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The Mouse Metabolic Phenotyping Center (MMPC)Live Program was established in 2023 by the National Institute for Diabetes, Digestive and Kidney Diseases (NIDDK) at the National Institutes of Health (NIH) to advance biomedical research by providing the scientific community with standardized, high quality phenotyping services for mouse models of diabetes and obesity. Emerging as the next iteration of the MMPC Program which served the biomedical research community for 20 years (2001-2021), MMPCLive is designed as an outwardly-facing consortium of service cores that collaborate to provide reduced-cost consultation and metabolic, physiologic, and behavioral phenotyping tests on live mice for U.S. biomedical researchers. Four MMPCLive Centers located at universities around the country perform complex and often unique procedures in vivo on a fee for service basis, typically on mice shipped from the client or directly from a repository or vendor. Current areas of expertise include energy balance and body composition, insulin action and secretion, whole body carbohydrate and lipid metabolism, cardiovascular and renal function, food intake and behavior, microbiome and xenometabolism, and metabolic pathway kinetics. Additionally, an opportunity arose to reduce barriers to access and expand the diversity of the biomedical research workforce by establishing the VIBRANT Program. Directed at researchers historically underrepresented in the biomedical sciences, VIBRANT-eligible investigators have access to testing services, travel and career development awards, expert advice and experimental design consultation, and short internships to learn test technologies. Data derived from experiments run by the Centers belongs to the researchers submitting mice for testing which can be made publicly available and accessible from the MMPCLive database following publication. In addition to services, MMPCLive staff provide expertise and advice to researchers, develop and refine test protocols, engage in outreach activities, publish scientific and technical papers, and conduct educational workshops and training sessions to aid researchers in unraveling the heterogeneity of diabetes and obesity.

Introduction Sodium-glucose cotransporter type 2 (SGLT2) inhibitors (SGLT2i) block glucose reabsorption in the renal proximal tubule, thereby inducing glycosuria and natriuresis and leading to reductions in hyperglycemia, body weight, and [...], Previous studies highlight the potential for sodium-glucose cotransporter type 2 (SGLT2) inhibitors (SGLT2i) to exert cardioprotective effects in heart failure by increasing plasma ketones and shifting myocardial fuel utilization toward ketone oxidation. However, SGLT2i have multiple in vivo effects and the differential impact of SGLT2i treatment and ketone supplementation on cardiac metabolism remains unclear. Here, using gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) methodology combined with infusions of [[sup.13][C.sub.6]]glucose or [[sup.13][C.sub.4]][beta]OHB, we demonstrate that acute SGLT2 inhibition with dapagliflozin shifts relative rates of myocardial mitochondrial metabolism toward ketone oxidation, decreasing pyruvate oxidation with little effect on fatty acid oxidation in awake rats. Shifts in myocardial ketone oxidation persisted when plasma glucose levels were maintained. In contrast, acute [beta]OHB infusion similarly augmented ketone oxidation, but markedly reduced fatty acid oxidation and did not alter glucose uptake or pyruvate oxidation. After inducing heart failure, dapagliflozin increased relative rates of ketone and fatty acid oxidation, but decreased pyruvate oxidation. Dapagliflozin increased mitochondrial redox and reduced myocardial oxidative stress in heart failure, which was associated with improvements in left ventricular ejection fraction after 3 weeks of treatment. Thus, SGLT2i have pleiotropic effects on systemic and heart metabolism, which are distinct from ketone supplementation and may contribute to the long-term cardioprotective benefits of SGLT2i.

Recent research has shed light on the cellular and molecular functions of bioactive lipids that go far beyond what was known about their role as dietary lipids. Bioactive lipids regulate inflammation and its resolution as signaling molecules. Genetic studies have identified key factors that can increase the risk of cardiovascular diseases and metabolic syndrome through their effects on lipogenesis. Lipid scientists have explored how these signaling pathways affect lipid metabolism in the liver, adipose tissue, and macrophages by utilizing a variety of techniques in both humans and animal models, including novel lipidomics approaches and molecular dynamics models. Dissecting out these lipid pathways can help identify mechanisms that can be targeted to prevent or treat cardiometabolic conditions. Continued investigation of the multitude of functions mediated by bioactive lipids may reveal additional components of these pathways that can provide a greater understanding of metabolic homeostasis.

