Cell Metabolism

Brown adipose tissue (BAT) regulates systemic metabolism beyond thermogenesis, yet the circulating mediators through which BAT communicates with other organs remain less defined. Here, we performed comprehensive serum metabolomics and lipidomics in BAT-ablated mice and human cohorts with varying BAT activity to delineate how BAT activity shapes the circulating metabolome. By integrating datasets across serum, tissues, extracellular fluids, and conditioned media, we assembled BAT-linked circulating molecular signatures. The analyses support a role for BAT in the clearance of circulating branched-chain amino acids and triglycerides, and also identify a cold-inducible metabolite, 3-hydroxystearic acid (3-OHSA), produced by BAT and released into circulation. 3-OHSA serves as a circulating readout of cold-activated BAT and acts on the liver to reduce mitochondrial membrane potential and reactive oxygen species (ROS) production, thereby limiting oxidative stress. This work provides a framework for identifying BAT-derived mediators and uncovers a BAT-liver axis that coordinates adaptation to metabolic stress. HIGHLIGHTSO_LIComprehensive analyses of BAT-linked circulating metabolome and lipidome in mice and humans. C_LIO_LIMulti-level metabolomics supports the role of BAT in circulating BCAA and triglyceride clearance. C_LIO_LICold-inducible 3-OHSA is secreted by BAT and signals to the liver. C_LIO_LI3-OHSA decreases hepatic oxidative stress by decreasing mitochondrial membrane potential. C_LI

Metabolic diseases such as type 2 diabetes (T2D) arise through complex interactions between physiological, molecular, and environmental processes. Clinical traits including age, sex, adiposity, and glycaemic status are strongly associated with disease risk and progression, yet most molecular studies examine these factors independently and assume relatively static molecular regulation. Consequently, how physiological state dynamically reshapes molecular organisation across omics layers remains poorly understood. Here, we integrated transcriptomic, proteomic, metabolomic, and genetic data from 3,027 individuals in the IMI DIRECT cohort to characterise the joint molecular effects of age, sex, body mass index (BMI), and glycated haemoglobin (HbA1c). We identified widespread associations between these traits and molecular phenotypes. However, interaction analyses revealed a more complex context-dependent regulation, showing that the molecular effect of one trait frequently depends on the state of another, with sex-specific effects of age being more prominent. We also investigated relationships between different types of molecular phenotypes and how these relationships are modulated by metabolic disease relevant traits, demonstrating that cross-omic molecular coordination is itself dynamically remodelled by physiological and metabolic state. Probabilistic causal inference identified a directionally structured network of age-associated molecules, revealing pathways through which age effects propagate across omics layers, showcased in the example of the mTOR signalling pathway. Integration of this directed network with genetic colocalisation analyses also identified a sub-network relevant for T2D. Collectively, our findings demonstrate that metabolic disease relevant traits not only independently influence molecular phenotype abundance but also jointly reshape the directional organisation of cross-omic molecular networks. These results support a model in which metabolic disease susceptibility emerges through dynamic rewiring of interconnected molecular systems and provide a framework for context-dependent biomarker discovery, disease stratification, and precision metabolic medicine.

During an immune response, metabolism changes dramatically. Metabolites are oxidized to power immune cell functions, serve as building blocks for proliferation, and act as effectors to regulate pathogen or host cells. Though metabolic changes in cultured cells have been studied extensively, metabolism changes in vivo are less understood. Here, we measured metabolomic changes across six mouse tissues in three models of immune activation: CpG-DNA cytokine storm, lymphocytic choriomeningitis virus infection, and polyI:C viral mimetic injection; and carried out metabolomics in cultured macrophages activated with different stimuli. We found most metabolomic changes were exclusive to either inflamed tissues or cultured macrophages, although itaconate was strongly induced in both contexts. We then mechanistically dissected the role of the soluble sialic acid N-glycolylneuraminic acid, which is highly induced in inflamed tissues yet only modestly in cultured macrophages. This metabolite rises in tissues in different models of inflammation, and the analogous human metabolite, N-acetylneuraminic acid, is increased in human patients experiencing inflammation. We found that N-glycolylneuraminic acid is produced in CD11b+ myeloid cells by cleavage of protein-bound sialic acid. However, blocking its production did not affect CpG-DNA liver inflammation or LCMV infection in mice. Therefore, these experiments identify soluble sialic acid as a conserved biomarker of inflammation in mice and humans and highlight the differences in metabolism between in vitro and in vivo models of inflammation.

