Transcriptional co-factor TBLR1 controls lipid mobilization in white adipose tissue

Obesity as a cause of diseases like metabolic syndrome, type 2 diabetes and cardiovascular disease is increasingly becoming a worldwide health problem. Dysfunctional lipid metabolism is a key catalyst for the development of obesity, as impaired triglyceride storage and mobilization (lipolysis) lead to lipotoxicity and cellular stress in white adipose tissue (WAT) and other metabolically active organs. WAT is central to systemic energy metabolism as it has the potential to adapt to external and internal signals by tightly regulated lipid uptake and removal as well as adipocytokine release. Although it is widely accepted that lipolysis in adipose tissue critically determines lipid turnover and obesity, the molecular mechanisms of WAT lipid handling are largely unknown. In this context, the transcriptional co-factors transducin beta like (TBL) 1 and TBL related (TBLR) 1, that have previously been described as regulators of lipid handling in liver, were investigated to establish co-factor function in adipose tissue triglyceride metabolism. Genetic inactivation of TBLR1, but not TBL1, in adipocytes increases triglyceride content of these cells by inhibiting lipolysis at the level of gene transcription. Gene expression profiling revealed an involvement of adipocyte TBLR1 in peroxisome proliferator-activated receptor (PPAR) and adipocytokine signaling and fatty acid metabolism pathways. Indeed, TBLR1 interacts with PPARγ and RXR, and treatment with the PPARγ agonist rosiglitazone partly reverses the effects of TBLR1 knockdown on triglyceride hydrolysis. Consistent with its role as a transcriptional co-factor TBLR1 regulates gene expression of the key lipases involved in lipolysis, hormone sensitive lipase (HSL) and adipocyte triglyceride lipase (ATGL). Apart from that, TBLR1 also influences hormone-stimulated activation of lipid breakdown by interfering with the activating adrenoceptor-cAMP-PKA axis at the level of receptor expression. Adipocyte specific deletion of TBLR1 in mice leads to increased body weight and adiposity, adipocyte hypertrophy, as well as impaired lipid mobilization in fasting. Consistent with the finding that impaired lipolysis favors the development of obesity, body weight and adiposity increase in the adipocyte specific TBLR1 knockout (ATKO) mice with proceeding age. When fed a high fat diet, ATKO mice gain more weight and body fat than their wild type littermates, are less glucose tolerant and insulin sensitive and show increased signs of adiposity, namely adipocyte hypertrophy and increased adipocytokine release. Importantly, TBLR1 levels in white adipose tissue increase in states with high lipolytic activity like fasting and obesity in both mice and human patients and correlate with serum parameters and adrenoceptor expression. In summary, TBLR1 expression is activated in situations with augmented lipid mobilization and required for efficient triglyceride breakdown in adipocytes. Thus, manipulating TBLR1 levels in adipocytes may represent a future perspective to treat metabolic diseases like obesity or metabolic syndrome

Altered glycolysis triggers impaired mitochondrial metabolism and mTORC1 activation in diabetic β-cells

Chronic hyperglycaemia causes a dramatic decrease in mitochondrial metabolism and insulin content in pancreatic β-cells. This underlies the progressive decline in β-cell function in diabetes. However, the molecular mechanisms by which hyperglycaemia produces these effects remain unresolved. Using isolated islets and INS-1 cells, we show here that one or more glycolytic metabolites downstream of phosphofructokinase and upstream of GAPDH mediates the effects of chronic hyperglycemia. This metabolite stimulates marked upregulation of mTORC1 and concomitant downregulation of AMPK. Increased mTORC1 activity causes inhibition of pyruvate dehydrogenase which reduces pyruvate entry into the tricarboxylic acid cycle and partially accounts for the hyperglycaemia-induced reduction in oxidative phosphorylation and insulin secretion. In addition, hyperglycaemia (or diabetes) dramatically inhibits GAPDH activity, thereby impairing glucose metabolism. Our data also reveal that restricting glucose metabolism during hyperglycaemia prevents these changes and thus may be of therapeutic benefit. In summary, we have identified a pathway by which chronic hyperglycaemia reduces β-cell function

Hyperglycaemia induces metabolic dysfunction and glycogen accumulation in pancreatic β-cells

