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Wronkowitz N.,Paul Langerhans Group for Integrative Physiology | Gorgens S.W.,Paul Langerhans Group for Integrative Physiology | Romacho T.,Paul Langerhans Group for Integrative Physiology | Villalobos L.A.,Autonomous University of Madrid | And 4 more authors.
Biochimica et Biophysica Acta - Molecular Basis of Disease | Year: 2014

DPP4 is an ubiquitously expressed cell-surface protease that is shedded to the circulation as soluble DPP4 (sDPP4). We recently identified sDPP4 as a novel adipokine potentially linking obesity to the metabolic syndrome. The aim of this study was to investigate direct effects of sDPP4 on human vascular smooth muscle cells (hVSMCs) and to identify responsible signaling pathways. Using physiological concentrations of sDPP4, we could observe a concentration-dependent activation of ERK1/2 (3-fold) after 6. h, which remained stable for up to 24. h. Additionally, sDPP4 treatment induced a 1.5-fold phosphorylation of the NF-κB subunit p65. In accordance with sDPP4-induced stress and inflammatory signaling, sDPP4 also stimulates hVSMC proliferation. Furthermore we could observe an increased expression and secretion of pro-inflammatory cytokines like interleukin (IL)-6, IL-8 and MCP-1 (2.5-, 2.4- and 1.5-fold, respectively) by the sDPP4 treatment. All direct effects of sDPP4 on signaling, proliferation and inflammation could completely be prevented by DPP4 inhibition. Bioinformatic analysis and signaling signature induced by sDPP4 suggest that sDPP4 might be an agonist for PAR2. After the silencing of PAR2, the sDPP4-induced ERK activation as well as the proliferation was totally abolished. Additionally, the sDPP4-induced upregulation of IL-6 and IL-8 could completely be prevented by the PAR2 silencing. In conclusion, we show for the first time that sDPP4 directly activates the MAPK and NF-κB signaling cascade involving PAR2 and resulting in the induction of inflammation and proliferation of hVSMC. Thus, our in vitro data might extend the current view of sDPP4 action and shed light on cardiovascular effects of DPP4-inhibitors. © 2014 Elsevier B.V.

Habich C.,Paul Langerhans Group for Integrative Physiology | Sell H.,Paul Langerhans Group for Integrative Physiology
Hormone Molecular Biology and Clinical Investigation | Year: 2015

Adipose tissue expansion is associated with adipocyte dysfunction and increased inflammatory processes. In the obese state, adipose tissue is characterized by an impaired intracellular stress defense system and dysbalanced heat shock response. Several members of the heat shock protein (HSP) family have been identified as novel adipokines released upon cellular stress, which might be a molecular link from adipose tissue inflammation to the cardiovascular system. Therefore, this review aims at summarizing and discussing our recent knowledge on HSPs in relation to obesity and their potential links to cardiovascular disease. Of particular importance/interest are two members of the HSP family, HSP60 and heme oxygenase 1 (HO-1), which have been well described as adipokines, and studied in the context of obesity and cardiovascular disease. HSP60 is regarded as a novel molecular link between adipose tissue inflammation and obesity-associated insulin resistance. The role of HO-1 induction in the obese state is well-documented, but a causal relationship between increased HO-1 levels and obesity-associated metabolic diseases is still controversial. Both HSP60 and HO-1 are also forthcoming targets for the treatment of cardiovascular disease, and the current knowledge will also be discussed in this review. © 2015 by De Gruyter.

Rohrborn D.,Paul Langerhans Group for Integrative Physiology | Eckel J.,Paul Langerhans Group for Integrative Physiology | Eckel J.,German Center for Diabetes Research | Sell H.,Paul Langerhans Group for Integrative Physiology
FEBS Letters | Year: 2014

Dipeptidyl peptidase 4 is an important drug target for diabetes and a novel adipokine. However, it is unknown how soluble DPP4 (sDPP4) is cleaved from the cell membrane and released into the circulation. We show here that MMP1, MMP2 and MMP14 are involved in DPP4 shedding from human vascular smooth muscle cells (SMC) and MMP9 from adipocytes. Hypoxia increased DPP4 shedding from SMC which is associated with increased mRNA expression of MMP1. Our data suggest that constitutive as well as hypoxia-induced DPP4 shedding occurs due to a complex interplay between different MMPs in cell type-specific manner. © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

