin neurons in the arcuate nucleus (Arc), and constitutive VMHBDNF activation blocks the orexigenic effect of AgRP activation. These data indicate an Arc → VMHBDNF → pMe5 circuit that senses the energy state of an animal and regulates consummatory behaviours in a state-dependent manner.

Effects of Chitosan and N-Succinyl Chitosan on Metabolic Disorders Caused by Oral Administration of Olanzapine in Mice.

The issue of human mental health is gaining more and more attention nowadays. However, most mental disorders are treated with antipsychotic drugs that cause weight gain and metabolic disorders, which include olanzapine (OLZ). The search for and development of natural compounds for the prevention of obesity when taking antipsychotic drugs is an urgent task. The biopolymer chitosan (Chi) and its derivatives have lipid-lowering and anti-diabetic properties, which makes them potential therapeutic substances for use in the treatment of metabolic disorders. The purpose of this work was to analyze the effect of the natural biopolymer Chi, its derivative N-succinyl chitosan (SuChi), and Orlistat (ORL) as a control on the effects caused by the intake of OLZ in a mouse model. Mice were fed with pearl barley porridge mixed with OLZ or combinations OLZ + Chi, OLZ + SuChi, or OLZ + ORL for 2 months. The weight, lipid profile, blood chemokines, expression of genes associated with appetite regulation, and behavior of the mice were analyzed in dynamics. For the first time, data were obtained on the effects of Chi and SuChi on metabolic changes during the co-administration of antipsychotics. Oral OLZ increased body weight, food and water intake, and glucose, triglyceride, and cholesterol levels in blood. ORL and SuChi better normalized lipid metabolism than Chi, decreasing triglyceride and cholesterol levels. OLZ decreased the production of all chemokines tested at the 4th week of treatment and increased CXCL1, CXCL13, and CCL22 chemokine levels at the 7th week. All of the supplements corrected the level of CXCL1, CXCL13, and CCL22 chemokines but did not recover suppressed chemokines. SuChi and ORL stimulated the expression of satiety associated proopiomelanocortin (POMC) and suppressed the appetite-stimulating Agouti-related protein (AgRP) genes. All supplements improved the locomotion of mice. Taken collectively, we found that SuChi more than Chi possessed an activity close to that of ORL, preventing metabolic disorders in mice fed with OLZ. As OLZ carries positive charge and SuChi is negatively charged, we hypothesized that SuChi's protective effect can be explained by electrostatic interaction between OLZ byproducts and SuChi in the gastrointestinal tract.

8369 Overexpression of Neurosecretory Protein GL, a Novel Small Secretory Protein, Induces Fat Accumulation in Mice

Abstract Disclosure: K. Ukena: None. Y. Narimatsu: None. A. Ogasawara: None. M. Furumitsu: None. E. Iwakoshi-Ukena: None. Hypothalamic neuropeptides and peripheral factors influence food intake, body mass, and energy expenditure. For instance, neuropeptide Y (NPY)/agouti-related peptide (AgRP) are potent orexigenic factors and α-melanocyte-stimulating hormone (α-MSH) is an anorexigenic factor, respectively. In addition, leptin and insulin derived from peripheral tissues act on the hypothalamus to influence energy homeostasis. Precise hypothalamic control of energy balance affects puberty, thermoregulation, energy storage, and survival during different life-history stages. We have previously discovered a novel cDNA encoding the precursor of a neurosecretory small protein in the hypothalamus of birds and rodents (1, 2). The precursor protein contained a signal peptide sequence, a mature peptide sequence with 80 amino acid residues, a glycine amidation signal, and a dibasic amino acid cleavage site. Because the predicted C-terminal amino acids of the peptide were Gly-Leu-NH2, the small protein was named neurosecretory protein GL (NPGL). Quantitative RT-PCR analysis demonstrated that NPGL mRNA was expressed exclusively in the mediobasal hypothalamus (MBH), including the arcuate nucleus, and the expression was elevated on food deprivation in rodents. This finding led us to predict that NPGL was involved in the regulation of energy homeostasis. Indeed, using NPGL administration and neutralizing antibody administration in rats, we established that NPGL increased lipid accumulation in white adipose tissue (3). In the present study, to investigate the physiological function of NPGL in mice, we induced its overexpression using an adeno-associated virus (AAV) vector in NPGL-Cre driver mice. We then monitored food intake and recorded body mass changes. Npgl overexpression increased body mass. We also found that the overexpression resulted in increased masses of white adipose tissue and interscapular brown adipose tissue. Taken together, these results provide evidence for NPGL as a novel regulator of fat deposition in adipose tissues. Reference: (1) Ukena et al., Biochem. Biophys. Res. Commun. 2014 446:298-303. (2) Ukena, Gen. Comp. Endocrinol. 2018 260:164-170. (3) Iwakoshi-Ukena et al., eLife 2017 6:e28527. Presentation: 6/3/2024

