1,720,959 research outputs found
Mitochondrial oxidative phosphorylation plasticity/adaptation triggered by disturbances and stresses and targeted by therapies
Full text linkMitochondrion is an important organelle for cells survival. In fact, it is responsible for many processes such as cellular metabolism, i.e. oxidative phosphorylation for ATP production, energy homeostasis and regulation of apoptosis and autophagy. Mitochondrion, due to this role, needs to be “plastic” in order to respond and adapt quickly to any perturbation and change of conditions in the different tissues of the human body. The induction of mitochondria biogenesis is required to meet different energetic demands under stress conditions. Thus, mitochondrial plasticity is the mechanism that controls modification in conditions of cellular stress or in response to environmental stimuli like exercise, caloric restriction, cold exposure, oxidative stress, cell division and renewal, and differentiation. Recently, mitochondrial modulation has become also a topic of interest as a therapeutic target. The master regulator gene of mitochondrial biogenesis is PGC1α that, through nuclear transcription factors and subsequent metabolic sensors and other signalling proteins, is capable to modulate mitochondrial abundance, activity and oxidative phosphorylation as a consequence of energy homeostasis unbalance. Mitochondrial plasticity during the last few years was extensively studied in skeletal muscle models, due to its fast adaptation in exercise and rest condition, but also in cancer cachexia, ageing and heart disease. Also in cancer, mitochondrial adaptations have become a fundamental topic, in particular to understand the underling pathogenic mechanism of disease progression, to identify prognostic factors and to design adjuvant therapies targeting mitochondria.
In this frame, this PhD Thesis investigates the role and adaptations of mitochondria in different pathophysiological models of skeletal muscle and brain tumors.
The expression of some key proteins of the signalling pathways involved in mitochondrial biogenesis regulation, such as PGC1α, LKB1-AMPK an energy sensing axis, Sirt3 a regulator of mitochondrial enzymes functionality, are investigated together with the OXPHOS complexes, HSP60, CS and TOM20 as mitochondrial mass markers.
The first model is aimed at testing the expression levels of the protein panel in skeletal muscle biopsies from a cohort of 16 elderly and 7 young people subjected to immobility (bed-rest) causing hypotrophy and subsequent rehabilitation via exercise training. Based on quantitative immunoblot data, there is a down-regulation of PGC1α, Sirt3 and OXPHOS complexes II, III and IV occurring during bed-rest with a subsequent up-regulation after rehabilitation in both groups. AMPK and LKB1 do not change during bed-rest and rehabilitation in elderly and young subjects suggesting that there is not energetic impairment. According to the down-regulation of OXPHOS biogenesis during bed-rest there is the up-regulation of GAPDH evocative of a metabolic shift during hypotrophy from oxidative phosphorylation towards glycolysis, which is reversed by exercise training. OXPHOS complex V is down-regulated in both groups during bed-rest, but after rehabilitation the complex expression does not increase, maybe due to an imbalance between protein biogenesis and degradation. It is tempting to speculate that exercise could regulate complex V activity, as a compensatory response, through deacetylation mediated by Sirt3, which is up-regulated after rehabilitation. CS and TOM20 present the same pattern: in elderly subjects there is a down-regulation during immobility that is counteracted by exercise training, whereas young subjects present a similar pattern but differences do not reach statistical significance. In conclusion, immobility is effective in down-regulation of mitochondria-related protein expression and training protocol counteracts this effect. The pattern is similar in both elderly and young subjects, with some differences for PGC1α, and Sirt3 appearing less responsive to rehabilitation in elderly.
Training is a fundamental tool to recover from immobility periods but also to maintain muscle tonicity as a non-pharmacologic therapeutic treatment for chronic heart failure patients (CHF). In the second model is studied the effect of aerobic exercise training (2 months) on mitochondrial respiration in skeletal muscle of CHF transgenic (Tgαq*44) mice, focusing also on the impact of CHF on skeletal muscle of sedentary mice. Oxidative phosphorylation and electron transport system capacity of biopsies from soleus muscle is assayed by high-resolution respirometry. Sedentary CHF mice exhibit in comparison to wild type an impaired complex I – State 3 respiration and ADP-stimulated respiration sustained by Complex I+II, in contrast to rotenone insensitive electron transport system respiration that is unchanged. This suggests an inactivation of complex I rather than an impairment of OXPHOS biogenesis in soleus muscle, also confirmed by unchanged value of PGC1α expression. Exercise training improves exercise performance, but it does not affect mitochondrial respiration. Factors “upstream” of mitochondria are likely mainly responsible for the functional improvement.
The third model focuses on the study of ATP synthase Inhibitory Factor 1 as prognostic marker in low-grade astrocytomas (LGA). 19 pairs of surgical specimens of LGA are evaluated for the tumor border zone in which IF1 abundance is significantly lower than in the tumoral zone. Immunohistochemistry analyses of 68 specimens by Tissue-MicroArrays prove a weak association of IF1 with NF-kB p65-subunit and consolidated radiologic indexes of tumor infiltration and resection. Kaplan–Meier estimation of patients overall survival indicates that IF1 may serve as a prognostic marker. Intriguingly, IF1 expression significantly increases in lesions with suspected first signs of anaplastic transformation (LGA*) as showed, in accordance, by immunofluorescence (12 specimens), immunohistochemistry (11) and immunoblot (9) analyses. Finally, immunoblot analyses provide a picture of mitochondrial and glycolytic markers, suggesting no improvement of glycolysis and little changes in mitochondrial mass. On the contrary, OXPHOS complexes show a significant upregulation in LGA*. IF1 expression levels could be proposed as a biomarker of OS in LGA, rare tumors with a good prognosis, which could nonetheless evolve in anaplastic lesions and are still without an adjuvant therap
Mitochondrial energy metabolism and signalling in human glioblastoma cell lines with different PTEN gene status
No full textGlioblastomas epidemiology and aggressiveness demand for a well characterization of biochemical mechanisms of the cells. The discovery of oxidative tumours related to chemoresistance is changing the prevalent view of dysfunctional mitochondria in cancer cells. Thus, glioblastomas metabolism is now an area of intense research, wherein was documented a high heterogeneity in energy metabolism and in particular in mitochondrial OxPhos. We report results gained by investigating mitochondrial OxPhos and bioenergetics, in a model of three human glioblastoma cell lines characterized by a different PTEN gene status. Functional data are analysed in relation to the expression levels of some main transcription factors and signalling proteins, which can be involved in the regulation of mitochondrial biogenesis and activity. Collectively, our observations indicate for the three cell lines a similar bioenergetic phenotype maintaining a certain degree of mitochondrial oxidative activity, with some difference for PTEN-wild type SF767 cells respect to PTEN-deleted A172 and U87MG characterized by a loss-of-function point mutation of PTEN. SF767 has lower ATP content and higher ADP/ATP ratio, higher AMPK activating-phosphorylation evoking energy impairment, higher OxPhos complexes and PGC1α-Sirt3-p53 protein abundance, in line with a higher respiration. Finally, SF767 shows a similar mitochondrial energy supply, but higher non-phosphorylating respiration linked to dissipation of protonmotive force. Intriguingly, it is now widely accepted that a regulated mitochondrial proton leak attenuate ROS generation and in tumours may be at the base of pro-survival advantage and chemoresistance
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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