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Tatu A. Miettinen - One of the best experts on this subject based on the ideXlab platform.
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choleSterol in vegetarians: effects of choleSterol feeding13
2016Co-Authors: Maui Vuoristo, Tatu A. MiettinenAbstract:ABSTRACT Serum concentrations and metabolism of cho-leSterol were studied in vegetarians basally and during a dietary choleSterol load. CholeSterol absorption efficiency was normal and synthesis was slightly enhanced, even though serum choles-terol precursors were not increased. The serum concentrations of total and low-density-lipoprotein choleSterol were decreased pro-portionally to the reduced intake and absolute absorption of cho-leSterol. Fecal plant Sterols were negatively correlated with the absorption efficiency ofcholeSterol and positively with fecal ster-ols and choleSterol synthesis, suggesting interference of high plant Sterol intakes with choleSterol absorption. CholeSterol sat-uration and bile acid composition of the bile were not changed. The increased serum plant Sterol-choleSterol ratios were posi-tively related to the intake and negatively to the biliary secretion of plant Sterols. CholeSterol feeding increased absolute choles-terol absorption and serum concentrations of total and low-den-sity-lipoprotein choleSterol, did not change absorption efficiency or synthesis of choleSterol, but increased fecal cholestanol excretion. Am J Clin Nutr l994;59:l325-3l. KEY WORDS Vegetarians, serum lipoproteins, cholestero
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the effects of statins and sitoSterols benefit or not
Current Atherosclerosis Reports, 2009Co-Authors: Tatu A. Miettinen, Helena GyllingAbstract:Statins reduce plasma plant Sterol concentrations and, less consistently, their ratios to choleSterol in short-term studies. They most likely accomplish this by decreasing their transport protein levels. In long-term treatment with large doses of effective statins, serum plant Sterol concentrations and frequently their ratios to choleSterol are consistently increased, especially with high, as opposed to low, baseline ratios. Enhanced intestinal absorption, decreased biliary secretion, and reversed choleSterol and plant Sterol transport could explain these findings. However, statin treatment increases plant Sterol ratios in serum and also in arterial plaques of endarterectomized patients. No trials of functional foods with plant Sterols or stanols are available for coronary heart disease, even though their combination with statins effectively reduces low-density lipoprotein choleSterol. Plant Sterols increase and plant stanols decrease serum plant Sterols. Long-term statin treatment lowers coronary heart disease events only in patients with low baseline plant Sterols who have high choleSterol synthesis. No convincing evidence is available that statin-induced phytoSterolemia worsens atherosclerosis.
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Effect of statins on noncholeSterol Sterol levels: implications for use of plant stanols and Sterols.
American Journal of Cardiology, 2005Co-Authors: Tatu A. MiettinenAbstract:Normal serum contains small amounts of noncholeSterol Sterols, including those reflecting choleSterol absorption and those that are markers of choleSterol synthesis. Absorption marker Sterols include serum plant Sterols, whereas choleSterol precursor Sterols correlate with whole-body synthesis of choleSterol. Thus, serum noncholeSterol Sterols, and especially their ratios to choleSterol, can be used to evaluate the major features of choleSterol metabolism (ie, synthesis and absorption). Statin treatment reduces serum choleSterol precursors but increases serum plant Sterols severalfold, especially in subjects with high-absorption marker Sterol levels indicative of efficient choleSterol and Sterol absorption in general. Statin therapy is most effective in subjects with high serum choleSterol precursor levels. In subjects with high-absorption Sterol markers, dietary choleSterol absorption inhibition (eg, with plant stanol and Sterol ester margarine) needs to be combined with a statin to achieve effective serum choleSterol reduction. However, whereas dietary plant stanol esters reduce statin-induced elevations of serum plant Sterol levels, serum plant Sterol levels remain elevated during dietary plant Sterol ester consumption. The clinical implication of high serum plant Sterol levels is under active investigation.
