Objective

Viral infection of cells leads to metabolic changes, but how viral infection changes whole-body and tissue metabolism in vivo has not been comprehensively studied. In particular, it is unknown how metabolism might be differentially affected by an acute infection that the immune system can successfully clear compared to a chronic persistent infection.

Methods

Here we used metabolomics and isotope tracing to identify metabolic changes in mice infected with acute or chronic forms of lymphocytic choriomeningitis virus (LCMV) for three or eight days.

Results

Both types of infection alter metabolite levels in blood and tissues, including itaconate and thymidine. However, we observed more dramatic metabolite changes in the blood and tissues of mice with persisting LCMV infection compared to those infected with the acute viral strain. Isotope tracing revealed that the contribution of both glucose and glutamine to the tricarboxylic acid (TCA) cycle increase in the spleen, liver, and kidneys of mice infected with chronic LCMV, while acute LCMV only increases the contribution of glutamine to the TCA cycle in the spleen. We found that whole-body turnover of both glutamine and thymidine increase during acute and chronic infection, whereas whole-body glucose turnover surprisingly does not change. Activated T cells in vitro produce thymidine and virus-specific T cells ex vivo have increased thymidine levels, nominating T lymphocytes as the source of thymidine in LCMV infection.

Conclusions

In sum, we provide comprehensive measurements of whole-body and tissue metabolism in acute and chronic viral infection, and identify altered thymidine metabolism as a marker of viral infection.

The clinical significance of interindividual variation in circulating adropin levels is unclear. To better understand adropin biology at the whole-body level, we surveyed transcriptional structures co-regulated with the Energy Homeostasis Associated (ENHO) gene encoding adropin across human tissues using Gene-Derived Correlations Across Tissues (GD-CAT). ENHO/adropin-related transcriptional structures with >1000 genes meeting the selection threshold (q < 0.001) occurred in 11/20 tissues. While most reflect local relationships, liver ENHO/adropin-related structures are dominated by transcripts expressed across metabolic tissues (skeletal muscle, adipose tissues, thyroid). Relationships between liver ENHO/adropin expression and skeletal muscle mitochondrial function were corroborated using liver-specific knockout mice. Within-liver ENHO/adropin transcriptional structures reflect lipoprotein metabolism (e.g., APOC1, p = 4.91 x 10⁻¹¹; APOA1, p = 8.03 x 10⁻⁹), confirmed by correlations between plasma concentrations of adropin and indices of lipoprotein metabolism in MAPT samples. Moreover, statin treatment which increases hepatic cholesterol efflux, reduces plasma adropin levels. The ENHO gene contains retinoic acid receptor-related orphan receptor response elements (RORE), suggesting circadian control. Pan-organ transcriptional structures with liver ENHO/adropin or RORC overlap, reflecting the liver clock. Strong, local relationships between ENHO/adropin and circadian genes were also observed in most non-hepatic tissues. ENHO/adropin expression widely reflects activation of oxidative metabolic pathways and suppression of ribosomal functions and cell division. Finally, hippocampal ENHO/adropin expression correlates strongly with Alzheimer's disease risk genes identified by GWAS. In summary, activation of ENHO/adropin expression reflects cellular circadian and mitochondrial oxidative processes, but with inhibition of anabolic processes. Plasma adropin concentrations may thus reflect hepatic lipoprotein production and activation of metabolic stress responses across human tissues.

Type 2 diabetes (T2D) can be classified into Severe Insulin-Deficient Diabetes (SIDD), Severe Insulin-Resistant Diabetes (SIRD), Mild Obesity-related Diabetes (MOD), and Mild Age-related Diabetes (MARD). This classification can help in predicting disease complications and determining the best treatment for individuals. However, the applicability of this classification to non-European populations and sensitivity to confounding factors remain unclear. We applied k-means clustering to a large Middle Eastern biobank cohort (Qatar Biobank; QBB, comprising 13,808 individuals; 2,687 with T2D). We evaluated the efficacy of the European cluster coordinates and analyzed the impact of using actual age on clustering outcomes. We examined sex differences, analyzed insulin treatment frequency, investigated the clustering of monogenic diabetes (MD) focusing on maturity-onset diabetes of the young (MODY), and evaluated the prevalence of chronic kidney disease (CKD) and Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) among T2D subtypes. We identified the four T2D subtypes within a large Arab cohort. Data-derived centers outperformed European coordinates in classifying T2D. The use of actual age, as opposed to age of diagnosis, impacted MOD and MARD classification. Obesity prevalence was significantly higher in females but it did not translate to worse disease severity, as indicated by comparable levels of HbA1C and HOMA2-IR. Insulin was predominantly prescribed to individuals in SIDD and SIRD. SIRD displayed the highest risk of CKD and MASLD, followed by MOD and SIDD compared to MARD. Interestingly, most MODY individuals were clustered within MARD, further highlighting the need for precise classification and tailored interventions. The observed sex differences underscore the importance of tailoring treatment plans for females compared to males. Individuals who are at a higher risk of CKD and MASLD may require closer monitoring and physician oversight. Additionally, in populations without access to genetic testing, likely MODY individuals can be identified within the MARD cluster. Our findings strongly support the need for a transition to more personalized, data-driven treatment approaches to minimize diabetes-related complications and improve disease outcomes.

