Volume 4 | No. 7 | July 2015Original Research ArticleA major role of insulin in promoting obesity-associated adipose tissue inflammationDavid J. Pedersen, Adilson Guilherme, Laura V. Danai, Lauren Heyda, Anouch Matevossian, Jessica Cohen, Sarah M. Nicoloro, Juerg Straubhaar, Hye Lim Noh, DaeYoung Jung, Jason K. Kim, Michael P. Czech Abstract
Adipose tissue (AT) inflammation is associated with systemic insulin resistance and hyperinsulinemia in obese rodents and humans. A longstanding concept is that hyperinsulinemia may promote systemic insulin resistance through downregulation of its receptor on target tissues. Here we tested the novel hypothesis that insulin also impairs systemic insulin sensitivity by specifically enhancing adipose inflammation.
Circulating insulin levels were reduced by about 50% in diet-induced and genetically obese mice by treatments with diazoxide or streptozotocin, respectively. We then examined AT crown-like structures, macrophage markers and pro-inflammatory cytokine expression in AT. AT lipogenesis and systemic insulin sensitivity was also monitored. Conversely, insulin was infused into lean mice to determine its affects on the above parameters.
Lowering circulating insulin levels in obese mice by streptozotocin treatment decreased macrophage content in AT, enhancing insulin stimulated Akt phosphorylation and de novo lipogenesis (DNL). Moreover, responsiveness of blood glucose levels to injected insulin was improved by streptozotocin and diazoxide treatments of obese mice without changes in body weight. Remarkably, even in lean mice, infusion of insulin under constant euglycemic conditions stimulated expression of cytokines in AT. Consistent with these findings, insulin treatment of 3T3-L1 adipocytes caused a 10-fold increase in CCL2 mRNA levels within 6 h, which was blocked by the ERK inhibitor PD98059.
Taken together, these results indicate that obesity-associated hyperinsulinemia unexpectedly drives AT inflammation in obese mice, which in turn contributes to factors that suppress insulin-stimulated adipocyte DNL and systemic insulin sensitivity. [Hide abstract]
Original Research ArticleFibroblast growth factor 21 is elevated in metabolically unhealthy obesity and affects lipid deposition, adipogenesis, and adipokine secretion of human abdominal subcutaneous adipocytesLucia Berti, Martin Irmler, Marty Zdichavsky, Tobias Meile, Anja Böhm, Norbert Stefan, Andreas Fritsche, Johannes Beckers, Alfred Königsrainer, Hans-Ulrich Häring, Martin Hrabě de Angelis, Harald Staiger Abstract
Serum concentrations of the hepatokine fibroblast growth factor (FGF) 21 are elevated in obesity, type-2 diabetes, and the metabolic syndrome. We asked whether FGF21 levels differ between subjects with metabolically healthy vs. unhealthy obesity (MHO vs. MUHO), opening the possibility that FGF21 is a cross-talker between liver and adipose tissue in MUHO. Furthermore, we studied the effects of chronic FGF21 treatment on adipocyte differentiation, lipid storage, and adipokine secretion.
In 20 morbidly obese donors of abdominal subcutaneous fat biopsies discordant for their whole-body insulin sensitivity (hereby classified as MHO or MUHO subjects), serum FGF21 was quantified. The impact of chronic FGF21 treatment on differentiation, lipid accumulation, and adipokine release was assessed in isolated preadipocytes differentiated in vitro
Serum FGF21 concentrations were more than two-fold higher in MUHO as compared to MHO subjects (457 ± 378 vs. 211 ± 123 pg/mL; p < 0.05). FGF21 treatment of human preadipocytes for the entire differentiation period was modestly lipogenic (+15%; p < 0.05), reduced the expression of key adipogenic transcription factors (PPARG
, -15% and -40%, respectively; p < 0.01 both), reduced adiponectin expression (-20%; p < 0.05), markedly reduced adiponectin release (-60%; p < 0.01), and substantially increased leptin (+60%; p < 0.01) and interleukin-6 (+50%; p < 0.001) release.
The hepatokine FGF21 exerts weak lipogenic and anti-adipogenic actions and marked adiponectin-suppressive and leptin and interleukin-6 release-promoting effects in human differentiating preadipocytes. Together with the higher serum concentrations in MUHO subjects, our findings reveal FGF21 as a circulating factor promoting the development of metabolically unhealthy adipocytes. [Hide abstract]
Original Research ArticlePeroxisome proliferator-activated receptor alpha plays a crucial role in behavioral repetition and cognitive flexibility in miceGiuseppe D'Agostino, Claudia Cristiano, David J. Lyons, Rita Citraro, Emilio Russo, Carmen Avagliano, Roberto Russo, Giuseppina Mattace Raso, Rosaria Meli, Giovambattista De Sarro, Lora K. Heisler, Antonio Calignano Abstract
Nuclear peroxisome proliferator activated receptor-α (PPAR-α) plays a fundamental role in the regulation of lipid homeostasis and is the target of medications used to treat dyslipidemia. However, little is known about the role of PPAR-α in mouse behavior.
To investigate the function of Ppar-α
in cognitive functions, a behavioral phenotype analysis of mice with a targeted genetic disruption of Ppar-α
was performed in combination with neuroanatomical, biochemical and pharmacological manipulations. The therapeutic exploitability of Ppar-α was probed in mice using a pharmacological model of psychosis and a genetic model (BTBR T + tf/J
) exhibiting a high rate of repetitive behavior.
