Reference Center of Inherited Metabolic Diseases, Imagine Institute, University Paris Descartes, Hospital Necker Enfants Malades, APHP, Paris, France.
Orphanet J Rare Dis. 2013 Dec 17;8:192. doi: 10.1186/1750-1172-8-192.
Synthesis 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.
Exome 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.
Exome 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.
We 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.
硫辛酸的合成和脱辅基酶结合已成为新的复杂代谢途径。最近已描述了几个参与从头合成硫辛酸途径的基因的突变（即 LIAS、NFU1、BOLA3、IBA57），但迄今为止尚未发现参与硫辛酸与脱辅基酶丙酮酸脱氢酶（PDHc）、α-酮戊二酸脱氢酶（α-KGDHc）和支链α-酮酸脱氢酶（BCKDHc）复合物结合的特定过程的基因突变。
对一名因肠胃炎后发展为 Leigh 病的男孩进行外显子捕获，该男孩同时存在 PDH 和 α-KGDH 缺乏症，其氨基酸谱部分类似于 E3 亚基（二氢硫辛酸脱氢酶/DLD）缺乏症。对患者成纤维细胞进行功能研究。对 LIPT1 同源物 lip3 缺失酵母菌株和患者成纤维细胞进行硫辛酸给药测试。
外显子组测序发现 LIPT1 基因的两个杂合突变（c.875C>G 和 c.535A>G），该基因编码一种线粒体脂酰转移酶，被认为催化 PDHc、α-KGDHc 和 BCKDHc 上的硫辛酸结合。抗硫辛酸抗体显示 PDH E2、BCKDH E2 和 α-KGDH E2 亚基表达缺失。因此，与对照组相比，患者成纤维细胞在孵育 14C 葡萄糖、14C 丁酸盐或 14C3OH 丁酸盐后产生 14CO2 的量非常低。患者成纤维细胞的 cDNA 转染实验挽救了 PDH 和 α-KGDH 活性，并使细胞上清液中丙酮酸和 3OH 丁酸盐的水平正常化。酵母 lip3 缺失菌株在补充硫辛酸后在乙醇培养基中的生长得到改善，并且培养患者成纤维细胞后细胞上清液中的乳酸水平降低。
我们在此报告了由于 LIPT1 突变导致游离或 H 蛋白衍生的硫辛酸结合受损的潜在病例，这是 PDH 和 α-KGDH 缺乏症的原因。我们的研究呼吁重新努力理解硫辛酸相关缺陷的病理机制及其异质生化表达，以便设计有效的诊断程序和可能的治疗方法。
