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The glycolytic enzyme Pfkfb3 is shown to be constitutively ubiquitylated by the APC/C ligase and degraded in neurons. These findings might explain the lower glycolytic metabolism in these cells relative to astrocytes. Neurons are known to have a lower glycolytic rate than astrocytes and when stressed they are unable to upregulate glycolysis 1 because of low Pfkfb3 (6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase-3) activity 2 . This enzyme generates fructose-2,6-bisphosphate (F2,6P 2 ) 3 , the most potent activator of 6-phosphofructo-1-kinase (Pfk1; ref. 4 ), a master regulator of glycolysis 5 . Here, we show that Pfkfb3 is absent from neurons in the brain cortex and that Pfkfb3 in neurons is constantly subject to proteasomal degradation by the action of the E3 ubiquitin ligase 6 , anaphase-promoting complex/cyclosome (APC/C)–Cdh1. By contrast, astrocytes have low APC/C–Cdh1 activity and therefore Pfkfb3 is present in these cells. Upregulation of Pfkfb3 by either inhibition of Cdh1 or overexpression of Pfkfb3 in neurons resulted in the activation of glycolysis. This, however, was accompanied by a marked decrease in the oxidation of glucose through the pentose phosphate pathway (a metabolic route involved in the regeneration of reduced glutathione 7 ) resulting in oxidative stress and apoptotic death. Thus, by actively downregulating glycolysis by APC/C–Cdh1, neurons use glucose to maintain their antioxidant status at the expense of its utilization for bioenergetic purposes.

Background Despite the fact that labour market flexibility has resulted in an expansion of precarious employment in industrialised countries, to date there is limited empirical evidence concerning its health consequences. The Employment Precariousness Scale (EPRES) is a newly developed, theory-based, multidimensional questionnaire specifically devised for epidemiological studies among waged and salaried workers. Objective To assess the acceptability, reliability and construct validity of EPRES in a sample of waged and salaried workers in Spain. Methods A sample of 6968 temporary and permanent workers from a population-based survey carried out in 2004–2005 was analysed. The survey questionnaire was interviewer administered and included the six EPRES subscales, and measures of the psychosocial work environment (COPSOQ ISTAS21) and perceived general and mental health (SF-36). Results A high response rate to all EPRES items indicated good acceptability; Cronbach's α coefficients, over 0.70 for all subscales and the global score, demonstrated good internal consistency reliability; exploratory factor analysis using principal axis analysis and varimax rotation confirmed the six-subscale structure and the theoretical allocation of all items. Patterns across known groups and correlation coefficients with psychosocial work environment measures and perceived health demonstrated the expected relations, providing evidence of construct validity. Conclusions Our results provide evidence in support of the psychometric properties of EPRES, which appears to be a promising tool for the measurement of employment precariousness in public health research.

Cell proliferation is known to be accompanied by activation of glycolysis. We have recently discovered that the glycolysis-promoting enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase, isoform 3 (PFKFB3), is degraded by the E3 ubiquitin ligase APC/C-Cdh1, which also degrades cell-cycle proteins. We now show in two different cell types (neoplastic and nonneoplastic) that both proliferation and aerobic glycolysis are prevented by overexpression of Cdh1 and enhanced by its silencing. Furthermore, we have coexpressed Cdh1 with PFKFB3--either wild-type or a mutant form resistant to ubiquitylation by APC/C-Cdh1--or with the glycolytic enzyme 6-phosphofructo-1-kinase and demonstrated that whereas glycolysis is essential for cell proliferation, its initiation in the presence of active Cdh1 does not result in proliferation. Our experiments indicate that the proliferative response, regardless of whether it occurs in normal or neoplastic cells, is dependent on a decrease in the activity of APC/C-Cdh1, which activates both proliferation and glycolysis. These observations have implications for cell proliferation, neoplastic transformation, and the prevention and treatment of cancer.