Biological aging greatly impacts the bodys ability to handle glucose, and represents a major risk factor the development and progression of type 2 diabetes (T2D). Nonetheless, despite advances in cellular senescence research and the development of new senolytic therapies, the heterogeneity of cellular senescence in the human endocrine pancreas, as well as its roles in normal aging, remains to be elucidated at the single-cell level. Here, we performed single-cell-resolved spatial proteomics and transcriptomics on intact pancreas from 26 donors (ages 20-80) and multiplexed single-cell RNA sequencing and functional assays on dispersed islets from 14 donors (ages 34-69). We identify two discrete SnC subpopulations distinguished by relative expression of CDKN1A and CDKN2A. CDKN1A senescent cells (SnCs) exhibit loss of {beta}-cell identity, impaired insulin secretion, and a proinflammatory SASP associated with increased islet immune infiltration. In contrast, CDKN2A SnCs retain transcriptional identity and functional competence, with lower inflammatory signaling. Together, these findings identify heterogeneous and functionally divergent senotypes in the human pancreas, distinguishing an adaptive (CDKN2A) from a maladaptive (CDKN1A) senescence program, thus providing a mechanism-guided framework for senescence-targeted therapies in T2D.

Type 2 diabetes is linked to systemic inflammation driven by metabolic stress and aging. Although pancreatic inflammation associated with these factors is well documented, the dynamics of immune cell populations and their molecular changes remain poorly understood. We characterized immune cell alterations in the pancreas and pancreatic islets during Western diet (WD) feeding and aging using imaging mass cytometry (IMC) and single-cell RNA sequencing (scRNA-seq). Spatial and transcriptional analyses were performed to define immune cell subtype composition, activation states, and inferred cell-cell communication programs under metabolic and age-related stress conditions. Our analyses identified expansion of an F4/80low macrophage subtype and activated effector-like CD8+ T cells throughout the pancreas during WD feeding and aging. Within pancreatic islets, single-cell RNA sequencing identified a type 1 interferon-responsive macrophage population with low F4/80 expression that expanded during overnutrition. Notably, the type 1 interferon responses elicited by these stressors diverged: aging was associated with a more canonical type 1 interferon response, whereas overnutrition induced a broader response that included STAT3-associated transcriptional programs. We further provide evidence for enhanced cytokine-mediated communication between macrophages and a CD8+ cytotoxic T-cell population under overnutrition and aging. These findings show that metabolic stress and aging remodel pancreatic inflammation through overlapping but distinct immune mechanisms, involving expansion of F4/80low macrophages, activation of divergent type 1 interferon programs, and enhanced macrophage-CD8+ T-cell communication. Together, these findings suggest that distinct therapeutic approaches may be required to preserve islet function in type 2 diabetes driven by metabolic stress versus aging.

The energy turnover and metabolic flexibility of the human brain extend beyond a primary reliance on carbohydrates and oxygen. Building on work in anesthetized patients with cerebrovascular pathology, we quantified trans-cerebral arteriovenous differences in healthy humans to isolate and characterize the most abundant cerebral metabolite and lipid species. We observed a net release of acylcarnitine from the cerebral circulation, indicating that these species are active in mitochondrial fatty acid {beta}-oxidation occurring in the healthy resting brain. Furthermore, a strong association was apparent between variability in the brains respiratory quotient (RQ) and activity within the purine salvage pathway, particularly with the uptake of guanosine monophosphate. In a larger sample size (n = 210), we further established that biological variability around an RQ of 1.0 - typically interpreted as exclusive carbohydrate oxidation - coincides with coordinated arteriovenous shifts in metabolomic and lipidomic pathways. The variability is not only visible through complex omics pathways, but is also strongly related to the oxygen carbohydrate index of the brain, further supporting that energy substrates other than glucose are exchanged and oxidized across the brain. These findings reveal substantial versatility and redundancy in how the healthy brain maintains its high energetic demands through flexible, interconnected metabolic and lipidomic networks.

