The GABA Transaminase, ABAT, Is Essential for Mitochondrial Nucleoside Metabolism

• Published in: Cell metabolism Vol. 21; no. 3; pp. 417 - 427
• Main Authors: Besse, Arnaud, Wu, Ping, Bruni, Francesco, Donti, Taraka, Graham, Brett H., Craigen, William J., McFarland, Robert, Moretti, Paolo, Lalani, Seema, Scott, Kenneth L., Taylor, Robert W., Bonnen, Penelope E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 03.03.2015
• Subjects: 4-Aminobutyrate Transaminase - genetics; 4-Aminobutyrate Transaminase - metabolism; Brain - metabolism; DNA, Mitochondrial - genetics; DNA, Mitochondrial - metabolism; Fibroblasts - metabolism; gamma-Aminobutyric Acid - genetics; gamma-Aminobutyric Acid - metabolism; Humans; Mitochondria - genetics; Mitochondria - metabolism; Mutation, Missense - genetics; Nucleosides - genetics; Nucleosides - metabolism
• ISSN: 1550-4131; 1932-7420; 1932-7420
• DOI: 10.1016/j.cmet.2015.02.008

ABAT is a key enzyme responsible for catabolism of principal inhibitory neurotransmitter γ-aminobutyric acid (GABA). We report an essential role for ABAT in a seemingly unrelated pathway, mitochondrial nucleoside salvage, and demonstrate that mutations in this enzyme cause an autosomal recessive neurometabolic disorder and mtDNA depletion syndrome (MDS). We describe a family with encephalomyopathic MDS caused by a homozygous missense mutation in ABAT that results in elevated GABA in subjects’ brains as well as decreased mtDNA levels in subjects’ fibroblasts. Nucleoside rescue and co-IP experiments pinpoint that ABAT functions in the mitochondrial nucleoside salvage pathway to facilitate conversion of dNDPs to dNTPs. Pharmacological inhibition of ABAT through the irreversible inhibitor Vigabatrin caused depletion of mtDNA in photoreceptor cells that was prevented through addition of dNTPs in cell culture media. This work reveals ABAT as a connection between GABA metabolism and nucleoside metabolism and defines a neurometabolic disorder that includes MDS. [Display omitted] •ABAT converts dNDP to dNTP in the mitochondrial nucleoside salvage pathway•Inhibition of ABAT causes decreased copy number of mitochondrial genome•mtDNA depletion induced by ABAT inhibition is rescued by dNTP supplementation in vitro•ABAT causes human mitochondrial DNA depletion syndrome ABAT is a key enzyme responsible for catabolism of principal inhibitory neurotransmitter γ-aminobutyric acid (GABA). Besse et al. report an essential role for ABAT in a seemingly unrelated pathway, mitochondrial nucleoside salvage, and demonstrate that mutations in this enzyme cause autosomal recessive mtDNA depletion syndrome.