With the increasing prevalence of type 2 diabetes and fatty liver disease, there is still an unmet need to better treat hyperglycemia and hyperlipidemia. Here, we identify isthmin-1 (Ism1) as an adipokine and one that has a dual role in increasing adipose glucose uptake while suppressing hepatic lipid synthesis. Ism1 ablation results in impaired glucose tolerance, reduced adipose glucose uptake, and reduced insulin sensitivity, demonstrating an endogenous function for Ism1 in glucose regulation. Mechanistically, Ism1 activates a PI3K-AKT signaling pathway independently of the insulin and insulin-like growth factor receptors. Notably, while the glucoregulatory function is shared with insulin, Ism1 counteracts lipid accumulation in the liver by switching hepatocytes from a lipogenic to a protein synthesis state. Furthermore, therapeutic dosing of recombinant Ism1 improves diabetes in diet-induced obese mice and ameliorates hepatic steatosis in a diet-induced fatty liver mouse model. These findings uncover an unexpected, bioactive protein hormone that might have simultaneous therapeutic potential for diabetes and fatty liver disease.

Nonalcoholic fatty liver disease (NAFLD) is the leading chronic liver disease worldwide. Its more advanced subtype, nonalcoholic steatohepatitis (NASH), connotes progressive liver injury that can lead to cirrhosis and hepatocellular carcinoma. Here we provide an in-depth discussion of the underlying pathogenetic mechanisms that lead to progressive liver injury, including the metabolic origins of NAFLD, the effect of NAFLD on hepatic glucose and lipid metabolism, bile acid toxicity, macrophage dysfunction, and hepatic stellate cell activation, and consider the role of genetic, epigenetic, and environmental factors that promote fibrosis progression and risk of hepatocellular carcinoma in NASH.

Muscle sn -1,2-diacylglycerol (DAG) and C18:0 ceramide accumulation in sarcolemmal and mitochondrial compartments have been proposed to regulate muscle insulin sensitivity. Here, we evaluated whether weight loss-induced improvements in insulin sensitivity were associated with changes in muscle sn -1,2-DAG and ceramide content in people with obesity and type 2 diabetes. We measured skeletal muscle insulin sensitivity, assessed by using the hyperinsulinemic-euglycemic clamp procedure in conjunction with stable isotopically labeled glucose tracer infusion, and skeletal muscle sn -1,2-DAG and ceramide contents by using liquid chromatography–tandem mass spectrometry after subcellular fractionation and DAG isomer separation in 14 adults with obesity and type 2 diabetes before and after marked (18.6 ± 2.1%) weight loss. Whole-body insulin sensitivity doubled after weight loss. Sarcolemmal sn -1,2-DAG and C18:0 ceramide contents after weight loss were not different from values before weight loss. In contrast, mitochondrial-endoplasmic reticulum (ER) C18:0 ceramide content decreased by ∼20% after weight loss (from 2.16 ± 0.08 to 1.71 ± 0.13 nmol/g, P < 0.005). These results suggest a decrease in muscle mitochondrial-ER C18:0 ceramide content could contribute to the beneficial effect of weight loss on skeletal muscle insulin sensitivity. Article Highlights: Importance of changes in muscle sn -1,2-diacylglycerols (DAG) or C18:0 ceramide in mediating the beneficial effects of weight loss on muscle insulin sensitivity in people is not known. We examined whether weight loss–induced increases in muscle insulin sensitivity in people with obesity and type 2 diabetes are accompanied by changes in muscle sn -1,2-DAG or C18:0 ceramide. Weight loss improved muscle insulin sensitivity, which was accompanied by a 20% decrease in mitochondrial–endoplasmic reticulum C18:0 ceramide without a change in sarcolemmal C18:0 ceramide or sn -1,2-DAG. These results suggest that decreased muscle mitochondrial–endoplasmic reticulum C18:0 ceramide content contributes to the beneficial effect of weight loss on muscle insulin sensitivity. [ABSTRACT FROM AUTHOR]

Disruption of hepatocyte growth hormone (GH) signaling through disruption of Jak2 (JAK2L) leads to fatty liver. Previously, we demonstrated that development of fatty liver depends on adipocyte GH signaling. We sought to determine the individual roles of hepatocyte and adipocyte Jak2 on whole-body and tissue insulin sensitivity and liver metabolism. On chow, JAK2L mice had hepatic steatosis and severe whole-body and hepatic insulin resistance. However, concomitant deletion of Jak2 in hepatocytes and adipocytes (JAK2LA) completely normalized insulin sensitivity while reducing liver lipid content. On high-fat diet, JAK2L mice had hepatic steatosis and insulin resistance despite protection from diet-induced obesity. JAK2LA mice had higher liver lipid content and no protection from obesity but retained exquisite hepatic insulin sensitivity. AKT activity was selectively attenuated in JAK2L adipose tissue, whereas hepatic insulin signaling remained intact despite profound hepatic insulin resistance. Therefore, JAK2 in adipose tissue is epistatic to liver with regard to insulin sensitivity and responsiveness, despite fatty liver and obesity. However, hepatocyte autonomous JAK2 signaling regulates liver lipid deposition under conditions of excess dietary fat. This work demonstrates how various tissues integrate JAK2 signals to regulate insulin/glucose and lipid metabolism.

