A genetically encoded bifunctional enzyme mitigates redox imbalance and lipotoxicity.

Dihydroxyacetone phosphate (DHAP), glycerol-3-phosphate (Gro3P) and reduced/oxidized nicotinamide adenine dinucleotide (NADH/NAD⁺) are key metabolites of the Gro3P shuttle, which transfers reducing equivalents between the cytosol and mitochondria. Targeted activation of Gro3P biosynthesis has recently emerged as a promising strategy to alleviate reductive stress. However, because Gro3P constitutes the backbone of triglycerides, its accumulation can promote extensive lipogenesis. Here we show that a genetically encoded tool based on a di-domain glycerol-3-phosphate dehydrogenase from the alga Chlamydomonas reinhardtii (CrGPDH) effectively operates both the alternative Gro3P shunt, which regenerates NAD⁺ while converting DHAP to Gro3P, and the glycerol shunt, which converts Gro3P to glycerol and inorganic phosphate, across transformed and primary mammalian cell cultures as well as mouse liver. CrGPDH expression supported proliferation of cancer cells under respiratory chain inhibition or hypoxia, as well as patient-derived fibroblasts with mitochondrial dysfunction. Moreover, CrGPDH decreased triglyceride levels in kidney cancer cell lines and reversed ethanol-induced triglyceride accumulation in mouse liver. Thus, CrGPDH represents a promising xenotopic tool to alleviate redox imbalance and associated impaired lipogenesis in conditions ranging from primary mitochondrial diseases to steatosis.