Objective

Epigenetic modifications including histone post translational modifications can influence gene expression in adipocytes, potentially contributing to metabolic dysfunctions, obesity, and insulin resistance. Despite recent advances in the characterization of the mouse adipocyte epigenome, epigenetic characterization of adipocytes in vivo has been challenging, particularly across different adipose depots and of several epigenetic modifications.

Methods

Here, we use specific reporter mice labelling brown, beige and white adipocytes, diphtheria toxin-mediated ablation of beige adipocytes, and Cleavage Under Targets and Tagmentation (CUT&Tag) to generate paired single mouse datasets of five histone marks. We perform an integrative multi-omics factor analysis (MOFA) of H3K4me3, H3K27me3, H3K4me1, H3K27ac and H3K9me3 in brown, white and beige adipocytes from three distinct mouse adipose tissue depots obtained during cold exposure and thermoneutrality.

Results

Our analysis reveals that enhancers distinguish adipocytes by their tissue of origin, with H3K4me1 deposition differentiating between beige and brown adipocytes. Beige adipocytes poised promoters associated to thermogenic genes during warming. Diphtheria toxin-mediated ablation of beige adipocytes shows that non-beigeing white adipocytes in inguinal adipose tissue and beige adipocytes are not inherently epigenetically different suggesting that they share a common developmental progenitor.

Conclusions

These paired multimodal data comprise an extensive resource (https://github.com/vonMeyennLab/mAT_CE_Atlas) for the further exploration of the mouse adipocyte epigenome which will enable discovery of regulatory elements governing adipocyte identity and gene regulation.

Objective

Cardiac fibrosis during Duchenne muscular dystrophy (DMD) arises from cellular damage and inflammation and is associated with metabolic dysfunction. The extent to which these relationships develop across all 4 cardiac chambers, particularly during early-stage disease, remains unknown.

Methods and Results

We discovered that very young D2.mdx mice exhibit fibrosis exclusively in the right ventricle (RV) and left atrium. Concurrent myocardial disorganization in the RV was related to a highly specific inflammatory signature of increased infiltrating pro-inflammatory macrophages (CD11b+CD45+CD64+F4/80+CCR2+), myofibre mitochondrial-linked apoptosis, and reduced carbohydrate and fat oxidation. This relationship did not occur in the left ventricle. Short-term daily administration of a peptidomimetic adiponectin receptor agonist, ALY688, prevented RV fibrosis, infiltrating macrophages, and mitochondrial stress as well as left atrial fibrosis.

Conclusions

Our discoveries demonstrate early-stage cardiac tissue pathology occurs in a chamber-specific manner and is prevented by adiponectin receptor agonism, thereby opening a new direction for developing therapies that prevent tissue remodeling during DMD.

Objective

The melanocortin receptor 4 (MC4R) plays a key role in the CNS regulation of metabolism. In addition to its role within the hypothalamus, other brain areas, including the dorsal raphe nucleus (DRN), express MC4R. However, the identity and role of these neurons in metabolism regulation are not fully understood. We performed studies to address these questions.

Methods

We generated Mc4r-cre;Vgat-FlpO and Mc4r-cre;Vglut2-FlpO mice to determine the contribution of these MC4R neuronal populations in DRN. We then chemogenetically activated or inhibited the GABAergic and glutamatergic populations of MC4R. Finally, we selectively deleted MC4R from these two neuronal populations and studied the impact on whole-body metabolism.

Results

We found that about 60% of DRN MC4R neurons are GABAergic (Vgat), while only about 20% are glutamatergic (Vglut2). Most of the projections onto DRN neurons originated from the arcuate nucleus (ARC)-POMC neurons, and only a small input from the nucleus of the solitary tract (NTS)-POMC neurons was identified. Significant projections of DRN MC4R/Vgat neurons were observed in the paraventricular nucleus of the hypothalamus (PVN). Chemogenetic activation or inhibition of MC4R/Vgat neurons increased or inhibited food intake, respectively. No effects were observed when the same approach was used in MC4R/Vglut2 neurons. Furthermore, only chemogenetic manipulation of the MC4R/Vgat neurons affected anxiety-like behavior, which was associated with changes in serotonin staining in the DRN. Finally, MC4R-selective deletion in Vgat but not Vglut2 neurons affected whole-body metabolism.