Van Herpen N.A.,Maastricht University | Sell H.,Paul Langerhans Group for Integrative Physiology | Eckel J.,Paul Langerhans Group for Integrative Physiology | Schrauwen P.,Maastricht University | Mensink R.P.,Maastricht University
Hormone and Metabolic Research | Year: 2013

Obesity and insulin resistance are associated with low-grade systemic inflammation, which is related to increased concentrations of plasma FFAs, glucose, or insulin. Prolonged fasting induces insulin resistance due to elevated plasma FFAs, but is not accompanied by hyperinsulinemia or hyperglycemia. This makes it possible to study effects of physiologically increased FFA concentrations on inflammatory markers, when insulin and glucose concentrations are not increased. In random order, 10 healthy young lean men (mean BMI: 22.8 kg/m2) were fasted or fed in energy balance for 60 h with a 2-week wash-out period. Subjects stayed in a respiration chamber during the 60-h periods. Blood samples were taken after 12, 36, and 60 h. Then, a hyperinsulinemic-euglycemic clamp was performed. Fasting decreased insulin sensitivity by 45% and increased FFA concentrations 5-fold. Fasting did not change concentrations of the inflammatory cytokines TNF-α, IL-1β, IL-6 and IL-8, or of hs-CRP. Effects on vascular endothelial growth factor (VEGF) - which may positively relate to insulin resistance, and on chemerin and leptin - adipokines related to obesity, and obesity-related pathologies, were also studied. At t=60 h, VEGF concentrations were significantly increased during the fasted period (p<0.05). At the same time point, chemerin (p<0.01) and leptin (p<0.01) were significantly decreased after fasting. For leptin, this decrease was also significant after 36 h (p<0.01). Adiponectin levels remained unchanged. In healthy young lean men, fasting-induced increases in FFAs leading to insulin resistance do not cause changes in concentrations of the inflammatory cytokines. VEGF concentrations increased and those of chemerin decreased. © Georg Thieme Verlag KG Stuttgart · New York.

Gorgens S.W.,Paul Langerhans Group for Integrative Physiology | Eckardt K.,Paul Langerhans Group for Integrative Physiology | Elsen M.,Paul Langerhans Group for Integrative Physiology | Tennagels N.,Sanofi S.A. | And 2 more authors.
Biochemical Journal | Year: 2014

CHI3L1 (chitinase-3-like protein 1) is a glycoprotein consisting of 383 amino acids with a molecular mass of 40 kDa, and its serum level is elevated in inflammatory diseases. Although CHI3L1 is described as a biomarker of inflammation, the function of this protein is not completely understood. In the present study, we examined the regulation of CHI3L1 in primary human skeletal muscle cells. Moreover, we analysed potential autocrine effects of CHI3L1. We show that myotubes express CHI3L1 in a differentiation-dependent manner. Furthermore, proinflammatory cytokines up-regulate CHI3L1 expression (6-fold) and release (3-fold). Importantly, CHI3L1 treatment blocked TNFa (tumour necrosis factor a)-induced inflammation by inhibiting NF-?B (nuclear factor ?B) activation in skeletal muscle cells. We show that this effect is mediated via PAR2 (protease-activated receptor 2). In addition, CHI3L1 treatment diminished the TNFa-induced expression and secretion of IL (interleukin)-8, MCP1 (monocyte chemoattractant protein 1) and IL-6. In addition, impaired insulin action at the level of Akt and GSK3a/ß (glycogen synthase kinase 3a/ß) phosphorylation and insulin-stimulated glucose uptake was normalized by CHI3L1. In conclusion, the novel myokine CHI3L1, which is induced by pro-inflammatory cytokines, can counteract TNFa-mediated inflammation and insulin resistance in human skeletal muscle cells, potentially involving an auto-and/or para-crine mechanism. © The Authors Journal compilation © 2014 Biochemical Society.