Insulin secretion from pancreatic β-cells is impaired in all forms of diabetes. The resultant hyperglycaemia has deleterious effects on many tissues, including β-cells. Here we use a mouse model of human neonatal diabetes to show that chronic hyperglycemia impairs glucose metabolism and alters expression of metabolic genes in pancreatic islets. This results in marked glycogen accumulation, and increased apoptosis in β-cells. Sulphonylurea therapy rapidly normalizes blood glucose levels, dissipates glycogen stores, increases autophagy, and restores β-cell metabolism. Insulin therapy has the same effect but with slower kinetics. Similar changes are observed in mice expressing an activating glucokinase mutation, in in vitro models of hyperglycaemia, and in islets from type-2 diabetes patients. Altered β-cell metabolism may underlie both the progressive impairment of insulin secretion and reduced β-cell mass in diabetes

Comparison of Two Approaches to Structured Physical Activity Surveys of Adolescents

Purpose - To compare the test-retest reliability, convergent validity, and overall feasibility/usability of activity-based (AB) and time-based (TB) approaches for obtaining self-reported moderate-to-vigorous physical activity (MVPA) from adolescents. Methods - Adolescents (206 females and 114 males) completed two 3-d physical activity recalls using the AB and TB surveys, which contained identical lists of physical activities. The participants wore an MTI Actigraph® accelerometer for the same period. Results - The TB instrument took about 3 min longer to complete (P=0.022). Overall 2-d test-retest correlations for MVPA were similar for the two surveys (r=0.676 and 0.667), but the girls had higher reliability on the AB survey than the boys (girls: r=0.713; boys: r=0.568). The overall 3-d correlations for MVPA surveys and Actigraph counts varied by gender (girls: AB=0.265 vs TB=0.314; boys: AB=0.340 vs TB=0.277). Correlations for vigorous physical activity and Actigraph counts were higher for the AB than for the TB (r=0.281 vs 0.162). As the interval between completing the surveys and the days being recalled increased, reliability and validity were lower, especially for the AB survey. Conclusion - For both genders, either approach is acceptable for obtaining MVPA information on a single day, but the TB approach appears to be slightly favored over the AB approach for obtaining multiple days of MVPA. A 3-d recall period appears to be too long for accurate recall of MVPA information from either instrument. For both genders, the surveys overestimate activity levels; thus, self-reports should be supplemented with objective data

Diabetes causes marked inhibition of mitochondrial metabolism in pancreatic β-cells

Diabetes is a global health problem caused primarily by the inability of pancreatic β-cells to secrete adequate levels of insulin. The molecular mechanisms underlying the progressive failure of β-cells to respond to glucose in type-2 diabetes remain unresolved. Using a combination of transcriptomics and proteomics, we find significant dysregulation of major metabolic pathways in islets of diabetic βV59M mice, a non-obese, eulipidaemic diabetes model. Multiple genes/proteins involved in glycolysis/gluconeogenesis are upregulated, whereas those involved in oxidative phosphorylation are downregulated. In isolated islets, glucose-induced increases in NADH and ATP are impaired and both oxidative and glycolytic glucose metabolism are reduced. INS-1 β-cells cultured chronically at high glucose show similar changes in protein expression and reduced glucose-stimulated oxygen consumption: targeted metabolomics reveals impaired metabolism. These data indicate hyperglycaemia induces metabolic changes in β-cells that markedly reduce mitochondrial metabolism and ATP synthesis. We propose this underlies the progressive failure of β-cells in diabetes.Peer reviewe

A sensitive one-step real-time PCR for detection of avian influenza viruses using a MGB probe and an internal positive control

BACKGROUND: Avian influenza viruses (AIVs) are endemic in wild birds and their introduction and conversion to highly pathogenic avian influenza virus in domestic poultry is a cause of serious economic losses as well as a risk for potential transmission to humans. The ability to rapidly recognise AIVs in biological specimens is critical for limiting further spread of the disease in poultry. The advent of molecular methods such as real time polymerase chain reaction has allowed improvement of detection methods currently used in laboratories, although not all of these methods include an Internal Positive Control (IPC) to monitor for false negative results. Therefore we developed a one-step reverse transcription real time PCR (RRT-PCR) with a Minor Groove Binder (MGB) probe for the detection of different subtypes of AIVs. This technique also includes an IPC. METHODS: RRT-PCR was developed using an improved TaqMan technology with a MGB probe to detect AI from reference viruses. Primers and probe were designed based on the matrix gene sequences from most animal and human A influenza virus subtypes. The specificity of RRT-PCR was assessed by detecting influenza A virus isolates belonging to subtypes from H1–H13 isolated in avian, human, swine and equine hosts. The analytical sensitivity of the RRT-PCR assay was determined using serial dilutions of in vitro transcribed matrix gene RNA. The use of a rodent RNA as an IPC in order not to reduce the efficiency of the assay was adopted. RESULTS: The RRT-PCR assay is capable to detect all tested influenza A viruses. The detection limit of the assay was shown to be between 5 and 50 RNA copies per reaction and the standard curve demonstrated a linear range from 5 to 5 × 10(8 )copies as well as excellent reproducibility. The analytical sensitivity of the assay is 10–100 times higher than conventional RT-PCR. CONCLUSION: The high sensitivity, rapidity, reproducibility and specificity of the AIV RRT-PCR with the use of IPC to monitor for false negative results can make this method suitable for diagnosis and for the evaluation of viral load in field specimens

