LIGHT (TNFSF14) inhibits adipose differentiation without affecting adipocyte metabolism.

OBJECTIVE: The member of the tumor necrosis factor family LIGHT (lymphotoxin-like inducible protein that competes with glycoprotein D for herpesvirus entry on T cells; TNFSF14 (tumor necrosis factor super family protein 14) is primarily expressed in lymphocytes, in which it induces the expression of pro-inflammatory cytokines and alterations of lipid homeostasis. Recently, the protein was shown to be upregulated in obesity and to induce cytokine secretion from adipocytes. RESEARCH METHODS AND PROCEDURES: Using an automated complementary DNA (cDNA) screen, LIGHT was identified to inhibit adipose differentiation. As cellular models for adipogenesis mouse 3T3-L1, human SGBS (Simpson-Golabi-Behmel syndrome) and primary human preadipocytes differentiated in vitro were used as well as primary human adipocytes to study adipocyte functions. Analysis of lipid deposition by Oil Red O staining, mRNA expression by quantitative reverse transcriptase-PCR, nuclear factor (NF)-κB activation as well as protein secretion by enzyme linked immunosorbent assay and Luminex technology was performed. RESULTS: LIGHT was found to inhibit lipid accumulation in the three models of preadipocytes in a dose-dependent manner without cytotoxic effects. This inhibition of differentiation was probably because of interference at early steps of adipogenesis, as early exposure during differentiation showed the strongest effect, as assessed by decreased peroxisome proliferator-activated receptor-γ (PPARγ) and CCAAT/enhancer-binding protein-α (C/EBPα) mRNA expression. In contrast to TNFα, basal and insulin-stimulated glucose uptake and lipolysis of terminally differentiated mature adipocytes were not altered in the presence of LIGHT. At a concentration sufficient to inhibit differentiation, secretion of proinflammatory cytokines was not significantly induced and NF-κB activity was only modestly induced compared with TNFα. CONCLUSION: LIGHT is a novel inhibitor of human adipocyte differentiation without adversely influencing central metabolic pathways in adipocytes.

Elevated UCP1 levels are sufficient to improve glucose uptake in human white adipocytes.

Brown adipose tissue (BAT) has been considered beneficial for metabolic health by participating in the regulation of glucose homoeostasis. The browning factors that improve glucose uptake beyond normal levels are still unknown but glucose uptake is not affected in UCP1 knockout mice. Here, we demonstrate in human white adipocytes that basal/resting glucose uptake is improved by solely elevating UCP1 protein levels. Generating human white Simpson-Golabi-Behmel syndrome (SGBS) adipocytes with a stable knockout and overexpression of UCP1, we discovered that UCP1 overexpressing adipocytes significantly improve glucose uptake by 40%. Mechanistically, this is caused by higher glycolytic flux, seen as increased oxygen consumption, extracellular acidification and lactate secretion rates. The improvements in glucose handling are comparable to white-to-brown transitions, as judged by, for the first time, directly comparing in vitro differentiated mouse brown vs white adipocytes. Although no adipogenic, metabolic and mitochondrial gene expressions were significantly altered in SGBS cells, pharmacological inhibition of GLUT1 completely abrogated differences between UCP1+ and control cells, thereby uncovering GLUT1-mediated uptake as permissive gatekeeper. Collectively, our data demonstrate that elevating UCP1 levels is sufficient to improve human white adipocytes as a glucose sink without adverse cellular effects, thus not requiring the adrenergic controlled, complex network of browning which usually hampers translational efforts.

Teneurin-2 (TENM2) deficiency induces UCP1 expression in differentiating human fat cells.

