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Samaneh Mafakheri, Alexandra Chadt, Hadi Al-Hasani
Rab (Ras-related proteins in brain) GTPases are key proteins responsible for a multiplicity of cellular trafficking processes. Belonging to the family of monomeric GTPases, they are regulated by cycling between their active GTP-bound and inactive GDP-bound conformations. Despite possessing a slow intrinsic GTP hydrolysis activity, Rab proteins rely on RabGAPs (Rab GTPase-activating proteins) that catalyze GTP hydrolysis and consequently inactivate the respective Rab GTPases. Two related RabGAPs, TBC1D1 and TBC1D4 (=AS160) have been described to be associated with obesity-related traits and type 2 diabetes in both mice and humans...
May 21, 2018: Biochemical Society Transactions
Nicolas O Jørgensen, Jørgen F P Wojtaszewski, Rasmus Kjøbsted
Exercise, contraction, and pharmacological activation of AMP-activated protein kinase (AMPK) by 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) have all been shown to increase muscle insulin sensitivity for glucose uptake. Intriguingly, improvements in insulin sensitivity following contraction of isolated rat and mouse skeletal muscle and prior AICAR stimulation of isolated rat skeletal muscle seem to depend on an unknown factor present in serum. One study recently questioned this requirement of a serum factor by showing serum-independency with muscle from old rats...
April 15, 2018: International Journal of Molecular Sciences
Mark A White, Efrosini Tsouko, Chenchu Lin, Kimal Rajapakshe, Jeffrey M Spencer, Sandi R Wilkenfeld, Sheiva S Vakili, Thomas L Pulliam, Dominik Awad, Fotis Nikolos, Rajasekhara Reddy Katreddy, Benny Abraham Kaipparettu, Arun Sreekumar, Xiaoliu Zhang, Edwin Cheung, Cristian Coarfa, Daniel E Frigo
Despite altered metabolism being an accepted hallmark of cancer, it is still not completely understood which signaling pathways regulate these processes. Given the central role of androgen receptor (AR) signaling in prostate cancer, we hypothesized that AR could promote prostate cancer cell growth in part through increasing glucose uptake via the expression of distinct glucose transporters. Here, we determined that AR directly increased the expression of SLC2A12 , the gene that encodes the glucose transporter GLUT12...
April 2018: Endocrine-related Cancer
Zhiyong Liu, Nicole Bryant, Ravindran Kumaran, Alexandra Beilina, Asa Abeliovich, Mark R Cookson, Andrew B West
Human genetic studies implicate LRRK2 and RAB7L1 in susceptibility to Parkinson disease (PD). These two genes function in the same pathway, as knockout of Rab7L1 results in phenotypes similar to LRRK2 knockout, and studies in cells and model organisms demonstrate LRRK2 and Rab7L1 interact in the endolysosomal system. Recently, a subset of Rab proteins have been identified as LRRK2 kinase substrates. Herein, we find that Rab8, Rab10, and Rab7L1 must be membrane and GTP-bound for LRRK2 phosphorylation. LRRK2 mutations that cause PD including R1441C, Y1699C, and G2019S all increase LRRK2 phosphorylation of Rab7L1 four-fold over wild-type LRRK2 in cells, resulting in the phosphorylation of nearly one-third the available Rab7L1 protein in cells...
January 15, 2018: Human Molecular Genetics
Mohammad Saeed
Objective Assimilation of SNPs Interacting in Synchrony (OASIS) is a locus-based clustering algorithm recently described that can potentially address false positives and negatives in genome-wide association studies (GWAS) of complex disorders. Diabetic nephropathy (DN) is incompletely understood due to a paucity of genes identified despite several GWAS. OASIS was applied to three DN dbGAP GWAS datasets (4725 subjects; 1.06 million SNPs). OASIS identified 19 DN genes which were verified using single variant replication in a standard association study and gene-based analysis using GATES...
November 16, 2017: Immunogenetics
Javier R Jaldin-Fincati, Martin Pavarotti, Scott Frendo-Cumbo, Philip J Bilan, Amira Klip
Glucose transport is rate limiting for dietary glucose utilization by muscle and fat. The glucose transporter GLUT4 is dynamically sorted and retained intracellularly and redistributes to the plasma membrane (PM) by insulin-regulated vesicular traffic, or 'GLUT4 translocation'. Here we emphasize recent findings in GLUT4 translocation research. The application of total internal reflection fluorescence microscopy (TIRFM) has increased our understanding of insulin-regulated events beneath the PM, such as vesicle tethering and membrane fusion...
August 2017: Trends in Endocrinology and Metabolism: TEM
Fatou K Ndiaye, Ana Ortalli, Mickaël Canouil, Marlène Huyvaert, Clara Salazar-Cardozo, Cécile Lecoeur, Marie Verbanck, Valérie Pawlowski, Raphaël Boutry, Emmanuelle Durand, Iandry Rabearivelo, Olivier Sand, Lorella Marselli, Julie Kerr-Conte, Vikash Chandra, Raphaël Scharfmann, Odile Poulain-Godefroy, Piero Marchetti, François Pattou, Amar Abderrahmani, Philippe Froguel, Amélie Bonnefond
OBJECTIVES: Genome-wide association studies (GWAS) have identified >100 loci independently contributing to type 2 diabetes (T2D) risk. However, translational implications for precision medicine and for the development of novel treatments have been disappointing, due to poor knowledge of how these loci impact T2D pathophysiology. Here, we aimed to measure the expression of genes located nearby T2D associated signals and to assess their effect on insulin secretion from pancreatic beta cells...
