The impact of mitochondrial tRNA mutations on the amount of ATP synthase differs in the brain compared to other tissues

Abstract

The impact of point mutations in mitochondrial tRNA genes on the amount and stability of respiratory chain complexes and ATP synthase (OXPHOS) has been broadly characterized in cultured skin fibroblasts, skeletal muscle samples, and mitochondrial cybrids. However, less is known about how these mutations affect other tissues, especially the brain. We have compared OXPHOS protein deficiency patterns in skeletal muscle mitochondria of patients with Leigh (8363G>A), MERRF (8344A>G), and MELAS (3243A>G) syndromes. Both mutations that affect mt-tRNA(Lys) (8363G>A, 8344A>G) resulted in severe combined deficiency of complexes I and IV, compared to an isolated severe defect of complex I in the 3243A>G sample (mt-tRNA(LeuUUR). Furthermore, we compared obtained patterns with those found in the heart, frontal cortex, and liver of 8363G>A and 3243A>G patients. In the frontal cortex mitochondria of both patients, the patterns of OXPHOS deficiencies differed substantially from those observed in other tissues, and this difference was particularly striking for ATP synthase. Surprisingly, in the frontal cortex of the 3243A>G patient, whose ATP synthase level was below the detection limit, the assembly of complex IV, as inferred from 2D-PAGE immunoblotting, appeared to be hindered by some factor other than the availability of mtDNA-encoded subunits.

YME1L controls the accumulation of respiratory chain subunits and is required for apoptotic resistance, cristae morphogenesis, and cell proliferation

“…In contrast to conventional spectrophotometric assays, high-resolution respirometry permits the evaluation of the function of relatively intact, membrane-embedded respiratory complexes (Wenchich et al , 2003; Pecina et al , 2004; Stiburek et al , 2007; Fornuskova et al , 2008). The measurements were performed in the presence of carbonyl cyanide p -(trifluoromethoxy) phenylhydrazone (FCCP; an uncoupler of oxidative phosphorylation) as multiple substrate-inhibitor analyses.…”

Genetics of stroke

“…Another T-to-C transition at nucleotide position 3271 occurred as a secondary common mutation [3] . The pathogenic mtDNA mutations can result in dysfunction of mitochondrial oxidative phosphorylation (OXPHOS) [22] , impairing respiratory capacity of the cell and ATP synthesis. Fornuskova et al [22] found that the 3243A→G frontal cortex mitochondria showed a marked loss of the complex IV holoenzyme, accompanied by accumulation of assembly intermediates.…”

Tissue- and cell-type–specific manifestations of heteroplasmic mtDNA 3243A>G mutation in human induced pluripotent stem cell-derived disease model

“…By far the most common finding in MELAS is complex I (CI) deficiency, whereas some patients have combined deficiencies of the RC CI, CIII, and CIV (13,14). Evidence from autopsy tissues suggest that RC complexes are differentially affected even in different tissues of one individual with m.3243A>G mutation with the CI deficiency dominating (15). Induction of nuclearencoded CII, succinate dehydrogenase (SDH), and mitochondrial accumulations in muscle and neurons are other typical findings in RC deficiencies (16,17), thought to be compensatory to the RC defect.…”