Greater lactate accumulation does not alter peripheral concentrations of key appetite-regulating neuropeptides.

The potential mechanisms involved in lactate's role in exercise-induced appetite suppression requires further examination. We used sodium bicarbonate (NaHCO3) supplementation in a double-blind, placebo controlled, randomized crossover design to explore lactate's role on neuropeptide Y (NPY), agouti-related peptide (AgRP), and alpha-melanocyte stimulating hormone (α-MSH) concentrations. Twelve adults (7 males; 24.2±3.4 kg‧m-2; 42.18±8.56 mL‧kg-1‧min-1) completed two identical high-intensity interval training sessions following ingestion of NaHCO3 (BICARB) or sodium chloride (PLACEBO) pre-exercise. Blood lactate, acylated ghrelin, NPY, AgRP, α-MSH, and appetite perceptions were measured pre-exercise, 0-, 30-, 60-, and 90-min post-exercise. Free-living energy intake (electronic food diaries) was measured the day before, of, and after each experimental session. In BICARB, blood lactate was greater post-exercise (p<0.002, d>0.70) though acylated ghrelin was similar (p=0.075, =0.206) at all time-points post-exercise (p>0.034, d<0.22). NPY (p=0.006, >0.509) and AgRP (p<0.001, >0.488) had main effects of time increasing following exercise and returning to baseline, with no differences between sessions (NPY: p=0.0.192, =0.149; AgRP: p=0.422, =0.060). α-MSH had no main effect of time (p=0.573, =0.063) or session (p=0.269, =0.110). Appetite perceptions were similar during BICARB and PLACEBO (p=0.007, d=0.28) increasing in both sessions post-exercise (p<0.088, d>0.57). Energy intake had a main effect of day (p=0.025, =0.825), where the experimental session day was greater than the day before (p=0.010, d=0.59) with no other differences between days (p>0.260, d<0.38). The lower accumulation of lactate than our previous work did not generate exercise-induced appetite suppression as there were no differences in acylated ghrelin, appetite perceptions, or peripheral concentrations of neuropeptides.

Cellular and metabolic function of GIRK1 potassium channels expressed by arcuate POMC and NPY/AgRP neurons

It is well known that the G protein-gated inwardly rectifying K+ (GIRK) channels are critical to maintain excitability of central neurons. GIRK channels consist of 4 subunits and GIRK1/GIRK2 heterotetramers are considered to be the neuronal prototype. We previously reported the metabolic significance of GIRK2 subunits expressed by the neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons of the arcuate nucleus of the hypothalamus (ARH). However, the role of GIRK1 subunits expressed by the neurons of ARH remains to be determined. In this study, we delineated the contribution of GIRK1 channel subunits to the excitability of the pro-opiomelanocortin (POMC) and NPY/AgRP neurons of the ARH. We further assessed the metabolic function of GIRK1 subunits expressed by these neurons. Our results provide insight how GIRK channels regulate arcuate POMC and NPY/AgRP neurons and shape metabolic phenotypes.

