High-fat-diet-induced hepatic insulin resistance attenuates murine lipogenesis.

Hepatic insulin resistance (IR) is often said to be "pathway-selective" with preserved insulin stimulation of lipogenesis (DNL) despite attenuated insulin signaling toward glucose metabolism. However, DNL has not been assessed in models of liver-specific IR. We studied mice with differential tissue-specific lipid-induced IR achieved by different durations of high-fat diet (HFD) feeding.

Humanized mouse liver reveals endothelial control of essential hepatic metabolic functions.

Hepatocytes, the major metabolic hub of the body, execute functions that are human-specific, altered in human disease, and currently thought to be regulated through endocrine and cell-autonomous mechanisms. Here, we show that key metabolic functions of human hepatocytes are controlled by non-parenchymal cells (NPCs) in their microenvironment. We developed mice bearing human hepatic tissue composed of human hepatocytes and NPCs, including human immune, endothelial, and stellate cells.

Rising NAFLD and metabolic severity during the Sars-CoV-2 pandemic among children with obesity in the United States.

Objective: Nonalcoholic fatty liver disease (NAFLD), the most common liver disease among youth with obesity, precedes more severe metabolic and liver diseases. However, the impact of the Sars-CoV-2 global pandemic on the prevalence and severity of NAFLD and the associated metabolic phenotype among youth with obesity is unknown.

Methods: Participants were recruited from the Yale Pediatric Obesity Clinic during the Sars-CoV-2 global pandemic (August 2020 to May 2022) and were compared with a frequency-matched control group of youth with obesity studied before the Sars-CoV-2 global pandemic (January 2017 to November 2019).

Insulin increases placental triglyceride as a potential mechanism for fetal adiposity in maternal obesity.

Objective: Maternal obesity increases the incidence of excess adiposity in newborns, resulting in lifelong diabetes risk. Elevated intrauterine fetal adiposity has been attributed to maternal hyperglycemia; however, this hypothesis does not account for the increased adiposity seen in newborns of mothers with obesity who have euglycemia. We aimed to explore the placental response to maternal hyperinsulinemia and the effect of insulin-like growth factor 2 (IGF-2) in promoting fetal adiposity by increasing storage and availability of nutrients to the fetus.

Metformin, phenformin, and galegine inhibit complex IV activity and reduce glycerol-derived gluconeogenesis.

SignificanceMetformin is the most commonly prescribed drug for the treatment of type 2 diabetes mellitus, yet the mechanism by which it lowers plasma glucose concentrations has remained elusive. Most studies to date have attributed metformin's glucose-lowering effects to inhibition of complex I activity. Contrary to this hypothesis, we show that inhibition of complex I activity in vitro and in vivo does not reduce plasma glucose concentrations or inhibit hepatic gluconeogenesis.

Deletion of the diabetes candidate gene Slc16a13 in mice attenuates diet-induced ectopic lipid accumulation and insulin resistance.

Genome-wide association studies have identified SLC16A13 as a novel susceptibility gene for type 2 diabetes. The SLC16A13 gene encodes SLC16A13/MCT13, a member of the solute carrier 16 family of monocarboxylate transporters. Despite its potential importance to diabetes development, the physiological function of SLC16A13 is unknown.

Insulin-stimulated endoproteolytic TUG cleavage links energy expenditure with glucose uptake.

TUG tethering proteins bind and sequester GLUT4 glucose transporters intracellularly, and insulin stimulates TUG cleavage to translocate GLUT4 to the cell surface and increase glucose uptake. This effect of insulin is independent of phosphatidylinositol 3-kinase, and its physiological relevance remains uncertain. Here we show that this TUG cleavage pathway regulates both insulin-stimulated glucose uptake in muscle and organism-level energy expenditure.

Mechanisms by which adiponectin reverses high fat diet-induced insulin resistance in mice.

