A novel deficiency of mitochondrial ATPase of nuclear origin

Abstract

We report a new type of fatal mitochondrial disorder caused by selective deficiency of mitochondrial ATP synthase (ATPase). A hypotrophic newborn from a consanguineous marriage presented severe lactic acidosis, cardiomegaly and hepatomegaly and died from heart failure after 2 days. The activity of oligomycin-sensitive ATPase was only 31-34% of the control, both in muscle and heart, but the activities of cytochrome c oxidase, citrate synthase and pyruvate dehydrogenase were normal. Electrophoretic and western blot analysis revealed selective reduction of ATPase complex but normal levels of the respiratory chain complexes I, III and IV. The same selective deficiency of ATPase was found in cultured skin fibroblasts which showed similar decreases in ATPase content, ATPase hydrolytic activity and level of substrate-dependent ATP synthesis (20-25, 18 and 29-33% of the control, respectively). Pulse-chase labelling of patient fibroblasts revealed low incorporation of [(35)S]methionine into assembled ATPase complexes, but increased incorporation into immunoprecipitated ATPase subunit beta, which had a very short half-life. In contrast, no difference was found in the size and subunit composition of the assembled and newly produced ATPase complex. Transmitochondrial cybrids prepared from enucleated fibroblasts of the patient and rho degrees cells derived from 143B. TK(-)human osteosarcoma cells fully restored the ATPase activity, ATP synthesis and ATPase content, when compared with control cybrids. Likewise, the pattern of [(35)S]methionine labelling of ATPase was found to be normal in patient cybrids. We conclude that the generalized deficiency of mitochondrial ATPase described is of nuclear origin and is caused by altered biosynthesis of the enzyme.

Mitochondrial diseases and ATPase defects of nuclear origin

“…1). Transmitochondrial cybrid cells made of patient's fibroblasts fully complemented the ATPase defect and confirmed the nuclear origin of impaired biogenesis of the enzyme complex [27]. Later on, two other similar cases of selective ATPase deficiency were found in the Czech Republic [22] and one in Austria [28].…”

“…An extremely low ATPase activity and low, tightly coupled, respiration rates were observed in muscle mitochondria, but no mutation was found in mtDNA genes encoding ATPase subunits. The nuclear origin of ATP synthase deficiency was demonstrated for the first time in 1999 [27] in a new type of fatal mitochondrial disorder. A child with severe lactic acidosis, cardiomyopathy and hepatomegaly died 2 days LA-lactic acidosis, CM-cardiomyopathy.…”

“…Native forms of ATPase can be easily revealed by Blue-Native electrophoresis [33] that became a very powerful approach to diagnostics of mitochondrial OXPHOS defects today. We have performed detailed studies on most of the diagnosed cases of selective ATPase deficiency and always found only a full-size ATPase complex to be present in cells and isolated mitochondria from the patient's tissues [27]. No accumulation of assembly intermediates analogous to subcomplexes observed in ATP6 mutations or cells with doxycycline-inhibited translation of mitochondrial proteins [13,15,32] could be detected in fibroblasts with ATPase defects of nuclear origin.…”

Oxidative Phosphorylation System: Nuclear Genes and Genetic Disease

“…Although complex V deficiency caused by nuclear gene mutations has already been shown in 1999 (Houstek et al, 1999), it took until 2004 when such a mutation was found in the ATP12 gene (De Meirleir et al, 2004). ATP11, ATP12 and FMC1 are the presently known genes that encode for proteins involved in the assembly of the F 1 part in yeast, of which only ATP11 and ATP12 are found in human.…”

Cardiac Involvement in Primary Myopathies

“…CI in RCE disorders comprises ECG abnormalities [4, 5, 6], myocardial thickening (fig. 2), dilatation [6]and heart failure [56, 57]. A dominant feature of CI in RCE disorders seems to be ILVAT [58, 59].…”