Depletion of TBC1D4 Improves the Metabolic Exercise Response by Overcoming Genetically Induced Peripheral Insulin Resistance.

The Rab-GTPase-activating protein (RabGAP) TBC1D4 (AS160) represents a key component in the regulation of glucose transport into skeletal muscle and white adipose tissue (WAT) and is therefore crucial during the development of insulin resistance and type 2 diabetes. Increased daily activity has been shown to be associated with improved postprandial hyperglycemia in allele carriers of a loss-of-function variant in the human TBC1D4 gene. Using conventional Tbc1d4-deficient mice (D4KO) fed a high-fat diet, we show that moderate endurance exercise training leads to substantially improved glucose and insulin tolerance and enhanced expression levels of markers for mitochondrial activity and browning in WAT from D4KO animals.

Effects of TM6SF2 rs58542926 polymorphism on hepatocellular lipids and insulin resistance in early type 2 diabetes.

Background And Aims: Increased hepatocellular lipid content (HCL) is linked to insulin resistance, risk of type 2 diabetes and related complications. Conversely, a single-nucleotide polymorphism (TM6SF2; rs58542926) in the transmembrane 6 superfamily member 2-gene has been associated with nonalcoholic fatty liver disease (NAFLD), but lower cardiovascular risk. This case-control study tested the role of this polymorphism for tissue-specific insulin sensitivity during early course of diabetes.

Chronic stress targets mitochondrial respiratory efficiency in the skeletal muscle of C57BL/6 mice.

Episodes of chronic stress can result in psychic disorders like post-traumatic stress disorder, but also promote the development of metabolic syndrome and type 2 diabetes. We hypothesize that muscle, as main regulator of whole-body energy expenditure, is a central target of acute and adaptive molecular effects of stress in this context. Here, we investigate the immediate effect of a stress period on energy metabolism in Musculus gastrocnemius in our established C57BL/6 chronic variable stress (Cvs) mouse model.

Polymorphism Is Associated With Physical Activity-Mediated Metabolic Changes in Type 2 Diabetes.

Unlabelled: The rs540467 SNP in the gene, encoding a mitochondrial complex I subunit, has been shown to modulate adaptations to exercise training. Interaction effects with diabetes mellitus remain unclear. We assessed associations of habitual physical activity (PA) levels with metabolic variables and examined a possible modifying effect of the rs540467 SNP.

Long-term adjustment of hepatic lipid metabolism after chronic stress and the role of FGF21.

Chronic stress leads to post-traumatic stress disorder (PTSD) and metabolic disorders including fatty liver. We hypothesized that stress-induced molecular mechanisms alter energy metabolism, thereby promoting hepatic lipid accumulation even after a stress-free recovery period. In this context, we investigated fibroblast growth factor-21 (FGF21) as protective for energy and glucose homeostasis.

Isolation and Quality Control of Functional Mitochondria.

Even in times, when the study of mitochondria in their natural cellular context is becoming more and more popular, some scientific questions still require the preparation of isolated mitochondria. Numerous protocols are available being adapted for different cell or tissue types allowing isolation of "pure" mitochondria trying to preserve their "structural and functional" integrity. In this chapter, we intend to provide a more general framework introducing differential isopycnic density gradient centrifugation strategy with a special focus sensitizing for the specific challenges coming along with this method and how to obtain "functional," enriched, "intact" mitochondria.

Preparation of "Functional" Mitochondria: A Challenging Business.

As the powerhouse of the cell, mitochondria, plays a crucial role in many aspects of life, whereby mitochondrial dysfunctions are associated with pathogenesis of many diseases, like neurodegenerative diseases, obesity, cancer, and metabolic as well as cardiovascular disorders. Mitochondria analysis frequently starts with isolation and enrichment procedures, which have become increasingly important in biomedical research. Unfortunately, isolation procedures can easily cause changes in the structural integrity of mitochondria during in vitro handling having impact on their function.

Investigating the Adipose Tissue Secretome: A Protocol to Generate High-Quality Samples Appropriate for Comprehensive Proteomic Profiling.

In this chapter we describe in detail how to prepare a sample containing the complete set of secretion products from primary adipocytes, which are suitable for comprehensive and sensitive secretome analysis. The underlying protocol should be seen as starting point guiding through critical steps of the complex workflow of preperation of secretomes. For diverse research questions and in the context of different sample types used, the protocol has to be carefully adjusted in order to approximate to the real secretome.

Lipodystrophies-Disorders of the Fatty Tissue.

