Biosynthèse | EPFL Graph Search

La biosynthèse est la formation de substances par un être vivant ou son symbiote, dans son milieu interne ou dans les excrêtats que sont le mucus, les coquilles des œufs ou des mollusques, l’écorce Elle intéresse les chimistes et les biotechnologistes qui découvrent dans les cellules ou les organismes de nouveaux moyens, moins polluants ou moins énergivores, de produire des molécules complexes. La pharmacochimie étudie les substances biosynthétisées susceptibles d'avoir un intérêt industriel, médical et commercial, en particulier en milieu tropical où la biodiversité est la plus élevée et ces substances les plus nombreuses. Elle intéresse aussi architectes et prospectivistes qui imaginent faire produire des biomatériaux ; biomimétiquement ou par des organismes (bactéries, coraux) susceptibles de pouvoir jouer le rôle de puits de carbone. De nombreux animaux peuvent synthétiser le que l'on retrouve dans les os, les coquilles, les coraux. Certains organismes produisent des matériaux

Role of the cystathionine beta-synthase / H2S pathway in the development of cellular metabolic dysfunction and pseudohypoxia in down syndrome

Theodora Panagaki

Background: Overexpression of the transsulfuration enzyme cystathionine-beta-synthase (CBS), and overproduction of its product, hydrogen sulfide (H2S) are recognized as potential pathogenetic factors in Down syndrome (DS). The purpose of the study was to determine how the mitochondrial function and core metabolic pathways are affected by DS and how pharmacological inhibition of CBS affects these parameters. Methods: 8 human control and 8 human DS fibroblast cell lines have been subjected to bioenergetic and fluxomic and proteomic analysis with and without treatment with a pharmacological inhibitor of CBS. Results: DS cells exhibited a significantly higher CBS expression than control cells, and produced more H2S. They also exhibited suppressed mitochondrial electron transport and oxygen consumption and suppressed Complex IV activity, impaired cell proliferation and increased ROS generation. Inhibition of H2S biosynthesis with aminooxyacetic acid reduced cellular H2S, improved cellular bioenergetics, attenuated ROS and improved proliferation. C-13 glucose fluxomic analysis revealed that DS cells exhibit a suppression of the Krebs cycle activity with a compensatory increase in glycolysis. CBS inhibition restored the flux from glycolysis to the Krebs cycle and reactivated oxidative phosphorylation. Proteomic analysis revealed no CBS-dependent alterations in the expression level of the enzymes involved in glycolysis, oxidative phosphorylation and the pentose phosphate pathway. DS was associated with the dysregulation of several components of the autophagy network; CBS inhibition normalized several of these parameters. Conclusions: Increased H2S generation in DS promotes pseudohypoxia and contributes to cellular metabolic dysfunction by causing a shift from oxidative phosphorylation to glycolysis.

ELSEVIER2022

Mitochondrial respiratory chain dysfunction disrupts intracellular cholesterol homeostasis

Christopher Tadhg James Wall

Mitochondrial diseases are rare and severe conditions with debilitating symptoms. Biochemical defects in mitochondria however are common. The difference between these two frequencies is suspected to lie in the capability of the cells to adapt to the homeostatic disbalance. Cells activate retrograde signalling pathways in response to mitochondrial dysfunction, activating cellular transcriptional programs to correct for the disbalance. The full extent of the retrograde signals that are induced by mitochondrial dysfunctions still remains unknown. Studying these retrograde signalling pathways can lead to insights how to make the difference between restoring the homeostasis and a detrimental disease. Investigating the transcriptional responses to artificially induced mitochondrial dysfunction has proven to be lucrative in unveiling novel responses to mitochondrial defects. In this work we studied the transcriptional responses to three chemical models of mitochondrial respiratory chain dysfunction. In line with recently published work, we found a commonly upregulated stress response in all models. Interestingly, shared between all the models was a downregulation of genes enriched in cholesterol biosynthesis pathways. Upon closer examination this encompassed, almost without exception, all transcripts of the mevalonate pathway. This coordinated downregulation of transcripts had functional consequences on the output of the pathway, lowering the abundance of cholesterol precursor metabolites. Other metabolites in more upstream regions of the pathway were changed differently depending on the complex affected, suggesting other regulatory influences involved. Upon closer mechanistic investigation to the cause of the transcriptional suppression we found the main transcription factor responsible for mevalonate pathway gene transcription, the Sterol Response Element Binding Protein 2 (SREBP2), to be inhibited during complex I impairment. This was most evident in sterol depleted conditions where SREBP2 did not activate to normal levels. A decreased activation of SREBP2 is signature for an elevated concentration of ER-cholesterol. Indeed, other ER-bound cholesterol sensitive proteins confirmed this, showing a similar decreased abundance following complex I impairment in both normal and low lipid conditions. To investigate the source of this cholesterol we measured various cholesterol levels. No changes in the levels of total cholesterol (free cholesterol plus esterified cholesterol) were detected. Also, the fraction of free cholesterol was not significantly affected by complex I inhibition. Using the fluorescent cholesterol stain filipin, we were able to measure a modest but reproducible increase in intracellular free cholesterol. This provided novel mechanistic insight into the inhibition of ER sterol sensors and mevalonate pathway activity by mitochondrial dysfunction. Several well-known retrograde signalling pathways AMPK, ISR and mTOR did not explain the changes observed. The exact mechanism through which mitochondria incite an increase in intracellular free cholesterol remains unknown. Taken together this work can provide a mechanistic link between mitochondrial function and intracellular cholesterol homeostasis and could possibly link mitochondrial function to circulating lipoprotein homeostasis. Further work should focus on elucidating the possible mechanism, where differences in complex functions could provide a hint in the right direction.

EPFL2022

A comprehensive reconstruction of the fatty acid biosynthesis in Saccharomyces cerevisiae

Vassily Hatzimanikatis, Iro Oikonomidi, Georgios Savoglidis

The role of lipids in eukaryotic cells is of high importance. They are one of the main components of cell membranes, act as storage of high potential energy as well as being a scaffold of signaling proteins or participate in signaling themselves. Many diseases are associated with alterations in the lipid distribution in the cell and the composition of membrane domains. Metabolic syndrome, obesity, atherosclerosis, as well as Alzheimer’s, Huttington diseases and cancer, all originate from alterations in some stage of lipid biosynthesis. Therefore, advancement of knowledge in the field of lipid metabolism will provide novel insights for further biomedical research and potential strategies for drug development. Fatty acids are the backbone of the lipid metabolism. Being lipids themselves they also participate in the biosynthesis of the majority of the lipid classes. Thus, the study of their synthesis and biotransformation in a cell constitutes the basic step towards a systematic investigation of the phenomena attributed to lipids. In the current study we reconstructed a comprehensive representation of the biosynthesis of fatty acids in a model eukaryote such as Saccharomyces cerevisiae. The model accounts for approximately 300 reactions and 230 metabolites, taking part in 3 compartments of the cell, describing the steps of synthesis, elongation and β-oxidation of fatty acids. We make use of other systems approaches in order to identify the input fluxes to the model and we explore the diverse capabilities of the network with respect to flux profiles and distribution of fatty acids.

2013

Mitochondrial respiratory chain dysfunction disrupts intracellular cholesterol homeostasis

Christopher Tadhg James Wall

EPFL2022