Biology subjects

Ayala, J. E.

Publications and source records attributed to Ayala, J. E..

11 recordsLinked to original sources

bioRxiv2025

Chronic semaglutide treatment reveals stage-dependent changes to feeding behavior and metabolic adaptations in male mice

Glucagon-like peptide-1 receptor (Glp1r) agonists have transformed obesity treatment, but weight loss responses to these drugs vary widely. Elucidating behavioral and metabolic phenotypes throughout Glp1r agonist treatment could identify mechanisms underlying this response spectrum. We characterized food intake, meal patterns, energy expenditure (EE), and substrate oxidation during chronic semaglutide treatment and post-treatment recovery in obese male mice at room temperature (RT) and thermoneutral temperature (TN). Semaglutide-induced weight loss and post-treatment weight regain were similar at RT and TN. Weight loss was divided into three stages at both temperatures: 1) rapid initial weight loss, 2) slower gradual weight loss, and 3) weight maintenance. Initial weight loss was marked by reduced food intake, smaller and less frequent meals, and increased lipid oxidation. Food intake gradually returned to pre-treatment levels through increased meal frequency, while meal size remained suppressed. Lipid oxidation gradually decreased while carbohydrate oxidation increased. Weight-adjusted EE and locomotor activity increased throughout semaglutide treatment. Mice rapidly regained weight after treatment cessation, and this was associated with increased food intake, meal size and frequency, carbohydrate oxidation, EE, and activity. These findings reveal that semaglutide-induced weight loss and regain after treatment cessation involve dynamic, stage-specific changes in feeding behavior, EE, and substrate oxidation. ARTICLE HIGHLIGHTSO_LIAlthough many studies demonstrate acute behavioral and metabolic effects of glucagon- like peptide-1 receptor (Glp1r) agonists, few have assessed chronic effects of these drugs on these phenotypes. C_LIO_LIWe wanted to assess changes to various behavioral and metabolic phenotypes throughout a chronic treatment regimen with semaglutide and post-treatment. C_LIO_LIWeight loss in response to chronic semaglutide treatment can be divided into distinct phases, and each phase is characterized by different effects on food intake, meal patterns, energy expenditure, and substrate oxidation. C_LIO_LIOur findings suggest that differences in behavioral changes and/or metabolic adaptations may underlie the degree of weight loss responsiveness to Glp1r agonists. C_LI

physiology↗

bioRxiv2024

Validation of a refined protocol for mouse oral glucose tolerance testing without gavage

A glucose tolerance test (GTT) is routinely used to assess glucose homeostasis in clinical settings and in preclinical research studies using rodent models. The procedure assesses the ability of the body to clear glucose from the blood in a defined time after a bolus dose. In the human clinical setting, glucose is ingested via voluntary consumption of a glucose-sweetened drink. Typically, in the rodent GTT oral gavage (gavage-oGTT) or (more commonly) intraperitoneal injection (IPGTT) are used to administer the glucose bolus. Although used less frequently, likely due to investigator technical and experience barriers, the former is the more physiologically relevant as it integrates the gastrointestinal tract (GI), including release of key incretin hormones. However, orally gavaging glucose in the GTT is also not without its limitations: gavaging glucose straight into the stomach bypasses potentially critical early glucose-sensing via the mouth (cephalic phase) and associated physiological responses. Furthermore, gavaging is stressful on mice, and this by itself can increase blood glucose levels. We have developed and validated a refined protocol for mouse oral GTT which uses a voluntary oral glucose dosing method, micropipette-guided drug administration (MDA), without the need for water deprivation. This approach is simple and non-invasive. It is less stressful for the mice, as evidenced by lower circulating corticosterone levels 10 minutes after glucose-dosing compared to oral gavage. This is significant for animal and investigator welfare, and importantly minimising the confounding effect of stress on mouse glucose homeostasis. Using a randomised cross-over design, we have validated the MDA approach in the oGTT against oral gavage in male and female C57BL/6J and C57BL/6N mice. We show the ability of this method to detect changes in glucose tolerance in diet-induced obese animals. Compared to oral gavage there was lower inter-animal variation in the MDA-oGTT. In addition to being more representative of the human procedure, the MDA-oGTT is easy and has lower barriers to adoption than the gavage oGTT as it is non-invasive and requires no specialist equipment or operator training. The MDA-oGTT a more clinically representative, accessible, and refined replacement for the gavage-oGTT for mouse metabolic phenotyping, which is simple yet overcomes significant deficiencies in the current standard experimental approaches.

