Lessons on Conditional Gene Targeting in Mouse Adipose Tissue

Conditional gene targeting has been extensively used for in vivo analysis of gene function in adipocyte cell biology but often with debate over the tissue specificity and the efficacy of inactivation. To directly compare the specificity and efficacy of different Cre lines in mediating adipocyte specific recombination, transgenic Cre lines driven by the adipocyte protein 2 (aP2) and adiponectin (Adipoq) gene promoters, as well as a tamoxifen-inducible Cre driven by the aP2 gene promoter (iaP2), were bred to the Rosa26R (R26R) reporter. All three Cre lines demonstrated recombination in the brown and white fat pads. Using different floxed loci, the individual Cre lines displayed a range of efficacy to Cre-mediated recombination that ranged from no observable recombination to complete recombination within the fat. The Adipoq-Cre exhibited no observable recombination in any other tissues examined, whereas both aP2-Cre lines resulted in recombination in endothelial cells of the heart and nonendothelial, nonmyocyte cells in the skeletal muscle. In addition, the aP2-Cre line can lead to germline recombination of floxed alleles in ∼2% of spermatozoa. Thus, different “adipocyte-specific” Cre lines display different degrees of efficiency and specificity, illustrating important differences that must be taken into account in their use for studying adipose biology

Characterization of cold-induced remodelling reveals depot-specific differences across and within brown and white adipose tissues in mice

Brown and beige adipose tissues dissipate energy in the form of heat via mitochondrial uncoupling protein 1, defending against hypothermia and potentially obesity. The latter has prompted renewed interest in understanding the processes involved in browning to realize the potential therapeutic benefits. To characterize the temporal profile of cold-induced changes and browning of brown and white adipose tissues in mice. Methods: Male C57BL/6J mice were singly housed in conventional cages under cold exposure (4°C) for 1, 2, 3, 4, 5 and 7days. Food intake and body weight were measured daily. Interscapular brown adipose tissue (iBAT), inguinal subcutaneous (sWAT) and epididymal white adipose tissue (eWAT) were harvested for histological, immunohistochemical, gene and protein expression analysis. Results: Upon cold exposure, food intake increased, whilst body weight and adipocyte size were found to be transiently reduced. iBAT mass was found to be increased, whilst sWAT and eWAT were found to be transiently decreased. A combination of morphological, genetic (Ucp-1, Pgc-1α and Elov13) and biochemical (UCP-1, PPARγ and aP2) analyses demonstrated the depot-specific remodelling in response to cold exposure. Conclusion: Our results demonstrate the differential responses to cold-induced changes across discrete BAT and WAT depots and support the notion that the effects of short-term cold exposure are achieved by expansion, activation and increasing thermogenic capacity of iBAT, as well as browning of sWAT and, to a lesser extent, eWAT. © 2016 Scandinavian Physiological Society. Published by John Wiley & Sons Lt

Ablation of TRIP-Br2, a novel regulator of fat lipolysis, thermogenesis and oxidative metabolism, prevents diet-induced obesity and insulin resistance

SUMMARY Obesity develops due to altered energy homeostasis favoring fat storage. Here we describe a novel transcription co-regulator for adiposity and energy metabolism, TRIP-Br2 (also called SERTAD2). TRIP-Br2 null mice are resistant to obesity and obesity-related insulin resistance. Adipocytes of the knockout (KO) mice exhibited greater stimulated lipolysis secondary to enhanced expression of hormone sensitive lipase (HSL) and β3-adrenergic (Adrb3) receptors. The KOs also exhibit higher energy expenditure due to increased adipocyte thermogenesis and oxidative metabolism by up-regulating key enzymes in respective processes. Our data show for the first time that a cell cycle transcriptional co-regulator, TRIP-Br2, modulates fat storage through simultaneous regulation of lipolysis, thermogenesis and oxidative metabolism. These data together with the observation that TRIP-BR2 expression is selectively elevated in visceral fat in obese humans suggests that this transcriptional co-regulator is a novel therapeutic target for counteracting the development of obesity, insulin resistance and hyperlipidemia

Fractalkine: A Cellular Link Between Adipose Tissue Inflammation and Vascular Pathologies

It is hard to imagine, given the wealth of new datareported over the recent past, that adipose tissue atone time was primarily considered as a passive res-ervoir for energy deposition and storage. However, research beginning in the early 1990s on the role of tumor necrosis factor (TNF)-a ushered in a new era of inves-tigation, and since that time, there has been an incredibly rapid and substantive increase in our understanding of underlying physiologic systems and molecular pathways linking obesity, inflammation, and insulin action (1,2). Spe-cifically, our understanding of the link between obesity and carbohydrate metabolism has been significantly enhanced with the elucidation of key regulators of energy balance and cellular insulin signaling that are complex and highly in-tegrated (3–6). We now readily accept adipose tissue as a key endocrine organ regulating processes throughout the body with its significant number of adipocyte secre-tions. What now appears to be emerging is the elucidatio

The Mouse IAPE Endogenous Retrovirus Can Infect Cells through Any of the Five GPI-Anchored EphrinA Proteins

The IAPE (Intracisternal A-type Particles elements with an Envelope) family of murine endogenous retroelements is present at more than 200 copies in the mouse genome. We had previously identified a single copy that proved to be fully functional, i.e. which can generate viral particles budding out of the cell and infectious on a series of cells, including human cells. We also showed that IAPE are the progenitors of the highly reiterated IAP elements. The latter are now strictly intracellular retrotransposons, due to the loss of the envelope gene and re-localisation of the associated particles in the course of evolution. In the present study we searched for the cellular receptor of the IAPE elements, by using a lentiviral human cDNA library and a pseudotype assay on transduced cells. We identified Ephrin A4, a GPI-anchored molecule involved in several developmental processes, as a receptor for the IAPE pseudotypes. We also found that the other 4 members of the Ephrin A family –but not those of the closely related Ephrin B family- were also able to mediate IAPE cell entry, thus significantly increasing the amount of possible cell types susceptible to IAPE infection. We show that these include mouse germline cells, as illustrated by immunohistochemistry experiments, consistent with IAPE genomic amplification by successive re-infection. We propose that the uncovered properties of the identified receptors played a role in the accumulation of IAPE elements in the mouse genome, and in the survival of a functional copy