Conclusions

These findings suggest that DRN MC4R/Vgat neurons receiving projections from the ARC POMC neurons and projecting to the hypothalamic PVN play a role in metabolism regulation. In addition, this same DRN neuronal subpopulation affects anxiety-like behavior by modulating DRN serotonin neurons.

Objective

Hypertrophied mesenteric adipose tissue (MAT) wrapped around the inflamed intestine, also known as creeping fat (CrF), is a classic pathological characteristic of Crohn’s disease (CD). Recent studies revealed that the abnormal mesentery in CD exhibits a white-to-beige transformation (known as white adipose browning), which may be a compensatory mechanism for disease attenuation. However, its underlying causes and mechanisms remain unknown.

Methods

The beige MAT samples from patients with CD and normal white MAT samples from patients without CD were collected, and targeted metabolome analysis was performed. Interleukin-10 gene knockout (IL-10^−/−) and 2,4,6-trinitrobenzenesulphonic acid solution (TNBS)-induced colitis mice were used to evaluate the effects of kynurenic acid (KYNA) on mesenteritis and colitis. Mesenteric explants and adipocytes were collected and cultured to assess the effects of KYNA on adipose tissue browning and macrophage inflammation.

Results

Targeted metabolomic sequencing revealed that KYNA exhibited the highest level of upregulation in the beige MAT of CD, which was tightly correlated with the browning marker UCP-1, inflammatory factors, and adipokines. In vivo experiments demonstrated that KYNA triggered the white-to-beige transformation of MAT in IL-10^−/− and TNBS-induced colitis mice, which further alleviated mesenteritis and colitis. Additionally, mesenteric explants and adipocytes displayed a browning phenotype with KYNA co-incubation, and their supernatants significantly induced M2 macrophage polarization and inhibited inflammation. Mechanistically, KYNA induced MAT browning and regulated disease procession of CD via GPR35-ERK1/2-PGC-1α signaling pathway.

Conclusions

This study provides novel insights into the browning transformation of the mesentery in CD and suggests a potential approach for clinical therapy.

The ketogenic diet —high in fat and low in carbohydrates— and intermittent fasting have gained popularity not only for weight management but also for their potential to delay cognitive decline associated with neurodegenerative diseases and aging. However, adherence to these diets remains low due to their restrictive nature and undesirable side effects. Both dietary approaches stimulate hepatic production of ketone bodies, primarily β-hydroxybutyrate (BHB), which serves as an alternative energy source for neurons. Here, we investigated whether BHB supplementation could mitigate AMPA receptor trafficking impairments, synaptic dysfunction, and cognitive decline induced by metabolic challenges such as a saturated fat-rich diet. Our results show that, in cultured primary cortical neurons, exposure to palmitic acid decreases surface levels of glutamate GluA1-containing AMPA receptors, whereas unsaturated fatty acids and BHB increase these levels. Furthermore, physiological concentrations of BHB (1–2 mM) countered the adverse effects of palmitic acid on synaptic GluA1 and GluA2 levels in hippocampal neurons, restoring AMPA receptor-mediated synaptic transmission. In hippocampal slices, BHB also reversed palmitate-induced impairments in excitability and synaptic plasticity (long-term potentiation; LTP). Additionally, daily intragastric administration of BHB (100 mg/kg/day for two months) prevented deficits in recognition and spatial memory induced by a saturated fat-rich diet (49% of calories from fat) in mice. In summary, our findings underscore the significant impact of fatty acids and ketone bodies on AMPA receptor abundance, synaptic function, and neuroplasticity, shedding light on the potential use of BHB as a dietary supplement to counteract cognitive impairments linked to metabolic diseases.

Objective

Mitochondrial uncouplers are used as chemical tools to study mitochondrial function in vitro and in vivo, and some molecules are in development for the treatment of metabolic diseases. One problem in the field is that any molecule that increases proton transport into the mitochondrial matrix independent of ATP production can be classified as an uncoupler regardless of off-target activities. Therefore, there are dozens of classes of molecules that exhibit a wide spectrum of phenotypes. Herein we directly compared 15 mitochondrial uncouplers side-by-side in a well-defined cell system to better understand their in vitro dose response profiles and the top molecules with suitable pharmacology and safety profiles were compared in db/db mice.