Structure elucidation of a human melanocortin-4 receptor specific orthosteric nanobody agonist

The melanocortin receptor 4 (MC4R) belongs to the melanocortin receptor family of G-protein coupled receptors and is a key switch in the leptin-melanocortin molecular axis that controls hunger and satiety. Brain-produced hormones such as α-melanocyte-stimulating hormone (agonist) and agouti-related peptide (inverse agonist) regulate the molecular communication of the MC4R axis but are promiscuous for melanocortin receptor subtypes and induce a wide array of biological effects. Here, we use a chimeric construct of conformation-selective, nanobody-based binding domain (a ConfoBody Cb80) and active state-stabilized MC4R-β2AR hybrid for efficient de novo discovery of a sequence diverse panel of MC4R-specific, potent and full agonistic nanobodies. We solve the active state MC4R structure in complex with the full agonistic nanobody pN162 at 3.4 Å resolution. The structure shows a distinct interaction with pN162 binding deeply in the orthosteric pocket. MC4R peptide agonists, such as the marketed setmelanotide, lack receptor selectivity and show off-target effects. In contrast, the agonistic nanobody is highly specific and hence can be a more suitable agent for anti-obesity therapeutic intervention via MC4R.

Exploring a novel toxicological mechanism: Ammonia-N induces neurotoxicity, oxidative damage in brain tissue, and modulates the expression of central appetite factors to suppress feeding in juvenile Siberian sturgeon (Acipenser baerii Brandt)

Ammonia-N is a common toxic factor in aquatic environment, known to inhibit fish feeding, yet its mechanism remains unclear. To investigate the toxicological mechanism of ammonia-N in inhibiting fish feeding, this study conducted experiments exposing juvenile Siberian sturgeon (Acipenser baerii) to ammonia-N at concentrations of 0, 5, 10, and 15 mg/L for 14 days. The results revealed a significant reduction in both daily and cumulative food intake. Obviously decreased condition factor (CF), hepatosomatic index (HSI), and viscerosomatic index (VSI) at 15 mg/L (P < 0.05). Besides, the serum ammonia concentration significantly increased on the 14th day, while the neurotoxic marker acetylcholinesterase (AchE) showed a consistent increase over the 14-day period (P < 0.05). Pathological examination of brain tissue demonstrated that ammonia-N induced damage, particularly evident in 15 mg/L ammonia-N group, where severe nerve fiber dissolution was observed. Moreover, the activity of superoxide dismutase (SOD) was significantly increased in the brain on the 1st, 3rd, and 7th day (P < 0.05). RNA-seq analysis o revealed 1566, 2188, and 2026 differentially expressed genes (DEGs) were obtained in the 5, 10, and 15 mg/L ammonia-N groups, respectively, compared to the control group, and 30 DEGs related to appetite regulation were identified. Further quantitative real-time PCR (qPCR) analysis indicated that ammonia-N exposure changed the expressions of appetite factors, including downregulation of agouti-related protein (agrp) and neuropeptide Y (npy), and upregulation of pro-opiomelanocortin (pomc), cocaine-and amphetamine-regulated transcript peptide (cart), and corticotropin releasing factor (crf) (P < 0.05). Therefore, these results suggest that ammonia-N inhibits feeding via neurotoxicity induced oxidative damage which primarily by downregulating appetite promoting factors and upregulating appetite-inhibiting factors. This study lays the groundwork for deeper understanding of the toxicological mechanism of ammonia-N on aquatic animals, particularly its detrimental effects on fish brain function and feeding behavior.

Identification of a neuropeptide in suppressing food intake in zebrafish

Neuropeptides play crucial roles in regulating various physiological processes in vertebrates. In this study, we identified a novel neuropeptide-encoding gene, nwk, in the genomes of some vertebrate species. The nwk cDNA was subsequently cloned from the brain of zebrafish. The Nwk precursor comprises 88 amino acids, with a putative mature peptide (Nwk-22) of 22 amino acids. Sequence analysis revealed that Nwk-22 is relatively conserved across vertebrate species. Nwk is predominantly expressed in the brain, with positive mRNA cells identified in the TPp and preoptic area. Intraperitoneal injection of Nwk-22 suppressed food intake and downregulated the mRNA expression of the orexigenic factor agouti-related peptide (agrp) in zebrafish. Additionally, a CRISPR/Cas9 approach was used to generate nwk mutant zebrafish. The nwk−/− zebrafish exhibited increased food consumption compared to wild-type controls. Furthermore, Nwk-22a injection in nwk−/− fish also suppressed agrp expression while stimulating the expression of the anorexigenic gene pomca, further supporting the anorexigenic role of Nwk. Taken together, these findings suggest that Nwk functions as an anorexigenic factor, reducing food intake by downregulating orexigenic genes like agrp and upregulating anorexigenic genes like pomc in zebrafish.

