Plant-based diet is growingly recommended, although switching the source of proteins from animal to plant regimen requires metabolic adaptations. According to its pivotal function in bridging amino acids and glucose homeostasis, we investigated the role of liver GDH in short-term adaptation to plant versus animal dietary proteins keeping the same spectrum of macronutrients. Control and Hep-Glud1-/- mice lacking liver GDH were fed for 4 days with either animal- or plant-based diets. Hepatic GDH was upregulated in control mice eating animal proteins compared to mice under the plant regimen. Glycemia of ad libitum fed control mice were lower under plant-based regimen compared to animal-based diet; not further changed in Hep-Glud1-/- mice. After 6h of fasting, glycemia remained within the physiological range but mice under the plant-based diet engaged a more robust fasting response versus animal protein regimen. In Hep-Glud1-/- mice, exhibiting impaired endogenous glucose production evoked by amino acids, plant-based diet was associated with reduced plasma concentrations of gluconeogenic alanine and L-carnitine precursor lysine, underscoring limited fasting adaptation. Liver in situ high-resolution metabolomics revealed higher pyruvate levels in periportal regions of mice fed the animal-based diet and the knockout of liver GDH induced elevated aspartate, while urea production was impaired. This resulted in high plasma ammonia concentrations in Hep-Glud1-/- mice, causing severe hyperammonemia in GDH null mice under plant-based diet. These mice exhibited reduced voluntary physical activity, an effect absent in Hep-Glud1-/- mice under animal-based proteins. Overall, dietary source of proteins shapes energy partitioning according to the respective amino acid availability.
Background Diabetic cardiomyopathy (DCM) is a prevalent and severe cardiovascular complication of diabetes mellitus, characterized by progressive cardiac dysfunction and pathological remodeling driven by myocardial metabolic disturbances. However, the underlying molecular mechanisms remain incompletely elucidated. Methods A type 2 DCM mouse model was established by feeding C57BL/6 mice a high-fat diet combined with streptozotocin injections. Cardiomyocyte-specific TRIM47 knockdown was achieved via AAV9-mediated delivery of a cardiomyocyte-specific cTnT promoter-driven shRNA. In vitro, primary neonatal mouse ventricular cardiomyocytes (NMCMs) were treated with palmitic acid (PA) to model cardiomyocyte injury. Results TRIM47 was significantly upregulated in diabetic hearts. Cardiomyocyte-specific TRIM47 knockdown improved left ventricular ejection fraction and fractional shortening, attenuated chamber dilation, and reduced heart weight-to-tibia length ratio. TRIM47 silencing attenuated cardiomyocyte hypertrophy, interstitial fibrosis, and cardiomyocyte apoptosis, alongside reduced myocardial inflammatory cytokine levels (TNF-α, IL-6, IL-1β). Furthermore, TRIM47 knockdown alleviated myocardial lipid accumulation and reduced triglyceride levels, accompanied by downregulation of the fatty acid translocase CD36. In vitro, PA-treated NMCMs exhibited elevated TRIM47 expression, and its knockdown mitigated PA-induced cardiomyocyte injury, inflammation, apoptosis, and lipid deposition. Mechanistically, the m6A reader YTHDF3 was upregulated under PA conditions and directly bound to m6A-modified TRIM47 mRNA, enhancing its stability. Rescue experiments demonstrated that YTHDF3 overexpression exacerbated PA-induced cardiomyocyte injury, whereas concurrent TRIM47 knockdown largely reversed these deleterious effects. Conclusion Our results revealed that TRIM47 may contribute to the progression of DCM by promoting abnormal cardiac lipid metabolism, exacerbating inflammation and apoptosis, and these effects are partially mediated through the upstream m6A reader YTHDF3.
