Objectives

G protein-coupled receptor 180 (GPR180) has been implicated in systemic energy metabolism, primarily in adipose tissue and the liver. Given impaired whole-body glucose tolerance following GPR180 dysfunction, we aimed to determine whether GPR180 regulates pancreatic β-cell function. We investigated whether GPR180 contributes to β-cell insulin secretion by modulating metabolic processes that couple glucose sensing to mitochondrial energy production.

Methods

Phenotyping of whole-body (Gpr180 ^−/−) and β cell-specific Gpr180 (bGpr180-KO) knockout mice was combined with gain- and loss-of-function studies in MIN6 cells. Glucose-stimulated insulin secretion, pancreatic endocrine architecture and identity, transcriptomic and metabolic profiles, as well as mitochondrial function were assessed using in vivo and in vitro approaches, including metabolic challenge tests, histology, RNA sequencing, targeted metabolomics, respirometry, and transmission electron microscopy.

Results

Loss of GPR180 impaired first-phase insulin secretion and glucose tolerance without affecting insulin sensitivity. These defects were β-cell-autonomous, as confirmed in the bGpr180-KO mice and in MIN6 cells. Functional studies revealed that GPR180 regulates mitochondrial substrate utilization, anaplerotic support of the TCA cycle, and ATP generation without affecting glucose uptake or mitochondrial biogenesis. In particular, Gpr180-deficient β cells showed mitochondrial membrane depolarization, reduced oxygen consumption, and endoplasmic reticulum remodeling, altering the local mitochondrial microenvironment. In vivo, Gpr180 deletion in β cells led to downregulation of mitochondrial gene programs in islets, along with altered endocrine cell identity.

Conclusions

GPR180 is a previously unrecognized regulator of pancreatic β-cell metabolic competence and identity, linking defects in insulin secretion with alterations in mitochondrial function and endocrine cell identity.

Objective

Ketone body metabolism is linked to brain health benefits, including delaying age-related cognitive decline. Exercise, particularly when combined with an overnight fast, stimulates ketone body turnover and improves brain metabolism and cognition. Yet, whether ketone metabolism is obligatory for this response is unknown. Here, we use chronic exercise via voluntary wheel running plus time-restricted feeding (VWR + TRF) to explore whether ketones mediate exercise-induced brain health benefits in middle-aged mice.

Methods

To distinguish the roles of neuronal ketone metabolism vs. hepatic ketone production, we studied middle-age female neuronal-specific SCOT knockout mice and hepatocyte-specific HMGCS2 knockout mice, respectively. VWR + TRF was compared to sedentary ad-libitum fed mice to assess the impact on whole-body metabolism, cognition, and hippocampal molecular adaptations. VWR + TRF upregulated systemic lipid oxidation in all mice during the fasting period.

Results

In female SCOT-Neuron-KO mice, we show impaired responses to VWR + TRF in indices of short- and long-term memory. Proteomic analysis of isolated hippocampi revealed that SCOT-Neuron-KO mice failed to globally upregulate key facilitators of synaptic function, including leucine-rich repeated transmembrane proteins, neurexins, and neuroligins. In female HMGCS2-Liver-KO mice, impaired responses to VWR + TRF in indices of short-term memory were paired with an upregulation in hippocampal ketogenesis machinery, suggesting potential in vivo evidence of cerebral ketogenesis, a mechanism mitigating an otherwise more pronounced behavioral phenotype.

Conclusion

Together, these findings suggest that neuronal ketone body utilization is essential for, while hepatic-derived ketone bodies contribute to, the full cognitive and synaptic adaptations to VWR + TRF, supporting ketone metabolism as a key mechanistic link between metabolic state and brain health in midlife.

Objectives

SAMM50 rs3761472 is associated with metabolic dysfunction-associated steatotic liver disease (MASLD), but its functional consequences in vivo remain unclear. We investigated whether this variant disrupts mitochondrial function and promotes MASLD progression.

Methods

Associations of rs3761472 with MASLD and liver-related traits were evaluated using Korea Biobank Array data. We generated Samm50 knock-in (KI) mice carrying the D110G substitution corresponding to human rs3761472 using CRISPR/Cas9 and assessed hepatic mitochondrial homeostasis and MASLD-related phenotypes in mice fed a normal diet or a high-fat diet.

