L-2-hydroxyglutaric aciduria
https://www.nature.com/articles/s41586-026-10564-x
This study shows that L‑2‑hydroxyglutarate (L‑2‑HG), a molecule long believed to be only a toxic by‑product plays an important and normal signalling role inside cells. Under healthy conditions, L‑2‑HG is kept at very low levels because a mitochondrial enzyme called L2HGDH rapidly converts it back into another molecule, 2‑oxoglutarate. When this enzyme is missing in humans, L‑2‑HG builds up, causing a rare childhood brain disorder, which is why it has traditionally been viewed as harmful. The researchers discovered that L‑2‑HG is produced naturally when the cell’s energy balance shifts and the mitochondrial NADH/NAD⁺ ratio increases. NADH/NAD+ are important coenzymes (molecules that help enzymes in their chemical reactions) for mitochondrial metabolism, sending signals to regulate cellular balance, and keeping different mitochondrial functions working correctly such as energy production. Another enzyme, MDH2, then converts 2‑oxoglutarate into L‑2‑HG. They also showed that L2HGDH can remove L‑2‑HG even when the mitochondrial respiratory chain is impaired, indicating it does not rely on the usual energy‑producing machinery. Importantly, the team identified the KDM4 family of histone demethylases (enzymes that remove methyl groups from histones which package DNA into structures and changes gene expression) as key molecular targets of L‑2‑HG. Higher L‑2‑HG levels increased a repressive chromatin mark (change to chromatin structure which is made of DNA and histones, so it is more compact and silences gene expression), H3K9me3 and reduced the activity of hundreds of genes in embryonic stem cells. In mice, lowering L‑2‑HG during early development caused growth problems, kidney abnormalities, and activation of stress and inflammation pathways. Overall, the study shows that L‑2‑HG is not just a toxic metabolite but a normal signalling molecule essential for regulating gene expression and healthy development.