Skeletal muscle O-GlcNAc transferase is important for muscle energy homeostasis and whole-body insulin sensitivity

Objective: Given that cellular O-GlcNAcylation levels are thought to be real-time measures of cellular nutrient status and dysregulated O-GlcNAc signaling is associated with insulin resistance, we evaluated the role of O-GlcNAc transferase (OGT), the enzyme that mediates O-GlcNAcylation, in skeletal muscle. Methods: We assessed O-GlcNAcylation levels in skeletal muscle from obese, type 2 diabetic people, and we characterized muscle-specific OGT knockout (mKO) mice in metabolic cages and measured energy expenditure and substrate utilization pattern using indirect calorimetry. Whole body insulin sensitivity was assessed using the hyperinsulinemic euglycemic clamp technique and tissue-specific glucose uptake was subsequently evaluated. Tissues were used for histology, qPCR, Western blot, co-immunoprecipitation, and chromatin immunoprecipitation analyses. Results: We found elevated levels of O-GlcNAc-modified proteins in obese, type 2 diabetic people compared with well-matched obese and lean controls. Muscle-specific OGT knockout mice were lean, and whole body energy expenditure and insulin sensitivity were increased in these mice, consistent with enhanced glucose uptake and elevated glycolytic enzyme activities in skeletal muscle. Moreover, enhanced glucose uptake was also observed in white adipose tissue that was browner than that of WT mice. Interestingly, mKO mice had elevated mRNA levels of Il15 in skeletal muscle and increased circulating IL-15 levels. We found that OGT in muscle mediates transcriptional repression of Il15 by O-GlcNAcylating Enhancer of Zeste Homolog 2 (EZH2). Conclusions: Elevated muscle O-GlcNAc levels paralleled insulin resistance and type 2 diabetes in humans. Moreover, OGT-mediated signaling is necessary for proper skeletal muscle metabolism and whole-body energy homeostasis, and our data highlight O-GlcNAcylation as a potential target for ameliorating metabolic disorders. Keywords: O-GlcNAc signaling, Type 2 diabetes, N-acetyl-d-glucosamine, Tissue cross talk, Epigenetic regulation of Il15 transcription, Insulin sensitivit

Advanced scanning electron microscopy techniques for structural characterization of zeolites

International audienceChemical etching after Ar ion beam cross sectioning enables the formation of zeolite internal nano structures to be observed directly using a newly developed highly sensitive scanning electron microscope

Finite-Element Simulation on NPGCS Precast Shear Wall Spatial Structure Model

Seismic performance is basically required in precast shear wall. This study focuses on evaluation and improvement on precast shear wall seismic performance. By carrying out the finite-element simulation on a precast shear wall spatial model with new connector from a practical high-rise precast residential building, which was named as NPGCS and experimentally tested by low-cyclic reversed lateral loads in early studies, the performance results including strengths, stiffness, stress, and concrete damage ratio distributions were obtained, and the reliability of NPGCS spatial model was verified. According to the testing results, the finite-element simulation for the NPGCS spatial model is reliable and relatively accurate, especially for applying contact and beam elements into numerical analysis of precast interfaces and dowel shear actions, respectively. The strengths, stiffness, stress, and concrete damage ratio distributions from the simulation also supported the experimental results and conclusions

The preparation of core-shell-like zeolite by diffusion controlled chemical etching

International audienceThe present work reports on the preparation of core-shell-like zeolites with Si-rich mesoporous shell. This is achieved by diffusion controlled chemical etching of zeolite crystals with a mixture containing oxalic acid and ammonium fluoride (OA-NH 4 F). The OA-NH 4 F served as a bifunctional etchant extracting both surface Si and Al and further dealuminating the periphery of the zeolite crystals. The fast dissolution kinetics and the relatively slow intra-crystalline diffusion of the OA-NH 4 F etching solutions resulted in a distinct core-shell-like structure with porous and Si-rich shell keeping the unique advantages of single crystals with interconnected micro-and mesopores

Defect-engineered zeolite porosity and accessibility

International audienc

Towards a comprehensive understanding of mesoporosity in zeolite Y at the single particle level

International audienceA full understanding of zeolite mesoporosity is not trivial and yet is necessary to understand and optimize the catalytic performance of zeolites. The present work reports an integrated approach for the comprehensive study of zeolite mesoporosity. The comprehensiveness and effectiveness of the methodology are exemplified by the characterization of hierarchical zeolite Y samples prepared by NH4F etching. In the present work, usually lacking information of mesopore morphology, connectivity and spatial location was obtained by the ultra-high-resolution FE-SEM imaging of the zeolite cross-section after surface coating with osmium (Os). The ultrahigh-resolution SEM study allowed both: (i) the macroscopic documentation of the interconnecting channel-like porosity separating intergrown crystals; and (ii) the nano-scale resolving of mesopore spatial distribution within an individual crystal. In addition, the combination of NH4F etching with the state-of-the-art ultra-high-resolution FE-SEM imaging technique proved as a powerful methodology to reveal otherwise inaccessible information regarding the mesopore formation mechanism. The hierarchical pore structure analysis of zeolite Y was combined with catalytic testing in the dealkylation of 1,3,5 tri-isopropylbenzene for deeper understanding of its physicochemical properties

The inner heterogeneity of ZSM-5 zeolite crystals

International audienceThe inner architecture of zeolite crystals beneath the zeolite surface is the missing part in understanding the crystallization of zeolites and in their thoughtful post-synthesis engineering. In this work, both the defect-zoning and Al-zoning in pseudo-single ZSM-5 crystals were revealed using unbiased NH 4 F etching of as-synthesized and calcined samples. The formation of defect-zoning leading to multiple core-shell structure was described with a three-stage process involving (i) nucleation resulting in the innermost core formation, (ii) fast aggregate growth leading to defect-rich zones, and (iii) layer-by-layer growth shaping the final morphology of the zeolite crystals. A clear correlation between Al zoning and the spatial distribution of C and Na was established. This distinct inner heterogeneity in the ZSM-5 crystals reveals the particularities of the crystal growth process of this very important zeolite, and this knowledge can be translated into novel framework structures with targeted properties