82 6 ART for Antiaging
including COX to simulate the NO-COX interaction. It is believed that CR enables
the synchronous decreases of ATP and reduced nicotinamide adenine dinucleotide
(NADH), which can separately activate adenosine monophosphate-activated protein
kinase (AMPK) and SIRT1 (Rodgers et al. 2005 ; Canto et al. 2009 ). In turn, AMPK
and SIRT1 can coordinately activate peroxisome proliferator-activated recep-
tor γ coactivator 1 alpha (PGC-1α) for mitochondrial biogenesis in mammals (Lee
et al. 2006 ). It is unambiguous that NAD+ and Sir2 (yeast homolog of mammalian
SIRT1) are required for yeast lifespan extension (Lin et al. 2000 ).
Here, we report CR-based “dual-phase responses”, which is composed of a
phase of mitochondrial enhancement (ME), or a respiratory burst phase, and a
phase of postmitochondrial enhancement (PME), or a respiratory decay phase.
The ME phase that is characterized by an enhanced antioxidative response is
transient and occurs at an acute CR stage, whereas the PME phase that is rep-
resented by an attenuated metabolic activity is maintained throughout a chronic
CR stage. Because CR can trigger NO and H 2 O 2 production, we assumed that
ART and H 2 O 2 may follow the dual-phase pattern to mimic CR for yeast lifes-
pan extension. To enable a systematical evaluation on CR-mediated a ntioxidative
augments and metabolic alterations, we analyzed the global expression profiles
of CR-treated yeast by whole transcriptomic microarray. Among which some
transcripts of critical genes were further confirmed by quantitative polymerase
chain reaction (qPCR) or enzyme activity determination. Comparatively, we
p arallelly examined the expression levels after treatment by ART or H 2 O 2 for
comparison. We expect that all those data should shed light into the elucidation
of bona fide mechanisms underlying CR prolongs yeast lifespan through NO-
and H 2 O 2 -involved signaling cascades.
6.2.2 Results and Analysis
6.2.2.1 Mimicry of CR by ART and H 2 O 2 to Extend Lifespan
in a Dose-Dependent Manner
To replay the episode of yeast lifespan extension by CR, yeast cells were incu-
bated on the cultural plates containing 0.5 % glucose. In parallel, yeast cultural
media were supplemented with different doses of ART. As compared with the
control, or calorie nonrestriction, low-dose (0.1 and 0.5 μm) ART was observed
to allow a significant increase of survived cells when colonies were counted after
treatment until 3 weeks. In contrast, high-dose (5, 25, and 50 μm) ART decreases
the survived cell numbers when observed after treatment for 2 weeks. From much
higher to relatively lower, CR, low-dose ART and calorie nonrestriction give rise
to the distinct percentages of viable cells. These results indicated that low-dose
ART extends yeast lifespan as a CR-mimetic, whereas high-dose ART shortens
yeast lifespan due to causing cell death.