Vorzeitiges Sterben in molekularbiologischer Perspektive

'In molekularer Perspektive ist Sterben nur dann als vorzeitig einzuordnen, wenn die Lebensspanne durch endogene Faktoren präzise vorgegeben ist und/ oder durch Vorgänge abgekürzt wird, die eindeutig außerhalb der physiologischen Funktionsabläufe des betroffenen Organismus liegen. Nach der allgemein anerkannten stochastischen Theorie über das Altern, die wiederum auf den Theorien zur Evolution von Medawar, Martin und Kirkwood basiert, ist die menschliche Lebensspanne durch einen multifaktoriellen stochastischen Prozess begrenzt ist, der keine genaue Vorhersage des Todeszeitpunkt zulässt. Daher hat das menschliche Leben keine eindeutige, intrinsische Begrenzung. In der Konsequenz bedeutet dies, dass der individuelle Todesfall auch nicht als vorzeitig beurteilt werden kann, während allgemeine Aussagen zu einer ganzen Bevölkerung auf Grundlage von epidemiologischen Daten sehr wohl getroffen werden können.' (Autorenreferat)'From a molecular point of view death is premature when life span is exactly delimited by endogenous factors and shortened by mechanisms and causes that are clearly no part of the internal delimination machinery. According to the most widely accepted, stochastic theory on aging based on the evolutionary theories of Medawar, Martin and Kirkwood, human lifespan is delimited by a multifactorial and stochastic process, not allowing a precise prediction of the endpoint in time. Thus, human life has no clear intrinsic deliminator. Consequently, human death cannot be judged by the above criteria quoad prematureness in the individual case, although general predictions can be made for whole populations on the basis of epidemiological data.' (author's abstract

C-Terminal regions of topoisomerase IIα and IIβ determine isoform-specific functioning of the enzymes in vivo

Topoisomerase II removes supercoils and catenanes generated during DNA metabolic processes such as transcription and replication. Vertebrate cells express two genetically distinct isoforms (α and β) with similar structures and biochemical activities but different biological roles. Topoisomerase IIα is essential for cell proliferation, whereas topoisomerase IIβ is required only for aspects of nerve growth and brain development. To identify the structural features responsible for these differences, we exchanged the divergent C-terminal regions (CTRs) of the two human isoforms (α 1173-1531 and β 1186-1621) and tested the resulting hybrids for complementation of a conditional topoisomerase IIα knockout in human cells. Proliferation was fully supported by all enzymes bearing the α CTR. The α CTR also promoted chromosome binding of both enzyme cores, and was by itself chromosome-bound, suggesting a role in enzyme targeting during mitosis. In contrast, enzymes bearing the β CTR supported proliferation only rarely and when expressed at unusually high levels. A similar analysis of the divergent N-terminal regions (α 1-27 and β 1-43) revealed no role in isoform-specific functions. Our results show that it is the CTRs of human topoisomerase II that determine their isoform-specific functions in proliferating cells. They also indicate persistence of some functional redundancy between the two isoforms

Living Long and Well: Prospects for a Personalized Approach to the Medicine of Ageing.

Research into ageing and its underlying molecular basis enables us to develop and implement targeted interventions to ameliorate or cure its consequences. However, the efficacy of interventions often differs widely between individuals, suggesting that populations should be stratified or even individualized. Large-scale cohort studies in humans, similar systematic 56 studies in model organisms, and detailed investigations into the biology of ageing can provide individual validated biomarkers and mechanisms, leading to recommendations for targeted interventions. Human cohort studies are already ongoing, and can be supplemented by in silico simulations. Systematic studies in animal models are made possible by the use of inbred strains, or genetic reference populations of mice. Combining both, the comprehensive picture of the various determinants of ageing and healthspan can be studied in detail, and an appreciation of the relevance of results from model organisms to humans emerges. The interactions between genotype and environment, particularly the psychosocial environment, are poorly studied in both humans and model organisms, presenting serious challenges to any approach to a personalized medicine of ageing. To increase success of preventive interventions, we argue that there is a pressing need for an individualized evaluation of interventions such as physical exercise, nutrition, nutraceuticals and calorie restriction mimetics as well as psychosocial and environmental factors, separately and in combination. The expected extension of healthspan enables us to refocus healthcare spending on individual prevention starting in late adulthood, and on the brief period of morbidity at very old age

