Objective

The adaptive response to different models of regular exercise involves complex tissue crosstalk. Our aim was to explore the involvement of extracellular vesicle (EV) microRNAs (miRNAs) in this process, the secretory role of skeletal muscle and its functional metabolic interaction with the liver.

Methods

Plasma EV miRNAs obtained from mice after 4-weeks of endurance or resistance training were sequenced. Subsequent experiments using trained genetically modified mouse models and in vitro approaches involving knock-down and electrostimulated cells, were conducted.

Results

Resistance training increased the expression of a group of 11 miRNAs functionally divided into two clusters. Among them, miR-29a-3p emerges as a molecular mediator released in EVs by skeletal muscle, with a relevant role in adaptation to endurance training, by contributing to modulate the expression and secretion of other miRNAs associated with training and regulating processes related to substrate availability, transport, and metabolic use in skeletal muscle and liver.

Conclusions

Our study suggests that miR-29a-3p is a training-induced molecular mediator in the response and adaptation to resistance training, possibly due to its regulatory role in energy metabolism in skeletal muscle in response to exercise.

Objective

Hypothalamic energy sensors, such as AMP-activated protein kinase (AMPK), and stress sensors, such as c-Jun N-terminal kinase 1 (JNK1, also known as MAPK8) modulate whole body energy balance. While the role of AMPK in steroidogenic factor 1 (SF1) neurons of the VMH has been investigated, the relevance of JNK1 in this neuronal population has not been addressed. Here, we investigated the involvement of JNK1 SF1 on energy homeostasis.

Methods

We generated mice bearing conditional JNK1 disruption through Mapk8 gene deletion in SF1 neurons (Sf1^Cre/Jnk1^fl/fl). Complete metabolic phenotyping, fasting/refeeding and cold challenges, as well as the central response to triiodothyronine (T3) on brown adipose tissue (BAT) thermogenesis and hepatic lipid metabolism were carried out.

Results

Sf1^Cre/Jnk1^fl/fl mice displayed decreased body weight, improved glucose tolerance, and reduced hepatic lipid levels. However, Sf1^Cre/Jnk1^fl/fl did not properly defend their temperature upon cold exposure. While central administration of T3 elicited feeding independent weight loss in both wildtype (Jnk1^fl/fl) and SF1^Cre/Jnk1^fl/fl mice, it did not promote hepatic lipid accretion in null animals.

Conclusions

Our data demonstrated for the first time that JNK1 in SF1 neurons is necessary for the regulation of hepatic lipid metabolism, cold adaptation and central T3 actions.

Objectives

G protein-coupled receptors (GPCRs) are the most druggable targets in biology due to their cell-type specificity, ligand binding, and cell surface accessibility. Underscoring this, agonists for GPCRs have recently revolutionized the treatment of diabetes and obesity. The rampant success of these compounds has invigorated interest in identifying additional GPCRs that modulate appetite and body weight homeostasis. One such potential therapeutic target is G-protein couped receptor 45 (Gpr45), an orphan GPCR expressed both centrally and peripherally. We aimed to explore the role of Gpr45 as well as neurons expressing Gpr45 in energy balance.

Methods

Three novel transgenic mouse models were engineered to investigate the functional contribution of Gpr45 to body weight and appetite regulation: 1) a global Gpr45 knockout, 2) a conditional floxed Gpr45 allele, and 3) a Gpr45-CreERT2 knock-in. Metabolic profiling was performed in global Gpr45 knockout animals including body weight, food intake, body mass, energy expenditure, and body temperature measurements. Animals harboring a conditional floxed Gpr45 allele were bred to mice expressing Cre-recombinase in excitatory neurons labeled via Vesicular glutamate transporter 2 (Vglut2), inhibitory cells expressing Vesicular GABA transporter (Vgat), or neurons marked by the transcription factor Single-minded 1 (Sim1) and monitored for body weight and food consumption. Additionally, floxed Gpr45 mice were bilaterally injected with AAV-Cre targeting the paraventricular nucleus of the hypothalamus (PVH) and body weight and food intake were evaluated. The Gpr45-CreERT2 knock-in model was used to express chronic and acute actuators to the PVH to assess the role of PVH^Gpr45 neurons in energy homeostasis.