Angiotensin in the Arcuate: Mechanisms Integrating Cardiometabolic Control.

The American Heart Association has identified obesity as a primary impediment to ongoing improvements in cardiovascular diseases, including hypertension. Although drugs, exercise, diets, and surgeries can each cause weight loss, few subjects maintain a reduced weight over the long term. Dysfunctional integrative control (ie, adaptation) of resting metabolic rate (RMR) appears to underlie this failed weight maintenance, yet the neurobiology of physiological and pathophysiological RMR control is poorly understood. Recent insights into the cellular and molecular control of RMR by Ang-II (angiotensin II) signaling within the arcuate nucleus of the hypothalamus are reviewed. Within a unique subset of AgRP (agouti-related peptide) neurons, AT1Rs (Ang-II type 1 receptors) are implicated in the integrative control of RMR. Furthermore, a spontaneous G protein signal switch of AT1R within this neuron type appears to underlie the pathogenesis of RMR adaptation by qualitatively changing the cellular response to AT1R activation from a β-arrestin-1/Gαi-mediated inhibitory response to a Gαq-mediated stimulatory response. Therapeutic approaches to obesity are likely hampered by the plasticity of the signaling mechanisms that mediate the normal integrative control of energy balance. The same stimulus that would increase RMR in the normal physiological state may decrease RMR during obesity due to qualitative changes in second-messenger coupling. Understanding the mechanisms that regulate interactions between receptors such as AT1R and its various second-messenger signaling cascades will provide novel insights into the pathogenesis of RMR adaptation and potentially point toward new therapeutic approaches for obesity and hypertension.

The modulatory effect of oat on brain-derived neurotrophic factor, orexigenic neuropeptides, and dopaminergic signaling in obesity-induced rat model: a comparative study to orlistat.

Obesity is a non-communicable complex disease that is the fifth leading cause of death worldwide. According to a novel viewpoint, the brain plays a significant role in the central regulation of satiety and energy homeostasis. Because of its rich nutritional profile and versatile uses, oat (Avena sativa) is one of the most popular functional foods recommended by many nutritionists. The anti-obesity effect of oat was hypothesized, focusing on the brain as the target organ. In the current study, the interplay between brain biomarkers, obesity, and its related complications was evaluated in diet-induced obese rats for 25 weeks, in which 60 adult male white albino Wistar rats were divided into three control and seven treatment groups given oat extracts in a dose-dependent manner. Oat significantly improved obesity-related metabolic complications. In terms of brain function, oat significantly increased dopaminergic signaling, brain-derived neurotrophic factor levels, vaspin, irisin, and uncoupling protein-1 brain levels, while decreasing the expression of agouti-related peptide and neuropeptide Y (P-value < 0.05). The current study proposes oat supplementation as a new conceptual framework with numerous implications for hedonic and homeostatic mechanisms that control satiety. © 2024 Society of Chemical Industry.

Physiologically relevant lactate accumulation from exercise or peripheral injection does not alter central or peripheral appetite signaling in mice

