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Cover Story Current Issue

Weaning involves a dietary switch in mammals, progressively decreasing the reliance on the consumption of a fat-rich milk diet in favour of a carbohydrate-rich diet. Metabolic adaptation to this shift in macronutrient consumption is characterized by reduced hepatic gluconeogenesis, increased liver glycogen content, and changes in lipid metabolism. Such metabolic changes are supported by various nutritional, hormonal, and neuronal factors. Dietary changes during weaning are shown to drive β-cell proliferation and maturation, which is important for the optimal endocrine function of the pancreas. A switch from the nutrient sensor target of rapamycin (mTORC1) to the energy sensor 5′-adenosine monophosphate-activated protein kinase (AMPK) was found critical for functional maturation of β-cells. Furthermore, changes in the macronutrient composition during the weaning process drive alterations in the gut microbiome, which is essential for the development of immune tolerance. The major calcium absorption pathway also changes during weaning, from the paracellular pathway during the suckling stage to the vitamin D dependent transcellular pathway post-weaning. However, the factors that regulate these post-weaning metabolic adaptations are not fully understood.
Current Issue
- Abstract
Vitamin D receptor signalling regulates the diet-driven metabolic shift during weaning
Objective
Weaning in mammals is associated with a shift in the metabolism, driven by the differences in the macronutrient composition of milk and post-weaning diet. Milk has a higher fat content compared with the carbohydrate-enriched solid food. Malnutrition during this stage could affect this transition with long-term adverse effects. The role of micronutrients during this transition is not well understood.
Methods
We used mice lacking a functional vitamin D receptor (VDR) to study the role of vitamin D signalling in the metabolic transition during weaning.
Results
We demonstrate that after weaning, VDR knockout mice exhibit systemic energy deprivation and higher lipolysis in inguinal white adipose tissue, probably due to increased norepinephrine signalling via protein kinase A (PKA) and extracellular signalling-regulated kinase (ERK) pathways. The energy deprivation in vdr−/− mice is associated with defective liver glycogenolysis, characterized by increased expression of protein phosphatase-1 alpha and decreased glycogen phosphorylase activity. However, restoration of serum calcium and phosphate levels by a rescue diet is sufficient to restore energy metabolism in vdr−/− mice. Interestingly, maintaining a high-fat-containing milk-based diet post-weaning could prevent the onset of energy deprivation, liver glycogen storage defect, and adipose atrophy in these mice.
Conclusion
Our data show that vitamin D-signalling is essential for the adaptation of mice to the dietary shift from high-fat-containing milk to post-weaning carbohydrate-enriched diets. It also reveals a novel macronutrient–micronutrient interaction that shapes the metabolic flexibility of the individual based on the dietary composition of nutrients.
- Abstract
Effects of children's microbiota on adipose and intestinal development in sex-matched mice persist into adulthood following a single fecal microbiota transplantation
Background
The global prevalence of obesity and type 2 diabetes, particularly among children, is rising, yet the long-term impacts of early-life fecal microbiota transplantation (FMT) on metabolic health remain poorly understood.
Objectives
To investigate how early-life FMT from children to young, sex-matched mice influences metabolic outcomes and adipose tissue function in later, adult life.
Methods
Germ-free mice were colonized with fecal microbiota from either lean children or children with obesity. The impacts on brown adipose tissue (BAT), white adipose tissue (WAT), glucose metabolism, and gut health were analyzed in male and female mice. Microbial communities and metabolite profiles were characterized using sequencing and metabolomics.
Results
Male mice receiving FMT from obese donors exhibited marked BAT whitening and impaired amino acid and glucose metabolism. In contrast, female recipients developed hyperglycemia, accompanied by gut barrier dysfunction and WAT impairment. Distinct microbial and metabolite profiles were associated with these phenotypes: Collinsella and trimethylamine in females; and Paraprevotella, Collinsella, Lachnospiraceae NK4A136, Bacteroides, Coprobacillus, and multiple metabolites in males. These phenotypic effects persisted despite changes in host environment and diet.
