@article{FeddersMuenznerWeberetal.2021, author = {Fedders, Ronja and Muenzner, Matthias and Weber, Pamela and Sommerfeld, Manuela and Knauer, Miriam and Kedziora, Sarah and Kast, Naomi and Heidenreich, Steffi and Raila, Jens and Weger, Stefan and Henze, Andrea and Schupp, Michael}, title = {Liver-secreted RBP4 does not impair glucose homeostasis in mice}, series = {The journal of biological chemistry}, volume = {293}, journal = {The journal of biological chemistry}, number = {39}, publisher = {American Society for Biochemistry and Molecular Biology}, address = {Bethesda}, issn = {1083-351X}, doi = {10.1074/jbc.RA118.004294}, pages = {15269 -- 15276}, year = {2021}, abstract = {Retinol-binding protein 4 (RBP4) is the major transport protein for retinol in blood. Recent evidence from genetic mouse models shows that circulating RBP4 derives exclusively from hepatocytes. Because RBP4 is elevated in obesity and associates with the development of glucose intolerance and insulin resistance, we tested whether a liver-specific overexpression of RBP4 in mice impairs glucose homeostasis. We used adeno-associated viruses (AAV) that contain a highly liver-specific promoter to drive expression of murine RBP4 in livers of adult mice. The resulting increase in serum RBP4 levels in these mice was comparable with elevated levels that were reported in obesity. Surprisingly, we found that increasing circulating RBP4 had no effect on glucose homeostasis. Also during a high-fat diet challenge, elevated levels of RBP4 in the circulation failed to aggravate the worsening of systemic parameters of glucose and energy homeostasis. These findings show that liver-secreted RBP4 does not impair glucose homeostasis. We conclude that a modest increase of its circulating levels in mice, as observed in the obese, insulin-resistant state, is unlikely to be a causative factor for impaired glucose homeostasis.}, language = {en} } @misc{KrsticReinischSchuppetal.2018, author = {Krstic, Jelena and Reinisch, Isabel and Schupp, Michael and Schulz, Tim Julius and Prokesch, Andreas}, title = {p53 functions in adipose tissue metabolism and homeostasis}, series = {International journal of molecular sciences}, volume = {19}, journal = {International journal of molecular sciences}, number = {9}, publisher = {MDPI}, address = {Basel}, issn = {1422-0067}, doi = {10.3390/ijms19092622}, pages = {21}, year = {2018}, abstract = {As a tumor suppressor and the most frequently mutated gene in cancer, p53 is among the best-described molecules in medical research. As cancer is in most cases an age-related disease, it seems paradoxical that p53 is so strongly conserved from early multicellular organisms to humans. A function not directly related to tumor suppression, such as the regulation of metabolism in nontransformed cells, could explain this selective pressure. While this role of p53 in cellular metabolism is gradually emerging, it is imperative to dissect the tissue-and cell-specific actions of p53 and its downstream signaling pathways. In this review, we focus on studies reporting p53's impact on adipocyte development, function, and maintenance, as well as the causes and consequences of altered p53 levels in white and brown adipose tissue (AT) with respect to systemic energy homeostasis. While whole body p53 knockout mice gain less weight and fat mass under a high-fat diet owing to increased energy expenditure, modifying p53 expression specifically in adipocytes yields more refined insights: (1) p53 is a negative regulator of in vitro adipogenesis; (2) p53 levels in white AT are increased in diet-induced and genetic obesity mouse models and in obese humans; (3) functionally, elevated p53 in white AT increases senescence and chronic inflammation, aggravating systemic insulin resistance; (4) p53 is not required for normal development of brown AT; and (5) when p53 is activated in brown AT in mice fed a high-fat diet, it increases brown AT temperature and brown AT marker gene expression, thereby contributing to reduced fat mass accumulation. In addition, p53 is increasingly being recognized as crucial player in nutrient sensing pathways. Hence, despite existence of contradictory findings and a varying density of evidence, several functions of p53 in adipocytes