Lactate has been implicated in exercise-induced appetite suppression though little work has explored the mechanisms underpinning its role. Recent work suggests lactate accumulation via exercise and intracerebroventricular injection can alter central appetite regulating pathways, though a supraphysiological dose of lactate was administered centrally and there was no assessment of peripheral appetite markers. Therefore, we examined how physiologically relevant lactate accumulation via exercise or intraperitoneal injection altered central and peripheral appetite signaling pathways and whether the lactate dehydrogenase inhibitor oxamate could blunt any exercise effect. Forty 10-week-old C57BL/6 J male mice (n = 10/group) were assigned to either: 1) sedentary (SED + SAL; saline); 2) exercise (EX+SAL; saline); 3) exercise with oxamate (EX+OX; 750 mg‧kg−1 body mass); or 4) lactate (SED + LAC; 1.0 g‧kg−1 body mass). Blood, stomach, and hypothalamus samples were collected ∼2 h post-exercise/injection. Though oxamate blunted exercise-induced lactate accumulation compared to the EX+SAL condition (P = 0.044, d = 0.73), there were no differences in circulating acylated ghrelin or stomach ghrelin O-acyltransferase content between groups (P > 0.213, ηp2<0.125). There were also no differences in hypothalamic content for neuropeptide Y, proopiomelanocortin, agouti-related peptide, and alpha melanocyte-stimulating hormone (P > 0.150, ηp2<0.170). Exercise did increase phosphorylated-total signal transducer and activator of transcription 3 (pSTAT3) compared to EX+OX (p = 0.065, d = 1.23) but there were no differences in other markers of lactate signaling: phosphorylated-total adenosine monophosphate activated protein kinase, and protein kinase b (P > 0.121, ηp2<0.160). Our results suggest that lactate accumulation due to exercise or peripheral injection does not alter central or peripheral appetite signaling when measured 2 h post-exercise/injection, though pSTAT3 was blunted with oxamate.

Intestinal gluconeogenesis controls the neonatal development of hypothalamic feeding circuits

ObjectiveIntestinal gluconeogenesis (IGN) regulates adult energy homeostasis in part by controlling the same hypothalamic targets as leptin. In neonates, leptin exhibits a neonatal surge controlling axonal outgrowth between the different hypothalamic nuclei involved in feeding circuits and autonomic innervation of peripheral tissues involved in energy and glucose homeostasis. Interestingly, IGN is induced during this specific time-window. We hypothesized that the neonatal pic of IGN also regulates the development of hypothalamic feeding circuits and sympathetic innervation of adipose tissues. MethodsWe genetically induced neonatal IGN by overexpressing G6pc1 the catalytic subunit of glucose-6-phosphatase (the mandatory enzyme of IGN) at birth or at twelve days after birth. The neonatal development of hypothalamic feeding circuits was studied by measuring Agouti-related protein (AgRP) and Pro-opiomelanocortin (POMC) fiber density in hypothalamic nuclei of 20-day-old pups. The effect of the neonatal induction of intestinal G6pc1 on sympathetic innervation of the adipose tissues was studied via tyrosine hydroxylase (TH) quantification. The metabolic consequences of the neonatal induction of intestinal G6pc1 were studied in adult mice challenged with a high-fat/high-sucrose (HFHS) diet for 2 months. ResultsInduction of intestinal G6pc1 at birth caused a neonatal reorganization of AgRP and POMC fiber density in the paraventricular nucleus of the hypothalamus, increased brown adipose tissue tyrosine hydroxylase levels, and protected against high-fat feeding-induced metabolic disorders. In contrast, inducing intestinal G6pc1 12 days after birth did not impact AgRP/POMC fiber densities, adipose tissue innervation or adult metabolism. ConclusionThese findings reveal that IGN at birth but not later during postnatal life controls the development of hypothalamic feeding circuits and sympathetic innervation of adipose tissues, promoting a better management of metabolism in adulthood.

Abstract 47: Deletion of PRR in AgRP Neurons of the Arcuate Nucleus Contributes to the Development of DOCA-Salt Hypertension