Conclusions
Early-life FMT induced long-lasting effects on the metabolic landscape, profoundly affecting adipose tissue function and systemic glucose homeostasis in adulthood. Donor dietary habits correlated with the fecal microbial profiles observed in recipient mice. These findings highlight the critical need for identifying and leveraging beneficial exposures during early development to combat obesity and diabetes.
- Abstract
14-3-3ζ allows for adipogenesis by modulating chromatin accessibility during the early stages of adipocyte differentiation
Objective
We previously established the scaffold protein 14-3-3ζ as a critical regulator of adipogenesis and adiposity, but whether 14-3-3ζ exerted its regulatory functions in mature adipocytes or in adipose progenitor cells (APCs) remained unclear.
Methods
To decipher which cell type accounted for 14-3-3ζ-regulated adiposity, adipocyte- (Adipoq14-3-3ζKO) and APC-specific (Pdgfra14-3-3ζKO) 14-3-3ζ knockout mice were generated. To further understand how 14-3-3ζ regulates adipogenesis, Tandem Affinity Purification (TAP)-tagged 14-3-3ζ-expressing 3T3-L1 preadipocytes (TAP-3T3-L1) were generated with CRISPR-Cas9, and affinity proteomics was used to examine how the nuclear 14-3-3ζ interactome changes during the initial stages of adipogenesis. ATAC-seq was used to determine how 14-3-3ζ depletion modulates chromatin accessibility during differentiation.
Results
We show a pivotal role for 14-3-3ζ in APC differentiation, whereby male and female Pdgfra14-3-3ζKO mice displayed impaired or potentiated weight gain, respectively, as well as fat mass. Proteomics revealed that regulators of chromatin remodeling, like DNA methyltransferase 1 (DNMT1) and histone deacetylase 1 (HDAC1), were significantly enriched in the nuclear 14-3-3ζ interactome and their activities were impacted upon 14-3-3ζ depletion. Enhancing DNMT activity with S-Adenosyl methionine rescued the differentiation of 14-3-3ζ-depleted 3T3-L1 cells. ATAC-seq revealed that 14-3-3ζ depletion impacted the accessibility of up to 1,244 chromatin regions corresponding in part to adipogenic genes, promoters, and enhancers during the initial stages of adipogenesis. Finally, 14-3-3ζ-regulated chromatin accessibility correlated with the expression of key adipogenic genes.
Conclusion
Our study establishes 14-3-3ζ as a crucial epigenetic regulator of adipogenesis and highlights the usefulness of deciphering the nuclear 14-3-3ζ interactome to identify novel pro-adipogenic factors and pathways.
- Abstract
Hepatic stellate cell-specific Kcnma1 deletion mitigates metabolic dysfunction-associated steatotic liver disease progression via upregulating Amphiregulin secretion
Objective
Metabolic dysfunction-associated steatotic liver disease (MASLD) is a growing global health concern, with limited effective treatments. KCNMA1 potassium channel has been implicated in the pathogenesis of various metabolic diseases. However, whether and how KCNMA1 regulates MASLD have been elusive.
Methods
Global, hepatic stellate cells (HSCs)-specific, and hepatocyte-specific Kcnma1 knockout mice were fed either a standard chow or a high-fat diet (HFD). Serum and liver tissues were collected and analyzed by biochemical assay, histology, qPCR and western blotting. HSCs conditioned medium (CM) treatment hepatocytes experiment model and three-dimensional (3D) hepatocytes-HSCs spheroids were employed to study lipid accumulation in hepatocytes. A Cytokine Antibody Array was used to analyze the cytokine profile.
