Multiple pathways regulating the calorie restriction response in yeast.

Area of Science:

• Cellular biology
• Genetics
• Metabolism

Background:

• Calorie restriction (CR) and SIR2 gene activation are known to extend lifespan in yeast.
• CR is hypothesized to activate Sir2 by reducing inhibitors like NADH or nicotinamide.
• NADH reduction links to increased respiration, while nicotinamide clearance involves PNC1 upregulation.

Purpose of the Study:

• To investigate the molecular mechanisms underlying calorie restriction (CR) in yeast lifespan extension.
• To determine if PNC1 and transcriptional stress responses are universally involved in CR-mediated lifespan extension.
• To identify alternative pathways regulating CR in yeast.

Main Methods:

• Yeast strains were subjected to different levels of calorie restriction (0.1% and 0.5% glucose).
• Gene expression analysis using microarrays was performed to assess transcriptional changes.
• PNC1 activation and protein levels were monitored under CR conditions.

Main Results:

• High CR (0.1% glucose) activated PNC1 and a 39-gene transcriptional stress response module, aligning with the hormesis hypothesis.
• Low CR (0.5% glucose) extended lifespan without PNC1 induction or stress response activation.
• Low CR led to increased mRNA levels of iron transport genes, suggesting a shift towards respiration and NADH reduction.

Conclusions:

• At least two distinct molecular pathways mediate calorie restriction's lifespan-extending effects in yeast.
• One pathway involves PNC1 and transcriptional stress responses (high CR).
• Another pathway, observed in low CR, relies on enhanced respiration and altered iron metabolism, independent of stress responses.