Agouti-related protein (AgRP) neurons, a key neuronal population within the arcuate nucleus (ARC), are known for their pivotal roles in regulating energy- and glucose homeostasis. However, their involvement in cardiovascular regulation remains poorly understood. Using RNAscope in situ hybridization, we found that 95.4% of the ARC AgRP neurons express the (pro)renin receptor (PRR), a component of the brain renin-angiotensin system that is crucial for blood pressure (BP) regulation. We therefore hypothesized that PRR signaling in the ARC AgRP neurons plays a regulatory role in the development of hypertension. To test this hypothesis, we selectively deleted PRR in ARC AgRP neurons by crossing AgRP-IRES-Cre mice with PRR fl/fl mice. Using RNAscope, as expected, AgRP Cre+ PRR fl/y mice displayed a significantly lower PRR mRNA in the ARC AgRP neurons than WT mice (76.3 ± 6.1 vs. 127.7 ± 2.9 AFU, p &lt; 0.05), indicating efficient ablation of PRR in ARC AgRP neurons. To examine the impact of PRR deletion in the ARC AgRP neurons on BP, the AgRP Cre+ PRR fl/y and control mice were implanted with telemetry probes to monitor BP continuously. After baseline recording, mice received DOCA-salt treatment (50 mg DOCA + saline as drinking water) for two weeks. BP variability and standard time domain heart rate variability (HRV) parameters, including overall HRV (SDNN) and short-term HRV (rMSSD), were analyzed from beat-to-beat intervals (n = 2-7 mice/group). At baseline, there was no difference between the two groups in BP, BP variability, and HRV. Two weeks of DOCA-salt induced a significantly higher BP in AgRP Cre+ PRR fl/y mice than the controls (156.2 ± 6 vs. 119.4 ± 3 mmHg, p &lt; 0.05), while BP variability did not differ between the two groups. Noteworthy, AgRP Cre+ PRR fl/y mice exhibited lower SDNN than the controls (13.3 ± 4 vs. 19.4 ± 4 ms), indicating increased sympathetic and/or reduced parasympathetic nervous activity. This lower SDNN suggests impaired cardiac autonomic function and adaptability to physiological demands in AgRP Cre+ PRR fl/y mice. Concurrently, AgRP Cre+ PRR fl/y mice showed a lower rMSSD (4.7 ± 0.5 vs. 10.8 ± 3.5 ms), implying reduced parasympathetic activity. In conclusion, deletion of PRR in the ARC AgRP neurons results in compromised cardiac autonomic function associated with the development of hypertension. Our findings underscore a novel protective role of PRR signaling in the ARC AgRP neurons in BP regulation.

Abstract 51: Targeted Apoptosis of the Angiotensin AT 1 R-Expressing Subtype of Agouti-Related Peptide Neurons Increases Resting Metabolism and Blood Pressure

Agouti-related peptide (AgRP) neurons in the hypothalamic arcuate nucleus (ARC) control feeding and resting metabolic rate (RMR) and may also contribute to blood pressure (BP) and heart rate (HR) control. Our recent studies demonstrate that three subtypes of ARC AgRP neurons can be distinguished by differential expression of angiotensin II (ANG) receptors and differential electrophysiological responses to ANG. The "Type 1" subtype of AgRP neurons in the ARC express the ANG type 1 receptor (AT 1 R), and application of ANG inhibits these cells via a Gi cascade, ultimately causing increased RMR. Other published data suggest that AT 1 R action in AgRP neurons may also stimulate BP. Thus, we hypothesized that cell-specific ablation of Type 1 AgRP neurons would disinhibit (increase) RMR and BP. Within the ARC, only Type 1 AgRP neurons express AT 1 R. Thus, cell-specific ablation of Type 1 AgRP neurons was achieved by injecting an Adeno-associated virus (AAV) encoding Cre-activatable Caspase3 into the ARC of adult AT 1 R CRE mice that express Cre-recombinase via the AT 1 R locus (n=10m+6f). Cre-deficient mice receiving AAV-Casp3 injection, mice receiving anesthesia but no virus, and AT 1 R CRE mice receiving an AAV vector encoding GFP were used as controls (n=21m+10f). Multiplexed metabolic phenotyping demonstrated that two weeks after injection, ablation of Type 1 cells grossly stimulated RMR (+11%: 0.331±0.007 vs. 0.366±0.008 kcal/h, p&lt;0.01) without affecting activity-dependent expenditure; and paradoxically increased meal initiations (+10%, p&lt;0.05) but reduced meal size (-14%, p&lt;0.05), yielding no net change in total food intake after correction for body size and composition (+7%, p=0.24). Ablation of Type 1 neurons also increased preferred ambient temperature in a thermal gradient (29.4±0.3 vs 30.9±0.1 °C, p&lt;0.01). In a separate cohort instrumented with radiotelemetric BP transducers (n=6m), HR progressively decreased (24h avg: -58±9 bpm, p&lt;0.01) as systolic BP tended toward an increase (24h avg: +6±3 mmHg, p=0.10) through 5-7 weeks after ablation. We conclude that AT 1 R-expressing AgRP Type 1 neurons critically contribute to RMR control and appear to also influence BP/HR and feeding control. Therefore, we posit that altered function of these cells may mechanistically contribute to changes in RMR, BP/HR, and feeding control associated with obesity.