Results
Our study demonstrated that global Kcnma1 deletion prevented diet-induced hepatic steatosis and improved insulin sensitivity. Further analyses using HSC-specific and hepatocyte-specific Kcnma1 knockout MASLD mouse models revealed that the protective effect against hepatic steatosis was predominantly mediated by Kcnma1 deletion in HSCs, rather than in hepatocytes. CM transfer experiment and 3D spheroid studies show Kcnma1 deletion effectively prevents lipid accumulation in hepatocytes. Mechanically, Kcnma1-deficient HSCs secrete Amphiregulin (AREG) to regulate lipid metabolism in hepatocytes via epidermal growth factor receptor (EGFR) signaling. Of clinical significance, AREG levels were notably reduced in the liver tissue of MASLD patients, while injection of recombinant AREG protein significantly ameliorated MASLD in mice.
Conclusions
Our study uncovers a novel mechanism in which Kcnma1 deletion in HSCs enhances AREG secretion, thereby reducing lipid accumulation in hepatocytes through the AREG/EGFR signaling, ultimately inhibiting the progression of MASLD.
- Abstract
Abundance of a metabolically active subpopulation in dedifferentiated adipocytes inversely correlates with body mass index
Objective
The cellular composition and functionality of adipose tissue are key determinants of metabolic diseases associated with adipose tissue dysregulation, such as obesity. We hypothesized that distinct subpopulations with unique gene expression profiles and functional characteristics exist within human adipocytes.
Methods
Dedifferentiated adipocytes (DFAT), obtained by ceiling culture of human adipocytes, were analyzed using single-cell RNA sequencing (10x Genomics). Clustering analysis identified one subpopulation with a particular gene signature containing muscle cell genes which was further characterized by bulk-sequencing and analyzed alongside different cohorts of human adipose tissue.
Results
This subpopulation, named cluster 7 (C7), was isolated by FACS using two specific surface markers: cluster of differentiation 36 (CD36) and melanoma cell adhesion molecule (MCAM/CD146). Upon differentiation into adipocytes, the FACS-isolated CD36+/CD146+ cells (C7∗) showed an increased oxygen consumption rate compared to CD36-/CD146-cells (control cells) and non-sorted cells. Bulk RNA-sequencing revealed important pathways regulated in the differentiated C7∗ subpopulation that may contribute to its increased metabolic activity. Furthermore, the relative abundance of this specific cluster varied across eleven different human donors, demonstrating an inverse correlation between the proportion of C7∗ cells and the body mass index (BMI) of the respective donor. Importantly, a subset of genes regulated within this subpopulation also correlates with clinically relevant metabolic parameters, including weight, BMI, glycated hemoglobin, and plasma insulin, when analyzed alongside the gene expression of a large cohort of human subcutaneous adipose tissue (1759 donors).
Conclusion
Our results not only characterize DFAT cells derived from human adipose tissue, but also identify a specific subpopulation with increased energy expenditure that may play a role in body weight control. Future efforts to identify possible therapeutic targets or to promote the enrichment or activation of these energy-burning cells in adipose tissue might be useful in the field of cardiometabolic diseases.
- Abstract
Functional regulation of macrophages by Ces1d-mediated lipid signaling in immunometabolism
Objective
Macrophage accumulation in metabolically active tissues during obesity is common in both animals and humans, but the lipid signaling mechanisms that trigger macrophage inflammation remain unclear. This study investigates the role of Ces1d, an unconventional lipase, in regulating macrophage inflammation under nutritional stress.
Methods
A myeloid-specific Ces1d knockout (LysM-Cre-Ces1d floxed/floxed, KO) mouse model was used for the studies. For in vitro tests, bone marrow-derived macrophages (BMDMs) from control (Ces1d floxed/floxed, WT) and KO mice were assessed for migration, polarization, and activation. For in vivo experiments, WT and KO mice were induced to obesity via a high-fat diet (HFD) and subjected to metabolic characterization. Adipose tissue, liver, and serum samples were analyzed histologically and biochemically. Endogenous macrophages and T cells from adipose tissue were isolated and analyzed for functional interactions by flow cytometry.