Under certain conditions UCP1 expressing adipocytes arise in white adipose tissue depots of both mice and humans. It is still not fully understood whether these cells differentiate de novo from specific progenitor cells or if they transdifferentiate from mature white adipocytes. Performing expression pattern analysis comparing adipocyte progenitor cells from deep and subcutaneous neck adipose tissue, we recently identified teneurin-2 (TENM2) enriched in white adipocyte progenitor cells. Here we tested whether TENM2 deficiency in adipocyte progenitor cells would lead to a brown adipocyte phenotype. By targeting TENM2 in SGBS preadipocytes using siRNA, we demonstrate that TENM2 knockdown induces both UCP1 mRNA and protein expression upon adipogenic differentiation without affecting mitochondrial mass. Furthermore, TENM2 knockdown in human SGBS adipocytes resulted in increased basal and leak mitochondrial respiration. In line with our previous observation these data suggest that TENM2 deficiency in human adipocyte precursors leads to induction of brown adipocyte marker genes upon adipogenic differentiation.

Direct evidence for continuous linear kinetics in the low-temperature degradation of Y-TZP.

The kinetics of the tetragonal to monoclinic (t-m) transformation of zirconia in a hydrous environment at 134°C and 3 bar pressure was studied. As surface X-ray diffraction, which is conventionally used to explore the progress, has a very limited depth of information, it distorts the quantitative results in a layer-on-layer situation and by itself is ill suited for this reason. Analyzing cross sections is more suitable; therefore, focused ion beam techniques were used to prepare artifact-free cuts. The material was subsequently investigated by scanning electron microscopy, electron backscatter diffraction and Raman spectroscopy. Only the combination of methods makes it possible to resolve the quantifiable details of the process. The transformation starts in the near-surface areas, forms a layer, and the growth of this layer proceeds into the bulk material following a simple linear time law (0.0624 µm h(-1) for material in the chosen condition), without apparent retardation or limit. The progress yields a gradientless layer with a fixed amount of residual tetragonal zirconia (~27% for 3Y-TZP in the present conditions) separated from unaffected material by a boundary, which has a roughness only in the grain size range. The kinetics indicates a reaction rate control, where the hydration reaction is the key factor, but is modified by the stepwise access of water to the reaction front opened by the autocatalytic transformation of zirconia with a critical hydration level.

TRAIL (TNF-related apoptosis-inducing ligand) regulates adipocyte metabolism by caspase-mediated cleavage of PPARgamma.

Tumor necrosis factor α (TNFα) and other members of the TNF family affect adipose tissue metabolism and contribute to the obesity-related inflammation of adipose tissue. Here, we sought to identify the effects of TRAIL (TNF-related apoptosis-inducing ligand) on fat cell biology. TRAIL-receptor 2 (TRAIL-R2) and its mouse homolog DR5 were regulated upon acute and chronic energy imbalance in murine and human adipose tissue. TRAIL inhibited insulin-stimulated glucose uptake and de novo lipogenesis in human adipocytes. Interestingly, TRAIL did not interfere with the phosphorylation of insulin-stimulated kinases such as Akt or Erk and did not activate the NF-κB pathway. Instead, TRAIL activated cleavage of caspase-8 and caspase-3. The subsequent cleavage of PPARγ led to its inactivation and resulted in reduced expression of lipogenic genes, such as Glut-4, FASN, and ACC. Taken together, we discovered a so far unknown function of the death ligand TRAIL in regulating adipocyte metabolism. Our results imply that TRAIL/TRAIL-R system might provide a new target for the prevention and treatment of obesity and its co-morbidities.

Experimental determination of the Raman sampling depth in zirconia ceramics.

This study provides experimentally determined values for the actual micro-Raman spectroscopy sampling depth in zirconia ceramics (ZrO2) via line scans on a wedge-shaped sample. Common instrumental settings with metallurgical objective lenses in dry air, argon-ion, and helium-neon laser radiation of approximately 10 mW were chosen. Under those conditions effective sampling depths, defined as the depth at which 99% of the information is recorded, range from 20 to more than 50 microm, depending on the numerical aperture of the lens and the laser wavelength. These results elucidate the pitfalls of the investigation of surface phenomena in zirconia ceramics such as low-temperature degradation or mechanically induced phase transformations by Raman spectroscopy.