Results

In human genetic analyses, rs3761472 was significantly associated with MASLD and higher serum levels of liver injury markers. Samm50-KI mice showed reduced hepatic SAMM50 expression, disrupted mitochondrial organization, impaired mitochondrial respiration and ATP production, increased mitochondrial oxidative stress, inflammatory activation, apoptosis, and liver injury. Following high-fat diet feeding, Samm50-KI mice exhibited greater hepatic lipid accumulation and liver injury, together with more pronounced insulin resistance and glucose intolerance, than wild-type mice.

Conclusions

Our findings establish rs3761472 as a functional genetic variant linking mitochondrial architecture to metabolic liver disease pathogenesis, with potential relevance as a genetic biomarker for MASLD susceptibility.

Inorganic pyrophosphate (PPi) is a key inhibitor of ectopic calcification, yet transcriptional regulation of genes controlling its systemic production and degradation (ABCC6, ALPL, ANKH, and ENPP1) remains poorly understood. We hypothesized that PPi homeostasis is regulated by an evolutionarily conserved transcription factor (TF) network. Promoter motif analysis combined with ATAC-seq revealed conserved enrichment of TF binding sites, including FOXA1, HNF4A, and SREBF1, across mouse and human orthologues. Bulk and single-cell RNA-seq together with RT-qPCR analyses in wild-type and Abcc6^−/− mice showed hepatocytes as major cell type expressing the most relevant genes maintaining PPi homeostasis. Further inference analysis identifies a conserved transcriptional program that regulates systemic PPi balance across mice and humans. Functionally, mice showed an age-dependent inverse correlation between plasma PPi and serum alkaline phosphatase (AP) activity, strongest during early life. Abcc6^−/− mice displayed persistently reduced but gradually increasing PPi levels and altered Pi/PPi ratios during aging. In humans, plasma PPi correlated inversely with AP activity and positively with Pi in both controls and ABCC6-deficient pseudoxanthoma elasticum patients. Together, these findings support a conserved TF-associated regulatory program linking PPi homeostasis gene expression with circulating mineralization-related factors across physiological and pathological states.

Objective

Thioredoxin-interacting protein (TXNIP) is a protein involved in redox metabolism, but also a key regulator of glucose and lipid metabolism in preclinical models. To date, four patients with biallelic loss-of-function variants in TXNIP have been described, presenting with lactic acidosis and variable hypoglycemia, hepatomegaly, developmental delay and seizures. However, the role of TXNIP in human metabolism and its mechanistic effects across different organs are not fully understood.

Methods

We clinically, biochemically and genetically characterized a cohort of six additional individuals with biallelic pathogenic variants in TXNIP. Organ specimens from patients and mice were analyzed by gene expression, histology, and lipidomic and proteomic profiling.

Results

We confirmed lactic acidosis as the main clinical sign and added adult-onset cardiomyopathy, skeletal muscle weakness, and dyslipidemia to the extended disease spectrum. Heart, liver and muscle patient specimens showed pathological lipid accumulation, and mechanistic studies uncovered increased fatty acid synthesis markers and complex rearrangements of the lipidome and proteome. In Txnip-deficient mice, restricting dietary carbohydrates partially rescued fatty acid synthesis markers and lipid storage in the heart but led to dyslipidemia.

Conclusions

Our studies show that TXNIP is an important metabolic modifier in cardiac and skeletal muscle as well as in lipoprotein metabolism and that biallelic pathogenic variants in TXNIP lead to a pleiotropic disease affecting cellular lipid metabolism in multiple organ systems, with potentially fatal adult-onset cardiomyopathy.

Objectives

Inhibitor-κB kinase epsilon (IKKε) is a non-canonical IκB kinase involved in NF-κB signaling and type I interferon responses. We recently demonstrated sex-dependent effects of IKKε deletion on atherosclerosis and metabolic dysfunction-associated steatotic liver disease (MASLD), with male knockout mice showing protection against both diseases, while female mice exhibited exacerbated inflammatory and metabolic disturbances. These divergent outcomes were linked to differential effects on inflammatory pathways and lipid metabolism.

Methods

To evaluate the therapeutic potential of pharmacological IKKε inhibition, we treated wild type mice with established atherosclerotic plaques and hepatic steatosis - induced by PCSK9 gain-of-function and Paigen diet - with the IKKε inhibitor amlexanox.

Results

Amlexanox modulated serum lipid levels and altered plaque composition but did not halt plaque progression. In the liver, treatment produced marked sex-specific effects: male mice exhibited substantial improvement in steatosis, whereas female mice showed worsened lipid accumulation. These outcomes were reflected in pronounced sex-dependent differences in serum and hepatic lipid and metabolite profiles, indicating regulation of fatty acid and bile-acid metabolism predominantly in males. Protein analyses in liver and adipose tissue further supported opposing metabolic and inflammatory responses between sexes after amlexanox treatment.

