Karen Ruschke

Serum Vaspin Concentrations in Human Obesity and Type 2 Diabetes

OBJECTIVE— Vaspin was identified as an adipokine with insulin-sensitizing effects, which is predominantly secreted from visceral adipose tissue in a rat model of type 2 diabetes. We have recently shown that vaspin mRNA expression in adipose tissue is related to parameters of obesity and glucose metabolism. However, the regulation of vaspin serum concentrations in human obesity and type 2 diabetes is unknown. RESEARCH DESIGN AND METHODS— For the measurement of vaspin serum concentrations, we developed an enzyme-linked immunosorbent assay (ELISA). Using this ELISA, we assessed circulating vaspin in a cross-sectional study of 187 subjects with a wide range of obesity, body fat distribution, insulin sensitivity, and glucose tolerance and in 60 individuals with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), or type 2 diabetes before and after a 4-week physical training program. RESULTS— Vaspin serum concentrations were significantly higher in female compared with male subjects. There was no difference in circulating vaspin between individuals with NGT and type 2 diabetes. In the normal glucose-tolerant group, circulating vaspin significantly correlated with BMI and insulin sensitivity. Moreover, physical training for 4 weeks resulted in significantly increased circulating vaspin levels. CONCLUSIONS— We found a sexual dimorphism in circulating vaspin. Elevated vaspin serum concentrations are associated with obesity and impaired insulin sensitivity, whereas type 2 diabetes seems to abrogate the correlation between increased circulating vaspin, higher body weight, and decreased insulin sensitivity. Low circulating vaspin correlates with a high fitness level, whereas physical training in untrained individuals causes increased vaspin serum concentrations.

Serum Progranulin Concentrations May Be Associated With Macrophage Infiltration Into Omental Adipose Tissue

OBJECTIVE—Progranulin is an important molecule in inflammatory response. Chronic inflammation is frequently associated with central obesity and associated disturbances; however, the role of circulating progranulin in human obesity, type 2 diabetes, and dyslipidemia is unknown. RESEARCH DESIGN AND METHODS—For the measurement of progranulin serum concentrations, we developed an enzyme-linked immunosorbent assay (ELISA). Using this ELISA, we assessed circulating progranulin in a cross-sectional study of 209 subjects with a wide range of obesity, body fat distribution, insulin sensitivity, and glucose tolerance and in 60 individuals with normal (NGT) or impaired (IGT) glucose tolerance or type 2 diabetes before and after a 4-week physical training program. Progranulin mRNA and protein expression was measured in paired samples of omental and subcutaneous adipose tissue (adipocytes and cells of the stromal vascular fraction) from 55 lean or obese individuals. Measurement of Erk activation and chemotactic activity induced by progranulin in vitro was performed using THP-1–based cell migration assays. RESULTS—Progranulin serum concentrations were significantly higher in individuals with type 2 diabetes compared with NGT and in obese subjects with predominant visceral fat accumulation. Circulating progranulin significantly correlates with BMI, macrophage infiltration in omental adipose tissue, C-reactive protein (CRP) serum concentrations, A1C values, and total cholesterol. Multivariable linear regression analyses revealed CRP levels as the strongest independent predictor of circulating progranulin. The extent of in vitro progranulin-mediated chemotaxis is similar to that of monocyte chemoattractant protein-1 but independent of Gα. Moreover, in type 2 diabetes, but not in IGT and NGT individuals, physical training for 4 weeks resulted in significantly decreased circulating progranulin levels. CONCLUSIONS—Elevated progranulin serum concentrations are associated with visceral obesity, elevated plasma glucose, and dyslipidemia. We identified progranulin as a novel marker of chronic inflammation in obesity and type 2 diabetes that closely reflects omental adipose tissue macrophage infiltration. Physical training significantly reduces elevated circulating progranulin in patients with type 2 diabetes.

Autocrine IGF-1 Action in Adipocytes Controls Systemic IGF-1 Concentrations and Growth

OBJECTIVE—IGF-1 and the IGF-1 receptor (IGF-1R) have been implicated in the regulation of adipocyte differentiation and lipid accumulation in vitro. RESEARCH DESIGN AND METHODS—To investigate the role of IGF-1 receptor in vivo, we have inactivated the Igf-1r gene in adipose tissue (IGF-1RaP2Cre mice) using conditional gene targeting strategies. RESULTS—Conditional IGF-1R inactivation resulted in increased adipose tissue mass with a predominantly increased lipid accumulation in epigonadal fat pads. However, insulin-stimulated glucose uptake into adipocytes was unaffected by the deletion of the IGF-1R. Surprisingly, IGF-1RaP2Cre mice exhibited markedly increased somatic growth in the presence of elevated IGF-1 serum concentrations, and IGF-1 mRNA expression was significantly increased in liver and adipose tissue. IGF-1 stimulation of wild-type adipocytes significantly decreased IGF-1 mRNA expression, whereas the opposite effect was observed in IGF-1R–deficient adipocytes. CONCLUSIONS—IGF-1R signaling in adipocytes does not appear to be crucial for the development and differentiation of adipose tissue in vivo, but we identified a negative IGF-1R–mediated feedback mechanism of IGF-1 on its own gene expression in adipocytes, indicating an unexpected role for adipose tissue IGF-1 signaling in the regulation of IGF-1 serum concentrations in control of somatic growth.