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non choleSterol Sterols in serum lipoproteins and red cells in statin treated fh subjects off and on plant stanol and Sterol ester spreads
Clinica Chimica Acta, 2005Co-Authors: Anna Ketomäki, Helena Gylling, Tatu A. MiettinenAbstract:Abstract Background Serum plant Sterol levels are increased by consumption of statins and dietary plant Sterols, and decreased by dietary plant stanols, but little is known about combination therapy of statin and plant Sterols. Methods We measured plant Sterols in serum, lipoproteins, and red cells in subjects with familial hypercholeSterolemia (FH) (n=18) treated with variable doses of statins off and on plant stanol (STA) and Sterol ester (STE) spreads. Results STA and STE spreads lowered LDL choleSterol ∼15%. Plant Sterols were decreased in serum, lipoproteins, and red cells by ∼25% with STA and increased from 37% to 80% with STE, especially with high statin doses. The changes in serum were related to those in red cells. The baseline levels of serum plant Sterols were negatively (r-range −0.639 to −0.935) and positively (r-range 0.526 to 0.598) correlated with the respective changes evoked by the STA and STE spreads. Conclusions STE reduces LDL choleSterol, but increases serum, lipoprotein, and red cell plant Sterol levels in statin-treated FH subjects, while all the respective values are decreased with STA. Recent predictions that elevated serum plant Sterols pose an increased coronary risk suggest that increases of serum plant Sterol levels should be avoided, especially in atherosclerosis-prone individuals, such as subjects with FH.
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plant Sterols biosynthesis biological function and their importance to human nutrition
Journal of the Science of Food and Agriculture, 2000Co-Authors: Vieno Piironen, Tatu A. Miettinen, Jari Toivo, David G Lindsay, Anna-maija LampiAbstract:Plant Sterols are an essential component of the membranes of all eukaryotic organisms. They are either synthesised de novo or taken up from the environment. Their function appears to be to control membrane fluidity and permeability, although some plant Sterols have a specific function in signal transduction. The phytoSterols are products of the isoprenoid pathway. The dedicated pathway to Sterol synthesis in photosynthetic plants occurs at the squalene stage through the activity of squalene synthetase. Although the activity of 3-hydroxymethyl-3-glutaryl coenzyme A (HGMR) is rate-limiting in the synthesis of choleSterol, this does not appear to be the case with the plant Sterols. Up-regulation of HGMR appears to increase the biosynthesis of cycloartenol but not the Δ5-Sterols. A decline in Sterol synthesis is associated with a suppression of squalene synthetase activity, which is probably a critical point in controlling carbon flow and end-product formation. The major post-squalene biosynthetic pathway is regulated by critical rate-limiting steps such as the methylation of cycloartenol into cycloeucalenol. Little is known about the factors controlling the biosynthesis of the end-point Sterol esters or stanols. The commonly consumed plant Sterols are sitoSterol, stigmaSterol and campeSterol which are predominantly supplied by vegetable oils. The oils are a rich source of the steryl esters. Less important sources of Sterols are cereals, nuts and vegetables. The nutritional interest derives from the fact that the Sterols have a similar structure to choleSterol, and have the capacity to lower plasma choleSterol and LDL choleSterol. Since the morbidity and mortality from cardiovascular disease have been dramatically reduced using choleSterol-lowering drugs (statins), the interest in plant Sterols lies in their potential to act as a natural preventive dietary product. Stanols (saturated at C-5) occur in low amounts in the diet and are equally effective in lowering plasma choleSterol and do not cause an increase in plasma levels, unlike the Sterols which can be detected in plasma. © 2000 Society of Chemical Industry
Jonathan Cohen - One of the best experts on this subject based on the ideXlab platform.
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selective Sterol accumulation in abcg5 abcg8 deficient mice
Journal of Lipid Research, 2004Co-Authors: Klaus Von Bergmann, Dieter Lutjohann, Helen H Hobbs, Jonathan CohenAbstract:The ATP binding cassette (ABC) transporters ABCG5 and ABCG8 limit intestinal absorption and promote biliary secretion of neutral Sterols. Mutations in either gene cause sitoSterolemia, a rare recessive disease in which plasma and tissue levels of several neutral Sterols are in- creased to varying degrees. To determine why patients with sitoSterolemia preferentially accumulate noncholeSterol ste- rols, levels of choleSterol and the major plant Sterols were compared in plasma, liver, bile, and brain of wild-type and ABCG5/ABCG8-deficient ( G5G8 � / � ) mice. The total Sterol content of liver and plasma was similar in G5G8 � / � mice and wild-type animals despite an � 30-fold increase in non- choleSterol Sterol levels in the knockout animals. The relative enrichment of each Sterol in the plasma and liver of G5G8 � / � mice (stigmaSterolsitoSterolcholestanolbassicas- terolcampeSterolcholeSterol) reflected its relative en- richment in the bile of wild-type mice. These results indi- cate that 24-alkylated, � 22 , and 5 � -reduced Sterols are preferentially secreted into bile and that preferential biliary secretion of noncholeSterol Sterols by ABCG5 and ABCG8 prevents the accumulation of these Sterols in normal ani- mals. The mRNA levels for 13 enzymes in the choleSterol biosynthetic pathway were reduced in the livers of the G5G8 � / � mice, despite a 50% reduction in hepatic choles- terol level. Thus, the accumulation of Sterols other than choleSterol is sensed by the choleSterol regulatory machin- ery. —Yu, L., K. von Bergmann, D. Lutjohann, H. H. Hobbs, and J. C. Cohen. Selective Sterol accumulation in ABCG5/ ABCG8-deficient mice. J. Lipid Res. 2004. 45: 301-307.