Results

Global Gpr45 disruption caused marked weight gain, increased food intake and fat mass, but no detectable alterations in core temperature or energy output. Selective deletion of Gpr45 from Sim1+ or excitatory Vglut2+ but not inhibitory Vgat+, neurons produced obesity and hyperphagia. Targeted deletion of Gpr45 from the PVH phenocopies these metabolic changes suggesting a major site of action of Gpr45 signaling is glutamatergic neurons residing in the PVH. Tetanus toxin light chain (TeNT) was used to permanently silence PVH^Gpr45 neuronal activity in Gpr45-CreER mice leading to rapid weight accumulation and escalated food intake. These experiments highlight the critical role of both Gpr45 signaling and neural network activity in the regulation of body weight and appetite. A mutated version of the bacterial sodium channel, NaChBac, was used to constitutively activate PVH^Gpr45 neuronal activity in Gpr45-CreER mice with limited to no effect on body weight and food consumption, implicating redundant circuitry acting in concert to bias weight loss protection. Acute chemogenetic stimulation of PVH^Gpr45 neurons durably suppressed food intake regardless of caloric need state or food palatability demonstrating the capacity of these cells to curb appetite.

Conclusions

Gpr45 is a putative therapeutic candidate that could be targeted to combat obesity and overeating.

www.sciencedirect.com/science/article/pii/S2212877825000821/pdfft

Objective

The interplay between calorie-dense food and chronic stress significantly accelerates obesity development, with neural circuits expressing Neuropeptide Y (NPY) in the central amygdala (CeA) emerging as the key mediator of this process. While these circuits are known to enhance hedonic feeding behavior and promote weight gain, the precise molecular mechanisms regulating NPY neuron activity at the translational level under the combined influence of high fat diet and stress conditions have remained poorly understood.

Methods

We employed translational ribosome affinity purification coupled with Next-Generation Sequencing (TRAPseq), allowing us to specifically identify RNA transcripts actively undergoing protein translation in NPY neurons under high fat diet (HFD) or high fat diet combined with stress conditions (HFDS).

Results

Our molecular profiling demonstrates that NPY neurons specifically co-express with genes marking the orexigenic (appetite-stimulating) population, while showing minimal overlap with anorexigenic (appetite-suppressing) markers. Gene ontology analysis identified distinct clusters involved in fatty acid metabolic processes, stress response pathways, and the production of feeding-related neuropeptides specifically under HFDS. Immunohistochemical investigations revealed in addition to local CeA (CeA^m) NPY connection pathways, long-range projections, to the lateral habenula (LHb), the periaqueductal gray (PAG) and parvicellular reticular formation (PCRt). These projections suggest a specific role for CeA NPY neurons in coordinating feeding and emotional responses.

Conclusion

Collectively, our findings identify specific lipid-sensing mechanisms and synaptic modulating pathways as principal targets of stress within the CeA-NPY circuit, revealing novel molecular mechanisms through which NPY neurons integrate and process both dietary and stress signals.

Objective

Metabolic flexibility refers to the ability of tissues to adjust cellular fuel choice in response to conditional changes in metabolic demand and activity. A loss of metabolic flexibility is a defining feature of various diseases and cellular dysfunction. This study investigated the role of microRNA-1 (miR-1), the most abundant microRNA in skeletal muscle, in maintaining whole-body metabolic flexibility.

Methods

We used an inducible, skeletal muscle-specific knockout (KO) mouse model to examine miR-1 function. Argonaute 2 enhanced crosslinking and immunoprecipitation sequencing (AGO2 eCLIP-seq) and RNA-seq analyses identified miR-1 target genes. Metabolism was investigated using metabolomics, proteomics, and comprehensive bioenergetic and activity phenotyping. Corroborating information was provided from cell culture, C. elegans, and exercised human muscle tissue.

Results

miR-1 KO mice demonstrated loss of diurnal oscillations in whole-body respiratory exchange ratio and higher fasting blood glucose. For the first time, we identified bona fide miR-1 target genes in adult skeletal muscle that regulated pyruvate metabolism through mechanisms including the alternative splicing of pyruvate kinase (Pkm). The maintenance of metabolic flexibility by miR-1 was necessary for sustained endurance activity in mice and in C. elegans. Loss of metabolic flexibility in the miR-1 KO mouse was rescued by pharmacological inhibition of the miR-1 target, monocarboxylate transporter 4 (MCT4), which redirects glycolytic carbon flux toward oxidation. The physiological down-regulation of miR-1 in response to hypertrophic stimuli caused a similar metabolic reprogramming necessary for muscle cell growth.

