Taken together, our data suggest that resveratrol influences adipose tissue mass and function in a way that may positively interfere with the development of obesity-related comorbidities. Thus, our findings open up the new perspective that resveratrol-induced intracellular pathways could be a target for prevention or treatment of obesity-associated endocrine and metabolic adverse effects.

The obesity-associated inflammation of white adipose tissue (WAT) is one of the factors leading to the development of related diseases such as insulin resistance and liver steatosis. Recently, microRNAs (miRNAs) were identified as important regulators of WAT functions. Herein, we cultured human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes with macrophage-conditioned medium (MacCM) and performed an Affimetrix miRNA array to identify miRNAs differentially expressed under inflammatory conditions. We identified 24 miRNAs differentially expressed upon inflammation in human adipocytes and miR-146a was the most up-regulated miRNA species. In subcutaneous WAT, miR-146a was elevated in both human and murine obesity. Transfection of miR-146a mimics prevented the MacCM-induced inflammatory response in SGBS adipocytes as seen by reduced levels of IL-8 and MCP-1 mRNA and protein. We identified IRAK1 and TRAF6 as targets of miR-146a in human adipocytes and detected a reduced inflammation-induced activation of JNK and p38 upon miR-146a transfection. Taken together, we could show that miR-146a reduces the inflammatory response in human adipocytes. In a negative feedback loop miR-146a might contribute to the regulation of inflammatory processes in WAT and possibly prevent an overwhelming inflammatory response.

Variants in the fat mass- and obesity-associated (FTO) gene are associated with obesity and body fat mass in genome-wide association studies. However, the mechanism by which FTO predisposes individuals to obesity is not clear so far. First mechanistic evidence was shown in Fto-negative mice. These mice are resistant to obesity due to enhanced energy expenditure, whereas the mass of brown adipose tissue remains unchanged. We hypothesize that FTO is involved in the induction of white adipose tissue browning, which leads to mitochondrial uncoupling and increases energy expenditure. Uncoupling protein 1 (Ucp-1) was significantly higher expressed in both gonadal and inguinal adipose depots of Fto(-/-) compared with Fto(+/+) littermates accompanied by the appearance of multivacuolar, Ucp-1-positive adipocytes in these tissues. By using lentiviral short hairpin RNA constructs, we established FTO-deficient human preadipocytes and adipocytes and analyzed key metabolic processes. FTO-deficient adipocytes showed an adipogenic differentiation rate comparable with control cells but exhibited a reduced de novo lipogenesis despite unchanged glucose uptake. In agreement with the mouse data, FTO-deficient adipocytes exhibited 4-fold higher expression of UCP-1 in mitochondria compared with control cells. The up-regulation of UCP-1 in FTO-deficient adipocytes resulted in enhanced mitochondrial uncoupling. We conclude that FTO deficiency leads to the induction of a brown adipocyte phenotype, thereby enhancing energy expenditure. Further understanding of the signaling pathway connecting FTO with UCP-1 expression might lead to new options for obesity and overweight treatment.

ObjectiveIn rodents and humans, besides brown adipose tissue (BAT), islands of thermogenic adipocytes, termed “brite” (brown-in-white) or beige adipocytes, emerge within white adipose tissue (WAT) after cold exposure or β3-adrenoceptor stimulation, which may protect from obesity and associated diseases. microRNAs are novel modulators of adipose tissue development and function. The purpose of this work was to characterize the role of microRNAs in the control of brite adipocyte formation.Methods/ResultsUsing human multipotent adipose derived stem cells, we identified miR-125b-5p as downregulated upon brite adipocyte formation. In humans and rodents, miR-125b-5p expression was lower in BAT than in WAT. In vitro, overexpression and knockdown of miR-125b-5p decreased and increased mitochondrial biogenesis, respectively. In vivo, miR-125b-5p levels were downregulated in subcutaneous WAT and interscapular BAT upon β3-adrenergic receptor stimulation. Injections of an miR-125b-5p mimic and LNA inhibitor directly into WAT inhibited and increased β3-adrenoceptor-mediated induction of UCP1, respectively, and mitochondrial brite adipocyte marker expression and mitochondriogenesis.ConclusionCollectively, our results demonstrate that miR-125b-5p plays an important role in the repression of brite adipocyte function by modulating oxygen consumption and mitochondrial gene expression.

No abstract

Sell H, Eckardt K, Taube A, Tews D, Gurgui M, Van EchtenDeckert G, Eckel J. Skeletal muscle insulin resistance induced by adipocyte-conditioned medium: underlying mechanisms and reversibility.

No abstract

The recent discovery of functional brown adipose tissue in human adults raised this tissue again into the focus of current investigations concerning human energy homeostasis. Brown fat is a key thermogenic tissue and is essential for non-shivering thermogenesis in the human newborn and hibernating mammals. This review highlights the biological and molecular aspects of brown adipose tissue development and function from the embryonic state to childhood and adolescence.