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heritability of plasma noncholeSterol Sterols and relationship to dna sequence polymorphism in abcg5 and abcg8
Journal of Lipid Research, 2002Co-Authors: Knut Erik Berge, Klaus Von Bergmann, Dieter Lutjohann, Rudy Guerra, Helen H Hobbs, Scott M. Grundy, Jonathan CohenAbstract:: The plasma concentrations of choleSterol precursor Sterols and plant Sterols vary over a 5- to 10-fold range among normolipidemic individuals, and provide indices of the relative rates of choleSterol synthesis and fractional absorption. In the present study, we examined the relative contributions of genetic and environmental factors to variation in the plasma concentrations and Sterol-choleSterol ratios of five noncholeSterol Sterols, including the 5alpha-saturated derivative of choleSterol (cholestanol), two precursors in the choleSterol biosynthesis pathway (desmoSterol and lathoSterol), and two phytoSterols (campeSterol and sitoSterol). Plasma Sterol concentrations were highly stable in 30 individuals measured over a 48 week period. Regression of offspring Sterol levels on the parental values indicated that plasma levels of all five noncholeSterol Sterols were highly heritable. Analysis of monozygotic and dizygotic twin pairs also indicated strong heritability of all five Sterols. Two common sequence variations (D19H and T400K) in ABCG8, an ABC half-transporter defective in sitoSterolemia, were associated with lower concentrations of plant Sterols in parents, and in their offspring.Taken together, these findings indicate that variation in the plasma concentrations of noncholeSterol Sterols is highly heritable, and that polymorphism in ABCG8 contributes to genetic variation in the plasma concentrations of plant Sterols.
Damien P. Devos - One of the best experts on this subject based on the ideXlab platform.
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essentiality of Sterol synthesis genes in the planctomycete bacterium gemmata obscuriglobus
Nature Communications, 2019Co-Authors: Elena Rivasmarin, Sean Stettner, Ekaterina Y Gottshall, Mitch Helling, Carlos Santanamolina, Naomi L Ward, Franco Basile, Damien P. DevosAbstract:Sterols and hopanoids are chemically and structurally related lipids mostly found in eukaryotic and bacterial cell membranes. Few bacterial species have been reported to produce Sterols and this anomaly had originally been ascribed to lateral gene transfer (LGT) from eukaryotes. In addition, the functions of Sterols in these bacteria are unknown and the functional overlap between Sterols and hopanoids is still unclear. Gemmata obscuriglobus is a bacterium from the Planctomycetes phylum that synthesizes Sterols, in contrast to its hopanoid-producing relatives. Here we show that Sterols are essential for growth of G. obscuriglobus, and that Sterol depletion leads to aberrant membrane structures and defects in budding cell division. This report of Sterol essentiality in a prokaryotic species advances our understanding of Sterol distribution and function, and provides a foundation to pursue fundamental questions in evolutionary cell biology. Sterols play essential functions in eukaryotic cell membranes, but are produced by few bacterial species. Here, the authors show that they are essential for growth of the planctomycete bacterium Gemmata obscuriglobus.
Dieter Lutjohann - One of the best experts on this subject based on the ideXlab platform.