Identification of genetic variants associated with Huntington's disease progression: a genome-wide association study

Background Huntington's disease is caused by a CAG repeat expansion in the huntingtin gene, HTT. Age at onset has been used as a quantitative phenotype in genetic analysis looking for Huntington's disease modifiers, but is hard to define and not always available. Therefore, we aimed to generate a novel measure of disease progression and to identify genetic markers associated with this progression measure. Methods We generated a progression score on the basis of principal component analysis of prospectively acquired longitudinal changes in motor, cognitive, and imaging measures in the 218 indivduals in the TRACK-HD cohort of Huntington's disease gene mutation carriers (data collected 2008–11). We generated a parallel progression score using data from 1773 previously genotyped participants from the European Huntington's Disease Network REGISTRY study of Huntington's disease mutation carriers (data collected 2003–13). We did a genome-wide association analyses in terms of progression for 216 TRACK-HD participants and 1773 REGISTRY participants, then a meta-analysis of these results was undertaken. Findings Longitudinal motor, cognitive, and imaging scores were correlated with each other in TRACK-HD participants, justifying use of a single, cross-domain measure of disease progression in both studies. The TRACK-HD and REGISTRY progression measures were correlated with each other (r=0·674), and with age at onset (TRACK-HD, r=0·315; REGISTRY, r=0·234). The meta-analysis of progression in TRACK-HD and REGISTRY gave a genome-wide significant signal (p=1·12 × 10−10) on chromosome 5 spanning three genes: MSH3, DHFR, and MTRNR2L2. The genes in this locus were associated with progression in TRACK-HD (MSH3 p=2·94 × 10−8 DHFR p=8·37 × 10−7 MTRNR2L2 p=2·15 × 10−9) and to a lesser extent in REGISTRY (MSH3 p=9·36 × 10−4 DHFR p=8·45 × 10−4 MTRNR2L2 p=1·20 × 10−3). The lead single nucleotide polymorphism (SNP) in TRACK-HD (rs557874766) was genome-wide significant in the meta-analysis (p=1·58 × 10−8), and encodes an aminoacid change (Pro67Ala) in MSH3. In TRACK-HD, each copy of the minor allele at this SNP was associated with a 0·4 units per year (95% CI 0·16–0·66) reduction in the rate of change of the Unified Huntington's Disease Rating Scale (UHDRS) Total Motor Score, and a reduction of 0·12 units per year (95% CI 0·06–0·18) in the rate of change of UHDRS Total Functional Capacity score. These associations remained significant after adjusting for age of onset. Interpretation The multidomain progression measure in TRACK-HD was associated with a functional variant that was genome-wide significant in our meta-analysis. The association in only 216 participants implies that the progression measure is a sensitive reflection of disease burden, that the effect size at this locus is large, or both. Knockout of Msh3 reduces somatic expansion in Huntington's disease mouse models, suggesting this mechanism as an area for future therapeutic investigation

Obesity and cancer – extracellular matrix, angiogenesis, and adrenergic signaling as unusual suspects linking the two diseases

Obesity is an established risk factor for several human cancers. Given the association between excess body weight and cancer, the increasing rates of obesity worldwide are worrisome. A variety of obesity-related factors has been implicated in cancer initiation, progression, and response to therapy. These factors include circulating nutritional factors, hormones, and cytokines, causing hyperinsulinemia, inflammation, and adipose tissue dysfunction. The impact of these conditions on cancer development and progression has been the focus of extensive literature. In this review, we concentrate on processes that can link obesity and cancer, and which provide a novel perspective: extracellular matrix remodeling, angiogenesis, and adrenergic signaling. We describe molecular mechanisms involved in these processes, which represent putative targets for intervention. Liver, pancreas, and breast cancers were chosen as exemplary disease models. In view of the expanding epidemic of obesity, a better understanding of the tumorigenic process in obese individuals might lead to more effective treatments and preventive measures