Mitochondria as integral modulators of cellular signaling
Date
2014-11-05
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Abstract
Mitokondreid on võrreldud rakus paiknevate elektrijaamadega kuna nende ülesandeks on päristuumsete rakkude elutegevuseks vajaliku energia tootmine. Lisaks on mitokondrid olulised raku metabolismis ehk toitainete ja struktuursete ehitusblokkide tootmise ja lagundamise protsessis. Selleks, et mitokondrites toodetud energia ja metaboolsete vaheühendite hulk vastaks raku vajadustele, on mitokondrite talitlus reguleeritud mitmete signaaliülekande radade poolt, sh cAMP-PKA ja TOR rajad. Viimased seiravad raku välis- ja sisekeskkonna tingimusi ning annavad signaali vastavast energia ja vaheühendite vajadusest edasi mitokondri masinavärgile. Lisaks reguleerivad need rajad ka selliseid rakulisi protsesse nagu morfoloogia ja vananemine.
Mitokondri väärtalitluse uurimiseks kasutatakse mudelorganismina laialdaselt pagaripärmi Saccharomyces cerevisiae. On teada, et mitokondrite normaalne talitlus on näljatingimustes hädavajalik morfoloogiliseks ümberlülitamiseks filamentsesse kasvuvormi. Seejuures ei ole teada, kuidas mitokondrite talitlus seda protsessi mõjutab. Kuna pärmi filamentne kasv on seotud virulentsusega inimese patogeenides, on tegu ühe olulise uurimisvaldkonnaga. Käesoleva uurimustöö peamiseks eesmärgiks oli iseloomustada S. cerevisiae mitokondri väärtalitlusega (rho) rakkude käitumist näljatingimustes ning välja selgitada, kuidas sekkub mitokondrite talitlus morfoloogilisse ümberlülitamisse. Selgus, et rho rakkudes on vähenenud rakupinna valku kodeeriva geeni FLO11 ekspressioon ja vastava valgu tootmise suurendamisega on võimalik taastada rho rakkude filamenteerumine. Mitmete signaaliradade aktiivsuse uurimine näitas, et rho rakkudes on vähenenud cAMP-PKA raja aktiivsus, mis on oluline FLO11 geeni ekspressiooniks ja filamenteerumise esilekutsumiseks. Selgus ka, et mitokondrite väärtalitluse mõju cAMP-PKA raja aktiivsusele sõltub konkreetsest pärmitüvest. Lisaks valideeriti töö käigus arvutusliku meetodi m:Explorer ennustusvõimet tuvastada süsiniku nälja poolt esile kutstud statsionaarse faasi (kronoloogilise vananemise) regulaatoreid. Näitasime, et transkriptsiooni regulaatorid Bas1, Mga2 ja Cst6 mängivad olulist rolli antud protsessis. Samuti selgus, et rho rakkude puhul sõltub kronoloogilise vananemise dünaamika konkreetsest rho fenotüüpi esile kutsuvast geenimutatsioonist. Seega on mitokondri väärtalitluse mõju vananemisprotsessile mõjutatav rakulise konteksti või konkreetse mitokondri defekti poolt. Kokkuvõttes võib järeldada, et mitokondrite väärtalitluse mõju raku morfoloogilisele ümberlülitamisele ja ka elulemusele hõlmab endas raku signaalivõrgustiku ümberkujundamist ja sõltub paljuski rakulisest kontekstist.