Methods

Fifteen mitochondrial uncouplers were characterised in vitro in CHO–K1 cells. The top five candidates were selected for further characterisation in male db/db mice based on their in vitro dose response and/or tolerability. We tested two doses of each mitochondrial uncoupler in mice and benchmarked their efficacy to a lifestyle intervention of 35% calorie restriction as well as to lean db/+ metabolically healthy mice. Eleven groups of mice were fed ad libitum either; 1) chow (control), 2) chow with 0.15% BAM15 (w/w), 3) chow with 0.2% BAM15 (w/w), 4) chow with 0.1% NEN (w/w), 5) chow with 0.25% NEN (w/w), 6) chow with 0.01% OPC-163493 (w/w), 7) chow with 0.02% OPC-63493 (w/w), 8) chow with 0.015% ES9 (w/w), 9) chow with 0.03% ES9 (w/w), 10) chow with 0.2% NTZ (w/w), and 11) chow with 0.4% NTZ (w/w). Another group of mice was fed chow to receive ∼65% of the average daily food intake of control mice as a model of calorie restriction (CR). Mice were metabolically phenotyped over 4 weeks of treatment with assessment of key readouts including body weight, HbA1c, blood glucose and glucose tolerance tests. At termination, key tissues were collected and plasma was analysed for markers of toxicity.

Results

Few mitochondrial uncouplers behaved similarly in vitro, with 11 molecules impairing maximal mitochondrial capacity. In vivo, BAM15 dose-dependently improved body weight and metabolic parameters in db/db mice, with 0.2% BAM15 treatment yielding statistically significant improvements in body weight, fat pad weight, glucose tolerance, blood glucose, HbA1c, liver weight and triglyceride content. The next-best treatment was 0.03% ES9 which significantly improved glucose tolerance, blood glucose levels, and HbA1c, but increased body weight, liver size and steatosis relative to db/db controls.

Conclusions

Mitochondrial uncouplers BAM15 and ES9 had the greatest dose tolerance range in vitro, while BAM15 had the best overall effects on body weight, glucose control and liver steatosis in db/db mice. This study reveals diverse phenotypes across 15 classes of mitochondrial uncouplers and underscores the need for rigorous evaluation to identify molecules that drive stable mitochondrial respiration without unwanted mitochondrial inhibition or off-target effects. Ultimately, mitochondrial uncouplers should not be generalized and each uncoupler molecule needs to be considered by its own actions in well-defined experimental conditions.

Objective

Nutrient-stimulated gut hormone peptide YY3–36 (PYY3–36) selectively activates the neuropeptide Y2 receptor (NPY2R) and reduces energy intake in humans. We describe the discovery and pharmacology of the long-acting NPY2R agonist BI 1820237 and its potential bodyweight-lowering efficacy alone and in combination with the glucagon receptor (GCGR)/glucagon-like peptide-1 receptor (GLP-1R) dual agonist survodutide.

Methods & Results

BI 1820237 dose-dependently reduced food intake and gastric emptying in lean mice. Significant bodyweight reductions were not observed with BI 1820237 alone in diet-induced obese mice, however combination with survodutide led to bodyweight reduction of 22% which was significantly (p < 0.01) greater than the 17% bodyweight reduction with survodutide alone. Regression-based interaction analysis demonstrated that BI 1820237 increased the efficacy of survodutide by 265% at an ED50 of 11.7 nmol/kg over a range of dose combinations.

Conclusion

Synergistic NPY2R and GCGR/GLP-1R agonism provides an attractive mode of action for clinically relevant weight loss in patients with obesity.

Fructose is a naturally-occurring sugar, consumed in excess as sweeteners, and is linked to the development of obesity. Fructose is consumed with glucose (dextrose) in added sugars, but while dextrose produces satiety, excessive fructose intake promotes hyperphagia through the brain. However, the neurological effects of dietary fructose are not clearly defined. We fed male and female mice standard chow, a 60% high fructose, or 60% high dextrose diet and found that fructose- and dextrose-fed mice ate more calories and gained more body fat despite increasing fat oxidation and energy expenditure. Furthermore, their metabolic syndromes were more prominent in male mice, who also developed glucose intolerance. To define the neurological effects underlying the obesogenic actions of fructose, we performed ex vivo patch-clamp recordings from orexigenic Neuropeptide Y/agouti-related peptide (NPY/AgRP) neurons in the arcuate nucleus. Fructose feeding uniquely increased synaptic excitation at NPY/AgRP neurons, which remained elevated with sustained fructose exposure; this excitation may arise from glutamatergic neurons in the dorsomedial hypothalamic nucleus. Terminating fructose feeding reversed this synaptic excitation at male but not female NPY/AgRP neurons. Furthermore, chronic but not acute fructose feeding in male mice also irreversibly activated NPY/AgRP neurons even following fructose withdrawal. Interestingly, despite sex-dependent fructose-mediated plasticity at NPY/AgRP neurons, a prolonged fructose withdrawal increased innate fructose preference in both male and female mice. Taken together, these findings showed that fructose elicited synaptic and neuronal excitation at NPY/AgRP neurons that can be long-lasting. These actions are consistent with that seen during hunger and may thus promote hyperphagia in the expression of fructose-mediated obesity.