PurposeTo assess the prevalence of poor mental health and of exposure to psychosocial risks among the working population in Spain in 2005, 2010 and 2016; to analyse the associations between workplace psychosocial exposures and mental health problems according to gender and occupation.MethodsThree representative samples of the Spanish working population were analysed, in 2005 (n = 7,023), 2010 (n = 4,979), and 2016 (n = 1,807). Prevalence ratios between mental health and the five dimensions – job demands, job control, social support, employment insecurity and insecurity over working conditions—were estimated using multilevel mixed-effects Poisson regressions. All the analyses were separated by gender and occupation.ResultsIn 2016, there were improvements in job control, job demands and social support, and deteriorations in employment insecurity and insecurity over working conditions. The risk of poor mental health among manual workers rose if they were exposed to high demands, low social support and high employment insecurity; among non-manual workers, the risk increased if they were exposed to high demands, low control, low social support and high insecurity over working conditions. There were no differences according to gender.ConclusionThe new findings shed light on the evolution of the working conditions and health of the wage-earning population in Spain over the last 11 years. The stratification by gender and occupational group is relevant, since it allows a detailed analysis of the social disparities in the associations between psychosocial risks and mental health. The most vulnerable groups can be identified and preventive measures developed at source.

During cell division, the activation of glycolysis is tightly regulated by the action of two ubiquitin ligases, anaphase-promoting complex/cyclosome–Cdh1 (APC/C-Cdh1) and SKP1/CUL-1/F-box protein–β-transducin repeat-containing protein (SCF-β-TrCP), which control the transient appearance and metabolic activity of the glycolysis-promoting enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase, isoform 3 (PFKFB3). We now demonstrate that the breakdown of PFKFB3 during S phase occurs specifically via a distinct residue (S273) within the conserved recognition site for SCF-β-TrCP. Glutaminase 1 (GLS1), the first enzyme in glutaminolysis, is also targeted for destruction by APC/C-Cdh1 and, like PFKFB3, accumulates after the activity of this ubiquitin ligase decreases in mid-to-late G1. However, our results show that GLS1 differs from PFKFB3 in that its recognition by APC/C-Cdh1 requires the presence of both a Lys-Glu-Asn box (KEN box) and a destruction box (D box) rather than a KEN box alone. Furthermore, GLS1 is not a substrate for SCF-β-TrCP and is not degraded until cells progress from S to G2/M. The presence of PFKFB3 and GLS1 coincides with increases in generation of lactate and in utilization of glutamine, respectively. The contrasting posttranslational regulation of PFKFB3 and GLS1, which we have verified by studies of ubiquitination and protein stability, suggests the different roles of glucose and glutamine at distinct stages in the cell cycle. Indeed, experiments in which synchronized cells were deprived of either of these substrates show that both glucose and glutamine are required for progression through the restriction point in mid-to-late G1, whereas glutamine is the only substrate essential for the progression through S phase into cell division.

Calorie restriction extends life span in organisms ranging from yeast to mammals. Here, we report that calorie restriction for either 3 or 12 months induced endothelial nitric oxide synthase (eNOS) expression and 3',5'-cyclic guanosine monophosphate formation in various tissues of male mice. This was accompanied by mitochondrial biogenesis, with increased oxygen consumption and adenosine triphosphate production, and an enhanced expression of sirtuin 1. These effects were strongly attenuated in eNOS null-mutant mice. Thus, nitric oxide plays a fundamental role in the processes induced by calorie restriction and may be involved in the extension of life span in mammals.

After inhibition of cytochrome c oxidase by nitric oxide 1 , 2 , 3 , astrocytes maintain energy production by upregulating glycolysis 4 , 5 — a response which does not seem to be available to neurons. Here, we show that in astrocytes, after inhibition of respiration by nitric oxide, there is a rapid, cyclic GMP-independent increase in the activity of 6-phosphofructo-1-kinase (PFK1), a master regulator of glycolysis 6 , and an increase in the concentration of its most powerful positive allosteric activator 7 , fructose-2,6-bisphosphate (F2,6P 2 ). In neurons, nitric oxide failed to alter F2,6P 2 concentration or PFK1 activity. This failure could be accounted for by the much lower amount of 6-phosphofructo-2-kinase (PFK2, the enzyme responsible for F2,6P 2 biosynthesis 8 ) in neurons. Indeed, full activation of neuronal PFK1 was achieved by adding cytosol from nitric oxide-treated astrocytes. Furthermore, using the small interfering RNA (siRNA) strategy 9 , we demonstrated that the rapid activation of glycolysis by nitric oxide is dependent on phosphorylation of the energy charge-sensitive AMP-activated protein kinase, resulting in activation of PFK2 and protection of cells from apoptosis. Thus the virtual absence of PFK2 in neurons may explain their extreme sensitivity to energy depletion and degeneration 4 , 5 , 10 .