Abstract P352: Transcriptomic Effects of Prolonged Diet-Induced Obesity in Subtypes of Agouti-Related Peptide Neurons of the Hypothalamic Arcuate Nucleus

Obesity is the greatest impediment to improving cardiovascular health. Despite many methods to lose weight, few people can keep it off in the long-term. The adaptation (suppression) of resting metabolic rate (RMR) appears to mediate weight re-gain after weight loss, yet the neurobiology that controls RMR remains unclear. Previously we published that the angiotensin II type 1 receptor (AT 1 R/ Agtr1a ) within Agouti-related peptide (AgRP/ Agrp ) neurons of the arcuate nucleus of the hypothalamus (ARC) is critical for integrative control of RMR. In the ARC, AT 1 R is only expressed by a subset of AgRP neurons (“Type 1”). In lean animals, AT 1 R inhibits this cell via a β-arrestin-1/Gαi-coupled cascade ("Type 1i”). Prolonged diet-induced obesity (DIO) causes RMR adaptation and is associated with a spontaneous G protein cascade switch by AT 1 R in the Type 1 neuron, in which AT 1 R activation begins stimulating the cell via the Gαq-coupled cascade (“Type 1s”). Our ongoing work aims to clarify the molecular mechanisms that govern AT 1 R coupling to Gαi versus Gαq within Type 1 AgRP neurons. First, using a dual-reporter mouse with tdTomato in AT 1 R-expressing cells plus green fluorescent protein in somatostatin (SST/ Sst )-expressing cells, we confirmed that SST expression is a selective marker of the Type 1 subtype of ARC AgRP neurons. Second, we reanalyzed our previously published single-nucleus RNA sequencing dataset describing the mouse ARC following prolonged DIO (PMC7347451) to explore the effects of DIO upon the transcriptomic profiles of AgRP neuron subtypes. Of 26 cell types initially identified, one cluster strongly expressed both Sst and Agrp (Cluster 5). Sub-clustering of Cluster 5 identified four cell types with strong Agrp expression (subclusters 0, 2, 5, and 6). Subcluster 6 may represent the Type 1i subtype due to high Sst expression, as well as enrichment for signatures of Gαi signaling events . Subcluster 6 also had very few DIO-induced differentially expressed genes (up=3, down=2). Interestingly, Subcluster 2 was comprised almost exclusively of nuclei from the DIO group (95%). Subcluster 2 was more closely related to Subcluster 6 than the other Agrp subclusters in the cluster phylogenetic tree, leading us to hypothesize that this cluster represents the DIO-induced Type 1s subtype. These data identify novel markers of AgRP neuron subtypes within the ARC, and a possible transcriptomic signature of subtype switching induced by prolonged DIO.

Abstract P436: Prorenin Increases the Firing Activity of Hypothalamic Arcuate Nucleus AgRP Neurons