and ATs have been emerging, positioning p53 as an essential regulatory hub in ATs. Future studies need to make use of more sophisticated in vivo model systems and should identify an AT-specific set of p53 target genes and downstream pathways upon different (nutrient) challenges to identify novel therapeutic targets to curb metabolic diseases}, language = {en} } @misc{KrsticGalhuberSchulzetal.2018, author = {Krstic, Jelena and Galhuber, Markus and Schulz, Tim Julius and Schupp, Michael and Prokesch, Andreas}, title = {p53 as a dichotomous regulator of liver disease}, series = {International journal of molecular sciences}, volume = {19}, journal = {International journal of molecular sciences}, number = {3}, publisher = {MDPI}, address = {Basel}, issn = {1422-0067}, doi = {10.3390/ijms19030921}, pages = {23}, year = {2018}, abstract = {Lifestyle-related disorders, such as the metabolic syndrome, have become a primary risk factor for the development of liver pathologies that can progress from hepatic steatosis, hepatic insulin resistance, steatohepatitis, fibrosis and cirrhosis, to the most severe condition of hepatocellular carcinoma (HCC). While the prevalence of liver pathologies is steadily increasing in modern societies, there are currently no approved drugs other than chemotherapeutic intervention in late stage HCC. Hence, there is a pressing need to identify and investigate causative molecular pathways that can yield new therapeutic avenues. The transcription factor p53 is well established as a tumor suppressor and has recently been described as a central metabolic player both in physiological and pathological settings. Given that liver is a dynamic tissue with direct exposition to ingested nutrients, hepatic p53, by integrating cellular stress response, metabolism and cell cycle regulation, has emerged as an important regulator of liver homeostasis and dysfunction. The underlying evidence is reviewed herein, with a focus on clinical data and animal studies that highlight a direct influence of p53 activity on different stages of liver diseases. Based on current literature showing that activation of p53 signaling can either attenuate or fuel liver disease, we herein discuss the hypothesis that, while hyper-activation or loss of function can cause disease, moderate induction of hepatic p53 within physiological margins could be beneficial in the prevention and treatment of liver pathologies. Hence, stimuli that lead to a moderate and temporary p53 activation could present new therapeutic approaches through several entry points in the cascade from hepatic steatosis to HCC.}, language = {en} } @misc{KrsticGalhuberSchulzetal.2018, author = {Krstic, Jelena and Galhuber, Markus and Schulz, Tim Julius and Schupp, Michael and Prokesch, Andreas}, title = {p53 as a dichotomous regulator of liver disease}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {963}, issn = {1866-8372}, doi = {10.25932/publishup-46812}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-468127}, pages = {25}, year = {2018}, abstract = {Lifestyle-related disorders, such as the metabolic syndrome, have become a primary risk factor for the development of liver pathologies that can progress from hepatic steatosis, hepatic insulin resistance, steatohepatitis, fibrosis and cirrhosis, to the most severe condition of hepatocellular carcinoma (HCC). While the prevalence of liver pathologies is steadily increasing in modern societies, there are currently no approved drugs other than chemotherapeutic intervention in late stage HCC. Hence, there is a pressing need to identify and investigate causative molecular pathways that can yield new therapeutic avenues. The transcription factor p53 is well established as a tumor suppressor and has recently been described as a central metabolic player both in physiological and pathological settings. Given that liver is a dynamic tissue with direct exposition to ingested nutrients, hepatic p53, by integrating cellular stress response, metabolism and cell cycle regulation, has emerged as an important regulator of liver homeostasis and dysfunction. The underlying evidence is reviewed herein, with a focus on clinical data and animal studies that highlight a direct influence of p53 activity on different stages of liver diseases. Based on current literature showing that activation of p53 signaling can either attenuate or fuel liver disease, we herein discuss the hypothesis that, while hyper-activation or loss of function can cause disease, moderate induction of hepatic p53 within physiological margins could be beneficial in the prevention and treatment of liver pathologies. Hence, stimuli that lead to a moderate and temporary p53 activation could present new therapeutic approaches through several entry points in the cascade from hepatic steatosis to HCC.