Polyunsaturated Fatty Acid Desaturation Is a Mechanism for Glycolytic NAD+ Recycling

Summary The reactions catalyzed by the delta-5 and delta-6 desaturases (D5D/D6D), key enzymes responsible for highly unsaturated fatty acid (HUFA) synthesis, regenerate NAD + from NADH. Here, we show that D5D/D6D provide a mechanism for glycolytic NAD + recycling that permits ongoing glycolysis and cell viability when the cytosolic NAD + /NADH ratio is reduced, analogous to lactate fermentation. Although lesser in magnitude than lactate production, this desaturase-mediated NAD + recycling is acutely adaptive when aerobic respiration is impaired in vivo . Notably, inhibition of either HUFA synthesis or lactate fermentation increases the other, underscoring their interdependence. Consistent with this, a type 2 diabetes risk haplotype in SLC16A11 that reduces pyruvate transport (thus limiting lactate production) increases D5D/D6D activity in vitro and in humans, demonstrating a chronic effect of desaturase-mediated NAD + recycling. These findings highlight key biologic roles for D5D/D6D activity independent of their HUFA end products and expand the current paradigm of glycolytic NAD + regeneration.