A mitochondrial mutator plasmid that causes senescence under dietary restricted conditions

Mitochondrial recombination increases with age in Podospora anserina

With uniparental inheritance of mitochondria, there seems little reason for homologous recombination in mitochondria, but the machinery for mitochondrial recombination is quite well-conserved in many eukaryote species. In fungi and yeasts heteroplasmons may be formed when strains fuse and transfer of organelles takes place, making it possible to study mitochondrial recombination when introduced mitochondria contain different markers. A survey of wild-type isolates from a local population of the filamentous fungus Podospora anserina for the presence of seven optional mitochondrial introns indicated that mitochondrial recombination does take place in nature. Moreover the recombination frequency appeared to be correlated with age: the more rapidly ageing fraction of the population had a significantly lower linkage disequilibrium indicating more recombination. Direct confrontation experiments with heterokaryon incompatible strains with different mitochondrial markers at different (relative) age confirmed that mitochondrial recombination increases with age. We propose that with increasing mitochondrial damage over time, mitochondrial recombination - even within a homoplasmic population of mitochondria - is a mechanism that may restore mitochondrial function.

Calorie restriction in the filamentous fungus Podospora anserina

Calorie restriction (CR) is a regimen of reduced food intake that, although the underlying mechanism is unknown, in many organisms leads to life span extension. Podospora anserina is one of the few known ageing filamentous fungi and the ageing process and concomitant degeneration of mitochondria have been well-studied. CR in P. anserina increases not only life span but also forestalls the ageing-related decline in fertility. Here we review what is known about CR in P. anserina and about possibly involved mechanisms like enhanced mitochondrial stability, reduced production of reactive oxygen species and changes in the OXPHOS machinery. Additionally, we present new microscopic data on mitochondrial dynamics under rich nutritional and CR conditions at different points in life. Lines that have grown under severe CR for more than 50x the normal life span, show no accumulation of age-related damage, though fecundity is reduced in some of these lines. Finally, we discuss the possible role of CR in P. anserina in nature and the effect of CR at different points in life.

Antiaging, longevity and calorie restriction

PURPOSE OF REVIEW

The role of calorie restriction in humans is controversial. Recently, new data in monkeys and humans have provided new insights into the potential role of calorie restriction in longevity.

RECENT FINDINGS

A study in rhesus monkeys showed a reduction in aging-associated mortality. A number of controlled studies have suggested a variety of beneficial effects during studies of 6-12 months in humans. Major negative effects in humans were loss of muscle mass, muscle strength and loss of bone.

SUMMARY

Dietary restriction in rodents has not been shown to be effective when started in older rodents. Weight loss in humans over 60 years of age is associated with increased mortality, hip fracture and increased institutionalization. Calorie restriction in older persons should be considered experimental and potentially dangerous. Exercise at present appears to be a preferable treatment for older persons.

A potential impact of DNA repair on ageing and lifespan in the ageing model organism Podospora anserina: decrease in mitochondrial DNA repair activity during ageing

The free radical theory of ageing states that ROS play a key role in age-related decrease in mitochondrial function via the damage of mitochondrial DNA (mtDNA), proteins and lipids. In the sexually reproducing ascomycete Podospora anserina ageing is, as in other eukaryotes, associated with mtDNA instability and mitochondrial dysfunction. Part of the mtDNA instabilities may arise due to accumulation of ROS induced mtDNA lesions, which, as previously suggested for mammals, may be caused by an age-related decrease in base excision repair (BER). Alignments of known BER protein sequences with the P. anserina genome revealed high homology. We report for the first time the presence of BER activities in P. anserina mitochondrial extracts. DNA glycosylase activities decrease with age, suggesting that the increased mtDNA instability with age may be caused by decreased ability to repair mtDNA damage and hence contribute to ageing and lifespan control in this ageing model. Additionally, we find low DNA glycosylase activities in the long-lived mutants grisea and DeltaPaCox17::ble, which are characterized by low mitochondrial ROS generation. Overall, our data identify a potential role of mtDNA repair in controlling ageing and life span in P. anserina, a mechanism possibly regulated in response to ROS levels.

Apoptosis pathways in fungal growth, development and ageing

Apoptosis is one type of programmed cell death with great importance for development and homeostasis of multicellular organisms. Unexpectedly, during the past decade, evidence has been obtained for the existence of a basal apoptosis machinery in yeast, as unicellular fungus, and in some filamentous fungi, a group of microorganisms that are neither true unicellular nor true multicellular biological systems but something in between. Here, we review evidence for a role of apoptotic processes in fungal pathogenicity, competitiveness, propagation, ageing and lifespan control.