Conclusions

These data identify a novel post-transcriptional mechanism of whole-body metabolism regulation mediated by a tissue-specific miRNA.

Objective

The bed nucleus of the stria terminalis (BNST) is involved in feeding, reward, aversion, and anxiety-like behavior. We identify BNST neurons defined by the expression of vesicular glutamate transporter 3, VGluT3.

Methods

A combination of in situ hybridization, tract tracing, ex vivo whole-cell electrophysiology, in vivo recording, optogenetic, and behavioral approaches were used.

Results

VGluT3 neurons were localized to anteromedial BNST, were molecularly distinct from accumbal VGluT3 neurons, and co-express vesicular GABA transporter (VGaT). BNST VGluT3 neurons projected to arcuate nucleus (ARC) and paraventricular nucleus of the hypothalamus (PVN), regions critical for feeding and homeostatic regulation. Most single BNST VGluT3 neurons projected to either PVN or ARC and a subset projected to both. BNST VGluT3 neurons functionally transmit GABA to both ARC and PVN, with rare glutamate co-transmission to ARC. In vivo, VGluT3 BNST neurons showed greater neuronal activity in response to sucrose consumption while sated compared with fasted. When fasted, optogenetic stimulation of BNST VGluT3 neurons decreased sucrose consumption using several stimulation conditions but not when stimulation occurred prior to sucrose access, suggesting that BNST VGluT3 activation concurrent with consumption in the fasted state reduces feeding. BNST VGluT3 activation had no effect on anxiety-like behavior in several paradigms (novelty-suppressed feeding, open field, and elevated zero maze). BNST VGluT3 activation also did not result in real-time place preference or aversion.

Conclusions

We interpret these data such that VGluT3 BNST neurons represent a unique cellular population within the BNST that provides inhibitory input to hypothalamic regions to decrease sucrose consumption.

Objective

A longstanding question in type 1 diabetes (T1D) research pertains to the selective loss of β-cells whilst neighboring islet α-cells remain unharmed. We examined molecular mechanisms that may underly this differential vulnerability, by investigating the role of RNA editing, a cellular process that prevents double-stranded RNA (dsRNA)-mediated interferon response, in mouse α- and β-cells.

Methods

The enzyme responsible for RNA editing, Adar, was selectively deleted in vivo in mouse β-cells, α-cells, or in both cell types. Subsequent analyses were performed to investigate the impact of deficient RNA editing in α- or β-cells on the interferon response, islet inflammation, cell viability and metabolic outcomes.

Results

Mosaic disruption of the Adar gene in mouse β-cells triggers a massive interferon response, islet inflammation and mutant β-cell destruction. Surprisingly, wild type β-cells are also eliminated, whereas neighboring α-cells are unaffected. α-cell Adar deletion leads to only a slight elevation in interferon signature and does not elicit inflammation nor a metabolic phenotype. Concomitant deletion of Adar in α- and β-cells leads to elimination of both cell populations, suggesting that in contrast to β-cells, α-cell death requires both cell autonomous deficiency in RNA editing and exogenous cytokines.

Conclusions

We demonstrate differential sensitivity of mouse α- and β-cells to deficient RNA editing. The resistance of α-cells to RNA editing deficiency and to cytokines mirrors their persistence in T1D, and constitutes a molecularly defined model of differential islet cell vulnerability.

Objective

Peroxisome Proliferator-Activated Receptors (PPARs) are nuclear receptors involved in the control of lipid metabolism. The PPARα isoform is highly expressed in brown adipose tissue (BAT). However, its precise role in BAT remains unclear. Here, we aimed to investigate the role of PPARα in BAT of high fat diet-induced obese mice in a thermoneutral environment.

Methods

We used tamoxifen-inducible-BAT specific PPARα knockout mice (PPARαBATKO) that were housed at thermoneutrality to minimize BAT basal activation, fed a high-fat diet for 20 weeks and challenged with a β₃-adrenergic agonist (CL316,243) during the last week. Both male and female mice were studied.

Results

Body weight and glucose tolerance tests were similar in both sexes and genotypes. However, BAT morphology was altered in PPARαBATKO mice, with more unilocular and larger lipid droplets compared to control mice, suggesting BAT impaired function. Indeed, when treated with CL316,243, both male and female mice had increased De Novo Lipogenesis (DNL), reflected by an increased expression of ChREBPβ and lipogenic enzymes ACLY, ACC1, FASN and SCD1. These changes were accompanied by an increase in fatty acids in triglycerides, and thus an increase in lipid storage. Moreover, lipid profiles in phospholipids were different, suggesting a modification in the membrane content with an increase of palmitoleate.