physiology↗

bioRxiv2024

AgRP neurons mediate activity-dependent development of oxytocin connectivity and autonomic regulation

During postnatal life, the adipocyte-derived hormone leptin is required for proper targeting of neural inputs to the paraventricular nucleus of the hypothalamus (PVH) and impacts the activity of neurons containing agouti-related peptide (AgRP) in the arcuate nucleus of the hypothalamus. Activity-dependent developmental mechanisms are known to play a defining role during postnatal organization of neural circuits, but whether leptin-mediated postnatal neuronal activity specifies neural projections to the PVH or impacts downstream connectivity is largely unexplored. Here, we blocked neuronal activity of AgRP neurons during a discrete postnatal period and evaluated development of AgRP inputs to defined regions in the PVH, as well as descending projections from PVH oxytocin neurons to the dorsal vagal complex (DVC) and assessed their dependence on leptin or postnatal AgRP neuronal activity. In leptin-deficient mice, AgRP inputs to PVH neurons were significantly reduced, as well as oxytocin-specific neuronal targeting by AgRP. Moreover, downstream oxytocin projections from the PVH to the DVC were also impaired, despite the lack of leptin receptors found on PVH oxytocin neurons. Blocking AgRP neuron activity specifically during early postnatal life reduced the density of AgRP inputs to the PVH, as well as the density of projections from PVH oxytocin neurons to the DVC, and these innervation deficits were associated with dysregulated autonomic function. These findings suggest that postnatal targeting of descending PVH oxytocin projections to the DVC requires leptin-mediated AgRP neuronal activity, and represents a novel activity-dependent mechanism for hypothalamic specification of metabolic circuitry, with consequences for autonomic regulation. Significance statementHypothalamic neural circuits maintain homeostasis by coordinating endocrine signals with autonomic responses and behavioral outputs to ensure that physiological responses remain in tune with environmental demands. The paraventricular nucleus of the hypothalamus (PVH) plays a central role in metabolic regulation, and the architecture of its neural inputs and axonal projections is a defining feature of how it receives and conveys neuroendocrine information. In adults, leptin regulates multiple aspects of metabolic physiology, but it also functions during development to direct formation of circuits controlling homeostatic functions. Here we demonstrate that leptin acts to specify the input-output architecture of PVH circuits through an activity-dependent, transsynaptic mechanism, which represents a novel means of sculpting neuroendocrine circuitry, with lasting effects on how the brain controls energy balance.

neuroscience↗

bioRxiv2024

Time dependent changes in feeding behavior and energy balance associated with weight gain in mice fed obesogenic diets

Obesity is characterized by dysregulated homeostatic mechanisms resulting in positive energy balance, yet when this dysregulation occurs is unknown. We assessed the time course of alterations to behaviors promoting weight gain in male and female mice switched to obesogenic 60% or 45% high fat diet (HFD). Switching mice to obesogenic diets promotes transient bouts of hyperphagia during the first 2 weeks followed by persistent caloric hyperphagia. Energy expenditure increases but not sufficiently to offset increased caloric intake, resulting in a sustained net positive energy balance. Hyperphagia is associated with consumption of calorically larger meals (impaired satiation) more frequently (impaired satiety) particularly during the light-cycle. Running wheel exercise delays weight gain in 60% HFD-fed male mice by enhancing satiation and increasing energy expenditure. However, exercise effects on satiation are no longer apparent after 2 weeks, coinciding with weight gain. Thus, exposure to obesogenic diets engages homeostatic regulatory mechanisms for [~]2 weeks that ultimately fail, and consequent weight gain is characterized by impaired satiation and satiety. Insights into the etiology of obesity can be obtained by investigating changes to satiation and satiety mechanisms during the initial [~]2 weeks of HFD exposure. What is already known about this subject?O_LIObesity is associated with dysregulated homeostatic mechanisms. C_LIO_LIIncreased caloric consumption contributes to obesity. C_LIO_LIObese rodents tend to eat larger, more frequent meals. C_LI What are the new findings in your manuscript?O_LIExposure to obesogenic diets promotes transient attempts to maintain weight homeostasis. C_LIO_LIAfter [~]2 weeks, caloric hyperphagia exceeds increased energy expenditure, promoting weight gain. C_LIO_LIThis is associated with consumption of larger, more frequent meals. C_LI How might your results change the direction of research or the focus of clinical practice?Our findings suggest that molecular studies focusing on mechanisms that regulate meal size and frequency, particularly those engaged during the first [~]2 weeks of obesogenic diet feeding that eventually fail, can provide unique insight into the etiology of obesity.