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effects of plant Sterol or stanol enriched margarine on fasting plasma oxyphytoSterol concentrations in healthy subjects
Atherosclerosis, 2013Co-Authors: Sabine Baumgartner, Dieter Lutjohann, Ronald P. Mensink, Constanze Husche, Jogchum PlatAbstract:Abstract Background Consumption of plant Sterols and plant stanols reduces low-density lipoprotein choleSterol (LDL-C) concentrations. At the same time, plasma plant Sterol concentrations will increase after plant Sterol consumption, but decrease after plant stanol consumption. In contrast to plant stanols, plant Sterols can undergo oxidation and form oxyphytoSterols. Findings from in vitro and animal studies suggest that oxyphytoSterols might be atherogenic. Objective The objective was to examine whether plant Sterol and stanol consumption changes fasting plasma oxyphytoSterol concentrations. Design A randomized, double blind, cross-over study was performed in which 43 healthy subjects (18–70 years) consumed for 4 weeks a plant Sterol-enriched (3.0 g/d of plant Sterols), a plant stanol-enriched (3.0 g/d of plant stanols), and a control margarine separated by wash-out periods of 4 weeks. OxyphytoSterol concentrations were determined in BHT-enriched plasma via GC–MS. Results Compared to control, serum LDL-C concentrations were reduced after plant Sterol (−8.1%; p p p p p Conclusions Daily consumption of a plant Sterol-enriched margarine does not increase oxyphytoSterol concentrations, while plant stanol consumption may reduce the concentrations of the oxidative plant Sterol metabolites 7β-OH-campeSterol and 7-keto-campeSterol. This trial is registered at clinicaltrials.gov as NCT01559428.
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selective Sterol accumulation in abcg5 abcg8 deficient mice
Journal of Lipid Research, 2004Co-Authors: Klaus Von Bergmann, Dieter Lutjohann, Helen H Hobbs, Jonathan CohenAbstract:The ATP binding cassette (ABC) transporters ABCG5 and ABCG8 limit intestinal absorption and promote biliary secretion of neutral Sterols. Mutations in either gene cause sitoSterolemia, a rare recessive disease in which plasma and tissue levels of several neutral Sterols are in- creased to varying degrees. To determine why patients with sitoSterolemia preferentially accumulate noncholeSterol ste- rols, levels of choleSterol and the major plant Sterols were compared in plasma, liver, bile, and brain of wild-type and ABCG5/ABCG8-deficient ( G5G8 � / � ) mice. The total Sterol content of liver and plasma was similar in G5G8 � / � mice and wild-type animals despite an � 30-fold increase in non- choleSterol Sterol levels in the knockout animals. The relative enrichment of each Sterol in the plasma and liver of G5G8 � / � mice (stigmaSterolsitoSterolcholestanolbassicas- terolcampeSterolcholeSterol) reflected its relative en- richment in the bile of wild-type mice. These results indi- cate that 24-alkylated, � 22 , and 5 � -reduced Sterols are preferentially secreted into bile and that preferential biliary secretion of noncholeSterol Sterols by ABCG5 and ABCG8 prevents the accumulation of these Sterols in normal ani- mals. The mRNA levels for 13 enzymes in the choleSterol biosynthetic pathway were reduced in the livers of the G5G8 � / � mice, despite a 50% reduction in hepatic choles- terol level. Thus, the accumulation of Sterols other than choleSterol is sensed by the choleSterol regulatory machin- ery. —Yu, L., K. von Bergmann, D. Lutjohann, H. H. Hobbs, and J. C. Cohen. Selective Sterol accumulation in ABCG5/ ABCG8-deficient mice. J. Lipid Res. 2004. 45: 301-307.
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heritability of plasma noncholeSterol Sterols and relationship to dna sequence polymorphism in abcg5 and abcg8
Journal of Lipid Research, 2002Co-Authors: Knut Erik Berge, Klaus Von Bergmann, Dieter Lutjohann, Rudy Guerra, Helen H Hobbs, Scott M. Grundy, Jonathan CohenAbstract:: The plasma concentrations of choleSterol precursor Sterols and plant Sterols vary over a 5- to 10-fold range among normolipidemic individuals, and provide indices of the relative rates of choleSterol synthesis and fractional absorption. In the present study, we examined the relative contributions of genetic and environmental factors to variation in the plasma concentrations and Sterol-choleSterol ratios of five noncholeSterol Sterols, including the 5alpha-saturated derivative of choleSterol (cholestanol), two precursors in the choleSterol biosynthesis pathway (desmoSterol and lathoSterol), and two phytoSterols (campeSterol and sitoSterol). Plasma Sterol concentrations were highly stable in 30 individuals measured over a 48 week period. Regression of offspring Sterol levels on the parental values indicated that plasma levels of all five noncholeSterol Sterols were highly heritable. Analysis of monozygotic and dizygotic twin pairs also indicated strong heritability of all five Sterols. Two common sequence variations (D19H and T400K) in ABCG8, an ABC half-transporter defective in sitoSterolemia, were associated with lower concentrations of plant Sterols in parents, and in their offspring.Taken together, these findings indicate that variation in the plasma concentrations of noncholeSterol Sterols is highly heritable, and that polymorphism in ABCG8 contributes to genetic variation in the plasma concentrations of plant Sterols.
