Ethylmalonic encephalopathy is an autosomal recessive, invariably fatal disorder characterized by early-onset encephalopathy, microangiopathy, chronic diarrhea, defective cytochrome c oxidase (COX) in muscle and brain, high concentrations of C4 and C5 acylcarnitines in blood and high excretion of ethylmalonic acid in urine. ETHE1, a gene encoding a β-lactamase-like, iron-coordinating metalloprotein, is mutated in ethylmalonic encephalopathy. In bacteria, ETHE1-like sequences are in the same operon of, or fused with, orthologs of TST, the gene encoding rhodanese, a sulfurtransferase. In eukaryotes, both ETHE1 and rhodanese are located within the mitochondrial matrix. We created a Ethe1-/- mouse that showed the cardinal features of ethylmalonic encephalopathy. We found that thiosulfate was excreted in massive amounts in urine of both Ethe1-/- mice and humans with ethylmalonic encephalopathy. High thiosulfate and sulfide concentrations were present in Ethe1-/- mouse tissues. Sulfide is a powerful inhibitor of COX and short-chain fatty acid oxidation, with vasoactive and vasotoxic effects that explain the microangiopathy in ethylmalonic encephalopathy patients. Sulfide is detoxified by a mitochondrial pathway that includes a sulfur dioxygenase. Sulfur dioxygenase activity was absent in Ethe1-/- mice, whereas it was markedly increased by ETHE1 overexpression in HeLa cells and Escherichia coli. Therefore, ETHE1 is a mitochondrial sulfur dioxygenase involved in catabolism of sulfide that accumulates to toxic levels in ethylmalonic encephalopathy.
Bibliographical noteFunding Information:
We thank A. Bradley (The Wellcome Trust Sanger Institute) for AB1 mouse embryonic stem cells. We are grateful to M. Bada for skillful technical assistance; to B. Garavaglia, E. Lamantea, F. Forlani and M.K. Grieshaber for valuable discussion; to the Chemical Analysis Laboratory, University of Georgia, for metal analysis; and to Primm for MALDI TOF mass spectometry analysis. This work was supported by the Pierfranco and Luisa Mariani Foundation Italy, Fondazione Telethon-Italy grant number GGP07019, the Italian Ministry of University and Research (FIRB 2003—project RBLA038RMA), MITOCIRCLE and EUMITOCOMBAT network grants from the European Union framework program 6 and by the Deutsche Forschungsgemeinschaft (GR 456/22-1).