Disturbed ATP synthase assembly and liver damage in mouse conditional knockout of Tmem70
J. Kovalcikova1, M. Vrbacky1, H. Nuskova1, K. Tauchmannova1, I. Beck2, O. Kucera3, Z. Cervinkova3, R. Sedlacek2, T. Mracek1, and J. Houstek1,
1Institute of Physiology, Czech Academy of Sciences, Prague; 2Institute of Molecular Genetics, Czech Academy of Sciences, Prague; 3Faculty of Medicine, Charles University, Hradec Kralove, Czech Republic
TMEM70 is a transmembrane protein localized in the inner mitochondrial membrane and involved in the biogenesis of the eukaryotic ATP synthase. TMEM70 mutations cause isolated deficiency of ATP synthase often resulting in a fatal neonatal mitochondrial encephalocardiomyopathy in patients. Essential role of TMEM70 was confirmed by the embryonal lethality of Tmem70-/- mice, where we also observed disturbed ATP synthase biogenesis in embryos .
To explore the molecular mechanism of TMEM70 action in adults, we generated conditional knockout, where Cre mediated gene excision can be induced by tamoxifen administration. Upon induction, the weight of mice decreased and they died by the week 8 post-induction. BNE showed pronounced decrease of the fully assembled F1Fo-ATP synthase with F1 subcomplex accumulation in most of tissues except heart. Heart was likely protected by relatively high expression levels of Tmem70, which were partially sustained even from the low remaining amount of wt Tmem70 gene. Still, there was some accumulation of F1 subcomplex in dependency to knockout efficiency. Histologically, we observed focal necrosis in liver. Liver damage was confirmed by hyperammonemia, increased blood levels of alanine aminotransferase and aspartate aminotransferase, and increased oxidative stress and apoptosis in tissue.
Furthermore, hrCNE analysis of liver mitochondria from Tmem70-/- animals revealed formation of large and labile vestigial ATP synthase complexes, which lacks subunit c and falls apart due to Coomassie blue in BNE analysis. Regarding the OXPHOS function, in Tmem70-/- liver mitochondria we observed higher membrane potential and poor inhibition of state 3 (ADP) respiration by oligomycin.
In conclusion, induction of Tmem70 knockout in adult mice impairs primarily liver function, and it resembles symptoms present during metabolic crises in patients. This contrasts with the mainly cardiologic presentation at disease onset in humans.
 Vrbacky et al., 2016, HMG, PMID: 28173120
Supported by grants 14-36804G and 16-33018A.