Conclusions

Collectively, our findings indicate that therapeutic IKKε inhibition with amlexanox does not prevent progression of advanced atherosclerosis in this model but effectively ameliorates MASLD in male mice. In contrast, female mice experience aggravated hepatic lipid deposition. These results underscore the importance of incorporating sex-specific analyses in metabolic and cardiovascular research and highlight the need to evaluate therapeutic strategies such as amlexanox in both sexes.

Efforts to fully characterize the diversity of mechanisms underlying energy balance control have led to the identification of atypical sites of action for metabolic signals. The locus coeruleus (LC), a major noradrenergic nucleus of the brain, has recently been shown to regulate aspects of food intake and energy expenditure. We use complementary pharmacological, behavioral, immunohistochemical, and genetic approaches in both rats and mice to demonstrate the role of LC calcitonin receptors (CTR) in feeding behavior. LC neurons robustly express CTRs that can be pharmacologically and chemogenetically activated to potently inhibit food intake and body weight without inducing nausea or changes in autonomic physiology including heart rate, body temperature, and gastric emptying. We next examined the ability of amylin and calcitonin gene-related peptide (CGRP), two endogenous anorectic peptides that signal through the CTR, to modulate feeding through signaling in the LC. RNAscope analysis revealed that LC CTRs are in fact capable of responding to amylin and CGRP, as they co-express RAMP1, and microinjections of either peptide to the LC induces anorexia without nausea. Together, these findings identify LC CTRs as a previously unrecognized neural substrate through which amylin and CGRP signaling suppress feeding, with direct relevance to the mechanisms underlying emerging amylin-based obesity therapeutics.

Background

MASLD/MASH can occur in lean individuals; however, the environmental triggers and molecular mechanisms underlying lean MASH are unclear, and suitable animal models are lacking.

Results

Mice fed a Western diet with liquid fructose (WDF) develops obesity and MASH (obese MASH). In contrast, high salt supplementation of WDF (HSWDF) produced a lean MASH phenotype with reduced steatosis but induced significant inflammation and fibrosis (lean MASH). In WDF-induced obese MASH, we observed decreased urea cycle activity and flux, along with reduced eukaryotic translation initiation factor 5 A hypusination (EIF5AH) and mitochondrial biosynthesis. High salt supplementation of WDF unexpectedly ameliorated these alterations, enhanced hepatic fatty acid oxidation and reduced hepatosteatosis. However, single-cell sequencing revealed that dietary high salt was associated with pro-inflammatory responses in hepatic immune cell subpopulations.

Conclusions

In summary, we have established a dietary mouse model of lean MASH that differs from obese-MASH in hepatic urea cycle, mitochondrial protein synthesis, and immune cell activation, providing new mechanistic insight into lean MASH.

Inhibitor of DNA binding/differentiation (ID) 4 is a member of the ID family of proteins. ID4 is involved in gene transcriptional regulation during diverse pathophysiological processes, including cellular differentiation, proliferation, and senescence. ID4-deficient (Id4^−/−) mice exhibit markedly reduced tissue and body mass and survive for only a few weeks after birth. However, the direct cause of this premature lethality remains unknown. This study demonstrated that ID4 deficiency leads to impaired hepatic fatty acid synthesis, accompanied by downregulation of the rate-limiting enzymes of fatty acid synthesis, such as fatty acid synthase (FASN) and acetyl-CoA carboxylase 1 (ACC1). Comprehensive histone modification profiling based on mass spectrometry revealed drastic alterations involving histone modification patterns in the livers of Id4^−/−mice compared to those of wild-type littermates. Furthermore, ID4 deficiency resulted in aberrant histone expression patterns. Integrative assay for transposase-accessible chromatin sequencing and RNA-sequencing analyses further revealed that ID4 deficiency induces chromatin closure at the promoter region of Srebf1 (encoding sterol regulatory element-binding protein), a master transcription factor upstream of Fasn (encoding FASN) and Acaca (encoding ACC1). Collectively, these findings indicate that ID4 functions as an important regulator of hepatic fatty acid metabolism by maintaining chromatin accessibility, rather than merely acting as a classical ID protein that regulates target gene transcription.

