Delaney et al, 2012 Experimental Gerontology
A paper from the Kaeberlein group ( http://www.ncbi.nlm.nih.gov/pubmed/23235143) showed the dietary restriction during chronologically aging can lead to extended replicative life span. This is a technically tricky experiment, because when chronologically aged cells start to lose viability, much more cells will be required to conduct the subsequent replicative life span assays. They author stated that they pick as much as 1000 cells to start the replicative lifespan assays.
One of my questions is a technique one: How did they carry out DR during chronological aging? It seems that starting cultures are SC with various glucose concentration. Five microliters of chronologically aged cultures were spread to YPD (2% glucose) plate for RLS assay, which is a standard practice. DR was achieved in 0.05% glucose in this study.
The authors double-stained yeast cells with 5nM SYTOX red and 17.5nM DiOC6, and monitor them by flow cytometry. DiOC6 is a mitochrondrial membrane potential dependent dye, and SYTOX Red is a used distinguish live and dead cells. SYTOX Red-negative cells are considered live cells.
This paper argues that both DR and buffering during chronological aging can delay the subsequent replicating aging process by maintiaing a low mitochondria membrane potential. Overall, the paper suggests that mitochondria is a link between post-mitotic and mitotic aging.
One question that I have is the role of mitochondria during chronological aging. The author conducted chronological aging in rich media. Although many cells are probably metabolically active during in the depleted media, many are also metabolically inactive. Is it possible that DR have differential effect on different cell sub-populations in different metabolic states?
For comparison, I often measure CLS in water, and many cells are metabolically much less active, if not domant in G0. DR cannot be studied in water-based chronological aging.
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