Semaglutide (SEMA), a glucagon-like peptide-1 (GLP-1) analogue approved for treatment of obesity, is now one of the most used anti-obesity pharmacotherapeutic agents worldwide. The effects of SEMA on body weight, appetite, and adiposity are well established. Moreover, sex differences in these effects are clearly emerging. Metabolism and reproduction are intimately intertwined; yet, whether and how these blockbuster drugs affect the reproductive system of males and females is poorly understood. To address this gap, we investigated the impact of chronic SEMA treatment on gonads and circulating reproductive hormones in diet-induced obese male and female rats. GLP-1 receptor is expressed in ovaries and testes, potentially allowing a direct effect of SEMA. Testicular expression of this receptor was 4-fold higher than in ovaries, supporting a potential male bias for potency of the drug effect. To disambiguate the direct effect of the drug from potential downstream effects of weight loss, and ensuing improvements in metabolism produced by the drug, we also evaluated pair-fed (PF) controls. After 4 weeks of treatment, PF and SEMA males displayed improvements in reproductive measures like sperm motility and mucus penetration parameters. Morphological analysis of male and female gonads largely suggested increased fertility. In males, changes in germinal epithelium and seminiferous tubules were detected. In females, increased folliculogenesis was identified in both SEMA and PF rats. Structural changes in the gonads were accompanied by changes in circulating gonadal hormones in a sex-specific manner. In males, SEMA attenuated the weight-loss-induced reduction in all androgens measured. In females, levels of progesterone, pregnenolone, and estradiol were reduced in a treatment specific manner. Pituitary hormones were also affected in both sexes. Altogether, this study highlights broad SEMA-specific, as well as weight loss induced but rescued by SEMA, effects at transcriptional, functional, and systemic levels on the reproductive systems of males and females.
Agonists of the lipid-sensing PPAR nuclear receptors, including PPARα, are being explored as therapies for metabolic disorders due to their roles in metabolic and anti-inflammatory processes. PPARα transcriptional programs have tissue-dependent features, yet there is a lack of genetic tools to study tissue-specific signaling activation without the addition of a systemic agonist. We aimed to investigate intestinal epithelial cell (IEC)-specific roles of PPARα signaling using a novel transgenic mouse that enables spatial and temporal control of Ppara overexpression. CAG-Ppara,-EGFP mice were bred to Villin-CreERT2 to establish the IEC-Ppara mouse, which was compared to littermate controls 2 weeks after tamoxifen exposure. IEC-Ppara mice had increased Ppara mRNA and PPARα protein in the intestinal epithelium. Transcriptional analysis of intestinal tissue from IEC-Ppara mice showed upregulation of PPARα target genes and functional enrichment for fatty acid catabolic processes. As expected, the enterocytes of IEC-Ppara mice were primed to absorb lipids following oral administration of an olive oil bolus. Unexpectedly, the enteroendocrine hormone Gip was among the most downregulated genes. GIP-positive cells were reduced in the intestines of IEC-Ppara mice and in mice treated with PPARα agonist WY-14643. Circulating GIP hormone was reduced in IEC-Ppara mice. GLP-1-positive cells and hormone were unchanged. Consistent with reduced GIP function, IEC-Ppara mice consumed more food. These findings reveal PPARα as a regulator of GIP and support a new framework in which PPARα signaling influences systemic energy balance via a gut hormone axis. This study could have future impact on understanding responses to therapies targeting PPAR or incretin signaling.
Objective Brain glucose sensing is critical for survival during hypoglycaemia, yet how glucose-sensing neurons access circulating glucose concentrations to maintain glucose homeostasis remains poorly understood. Here we tested the hypothesis that adult oligodendrogenesis in the median eminence (ME) is responsive to changes in blood glucose levels and contributes to hypothalamic glucose sensing through regulation of the blood-hypothalamus barrier. Methods We used glycemic challenges and hypoinsulinaemic clamp studies to identify the effect of systemic changes in glycaemia on hypothalamic oligodendrocyte lineage cells. We used conditional knockout mouse models to dissect the respective contributions of adult oligodendrogenesis and new myelin formation to glucose homeostasis in adult male mice. Analyses combined immunofluorescence, serial electron microscopy, whole-brain tissue clearing, and transcriptomic analyses. Results We found that adult oligodendrogenesis in the median eminence (ME) is modulated by changes in circulating glucose levels and rapidly upregulated by hypoglycaemia. Genetic blockade of new oligodendrocyte production in adult male mice impairs the regulation of glucose homeostasis, the integrity of the ME blood-hypothalamus barrier, and hypothalamic glucose sensing. Unexpectedly, functional integrity of adult-formed myelin is not required for the maintenance of glucose homeostasis. Instead, we show that blockade of adult oligodendrogenesis disrupts hypothalamic expression of A disintegrin and metallopeptidase with thrombospondin motifs 4 (ADAMTS4), a metallopeptidase whose brain expression is restricted to the oligodendrocyte lineage and whose ME expression requires ongoing adult oligodendrogenesis. We show that ADAMTS4 regulates hypothalamic perineuronal net deposition, vascular permeability and glucose sensing. Finally, we show that ME ADAMTS4 expression is regulated by changes in peripheral glycaemia and is dysregulated in diabetes, providing a mechanism by which ME oligodendrocytes contribute to the regulation of glucose homeostasis.
