Biology subjects

Shulman, G. I.

Publications and source records attributed to Shulman, G. I..

6 recordsLinked to original sources

bioRxiv2025

High-fat diet ablates an insulin-responsive pool of GLUT4 glucose transporters in skeletal muscle

To stimulate glucose uptake in muscle, insulin mobilizes GLUT4 glucose transporters to the cell surface. During fasting, GLUT4 and the transmembrane aminopeptidase IRAP are trapped in intracellular, insulin-responsive vesicles bound by TUG, AS160, and Usp25m proteins. Here we show that Usp25m, a protease, is required for the bulk of insulin-stimulated TUG cleavage and consequent vesicle mobilization and glucose uptake. Efficient TUG cleavage also requires AS160. In mice with diet-induced insulin resistance, Usp25m abundance is reduced, IRAP is mislocalized during fasting, and TUG cleavage is impaired; effects of Usp25m and TUG deletion to alter insulin-stimulated and fasting glucose uptake, respectively, are ablated. We conclude that skeletal muscle insulin resistance results in part from altered membrane trafficking of GLUT4 and IRAP during fasting. This alteration depletes the pool of insulin-responsive vesicles marked by TUG and Usp25m. Mistargeting of GLUT4 and IRAP may contribute to distinct aspects of the metabolic syndrome in humans.

physiology↗

bioRxiv2025

Metabolic reprogramming by endothelial ANGPTL4 depletion protects against diabetic kidney disease

The role of cell-specific ANGPTL4 is not well known in the context of ECs, specifically in pathological angiogenesis and its relation to diabetic kidney disease. Here, we demonstrate that endothelial ANGPTL4 is required to induce a metabolic phenotype that favors mesenchymal activation in ECs and tubules in diabetic conditions. Diabetes accelerates mesenchymal activation and fibrogenesis in control mice however, the same effects were not observed in endothelial-cell specific knock out mice. This mesenchymal activation in diabetes is directly linked with pathological neovascularization, endothelial leakage, lipid and glycolysis metabolite load, de novo lipogenesis (DNL) and related mitochondrial damage, activation of the immune system, c-GAS-STING activation and transcription of pro-inflammatory cytokines. However, endothelial ANGPTL4-depleted mice had stable vessels, improved levels of lipid and glucose metabolism, suppressed levels of DNL, restored mitochondrial function, and mitigated levels of c-GAS-STING-mediated inflammation. Moreover, Inhibition of DNL, and STING via small molecule inhibitors suppressed pathological neovascularization and endothelial leakage, normalized fatty acid oxidation and reduced pathological glycolysis and de novo lipogenesis (DNL). These data demonstrate the crucial roles of endothelial ANGPTL4 in regulating pathogenic angiogenesis in the renal vasculature during diabetes.

molecular biology↗

bioRxiv2025

Liver lipid droplet cholesterol content is a key determinant of metabolic dysfunction-associated steatohepatitis

Metabolic dysfunction-associated steatohepatitis (MASH) represents a progressive form of steatotic liver disease which increases the risk for fibrosis and advanced liver disease. The accumulation of discrete species of bioactive lipids has been postulated to activate signaling pathways that promote inflammation and fibrosis. However, the key pathogenic lipid species is a matter of debate. We explored candidates using various dietary, molecular, and genetic models. Mice fed a choline-deficient L-amino acid-defined high-fat diet (CDAHFD) developed steatohepatitis and manifested early markers of liver fibrosis associated with increased cholesterol content in liver lipid droplets within 5 days without any changes in total liver cholesterol content. Treating mice with antisense oligonucleotides (ASOs) against Coenzyme A synthase (Cosay) or treatment with bempedoic acid or atorvastatin decreased liver lipid droplet cholesterol content and prevented CDAHFD-induced MASH and the fibrotic response. All these salutary effects were abrogated with dietary cholesterol supplementation. Analysis of human liver samples demonstrated that cholesterol in liver lipid droplets was increased in humans with MASH and liver fibrosis and was higher in PNPLA3 I148M (variants rs738409) than in HSD17B13 variants (rs72613567). Together, these data identify cholesterol in liver lipid droplets as a critical mediator of MASH and demonstrate that COASY knockdown and bempedoic acid are novel therapeutic approaches to reduce liver lipid droplet cholesterol content and thereby prevent the development of MASH and liver fibrosis. Significance StatementMetabolic dysfunction-associated steatohepatitis (MASH) is a progressive liver disease linked to fibrosis. The role of specific lipid species in its pathogenesis remains debated. Using dietary, molecular, and genetic models, we found that mice on a choline-deficient, high-fat diet (CDAHFD) developed steatohepatitis and early fibrosis, marked by increased cholesterol in liver lipid droplets within five days. Targeting COASY with antisense oligonucleotides or treating with bempedoic acid or atorvastatin reduced lipid droplet cholesterol and prevented MASH. However, dietary cholesterol supplementation negated these effects. Human liver samples confirmed elevated lipid droplet cholesterol in MASH and fibrosis, especially in PNPLA3 I148M carriers. These findings highlight cholesterol reduction as a potential MASH therapy.

