Mitochondrial Dysfunction and AKT Isoform-Specific Regulation in 3T3-L1 Adipocytes: A Dissertation

Excess food consumption and/or lack of exercise have dramatically contributed to the prevalence of overweight (BMI≥25) and obesity (BMI≥30) in modern society. The obesity epidemic has been linked to the rise in type 2 diabetes. In recent years, evidence has pointed to a close association between mitochondrial dysfunction in white adipose tissue (WAT) and insulin resistance, a key feature of type 2 diabetes. In order to dissect the cause and effect relationship between WAT mitochondrial dysfunction and insulin resistance, we established an in vitro cell line system to investigate this issue. We artificially introduced mitochondrial dysfunction in 3T3-L1 adipocytes by depleting the mitochondrial transcription factor A (Tfam) during adipogenesis, without changing the overall adipocyte differentiation program. We found that these Tfam-depleted 3T3-L1 adipocytes showed symptoms of insulin resistance, evidenced by impaired insulin stimulated GLUT4 translocation and glucose uptake. This result suggested that mitochondrial dysfunction could be a primary contributor to insulin resistance in fat tissue. However, the exact mechanism underlying this finding remains unclear. As part of a comprehensive understanding of insulin signaling in fat cells, we also investigated the involvement of the endosomal protein WDFY2 in the regulation of Akt isoform-specific effect on glucose uptake. In 3T3-L1 adipocytes, both Akt1 and Akt2 isoforms are expressed, but only Akt2 plays an indispensible role in insulin-stimulated GLUT4 translocation and glucose uptake. Previous studies implied that endosomal proteins may take a part in determining Akt substrate specificity. Here we found that WDFY2 preferentially co-localized with Akt2 and that knockdown of WDFY2 inhibited insulin-stimulated glucose uptake in 3T3-L1 adipocytes, suggesting that endosomes are involved in this regulation. The effect of WDFY2 knockdown on insulin-stimulated glucose uptake worked through the down-regulation of Akt2, but not Akt1, protein level. We concluded that, endosomal protein WDFY2, by preferentially interacting with Akt2, regulates insulin signaling in glucose uptake in 3T3-L1 adipocytes. Our findings may help to develop specific therapeutic interventions for treatment of insulin resistance and type 2 diabetes

Loss of TRIM33 causes resistance to BET bromodomain inhibitors through MYC- and TGF-β-dependent mechanisms

ACKNOWLEDGMENTS. We thank Phillip B. Murray for help with the shRNA mapping pipeline and Francesc Lopez-Giraldez for help with RNAseq mapping software.Peer reviewedPostprintPostprin

Patterns of Genetic Diversity in Remaining Giant Panda Populations

The giant panda (Ailuropoda melanoleuca) is among the more familiar symbols of species conservation. The protection of giant panda populations has been aided recently by the establishment of more and better-managed reserves in existing panda habitat located in six mountain ranges in western China. These remaining populations are becoming increasingly isolated from one another, however, leading to the concern that historic patterns of gene flow will be disrupted and that reduced population sizes will lead to diminished genetic variability. We analyzed four categories of molecular genetic markers (mtDNA restriction-fragment-length polymorphisms [RFLP], mtDNA control region sequences, nuclear multilocus DNA fingerprints, and microsatellite size variation) in giant pandas from three mountain populations (Qionglai, Minshan, and Qinling) to assess current levels of genetic diversity and to detect evidence of historic population subdivisions. The three populations had moderate levels of genetic diversity compared with similarly studied carnivores for all four gene measures, with a slight but consistent reduction in variability apparent in the smaller Qinling population. That population also showed significant differentiation consistent with its isolation since historic times. From a strictly genetic perspective, the giant panda species and the three populations look promising insofar as they have retained a large amount of genetic diversity in each population, although evidence of recent population reduction—likely from habitat loss—is apparent. Ecological management to increase habitat, population expansion, and gene flow would seem an effective strategy to stabilize the decline of this endangered species