Conclusions

Altogether, our results reveal a key role for PPARα in DNL in BAT and in the regulation of lipid metabolism in HFD-induced obesity.

Objectives

Methylglyoxal (MG), a reactive aldehyde generated as a byproduct of glucose and lipid metabolism, is known to modify nucleic acids and proteins, altering their structure and function. While MG-induced DNA and protein adducts have been extensively studied and associated with type 2 diabetes (T2D) and its complications, the formation, biological relevance, and functional consequences of MG-induced RNA adducts remain poorly understood. This study aimed to define the chemical structures of MG-derived RNA adducts, assess their presence in clinical samples, and determine their impact on RNA stability and translation.

Methods

We employed liquid chromatography-tandem mass spectrometry (LC-MS/MS), nuclear magnetic resonance (NMR), and other spectroscopic techniques to characterize MG-induced RNA adducts formed in vitro and in biological samples. RNA was isolated from cultured cells and clinical urine specimens from individuals with and without T2D. RNA stability and translation were assessed using firefly luciferase reporter mRNAs modified with MG in cell-based assays.

Results

In vitro MG treatment resulted in the formation of an unstable product, tentatively identified as N²-(1,2-dihydroxy-2-methyl)ethano-guanosine (cMG-guanosine), and two stable adducts: N²-(1-carboxyethyl)-guanosine (CEG) and N²-(1-carboxyethyl)-7–1-hydroxy-2-oxopropyl-guanosine (MG-CEG). In cellular RNA and urine from patients, only the stereoisomers of CEG were detected. CEG levels were significantly elevated in patients with T2D compared to controls and showed a stronger association with T2D than the DNA adduct N²-(1-carboxyethyl)-deoxyguanosine (CEdG). Furthermore, CEG levels were higher in T2D patients who had developed complications compared to those without complications. Functionally, MG-modified luciferase mRNA exhibited decreased stability and reduced translational efficiency relative to unmodified mRNA.

Conclusions

This study provides the first structural and functional characterization of MG-induced RNA adducts and demonstrates their accumulation in individuals with T2D, particularly in those with disease complications. These findings highlight RNA MG-adducts as clinically relevant epitranscriptomic modifications that may contribute to RNA destabilization and impaired translation, suggesting a novel molecular mechanism by which metabolic stress may exacerbate disease progression.

Objective

Metabolic disruption is a central feature to many neurodegenerative diseases. Despite this, many gaps exist in our understanding of how these perturbations link to the mechanisms of neural disease. In this study, we sought to understand how genetically-controlled, cell-specific loss of pyruvate kinase (PyK) impacts motor neuron synaptic integrity and how the canonical neurodegenerative proteins DLK and SARM1 respond to this break in homeostasis.

Methods

This study made use of the genetically-tractable Drosophila melanogaster to cell-specifically express proteins (via the GAL4/UAS binary system), knockdown gene transcripts (via RNA interference), and knockout gene loci (via guide RNA-directed Cas9). Synaptic and axonal degeneration were measured through immunohistochemistry, microscopy, and blinded scoring of fly larvae at both early and later 3rd instar stages to test for progressive phenotypes. Nervous system injury through a physical nerve crush assay was used to assay functional outcomes of protective stress responses.

Results

We found that knockdown or knockout of PyK results in progressive axonal and synaptic degeneration, dependent on signaling through DLK and SARM1. This degeneration is preceded by nuclear transcriptional activation by DLK and the downstream AP-1 transcription factor Fos. We also found evidence of a neuroprotective response through injury of PyK-deficient axons (before progressive degeneration has occurred), which results in delayed Wallerian degeneration. This delay shows dependence on DLK and Fos, and coincides with reduced axonal localization of SARM1 whose overexpression fully restores degeneration speed.

Conclusions

These data support a rheostat model of DLK signaling that both promotes and inhibits axon degeneration in response to metabolic disruption. This rheostat likely converges on regulation of SARM1, which is required for the progressive synapse loss following PyK, but also abolishes the protective delay in injury-induced Wallerian degeneration when overexpressed. Overall, we conclude that metabolic signaling through PyK is essential for the integrity of motor neuron axons and synapses, and that its disruption activates both neurodegenerative and neuroprotective mechanisms

Objectives

Endurance exercise reduces the risk of metabolic diseases by improving skeletal muscle metabolism, particularly in individuals with overweight and obesity. As biological sex impacts glucose and fatty acid handling in skeletal muscle, we hypothesized sex differences at the transcriptomic and proteomic level in the acute response to exercise and after an 8-week exercise intervention.