June 2017: Molecular Metabolism
Ju Rang Woo, Soon-Jong Kim, Keon Young Kim, Hyonchol Jang, Steven E Shoelson, SangYoun Park
TBC1D4 (also known as AS160) is a Rab·GTPase-activating protein (RabGAP) which functions in insulin signaling. TBC1D4 is critical for translocation of glucose transporter 4 (GLUT4), from an inactive, intracellular, vesicle-bound site to the plasma membrane, where it promotes glucose entry into cells. The TBC1D4 protein is structurally subdivided into two N-terminal phosphotyrosine-binding (PTB) domains, a C-terminal catalytic RabGAP domain, and a disordered segment in between containing potential Akt phosphorylation sites...
October 2017: International Journal of Biological Macromolecules
Kim A Sjøberg, Christian Frøsig, Rasmus Kjøbsted, Lykke Sylow, Maximilian Kleinert, Andrew C Betik, Christopher S Shaw, Bente Kiens, Jørgen F P Wojtaszewski, Stephen Rattigan, Erik A Richter, Glenn K McConell
Insulin resistance is a major health risk, and although exercise clearly improves skeletal muscle insulin sensitivity, the mechanisms are unclear. Here we show that initiation of a euglycemic-hyperinsulinemic clamp 4 h after single-legged exercise in humans increased microvascular perfusion (determined by contrast-enhanced ultrasound) by 65% in the exercised leg and 25% in the rested leg ( P < 0.05) and that leg glucose uptake increased 50% more ( P < 0.05) in the exercised leg than in the rested leg...
June 2017: Diabetes
Rasmus Kjøbsted, Jørgen F P Wojtaszewski, Jonas T Treebak
Skeletal muscle insulin resistance precedes development of type 2 diabetes (T2D). As skeletal muscle is a major sink for glucose disposal, understanding the molecular mechanisms involved in maintaining insulin sensitivity of this tissue could potentially benefit millions of people that are diagnosed with insulin resistance. Regular physical activity in both healthy and insulin-resistant individuals is recognized as the single most effective intervention to increase whole-body insulin sensitivity and thereby positively affect glucose homeostasis...
2016: EXS
Rasmus Kjøbsted, Nanna Munk-Hansen, Jesper B Birk, Marc Foretz, Benoit Viollet, Marie Björnholm, Juleen R Zierath, Jonas T Treebak, Jørgen F P Wojtaszewski
Earlier studies have demonstrated that muscle insulin sensitivity to stimulate glucose uptake is enhanced several hours after an acute bout of exercise. Using AICAR, we recently demonstrated that prior activation of AMPK is sufficient to increase insulin sensitivity in mouse skeletal muscle. Here we aimed to determine whether activation of AMPK is also a prerequisite for the ability of muscle contraction to increase insulin sensitivity. We found that prior in situ contraction of m. extensor digitorum longus (EDL) and treadmill exercise increased muscle and whole-body insulin sensitivity in wild-type (WT) mice, respectively...
March 2017: Diabetes
Agnieszka Mikłosz, Bartłomiej Łukaszuk, Małgorzata Żendzian-Piotrowska, Justyna Brańska-Januszewska, Halina Ostrowska, Adrian Chabowski
The Akt substrate of 160 kDa (AS160) is a key regulator of GLUT4 translocation from intracellular depots to the plasma membrane in myocytes. Likely, AS160 also controls LCFAs transport, which requires relocation of fatty acid transporters. The aim of the present study was to determine the impact of AS160 knockdown on lipid milieu in L6 myotubes incubated with palmitate (PA). Therefore, we compared two different settings, namely: 1) AS160 knockdown prior to palmitate incubation (pre-PA-silencing, AS160(-) /PA); 2) palmitate incubation with subsequent AS160 knockdown (post-PA-silencing, PA/AS160(-) )...
September 2017: Journal of Cellular Physiology
Despoina Manousaki, Jack W Kent, Karin Haack, Sirui Zhou, Pingxing Xie, Celia M Greenwood, Paul Brassard, Deborah E Newman, Shelley Cole, Jason G Umans, Guy Rouleau, Anthony G Comuzzie, J Brent Richards
OBJECTIVE: A common nonsense mutation in TBC1D4 was recently found to substantially increase the odds of type 2 diabetes in Greenlandic Inuit, leading to exclusively increased postprandial glucose. We investigated the frequency and effect of the TBC1D4 mutation on glucose metabolism and type 2 diabetes diagnosis among Canadian and Alaskan Inuit. RESEARCH DESIGN AND METHODS: Exome sequencing of the TBC1D4 variant was performed in 114 Inuit from Nunavik, Canada, and Sanger sequencing was undertaken in 1,027 Alaskan Inuit from the Genetics of Coronary Artery Disease in Alaskan Natives (GOCADAN) Study...