Vascular endothelial cells are highly glycolytic and consume relatively low amounts of oxygen (O₂) compared with other cells. We have confirmed that oxidative phosphorylation is not the main source of ATP generation in these cells. We also show that at a low O₂ concentration (<1%) endogenous NO plays a key role in preventing the accumulation of the a-subunit of hypoxia-inducible factor 1. At higher O₂ concentrations (1-3%) NO facilitates the production of mitochondrial reactive oxygen species. This production activates the AMP-activated protein kinase by a mechanism independent of nucleotide concentrations. Thus, the primary role of mitochondria in vascular endothelial cells may not be to generate ATP but, under the control of NO, to act as signaling organelles using either O₂ or O₂-derived species as signaling molecules. Diversion of O₂ away from endothelial cell mitochondria by NO might also facilitate oxygenation of vascular smooth muscle cells.

Background Hyperglycemia is acknowledged as a pro-inflammatory condition and a major cause of vascular damage. Nevertheless, we have previously described that high glucose only promotes inflammation in human vascular cells previously primed with pro-inflammatory stimuli, such as the cytokine interleukin (IL)1β. Here, we aimed to identify the cellular mechanisms by which high glucose exacerbates the vascular inflammation induced by IL1β. Methods Cultured human aortic smooth muscle cells (HASMC) and isolated rat mesenteric microvessels were treated with IL1β in medium containing 5.5–22 mmol/L glucose. Glucose uptake and consumption, lactate production, GLUT1 levels, NADPH oxidase activity and inflammatory signalling (nuclear factor-κB activation and inducible nitric oxide synthase expression) were measured in HASMC, while endothelium-dependent relaxations to acetylcholine were determined in rat microvessels. Pharmacological inhibition of IL1 receptors, NADPH oxidase and glucose-6-phosphate dehydrogenase (G6PD), as well as silencing of G6PD, were also performed. Moreover, the pentose phosphate pathway (PPP) activity and the levels of reduced glutathione were determined. Results We found that excess glucose uptake in HASMC cultured in 22 mM glucose only occurred following activation with IL1β. However, the simple entry of glucose was not enough to be deleterious since over-expression of the glucose transporter GLUT1 or increased glucose uptake following inhibition of mitochondrial respiration by sodium azide was not sufficient to trigger inflammatory mechanisms. In fact, besides allowing glucose entry, IL1β activated the PPP, thus permitting some of the excess glucose to be metabolized via this route. This in turn led to an over-activation NADPH oxidase, resulting in increased generation of free radicals and the subsequent downstream pro-inflammatory signalling. Moreover, in rat mesenteric microvessels high glucose incubation enhanced the endothelial dysfunction induced by IL1β by a mechanism which was abrogated by the inhibition of the PPP. Conclusions A pro-inflammatory stimulus like IL1β transforms excess glucose into a vascular deleterious agent by causing an increase in glucose uptake and its subsequent diversion into the PPP, promoting the pro-oxidant conditions required for the exacerbation of pro-oxidant and pro-inflammatory pathways. We propose that over-activation of the PPP is a crucial mechanism for the vascular damage associated to hyperglycemia.

During cell proliferation, the abundance of the glycolysis-promoting enzyme, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase, isoform 3 (PFKFB3), is controlled by the ubiquitin ligase APC/C-Cdh1 via a KEN box. We now demonstrate in synchronized HeLa cells that PFKFB3, which appears in mid-to-late G1, is essential for cell division because its silencing prevents progression into S phase. In cells arrested by glucose deprivation, progression into S phase after replacement of glucose occurs only when PFKFB3 is present or is substituted by the downstream glycolytic enzyme 6-phosphofructo-1-klnase. PFKFB3 ceases to be detectable during late G1/S despite the absence of Cdh1; this disappearance is prevented by proteasomal inhibition. PFKFB3 contains a DSG box and is therefore a potential substrate for SCF-β-TrCP, a ubiquitin ligase active during S phase. In synchronized HeLa cells transfected with PFKFB3 mutated in the KEN box, the DSG box, or both, we established the breakdown routes of the enzyme at different stages of the cell cycle and the point at which glycolysis is enhanced. Thus, the presence of PFKFB3 is tightly controlled to ensure the up-regulation of glycolysis at a specific point in G1. We suggest that this up-regulation of glycolysis and its associated events represent the nutrient-sensitive restriction point in mammalian cells.