Lipodystrophies are a heterogeneous group of physiological changes characterized by a selective loss of fatty tissue. Here, no fat cells are present, either through lack of differentiation, loss of function or premature apoptosis. As a consequence, lipids can only be stored ectopically in non-adipocytes with the major health consequences as fatty liver and insulin resistance.

Association of cardiac autonomic dysfunction with higher levels of plasma lipid metabolites in recent-onset type 2 diabetes.

Aims/hypothesis: Emerging evidence suggests that in addition to hyperglycaemia, dyslipidaemia could represent a contributing pathogenetic factor to diabetic neuropathy, while obesity and insulin resistance play a role in the development of diabetic cardiac autonomic neuropathy (CAN) characterised by reduced heart rate variability (HRV), particularly in type 2 diabetes. We hypothesised that distinct lipid metabolites are associated with diminished HRV in recent-onset type 2 diabetes rather than type 1 diabetes.

Methods: We analysed 127 plasma lipid metabolites (11 acylcarnitines, 39 NEFA, 12 sphingomyelins (SMs), 56 phosphatidylcholines and nine lysophosphatidylcholines) using MS in participants from the German Diabetes Study baseline cohort recently diagnosed with type 1 (n = 100) and type 2 diabetes (n = 206).

Role of Patatin-Like Phospholipase Domain-Containing 3 Gene for Hepatic Lipid Content and Insulin Resistance in Diabetes.

Objective: The rs738409(G) single nucleotide polymorphism (SNP) in the patatin-like phospholipase domain-containing 3 () gene associates with increased risk and progression of nonalcoholic fatty liver disease (NAFLD). As the recently described severe insulin-resistant diabetes (SIRD) cluster specifically relates to NAFLD, this study examined whether this SNP differently associates with hepatic lipid content (hepatocellular lipids [HCL]) and insulin sensitivity in recent-onset diabetes.

Research Design And Methods: A total of 917 participants in the German Diabetes Study (GDS) underwent genotyping, hyperinsulinemic-euglycemic clamps with stable isotopic tracer dilution, and MRS.

The RabGAPs TBC1D1 and TBC1D4 Control Uptake of Long-Chain Fatty Acids Into Skeletal Muscle via Fatty Acid Transporter SLC27A4/FATP4.

The two closely related RabGTPase-activating proteins (RabGAPs) TBC1D1 and TBC1D4 play a crucial role in the regulation of GLUT4 translocation in response to insulin and contraction in skeletal muscle. In mice, deficiency in one or both RabGAPs leads to reduced insulin- and contraction-stimulated glucose uptake and to elevated fatty acid (FA) uptake and oxidation in both glycolytic and oxidative muscle fibers without altering mitochondrial copy number and the abundance of proteins for oxidative phosphorylation. Here we present evidence for a novel mechanism of skeletal muscle lipid utilization involving the two RabGAPs and the FA transporter SLC27A4/FATP4.

Physiological Disturbance in Fatty Liver Energy Metabolism Converges on IGFBP2 Abundance and Regulation in Mice and Men.

Fatty liver occurs from simple steatosis with accumulated hepatic lipids and hepatic insulin resistance to severe steatohepatitis, with aggravated lipid accumulation and systemic insulin resistance, but this progression is still poorly understood. Analyses of hepatic gene expression patterns from alb-SREBP-1c mice with moderate, or aP2-SREBP-1c mice with aggravated, hepatic lipid accumulation revealed IGFBP2 as key nodal molecule differing between moderate and aggravated fatty liver. Reduced IGFBP2 expression in aggravated fatty liver was paralleled with promoter hypermethylation, reduced hepatic IGFBP2 secretion and IGFBP2 circulating in plasma.

Rhein, a novel Histone Deacetylase (HDAC) inhibitor with antifibrotic potency in human myocardial fibrosis.

Although fibrosis depicts a reparative mechanism, maladaptation of the heart due to excessive production of extracellular matrix accelerates cardiac dysfunction. The anthraquinone Rhein was examined for its anti-fibrotic potency to mitigate cardiac fibroblast-to-myofibroblast transition (FMT). Primary human ventricular cardiac fibroblasts were subjected to hypoxia and characterized with proteomics, transcriptomics and cell functional techniques.

Fatty Liver Due to Increased Lipogenesis: Alterations in the Hepatic Peroxisomal Proteome.