Burciaga Monge, Alma Delia - One of the best experts on this subject based on the ideXlab platform.
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Metabolismo de eSteroles esterificados en plantas: implicación en el desarrollo y la respuesta a estrés
'Edicions de la Universitat de Barcelona', 2020Co-Authors: Burciaga Monge, Alma DeliaAbstract:[spa] Los eSteroles son una familia de compuestos triterpénicos que se presentan en forma libre o conjugada, como ésteres, glicósidos y acilglicósidos de eSteroles. Cada especie vegetal tiene su propio perfil cualitativo y cuantitativo de eSteroles libres y conjugados, aunque en las distintas fracciones el β-sitoeSterol, el estigmaSterol y el campeSterol son los eSteroles más abundantes. Los eSteroles libres y sus derivados glicosilados se localizan en las membranas celulares, principalmente en la membrana plasmática, donde actúan como componentes estructurales que contribuyen a mantener la fluidez y la permeabilidad de las mismas. Por otra parte, los eSteroles esterificados se acumulan en cuerpos lipídicos citoplasmáticos, constituyendo una reserva de eSteroles que se almacena o se moviliza en función de las necesidades celulares (exceso o defecto) de eSteroles libres y glicosilados en las membranas celulares. La esterificación de los eSteroles está mediada por las eSterol aciltransferasas, enzimas que desempeñan un papel muy relevante en el mantenimiento de la homeostasis de los eSteroles en las membranas celulares. Hay evidencias que indican que los niveles de los eSteroles esterificados experimentan cambios importantes durante la senescencia de los tejidos vegetales y cuando las plantas se enfrentan a situaciones de estrés. Sin embargo, el conocimiento acerca de las eSterol aciltransferasas de plantas es todavía limitado. Hasta hace muy poco tiempo sólo se habían clonado y caracterizado dos eSterol aciltransferasas de Arabidopsis: una fosfolípido:eSterol aciltransferasa (PSAT1) y una acil CoA:eSterol aciltransferasa (ASAT1). Recientemente, en una tesis doctoral previa de nuestro grupo de investigación se identificaron y comenzaron a caracterizar las enzimas ASAT1 y PSAT1 de tomate (SlASAT1 y SlPSAT1). A partir de estos antecedentes, en este trabajo de Tesis Doctoral se ha seguido avanzando en el estudio de la función biológica de las eSterol aciltransferasas de plantas ASAT1 y PSAT1, empleando Arabidopsis thaliana y Solanum lycopersicum (cv Micro-Tom), prestando especial atención al estudio de su función y la de los eSteroles esterificados en el crecimiento, desarrollo y la respuesta frente al estrés. Los resultados obtenidos mediante complementación funcional de los mutantes asat1-1 y psat1-2 de Arabidopsis con las proteínas SlPSAT1 y SlASAT1 han confirmado la diferente capacidad de estas proteínas para esterificar eSteroles mayoritarios finales e intermediarios, respectivamente. Además, en semillas y hojas de los mutantes de tomate con la enzima SlPSAT1 inactivada (CR-psat1) obtenidas mediante el sistema de edición génica CRISPR/Cas9, se observa una reducción muy marcada del contenido de eSteroles esterificados que se correlaciona con un incremento en los niveles de eSteroles libres y en el caso de las hojas, con una clara disminución del número de cuerpos lipídicos, en comparación con lo observado en plantas wild type. Sin embargo, estos cambios no se producen en las líneas de tomate que tienen inactivada la enzima SlASAT1 (CR-asat1). Estos resultados apoyan la idea de que, tal y como se ha propuesto en Arabidopsis, la SlPSAT1 participa de forma más activa que la SlASAT1 en la síntesis de eSteroles esterificados y en la homeostasis de eSteroles libres. La pérdida de función de SlASAT1 produce un ligero retraso en el inicio de la germinación sin que se afecte la tasa final de la misma. Sin embargo, la inactivación de SlPSAT1 afecta a ambos parámetros e induce un fenómeno de germinación atípica, en el que se observa la aparición de los cotiledones previa a la de las radículas, con las consiguientes anomalías en el establecimiento de las plántulas. Las líneas CR-psat1 presentan también un fenotipo de enanismo moderado y alteraciones en la morfología de las hojas. Por otra parte, la reducción del contenido de eSteroles esterificados en Arabidopsis se traduce en mayor sensibilidad a la infección con Pseudomonas syringae, ya que el mutante psat1-2, pero no el asat1-1, es más sensible a la bacteria que las plantas wild type. En tomate la pérdida de función de PSAT1 parece incrementar la sensibilidad a estrés salino, ya que el crecimiento de los mutantes CR-psat1 en presencia de concentraciones elevadas de NaCl es menor que el de las plantas wild type, un efecto que no se observa en los mutantes CR-asat1. En conjunto los resultados de este trabajo sugieren que los eSteroles esterificados y SlPSAT1 desempeñan un papel importante tanto en el desarrollo y crecimiento de las plantas como en la respuesta a diferentes tipos de estrés, y establecen las bases para estudios posteriores dedicados a comprender el mecanismo de acción de los eSteroles esterificados y las eSterol aciltransferasas en estos procesos fisiológicos.