An unexpected role for brain Ppar-α
in the regulation of cognitive behavior in mice was revealed. Specifically, we observed that Ppar-α
genetic perturbation promotes rewiring of cortical and hippocampal regions and a behavioral phenotype of cognitive inflexibility, perseveration and blunted responses to psychomimetic drugs. Furthermore, we demonstrate that the antipsychotic and autism spectrum disorder (ASD) medication risperidone ameliorates the behavioral profile of Ppar-α
deficient mice. Importantly, we reveal that pharmacological Ppar-α agonist treatment in mice improves behavior in a pharmacological model of ketamine-induced behavioral dysinhibition and repetitive behavior in BTBR T + tf/J
Our data indicate that Ppar-α
is required for normal cognitive function and that pharmacological stimulation of Ppar-α improves cognitive function in pharmacological and genetic models of impaired cognitive function in mice. These results thereby reveal an unforeseen therapeutic application for a class of drugs currently in human use. [Hide abstract]
Brief CommunicationGenetic disruption of uncoupling protein 1 in mice renders brown adipose tissue a significant source of FGF21 secretionSusanne Keipert, Maria Kutschke, Daniel Lamp, Laura Brachthäuser, Frauke Neff, Carola W. Meyer, Rebecca Oelkrug, Alexei Kharitonenkov, Martin Jastroch Abstract
Circulating fibroblast growth factor 21 (FGF21) is an important auto- and endocrine player with beneficial metabolic effects on obesity and diabetes. In humans, thermogenic brown adipose tissue (BAT) was recently suggested as a source of FGF21 secretion during cold exposure. Here, we aim to clarify the role of UCP1 and ambient temperature in the regulation of FGF21 in mice.
Wildtype (WT) and UCP1-knockout (UCP1 KO) mice, the latter being devoid of BAT-derived non-shivering thermogenesis, were exposed to different housing temperatures. Plasma metabolites and FGF21 levels were determined, gene expression was analyzed by qPCR, and tissue histology was performed with adipose tissue.
At thermoneutrality, FGF21 gene expression and serum levels were not different between WT and UCP1 KO mice. Cold exposure led to highly increased FGF21 serum levels in UCP1 KO mice, which were reflected in increased FGF21 gene expression in adipose tissues but not in liver and skeletal muscle. Ex vivo
secretion assays revealed FGF21 release only from BAT, progressively increasing with decreasing ambient temperatures. In association with increased FGF21 serum levels in the UCP1 KO mouse, typical FGF21-related serum metabolites and inguinal white adipose tissue morphology and thermogenic gene expression were altered.
Here we show that the genetic ablation of UCP1 increases FGF21 gene expression in adipose tissue. The removal of adaptive nonshivering thermogenesis renders BAT a significant source of endogenous FGF21 under thermal stress. Thus, the thermogenic competence of BAT is not a requirement for FGF21 secretion. Notably, high endogenous FGF21 levels in UCP1-deficient models and subjects may confound pharmacological FGF21 treatments. [Hide abstract]
Brief CommunicationNotch intracellular domain overexpression in adipocytes confers lipodystrophy in miceDionysios V. Chartoumpekis, Dushani L. Palliyaguru, Nobunao Wakabayashi, Nicholas K.H. Khoo, Gabriele Schoiswohl, Robert M. O'Doherty, Thomas W. Kensler Abstract
The Notch family of intermembrane receptors is highly conserved across species and is involved in cell fate and lineage control. Previous in vitro
studies have shown that Notch may inhibit adipogenesis. Here we describe the role of Notch in adipose tissue by employing an in vivo
murine model which overexpresses Notch in adipose tissue.
Albino C57BL/6J RosaNICD/NICD
::Adipoq-Cre (Ad-NICD) male mice were generated to overexpress the Notch intracellular domain (NICD) specifically in adipocytes. Male RosaNICD/NICD
mice were used as controls. Mice were evaluated metabolically at the ages of 1 and 3 months by assessing body weights, serum metabolites, body composition (EchoMRI), glucose tolerance and insulin tolerance. Histological sections of adipose tissue depots as well as of liver were examined. The mRNA expression profile of genes involved in adipogenesis was analyzed by quantitative real-time PCR.
The Ad-NICD mice were heavier with significantly lower body fat mass compared to the controls. Small amounts of white adipose tissue could be seen in the 1-month old Ad-NICD mice, but was almost absent in the 3-months old mice. The Ad-NICD mice also had higher serum levels of glucose, insulin, triglyceride and non-esterified fatty acids. These differences were more prominent in the older (3-months) than in the younger (1-month) mice. The Ad-NICD mice also showed severe insulin resistance along with a steatotic liver. Gene expression analysis in the adipose tissue depots showed a significant repression of lipogenic (Fasn, Acacb) and adipogenic pathways (C/ebpα, C/ebpβ, Pparγ2, Srebf1).
Increased Notch signaling in adipocytes in mice results in blocked expansion of white adipose tissue which leads to ectopic accumulation of lipids and insulin resistance, thus to a lipodystrophic phenotype. These results suggest that further investigation of the role of Notch signaling in adipocytes could lead to the manipulation of this pathway for therapeutic interventions in metabolic disease. [Hide abstract]
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