Objectives

Endurance training is known to elicit numerous changes in skeletal muscle to enhance performance and function. Many of these adaptations are controlled by the modulation of transcriptional programs in myonuclei. While previous studies have explored alterations in DNA methylation and histone modifications in response to exercise, the specific changes in chromatin restructuring and accessibility, a prerequisite for transcription, are still poorly understood.

Methods

A multi-omics analysis was performed: ATAC-sequencing was used to map chromatin accessibility in myonuclei isolated from endurance-trained and untrained mice at multiple time points (0 h, 6 h, and 72 h) post-exercise. Gene expression was assessed via RNA-sequencing, and motif activity analysis identified regulatory factors involved in exercise-induced chromatin remodeling and transcriptomic response.

Results

Endurance training amplified rapid chromatin closing immediately after exercise, with trained muscle exhibiting a more pronounced loss of chromatin accessibility at 0 h and 6 h post-exercise compared to untrained muscle. These chromatin accessibility changes persisted longer in trained muscle, with significant retention until 72 h post-exercise. Immediate early transcription factors, such as Fos and Jun, showed a training state-dependent shift in activation dynamics. Similarly, specific modulation of genes involved in metabolism, insulin response and angiogenesis was observed.

Conclusions

Endurance training triggers rapid and persistent chromatin remodeling in muscle, contributing to the transcriptional response to exercise. Our findings suggest that training induces long-lasting epigenetic changes, potentially underpinning muscle memory and improved physiological resilience. These new insights into the molecular mechanisms of muscle adaptation help to understand the training response, and might become relevant in disease prevention.

Objective

Estrogens play a pivotal role in energy balance control, by acting on its CNS receptors. It is generally assumed that the gonads are the main source of estradiol for these receptors. However, aromatase, the sole enzyme responsible for estradiol synthesis, is also present in the brain, and its role in energy balance remains largely unexplored.

Methods and Results

We identified high aromatase expression in the neurons of rat amygdala and investigated whether brain-derived estradiol, particularly within the amygdala, plays a role in energy balance and food reward control. Both whole brain chronic pharmacological inhibition of aromatase with a clinically utilized inhibitor, Letrozole, and a virogenetic approach to manipulate aromatase specifically in the amygdala were used in adult male and female rats, in conjunction with an array of measurements assessing feeding behavior and thermoregulation. Our results show that inhibition of brain aromatase results in increased food intake and body weight gain in females, but reduced food intake in males. This was driven by opposing effects on food preference for a high-fat diet. Amygdala aromatase knockdown was sufficient to increase feeding and body weight in lean and obese females, with increased visceral adiposity; effects not observed in males. Even in the absence of ovarian steroids, which already results in obesity, loss of amygdala aromatase further exacerbated weight gain and hyperphagia on an obesogenic diet. In females, hyperphagia was driven by increased meal size and increased food-motivated behavior, with increased preference for fat-rich but not sucrose-rich foods. Loss of amygdala aromatase also led to disrupted thermoregulation, with increased temperature in males but reduced in females, linked to alteration in brown adipose tissue thermogenesis.

Conclusions

Collectively, our data reveal that estradiol synthesis in the brain is necessary for body weight and feeding behavior control, as well as thermoregulation, in a sex specific manner. Our findings may have translational and clinical relevance, as aromatase inhibitors are widely used in the clinic, and aromatase has recently been found in the human amygdala.

Declines in skeletal muscle and cognitive function in older adults have been linked to abnormalities in abdominal subcutaneous adipose tissue (ASAT), yet the underlying molecular mediators remain poorly understood. Here, leveraging ASAT transcriptomics and explant-conditioned media proteomics from participants in the Study of Muscle, Mobility and Aging (SOMMA; age ≥70 years, n = 229), we identified ASAT gene clusters and secreted proteins strongly associated with comprehensive assessments of physical and cognitive function in older adults. ASAT inflammation and secreted immunoglobulins were identified as key signatures of aging-associated physical and cognitive performance limitations. Systems genetics analysis confirmed secreted-SERPINF1 as a negative regulator of skeletal muscle contraction and highlighted its potential role in inducing inflammation in the heart in silico. Additionally, novel ASAT-secreted proteins such as NID2 and APOA4 were implicated in mediating ASAT crosstalk with skeletal muscle and brain in silico. Our framework provides insights into ASAT-driven tissue crosstalk underlying physical and cognitive performance in older adults and offers a valuable resource for understanding the role of ASAT in human aging.

