117 research outputs found
Mitochondrial bioenergetics and neurodegeneration: A paso doble
No full textMitochondria and neuronal activity: The brain is one of the highest energy demanding organs, consuming ~20% of the total ATP produced by the whole body. Importantly, neurons mainly rely on ATP synthesized by mitochondrial bioenergetics and neuronal activity is strictly dependent on specific mitochondrial localization at synapses, sites consuming a high amount of energy requested for both pre- and post-synaptic processes. Here, mitochondria produce ATP and buffer Ca2+ rises, two essential processes for neurotransmission and generation of membrane potential along the axon
Calcium, mitochondria and cell metabolism: A functional triangle in bioenergetics
No full textThe versatility of mitochondrial metabolism and its fine adjustments to specific physiological or pathological conditions regulate fundamental cell pathways, ranging from proliferation to apoptosis. In particular, Ca 2+ signalling has emerged as a key player exploited by mitochondria to tune their activity according with cell demand. The functional interaction between mitochondria and endoplasmic reticulum (ER) deeply impacts on the correct mitochondrial Ca 2+ signal, thus modulating cell bioenergetics and functionality. Indeed, Ca 2+ released by the ER is taken up by mitochondria where, both in the intermembrane space and in the matrix, it regulates the activity of transporters, enzymes and proteins involved in organelles' metabolism. In this review, we will briefly summarize Ca 2+ -dependent mechanisms involved in the regulation of mitochondrial activity. Moreover, we will discuss some recent reports, in which alterations in mitochondrial Ca 2+ signalling have been associated with specific pathological conditions, such as neurodegeneration and cancer
A meta-analysis assessing the effectiveness of demand-side interventions for sustainable food consumption and food waste reduction
No full textReplication package for "Demand-side interventions for sustainable food systems: A meta-analysis of food-policy interventions targeting food consumption and waste behaviours" by Paul M. Lohmann, Alice Pizzo, Jan M. Bauer, Tarun M. Khanna, Max Callaghan, Jan Minx, Lucia A. Reisc
A Critical Discourse Analysis of the Volkswagen Letter to Shareholders after the Diesel Scandal
No full textCorporate scandals are events frequently followed by public distrust, intensified scrutiny and corporate measures aimed at explaining the wrongdoing. In the attempt to cope with these adverse consequences, companies may adopt a responsibility-driven approach to reporting and leverage on voluntary reporting to fulfil share/stakeholders’ informational rights. Letter to shareholders (LS) is one of the most important form of voluntary reporting that facilitates the company (in the person of the signer) to address a message to share/stakeholders. Drawing on Gray, Owen, and Adams’s (1996) definition of accountability, this study aims to inspect how LS helps discharge the duty to provide explanations in time of scandals. It particularly focuses on the Volkswagen “dieselgate” and critically examines the discourses that dominate the LS issued in the annual report 2015. The findings point out that the LS serves as an official document to openly apologise about the occurrence and refers to the scandal through metaphors and value assumptions. In particular, Volkswagen Chief Executive Officer writes about the scandal throughout the LS, however without mentioning the word “dieselgate”, and represents all the social actors involved in, and affected by, the scandal. This study contributes to prior literature on the Volkswagen dieselgate by providing insights on the company communication behaviour. It also contributes to extant literature on the LS by adding understandings of the discourses that may help companies discharge accountability through this document, especially in time of scandals
Gendering the comic body: Physical humour in <i>Shirley</i>
No full textThe mock-battles and slap-stick scenes that arise at pivotal moments in Shirley encourage us to reexamine Brontë’s sense of humour, which is neither as grim, nor as naively crude as critics from George Henry Lewes to Virginia Woolf have deemed it. Drawing on Brontë’s engagement with the theatrical traditions of European Carnival and British pantomime, this chapter demonstrates how physical humour in Shirley satirises the gendered dictates of literary realism that Lewes had laid out for the author in public reviews and private correspondence. By rejecting the witty drawing-room comedy often associated with her predecessor Jane Austen, and adopting the brash language of the body common to both popular performance and the work of her male peers Charles Dickens and William Makepeace Thackeray, Brontë participates in important mid-nineteenth-century debates about gendered authorship and the literary marketplace.<br/
PSEN2 (presenilin 2) mutants linked to familial Alzheimer disease impair autophagy by altering Ca2+ homeostasis.