Purpose

Cancer cachexia is a life-threatening complication of advanced malignancies, driven by profound systemic metabolic reprogramming and anorexia. Insulin action is markedly impaired in patients with cancer and may contribute directly to cachexia pathogenesis. However, the interplay between weight loss, food intake, and cancer-associated metabolic rewiring in cachexia remains poorly defined. Clarifying this relationship is essential for identifying the fundamental drivers of cachexia and for developing effective therapeutic strategies.

Methods

We assessed metabolic rewiring by temporal evaluation of glucose tolerance and isotopic tracers to determine muscle insulin-stimulated glucose uptake in male cachectic and non-cachectic C26- and KPC-tumor-bearing, as well as healthy mice undergoing food restriction.

Results

Cachectic C26- and KPC-tumor mice showed increased glucose tolerance compared to non-tumor-bearing control mice, and non-cachectic tumor-bearing mice. Increased glucose tolerance appeared prior to overt muscle loss, independent of tumor size and changes in food intake. Ex vivo insulin-stimulated glucose uptake was elevated in soleus (+78%) and extensor digitorum longus (+35%) muscle from cachectic C26-tumor mice with anorexia compared to weight stable C26-tumor mice and control mice. This increase was associated with enhanced AKT signaling. Food restriction in healthy mice increased glucose tolerance, insulin-stimulated glucose uptake ex vivo, and AKT signaling.

Conclusions

Our findings suggest that glucose hypermetabolism appears prior to overt weight loss in pre-clinical cachexia, whereas late-stage cachexia with anorexia increased skeletal muscle insulin responsiveness. This highlights AKT signaling as a key node connecting nutrient status with muscle metabolism in cancer cachexia.

N-acetylated amino acids (Ac-AAs) have been repeatedly reported in metabolomics studies of high-intensity exercise, cold-exposed brown adipose tissue (BAT), and various pathological conditions. Despite their recurrent detection, the origins and physiological functions of Ac-AAs remain poorly understood, and evidence is fragmented across diverse scientific disciplines. While Ac-AAs have traditionally been attributed to the degradation of N-terminally acetylated proteins, this mechanism alone cannot fully account for their diversity and context-dependent regulation. Instead, accumulating evidence supports a model in which Ac-AA formation is driven by elevated intracellular acetyl-CoA and amino acid availability. Under these conditions, Ac-AA formation may represent a previously unrecognized metabolic mechanism involved in acetyl-CoA and amino acid homeostasis. In this review, we provide an overview of Ac-AA alterations across physiological contexts, synthesize current evidence on their origins, regulation, and physiological functions, and propose a mechanistic framework for the role of Ac-AAs in metabolic regulation. By integrating findings across diverse scientific disciplines, this review establishes a foundation for a more consistent interpretation of Ac-AAs across physiological and pathological contexts.

Intermuscular adipose tissue (IMAT) is increasingly recognized as a contributor to insulin resistance and metabolic dysfunction in type 2 diabetes (T2D). Accumulation of IMAT was found to correlate with impaired skeletal muscle insulin sensitivity, as well as a generally reduced muscle strength and physical performance in humans. Beyond serving as an energy depot at physiological levels, increased IMAT is thought to actively impair muscle metabolism through secretion of adipokines, cytokines and lipid intermediates that create an inflammatory environment and modulate insulin signaling pathways. This review discusses current evidence on the pathophysiological role of IMAT based on clinical studies, including interventions, and current mechanistic insight from biopsied human IMAT. We further explore traditional and emerging methods to investigate IMAT that could expand mechanistic understanding of IMAT-muscle-crosstalk, highlighting their strengths and limitations. Human in vitro co-culture-models are valuable future tools for dissecting cellular and molecular responses. Despite growing interest in IMAT as a potential key player in metabolic disease, uncertainty remains about its origin, regulation and functionality. We suggest further research to integrate and intertwine traditional imaging techniques, multi-omics characterization of IMAT biopsies and advanced, physiologically relevant human in vitro systems to close these knowledge gaps to develop therapeutic strategies targeting metabolic disease.