We assessed in vivo rates of hepatic mitochondrial oxidation, gluconeogenesis, and β-hydroxybutyrate (β-OHB) turnover by positional isotopomer NMR tracer analysis (PINTA) in individuals with metabolic-dysfunction-associated steatotic liver (MASL) (fatty liver) and MASL disease (MASLD) (steatohepatitis) compared with BMI-matched control participants with no hepatic steatosis. Hepatic fat content was quantified by localized 1H magnetic resonance spectroscopy (MRS). We found that in vivo rates of hepatic mitochondrial oxidation were unaltered in the MASL and MASLD groups compared with the control group. A physiological increase in plasma glucagon concentrations increased in vivo rates of hepatic mitochondrial oxidation by 50%–75% in individuals with and without MASL and increased rates of glucose production by ∼50% in the MASL group, which could be attributed in part to an ∼30% increase in rates of mitochondrial pyruvate carboxylase flux. These results demonstrate that (1) rates of hepatic mitochondrial oxidation are not substantially altered in individuals with MASL and MASLD and (2) glucagon increases rates of hepatic mitochondrial oxidation. [Display omitted] • Hepatic mitochondrial oxidation is not altered in humans with fatty liver • Hepatic mitochondrial oxidation is not altered in humans with steatohepatitis • Glucagon increases hepatic mitochondrial oxidation in humans without fatty liver • Glucagon increases hepatic mitochondrial oxidation in humans with fatty liver It is unclear whether rates of hepatic mitochondrial oxidation are altered in individuals with MASLD and MASH. Here, Petersen et al. show that rates of hepatic mitochondrial oxidation are not altered in humans with fatty liver or steatohepatitis and that glucagon can increase rates of hepatic mitochondrial oxidation in humans with and without fatty liver by 50%–75%. [ABSTRACT FROM AUTHOR]

Pompe disease is a rare genetic disorder caused by a deficiency of the enzyme acid alpha-glucosidase (GAA). This enzyme is responsible for breaking down glycogen, leading to the abnormal accumulation of glycogen, which results in progressive muscle weakness and metabolic dysregulation. In this study, we investigated the hypothesis that the small molecule inhibition of glycogen synthase I (GYS1) may reduce muscle glycogen content and improve metabolic dysregulation in a mouse model of Pompe disease. To address this hypothesis, we studied four groups of male mice: a control group of wild-type (WT) B6129SF1/J mice fed either regular chow or a GYS1 inhibitor (MZ-101) diet (WT-GYS1), and Pompe model mice B6;129-Gaatm1Rabn/J fed either regular chow (GAA-KO) or MZ-101 diet (GAA-GYS1) for 7 days. Our findings revealed that GAA-KO mice exhibited abnormal glycogen accumulation in the gastrocnemius, heart, and diaphragm. In contrast, inhibiting GYS1 reduced glycogen levels in all tissues compared with GAA-KO mice. Furthermore, GAA-KO mice displayed reduced spontaneous activity during the dark cycle compared with WT mice, whereas GYS1 inhibition counteracted this effect. Compared with GAA-KO mice, GAA-GYS1 mice exhibited improved glucose tolerance and whole body insulin sensitivity. These improvements in insulin sensitivity could be attributed to increased AMP-activated protein kinase phosphorylation in the gastrocnemius of WT-GYS1 and GAA-GYS1 mice. Additionally, the GYS1 inhibitor led to a reduction in the phosphorylation of GSS641 and the LC3 autophagy marker. Together, our results suggest that targeting GYS1 could serve as a potential strategy for treating glycogen storage disorders and metabolic dysregulation. NEW & NOTEWORTHY: We investigated the effects of small molecule inhibition of glycogen synthase I (GYS1) on glucose metabolism in a mouse model of Pompe disease. GYS1 inhibition reduces abnormal glycogen accumulation and molecular biomarkers associated with Pompe disease while also improving glucose intolerance. Our results collectively demonstrate that the GYS1 inhibitor represents a novel approach to substrate reduction therapy for Pompe disease. [ABSTRACT FROM AUTHOR]

Introduction Within minutes of consuming a meal containing carbohydrate and/or protein, both humans and rodents exhibit an increase in energy expenditure and body temperature, typically described as diet-induced or meal [...], Meal ingestion increases body temperature in multiple species, an effect that is blunted by obesity. However, the mechanisms responsible for these phenomena remain incompletely understood. Here we show that refeeding increases plasma leptin concentrations approximately 8-fold in 48-hour-fasted lean rats, and this normalization of plasma leptin concentrations stimulates adrenomedullary catecholamine secretion. Increased adrenal medulla-derived plasma catecholamines were necessary and sufficient to increase body temperature postprandially, a process that required both fatty acids generated from adipose tissue lipolysis and [beta]-adrenergic activation of brown adipose tissue (BAT). Diet-induced obese rats, which remained relatively hyperleptinemic while fasting, did not exhibit fasting-induced reductions in temperature. To examine the impact of feeding-induced increases in body temperature on energy balance, we compared rats fed chronically by either 2 carbohydraterich boluses daily or a continuous isocaloric intragastric infusion. Bolus feeding increased body temperature and reduced weight gain compared with continuous feeding, an effect abrogated by treatment with atenolol. In summary, these data demonstrate that leptin stimulates a hypothalamus-adrenal medulla-BAT axis, which is necessary and sufficient to induce lipolysis and, as a result, increase body temperature after refeeding.