physiology↗

bioRxiv2023

Liver Fibroblast Growth Factor 21 (FGF21) is Required for the Full Anorectic Effect of the Glucagon-Like Peptide-1 Receptor Agonist Liraglutide in Male Mice fed High Carbohydrate Diets

Glucagon-like peptide-1 receptor (GLP-1R) agonists and fibroblast growth factor 21 (FGF21) confer similar metabolic benefits. Studies report that GLP-1RA induce FGF21. Here, we investigated the mechanisms engaged by the GLP-1R agonist liraglutide to increase FGF21 levels and the metabolic relevance of liraglutide-induced FGF21. We show that liraglutide increases FGF21 levels via neuronal GLP-1R activation. We also demonstrate that lack of liver Fgf21 expression confers partial resistance to liraglutide-induced weight loss. Since FGF21 reduces carbohydrate intake, we tested whether the contribution of FGF21 to liraglutide-induced weight loss is dependent on dietary carbohydrate content. In control and liver Fgf21 knockout (LivFgf21-/-) mice fed calorically matched diets with low- (LC) or high-carbohydrate (HC) content, we found that only HC-fed LivFgf21-/- mice were resistant to liraglutide-induced weight loss. Similarly, liraglutide-induced weight loss was partially impaired in LivFgf21-/- mice fed a high-fat, high-sugar (HFHS) diet. Lastly, we show that loss of neuronal {beta}-klotho expression also diminishes liraglutide-induced weight loss in mice fed a HC or HFHS diet, indicating that FGF21 mediates liraglutide-induced weight loss via neuronal FGF21 action. Our findings support a novel role for a GLP-1R-FGF21 axis in regulating body weight in the presence of high dietary carbohydrate content.

physiology↗

bioRxiv2022

Glucagon-Like Peptide-1 Receptor Activation Stimulates PKA-Mediated Phosphorylation of Raptor and this Contributes to the Weight Loss Effects of Liraglutide

The canonical target of the glucagon-like peptide-1 receptor (GLP-1R), Protein Kinase A (PKA), has been shown to stimulate mechanistic Target of Rapamycin Complex 1 (mTORC1) by phosphorylating the mTOR-regulating protein Raptor at Ser791 following {beta}-adrenergic stimulation. The objective of these studies is to test whether GLP-1R agonists similarly stimulate mTORC1 via PKA phosphorylation of Raptor at Ser791 and whether this contributes to the weight loss effect of the therapeutic GLP-1R agonist liraglutide. We measured phosphorylation of the mTORC1 signaling target ribosomal protein S6 in Chinese Hamster Ovary cells expressing GLP-1R (CHO-Glp1r) treated with liraglutide in combination with PKA inhibitors. We also assessed liraglutide-mediated phosphorylation of the PKA substrate RRXS*/T* motif in CHO-Glp1r cells expressing Myc-tagged wild-type (WT) Raptor or a PKA-resistant (Ser791Ala) Raptor mutant. Finally, we measured the body weight response to liraglutide in WT mice and mice with a targeted knock-in of PKA-resistant Ser791Ala Raptor. Liraglutide increased phosphorylation of S6 and the PKA motif in WT Raptor in a PKA-dependent manner but failed to stimulate phosphorylation of the PKA motif in Ser791Ala Raptor in CHO-Glp1r cells. Lean Ser791Ala Raptor knock-in mice were resistant to liraglutide-induced weight loss but not setmelanotide-induced (melanocortin-4 receptor-dependent) weight loss. Diet-induced obese Ser791Ala Raptor knock-in mice were not resistant to liraglutide-induced weight loss; however, there was weight-dependent variation such that there was a tendency for obese Ser791Ala Raptor knock-in mice of lower relative body weight to be resistant to liraglutide-induced weight loss compared to weight-matched controls. Together, these findings suggest that PKA-mediated phosphorylation of Raptor at Ser791 contributes to liraglutide-induced weight loss.