In non-alcoholic fatty liver disease (NAFLD) caused by ectopic lipid accumulation, lipotoxicity is a crucial molecular risk factor. Mechanisms to eliminate lipid overflow can prevent the liver from functional complications. This may involve increased secretion of lipids or metabolic adaptation to ß-oxidation in lipid-degrading organelles such as mitochondria and peroxisomes.

Identification of the Secreted Proteins Originated from Primary Human Hepatocytes and HepG2 Cells.

The liver plays a pivotal role in whole-body carbohydrate, lipid, and protein metabolism. One of the key regulators of glucose and lipid metabolism are hepatokines, which are found among the liver secreted proteins, defined as liver secretome. To elucidate the composition of the human liver secretome and identify hepatokines in primary human hepatocytes (PHH), we conducted comprehensive protein profiling on conditioned medium (CM) of PHH.

The adipokine sFRP4 induces insulin resistance and lipogenesis in the liver.

Secreted frizzled-related protein (sFRP) 4 is an adipokine with increased expression in white adipose tissue from obese subjects with type 2 diabetes and non-alcoholic fatty liver disease (NAFLD). Yet, it is unknown whether sFRP4 action contributes to the development of these pathologies. Here, we determined whether sFRP4 expression in visceral fat associates with NAFLD and whether it directly interferes with insulin action and lipid and glucose metabolism in primary hepatocytes and myotubes.

Adipokinome Signatures in Obese Mouse Models Reflect Adipose Tissue Health and Are Associated with Serum Lipid Composition.

Adipocyte and hepatic lipid metabolism govern whole-body metabolic homeostasis, whereas a disbalance of de novo lipogenesis (DNL) in fat and liver might lead to obesity, with severe co-morbidities. Nevertheless, some obese people are metabolically healthy, but the "protective" mechanisms are not yet known in detail. Especially, the adipocyte-derived molecular mediators that indicate adipose functionality are poorly understood.

The natural history of classic galactosemia: lessons from the GalNet registry.

Background: Classic galactosemia is a rare inborn error of carbohydrate metabolism, caused by a severe deficiency of the enzyme galactose-1-phosphate uridylyltransferase (GALT). A galactose-restricted diet has proven to be very effective to treat the neonatal life-threatening manifestations and has been the cornerstone of treatment for this severe disease. However, burdensome complications occur despite a lifelong diet.

Exosomal proteins constitute an essential part of the human adipose tissue secretome.

Adipose tissue is an endocrine organ, secreting various adipokines, either directly or via extracellular vesicles, including exosomes. Exosomes are vesicles of 40-150 nm size that represent a novel concept of biomolecule release. We purified exosomes from isolated primary human preadipocytes differentiated to mature adipocytes.

Development of the Metabolic Syndrome: Study Design and Baseline Data of the Lufthansa Prevention Study (LUPS), A Prospective Observational Cohort Survey.

The (LUPS) study is a prospective observation of a healthy worker cohort to identify early changes in metabolism leading to the Metabolic Syndrome (MetS) and to analyze their relation to behavioral factors like nutrition, physical activity, psychological status, and to underlying genetic conditions. The LUPS study recruited a sample of 1.962 non-diabetic healthy adults between 25-60 years, employed at a flight base of Lufthansa Technik GmbH in Hamburg, Germany.

A variant of the glucose transporter gene SLC2A2 modifies the glycaemic response to metformin therapy in recently diagnosed type 2 diabetes.

Aims/hypothesis: The aim of this study was to investigate the modifying effect of the glucose transporter (GLUT2) gene SLC2A2 (rs8192675) variant on the glycaemic response to metformin in individuals recently diagnosed with type 2 diabetes.

Methods: Individuals with type 2 diabetes (n = 508) from the prospective German Diabetes Study (age [mean ± SD] 53 ± 10 years; 65% male; BMI 32 ± 6 kg/m, metformin use 57%) underwent detailed metabolic characterisation (hyperinsulinaemic-euglycaemic clamp, IVGTT) during the first year after diagnosis. Participants provided self-reported data from the time of diagnosis.

Insulin Resistance and Vulnerability to Cardiac Ischemia.

Hepatic and myocardial ectopic lipid deposition has been associated with insulin resistance (IR) and cardiovascular risk. Lipid overload promotes increased hepatic oxidative capacity, oxidative stress, and impaired mitochondrial efficiency, driving the progression of nonalcoholic fatty liver disease (NAFLD). We hypothesized that higher lipid availability promotes ischemia-induced cardiac dysfunction and decreases myocardial mitochondrial efficiency.