Rohrborn D.,Paul Langerhans Group for Integrative Physiology | Wronkowitz N.,Paul Langerhans Group for Integrative Physiology | Eckel J.,Paul Langerhans Group for Integrative Physiology
Frontiers in Immunology | Year: 2015

Dipeptidyl-peptidase 4 (DPP4) is a glycoprotein of 110 kDa, which is ubiquitously expressed on the surface of a variety of cells. This exopeptidase selectively cleaves N-terminal dipeptides from a variety of substrates, including cytokines, growth factors, neuropeptides, and the incretin hormones. Expression of DPP4 is substantially dysregulated in a variety of disease states including inflammation, cancer, obesity, and diabetes. Since the incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide (GIP), are major regulators of post-prandial insulin secretion, inhibition of DPP4 by the gliptin family of drugs has gained considerable interest for the therapy of type 2 diabetic patients. In this review, we summarize the current knowledge on the DPP4-incretin axis and evaluate most recent findings on DPP4 inhibitors. Furthermore, DPP4 as a type II transmembrane protein is also known to be cleaved from the cell membrane involving different metalloproteases in a cell-type-specific manner. Circulating, soluble DPP4 has been identified as a new adipokine, which exerts both para- and endocrine effects. Recently, a novel receptor for soluble DPP4 has been identified, and data are accumulating that the adipokine-related effects of DPP4 may play an important role in the pathogenesis of cardiovascular disease. Importantly, circulating DPP4 is augmented in obese and type 2 diabetic subjects, and it may represent a molecular link between obesity and vascular dysfunction. A critical evaluation of the impact of circulating DPP4 is presented, and the potential role of DPP4 inhibition at this level is also discussed. © 2015 Röhrborn, Wronkowitz and Eckel.

Wronkowitz N.,Paul Langerhans Group for Integrative Physiology | Romacho T.,Paul Langerhans Group for Integrative Physiology | Sell H.,Paul Langerhans Group for Integrative Physiology | Eckel J.,Paul Langerhans Group for Integrative Physiology
Frontiers of Hormone Research | Year: 2014

Adipose tissue (AT) was long perceived as a passive lipid storage depot but it is now considered as an endocrine organ that produces a large number of mediators that affect metabolism, inflammation and coagulation. In obesity, the increased size of adipocytes and chronic low-grade inflammation within AT alter its normal physiological function. AT dysfunction results in altered production and secretion of adipokines, which in turn affect several tissues, e.g. the liver, skeletal muscles and vasculature, in a para- or endocrine manner. Numerous circulating proinflammatory mediators involved in the development of cardiovascular disease (CVD) are directly released from adipocytes, thereby linking obesity to an increased cardiovascular risk. In the current chapter, we focus, on the one hand, on a small selection of novel adipokines with a potentially strong link to CVD: soluble dipeptidyl peptidase-4, visfatin and lipocalin-2. On the other hand, we summarize the most recent findings on the novel cardioprotective adipokines omentin and apelin. © 2014 S. Karger AG, Basel.

Elsen M.,Paul Langerhans Group for Integrative Physiology | Raschke S.,Paul Langerhans Group for Integrative Physiology | Eckel J.,Paul Langerhans Group for Integrative Physiology
Journal of Endocrinology | Year: 2014

The discovery of irisin as an exercise-regulated myokine inducing browning of WAT has gained interest as a potential new strategy to combat obesity and its associated disorders, such as type 2 diabetes. However, there are inconsistencies regarding the relevance of irisin in humans. The regulation of FNDC5 mRNA expression by exercise and contraction could not be reproduced by a number of human studies using several exercise protocols and in vitro approaches. Furthermore, the nature of FNDC5 fragments and the presence of irisin in humans are questionable and probably contribute to conflicting data obtained with commercially available ELISA kits. Most importantly, the information regarding the concentration of circulating irisin in humans is not clear, as different studies using different kits measure irisin levels in a wide range. Data about the role of irisin in states of human obesity and metabolic diseases are conflicting and, in some cases, changes in irisin levels have been observed; they were only moderate in 10-20%. Independent of the presence and regulation of FNDC5/irisin in humans, the application of recombinant irisin could still represent a therapeutic strategy to fight obesity. However, the current data obtained from human cell models reveal that FNDC5/irisin has no effect on browning of the major WAT depots in humans and is likely to selectively target a small subpopulation of adipocytes, which are located in classical BAT regions, such as the supraclavicular adipose tissue. Thus, other candidates, such as BMP7 or CNPs, seem to be more prominent candidates as inducers of browning in humans. © 2014 Society for Endocrinology.

