Altered 2-thiouridylation impairs mitochondrial translation in reversible infantile respiratory chain deficiency

Abstract

Childhood-onset mitochondrial encephalomyopathies are severe, relentlessly progressive conditions. However, reversible infantile respiratory chain deficiency (RIRCD), due to a homoplasmic mt-tRNAGlu mutation, and reversible infantile hepatopathy, due to tRNA 5-methylaminomethyl-2-thiouridylate methyltransferase (TRMU) deficiency, stand out by showing spontaneous recovery, and provide the key to treatments of potential broader relevance. Modification of mt-tRNAGlu is a possible functional link between these two conditions, since TRMU is responsible for 2-thiouridylation of mt-tRNAGlu, mt-tRNALys and mt-tRNAGln. Here we show that down-regulation of TRMU in RIRCD impairs 2-thiouridylation and exacerbates the effect of the mt-tRNAGlu mutation by triggering a mitochondrial translation defect in vitro. Skeletal muscle of RIRCD patients in the symptomatic phase showed significantly reduced 2-thiouridylation. Supplementation with l-cysteine, which is required for optimal TRMU function, rescued respiratory chain enzyme activities in human cell lines of patients with RIRCD as well as deficient TRMU. Our results show that l-cysteine supplementation is a potential treatment for RIRCD and for TRMU deficiency, and is likely to have broader application for the growing group of intra-mitochondrial translation disorders.

Mitochondrial complex IV deficiency, caused by mutated COX6B1, is associated with encephalomyopathy, hydrocephalus and cardiomyopathy

“…17 In vitro studies in patient fibroblasts showed that copper 18 and copper with bezafibrate supplementation rescued cells harboring mutations in SCO2 encoding a COX copper-chaperone 19 while L-cystein supplementation improved mitochondrial function in cells with TRMU mutations. 20 However, as the COX6B1 defect does not cause LS and the protein is not a copper chaperone but an integral COX subunit, we evaluated a number of other potentially beneficial molecules for their ability to improve mitochondrial function in the patient's fibroblasts. The significantly beneficial effect of AICAR on ATP content, and resveratrol on both ATP content and growth resembles the effect of these mitochondrial biogenesis inducers, on defects due to GFM1 and MRPS22, mutations in the mitochondrial translation machinery.…”

Modification of the wobble uridine in bacterial and mitochondrial tRNAs reading NNA/NNG triplets of 2-codon boxes

“…87,109 In line with this, TRMU, which carries the sulfur moiety that is finally transferred to mt-tRNAs, has been suggested to be involved in the assembly of enzyme complexes containing iron-sulfur clusters, since an intermediate of the OXPHOS Complex II accumulates in TRMU-depleted cells. 8,95 However, this hypothesis does not explain why the accumulation of subunits of complex IV, which does not contain an iron-sulfur center, is also affected in the depleted cells. 95 Hence further work is required to clarify the hypothetical role of TRMU in sulfur trafficking.…”

“…8,95 However, this hypothesis does not explain why the accumulation of subunits of complex IV, which does not contain an iron-sulfur center, is also affected in the depleted cells. 95 Hence further work is required to clarify the hypothetical role of TRMU in sulfur trafficking.…”

“…73,[88][89][90][91][92][93][94] Notably, acute infantile liver failure associated with TRMU mutations is reversible in some patients through a yet unknown mechanism. 3,95 Even though a compensatory mechanism of the translation defect may exist, the OXPHOS system function may be impaired, as observed in patient cells carrying MTO1 and TRMU mutations, and in TRMU-knocked-down cells. 4,8,96 This suggests that other mechanisms, in addition to altered translation, might contribute to mitochondrial dysfunction.…”

Abbreviated Pathway for Biosynthesis of 2-Thiouridine in Bacillus subtilis

“…Inactivation of the s 2 U pathway in E. coli is not lethal, but it causes growth defects associated with loss of reading frame maintenance (36,37). Similarly, inactivation of the nonessential 2-thiouridylase gene MTU1, while leaving the organism viable, causes respiratory defects in yeast and humans (38,39). On the other hand, the archaeal 2-thiouridylase gene Ncs6 is essential in Methanococcus maripaludis (33) and necessary for growth at high temperatures in Haloferax volcanii (34).…”