Hibernating mammals possess a unique ability to reduce their body temperature to ambient levels, which can be as low as -2.9 °C, by active down-regulation of metabolism. Despite such a depressed physiologic phenotype, hibernators still maintain activity in their nervous systems, as evidenced by their continued sensitivity to auditory, tactile, and thermal stimulation. The molecular mechanisms that underlie this adaptation remain unknown. We report, using differential transcriptomics alongside immunohistologic and biochemical analyses, that neurons from thirteen-lined ground squirrels (Ictidomys tridecemlineatus) express mitochondrial uncoupling protein 1 (UCP1). The expression changes seasonally, with higher expression during hibernation compared with the summer active state. Functional and pharmacologic analyses show that squirrel UCP1 acts as the typical thermogenic protein in vitro. Accordingly, we found that mitochondria isolated from torpid squirrel brain show a high level of palmitate-induced uncoupling. Furthermore, torpid squirrels during the hibernation season keep their brain temperature significantly elevated above ambient temperature and that of the rest of the body, including brown adipose tissue. Together, our findings suggest that UCP1 contributes to local thermogenesis in the squirrel brain, and thus supports nervous tissue function at low body temperature during hibernation.

Author(s): Michael Roden [sup.1] [sup.2] [sup.3] , Gerald I. Shulman [sup.4] Author Affiliations: (1) Division of Endocrinology and Diabetology, Medical Faculty, Heinrich-Heine University, Düsseldorf, Germany (2) Institute for Clinical Diabetology, [...], Obesity and type 2 diabetes are the most frequent metabolic disorders, but their causes remain largely unclear. Insulin resistance, the common underlying abnormality, results from imbalance between energy intake and expenditure favouring nutrient-storage pathways, which evolved to maximize energy utilization and preserve adequate substrate supply to the brain. Initially, dysfunction of white adipose tissue and circulating metabolites modulate tissue communication and insulin signalling. However, when the energy imbalance is chronic, mechanisms such as inflammatory pathways accelerate these abnormalities. Here we summarize recent studies providing insights into insulin resistance and increased hepatic gluconeogenesis associated with obesity and type 2 diabetes, focusing on data from humans and relevant animal models. A Review of studies into insulin resistance and hepatic gluconeogenesis associated with obesity and type 2 diabetes.

Introduction The glucose-alanine cycle represents a critical link between carbohydrate and amino acid metabolism and comprises a series of reactions in which pyruvate, derived mostly from intramyocellular glycolysis, is transaminated [...], In order to determine whether the glucose-alanine cycle regulates rates of hepatic mitochondrial oxidation in humans, we applied positional isotopomer NMR tracer analysis (PINTA) to assess rates of hepatic mitochondrial oxidation and pyruvate carboxylase flux in healthy volunteers following both an overnight (12 hours) and a 60-hour fast. Following the 60-hour fast, rates of endogenous glucose production and mitochondrial oxidation decreased, whereas rates of hepatic pyruvate carboxylase flux remained unchanged. These reductions were associated with reduced rates of alanine turnover, assessed by [3-[sup.13]C]alanine, in a subgroup of participants under similar fasting conditions. In order to determine whether this reduction in alanine turnover was responsible for the reduced rates of hepatic mitochondrial oxidation, we infused unlabeled alanine into another subgroup of 60-hour fasted subjects to increase rates of alanine turnover, similar to what was measured after a 12-hour fast, and found that this perturbation increased rates of hepatic mitochondrial oxidation. Taken together, these studies demonstrate that 60 hours of starvation induce marked reductions in rates of hepatic mitochondrial oxidation, which in turn can be attributed to reduced rates of glucose-alanine cycling, and reveal a heretofore undescribed role for glucose-alanine in the regulation of hepatic mitochondrial oxidation in humans.

Previous work has shown that certain β(3)-peptides can effectively mimic the side chain display of an α-helix and inhibit interactions between proteins, both in vitro and in cultured cells. Here we describe a β(3)-peptide analog of GLP-1, CC-3(Act), that interacts with the GLP-1R extracellular domain (nGLP-1R) in vitro in a manner that competes with exendin-4 and induces GLP-1R-dependent cAMP signaling in cultured CHO-K1 cells expressing GLP-1R.