November 2016: Diabetes Care
Cathrine Laustrup Møller, Rasmus Kjøbsted, Pablo J Enriori, Thomas Elbenhardt Jensen, Cecilia Garcia-Rudaz, Sara A Litwak, Kirsten Raun, Jørgen Wojtaszewski, Birgitte Schjellerup Wulff, Michael A Cowley
The melanocortin system includes five G-protein coupled receptors (family A) defined as MC1R-MC5R, which are stimulated by endogenous agonists derived from proopiomelanocortin (POMC). The melanocortin system has been intensely studied for its central actions in body weight and energy expenditure regulation, which are mainly mediated by MC4R. The pituitary gland is the source of various POMC-derived hormones released to the circulation, which raises the possibility that there may be actions of the melanocortins on peripheral energy homeostasis...
2016: PloS One
E Molinari, H Bar, A M Pyle, P Patrizio
STUDY QUESTION: Can RNA sequencing of human cumulus cells (CC) reveal molecular pathways involved in the physiology of reproductive aging? STUDY FINDING: Senescent but not young CC activate gene pathways associated with hypoxia and oxidative stress. WHAT IS KNOWN ALREADY: Shifts in socioeconomic norms are resulting in larger numbers of women postponing childbearing. The reproductive potential is sharply decreased with aging, and the reasons are poorly understood...
August 2016: Molecular Human Reproduction
Pianchou Gongpan, Yanting Lu, Fang Wang, Yuhui Xu, Wenyong Xiong
AS160 (TBC1D4) has been implicated in multiple biological processes. However, the role and the mechanism of action of AS160 in the regulation of cell proliferation remain unclear. In this study, we demonstrated that AS160 knockdown led to blunted cell proliferation in multiple cell types, including fibroblasts and cancer cells. The results of cell cycle analysis showed that these cells were arrested in the G1 phase. Intriguingly, this inhibition of cell proliferation and the cell cycle arrest caused by AS160 depletion were glucose independent...
July 2, 2016: Cell Cycle
Niels Grarup, Ida Moltke, Anders Albrechtsen, Torben Hansen
Type 2 diabetes (T2D) is an increasing health problem worldwide with particularly high occurrence in specific subpopulations and ancestry groups. The high prevalence of T2D is caused both by changes in lifestyle and genetic predisposition. A large number of studies have sought to identify the genetic determinants of T2D in large, open populations such as Europeans and Asians. However, studies of T2D in population isolates are gaining attention as they provide several advantages over open populations in genetic disease studies, including increased linkage disequilibrium, homogeneous environmental exposure, and increased allele frequency...
October 2015: Review of Diabetic Studies: RDS
Anup K Nair, Leslie J Baier
Genetic studies in large outbred populations have documented a complex, highly polygenic basis for type 2 diabetes (T2D). Most of the variants currently known to be associated with T2D risk have been identified in large studies that included tens of thousands of individuals who are representative of a single major ethnic group such as European, Asian, or African. However, most of these variants have only modest effects on the risk for T2D; identification of definitive 'causal variant' or 'causative loci' is typically lacking...
October 2015: Review of Diabetic Studies: RDS
Rasmus Kjøbsted, Andreas J T Pedersen, Janne R Hingst, Rugivan Sabaratnam, Jesper B Birk, Jonas M Kristensen, Kurt Højlund, Jørgen F P Wojtaszewski
Current evidence on exercise-mediated AMPK regulation in skeletal muscle of patients with type 2 diabetes (T2D) is inconclusive. This may relate to inadequate segregation of trimeric complexes in the investigation of AMPK activity. We examined the regulation of AMPK and downstream targets ACC-β, TBC1D1, and TBC1D4 in muscle biopsy specimens obtained from 13 overweight/obese patients with T2D and 14 weight-matched male control subjects before, immediately after, and 3 h after exercise. Exercise increased AMPK α2β2γ3 activity and phosphorylation of ACCβ Ser(221), TBC1D1 Ser(237)/Thr(596), and TBC1D4 Ser(704) Conversely, exercise decreased AMPK α1β2γ1 activity and TBC1D4 Ser(318)/Thr(642) phosphorylation...
May 2016: Diabetes
Paul Duffield Brewer, Estifanos N Habtemichael, Irina Romenskaia, Cynthia Corley Mastick, Adelle C F Coster
The RabGAP AS160/TBC1D4 controls exocytosis of the insulin-sensitive glucose transporter Glut4 in adipocytes. Glut4 is internalized and recycled through a highly regulated secretory pathway in these cells. Glut4 also cycles through a slow constitutive endosomal pathway distinct from the fast transferrin (Tf) receptor recycling pathway. This slow constitutive pathway is the only Glut4 cycling pathway in undifferentiated fibroblasts. The α2-macroglobulin receptor LRP1 cycles with Glut4 and the Tf receptor through all three exocytic pathways...
January 8, 2016: Journal of Biological Chemistry
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