Adiponectin has emerged as a potential therapy for type 2 diabetes mellitus, but the molecular mechanism by which adiponectin reverses insulin resistance remains unclear. Two weeks of globular adiponectin (gAcrp30) treatment reduced fasting plasma glucose, triglyceride (TAG), and insulin concentrations and reversed whole-body insulin resistance, which could be attributed to both improved insulin-mediated suppression of endogenous glucose production and increased insulin-stimulated glucose uptake in muscle and adipose tissues. These improvements in liver and muscle sensitivity were associated with ∼50% reductions in liver and muscle TAG and plasma membrane (PM)-associated diacylglycerol (DAG) content and occurred independent of reductions in total ceramide content.

Hepatic Insulin Resistance Is Not Pathway Selective in Humans With Nonalcoholic Fatty Liver Disease.

Objective: Both glucose and triglyceride production are increased in type 2 diabetes and nonalcoholic fatty liver disease (NAFLD). For decades, the leading hypothesis to explain these paradoxical observations has been selective hepatic insulin resistance wherein insulin drives de novo lipogenesis (DNL) while failing to suppress glucose production. Here, we aimed to test this hypothesis in humans.

Membrane-bound -1,2-diacylglycerols explain the dissociation of hepatic insulin resistance from hepatic steatosis in MTTP knockout mice.

Microsomal triglyceride transfer protein (MTTP) deficiency results in a syndrome of hypolipidemia and accelerated NAFLD. Animal models of decreased hepatic MTTP activity have revealed an unexplained dissociation between hepatic steatosis and hepatic insulin resistance. Here, we performed comprehensive metabolic phenotyping of liver-specific MTTP knockout (L-) mice and age-weight matched wild-type control mice.

Metabolic control analysis of hepatic glycogen synthesis in vivo.

Multiple insulin-regulated enzymes participate in hepatic glycogen synthesis, and the rate-controlling step responsible for insulin stimulation of glycogen synthesis is unknown. We demonstrate that glucokinase (GCK)-mediated glucose phosphorylation is the rate-controlling step in insulin-stimulated hepatic glycogen synthesis in vivo, by use of the somatostatin pancreatic clamp technique using [C]glucose with metabolic control analysis (MCA) in three rat models: 1) regular chow (RC)-fed male rats (control), 2) high fat diet (HFD)-fed rats, and 3) RC-fed rats with portal vein glucose delivery at a glucose infusion rate matched to the control. During hyperinsulinemia, hyperglycemia dose-dependently increased hepatic glycogen synthesis.

Adipose glucocorticoid action influences whole-body metabolism modulation of hepatic insulin action.

The connection between adipose glucocorticoid action and whole-body metabolism is incompletely understood. Thus, we generated adipose tissue-specific glucocorticoid receptor-knockout (Ad-GcR) mice to explore potential mechanisms. Ad-GcR mice had a lower concentration of fasting plasma nonesterified fatty acids and less hepatic steatosis.

Author Correction: Metformin inhibits gluconeogenesis via a redox-dependent mechanism in vivo.

In the version of this article originally published, the V and V flux data shown in Fig. 6e,f were inadvertently duplicated from Fig. 5j,k.

Ectopic lipid deposition mediates insulin resistance in adipose specific 11β-hydroxysteroid dehydrogenase type 1 transgenic mice.

Context: Excessive adipose glucocorticoid action is associated with insulin resistance, but the mechanisms linking adipose glucocorticoid action to insulin resistance are still debated. We hypothesized that insulin resistance from excess glucocorticoid action may be attributed in part to increased ectopic lipid deposition in liver.

Methods: We tested this hypothesis in the adipose specific 11β-hydroxysteroid dehydrogenase-1 (HSD11B1) transgenic mouse, an established model of adipose glucocorticoid excess.

PEPCK1 Antisense Oligonucleotide Prevents Adiposity and Impairs Hepatic Glycogen Synthesis in High-Fat Male Fed Rats.