physiology↗

bioRxiv2022

Glucagon-like peptide-1 receptor differentially controls mossy cell activity across the dentate gyrus longitudinal axis

Understanding the role of dentate gyrus (DG) mossy cells (MCs) in learning and memory has rapidly evolved due to increasingly precise methods for targeting MCs and for in vivo recording and activity manipulation in rodents. These studies have shown MCs are highly active in vivo, strongly remap to contextual manipulation, and that their inhibition or hyperactivation impairs pattern separation and location or context discrimination. What is not well understood is how MC activity is modulated by neurohormonal mechanisms, which might differentially control the participation of MCs in cognitive functions during discrete states, such as hunger or satiety. In this study, we demonstrate that glucagon-like peptide-1 (GLP-1), a neuropeptide produced in the gut and the brain that regulates food consumption and hippocampal-dependent mnemonic function, might regulate MC function through selective expression of its receptor, GLP-1R. RNA-seq demonstrated that most Glp1r in hippocampal principal neurons is expressed in MCs, and in situ hybridization revealed strong expression of Glp1r in hilar neurons. Glp1r-ires-Cre mice crossed with Ai14D reporter mice followed by co-labeling for the MC marker GluR2/3 revealed that almost all MCs in the ventral DG expressed Glp1r and that almost all Glp1r-expressing hilar neurons were MCs. However, only ~60% of dorsal DG MCs expressed Glp1r, and Glp1r was also expressed in small hilar neurons that were not MCs. Consistent with this expression pattern, peripheral administration of the GLP-1R agonist exendin-4 (5 g/kg) increased cFos expression in ventral but not dorsal DG hilar neurons. Finally, whole-cell patch-clamp recordings from ventral MCs showed that bath application of exendin-4 (200 nM) depolarized MCs and increased action potential firing. Taken together, this study identifies a potential neurohormonal mechanism linking a critically important satiety signal with activity of MCs in the ventral DG that might have functional effects on learning and memory during distinct states.

neuroscience↗

bioRxiv2022

High Fat Diet Blunts Stress-Induced Hypophagia and Activation of Glp1r Dorsal Lateral Septum Neurons in Male but not in Female Mice

While stress typically reduces caloric intake (hypophagia) in chow-fed rodents, presentation of palatable, high calorie substances during stress can increase caloric consumption (i.e. "comfort feeding") and promote obesity. However, little is known about how obesity itself affects feeding behavior in response to stress and the mechanisms that can influence stress-associated feeding in the context of obesity. We show that lean male mice display the expected hypophagic response following acute restraint stress, but obese male mice are resistant to this acute stress-induced hypophagia. Activation of the glucagon-like peptide-1 (Glp1) receptor (Glp1r) in various brain regions leads to hypophagia in response to stress. Here we show that Glp1r-positive neurons in the dorsal lateral septum (dLS) are robustly activated during acute restraint stress in lean but not in obese male mice. This raises the possibility that activation of dLS Glp1r neurons during restraint stress contributes to subsequent hypophagia. Supporting this, we show that chemogenetic inhibition of dLS Glp1r neurons attenuates acute restraint stress hypophagia in male mice. Surprisingly, we show that both lean and obese female mice are resistant to acute restraint stress-induced hypophagia and activation of dLS Glp1r neurons. Taken together, these results suggest that dLS Glp1r neurons contribute to the hypophagic response to acute restraint stress in male mice, but not in female mice, and that obesity disrupts this response in male mice. Broadly, these findings show sexually dimorphic mechanisms and feeding behaviors in lean vs. obese mice in response to acute stress.

neuroscience↗

bioRxiv2020

Innate fear responses are reflected in the blood epigenome of rhesus macaques.