The arcuate nucleus of the hypothalamus (ARC) serves as a key regulator of the cardiovascular and sympathetic regulating center. While neurons in the ARC expressing agouti-related peptide (AgRP) are implicated in the regulation of energy- and glucose homeostasis, our recent findings show that acute chemogenic activation of ARC AgRP neurons reduces blood pressure (BP), whereas inhibition of these neurons has the opposite effect. Together, these observations indicate ARC AgRP neuronal activity as a determinant of basal BP and suggest that tonic activity of these neurons may be required to maintain BP in the normal range. Importantly, most AgRP neurons express the (pro)renin receptor (PRR), a pivotal component of the brain renin-angiotensin system critical for BP regulation. Accordingly, we hypothesized that prorenin may regulate AgRP neuron activity through PRR, and thereby contributing to the autonomic regulation of BP. This study employed whole-cell patch clamp methodology in brain slices of ARC to investigate the effect of prorenin on AgRP neuron firing activity and understand mechanisms. Male and female mice expressing tdTomato in the AgRP neurons were used. Prorenin (2.5 nM) depolarized the resting membrane potential (-41.9 ± 8.7 mV vs. -47.2 ± 7.8 mV, P &lt; 0.001) and increased the frequency of action potential (AP) (2.3 ± 1.3 Hz vs. 1.2 ± 0.8 Hz, P &lt; 0.001) compared with the control (artificial cerebrospinal fluid (aCSF), n=10 neurons from 7mice). Analysis of AP waveforms revealed that prorenin decreased the amplitude of AP (61.0 ± 14.4 mV vs. 70.2 ± 14.3 mV, P &lt; 0.001) and threshold potential (-31.8 ± 6.0 mV vs. -35.5 ± 4.8 mV, P &lt; 0.001), and increased the rise time (2.3 ± 0.7 ms vs. 1.9 ± 0.6 ms, P &lt; 0.001), decay time (2.6 ± 1.1 ms vs. 2.0 ± 0.9 ms, P &lt; 0.01) and half-width (2.2 ± 0.7 ms vs. 1.8 ± 0.6 ms, P &lt;0.01) compared with the control. These changes suggest that alterations in the intrinsic conductance underlying the AP waveform likely coincide with the observed decrease in resting membrane potentials, while the ion channels involved remained to be determined. In summary, prorenin increases the firing activity of the ARC AgRP neurons by depolarizing the resting membrane potential, implicating that activation of PRR in the ARC AgRP neurons may reduce BP and protect against hypertension development.

Dietary fat content and absorption shape standard diet devaluation through hunger circuits

ObjectiveExposure to 60% high fat diet (HFD) leads to a robust consummatory preference over well-balanced chow standard diet (SD) when mice are presented with a choice. This passive HFD-induced SD devaluation following HFD challenge and withdrawal is highlighted by the significant reduction in SD food intake even in states of caloric deprivation. The elements of HFD that lead to this SD depreciation remains unclear. Possibly important factors include the amount and type of fat contained in a diet as well as past eating experiences dependent on sensory properties including taste and post ingestive feedback. We aimed to explore the role of these components to HFD-induced SD devaluation. MethodsWildtype mice were longitudinally presented discrete HFDs in conjunction with SD and feeding and metabolic parameters were analyzed. A separate cohort of animals were assessed for acute HFD preference in 3 conditions: 1) ad libitum fed (sated), 2) overnight fasted (physiologically hungry), and 3) ad libitum fed (artificially hungry), elicited through chemogenetic Agouti-related peptide (AgRP) neuron activation. Population dynamics of AgRP neurons were recorded to distinct inaccessible and accessible diets both before and after consummatory experience. Transient receptor potential channel type M5 (TRPM5) knockout mice were used to investigate the role of fat taste perception and preference to HFD-induced SD devaluation. The clinically approved lipase inhibitor orlistat was used to test the contribution of fat absorption to HFD-induced SD devaluation. ResultsHFD-induced SD devaluation is dependent on fat content, composition, and preference. This effect scaled both in strength and latency with higher percentages of animal fat. 60% HFD was preferred and almost exclusively consumed in preference to other diets across hours and days, but this was not as evident upon initial introduction over seconds and minutes, suggesting ingestive experience is critical. Optical fiber photometry recordings of AgRP activity supported this notion as neuronal suppression by the different diets was contingent on prior intake. While taste transduced via TRPM5 influenced HFD-evoked weight gain, it failed to impact either HFD preference or HFD-induced SD devaluation. Perturbation of post ingestive feedback through orlistat-mediated diminishment of fat absorption prevented HFD-evoked weight gain and abolished HFD-induced SD devaluation. ConclusionsPost ingestive feedback via fat digestion is vital for expression of HFD-induced SD devaluation.