Methods

We analyzed skeletal muscle biopsies from 25 sedentary subjects (16f/9 m) with overweight and obesity using transcriptomics and proteomics at baseline, after acute exercise, and following an 8-week endurance training program. Regulation of sex-specific differences was studied in primary myotubes from the donors.

Results

At baseline, differentially methylated CpG-sites potentially explain up to 59% of transcriptomic and 67% of proteomic sex differences. Differences were dominated by higher abundance of fast-twitch fiber type proteins, and transcripts and proteins regulating glycogen degradation and glycolysis in males. Females showed higher abundance of proteins regulating fatty acid uptake and storage. Acute exercise induced stress-responsive transcripts and serum myoglobin predominantly in males. Both sexes adapted to 8-week endurance training by upregulating mitochondrial proteins involved in TCA cycle, oxidative phosphorylation, and β-oxidation. Training equalized fast-twitch fiber type protein levels, mainly by reducing them in males. In vivo sex differences in autosomal genes were poorly retained in myotubes but partially restored by sex hormone treatment.

Conclusions

Our findings highlight sex-specific molecular signatures that reflect known differences in glucose and lipid metabolism between female and male skeletal muscle. After just 8 weeks of endurance training, these sex differences were attenuated, suggesting a convergence towards a shared beneficial adaptation at the molecular level.

Diet-induced obesity in mice is an important model for investigating host–diet interactions as well as dietary and pharmacological treatments of metabolic diseases. Experimental reproducibility is, however, a recurrent challenge. To determine key controllable experimental drivers of mouse metabolism, we distributed 338C57BL/6JBomTac mice (males and females) into six research units across two countries, divided them into a variety of housing conditions (i.e., diets, cage types, temperatures, group-housing vs. single-housing) and kept 26 reference mice at the vendor. We applied linear mixed models to rank the influence of each variable on metabolic phenotype (i.e., body weight gain, glucose intolerance, liver, and visceral adipose tissue weight). Group-housing was the most potent driver of metabolic dysfunction apart from sex and diet. Accordingly, single-housed mice exhibited reduced weight gain (∼50%), increased energy expenditure, and diminished respiratory exchange ratio concomitant with improved glucose tolerance (∼20%) compared to their group-housed counterparts. Our results may aid in clarifying the impact of experimental design and promote rational, transparent reporting to increase reproducibility.

Objectives

Hypothalamic Fatty Acid Synthase (FASN) plays a critical role in regulating energy balance by influencing food intake and body weight. This study aimed to investigate the neuronal mechanisms by which FASN impacts metabolism, focusing on its role in Pro-Opiomelanocortin (POMC) neurons.

Methods

We used transgenic mouse models with pre- or postnatal deletion of FASN specifically in POMC neurons in male mice. We evaluated changes in adiposity, glucose metabolism and metabolic parameters including food intake, energy expenditure and substrate utilization using metabolic chambers. Changes in neuronal activity were assessed using electrophysiology and further validated by optogenetic stimulation of POMC neurons. Additionally, the role of adrenergic signaling was examined using pharmacological approaches and gene expression analyses.

Results

FASN deletion in POMC neurons reduced food intake, decreased adiposity, and altered glucose metabolism. FASN-deficient POMC neurons exhibited increased baseline activity. The developmental stage of FASN deletion influenced its effects on energy expenditure and body weight regulation. Additionally, FASN in POMC neurons was found to be essential for maintaining glucose homeostasis and insulin release via adrenergic signaling.

Conclusions

FASN in POMC neurons plays an age- and neuron-specific role in regulating feeding, energy expenditure, and glucose homeostasis through mechanisms including the sympathetic nervous system. These findings highlight FASN as a potential therapeutic target for metabolic diseases by improving energy expenditure and insulinemia. Given the developmental programming of metabolic outcomes, interventions aimed at modulating FASN activity may have long-lasting benefits in managing metabolic diseases.

Objective

Cachexia in chronic kidney disease (CKD) is a wasting syndrome. The futile creatine cycle (FCC) contributes to energy waste in adipocytes. Creatinine is metabolite of creatine. Whether creatinine involves in adipose wasting in CKD remains elusive.

