Transgenic rescue approach ameliorates ATP synthase deficiency caused by the dysfunction of TMEM70 assembly factor in rat

Mutations of the TMEM70 gene disrupt the biogenesis of the ATP synthase and represent the most frequent cause of autosomal recessive encephalo-cardio-myopathy with neonatal onset. Patient tissues present with isolated defects of ATP synthase, impaired mitochondrial ATP synthesis, and insufficient energy provision. In the current study, we utilised transgenic rescue approach to validate the efficiency of Tmem70 defect complementation in spontaneously hypertensive rats with previously targeted Tmem70 gene (SHR-Tmem70ko/ko). We generated SHR-Tmem70ko/ko knockout rats expressing the Tmem70 wild-type transgene (SHR-Tmem70ko/ko,tg/tg) under the control of the EF-1 universal promoter. Transgenic rescue resulted in fully viable animals with variable expression of the Tmem70 transgene across the range of tissues and only minor differences in terms of the growth parameters. The TMEM70 protein was restored to 16–49% of the controls in the liver and heart, which was sufficient for the full biochemical complementation of ATP synthase biogenesis as well as for mitochondrial energetic function in the liver. To the contrary, we observed only partial biochemical complementation in the heart, especially in SHR-Tmem70ko/ko,tg/0 hemizygotes. Such incomplete biochemical complementation translated into a minor impairment in left ventricle function. Overall, the transgenic rescue of Tmem70 in SHR-Tmem70ko/ko knockout rats resulted in the efficient complementation of ATP synthase deficiency and thus in the successful genetic treatment of an otherwise fatal mitochondrial disorder.