Post-meal activity can attenuate glucose excursions; however, the exact magnitude of this effect remains unquantified, and guidance is rarely personalized to the meal occasion. We linked Human Phenotype Project diet logs, continuous glucose monitoring and wearable step counts to test whether glycemic risk estimated before activity occurs can prioritize post-meal movement. An activity-blind PPGR model trained on 391,214 PPGR-valid meals from 9,561 participants generated pre-activity meal scores. Among 55,949 step-linked meals from 1,627 adults without diabetes, higher 0-120-min post-meal steps were associated with lower within-participant PPGR (-53.0 mg/dL*min per 1 s.d. higher log steps; 95% CI, -64.2 to -41.7), with larger adjusted PPGR iAUC contrasts at 1,501-2,500 observed steps (-154.4 mg/dL*min versus 0-50 steps). Associations were stronger among participants with higher glycemic-adiposity burden and after meals with higher predicted PPGR. A held-out pre-activity step-response ranking concentrated larger inverse step-PPGR associations (-79.1 top versus -15.0 mg/dL*min bottom quintile), providing a testable strategy for prediction-guided, post-meal movement prompts.

Glycosuria, whether genetically induced or triggered by SGLT2 inhibitors, activates compensatory glucose-producing pathways that limit glucose lowering in type 2 diabetes. To define these pathways, we studied renal Glut2 knockout mice, which progressively lose Slc5a2 (encoding SGLT2) expression yet maintain normoglycemia despite marked urinary glucose loss. Metabolic profiling and isotope tracing revealed coordinated adaptations in mannose and glutamine metabolism during glycosuria. Skeletal muscle reduced glucose utilization and instead oxidized mannose, while whole-body glycolysis declined, establishing a systemic glucose-sparing state. Disruption of glutamine transport or mannose utilization caused hypoglycemia in mice treated with an SGLT2 inhibitor, demonstrating dependence on these substrates to maintain glucose homeostasis during glycosuria. Multiomic profiling revealed increased expression and chromatin accessibility of mannose and glutamine transport pathways. These findings identify a kidney-driven metabolic program that preserves systemic glucose homeostasis during glycosuria and may inform strategies to optimize the glucose-lowering efficacy of SGLT2 inhibitors.

Mitochondrial protein homeostasis intersects with metabolic control, but the in vivo roles of specific mitochondrial co-chaperones remain unclear. The chaperone mtHSP70 plays a key role in import and folding of nuclear-encoded proteins targeted to mitochondrial matrix. Its protein folding cycle is regulated by the GrpE-like nucleotide exchange factor GRPEL1. Vertebrates also have a GRPEL2 paralog, postulated as the stress-sensitive counterpart, but its physiological relevance is not known. We show here that GRPEL2 is not essential for viability in mice, and its absence does not induce proteotoxic stress responses in stark contrast to GRPEL1. However, we find that GRPEL2 has a role in regulating body weight homeostasis. GRPEL2 knockout mice are protected from age- and diet-induced weight gain and maintain a better metabolic health and insulin sensitivity. Transcriptional profiling revealed minimal changes in liver and skeletal muscle, whereas white adipose tissue from Grpel2-deficient mice lacked the obesity-associated remodeling seen in controls. We propose that GRPEL2 fine-tunes metabolic setpoints without broadly perturbing mitochondrial protein import, thereby maintaining adipose tissue health during nutritional excess. These findings show that subtle alterations in mitochondrial chaperone systems reshape systemic metabolism and could suggest strategies to mitigate obesity and insulin resistance through targeted modulation of mitochondrial proteostasis.