Objective

Though Tcf7l2 harbors the strongest genetic association with diabetes identified thus far, how it promotes metabolic disease remains unclear. Our aim was to dissect the contribution of hepatic TCF7L2.

Methods

Mice with liver-specific knockout of Tcf7l2 produced by targeted deletion of exon 1 were subjected to physiological characterization, single nucleus sequencing, and metabolite profiling. In parallel, a phenome-wide association study was performed in humans.

Results

We found that liver-specific deletion of Tcf7l2 had little effect on plasma glucose, but disrupted hepatic zonation. That is, many genes normally show gradients of expression across the liver lobule; in the absence of Tcf7l2, these gradients collapsed. One major consequence was the disorganization of glutamine metabolism, with a loss of the glutamine production program, ectopic expression of the glutamine consumption program, and a decrease in glutamine levels. In parallel, glutamine was found to be the most significantly decreased metabolite in the plasma of individuals harboring the rs7903146 variant in Tcf7l2.

Conclusions

Taken together, these data indicate that hepatic TCF7L2 has a secondary role in glycemic control, but a primary role in maintaining transcriptional architecture and glutamine homeostasis.

Objectives

Dual glucagon-like peptide-1 receptor and glucose-dependent insulinotropic polypeptide receptor agonists (GLP1RA and GIPRA, respectively) synergise to reduce body weight. Though this synergy depends on receptors within the brain, where and how this occurs is unclear.

Methods

We employed a combination of neuroanatomical approaches in the mouse to investigate access of the dual GLP1RA/GIPRA, tirzepatide, and study the central targets engaged by single agonist, dual agonist and combined agonist treatments. Genetic manipulations were then used to further investigate the functional significance of specific brain regions and distinct neuronal subtypes.

Results

We recorded penetration of fluorescently labelled tirzepatide limited mainly to circumventricular organs and confirmed the importance both GLP1R and GIPR in the dorsal vagal complex for the actions of systemically administered agonists. Receptor expression indicates GIPRA alone activates a distinct population of GABA neurons in the area postrema directly, but also neurotensin neurons in the central amygdala (Nts^CeA) indirectly. Disabling Nts^CeA neurons selectively reduces the synergistic effect of dual GLP1R/GIPR agonist administration on body weight.

Conclusions

As with selective GLP1RA, the actions of dual GLP1RA/GIPA appear to be dependent on the dorsal vagal complex for their action, probably most importantly by gaining access through the area postrema. Downstream targets include the central amygdala where signals following dual receptor agonism interact. Specifically, Nts^CeA neurons are required for the full synergistic effect of dual receptor agonism on body weight.

Objectives

The hypothalamic agouti-related protein (AgRP)- expressing neurons regulate feeding and whole-body energy homeostasis. A growing body of evidence indicates that changes in mitochondrial dynamics, such as fission and fusion, play a crucial role in regulating AgRP neuronal activity. However, the mechanisms underlying this process remain to be elucidated. Here, we showed a role of mitochondrial UCP2-mediated mitochondrial dynamics in AgRP neurons in regulating AgRP neuronal activity and fasting-induced feeding behavior.

Methods

We analyzed mitochondrial morphology, expression of activated dynamin-related protein 1 (DRP1), and mRNA expression levels of uncoupling protein 2 (Ucp2) in AgRP neurons of mice that were either in fed or fasted states. We then generated a mouse model in which Ucp2 was selectively deleted from adult AgRP neurons to assess the role of this mitochondrial protein in feeding behavior and whole-body energy metabolism.

Results

We show fasting-induced AgRP neuronal activation is associated with UCP2-mediated mitochondrial fission and mitochondrial fatty acid utilization in AgRP neurons. In line with this, mice lacking UCP2 in AgRP neurons (Ucp2^AgRPKO) show attenuated fasting- or ghrelin-induced AgRP neuronal activation and feeding behaviors and exhibited a significant decrease in body weight and fat mass accompanied by a significant increase in energy expenditure.

Conclusions

Altogether, our data revealed that UCP2-mediated mitochondrial dynamics and fatty acids oxidation in the hypothalamic AgRP neurons is necessary for AgRP neuronal function and fasting-induced food intake.

Objectives

The brain mobilizes glucose in emergency situations such as hypoglycemia as well as during day-to-day physiology such as fasting. While most hypothalamic neuronal populations that contribute to glucose mobilization also contribute to other aspects of metabolism, neurons in the ventromedial nucleus of the hypothalamus that express the cholecystokinin b receptor (VMH^Cckbr neurons) support glucose production during hypoglycemia without controlling energy homeostasis. However, their role in day-to-day glucose physiology and the mechanisms they engage to support glucose mobilization is unclear.