pathology↗

bioRxiv2024

Role of AMPK in Atrial Metabolic Homeostasis and Substrate Preference

Atrial fibrillation is the most common clinical arrhythmia and may be due in part to metabolic stress. Atrial specific deletion of the master metabolic sensor, AMP-activated protein kinase (AMPK), induces atrial remodeling culminating in atrial fibrillation in mice, implicating AMPK signaling in the maintenance of atrial electrical and structural homeostasis. However, atrial substrate preference for mitochondrial oxidation and the role of AMPK in regulating atrial metabolism are unknown. Here, using LC-MS/MS methodology combined with infusions of [13C6]glucose and [13C4]{beta}-hydroxybutyrate in conscious mice, we demonstrate that conditional deletion of atrial AMPK catalytic subunits shifts mitochondrial atrial metabolism away from fatty acid oxidation and towards pyruvate oxidation. LC-MS/MS-based quantification of acyl-CoAs demonstrated decreased atrial tissue content of long-chain fatty acyl-CoAs. Proteomic analysis revealed a broad downregulation of proteins responsible for fatty acid uptake (LPL, CD36, FABP3), acylation and oxidation. Atrial AMPK deletion reduced expression of atrial PGC1- and downstream PGC1-/PPAR/RXR regulated gene transcripts. In contrast, atrial [14C]2-deoxyglucose uptake and GLUT1 expression increased with fasting in mice with AMPK deletion, while the expression of glycolytic enzymes exhibited heterogenous changes. Thus, these results highlight the crucial homeostatic role of AMPK in the atrium, with loss of atrial AMPK leading to downregulation of the PGC1-/PPAR pathway and broad metabolic reprogramming with a loss of fatty acid oxidation, which may contribute to atrial remodeling and arrhythmia.

physiology↗

bioRxiv2020

Obesity-linked PPARγ S273 phosphorylation promotes insulin resistance through Growth Differentiation Factor 3

Overnutrition and obesity promote adipose tissue dysfunction, often leading to systemic insulin resistance. The thiazolidinediones (TZDs) are a potent class of insulin-sensitizing drugs and ligands of PPAR{gamma} that improve insulin sensitivity, but their use is limited due to significant side effects. Recently, we demonstrated a mechanism by which TZDs improve insulin sensitivity distinct from receptor agonism and adipogenesis: reversal of obesity-linked phosphorylation of PPAR{gamma} at Serine 273. However, the role of this modification has not been tested genetically. Here we demonstrate that mice encoding an allele of PPAR{gamma} which cannot be phosphorylated at S273 are protected from insulin resistance, without exhibiting differences in body weight or TZD-associated side effects. Indeed, hyperinsulinemic-euglycemic clamp experiments confirm improved insulin sensitivity, as evidenced by increased whole-body glucose uptake. RNA-seq experiments reveal PPAR{gamma} S273 phosphorylation specifically enhances transcription of Gdf3, a BMP family member. Ectopic expression of Gdf3 is sufficient to induce insulin resistance in lean, healthy mice. We find that Gdf3 can impact metabolism by inhibition of BMP signaling. Together, these results highlight the diabetogenic role of PPAR{gamma} S273 phosphorylation and focuses attention on a putative target, Gdf3.

cell biology↗

bioRxiv2019

An insulin-stimulated proteolytic mechanism links energy expenditure with glucose uptake

Mechanisms to coordinately regulate energy expenditure and glucose uptake into muscle and fat cells are not well described. Insulin stimulates glucose uptake in part by causing site-specific endoproteolytic cleavage of TUG, which mobilizes GLUT4 glucose transporters to the cell surface. Here, we show that the TUG C-terminal cleavage product enters the nucleus, binds the transcriptional regulators PGC-1 and PPAR{gamma}, and increases oxidative metabolism and thermogenic protein expression. Muscle-specific genetic manipulation of this pathway impacts whole-body energy expenditure, independent of glucose uptake. The PPAR{gamma}2 Pro12Ala polymorphism, which reduces diabetes risk, enhances TUG binding. The TUG cleavage product stabilizes PGC-1 and is itself susceptible to an Ate1 arginyltransferase -dependent degradation mechanism; binding of the TUG product confers Ate1-dependent stability upon PGC-1. We conclude that TUG cleavage coordinates energy expenditure with glucose uptake, that this pathway may contribute to the thermic effect of food, and that its attenuation may be important in obesity.

physiology↗