Caloric Restriction Extends Yeast Chronological Life Span by Optimizing the Snf1 (AMPK) Signaling Pathway

ABSTRACT

AMP-activated protein kinase (AMPK) and the homologous yeast SNF1 complex are key regulators of energy metabolism that counteract nutrient deficiency and ATP depletion by phosphorylating multiple enzymes and transcription factors that maintain energetic homeostasis. AMPK/SNF1 also promotes longevity in several model organisms, including yeast. Here we investigate the role of yeast SNF1 in mediating the extension of chronological life span (CLS) by caloric restriction (CR). We find that SNF1 activity is required throughout the transition of log phase to stationary phase (diauxic shift) for effective CLS extension. CR expands the period of maximal SNF1 activation beyond the diauxic shift, as indicated by Sak1-dependent T210 phosphorylation of the Snf1 catalytic α-subunit. A concomitant increase in ADP is consistent with SNF1 activation by ADP in vivo. Downstream of SNF1, the Cat8 and Adr1 transcription factors are required for full CR-induced CLS extension, implicating an alternative carbon source utilization for acetyl coenzyme A (acetyl-CoA) production and gluconeogenesis. Indeed, CR increased acetyl-CoA levels during the diauxic shift, along with expression of both acetyl-CoA synthetase genes ACS1 and ACS2. We conclude that CR maximizes Snf1 activity throughout and beyond the diauxic shift, thus optimizing the coordination of nucleocytosolic acetyl-CoA production with massive reorganization of the transcriptome and respiratory metabolism.

KEYWORDS:

• Snf1
• AMPK
• aging
• yeast
• caloric restriction
• ADP
• diauxic shift
• acetyl-CoA

ACKNOWLEDGMENTS

We thank Martin Schmidt and Rhonda McCartney for strains and plasmids, as well as extensive advice with Snf1 protocols. We also thank Flora Rutaganira and Kevan Shokat for 2NM-PP1 and Margaret Shirra and Karen Arndt for the snf1-as strain. We thank Ben Tu and Zheng Kuang for advice on acetyl-CoA measurements, David Auble and Martin Schmidt for critically reading the manuscript, and Smith lab members for helpful discussions.

This work was supported in part by funding from the University of Virginia School of Medicine and the Department of Biochemistry and Molecular Genetics, as well as NIH grant GM075240.