Biology subjects

Stefanatos, R.

Publications and source records attributed to Stefanatos, R..

4 recordsLinked to original sources

bioRxiv2023

Developmental mitochondrial Complex I activity determines lifespan

Aberrant mitochondrial function has been associated with an increasingly large number of human disease states. Observations from in vivo models where mitochondrial function is altered suggest that adaptations to mitochondrial dysfunction may underpin disease pathology. We hypothesized that the severity of these maladaptations could be shaped by the plasticity of the system when mitochondrial dysfunction manifests. To investigate this, we have used inducible fly models of mitochondrial complex I (CI) dysfunction to reduce mitochondrial function at two stages of the fly lifecycle, from early development and adult eclosion. Here, we show that in early life (developmental) mitochondrial dysfunction results in severe reductions in survival and stress resistance in adulthood, while flies where mitochondrial function is perturbed from adulthood, are long-lived and stress resistant despite having up to an 75% reduction in CI activity. After excluding developmental defects as a cause, we went on to molecularly characterize these two populations of mitochondrially compromised flies, short- and long-lived. We find that our short-lived flies have unique transcriptomic and metabolomic responses which overlap significantly in discreet models of CI dysfunction. Our data demonstrate that early mitochondrial dysfunction via CI depletion elicits an adaptive response which severely reduces survival, while CI depletion from adulthood is not sufficient to reduce survival and stress resistance.

molecular biology↗

bioRxiv2023

The Role of Respiratory Complex IV in Lifespan Length and Quality

The contribution of mitochondria to lifespan determination remains controversial, as impaired mitochondrial function can paradoxically both shorten and extend longevity. During ageing, mitochondria accumulate defects that disrupt electron transport and elevate the production of reactive oxygen species (ROS) per unit of ATP. Here, we developed Drosophila melanogaster models carrying mitochondria that phenocopy aged organelles--termed "aged-like" mitochondria--to dissect the developmental versus adult contributions of mitochondrial dysfunction to lifespan regulation. Inducing aged-like mitochondria during development caused profound metabolic maladaptation and markedly reduced adult lifespan, without signs of accelerated ageing. In contrast, restricting their expression to adulthood resulted in only a modest reduction in lifespan, accompanied by an increased mortality rate, indicative of accelerated ageing. Enhancing mitochondrial function exclusively during development by expressing the alternative oxidase (AOX) mitigated these metabolic defects and significantly extended adult survival. Likewise, developmental overexpression of Rheb, an activator of Target of Rapamycin (TOR) signalling, improved adult survival without restoring mitochondrial respiration. Finally, we show that mitochondrial respiratory capacity cannot be reinstated in adults with "aged-like" mitochondria, as oxidative phosphorylation (OXPHOS) protein levels are largely established during development and remain stable throughout adult life. We propose that Drosophila permanently tunes adult metabolism according to developmental cues to optimise reproductive fitness, at the expense of long-term survival.

molecular biology↗

bioRxiv2021

ROS signalling requires uninterrupted electron flow and is lost during ageing in flies

Mitochondrial Reactive Oxygen Species (mtROS) are cellular messengers essential for cellular homeostasis. In response to stress, reverse electron transport (RET) by respiratory complex I generates high levels of mtROS. Suppression of ROS produced via RET (ROS-RET) reduces survival under stress, while activation of ROS-RET extends lifespan in basal conditions. Here, we demonstrate that ROS-RET signalling requires increased electron entry and uninterrupted electron flow through the electron transport chain (ETC). We found that ROS-RET is abolished in old fruit flies where electron flux is reduced. Instead, mitochondria in aged flies produce consistently high levels of mtROS. Finally, we demonstrate that in young flies reduction of electron exit from the ETC, but not electron entry, phenocopies mtROS generation observed in old individuals. Our results define the mechanism by which ROS signalling is lost during ageing. HighlightsO_LIROS-RET signalling requires an uninterrupted flow of electrons through the ETC. C_LIO_LIROS-RET signalling fails during ageing, with mitochondria producing persistently high levels of ROS. C_LIO_LIInterruption of ROS-RET signalling compromises stress adaptation in old flies. C_LIO_LIReducing electron exit suppresses ROS-RET signalling and phenocopies ROS production observed in old mitochondria. C_LI

physiology↗

bioRxiv2020

Autophagy promotes cell and organismal survival by maintaining NAD(H) pools

Autophagy is an essential catabolic process that promotes clearance of surplus or damaged intracellular components1. As a recycling process, autophagy is also important for the maintenance of cellular metabolites during periods of starvation2. Loss of autophagy is sufficient to cause cell death in animal models and is likely to contribute to tissue degeneration in a number of human diseases including neurodegenerative and lysosomal storage disorders3-7. However, it remains unclear which of the many cellular functions of autophagy primarily underlies its role in cell survival. Here we have identified a critical role of autophagy in the maintenance of nicotinamide adenine dinucleotide (NAD+/NADH) levels. In respiring cells, loss of autophagy caused NAD(H) depletion resulting in mitochondrial membrane depolarisation and cell death. We also found that maintenance of NAD(H) is an evolutionary conserved function of autophagy from yeast to human cells. Importantly, cell death and reduced viability of autophagy-deficient animal models can be partially reversed by supplementation with an NAD(H) precursor. Our study provides a mechanistic link between autophagy and NAD(H) metabolism and suggests that boosting NAD(H) levels may be an effective intervention strategy to prevent cell death and tissue degeneration in human diseases associated with autophagy dysfunction.

cell biology↗