Gene expression of PPARγ and PGC-1α in human omental and subcutaneous adipose tissues is related to insulin resistance markers and mediates beneficial effects of physical training

OBJECTIVE Obesity and type 2 diabetes (T2D) are reaching epidemic proportions in Western societies, and they contribute to substantial morbidity and mortality. The peroxisome proliferator-activated receptor gamma (PPARgamma) and PPARgamma coactivator-1alpha (PGC-1alpha) system plays an important role in the regulation of efficient energy utilization and oxidative phosphorylation, both of which are decreased in obesity and insulin resistance. DESIGN AND METHODS We measured the metabolic parameters and the expression of PPARgamma and PGC-1alpha mRNA using quantitative real-time PCR in omental and subcutaneous (SC) adipose tissues in an observational study of 153 individuals as well as in SC fat and skeletal muscle in an interventional study of 60 subjects (20 each with normal glucose tolerance, impaired glucose tolerance, and T2D) before and after intensive physical training for 4 weeks. RESULTS PPARgamma and PGC-1alpha mRNA expression in both fat depots as well as in skeletal muscle is associated with markers of insulin resistance and cardiovascular risk. PGC-1alpha mRNA expression is significantly higher in SC fat than in omental fat, whereas PPARgamma mRNA expression is not significantly different between these fat depots. Skeletal muscle and SC fat PPARgamma and PGC-1alpha mRNA expression increased significantly in response to physical training. CONCLUSIONS Gene expression of PPARgamma and PGC-1alpha in human adipose tissue is related to markers of insulin resistance and cardiovascular risk. Increased muscle and adipose tissue PPARgamma and PGC-1alpha expression in response to physical training may mediate the beneficial effects of exercise on insulin sensitivity.

Adipose Tissue Expression and Genetic Variants of the Bone Morphogenetic Protein Receptor 1A Gene (BMPR1A) Are Associated With Human Obesity

OBJECTIVE Members of the family of bone morphogenetic proteins (BMPs) are important regulators of adipogenesis. We examined the role of the BMP receptor 1A gene (BMPR1A) in the pathophysiology of human obesity. RESEARCH DESIGN AND METHODS We measured BMPR1A mRNA expression in paired samples of visceral and subcutaneous adipose tissue from 297 subjects and sequenced the BMPR1A in 48 nonrelated white subjects. Twenty-one representative variants including HapMap tagging single nucleotide polymorphisms (SNPs) were then genotyped for association studies in German whites (n = 1,907). For replication analyses, we used a population of Sorbs from Germany (n = 900) and German childhood cohorts (n = 1,029 schoolchildren and 270 obese children). RESULTS mRNA expression of the BMPR1A was significantly increased in both visceral and subcutaneous adipose tissue of overweight and obese subjects compared with lean subjects (P < 0.05). In a case-control study, four SNPs (rs7095025, rs11202222, rs10788528, and rs7922846) were nominally associated with obesity (adjusted P < 0.05). For three SNPs (rs7095025, rs11202222, and rs10788528), the association with obesity was confirmed in the independent cohort of Sorbs (adjusted P < 0.005). Consistent with this, BMPR1A SNPs were nominally associated with obesity-related quantitative traits in nondiabetic subjects in both adult cohorts. Furthermore, homozygous carriers of the obesity risk alleles had higher BMPR1A mRNA expression in fat than noncarriers. CONCLUSIONS Our data suggest that genetic variation in the BMPR1A may play a role in the pathophysiology of human obesity, possibly mediated through effects on mRNA expression.

NSCL-1 and NSCL-2 synergistically determine the fate of GnRH-1 neurons and control necdin gene expression

To study the role of the bHLH genes NSCL‐1 and NSCL‐2 in the development of GnRH‐1 neurons, we have generated compound mutant mice. Mutant animals die at birth and show a virtually complete absence of GnRH‐1 neurons in the posterior parts of the brain at E18.5 and an aberrant morphology of the remaining GnRH‐1 neurons in the anterior parts of the brain indicating that NSCL‐1 and NSCL‐2 might concomitantly control differentiation/migration of GnRH‐1 neurons in a cell autonomous manner. To gain further insights into this process, we screened for NSCL target genes using DNA array hybridization and detected necdin, which is deleted in the human Prader–Willi syndrome phenotypically resembling the NSCL‐2 mutation. Using chromatin immunoprecipitation and site‐directed mutagenesis of the necdin promoter, we demonstrate that NSCLs together with additional cofactors directly control transcription of the necdin gene. NSCL‐dependent control of necdin expression might be instrumental for proper neuronal cell differentiation and enable GnRH‐1 neurons to migrate.