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.
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.
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.
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.
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.
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.
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: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.
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.
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.
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.
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.
Introduction Phthalates are widely used as plasticizers in consumer products and are suspected to be metabolism-disrupting chemicals. Di-isononyl phthalate (DINP) is commonly recognized as less hazardous substitute for more studied di(2-ethylhexyl) phthalate (DEHP). Materials and methods The effects of DINP on hepatic lipid metabolism were studied using C57BL/6J mice with diet-induced obesity, and human HepaRG and C3A cell lines. The mice were orally exposed to 0, 1.5, 15 or 150 mg/kg bw/d DINP for 20 weeks, followed by assessment of glucose and insulin tolerance, hepatic histology, transcriptome and metabolome. The cells were exposed to DINP and its metabolites, followed by measurement of mitochondrial function and nuclear receptor activation. Results The highest dose of DINP decreased hepatic lipid droplets and slightly attenuated weight gain and glucose tolerance of the mice. DINP exposure elevated acylcarnitine levels, indicating altered fatty acid beta-oxidation, which was accompanied by enrichment in mitochondrial and peroxisomal lipid metabolism pathways at transcriptomics level. In vitro, monoisononyl phthalate (MINP), the primary metabolite of DINP, increased mitochondrial respiration and beta-oxidation in presence of long-chain fatty acids. DINP metabolites activated peroxisome proliferator-activated receptors (PPARs) of both mouse and human, with an activation profile partially distinct from DEHP. Conclusions Our findings indicate that DINP remodels hepatic lipid metabolism through its active metabolites via PPARs at high doses, with additional modes of action at lower exposure levels. Due to species-specific differences in nuclear receptor activation potencies, the adverse or potentially beneficial nature of these effects in humans remains ambiguous.
Chronic choline insufficiency reprograms hepatic metabolism and drives insulin resistance independent of obesity. While complete choline deficiency causes liver injury, the metabolic consequences of sustained, suboptimal intake, observed in ∼90% of US adults, remain poorly defined. Here, we used integrated lipidomic, metabolomic, and transcriptomic profiling to determine how graded choline intake (0.5, 1.4, or 6.3 g/kg) regulates hepatic metabolism during a control (Con) or high-fat (HF) diet-induced obesity regimen. Under Con diets, low choline intake induced a distinct metabolic state characterized by remodeled hepatic lipid architecture, particularly within triglyceride and glycerolipid species, without altering bulk triglyceride accumulation. Mechanistically, low choline disrupted phospholipid balance and induced a coordinated, sex-dependent transcriptional response, identifying ethanolamine-phosphate phospho-lyase (ETNPPL) and the fatty acid transporter CD36 as top choline-responsive genes. These metabolic effects were unique to the Con low choline group, as a high-fat diet masked all choline-dependent variations. Specifically, ETNPPL protein abundance increased under low choline Con conditions in males but not females. Functionally, this sustained restriction led to progressive hyperglycemia and insulin resistance exclusively in male mice, whereas females remained metabolically protected. Together, these findings demonstrate that chronic choline restriction remodels hepatic lipid metabolism in the absence of obesity and define a CD36-ETNPPL axis linking choline availability to sex-specific insulin resistance.