[eng] Sterols are a family of triterpenoid compounds that occur as free form or conjugated like steryl esters, steryl glycosides and acylated steryl glycosides. Each plant species has its own qualitative and quantitative profile of free and conjugated Sterols, although the most abundant Sterols in the different fractions are β-sitoeSterol, stigmaSterol and campeSterol. Free Sterols and their glycosylated derivatives are localized in cell membranes, mainly in the plasma membrane, where they act as key structural components involved in maintaining membrane fluidity and permeability. On the contrary, steryl esters accumulate in cytoplasmic lipid droplets, where they served as a reservoir of Sterols that can be stored or mobilized depending on the cellular needs (excess or shortage) of free and glycosylated Sterols in cell membranes. The synthesis of steryl esters is catalyzed by Sterol acyltransferases that are essencial players in maintaining Sterol homeostasis in cell membranes. There is ample evidence that steryl esters levels undergo significant changes during plant tissues senescence and when plants face different type of stress, in spite of which the current knowledge about Sterol acyltransferases in plants is still limited. Until very recently, two Arabidopsis Sterol acyltransferases where the only plant Sterol acyltransferases cloned and characterized, phospholipid:Sterol acyltransferase (PSAT1) and acyl-CoA:Sterol acyltransferase (ASAT1). Recently, in a previous work carried out in our research group, the tomato enzymes ASAT1 and PSAT1 (SlASAT1 and SlPSAT1) where indetified, cloned and preliminary characterized. Using this knowledge as background, in this PhD Thesis project, progress has been made in the study of the biological function of the plant Sterol acyltransferases ASAT1 and PSAT1 using Arabidopsis thaliana and Solanum lycopersicum (cv Micro-Tom), paying special attention to the study of their function, and the role of steryl esters in plant growth, development and response to stress. The results obtained by functional complementation of the Arabidopsis asat1-1 and psat1-2 mutants with SlPSAT1 and SlASAT1 have confirmed the different ability of these enzymes to esterify Sterol end products and Sterol precursors, respectively. Besides, in seeds and leaves of mutants with inactive SlPSAT1 (CR-psat1) generated using CRISPR/Cas9 genome editing system, there is a strong reduction in the content of steryl esters that correlates with a moderate increase in free Sterol levels, while in leaves theres is also a decrease of the number of lipid droplets compared to the one observed in wild type leaves. These changes did not occur in the tomato mutant lines with inactive SlASAT1 (CR-asat1). Altogether these results provide further support to the proposal that SlPSAT1 participates more actively than SlASAT1 in the biosynthesis of steryl esters and free Sterol homeostasis. Loss of function of SlASAT1 causes a delay of seed germination but has no effect on the final germination percentage. However, the inactivation of SlPSAT1 affects both parameters and induces an atypical germination phenomenon, where cotyledones emerge first than the radical leading to anomalies on seedling establishment. The CR-psat1 lines show also a mild dwarf phenotype and alterations on leaf morphology. Reduces levels of steryl esters in Arabidopsis lead to a higher sensitivity of plants to the infection of Pseudomonas syringae, since the psat1-2 mutant, but not the asat1-1 mutant, is more sensitive to this bacterial pathogen than the wild-type plants. In tomato, loss of function of SlPSAT1 increases the sensitivity to salt stress, because CR-psat1 mutant plants are less toletant to NaCl than wild type plants, an effect that was not observed in the case of CR-asat1 mutants. Altogether, the results obtained from this work suggest that steryl esters and SlPSAT1 play an important role both in plant growth and development and also in plant response to different type of stress. This work set the bases for further studies aimed at a better understanding of the mechanism of action of steryl esters and Sterol acyltransferases in these physiological processes