Stress involves the activation of cellular, physiological, and emotional processes that cost energy--nothing is free in biology. In mammals, the stress response involves hormone release, including norepinephrine (NE), which increases energy expenditure. To quantify the energetic cost of NE signaling in a simple cellular system, we interrogated the dose (0-10 M NE) and time-dependent (up to 10 hours) effects of adrenergic signaling in primary human fibroblasts. Oxygen consumption rates (OCR, reflecting ATP generated by mitochondria) and extracellular acidification rate (ECAR, reflecting ATP generated by glycolysis) were measured continuously using extracellular flux analysis, allowing us to estimate the ATP turnover rates, and thus cellular energy expenditure. Within the first 18 minutes (early phase), glycolysis increases up to 47% whereas respiration decreased 2-5%. Both parameters normalized within 1-2 hours for low NE concentrations. This was followed by an increase in oxidative phosphorylation (OxPhos), peaking around 9-12% by 2-6 hours (mid or late-phase). These minutes-to-hours data reveal the temporal dynamics whereby NE increases cellular energy expenditure in fibroblasts. Blocking OxPhos with oligomycin or piericidin A abolished OxPhos changes post-NE addition while conserving the glycolytic response. Withdrawal of glucose from the media significantly dampened the absolute rise in ECAR in response to NE, and instead increased OxPhos, revealing the metabolic flexibility in fibroblasts. Finally, cells with genetic defects impairing OxPhos exhibited a 50% blunted NE-driven metabolic response, consistent with the existence of an energy constraint in mitochondrial diseases. In summary, we have resolved the dynamics and flexible bioenergetic recalibrations associated with NE-driven hypermetabolism in primary human fibroblasts. Mapping the nature and magnitude of these recalibrations in humans would advance our understanding of the potential energetic forces underlying the damage to health by chronic stress.

Pathogenic mitochondrial DNA (mtDNA) defects provide an opportunity to test how impaired oxidative phosphorylation reshapes human energy expenditure. We studied adults with confirmed mtDNA defects (MitoD) and healthy controls using whole-room indirect calorimetry, doubly labeled water, quantitative magnetic resonance, actigraphy, autonomic monitoring, mood assessments, plasma inflammatory markers, and growth differentiation factor 15 (GDF15). Under behaviorally clamped conditions, fat-free mass-adjusted total energy expenditure (TEE) was consistently higher in MitoD, with higher non-resting expenditure per unit wrist acceleration by day, and blunted sleep-related metabolic suppression at night. In contrast, free-living TEE was similar between groups despite lower physical activity in MitoD, consistent with behavioral compensation within a constrained energy budget. Plasma GDF15 was ~5-fold higher in MitoD and tracked with disease severity, systemic inflammation, fatigue, energetic burden, and lower habitual activity. These findings identify a persistent energetic burden in MitoD that is buffered in daily life and associated with elevated plasma GDF15.

Skeletal muscle can release endocrine stress signals during aging and wasting, but the upstream mechanisms that restrain this response remain incompletely defined. Here we identify March5 as a muscle proteostatic checkpoint that limits ATF4-dependent GDF15 production. March5 expression declined in aged and atrophic muscle, whereas muscle-specific March5 deletion induced ATF4 accumulation, marked GDF15 elevation, reduced food intake and progressive loss of body, muscle and bone mass. Restoration of feeding, GDF15 neutralization or muscle Atf4 deletion substantially attenuated the wasting phenotype. Mechanistically, March5 interacted with ATF4 and promoted its ubiquitination at K92, thereby limiting ATF4 stability and Gdf15 expression. Conversely, muscle March5 gain-of-function or pharmacological attenuation of ATF4 signaling improved feeding, body composition and physical performance in aged mice. These findings define a March5-ATF4-GDF15 endocrine stress axis linking muscle proteostatic control to feeding suppression and systemic body-composition remodeling.

Cell membrane proteins (CMPs), notably G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs), represent the largest class of druggable targets. Despite their therapeutic importance, how the CMP landscape is systemically remodeled during metabolic disease progression and in response to exercise remains poorly understood. Here, we constructed the most comprehensive CMP proteome atlas to date across 22 male mouse tissues and established the first multi-tissue map of GPCR-associated protein hormones/prohormones. Integrated CMP proteomic and transcriptomic analysis revealed that diet-induced obesity and its progression to type 2 diabetes remodel the CMP repertoire in patterns distinct from those induced by exercise. We found that numerous GPCRs and RTKs critical for energy homeostasis are dysregulated during obesity in a tissue-specific manner, and these alterations are reversed to varying extents by exercise training. Importantly, our CMP-centric omics study identified two parathyroid hormone receptors (PTHRs) in the hypothalamus as negative regulators of feeding and body weight. Genetically silencing these hypothalamic PTHRs led to severe obesity even on a chow diet and markedly blunted exercise-induced weight loss. Collectively, our study provides not only new insights into systematic CMP regulation underlying metabolic deterioration versus exercise adaptation, but also nominates potential receptor targets for obesity management.