No full textPS2 (presenilin 2) is one of the 3 proteins that, when mutated, causes early onset familial Alzheimer disease (FAD) cases. In addition to its well-known role within the -secretase complex (the enzyme ultimately responsible for A peptides formation), PS2 is endowed with some -secretase-independent functions in distinct cell signaling pathways, such as the modulation of intracellular Ca2+ homeostasis. Here, by using different FAD-PS2 cell models, we demonstrate that mutated PS2 impairs autophagy by causing a block in the degradative flux at the level of the autophagosome-lysosome fusion step. The defect does not depend on an altered lysosomal functionality but rather on a decreased recruitment of the small GTPase RAB7 to autophagosomes, a key event for normal autophagy progression. Importantly, FAD-PS2 action on autophagy is unrelated to its -secretase activity but depends on its previously reported ability to partially deplete ER Ca2+ content, thus reducing cytosolic Ca2+ response upon IP3-linked cell stimulations. Our data sustain the pivotal role for Ca2+ signaling in autophagy and reveal a novel mechanism by which FAD-linked PSs alter the degradative process, reinforcing the view of a causative role for a dysfunctional quality control pathway in AD neurodegeneration
Mitochondrial Ca2+ handling and behind: the importance of being in contact with other organelles.
No full text
Effects of Presenilin 2 mutations associated with Familial Alzheimer's Disease on mitochondrial bioenergetics
No full textAlzheimer’s Disease (AD) is a neurodegenerative disorder of the central nervous system. It is mainly sporadic, however, a little percentage of cases is inherited (Familial AD, FAD) and due to autosomal dominant mutations on three different genes, coding for Amyloid Precursor Protein (APP), Presenilin 1 (PS1) and Presenilin 2 (PS2). Presenilins, mainly localized at Endoplasmic Reticulum (ER) membranes, are the catalytic core of the ɣ-secretase complex, although several ɣ-secretase-independent activities of PSs, such as modulation of neurites outgrowth, apoptosis, autophagy, synaptic functions and regulation of Ca2+ homeostasis, have been described.
Ca2+, a key intracellular second messenger, is involved in multiple cellular functionalities. Interestingly, alterations in Ca2+ homeostasis have been proposed as an early event in different neurodegenerative diseases, including AD. Notably, FAD-PS mutants have been reported to be directly involved in these dysregulations. In our lab, it has been previously showed that PS2 expression, both WT and, more potently, FAD mutants (such as PS2-T122R), but not PS1, decreases the ER Ca2+ content, mainly by inhibiting SERCA pump activity. Moreover, PS2 increases ER-mitochondria physical and functional coupling, favouring the process of ER to mitochondria Ca2+ transfer. However, due to its effect on ER [Ca2+], which results in a lower amount of available Ca2+ within the ER, its expression dampens mitochondrial Ca2+ rises upon cell stimulation.
Based on the well-established role of Ca2+ on mitochondrial metabolism, here we investigate the possible effects on mitochondrial functionalities of the complex balance between alterations in ER Ca2+ content and increased ER-mitochondria coupling, induced by FAD-PS2 mutants expression. A neuroblastoma cell line (SH-SY5Y) grown in a medium containing galactose, as a substitute of glucose, has been used. This growth condition enhances mitochondrial metabolism and results in an excellent experimental protocol to visualize possible mitochondrial defects.
Lower total cellular ATP levels were measured in FAD-PS2-T122R expressing cells, grown either in glucose- or galactose-containing medium, with the reduction more evident in the latter condition, thus suggesting possible mitochondrial defects induced by PS2 expression.
In order to investigate how Ca2+ dysregulation induced by PS2 could influence mitochondrial metabolism, we stimulated mitochondrial ATP production inducing ER Ca2+ release, followed by mitochondria Ca2+ uptake, using both bradykinin, as a maximal IP3R stimulation, and Fetal Calf Serum (FCS), as a more physiological stimulus. In both conditions, a reduction in mitochondrial ATP production, measured by a mitochondrial luciferase-based ATP probe, has been observed in cells expressing FAD-PS2, but not PS1. The defects in ATP synthesis were observed in SH-SY5Y, MEF, HT22 cells and in cortical neurons from PS2-N141I transgenic (Tg) mice (PS2.30H), by employing FRET-based ATP probes (ATeam 1.03) specifically targeted to the mitochondrial matrix or the nucleus. We also evaluated the glycolytic flux in these cells, by both employing a cytosolic luciferase-based ATP probe and measuring the extracellular medium acidification, but we did not observed any difference in these two parameters in FAD-PS2 expressing cells, compared to controls.