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Metabolismo de eSteroles esterificados en plantas: implicación en el desarrollo y la respuesta a estrés
'Edicions de la Universitat de Barcelona', 2020Co-Authors: Burciaga Monge, Alma DeliaAbstract:Los eSteroles son una familia de compuestos triterpénicos que se presentan en forma libre o conjugada, como ésteres, glicósidos y acilglicósidos de eSteroles. Cada especie vegetal tiene su propio perfil cualitativo y cuantitativo de eSteroles libres y conjugados, aunque en las distintas fracciones el β-sitoeSterol, el estigmaSterol y el campeSterol son los eSteroles más abundantes. Los eSteroles libres y sus derivados glicosilados se localizan en las membranas celulares, principalmente en la membrana plasmática, donde actúan como componentes estructurales que contribuyen a mantener la fluidez y la permeabilidad de las mismas. Por otra parte, los eSteroles esterificados se acumulan en cuerpos lipídicos citoplasmáticos, constituyendo una reserva de eSteroles que se almacena o se moviliza en función de las necesidades celulares (exceso o defecto) de eSteroles libres y glicosilados en las membranas celulares. La esterificación de los eSteroles está mediada por las eSterol aciltransferasas, enzimas que desempeñan un papel muy relevante en el mantenimiento de la homeostasis de los eSteroles en las membranas celulares. Hay evidencias que indican que los niveles de los eSteroles esterificados experimentan cambios importantes durante la senescencia de los tejidos vegetales y cuando las plantas se enfrentan a situaciones de estrés. Sin embargo, el conocimiento acerca de las eSterol aciltransferasas de plantas es todavía limitado. Hasta hace muy poco tiempo sólo se habían clonado y caracterizado dos eSterol aciltransferasas de Arabidopsis: una fosfolípido:eSterol aciltransferasa (PSAT1) y una acil CoA:eSterol aciltransferasa (ASAT1). Recientemente, en una tesis doctoral previa de nuestro grupo de investigación se identificaron y comenzaron a caracterizar las enzimas ASAT1 y PSAT1 de tomate (SlASAT1 y SlPSAT1). A partir de estos antecedentes, en este trabajo de Tesis Doctoral se ha seguido avanzando en el estudio de la función biológica de las eSterol aciltransferasas de plantas ASAT1 y PSAT1, empleando Arabidopsis thaliana y Solanum lycopersicum (cv Micro-Tom), prestando especial atención al estudio de su función y la de los eSteroles esterificados en el crecimiento, desarrollo y la respuesta frente al estrés. Los resultados obtenidos mediante complementación funcional de los mutantes asat1-1 y psat1-2 de Arabidopsis con las proteínas SlPSAT1 y SlASAT1 han confirmado la diferente capacidad de estas proteínas para esterificar eSteroles mayoritarios finales e intermediarios, respectivamente. Además, en semillas y hojas de los mutantes de tomate con la enzima SlPSAT1 inactivada (CR-psat1) obtenidas mediante el sistema de edición génica CRISPR/Cas9, se observa una reducción muy marcada del contenido de eSteroles esterificados que se correlaciona con un incremento en los niveles de eSteroles libres y en el caso de las hojas, con una clara disminución del número de cuerpos lipídicos, en comparación con lo observado en plantas wild type. Sin embargo, estos cambios no se producen en las líneas de tomate que tienen inactivada la enzima SlASAT1 (CR-asat1). Estos resultados apoyan la idea de que, tal y como se ha propuesto en Arabidopsis, la SlPSAT1 participa de forma más activa que la SlASAT1 en la síntesis de eSteroles esterificados y en la homeostasis de eSteroles libres. La pérdida de función de SlASAT1 produce un ligero retraso en el inicio de la germinación sin que se afecte la tasa final de la misma. Sin embargo, la inactivación de SlPSAT1 afecta a ambos parámetros e induce un fenómeno de germinación atípica, en el que se observa la aparición de los cotiledones previa a la de las radículas, con las consiguientes anomalías en el establecimiento de las plántulas. Las líneas CR-psat1 presentan también un fenotipo de enanismo moderado y alteraciones en la morfología de las hojas. Por otra parte, la reducción del contenido de eSteroles esterificados en Arabidopsis se traduce en mayor sensibilidad a la infección con Pseudomonas syringae, ya que el mutante psat1-2, pero no el asat1-1, es más sensible a la bacteria que las plantas wild type. En tomate la pérdida de función de PSAT1 parece incrementar la sensibilidad a estrés salino, ya que el crecimiento de los mutantes CR-psat1 en presencia de concentraciones elevadas de NaCl es menor que el de las plantas wild type, un efecto que