}, language = {en} } @misc{KrsticReinischSchuppetal.2018, author = {Krstic, Jelena and Reinisch, Isabel and Schupp, Michael and Schulz, Tim Julius and Prokesch, Andreas}, title = {p53 functions in adipose tissue metabolism and homeostasis}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1047}, issn = {1866-8372}, doi = {10.25932/publishup-46906}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-469069}, pages = {21}, year = {2018}, abstract = {As a tumor suppressor and the most frequently mutated gene in cancer, p53 is among the best-described molecules in medical research. As cancer is in most cases an age-related disease, it seems paradoxical that p53 is so strongly conserved from early multicellular organisms to humans. A function not directly related to tumor suppression, such as the regulation of metabolism in nontransformed cells, could explain this selective pressure. While this role of p53 in cellular metabolism is gradually emerging, it is imperative to dissect the tissue-and cell-specific actions of p53 and its downstream signaling pathways. In this review, we focus on studies reporting p53's impact on adipocyte development, function, and maintenance, as well as the causes and consequences of altered p53 levels in white and brown adipose tissue (AT) with respect to systemic energy homeostasis. While whole body p53 knockout mice gain less weight and fat mass under a high-fat diet owing to increased energy expenditure, modifying p53 expression specifically in adipocytes yields more refined insights: (1) p53 is a negative regulator of in vitro adipogenesis; (2) p53 levels in white AT are increased in diet-induced and genetic obesity mouse models and in obese humans; (3) functionally, elevated p53 in white AT increases senescence and chronic inflammation, aggravating systemic insulin resistance; (4) p53 is not required for normal development of brown AT; and (5) when p53 is activated in brown AT in mice fed a high-fat diet, it increases brown AT temperature and brown AT marker gene expression, thereby contributing to reduced fat mass accumulation. In addition, p53 is increasingly being recognized as crucial player in nutrient sensing pathways. Hence, despite existence of contradictory findings and a varying density of evidence, several functions of p53 in adipocytes and ATs have been emerging, positioning p53 as an essential regulatory hub in ATs. Future studies need to make use of more sophisticated in vivo model systems and should identify an AT-specific set of p53 target genes and downstream pathways upon different (nutrient) challenges to identify novel therapeutic targets to curb metabolic diseases.}, language = {en} } @article{HesseJaschkeKanzleiteretal.2012, author = {Hesse, Deike and Jaschke, Alexander and Kanzleiter, Timo and Witte, Nicole and Augustin, Robert and Hommel, Angela and P{\"u}schel, Gerhard Paul and Petzke, Klaus-J{\"u}rgen and Joost, Hans-Georg and Schupp, Michael and Sch{\"u}rmann, Annette}, title = {GTPase ARFRP1 is essential for normal hepatic glycogen storage and insulin-like growth factor 1 secretion}, series = {Molecular and cellular biology}, volume = {32}, journal = {Molecular and cellular biology}, number = {21}, publisher = {American Society for Microbiology}, address = {Washington}, issn = {0270-7306}, doi = {10.1128/MCB.00522-12}, pages = {4363 -- 4374}, year = {2012}, abstract = {The GTPase ADP-ribosylation factor-related protein 1 (ARFRP1) is located at the trans-Golgi compartment and regulates the recruitment of Arf-like 1 (ARL1) and its effector golgin-245 to this compartment. Here, we show that liver-specific knockout of Arfrp1 in the mouse (Arfrp1(liv-/-)) resulted in early growth retardation, which