Type 2 diabetes (T2D) arises from distinct diabetogenic mechanisms, but whether these mechanisms differ in their associations with hallmarks of aging remains unclear. We analyzed 449,505 UK Biobank and 374,973 All of Us participants using an overall T2D polygenic score (oPS) and eight partitioned polygenic scores (pPSs) representing distinct T2D-related mechanisms. Across organ systems, 81 age-related diseases were assigned to nine hallmarks of aging. UK Biobank analyses used Cox regression for incident hallmark-level outcomes, and All of Us analyses used logistic regression for prevalent hallmark-level outcomes. In both cohorts, the oPS was associated with disease burden across hallmarks, whereas pPS associations varied by mechanism. The obesity pPS showed the strongest and most consistent associations, while other insulin-resistance-related pPSs, including the lipodystrophy pPS, showed more modest positive associations. Beta-cell dysfunction pPS associations were close to null across hallmarks. Obesity pPS-hallmark associations were significantly attenuated after adjustment for BMI, and lipodystrophy pPS-hallmark associations after adjustment for triglyceride-to-HDL cholesterol ratio (TG/HDL-C), a marker of insulin resistance. These findings suggest that adiposity and insulin resistance, indexed by BMI and TG/HDL-C, may act as modifiable factors in the T2D genetic burden on aging hallmarks.

Energy supply is fundamental to cardiac performance, yet the mechanisms by which the heart adapts to nutrient scarcity remain incompletely understood. Here, we identify acetate as a pivotal metabolic substrate that sustains cardiac contractile function during fasting-induced energy deficiency. Fasted mice reveal significant elevation of circulating acetate derived from hepatic fatty acid catabolism. Physiological concentrations of acetate alone can maintain ex vivo beating and electrical stability in Langendorff-perfused hearts. Primary mouse cardiomyocytes preferentially utilize acetate under energy-restricted conditions, which is abolished by knockdown of mitochondrial Acss1, the enzyme responsible for converting acetate to acetyl-CoA. Isotopic tracing with 13C-acetate demonstrated selective cardiac uptake during fasting. In vivo, acetate supplementation preserved heart rate and systolic function in fasted wild-type mice but not in Acss1-deficient hearts. These findings reveal an Acss1-dependent metabolic pathway enabling the heart to harness hepatic acetate as an endogenous fuel, representing a nutrient stress-responsive adaptation based on inter-organ crosstalk and implying therapeutic potential of acetate to energy-deficient heart diseases.

Malonate is often described as an endogenous inhibitor of complex II of the electron transport chain. However, the cellular source of malonate is unclear, and current knowledge concerning its metabolism is limited to the action of a single enzyme, Acyl-CoA Synthetase Family Member 3 (ACSF3), which converts malonate to malonyl-CoA in the mitochondrial matrix. One potential route of malonate metabolism downstream of ACSF3 is its consumption by the mitochondrial fatty acid synthesis (mtFAS) pathway. However, studies examining the link between ACSF3 and mtFAS have yielded conflicting results. We developed a novel mass spectrometry approach to perform stable isotope tracing into products of mtFAS, and found that while malonate is in fact a carbon source for mtFAS, ACSF3 is not required for malonate incorporation into mtFAS products. Using this method to trace other nutrients into mtFAS, we also found evidence of acetyl-CoA carboxylase 1 (ACC1)-dependent malonate synthesis from glucose. We further show that ACC1 is required for optimal mtFAS activity, with downstream effects on oxidative phosphorylation. Together these findings establish the malonate as a regulated endogenous intermediate that supports mtFAS activity and mitochondrial oxidative function.