Results
Ces1d expression changes during the differentiation of monocytes into macrophages in both mice and humans. Loss of Ces1d causes larger lipid droplets, with increased accumulation of triacylglycerol (TAG) and diacylglycerol (DAG), and impaired lipid signaling in KO macrophages. Lipid dysregulation in macrophages triggers pro-inflammatory activation, enhancing migration, activation, and polarization toward an M1-like phenotype. The pro-inflammatory macrophages further promote CD3+CD8+ T cell accumulation in obese adipose tissue, which contributes to worsened metabolic disorders, including more severe fatty liver, increased local inflammation in adipose tissue, and impaired systemic glucose tolerance in KO mice on a high-fat diet.
Conclusions
This study demonstrates Ces1d is a crucial factor in maintaining lipid homeostasis in macrophages. Loss of Ces1d leads to metabolic dysregulation in macrophages and other immune cells during obesity.
- Abstract
Gut microbiota mediates SREBP-1c-driven hepatic lipogenesis and steatosis in response to zero-fat high-sucrose diet
Objectives
Sucrose-rich diets promote hepatic de novo lipogenesis (DNL) and steatosis through interactions with the gut microbiota. However, the role of sugar-microbiota dynamics in the absence of dietary fat remains unclear. This study aimed to investigate the effects of a high-sucrose, zero-fat diet (ZFD) on hepatic steatosis and host metabolism in conventionally raised (CONVR) and germ-free (GF) mice.
Methods
CONVR and GF mice were fed a ZFD, and hepatic lipid accumulation, gene expression, and metabolite levels were analyzed. DNL activity was assessed by measuring malonyl-CoA levels, expression of key DNL enzymes, and activation of the transcription factor SREBP-1c. Metabolomic analyses of portal vein plasma identified microbiota-derived metabolites linked to hepatic steatosis. To further examine the role of SREBP-1c, its hepatic expression was knocked down using antisense oligonucleotides in CONVR ZFD-fed mice.
Results
The gut microbiota was essential for sucrose-induced DNL and hepatic steatosis. In CONVR ZFD-fed mice, hepatic fat accumulation increased alongside elevated expression of genes encoding DNL enzymes, higher malonyl-CoA levels, and upregulation of SREBP-1c. Regardless of microbiota status, ZFD induced fatty acid elongase and desaturase gene expression and increased hepatic monounsaturated fatty acids. Metabolomic analyses identified microbiota-derived metabolites associated with hepatic steatosis. SREBP-1c knockdown in CONVR ZFD-fed mice reduced hepatic steatosis and suppressed fatty acid synthase expression.
Conclusions
Sucrose-microbiota interactions and SREBP-1c are required for DNL and hepatic steatosis in the absence of dietary fat. These findings provide new insights into the complex interplay between diet, gut microbiota, and metabolic regulation.
- Abstract
Tetraspanin7 in adipose tissue remodeling and its impact on metabolic health
Objective
We previously identified tetraspanin 7 (Tspan7) as a candidate gene influencing body weight in an obesity-related gene screening study. However, the mechanisms underlying its involvement in body weight regulation remained unclear. This study aims to investigate the role of TSPAN7 from a metabolic perspective.
Methods
We utilized genetically modified mice, including adipose tissue-specific Tspan7-knockout and Tspan7-overexpressing models, as well as human adipose-derived stem cells with TSPAN7 knockdown and overexpression. Morphological, molecular, and omics analyses, including proteomics and transcriptomics, were performed to investigate TSPAN7 function. Physiological effects were assessed by measuring blood markers associated with lipid regulation under metabolic challenges, such as high-fat feeding and aging.
Results
We show that TSPAN7 is involved in regulating lipid droplet formation and stabilization. Tspan7-knockout mice exhibited an increased proportion of small-sized adipocytes and a reduced visceral-to-subcutaneous fat ratio. This shift in fat distribution was associated with improved insulin sensitivity and altered branched-chain amino acid metabolism, as evidenced by increased expression of the branched-chain α-keto acid dehydrogenase complex subunit B in Tspan7-modified mice. Mechanistically, TSPAN7 deficiency promoted subcutaneous fat expansion, alleviating metabolic stress on visceral fat, a major contributor to insulin resistance.
