Compound heterozygous missense mutations of the SLC25A1 gene give raise to combined D/L-2- HydroxyGlutaric Aciduria (D/L-2HGA) [1-10], a disease hallmarked by the accumulation of the two enantiomeric forms of 2-hydroxyglutaric acid (2HG), D and L. D/L-2HGA is considered a rare disorder, with 150 cases described worldwide. Both enantiomers of 2HG are thought to be neurotoxic during development based on the clinical manifestations seen in patients with L- or D-2HGAs. However, their specific functions in normal cells and tissues remains unclear. The main activity of Slc25a1 consists of promoting the efflux of the lipid precursor, citrate, from the mitochondria into the cytosol, where citrate provides the main source for lipid biosynthesis. The current model thus envisions that lack of Slc25a1 mitochondrial transport activity leads to a deficit in the cytosolic citrate pool in turn hampering lipogenesis. Consequently, supplementation with dietary citrate has been advocated and clinically attempted, but the prognosis of these patients is still dismal. Our current work challenges this dogma and is paradigm shifting in several aspects. We have developed the first murine models of Slc25a1 deficiency (Slc25a1-/- mice) and we have discovered that the phenotypic alterations in these animals recapitulate those seen in the currently known human disorders of combined D/L-2HGA. We used a multifaceted approach inclusive of biochemical studies, metabolomics and transriptomic profiling to identify the pathways altered in Slc25a1-/- mice. As expected, Slc25a1-/- accumulate 2HG in all body fluids hence providing a novel model of 2-Hydroxyglutaric aciduria. However, in contrast with the prevalent mechanistic view of this disease, Slc25a1-/- mice compensate for lack of cytosolic citrate by igniting alternative pathways for citrate production which in turn lead to excess citrate and lipid build up. Transcriptomic analysis further revealed the enrichment of gene sets involved in inflammation and in the induction of premature senescence. Similarly, fibroblasts derived from patients affected by D/L2HGA harboring loss of function Slc25a1 mutations, also undergo premature senescence. Finally, we report here for the first time that the D- and L- 2HG enantiomers are able, per se, to induce senescence in normal cells. Thereby empowered by the availability of both murine and human models of Slc25a1-driven 2HGA, the main scope of this proposal is to solve two standing conundrums in the field: first, we will identify the pathways by which D/L-2HG is produced in the context of Slc25a1 mutations or Slc25a1 loss. Second, we will assess, for the first time, how D/L2HG affect embryonic development with the specific intent to dissect pathogenic events unrelated to- or sustained by- 2HG accumulation. We predict that these studies will enlighten metabolic and molecular pathways that can be targeted in the future and will ameliorate the outcome of devastating disorders associated with Slc...