GLP-1 receptor agonists (GLP-1 RAs) effectively reduce weight in obesity, although significant weight regain typically follows discontinuation. Here, in a randomized clinical trial (ChiCTR2200066014), we found that GLP-1 RA (semaglutide) and a high-fibre diet achieved similar 12-week weight reduction, but semaglutide recipients exhibited significantly higher weight rebound at the 14th week after intervention cessation. Shotgun metagenomic sequencing revealed that semaglutide aggravated the proinflammatory signature in the gut microbiome, which contrasted with high-fibre diet intervention. The microbiota transplanted from semaglutide-treated subjects to germ-free mice induced gut barrier dysfunction, systemic inflammation and an increase in the bacterial antigen load in the liver and adipose tissue, which activated the NF-{kappa}B pathway to drive lipid accumulation. Using a diet-induced obesity mouse model, we found that semaglutide exacerbated gut microbiome dysbiosis by weakening host immune surveillance of the gut microbiota through downregulating IFN-{gamma} to reduce antimicrobial peptides expression and delaying gut transit time to shift microbial metabolism from saccharolysis towards proteolysis. Crucially, combining semaglutide with dietary fibre in mice mitigated microbiome dysbiosis and attenuated weight regain post-cessation. These findings suggest that GLP-1 RA-exacerbated gut microbiome dysbiosis in obesity as a key mediator of post-treatment weight rebound and propose adjunctive fibre supplementation as a strategy to sustain weight loss.

Pathologic white adipose tissue (WAT) remodeling, characterized by fibrosis, inflammation, and adipocyte dysfunction, is a hallmark and driver of metabolic disease in obesity1. Here, we show that legacy effects of early physiological or pharmacological interventions driving adaptive adipose remodeling can mitigate maladaptive WAT remodeling and metabolic dysfunction when developing obesity later in life. Cold exposure or beta3-adrenergic receptor (beta3AR) agonism (CL316,243) induced thermogenic remodeling of WAT in male mice. After a prolonged recovery at room temperature, trained epididymal WAT reverted to an energy-storing state but retained a population of adipocytes resembling metabolically flexible visceral adipocytes found in human metabolically healthy obesity. The legacy of the antecedent treatment conferred lasting protection against glucose intolerance when later developing high fat diet (HFD)-induced obesity, with insulin sensitivity persisting for at least 20 weeks of overnutrition. This metabolic resilience was accompanied by healthy epididymal WAT expansion with reduced fibrosis and inflammation. Our findings demonstrate that short-term interventions, without genetic manipulation, can train adipose tissue, enhancing its long-term plasticity and conferring durable protection against future obesity-associated insulin resistance.

Neurons can utilize either glucose or lactate, yet fuel selection during periods of activity remains unresolved. By combining optical monitoring of cytosolic pyruvate and NADH with mathematical modelling, we systematically evaluated mitochondrial fuelling in cultured neurons and acute brain slices. Under substrate concentrations typical of resting brain tissue, neurons rely almost exclusively on glucose, with a minor contribution from pyruvate. However, when extracellular lactate rises to levels mimicking tissue activity, glycolysis is inhibited and lactate becomes a major substrate, irrespective of ongoing neuronal activity. Ultimately, neuronal fuel selection is dictated not by internal energy demand, but by extracellular lactate availability, which fluctuates with local glial metabolism and systemic states such as exercise. These findings redefine our understanding of short-term metabolic flexibility in the brain and underscore the significant yet understudied role of extracellular pyruvate.

COVID-19 risk scores developed during the pandemic relied on measurements contemporaneous with infection, leaving unresolved whether the metabolic and inflammatory vulnerability they capture pre-existed as a stable trait or was triggered by acute illness. Here, using 501,946 UK Biobank participants whose blood was drawn between 2006 and 2010---at least ten years before SARS-CoV-2 emerged---we show that baseline proteomic and metabolic profiles predict both COVID-19 hospitalization (2,783 events; C-statistic =0.676 [0.666--0.686]) and COVID-19 mortality (1,564 deaths; C-statistic =0.730 [0.701--0.760]) from parsimonious, regularized feature sets. The IL-1 pathway index (xIL1, +0.093) was independently selected for hospitalization but not mortality, while the IL-6 trans-signaling index (xIL6, + 0.040) was selected for mortality but not hospitalization---a differential pathway weighting corroborated by independent LightGBM/SHAP analysis and mirroring the subsequent success of tocilizumab (anti-IL-6R) and the limited efficacy of anakinra (anti-IL-1R) in reducing COVID-19 mortality in randomized trials conducted years later. The mortality model was additionally characterized by central adiposity (waist-hip ratio, +0.386), a respiratory compromise index (xRSP, +0.149), and prodromal cardiovascular disease (pCVD, +0.246). These findings establish that vulnerability to a novel pathogen is, in substantial part, a pre-existing and measurable prodromal state, with implications for pandemic preparedness and population-level risk stratification.