was associated with reduced hepatic insulin-like growth factor 1 (IGF1) secretion. Accordingly, suppression of Arfrp1 in primary hepatocytes resulted in a significant reduction of IGF1 release. However, the hepatic secretion of IGF-binding protein 2 (IGFBP2) was not affected in the absence of ARFRP1. In addition, Arfrp1(liv-/-) mice exhibited decreased glucose transport into the liver, leading to a 50\% reduction of glycogen stores as well as a marked retardation of glycogen storage after fasting and refeeding. These abnormalities in glucose metabolism were attributable to reduced protein levels and intracellular retention of the glucose transporter GLUT2 in Arfrp1(liv-/-) livers. As a consequence of impaired glucose uptake into the liver, the expression levels of carbohydrate response element binding protein (ChREBP), a transcription factor regulated by glucose concentration, and its target genes (glucokinase and pyruvate kinase) were markedly reduced. Our data indicate that ARFRP1 in the liver is involved in the regulation of IGF1 secretion and GLUT2 sorting and is thereby essential for normal growth and glycogen storage.}, language = {en} } @article{NeuschaeferRubeLieskeKunaetal.2014, author = {Neuschaefer-Rube, Frank and Lieske, Stefanie and Kuna, Manuela and Henkel, Janin and Perry, Rachel J. and Erion, Derek M. and Pesta, Dominik and Willmes, Diana M. and Brachs, Sebastian and von Loeffelholz, Christian and Tolkachov, Alexander and Schupp, Michael and Pathe-Neuschaefer-Rube, Andrea and Pfeiffer, Andreas F. H. and Shulman, Gerald I. and P{\"u}schel, Gerhard Paul and Birkenfeld, Andreas L.}, title = {The mammalian INDY homolog is induced by CREB in a rat model of type 2 diabetes}, series = {Diabetes : a journal of the American Diabetes Association}, volume = {63}, journal = {Diabetes : a journal of the American Diabetes Association}, number = {3}, publisher = {American Diabetes Association}, address = {Alexandria}, issn = {0012-1797}, pages = {1048 -- 1057}, year = {2014}, language = {en} } @article{MuenznerTuviaDeutschmannetal.2013, author = {M{\"u}nzner, Matthias and Tuvia, Neta and Deutschmann, Claudia and Witte, Nicole and Tolkachov, Alexander and Valai, Atijeh and Henze, Andrea and Sander, Leif E. and Raila, Jens and Schupp, Michael}, title = {Retinol-binding protein 4 and its membrane receptor STRA6 control adipogenesis by regulating cellular retinoid homeostasis and retinoic acid receptor alpha activity}, series = {Molecular and cellular biology}, volume = {33}, journal = {Molecular and cellular biology}, number = {20}, publisher = {American Society for Microbiology}, address = {Washington}, issn = {0270-7306}, doi = {10.1128/MCB.00221-13}, pages = {4068 -- 4082}, year = {2013}, abstract = {Retinoids are vitamin A (retinol) derivatives and complex regulators of adipogenesis by activating specific nuclear receptors, including the retinoic acid receptor (RAR) and retinoid X receptor (RXR). Circulating retinol-binding protein 4 (RBP4) and its membrane receptor STRA6 coordinate cellular retinol uptake. It is unknown whether retinol levels and the activity of RAR and RXR in adipocyte precursors are linked via RBP4/STRA6. Here, we show that STRA6 is expressed in precursor cells and, dictated by the apo-and holo-RBP4 isoforms, mediates bidirectional retinol transport that controls RAR alpha activity and subsequent adipocyte differentiation. Mobilization of retinoid stores in mice by inducing RBP4 secretion from the liver activated RAR alpha signaling in the precursor cell containing the stromal-vascular fraction of adipose tissue. Retinol-loaded holo-RBP4 blocked adipocyte differentiation of cultured precursors by activating RAR alpha. Remarkably, retinol-free apo-RBP4 triggered retinol efflux that reduced cellular retinoids, RAR alpha activity, and target gene expression and enhanced adipogenesis synergistically with ectopic STRA6. Thus, STRA6 in adipocyte precursor cells links nuclear RAR alpha activity to the circulating RBP4 isoforms, whose ratio in obese mice was shifted toward limiting the adipogenic potential of their precursors. This novel cross talk identifies a retinoldependent metabolic function of RBP4 that may have important implications for the treatment of obesity.}, language = {en} }