Romacho T.,Paul Langerhans Group for Integrative Physiology | Elsen M.,Paul Langerhans Group for Integrative Physiology | Rohrborn D.,Paul Langerhans Group for Integrative Physiology | Eckel J.,Paul Langerhans Group for Integrative Physiology | Eckel J.,German Center for Diabetes Research e.V.
Acta Physiologica | Year: 2014

The discovery of adipokines has revealed adipose tissue as a central node in the interorgan crosstalk network, which mediates the regulation of multiple organs and tissues. Adipose tissue is a true endocrine organ that produces and secretes a wide range of mediators regulating adipose tissue function in an auto-/paracrine manner and important distant targets, such as the liver, skeletal muscle, the pancreas and the cardiovascular system. In metabolic disorders such as obesity, enlargement of adipocytes leads to adipose tissue dysfunction and a shift in the secretory profile with an increased release of pro-inflammatory adipokines. Adipose tissue dysfunction has a central role in the development of insulin resistance, type 2 diabetes, and cardiovascular diseases. Besides the well-acknowledged role of adipokines in metabolic diseases, and the increasing number of adipokines being discovered in the last years, the mechanisms underlying the release of many adipokines from adipose tissue remain largely unknown. To combat metabolic diseases, it is crucial to better understand how adipokines can modulate adipose tissue growth and function. Therefore, we will focus on adipokines with a prominent role in auto-/paracrine crosstalk within the adipose tissue such as RBP4, HO-1, WISP2, SFRPs and chemerin. To depict the endocrine crosstalk between adipose tissue with skeletal muscle, the cardiovascular system and the pancreas, we will report the main findings regarding the direct effects of adiponectin, leptin, DPP4 and visfatin on skeletal muscle insulin resistance, cardiovascular function and β-cell growth and function. © 2014 Scandinavian Physiological Society. Published by John Wiley & Sons Ltd.

Elsen M.,Paul Langerhans Group for Integrative Physiology | Raschke S.,Paul Langerhans Group for Integrative Physiology | Tennagels N.,Sanofi S.A. | Schwahn U.,Sanofi S.A. | And 5 more authors.
American Journal of Physiology - Cell Physiology | Year: 2014

While white adipose tissue (AT is an energy storage depot, brown AT is specialized in energy dissipation. Uncoupling protein 1 (UCP1-expressing adipocytes with a different origin than classical brown adipocytes have been found in white AT. These "brite" (brown-in-white adipocytes may represent a therapeutic target to counteract obesity. Bone morphogenetic proteins (BMPs play a role in the regulation of adipogenesis. Based on studies with murine cells, BMP4 is assumed to induce stem cell commitment to the white adipocyte lineage, whereas BMP7 promotes brown adipogenesis. There is evidence for discrepancies between mouse and human AT. Therefore, we compared the effect of BMP4 and BMP7 on white-to-brown transition in primary human adipose stem cells (hASCs from subcutaneous AT. Long-term exposure of hASCs to recombinant BMP4 or BMP7 during differentiation increased adipogenesis, as determined by lipid accumulation and peroxisome proliferator-activated receptor-γ (PPARγ expression. Not only BMP7, but also BMP4, increased UCP1 expression in hASCs and decreased expression of the white-specific marker TCF21. The ability of hASCs to induce UCP1 in response to BMP4 and BMP7 markedly differed between donors and could be related to the expression of the brite marker CD137. However, mitochondrial content and oxygen consumption were not increased in hASCs challenged with BMP4 and BMP7. In conclusion, we showed for the first time that BMP4 has similar effects on white-to-brown transition as BMP7 in our human cell model. Thus the roles of BMP4 and BMP7 in adipogenesis cannot always be extrapolated from murine to human cell models. © 2014 the American Physiological Society.

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