AO_SCPLOWBSTRACTC_SCPLOWFear and anxiety are complex physiological states aimed at promoting adaptive behaviors. They are also core symptoms of many neuropsychiatric disorders; yet, our knowledge of the underlying biological correlates remains fragmented. Non-human primate models are critical for our understanding of mechanisms associated with complex higher-order behavioral phenotypes. Here we investigated individual variations in innate fear responses to a snake stimulus in free-ranging rhesus macaques and discovered an unusual bimodal distribution of fearful and fearless behavior, likely as a result of an environmental insult by a hurricane. In a translational approach, we discovered a DNA methylation profile associated with fear behavior in these monkeys. We also found evidence that this epigenetic signature is associated with innate fear responses in humans in the form of acoustic startle. Our data highlight the importance and translational utility of non-human primate models for neuropsychiatric research and provide a potential epigenetic signature of innate fear.

neuroscience↗

bioRxiv2020

Chop/Ddit3 depletion in β-cells alleviates ER stress and corrects hepatic steatosis

Type 2 diabetes (T2D) is a metabolic disorder characterized by hyperglycemia, hyperinsulinemia and insulin resistance (IR). During the early phase of T2D, insulin synthesis and secretion by pancreatic {beta} cells is enhanced, which can lead to proinsulin (ProIns) misfolding that aggravates endoplasmic reticulum (ER) homeostasis in {beta} cells. Moreover, increased insulin in the circulation may contribute to fatty liver disease. Medical interventions aimed at alleviating ER stress in {beta} cells while maintaining optimal insulin secretion are therefore an attractive therapeutic strategy for T2D. Previously, we demonstrated that germline Chop gene deletion preserved {beta} cells in high fat diet (HFD) fed mice and in leptin receptor-deficient db/db mice. In the current study, we further investigated whether targeting Chop/Ddit3 specifically in murine {beta} cells confers therapeutic benefits. First, we show that Chop deletion in {beta} cells alleviates {beta} cell ER stress and delays glucose-stimulated insulin secretion (GSIS) in HFD fed mice. Second, importantly, {beta} cell-specific Chop deletion prevented liver steatosis and hepatomegaly in aged HFD fed mice without affecting basal glucose homeostasis. Third, we provide the first mechanistic evidence that ER remodeling secondary to Chop deletion modulates glucose-induced islet Ca2+ oscillations. Finally, using state-of-the-art GLP1-conjugated Chop AntiSense Oligonucleotides (GLP1-Chop ASO), we demonstrated that the Chop deletion induced GSIS change is a long term complex event in {beta} cells. In summary, our results demonstrate that Chop depletion in {beta} cells is a new therapeutic strategy to alleviate dysregulated insulin secretion and the consequently fatty liver disease in T2D.

physiology↗

bioRxiv2017

Metabolite profile and mitochondrial energetics characterize poor early recovery of muscle mass following hind limb unloading in old mice

The progression of age-related sarcopenia can be accelerated by impaired recovery of muscle mass following periods of disuse due to illness or immobilization. The molecular underpinnings of poor recovery of aging muscle following disuse remain largely unknown. However, recent evidence suggests that mitochondrial energetics may play an important role. Here, we report that 22-24 month old mice with low muscle mass and insulin resistance display poor early recovery of muscle mass following 10 days of hind limb unloading. We took an unbiased approach to identify changes in energy metabolism gene expression and metabolite pools and show for the first time that persistent mitochondrial dysfunction, dysregulated fatty acid {beta}-oxidation and elevated H2O2 emission underlie poor early recovery of muscle mass following a period of disuse in old mice. Importantly, this is linked to more severe whole-body insulin resistance. The findings suggest that muscle fuel metabolism and mitochondrial energetics should be a focus for mining therapeutic targets to improve recovery of muscle mass following periods of disuse in older animals.

physiology↗