Methods

We used continuous glucose monitoring in mice with chronically silenced VMH^Cckbr neurons to establish whether these neurons are required during day-to-day glucose homeostasis. Tetanus-toxin based chronic silencing and acute optogenetic activation were followed by analysis of hepatic glucose metabolism and white adipose tissue lipolysis.

Results

We found that VMH^Cckbr neurons support glucose homeostasis during short fasts and contribute to gluconeogenic substrate mobilization and lipolysis. VMH^Cckbr neurons mobilize glucose without depleting hepatic glycogen or increasing gluconeogenic gene expression, but instead mobilize glycerol in a β3-adrenergic receptor (β3-AR)-dependent manner. Restoring glycerol availability following VMH^Cckbr neuron silencing restores glucose. Finally, acute activation of VMH^Cckbr neurons mobilizes additional gluconeogenic substrates beyond glycerol.

Conclusions

VMH^Cckbr neurons represent a distinct subset of glucose-mobilizing VMH neurons that support physiologic glucose homeostasis, likely through control of β3-AR-mediated gluconeogenic substrate mobilization and lipolysis. The presence of different glucose-mobilizing neuronal populations that engage distinct mechanisms in a context-dependent manner may provide the brain with flexibility to coordinate the appropriate glycemic response to different circumstances.

Objective

Muscle loss with cancer causes weakness, worsens quality of life, and predicts reduced overall survival rates. Recently, muscle weakness was identified during early-stage cancer before atrophy develops. This discovery indicates that mechanisms independent of muscle loss must contribute to progressive weakness. While mitochondrial stress responses are associated with early-stage ‘pre-cachexia’ weakness, a causal relationship has not been established.

Methods and Results

Here, using a mouse model of metastatic ovarian cancer cachexia, we identified that the well-established mitochondrial-targeted plastoquinone SkQ1 partially prevents muscle weakness occurring before the development of atrophy in the diaphragm. Furthermore, SkQ1 improved force production during atrophy without preventing atrophy itself in the tibialis anterior and diaphragm. These findings indicate that atrophy-independent mechanisms of muscle weakness occur in different muscle types throughout ovarian cancer. Ovarian cancer reduced flexor digitorum brevis (FDB) whole muscle force production and myoplasmic free calcium ([Ca²⁺]_i) during contraction in intact single muscle fibers, both of which were prevented by SkQ1. Remarkably, changes in mitochondrial reactive oxygen species and pyruvate metabolism were heterogeneous across time and between muscle types which highlights a considerable complexity in the relationships between mitochondria and muscle remodeling throughout ovarian cancer.

Conclusions

These discoveries identify that muscle weakness can occur independent of atrophy throughout ovarian cancer in a manner that is linked to improved calcium handling. The findings also demonstrate that mitochondrial-targeted therapies exert a robust effect in preserving muscle force early during ovarian cancer during the pre-atrophy period and in late stages once cachexia has become severe.

Objective

Gene discovery studies in individuals with diabetes diagnosed within 6 months of life (neonatal diabetes, NDM) can provide unique insights into the development and function of human pancreatic beta-cells.

Methods

We performed genome sequencing in a cohort of 43 consanguineous individuals with NDM in whom all the known genetic causes had previously been excluded. We used quantitative PCR and RNA-sequencing in CRISPR-edited human induced pluripotent stem cells (iPSCs), and CUT&RUN-sequencing in EndoC-βH1 cells to investigate the effect of PAX4 loss on human pancreatic development.

Results

We describe the identification of homozygous PAX4 loss-of-function variants in 2 individuals with transient NDM: a p.(Arg126∗) stop-gain variant and a c.-352_104del deletion affecting the first 4 PAX4 exons. We confirmed the p.(Arg126∗) variant causes nonsense mediated decay in CRISPR-edited iPSC-derived pancreatic endoderm cells. Integrated analysis of CUT&RUN-sequencing in EndoC-βH1 cells and RNA-sequencing in PAX4-depleted islet stem cell models identified genes directly regulated by PAX4 involved in both pancreatic islet development and glucose-stimulated insulin secretion.

Conclusion

We report the first human cases of complete loss of PAX4, establishing it as a novel cause of NDM and highlighting its role in human beta cell development. Both probands had transient NDM which remitted in early infancy but relapsed at the ages of 2.4 and 6.7 years, demonstrating that in contrast to mouse models, PAX4 is not essential for the development of human pancreatic beta-cells.