Conclusions
TSPAN7 influences lipid metabolism by modulating adipose tissue remodeling, particularly under metabolic challenges, such as high-fat diet exposure and aging. Its modulation enhances subcutaneous fat storage capacity while mitigating visceral fat accumulation, leading to improved insulin sensitivity. These findings position TSPAN7 as a potential target for therapeutic interventions aimed at improving metabolic health and preventing obesity-related diseases.
- Abstract
Reduced liver mitochondrial energy metabolism impairs food intake regulation following gastric preloads and fasting
Objective
The capacity of the liver to serve as a peripheral sensor in the regulation of food intake has been debated for over half a century. The anatomical position and physiological roles of the liver suggest it is a prime candidate to serve as an interoceptive sensor of peripheral tissue and systemic energy state. Importantly, maintenance of liver ATP levels and within-meal food intake inhibition is impaired in human subjects with obesity and obese pre-clinical models. Previously, we have shown decreased hepatic mitochondrial energy metabolism (i.e., oxidative metabolism & ADP-dependent respiration) in male liver-specific, heterozygous PGC1a mice results in increased short-term diet-induced weight gain with increased within meal food intake. Herein, we tested the hypothesis that decreased liver mitochondrial energy metabolism impairs meal termination following nutrient oral pre-loads.
Methods
Liver mitochondrial respiratory response to changes in ΔGATP and adenine nucleotide concentration following fasting were examined in male liver-specific, heterozygous PGC1a mice. Further, food intake and feeding behavior during basal conditions, following nutrient oral pre-loads, and following fasting were investigated.
Results
We observed male liver-specific, heterozygous PGC1a mice have reduced mitochondrial response to changes in ΔGATP and tissue ATP following fasting. These impairments in liver energy state are associated with larger and longer meals during chow feeding, impaired dose-dependent food intake inhibition in response to mixed and individual nutrient oral pre-loads, and greater acute fasting-induced food intake.
Conclusions
These data support previous work proposing liver-mediated food intake regulation through modulation of peripheral satiation signals.
- Abstract
Whole body and hematopoietic cell-specific deletion of G-protein coupled receptor 65 (GPR65) improves insulin sensitivity in diet-induced obese mice
Objective
Acidic extracellular microenvironments, resulting from enhanced glycolysis and lactic acid secretion by immune cells, along with metabolic acidosis may interfere with the insulin signaling pathway and contribute to the development of insulin resistance. In the present study, we investigated the role of G protein-coupled receptor GPR65, an extracellular pH sensing protein, in modulating insulin resistance.
Methods
We measured GPR65 expression in the adipose tissue (AT) of subjects with varying metabolic health states. We utilized whole-body and hematopoietic cell-specific GPR65 knockout (KO) mice to investigate the mechanism underlying the associations between GPR65, inflammatory response, and insulin resistance.
Results
Elevated GPR65 expression was observed in the AT of subjects with obesity, compared to their lean counterparts, and was inversely correlated with insulin resistance. In GPR65 KO mice, improved insulin sensitivity and decreased hepatic lipid content were observed, attributed to concomitant increases in mitochondrial activity and fatty acid β-oxidation in liver. GPR65 KO mice also exhibited increased Akt phosphorylation in skeletal muscle, suppressed proinflammatory gene expression in AT, and decreased serum cytokine levels, collectively suggesting the anti-inflammatory effects of GPR65 depletion. This was further confirmed by observations of decreased macrophage chemotaxis towards AT in vitro, and depressed inflammatory signaling pathway activation in bone marrow-derived dendritic cells from GPR65 KO mice. Additionally, hematopoietic lineage-specific GPR65 KO mice exhibited improved whole body insulin sensitivity in clamp studies, demonstrating GPR65 signaling in immune cells mediates this effect.
Conclusions
Our data suggests that macrophage-specific GPR65 signaling contributes to inflammation and the development of insulin resistance.