In order to understand the mechanism through which PS2 causes the observed mitochondrial dysfunction, we firstly considered the marked Ca2+ dysregulation induced by PS2 expression. We thus decided to modulate Ca 2+ handling in control cells, to mimic the ER Ca2+ depletion caused by PS2 expression. We used two different approaches: i) treating control cells with a SERCA pump inhibitor (Cyclopiazonic acid, CPA), to partially reduce the ER Ca2+ content, or ii) overexpressing a mutated-MICU1 (MICU1mut), a component of the mitochondrial Ca2+ uniporter complex. Although both approaches were able to reduce the capacity of control cells to produce ATP, for similar mitochondrial Ca2+ uptake in control and PS2-expressing cells, a lower mitochondrial ATP production in FAD-PS2 expressing-cells compared to CPA-treated or MICU1mut expressing controls was still observed. Taken together, these results suggest that part of the FAD-PS2-induced defects in mitochondrial metabolism is due to a reduced ER Ca2+ content and, consequently, mitochondrial Ca2+ uptake, negatively regulating the Ca2+-dependent mitochondrial metabolism. However, additional mechanisms, induced by FAD-PS2, are likely involved in mitochondrial dysfunctions. We thus evaluated the respiratory chain activity measuring the oxygen consumption rate (OCR): both basal and maximal OCR were reduced in FAD-PS2, but not in FAD-PS1, expressing cells. Moreover, a reduced mitochondrial ATP-linked respiration was measured in PS2-T122R expressing cells, while no difference was found in the proton leak.
Since the expression levels of the ATP synthase and the respiratory chain complexes were not affected by FAD-PS2 expression, and isolated mitochondria from WT and PS2-N141I Tg mice did not reveal substantial differences in mitochondrial respiratory activity, we reasoned that the impairment in ATP production observed in intact cells is not due to defective mitochondria per se, but likely depends on the cellular environment.
Importantly, for a proper mitochondrial metabolism, the right amount of substrates produced through glycolysis in the cytosol has to reach the mitochondrial matrix to support the TCA cycle and the respiratory chain activity. Hexokinase1 (HK1), the enzyme that catalyses the first step of glycolysis converting glucose to glucose 6-phosphate, seems to be involved in the modulation of the mitochondrial substrates import, since HK1 interaction/detachment with/from mitochondria can modulate mitochondrial substrates permeability. Firstly, we measured a reduced HK1-mitochondria co-localization in FAD-PS2 expressing SH-SY5Y cells, in FAD-PS2 patient-derived fibroblasts and in primary cortical neurons from FAD-PS2-N141I Tg mice, compared to controls. By mimicking the FAD-PS2 effect on HK1-mitochondria interaction treating control cells with Clotrimazole, a drug capable to detach HK1 from mitochondria, a reduced mitochondrial ATP production was measured; however, the impairment on ATP production induced by clotrimazole was less marked than that caused by FAD-PS2 expression. These results indicate that, although the detachment of HK1 from mitochondria plays a pivotal role in causing mitochondrial defects upon FAD-PS2 expression, the PS2-induced Ca2+ dysregulation, described above, may additionally contribute to the overall mitochondrial impairment. These results have been confirmed also by a genetic approach. We down-regulated the expression of endogenous HK1, by specific siRNAs, and we rescued HK1 protein level by over-expressing siRNA-resistant full-length- (FL-HK1) or truncated- (Tr-HK1) HK1. This latter protein lacks the mitochondrial binding domain, but still conserves the catalytic activity. We found that, upon endogenous HK1 silencing, mitochondrial ATP production is strongly reduced. Interestingly, while the re-expression of FL-HK1 was able to completely rescue the reduced ATP production, the Tr-HK1 was unable to do it, again confirming that the detachment of HK1 from mitochondria is involved in the mitochondrial impairment caused by FAD-PS2.
Related to HK1 and its role in the regulation of mitochondrial substrates permeability, an increase in the cytosolic amount of pyruvate was measured in FAD-PS2 expressing cells, compared to controls, employing a cytosolic FRET-based pyruvate probe, Pyronic. Importantly, by pharmacologically blocking mitochondrial pyruvate carrier (MPC), the protein responsible for mitochondrial pyruvate uptake, with two different drugs, UK5099 and Pioglitazone, no differences were anymore detected between control and FAD-PS2 expressing cells, suggesting that FAD-PS2 is acting on this pathway.
Overall, we have showed that FAD-PS2 mutants decrease cellular ATP levels, in particular mitochondrial ATP production, by two different mechanisms: 1) causing Ca2+ dysregulation, mainly decreasing the ER Ca2+ content, and thus the amount of Ca2+ available for mitochondrial Ca2+ uptake; 2) inducing the detachment of HK1 from mitochondria, likely affecting the availability of substrates (i.e., pyruvate) for mitochondria. Further experiments will be aimed at: i) evaluate the impact of the PS2-dependent strengthened ER-mitochondria coupling on the reported mitochondrial defects; ii) defining the molecular mechanism through which FAD- PS2 mutants affect HK1 intracellular distribution; iii) evaluate the impact of these alterations on the onset/progression of the AD phenotype
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