The increased hepatic gluconeogenesis in type 2 diabetes mellitus has often been ascribed to increased transcription of phosphoenolpyruvate carboxykinase 1, cystolic form (PEPCK1), although recent evidence has questioned this attribution. To assess the metabolic role of PEPCK1, we treated regular chow fed and high-fat fed (HFF) male Sprague-Dawley rats with a 2'-O-methoxyethyl chimeric antisense oligonucleotide (ASO) against PEPCK1 and compared them with control ASO-treated rats. PEPCK1 ASO effectively decreased PEPCK1 expression in the liver and white adipose tissue.

Metformin inhibits gluconeogenesis via a redox-dependent mechanism in vivo.

Metformin, the universal first-line treatment for type 2 diabetes, exerts its therapeutic glucose-lowering effects by inhibiting hepatic gluconeogenesis. However, the primary molecular mechanism of this biguanide remains unclear, though it has been suggested to act, at least partially, by mitochondrial complex I inhibition. Here we show that clinically relevant concentrations of plasma metformin achieved by acute intravenous, acute intraportal or chronic oral administration in awake normal and diabetic rats inhibit gluconeogenesis from lactate and glycerol but not from pyruvate and alanine, implicating an increased cytosolic redox state in mediating metformin's antihyperglycemic effect.

Acetyl-CoA Carboxylase Inhibition Reverses NAFLD and Hepatic Insulin Resistance but Promotes Hypertriglyceridemia in Rodents.

Pharmacologic inhibition of acetyl-CoA carboxylase (ACC) enzymes, ACC1 and ACC2, offers an attractive therapeutic strategy for nonalcoholic fatty liver disease (NAFLD) through simultaneous inhibition of fatty acid synthesis and stimulation of fatty acid oxidation. However, the effects of ACC inhibition on hepatic mitochondrial oxidation, anaplerosis, and ketogenesis in vivo are unknown. Here, we evaluated the effect of a liver-directed allosteric inhibitor of ACC1 and ACC2 (Compound 1) on these parameters, as well as glucose and lipid metabolism, in control and diet-induced rodent models of NAFLD.

Absence of ANGPTL4 in adipose tissue improves glucose tolerance and attenuates atherogenesis.

Alterations in ectopic lipid deposition and circulating lipids are major risk factors for developing cardiometabolic diseases. Angiopoietin-like protein 4 (ANGPTL4), a protein that inhibits lipoprotein lipase (LPL), controls fatty acid (FA) uptake in adipose and oxidative tissues and regulates circulating triacylglycerol-rich (TAG-rich) lipoproteins. Unfortunately, global depletion of ANGPTL4 results in severe metabolic abnormalities, inflammation, and fibrosis when mice are fed a high-fat diet (HFD), limiting our understanding of the contribution of ANGPTL4 in metabolic disorders.

Angptl8 antisense oligonucleotide improves adipose lipid metabolism and prevents diet-induced NAFLD and hepatic insulin resistance in rodents.

Aims/hypothesis: Targeting regulators of adipose tissue lipoprotein lipase could enhance adipose lipid clearance, prevent ectopic lipid accumulation and consequently ameliorate insulin resistance and type 2 diabetes. Angiopoietin-like 8 (ANGPTL8) is an insulin-regulated lipoprotein lipase inhibitor strongly expressed in murine adipose tissue. However, Angptl8 knockout mice do not have improved insulin resistance.

studies on the mechanism of methylene cyclopropyl acetic acid and methylene cyclopropyl glycine-induced hypoglycemia.

Exposure to the toxins methylene cyclopropyl acetic acid (MCPA) and methylene cyclopropyl glycine (MCPG) of unripe ackee and litchi fruit can lead to hypoglycemia and death; however, the molecular mechanisms by which MCPA and MCPG cause hypoglycemia have not been established To determine the mechanisms of action of these toxins, we infused them into conscious rodents and assessed rates of hepatic gluconeogenesis and ketogenesis, hepatic acyl-CoA and hepatic acetyl-CoA content, and hepatocellular energy charge. MCPG suppressed rates of hepatic β-oxidation as reflected by reductions in hepatic ketogenesis, reducing both short- and medium-chain hepatic acyl-CoA concentrations. Hepatic acetyl-CoA content decreased, and hepatic glucose production was inhibited.