- Abstract
IL-6 decodes sex and diet-dependent circadian and metabolic rhythms
Objective
Interleukin-6 (IL-6) is a pleiotropic cytokine involved in immune regulation and energy metabolism. Its diurnal secretion influences core circadian components, emphasizing its critical role in circadian biology. Despite known sex differences in immune, circadian, and metabolic processes, how IL-6 integrates these processes remains poorly understood.
Methods
IL6 knockout (KO) and control mice of both sexes were phenotyped for circadian and metabolic traits under standard (STD) and high-fat diet (HFD), fasting, and time-restricted feeding. Molecular analyses in muscle, liver, and hypothalamus assessed clock gene expression and IL-6 signaling pathway. Circulating sex steroid hormones were quantified to examine their contribution to the observed sex-specific phenotypes.
Results
IL-6 deficiency disrupts circadian locomotor and metabolic rhythms in a sex- and diet-dependent manner. Males exhibit impaired light-driven circadian rhythms under STD conditions and metabolic misalignment under HFD, whereas females display greater circadian resilience under STD conditions but increased vulnerability to circadian disruption during HFD. Additionally, IL-6 emerges as a novel regulator of the food-entrainable oscillator (FEO), linking food anticipatory activity and metabolic cycles under both STD and HFD in a sex-dependent manner.
Conclusions
These findings identify IL-6 as a critical mediator of circadian-metabolic plasticity, shaping sex- and diet-specific trade-offs between circadian stability and metabolic homeostasis. Our study highlights IL-6 as a potential therapeutic target for mitigating circadian misalignment-associated metabolic disorders, with implications for the timed modulation of IL-6 signaling.
- Abstract
Pervasive glycative stress links metabolic imbalance and muscle atrophy in early-onset Parkinson's disease
Objective
Parkinson’s disease (PD) is recognized as a systemic condition, with clinical features potentially modifiable by dietary intervention. Diets high in saturated fats and refined sugars significantly increase PD risk and exacerbate motor and non-motor symptoms, yet precise metabolic mechanisms are unclear. Our objective here was to investigate the interplay between diet and PD-associated phenotypes from a metabolic perspective.
Methods
We explored PARK7 KO mice under chronic glycative stress induced by prolonged high-fat high-sucrose (HFHS) diet. We investigated metabolic consequences by combining classical metabolic phenotyping (body composition, glucose tolerance, indirect calorimetry, functional assays of isolated mitochondria) with metabolomics profiling of biospecimens from mice and PD patients.
Results
We found this obesogenic diet drives loss of fat and muscle mass in early-onset PD mice, with a selective vulnerability of glycolytic myofibers. We show that PD mice and early-onset familial PD patients are under pervasive glycative stress with pathological accumulation of advanced glycation end products (AGEs), including N-α-glycerinylarginine (α-GR) and N-α-glycerinyllysine (α-GK), two previously unknown glycerinyl-AGE markers.
Conclusions
Our results offer the first proof for a direct link between diet, accumulation of AGEs and genetics of PD. We also expand the repertoire of clinically-relevant glycative stress biomarkers to potentially define at-risk patients before neurological or metabolic symptoms arise, and/or to monitor disease onset, progression, and effects of interventions.
- Abstract
Off-target depletion of plasma tryptophan by allosteric inhibitors of BCKDK
The activation of branched chain amino acid (BCAA) catabolism has garnered interest as a potential therapeutic approach to improve insulin sensitivity, enhance recovery from heart failure, and blunt tumor growth. Evidence for this interest relies in part on BT2, a small molecule that promotes BCAA oxidation and is protective in mouse models of these pathologies. BT2 and other analogs allosterically inhibit branched chain ketoacid dehydrogenase kinase (BCKDK) to promote BCAA oxidation, which is presumed to underlie the salutary effects of BT2. Potential “off-target” effects of BT2 have not been considered, however. We therefore tested for metabolic off-target effects of BT2 in Bckdk−/− animals. As expected, BT2 failed to activate BCAA oxidation in these animals. Surprisingly, however, BT2 strongly reduced plasma tryptophan levels and promoted catabolism of tryptophan to kynurenine in both control and Bckdk−/− mice. Mechanistic studies revealed that none of the principal tryptophan catabolic or kynurenine-producing/consuming enzymes (TDO, IDO1, IDO2, or KATs) were required for BT2-mediated lowering of plasma tryptophan. Instead, using equilibrium dialysis assays and mice lacking albumin, we show that BT2 avidly binds plasma albumin and displaces tryptophan, releasing it for catabolism. These data confirm that BT2 activates BCAA oxidation via inhibition of BCKDK but also reveal a robust off-target effect on tryptophan metabolism via displacement from serum albumin. The data highlight a potential confounding effect for pharmaceutical compounds that compete for binding with albumin-bound tryptophan.