Adaptation of topoisomerase I paralogs to nuclear and mitochondrial DNA

Topoisomerase I is essential for DNA metabolism in nuclei and mitochondria. In yeast, a single topoisomerase I gene provides for both organelles. In vertebrates, topoisomerase I is divided into nuclear and mitochondrial paralogs (Top1 and Top1mt). To assess the meaning of this gene duplication, we targeted Top1 to mitochondria or Top1mt to nuclei. Overexpression in the fitting organelle served as control. Targeting of Top1 to mitochondria blocked transcription and depleted mitochondrial DNA. This was also seen with catalytically inactive Top1 mutants, but not with Top1mt overexpressed in mitochondria. Targeting of Top1mt to the nucleus revealed that it was much less able to interact with mitotic chromosomes than Top1 overexpressed in the nucleus. Similar experiments with Top1/Top1mt hybrids assigned these functional differences to structural divergences in the DNA-binding core domains. We propose that adaptation of this domain to different chromatin environments in nuclei and mitochondria has driven evolutional development and conservation of organelle-restricted topoisomerase I paralogs in vertebrates

Proteome-wide analysis reveals an age-associated cellular phenotype of in situ aged human fibroblasts

We analyzed an ex vivo model of in situ aged human dermal fibroblasts, obtained from 15 adult healthy donors from three different age groups using an unbiased quantitative proteome-wide approach applying label-free mass spectrometry. Thereby, we identified 2409 proteins, including 43 proteins with an age-associated abundance change. Most of the differentially abundant proteins have not been described in the context of fibroblasts' aging before, but the deduced biological processes confirmed known hallmarks of aging and led to a consistent picture of eight biological categories involved in fibroblast aging, namely proteostasis, cell cycle and proliferation, development and differentiation, cell death, cell organization and cytoskeleton, response to stress, cell communication and signal transduction, as well as RNA metabolism and translation. The exhaustive analysis of protein and mRNA data revealed that 77 % of the age-associated proteins were not linked to expression changes of the corresponding transcripts. This is in line with an associated miRNA study and led us to the conclusion that most of the age-associated alterations detected at the proteome level are likely caused post-transcriptionally rather than by differential gene expression. In summary, our findings led to the characterization of novel proteins potentially associated with fibroblast aging and revealed that primary cultures of in situ aged fibroblasts are characterized by moderate age-related proteomic changes comprising the multifactorial process of aging

Differential Allocation of Constitutive and Induced Chemical Defenses in Pine Tree Juveniles: A Test of the Optimal Defense Theory

Optimal defense theory (ODT) predicts that the within-plant quantitative allocation of defenses is not random, but driven by the potential relative contribution of particular plant tissues to overall fitness. These predictions have been poorly tested on long-lived woody plants. We explored the allocation of constitutive and methyl-jasmonate (MJ) inducible chemical defenses in six half-sib families of Pinus radiata juveniles. Specifically, we studied the quantitative allocation of resin and polyphenolics (the two major secondary chemicals in pine trees) to tissues with contrasting fitness value (stem phloem, stem xylem and needles) across three parts of the plants (basal, middle and apical upper part), using nitrogen concentration as a proxy of tissue value. Concentration of nitrogen in the phloem, xylem and needles was found to be greater higher up the plant. As predicted by the ODT, the same pattern was found for the concentration of non-volatile resin in the stem. However, in leaf tissues the concentrations of both resin and total phenolics were greater towards the base of the plant. Two weeks after MJ application, the concentrations of nitrogen in the phloem, resin in the stem and total phenolics in the needles increased by roughly 25% compared with the control plants, inducibility was similar across all plant parts, and families differed in the inducibility of resin compounds in the stem. In contrast, no significant changes were observed either for phenolics in the stems, or for resin in the needles after MJ application. Concentration of resin in the phloem was double that in the xylem and MJ-inducible, with inducibility being greater towards the base of the stem. In contrast, resin in the xylem was not MJ-inducible and increased in concentration higher up the plant. The pattern of inducibility by MJ-signaling in juvenile P. radiata is tissue, chemical-defense and plant-part specific, and is genetically variable