The ARF-like GTPase ARFRP1 is essential for lipid droplet growth and is involved in the regulation of lipolysis.

ABSTRACT ADP-ribosylation factor (ARF)-related protein 1 (ARFRP1) is a GTPase regulating protein trafficking between intracellular organelles. Here we show that mice lacking Arfrp1 in adipocytes (Arfrp1ad−/−) are lipodystrophic due to a defective lipid droplet formation in adipose cells. Ratios of mono-, di-, and triacylglycerol, as well as the fatty acid composition of triglycerides, were unaltered. Lipid droplets of brown adipocytes of Arfrp1ad−/− mice were considerably smaller and exhibited ultrastructural alterations, such as a disturbed interaction of small lipid-loaded particles with the larger droplets, suggesting that ARFRP1 mediates the transfer of newly formed small lipid particles to the large storage droplets. SNAP23 (synaptosomal-associated protein of 23 kDa) associated with small lipid droplets of control adipocytes but was located predominantly in the cytosol of Arfrp1ad−/− adipocytes, suggesting that lipid droplet growth is defective in Arfrp1ad−/− mice. In addition, levels of phosphorylated hormone-sensitive lipase (HSL) were elevated, and association of adipocyte triglyceride lipase (ATGL) with lipid droplets was enhanced in brown adipose tissue from Arfrp1ad−/− mice. Accordingly, basal lipolysis was increased after knockdown of Arfrp1 in 3T3-L1 adipocytes. The data indicate that disruption of ARFRP1 prevents the normal enlargement of lipid droplets and produces an activation of lipolysis.

Defective peripheral nerve development is linked to abnormal architecture and metabolic activity of adipose tissue in Nscl-2 mutant mice.

Background In mammals the interplay between the peripheral nervous system (PNS) and adipose tissue is widely unexplored. We have employed mice, which develop an adult onset of obesity due to the lack the neuronal specific transcription factor Nscl-2 to investigate the interplay between the nervous system and white adipose tissue (WAT). Methodology Changes in the architecture and innervation of WAT were compared between wildtype, Nscl2−/−, ob/ob and Nscl2−/−//ob/ob mice using morphological methods, immunohistochemistry and flow cytometry. Metabolic alterations in mutant mice and in isolated cells were investigated under basal and stimulated conditions. Principal Findings We found that Nscl-2 mutant mice show a massive reduction of innervation of white epididymal and paired subcutaneous inguinal fat tissue including sensory and autonomic nerves as demonstrated by peripherin and neurofilament staining. Reduction of innervation went along with defects in the formation of the microvasculature, accumulation of cells of the macrophage/preadipocyte lineage, a bimodal distribution of the size of fat cells, and metabolic defects of isolated adipocytes. Despite a relative insulin resistance of white adipose tissue and isolated Nscl-2 mutant adipocytes the serum level of insulin in Nscl-2 mutant mice was only slightly increased. Conclusions We conclude that the reduction of the innervation and vascularization of WAT in Nscl-2 mutant mice leads to the increase of preadipocyte/macrophage-like cells, a bimodal distribution of the size of adipocytes in WAT and an altered metabolic activity of adipocytes.

Functional regulation of YAP mechanosensitive transcriptional coactivator by Focused Low-Intensity Pulsed Ultrasound (FLIPUS) enhances proliferation of murine mesenchymal precursors

Yes-associated protein (YAP) acts as a mechanotransducer in determining the cell fate of murine C2C12 mesenchymal precursors as investigated after stimulation with ultrasound. We applied Focused Low-Intensity Pulsed Ultrasound (FLIPUS) at a sound frequency of 3.6 MHz, 100 Hz pulse repetition frequency (PRF), 27.8% duty cycle (DC), and 44.5 mW/cm2 acoustic intensity ISATA for 5 minutes and evaluated early cellular responses. FLIPUS decreased the level of phosphorylated YAP on Serine 127, leading to higher levels of active YAP in the nucleus. This in turn enhanced the expression of YAP-target genes associated with actin nucleation and stabilization, cytokinesis, and cell cycle progression. FLIPUS enhanced proliferation of C2C12 cells, whereas silencing of YAP expression abolished the beneficial effects of ultrasound. The expression of the transcription factor MyoD, defining cellular myogenic differentiation, was inhibited by mechanical stimulation. This study shows that ultrasound exposure regulates YAP functioning, which in turn improves the cell proliferative potential, critical for tissue regeneration process.