Articles in Press
- Abstract
Inactivity-induced NR4A3 downregulation in human skeletal muscle affects glucose metabolism and translation: insights from in vitro analysis
Background
Physical activity promotes health, whereas inactivity is associated with metabolic impairment. The transcription factor nuclear receptor subfamily 4 group A member 3 (NR4A3) is a pleiotropic regulator of skeletal muscle exercise adaptation and metabolism. However, the consequence of lower NR4A3 expression remains largely unexplored. We investigated the impact of NR4A3 downregulation on human skeletal muscle metabolism.
Methods
Published transcriptomic datasets from human bed rest and limb immobilisation studies were curated to meta-analyse the effect of physical inactivity on skeletal muscle NR4A3 levels. In primary human skeletal myotubes, siRNA and lentivirus were used to silence and overexpress NR4A3, respectively. Basal and stimulated (insulin ± leucine) signal transduction was determined by immunoblot analysis. Effects on glucose, fatty acid, and protein metabolism were measured using radiolabelled substrate assays. Lactate production was assessed in culture supernatant by colourimetry. Cell morphology was analysed by immunocytochemistry and gene expression was quantified by RT-qPCR.
Results
Physical inactivity decreased skeletal muscle NR4A3 (-27%), concomitant with pathways related to mitochondrial function, cytoskeleton organization, chromatin regulation, protein synthesis and degradation. Silencing of nuclear-localised NR4A3 protein (-30%) reduced glucose oxidation (-18%) and increased lactate production (+23%) in vitro. This coincided with greater signalling downstream of AMPK and elevated rates of basal (+26%) and FCCP-stimulated (+55%) fatty acid oxidation. NR4A3 downregulation lowered protein synthesis (-25%), and impaired mTORC1 signalling and ribosomal transcription. Alternatively, overexpression of the canonical NR4A3 protein isoform (+290%) augmented translation and total cellular protein content, which protected myotubes against dexamethasone-induced atrophy. Moreover, partial restoration of NR4A3 levels rescued glucose oxidation in NR4A3-silenced muscle cells and restored phosphorylation of mTORC1 substrates. NR4A3 depletion reduced myotube area (-48%) and further altered protein and gene expression of key contractile elements in skeletal muscle.
Conclusions
Our study connects reduced NR4A3 expression with physical inactivity and indicates that NR4A3 downregulation in human skeletal muscle has adverse effects on glucose metabolism and protein synthesis. Thus, decrements in NR4A3 abundance could be causal in the deleterious health consequences resulting from sedentary lifestyles and targeting NR4A3 may offer new avenues for combating conditions such as disuse muscle atrophy.
- Abstract
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.
- Abstract
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.
Conclusion
These paired multimodal data comprise an extensive resource (https://nme.ethz.ch/mAT_CEAtlas.html) for the further exploration of the mouse adipocyte epigenome which will enable discovery of regulatory elements governing adipocyte identity and gene regulation.
- Abstract
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=4.91x10-11; APOA1, p=8.03x10-9), 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.
- Abstract
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. 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. 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 was surprisingly unchanged. 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. 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.
- Abstract
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. However, that did not translate to worse disease severity, as indicated by comparable levels of HbA1C and HOMA2-IR. Insulin was predominantly prescribed for individuals in SIDD and SIRD, who also displayed the highest risk of CKD, followed by MOD. 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. These findings strongly support the need for a transition to more personalized, data-driven treatment approaches to minimize diabetes-related complications and improve disease outcomes.