Skeletal muscle atrophy is driven by an imbalance between anabolic and catabolic signaling pathways, often involving suppression of the PI3K/Akt/mTOR axis. Thyroid Hormones (THs) are key endocrine regulators of skeletal muscle metabolism and adaptation, exerting context-dependent effects that promote either muscle atrophy or hypertrophy. Here, we identify Phosphoinositide-3-kinase interacting protein 1, Pik3ip1, as a critical regulator of TH-dependent muscle homeostasis. Transcriptomic profiling of skeletal muscle from muscle-specific D2 knockout (mD2KO) and TH Receptor knockout (TRKO) mice revealed a catabolic transcriptional program associated with increased Pik3ip1 expression. Consistently, Pik3ip1 expression negatively correlated with TH signaling in vivo and in vitro. Functional studies in C2C12 myotubes showed that Pik3ip1 overexpression suppresses Akt/mTOR signaling, indicating that its induction is sufficient to impair anabolic pathway activation. In vivo, Pik3ip1 expression was rapidly induced during denervation-induced muscle atrophy and remained persistently elevated in mD2KO and TRKO muscles, characterized by altered TH signaling. Sustained Pik3ip1 expression was associated with impaired activation of the Akt/mTOR pathway and enhanced muscle wasting. Conversely, TH treatment reduced Pik3ip1 levels, restored Akt/mTOR signaling, and promoted anabolic responses. Forced Pik3ip1 expression attenuated TH-induced Akt/mTOR phosphorylation, confirming its role as a mediator of TH-dependent anabolic regulation. Collectively, these findings identify Pik3ip1 as a key negative regulator of PI3K/Akt/mTOR signaling in skeletal muscle and establish the TH-Pik3ip1 axis as an important mechanism controlling muscle mass maintenance during atrophic conditions.

Background

Calcium/calmodulin-dependent protein kinase II (CaMKII) is activated in skeletal muscle with exercise, yet its physiological role in endurance training adaptation remains unclear. This study determined whether endogenous CaMKIIγ/δ in skeletal muscle is required for endurance training–induced metabolic remodeling and exercise adaptation.

Methods

We generated male skeletal muscle-specific CaMKIIγ/δ knockout (CaMKII mKO) mice and assessed muscle phenotype, exercise capacity, and training adaptation. Acute exercise–induced CaMKII activation was evaluated by phosphorylation status. Transcriptomic changes were analyzed by RNA sequencing before and after 4 weeks of treadmill endurance training. Mitochondrial protein abundance, ultrastructure, and bioenergetics were examined by immunoblotting, transmission electron microscopy, and Seahorse extracellular flux analysis in myotubes with acute CaMKIIγ/δ deletion.

Results

Acute treadmill exercise induced CaMKII phosphorylation in muscle without altering total CaMKII abundance. CaMKII mKO mice showed normal muscle mass, grip strength, and baseline performance. However, endurance training–induced improvement in running capacity was significantly blunted. Transcriptomic analyses revealed downregulation of oxidative phosphorylation and glycolytic gene programs in CaMKII-deficient muscle at baseline and after training. OXPHOS complex protein abundance was partially reduced at baseline and markedly reduced across complexes I–V after training. CaMKII deficiency increased ultrastructurally abnormal mitochondria without reducing mitochondrial number. Consistently, CaMKII-deficient myotubes showed lower absolute per-well oxygen consumption and extracellular acidification rate.

Conclusions

In male mice, endogenous CaMKIIγ/δ in muscle is dispensable for baseline locomotor performance but essential for endurance training-induced metabolic remodeling and mitochondrial integrity. These findings support a role for CaMKII in linking contraction-induced calcium signaling to metabolic adaptation in muscle.

Endurance exercise protects against metabolic dysfunction–associated steatotic liver disease (MASLD), yet whether these effects persist following cessation of training remains unclear. Here, we employed endurance training cycles in mice to isolate the hepatic memory of exercise. Our results indicate that endurance retraining potentiates systemic and hepatic glucoregulatory benefits. Exercise retraining persistently reduced hepatic steatosis, hallmarked by decreases in diacylglycerols and increased phosphatidylcholines (PC). Liver transcriptomic analysis identified lipid and protein secretory pathways induced by endurance retraining. Importantly, retraining enhanced hepatic expression of carboxylesterases (CES), including Ces2b, Ces3a, Ces3b, and Ces4a, and increased circulating carboxylesterase activity and CES4A protein levels. Exercise retraining reduced serum LDL-c and increased HDL-c, while enhancing the delivery of lysoPC and PC, predicted targets of CES, to the working muscle. Similarly, mice fed an obesogenic diet demonstrate that this hepatic memory of exercise persists under an obesogenic challenge. In humans, we show that a 6-week training period increases serum CES activity primarily in individuals with prior training. Lastly, our studies identify the PPAR-RXR-clock axis as a potential trigger that may engage the synchronized lipid delivery to skeletal muscle and support fatty acid oxidation. Together, these findings suggest that endurance retraining elicits a hepatic exercise memory characterized by persistent transcriptional reprogramming and lipid remodeling that restore metabolic benefits after inactivity and confer resilience against MASLD.