Mitochondria are often compared to powerhouses of the cell since they are responsible for energy production through oxidative phosphorylation. They also coordinate cellular metabolism through synthesis and degradation of metabolic intermediates. To ensure that the amount of energy equivalents and metabolic intermediates produced by the mitochondria matches the cellular requirements, the mitochondrial function(s) and activities are modulated by the conserved signaling pathways, such as the cAMP-PKA and TOR signaling. These pathways monitore both intra- and extracellular nutritional environment and coordinate diverce processes, among them mitochondrial activities, cellular morphology and aging. The model yeast Saccharomyces cerevisiae has been widely used to study the effects of mitochondrial dysfunction on various cellular processes. It has been shown previously that the functional mitochondria are essential for switch to filamentous growth in this yeast. However, it is unclear by which mechanism mitochondrial dysfunction influences this process. Since the filamentous growth has been connected to virulence determinants in opportunistic commensal fungi, it has remained under extensive study in S. cerevisiae. The main objective of this study was to determine how the dysfunctional state of mitochondria interferes with filamentous growth and affects responses to starvation conditions. It was shown that in the respiratory deficient mutants the transcription of well described filamentous growth target FLO11 is downregulated and induction of FLO11 expression restores the response. By monitoring the activities of several signaling pathways it was shown that mitochondrial dysfunction specifically downregulates the cAMP-PKA signaling. Analysis of phenotypic traits indicated that the effect of respiratory dysfunction on cAMP-PKA pathway activity depends on genetic background of the strain and is therefore probably interpreted according to specific cellular metabolic context. In addition, validation of computational method m:Explorer revealed several new candidate regulators of chronological aging in yeast. The most pronounced effects were observed with BAS1, MGA2, CST6 deletion strains where significant life span extension was demonstrated. It was further shown that respiratory deficiency of different mutants does not lead to uniformly decreased viability dynamics and the exact type of mitochondrial dysfunction, or accompanying cellular rearrangements of specific mutants appear to play a role in longevity determination. It can be concluded that mitochondrial dysfunction affects morphological differentiation program through rearrangement of cellular signaling network. Importantly, the effect of mitochondrial dysfunction on morphological differentiation and also on chronological aging is probably interpreted according to specific cellular context and depends on yeast strain and/or metabolic context of the cell.
Mitochondria are often compared to powerhouses of the cell since they are responsible for energy production through oxidative phosphorylation. They also coordinate cellular metabolism through synthesis and degradation of metabolic intermediates. To ensure that the amount of energy equivalents and metabolic intermediates produced by the mitochondria matches the cellular requirements, the mitochondrial function(s) and activities are modulated by the conserved signaling pathways, such as the cAMP-PKA and TOR signaling. These pathways monitore both intra- and extracellular nutritional environment and coordinate diverce processes, among them mitochondrial activities, cellular morphology and aging. The model yeast Saccharomyces cerevisiae has been widely used to study the effects of mitochondrial dysfunction on various cellular processes. It has been shown previously that the functional mitochondria are essential for switch to filamentous growth in this yeast. However, it is unclear by which mechanism mitochondrial dysfunction influences this process. Since the filamentous growth has been connected to virulence determinants in opportunistic commensal fungi, it has remained under extensive study in S. cerevisiae. The main objective of this study was to determine how the dysfunctional state of mitochondria interferes with filamentous growth and affects responses to starvation conditions. It was shown that in the respiratory deficient mutants the transcription of well described filamentous growth target FLO11 is downregulated and induction of FLO11 expression restores the response. By monitoring the activities of several signaling pathways it was shown that mitochondrial dysfunction specifically downregulates the cAMP-PKA signaling. Analysis of phenotypic traits indicated that the effect of respiratory dysfunction on cAMP-PKA pathway activity depends on genetic background of the strain and is therefore probably interpreted according to specific cellular metabolic context. In addition, validation of computational method m:Explorer revealed several new candidate regulators of chronological aging in yeast. The most pronounced effects were observed with BAS1, MGA2, CST6 deletion strains where significant life span extension was demonstrated. It was further shown that respiratory deficiency of different mutants does not lead to uniformly decreased viability dynamics and the exact type of mitochondrial dysfunction, or accompanying cellular rearrangements of specific mutants appear to play a role in longevity determination. It can be concluded that mitochondrial dysfunction affects morphological differentiation program through rearrangement of cellular signaling network. Importantly, the effect of mitochondrial dysfunction on morphological differentiation and also on chronological aging is probably interpreted according to specific cellular context and depends on yeast strain and/or metabolic context of the cell.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
mitokondrid, signaali transduktsioon, geeniekspressioon, transkriptsioon (biol.), regulatsioon, mitochondria, signal transduction, gene expression, transcription (biol.), regulation