no se observa en los mutantes CR-asat1. En conjunto los resultados de este trabajo sugieren que los eSteroles esterificados y SlPSAT1 desempeñan un papel importante tanto en el desarrollo y crecimiento de las plantas como en la respuesta a diferentes tipos de estrés, y establecen las bases para estudios posteriores dedicados a comprender el mecanismo de acción de los eSteroles esterificados y las eSterol aciltransferasas en estos procesos fisiológicos.Sterols are a family of triterpenoid compounds that occur as free form or conjugated like steryl esters, steryl glycosides and acylated steryl glycosides. Each plant species has its own qualitative and quantitative profile of free and conjugated Sterols, although the most abundant Sterols in the different fractions are β-sitoeSterol, stigmaSterol and campeSterol. Free Sterols and their glycosylated derivatives are localized in cell membranes, mainly in the plasma membrane, where they act as key structural components involved in maintaining membrane fluidity and permeability. On the contrary, steryl esters accumulate in cytoplasmic lipid droplets, where they served as a reservoir of Sterols that can be stored or mobilized depending on the cellular needs (excess or shortage) of free and glycosylated Sterols in cell membranes. The synthesis of steryl esters is catalyzed by Sterol acyltransferases that are essencial players in maintaining Sterol homeostasis in cell membranes. There is ample evidence that steryl esters levels undergo significant changes during plant tissues senescence and when plants face different type of stress, in spite of which the current knowledge about Sterol acyltransferases in plants is still limited. Until very recently, two Arabidopsis Sterol acyltransferases where the only plant Sterol acyltransferases cloned and characterized, phospholipid:Sterol acyltransferase (PSAT1) and acyl-CoA:Sterol acyltransferase (ASAT1). Recently, in a previous work carried out in our research group, the tomato enzymes ASAT1 and PSAT1 (SlASAT1 and SlPSAT1) where indetified, cloned and preliminary characterized. Using this knowledge as background, in this PhD Thesis project, progress has been made in the study of the biological function of the plant Sterol acyltransferases ASAT1 and PSAT1 using Arabidopsis thaliana and Solanum lycopersicum (cv Micro-Tom), paying special attention to the study of their function, and the role of steryl esters in plant growth, development and response to stress. The results obtained by functional complementation of the Arabidopsis asat1-1 and psat1-2 mutants with SlPSAT1 and SlASAT1 have confirmed the different ability of these enzymes to esterify Sterol end products and Sterol precursors, respectively. Besides, in seeds and leaves of mutants with inactive SlPSAT1 (CR-psat1) generated using CRISPR/Cas9 genome editing system, there is a strong reduction in the content of steryl esters that correlates with a moderate increase in free Sterol levels, while in leaves theres is also a decrease of the number of lipid droplets compared to the one observed in wild type leaves. These changes did not occur in the tomato mutant lines with inactive SlASAT1 (CR-asat1). Altogether these results provide further support to the proposal that SlPSAT1 participates more actively than SlASAT1 in the biosynthesis of steryl esters and free Sterol homeostasis. Loss of function of SlASAT1 causes a delay of seed germination but has no effect on the final germination percentage. However, the inactivation of SlPSAT1 affects both parameters and induces an atypical germination phenomenon, where cotyledones emerge first than the radical leading to anomalies on seedling establishment. The CR-psat1 lines show also a mild dwarf phenotype and alterations on leaf morphology. Reduces levels of steryl esters in Arabidopsis lead to a higher sensitivity of plants to the infection of Pseudomonas syringae, since the psat1-2 mutant, but not the asat1-1 mutant, is more sensitive to this bacterial pathogen than the wild-type plants. In tomato, loss of function of SlPSAT1 increases the sensitivity to salt stress, because CR-psat1 mutant plants are less toletant to NaCl than wild type plants, an effect that was not observed in the case of CR-asat1 mutants. Altogether, the results obtained from this work suggest that steryl esters and SlPSAT1 play an important role both in plant growth and development and also in plant response to different type of stress. This work set the bases for further studies aimed at a better understanding of the mechanism of action of steryl esters and Sterol acyltransferases in these physiological processes