Methods

Cachexia were assessed in unilateral ureteral obstruction induced CKD mice model. Cellular oxygen consumption and FCC-related genes expression were analyzed in adipocytes treated with creatinine in the presence of FCC inhibitor (SBI-425, inhibitor of TNAP) or creatine disruption (β-GPA, a creatine analogue that inhibits creatine transport into cells). The fate of labeled deuterated creatinine (D-3 creatinine) were traced by mass spectrometer. To determine creatinine drives adipose tissue wasting in vivo, two mice models of CKD were established by unilateral ureteral obstruction or renal ischemia and reperfusion injury. 206 patients diagnosed CKD were collected to analyze correlationship between creatinine in serum and adiposity.

Results

Adipose tissue wasting presented in CKD mice with serumal creatinine retention. In vitro, creatinine treatment at the concentration relevant of CKD elevated cellular oxygen consumption and FCC-related genes expression by converting into intracellular creatine. In the established CKD mice models, intraperitoneal injection of creatinine enhanced adipose tissue wasting, through increasing creatine accumulation. In contrast, disruption of creatine accumulation by β-GPA ameliorated tissue wasting. In patients with CKD, creatinine in serum negatively correlated with adiposity.

Conclusions

Our results show that elevated serumal creatinine induces creatine accumulation, FCC activation and adipose tissue wasting in CKD, targeting creatinine-induced tissue wasting providing a promising therapeutic to ameliorate cachexia in CKD.

Objective

Kidney glucose reabsorption, primarily mediated by glucose transporter 2 (GLUT2), is essential for systemic glucose homeostasis. While GLUT2's role has been studied in diabetic conditions, its function in kidney proximal tubule cells (KPTCs) under normo-physiological conditions remains unclear. This study aimed to delineate the metabolic consequences of KPTC-specific GLUT2 deletion on renal and whole-body energy homeostasis.

Methods

We utilized a conditional mouse model with KPTC-specific deletion of GLUT2 to assess the impact of impaired renal glucose reabsorption on systemic metabolism. Comprehensive metabolic and behavioral phenotyping, tissue-specific glucose uptake assays, and multi-omics analyses were performed to evaluate changes in energy balance, organ-specific metabolism, and signaling pathways.

Results

Loss of KPTC-GLUT2 led to increased food intake, enhanced systemic carbohydrate oxidation, and elevated fat and muscle mass. These changes were accompanied by altered glucose utilization across metabolic organs and improvements in whole-body lipid profile. Mechanistically, the phenotype was linked to metabolic reprogramming in the kidney, characterized by increased reabsorption and bioavailability of taurine and creatine, overactivation of mTORC1 signaling, and elevated endocannabinoid tone.

Conclusions

KPTC-GLUT2 plays a previously unrecognized role in regulating renal and systemic energy metabolism. Its deletion induces a systemic energy-conserving phenotype driven by kidney-intrinsic changes, highlighting the kidney's contribution to whole-body metabolic homeostasis beyond glucose filtration.

Graphical abstract

Energy conserving phenotype - proposed mechanism in KPTC^GLUT2-/- mice. GLUT2 nullification inhibits glucose reabsorption by the kidney, resulting in glucose retention in the KPTCs and enhanced kidney energy metabolism. In turn, mTORC1 activation is enhanced in the KPTCs, accompanied by elevated levels of taurine, creatine, and AEA. These metabolic hubs enhanced kidney and systemic bioavailability results in a pronounced systemic energy-consuming/preservation phenotype. Figure created with BioRender.com. BCAA, branched-chain amino acids; DHAP, dihydroxyacetone phosphate; NATs, N-acyl taurines; NAEs, N-acylethanolamines; FAAH, fatty acid amid hydrolase; FFA, free fatty acid.

Objectives

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 and in vitro 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 fat depot.

Objectives

Adipose tissue plays a critical role in obesity, as its dysfunction can impair lipid homeostasis and result in lipid overflow and ectopic lipid deposition in the liver. We previously demonstrated that Isthmin-1 (Ism1) regulates glucose uptake into the adipose tissue and suppresses hepatic steatosis, but the role of adipose-derived Ism1 is unknown. Here, we investigate the role of adipose-derived Ism1 in metabolic health and its impact on hepatic steatosis and lipid metabolism.