Lipids, in particular ceramides and diacylglycerols (DAGs), are implicated in insulin resistance (IR), however their precise roles remain unclear. Here, we leverage natural genetic variation to examine muscle lipids and systemic IR in 399 Diversity Outbred Australia mice fed either chow or a high-fat diet. Adipose tissue mass was significantly associated with 55% of muscle lipid features and whole-body insulin sensitivity, with DAGs as the only lipid class enriched in this association. To disentangle the contribution of adiposity and muscle lipids to whole-body insulin sensitivity, we employed two independent approaches: (1) a linear model correcting muscle lipid features for adipose tissue mass to assess their relationship with insulin sensitivity, and (2) stratifying mice into insulin sensitivity quartiles within adiposity bins. Both revealed that very long-chain ceramides, but not DAGs, were linked to IR. RNA sequencing and proteomics from the same muscles further associated these very long-chain ceramides with cellular stress, mitochondrial dysfunction, and protein synthesis. Meanwhile, DAGs correlated with leptin gene expression in skeletal muscle, suggesting they originate from contaminating adipocytes rather than myocytes per se. We propose that many muscle lipids, including DAGs, associate with muscle and systemic IR due to accumulation of adipose tissue rather than directly influencing muscle insulin sensitivity. By addressing the relationship between adiposity and metabolic state, we identified very long-chain muscle ceramides as being highly associated with IR independently of adiposity.

Increasing evidence suggests that adipose tissue plays a key role in the development, progression, and treatment of the globally epidemic disease type 2 diabetes (T2D). For example, adipose tissue dysfunction, lipotoxicity, and insulin resistance (IR) are major contributors and targets for the treatment of T2D. We previously identified the Fibroblast growth factor 1 (FGF1)/Phosphodiesterase 4D (PDE4D) pathway, which lowers plasma glucose concentration by suppressing lipolysis in adipose tissue and ultimately regulating hepatic glucose production in obese insulin-resistant mice. While phosphorylation of PDE4D is critical for its activity, the upstream signaling mechanisms remain unclear. In this study, we identified p21-activated kinases (PAKs) as regulator of PDE4D phosphorylation and suppression of lipolysis by FGF1. Inhibition of PAK-induced cAMP accumulation prevented antilipolytic function of FGF1, and reversed suppression of lipolysis caused by PDE4D overexpression, linking PAKs to the regulation of cAMP by PDE4D in murine adipocytes in vitro. Chronic inhibition of PAKs decreased lipid accumulation in both mouse and human adipocyte cultures, lowered expression of adipogenic markers, and induced IR, suggesting a previously unidentified role of PAKs in adipocyte function and differentiation. We conclude that PAKs play a crucial role in regulating the FGF1/PDE4D antilipolytic pathway, adipogenesis and IR, thereby highlighting their potential as therapeutic targets for T2D.

Graphical abstract

Activation of the FGF1/FGFR1 signaling pathway induces phosphorylation of PDE4D depending on RAFand PAKs. Phosphorylation of PDE4D at S44 is required for inhibition of the cAMP/PKA signaling cascade. Consequently, phosphorylation of HSL at S660 is reduced, resulting in the suppression of lipolysis. In addition to this indirect regulation, PAKs can also directly inhibit HSL activity. Chronic inhibition of PAKs impairs adipogenesis and induces insulin resistance.PAKs: p21-activated kinasesPDE4D: Phosphodiesterase 4DcAMP: cyclicadenosinemonophosphatePKA: Protein Kinase AHSL: Hormone-sensitive lipasePI3K: Phosphoinositide 3-kinaseAKT: Protein Kinase BIRS2: Insulin receptor substrate 2FGF1: Fibroblast growth factor 1INS: Insulin

Background

Exercise induces organism-wide molecular adaptations, partly mediated by humoral factors released in response to acute and chronic physical activity. However, the extent and specificity of endocrine effects from training-induced secreted factors remain unclear.

Methods

Here, we applied systems genetics approaches to quantify inter-organ endocrine networks using multi-tissue transcriptomics and proteomics data collected from endurance-trained rats in The Molecular Transducers of Physical Activity Consortium (MoTrPAC).

Results

Eight weeks of endurance training significantly altered both the magnitude and specificity of endocrine effects across multiple origin-target tissue pairs. Subcutaneous white adipose tissue emerged as a key endocrine regulator impacted by training, while extracellular matrix-derived factors were identified as globally regulated secretory features in trained vs sedentary animals. Notably, secretory Wnt signaling factors were identified as key mediators of exercise-induced endocrine adaptations in multiple tissues.

Conclusion

Our systems genetics framework provides an unprecedented atlas of inter-organ communication significantly remodeled by endurance exercise, serving as a valuable resource for novel exerkine discovery.