Telomerase activity in `immortal' fish1We dedicate this publication to E.S. Quabius. This study would have been impossible without her initiating ideas.1

AbstractEukaryotic chromosome termini consist of telomeres, short sequence repeats. According to the telomere hypothesis, DNA replication leads to telomere shortening, resulting in a cellular mitotic clock. Telomerase resets it by telomere synthesis. In mammals with a limited growth phase, telomerase activity in somatic tissues is restricted to stem cell derivatives with high proliferation potential. But other animals, like some fish, grow throughout their life with little senescence. All somatic cells require a high proliferation capacity and telomerase should be active in all cells, irrespective of fish age. Indeed, we detected high telomerase activities in all analyzed organs of rainbow trout (Oncorhynchus mykiss)

Longevity of lobsters is linked to ubiquitous telomerase expression

AbstractMammals have high growth rates in embryonic and juvenile phases and no growth in adult and senescent phases. We analyzed telomerase activity in a fundamentally different animal which grows indeterminately. Lobsters (Homarus americanus) grow throughout their life and the occurrence of senescence is slow. A modified TRAP assay was developed and the lobster telomeric repeat sequence TTAGG was determined. We detected telomerase activities which were dependent on RNA and protein components, required dGTP, dATP and dTTP, but not dCTP. Telomerase products with a five nucleotide periodicity were generated. High telomerase activities were detected in all lobster organs. We conclude that telomerase activation is a conserved mechanism for maintaining long-term cell proliferation capacity and preventing senescence, not only in cellular models or embryonic life stages but also in adult multicellular organisms

Citrulline Improves Early Post-Ischemic Recovery or Rat Hearts In Vitro by Shifting Arginine Metabolism From Polyamine to Nitric Oxide Formation

Background: Reperfusion or reopening of occluded vessels is the gold standard to terminate ischemia. However, early functional recovery after reperfusion is often low requiring inotropic intervention. Although catecholamines increase inotropy and chronotropy, they are not the best choice because they increase myocardial oxygen and substrate demand. As nitric oxide (NO) contributes to cardiac function, we tested the hypothesis that addition of citrulline during the onset of reperfusion improves post-ischemic recovery because citrulline can reenter arginine consumption of NO synthases (NOS) but not of arginases. Methods: Hearts from adult rats were used in this study, exposed to 45-minute global ischemia and subsequently reperfused for 180 minutes. Citrulline (100 µM) or arginine (100 µM) was added with reperfusion and remained in the perfusion buffer for 180 minutes. Nω-nitro- l -arginine methyl ester ( l -NAME) was used to antagonize NOS activity. Results: Citrulline increased load-free cell shortening of isolated adult rat cardiomyocytes and improved left ventricular developed pressure (LVDP) under normoxic conditions, indicating that citrulline can affect heart function. Ischemia/reperfusion caused a constitutive loss of function during 3 hours of reperfusion, whereas citrulline, but not arginine, improved the functional recovery during reperfusion. This effect was attenuated by co-administration of l -NAME. Although citrulline increased the formation of nitrite, l -NAME attenuated this effect indicating again a positive effect of citrulline on NO formation. Citrulline, but not arginine, increased the expression of arginase-1 (protein and mRNA) but l -NAME attenuated this effect again. Collectively, citrulline improved the post-ischemic recovery in an NO-dependent way. Conclusions: Citrulline, known to block arginase and to support NO formation, improves the early functional recovery of post-ischemic hearts and may be an alternative to catecholamines to improve early post-ischemic recovery

Niklas Luhmann, Carl Schmitt and the Modern Form of the Political

Niklas Luhmann elaborated his account of the political system in a complex, though often implicit, debate with Carl Schmitt. Underlying his systems-theoretical model of politics, and of the legitimacy of politics, is the anti-Schmittian view that modern society's communications about itself are neither coordinated by, nor embodied in, a political centre, and that politics is always an unemphatic aspect of these communications. However, this article proposes an immanent critique of Luhmann's analysis of the political system, and it argues that his theory uses highly selective and puristic techniques to support its limitation of society's politics. If interpreted critically, in fact, Luhmann's political sociology illuminates the specific politicality and political emphasis of certain communications, it underlines the distinction of politics from other systems of social communication, and it calls for a re-insistence on the political as a primary category of social analysis. Copyright © 2007 Sage Publications

Mechanism of MEK inhibition determines efficacy in mutant KRAS- versus BRAF-driven cancers

KRAS and BRAF activating mutations drive tumorigenesis through constitutive activation of the MAPK pathway. As these tumours represent an area of high unmet medical need, multiple allosteric MEK inhibitors, which inhibit MAPK signalling in both genotypes, are being tested in clinical trials. Impressive single-agent activity in BRAF-mutant melanoma has been observed; however, efficacy has been far less robust in KRAS-mutant disease. Here we show that, owing to distinct mechanisms regulating MEK activation in KRAS- versus BRAF-driven tumours, different mechanisms of inhibition are required for optimal antitumour activity in each genotype. Structural and functional analysis illustrates that MEK inhibitors with superior efficacy in KRAS-driven tumours (GDC-0623 and G-573, the former currently in phase I clinical trials) form a strong hydrogen-bond interaction with S212 in MEK that is critical for blocking MEK feedback phosphorylation by wild-type RAF. Conversely, potent inhibition of active, phosphorylated MEK is required for strong inhibition of the MAPK pathway in BRAF-mutant tumours, resulting in superior efficacy in this genotype with GDC-0973 (also known as cobimetinib), a MEK inhibitor currently in phase III clinical trials. Our study highlights that differences in the activation state of MEK in KRAS-mutant tumours versus BRAF-mutant tumours can be exploited through the design of inhibitors that uniquely target these distinct activation states of MEK. These inhibitors are currently being evaluated in clinical trials to determine whether improvements in therapeutic index within KRAS versus BRAF preclinical models translate to improved clinical responses in patients. 2013 Macmillan Publishers Limited. All rights reserve