Methods

In this study, we employed both a genetic knockout approach, selectively deleting Ism1 in adipose tissue of mice (AdipoQ-Ism1-KO), and a pharmacological approach by administering recombinant Ism1 protein to mice. These mice were subjected to a high fat-high fructose diet to simulate conditions that promote Metabolic-dysfunction Associated Steatotic Liver Disease (MASLD).

Results

AdipoQ-Ism1-KO are of normal weight, but prone to severe hepatic steatosis in response to high fat-high fructose feeding. Lipidomic profiling through untargeted analyses in both gain-of-function and loss-of-function models was used to assess changes in hepatic lipid homeostasis. These results provide in vivo genetic support for the role of Ism1 as a regulator of the adipose–hepatic axis.

Conclusions

Collectively, these data demonstrate that loss of adipose-derived Ism1 disrupts lipid homeostasis and accelerates the development of hepatic steatosis. This study provides a genetic basis for Ism1's involvement in metabolic regulation, suggesting a potential therapeutic target for treating metabolic disorders.

Investigations of human pancreatic islets have been empowered by strategies to isolate and study live islet cell subsets, like β cells and α cells. To advance experimentation with human islet δ cells, which remain relatively understudied, we generated combinatorial cell sorting approaches to separate human δ cells from β cells, yielding highly-enriched human δ cells. We used molecular analysis, immunohistology, and electroporation-based targeting to demonstrate the quality of δ cell purification. We also demonstrated the feasibility of prospectively studying human δ cell function in pseudoislet organoids. Innovations detailed here should promote discovery of genetic, signaling and physiological mechanisms governing δ cell function and roles in human islets.

The circadian clock regulates tissue-specific homeostasis, and its disruption is associated with metabolic disorders. Both host metabolic processes and the gut microbiota exhibit diurnal regulation, and both contribute to the maintenance of glucose homeostasis (Thaiss et al., 2014; Bishehsari et al., 2020; Frazier et al., 2023) [1–3]. However, how the gut microbiota and the circadian rhythm interplay to control host glucose homeostasis is not fully understood. Here, we identified gut microbiota-derived extracellular vesicles (MEV) as a potential peripheral Zeitgeber (time cue) for the hepatic circadian clock, controlling hepatic gluconeogenesis. Host feeding patterns influence the gut microbiota, driving the diurnal production of MEV. Gut MEV levels coincide with the activity of hepatic gluconeogenesis, with overnight fasting associated with increased production of MEV by gut bacteria. MEV directly activates hepatic gluconeogenesis and chronic increase in MEV exposure impairs glucose homeostasis in vivo. Our finding highlights a mechanism by which the gut microbiota has co-evolved with the host to support its glucose needs during periods of energy demands (such as during fasting or starvation). On the contrary, an abnormal increase in MEV production, leading to dysregulated gluconeogenesis, may underlie various glucose-associated disorders, such as type 2 or gestational diabetes. Together, our data reconcile the gut microbiota and circadian rhythm in the control of host glucose homeostasis and metabolic health.

Regulation of lipid metabolism is fundamental for metabolic health, and adipose tissue is a central component in this process. Adipose tissue differs considerably between women and men in terms of a higher subcutaneous capacity for storage, which is linked to metabolic health, in women. Sex hormone-binding globulin (SHBG) contributes to the regulation of circulating sex hormone bioavailability and has been shown to predict risk of metabolic dysfunction. Here, we investigate the sex-specific relationship of SHBG with metabolic status and adipocyte-dependent lipolysis. We measured serum concentrations of sex hormones, SHBG, fasting glucose, and insulin in a cohort of 63 women and 27 men from which adipose biopsies were collected and mature adipocytes isolated. In women, high serum SHBG concentrations were strongly associated with low in vivo Homeostatic Model Assessment for Insulin Resistance (HOMA-IR), and lower unstimulated ex vivo lipolysis but higher isoprenaline stimulated ex vivo lipolysis. In contrast, no effect of SHBG on the above-mentioned parameters were observed in men. In vitro cultured human adipocytes also increased lipolytic activity in response to SHBG, but only in the absence of testosterone, suggesting that testosterone inhibits the catecholamine-induced lipolysis of SHBG in adipose tissue. In conclusion, we identify SHBG as a novel sex-specific regulator of adipocyte lipolysis and lipid metabolism. At the same time, our data emphasize sex-dependent effects of SHBG on adipocyte lipid metabolism, and we propose testosterone binding to SHBG as a driving factor mediating these sex differences.