- Abstract
Objective
Creatine kinase B (CKB) is the main isoenzyme driving creatine kinase (CK) activity in classical brown adipocytes. However, the specific CK isoenzyme active in beige adipocytes remains unknown. This study aimed to identify the predominant CK isoenzyme expressed and functionally active in beige adipocytes.
Methods
CK activity was tracked using D3-creatine tracing in inguinal adipocytes from mice with adipocyte-specific Ckb deletion and their littermate controls, across in vivo, in vitro, and ex vivo settings.
Results
CKB was essential for CK activity in protein lysates and intact white and beige adipocytes isolated from inguinal fat and drives thermogenesis through the Futile Creatine Cycle.
Conclusions
Similar to classical brown adipocytes, CKB is the key functional CK isoenzyme in white and beige adipocytes from the inguinal depot.
- Abstract
Kidney glucose reabsorption is vital for maintaining glucose homeostasis and ensuring proper physiological functioning. This process is primarily regulated by the glucose transporter 2 (GLUT2), which plays a central role in facilitating glucose transport across various metabolic organs, including the liver, pancreas, intestine, and kidney. Recently, we demonstrated that nullification of GLUT2 in kidney proximal tubule cells (KPTCs) in mice prevents diabetic kidney disease. However, the role of KPTC-GLUT2 on renal and systemic metabolism under normo-physiological conditions remains unexplored. Here, we provide evidence indicating that targeted removal of KPTC-GLUT2, thus impeding glucose reabsorption, resulted in increased food intake, enhanced systemic carbohydrate oxidation, and elevated fat and muscle mass. Additionally, alterations in glucose uptake and utilization across various organs was observed, accompanied by an improved whole-body lipid profile. This phenotypic shift towards thriftiness and sustained energy expenditure arose from metabolic reprogramming within the kidney, characterized by augmented taurine and creatine reabsorption and bioavailability, overactivation of mTORC1, and increased endocannabinoid 'tone'. These findings uncover a novel regulatory function of KPTC-GLUT2 in cellular and systemic whole-body energy metabolism, crucial for maintaining cellular homeostasis and overall health.
- Abstract
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. 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. 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.
- Abstract
Objective
Glucagon-like peptide 1 (GLP-1) receptor (GLP-1R) agonism is foundational to modern obesity pharmacotherapies. These compounds were engineered for maximal G protein alpha(s) (Gsα) signaling potency and downstream cAMP production. However, this strategy requires reconsideration as partial, biased GLP-1R agonists characterized by decreased Gsα signaling and disproportionate reductions in β-arrestin recruitment relative to the native ligand provide greater weight loss than full, balanced agonists in preclinical models.
Methods
We tested the hypothesis that in vitro signaling bias, which considers both cAMP signaling and β-arrestin recruitment, better predicts weight loss efficacy in diet induced obese (DIO) rodents than cAMP potency alone.
Results
Our data demonstrate that signaling bias significantly correlates to GLP-1R agonist mediated weight loss in diet-induced obese mice. We further characterized a protracted GLP-1 analogue (NNC5840) which exhibits a partial-Gsα, cAMP-biased GLP-1R signaling profile in vitro and demonstrates superior maximal body weight reduction compared to semaglutide in DIO mice. The NNC5840 weight loss profile is characterized by reduced in vivo potency but increased maximal efficacy.
Conclusion
The data demonstrate that biased agonism is a strong predictor of in vivo efficacy for GLP-1R agonists independent of factors like intrinsic cAMP potency or pharmacokinetics. These data suggest that drug discovery screening strategies which take a holistic approach to target receptor signaling may provide more efficacious candidate molecules. The interpretations of these studies are limited by unknowns including how structural modifications to the biased GLP-1R agonist effect physiochemical properties of the molecules.
Save the Date

12th Helmholtz
Diabetes Conference
22-24. Sep, Munich
2022 impact factor: 6.6
You are what you eat
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