Mutations in human lipoyltransferase gene LIPT1cause a Leigh disease with secondary deficiency for pyruvate and alpha-ketoglutarate dehydrogenase

Abstract

BackgroundSynthesis and apoenzyme attachment of lipoic acid have emerged as a new complex metabolic pathway. Mutations in several genes involved in the lipoic acid de novo pathway have recently been described (i.e., LIAS, NFU1, BOLA3, IBA57), but no mutation was found so far in genes involved in the specific process of attachment of lipoic acid to apoenzymes pyruvate dehydrogenase (PDHc), α-ketoglutarate dehydrogenase (α-KGDHc) and branched chain α-keto acid dehydrogenase (BCKDHc) complexes.MethodsExome capture was performed in a boy who developed Leigh disease following a gastroenteritis and had combined PDH and α-KGDH deficiency with a unique amino acid profile that partly ressembled E3 subunit (dihydrolipoamide dehydrogenase / DLD) deficiency. Functional studies on patient fibroblasts were performed. Lipoic acid administration was tested on the LIPT1 ortholog lip3 deletion strain yeast and on patient fibroblasts.ResultsExome sequencing identified two heterozygous mutations (c.875C > G and c.535A > G) in the LIPT1 gene that encodes a mitochondrial lipoyltransferase which is thought to catalyze the attachment of lipoic acid on PDHc, α-KGDHc, and BCKDHc. Anti-lipoic acid antibodies revealed absent expression of PDH E2, BCKDH E2 and α-KGDH E2 subunits. Accordingly, the production of 14CO2 by patient fibroblasts after incubation with 14Cglucose, 14Cbutyrate or 14C3OHbutyrate was very low compared to controls. cDNA transfection experiments on patient fibroblasts rescued PDH and α-KGDH activities and normalized the levels of pyruvate and 3OHbutyrate in cell supernatants. The yeast lip3 deletion strain showed improved growth on ethanol medium after lipoic acid supplementation and incubation of the patient fibroblasts with lipoic acid decreased lactate level in cell supernatants.ConclusionWe report here a putative case of impaired free or H protein-derived lipoic acid attachment due to LIPT1 mutations as a cause of PDH and α-KGDH deficiencies. Our study calls for renewed efforts to understand the mechanisms of pathology of lipoic acid-related defects and their heterogeneous biochemical expression, in order to devise efficient diagnostic procedures and possible therapies.

Assembly of Lipoic Acid on Its Cognate Enzymes: an Extraordinary and Essential Biosynthetic Pathway

“…The E2 subunits of all three dehydrogenases showed low levels of lipoylation, concomitant with the results of the 2-oxoacid dehydrogenase activity assays, whereas liver tissue glycine cleavage H protein lipoylation appeared to be increased somewhat above control levels in the patient tested (154). The addition of lipoic acid to the growth medium of fibroblasts derived from both patients failed to restore lipoylation (153,154), whereas the introduction of a wild-type LIPT1 gene restored fibroblast 2-oxoacid dehydrogenase activities (153).…”

“…In contrast to the LIAS patients, two children with LIPT1 mutations had normal levels of glycine cleavage activity, H protein lipoylation, and glycine in body fluids (153,154). As seen in the LIAS cases, pyruvate and 2-oxoglutarate dehydrogenase activities were very low.…”

“…As seen in the LIAS cases, pyruvate and 2-oxoglutarate dehydrogenase activities were very low. Both patients showed a severe lack of muscle tone and excreted very high levels of lactate (the product of pyruvate reduction) and 2-oxoglutarate (153,154). The E2 subunits of all three dehydrogenases showed low levels of lipoylation, concomitant with the results of the 2-oxoacid dehydrogenase activity assays, whereas liver tissue glycine cleavage H protein lipoylation appeared to be increased somewhat above control levels in the patient tested (154).…”

“…LplA is known to attach lipoic acid to the human 2-oxoacid dehydrogenase E2 subunits (23,159) and bovine H protein (160). Indeed, it has been proposed that LIPT1 and yeast Lip3 have the same function (153). If so, an experiment parallel to alleviation of LIPT1 deficiency has been done in yeast.…”

Drug-target interaction prediction: A Bayesian ranking approach

“…Next, we will illustrate that the predictions of BRDTI may contribute to promising thera- Finally, we point out that Lipoyltransferase 1 gene (LIPT1) defects cause Leigh disease [48] and, in case of severe defects, fatal lactic acidosis [49,50]. We hypothesize that in some cases of LIPT mutations, an agonist could help to increase enzymatic activity.…”