What is known: Disulfide reduction-fueled enzymes s!upport homeostasis and combat oxidative damage that
contributes to neurodegeneration, inflammatory diseases, and cancer. NADPH provides the reducing power for
most anabolic and cytoprotective reduction reactions, yet only two enzymes can use NADPH to reduce
cytosolic disulfides: thioredoxin reductase-1 (TrxR1) and glutathione reductase (Gsr) 1. Both TrxR1 and Gsr
have active sites that are dominantly inhibited by electrophilic toxins and oxidants 2, 3. In Co-PI Schmidt's lab,
mice with TrxR1/Gsr-null livers uncovered unexpected robustness in the disulfide reductase systems, including
an NADPH-independent pathway that uses catabolism of methionine (Met) to sustain redox homeostasis 4.
Importantly, this pathway is also thought to sustain normal cells under oxidative or electrophilic stress 5. Met
and Cys are the 2 sulfur (S)-amino acids found in proteins, but S-containing molecules synthesized from Met or
Cys, including S-adenosyl-Met (SAM), glutathione (GSH), CoA, and others, are also important in redox, detox,
energetics, biosynthesis, regulation, and other processes. Co-PI DeNicola has been studying the roles of
altered S-amino acid metabolism in sustaining some cancers 6. These studies are revealing how some cancers
use altered S-amino acid redox metabolism, which could uncover targetable cancer-specific susceptibilities.
Unresolved questions: It remains unknown how other metabolic activities, including those that directly utilize
Met or Cys, as well as more peripheral systems that either (i) supply resources to these pathways; (ii) depend
upon these pathways; or (iii) might, in some conditions, compete with these pathways for substrates, are
realigned to help cells survive stress. We hypothesize that conversion to Met-dependence involves
realignment of diverse metabolic pathways. A better understanding of these processes will uncover processes
that can be therapeutically targeted to either specifically increase the robustness of critical cells under oxidative
or toxic stress, or specifically increase the vulnerability of pathogenic cells in cancer or inflammatory diseases.
What is proposed: In this collaborative project, we will define the metabolic pathway realignments that occur
when hepatocytes switch from NADPH-dependent to -independent disulfide reduction. We propose 3 Specific
Aims: Aim 1, Define how NADPH- versus Met-fueled disulfide reductase homeostasis influences S-metabolism
prioritization. Aim 2, Define how re-wiring of serine metabolism supports Met-fueled disulfide reductase
homeostasis. Aim 3, Test whether Met-dependent survival increases the activity and dependence on liver
methyltransferases.
Anticipated outcomes, value: This project will help us understand how global shifts in hepatic metabolism
occurs in response to severe oxidative or electrophilic stress in liver, and how this helps sustain health.