Stabilization of mtDNA in Phb2^NKO mice upon Oma1 deletion. (A) Assembly of respiratory chain supercomplexes is impaired in Phb2^NKO and Phb2^NKOOma1^ko/ko mice. Digitonin-solubilized hippocampal mitochondria isolated from 18-wk-old mice were analyzed by BN-PAGE and immunoblotting using the indicated antibodies. I, complex I; III, complex III; IV, complex IV; M, monomer. (B) Relative activities of complexes I and IV are decreased in Phb2^NKO and Phb2^NKOOma1^ko/ko mice. Mitochondria isolated from the hippocampus of 18-wk-old mice were subjected to BN-PAGE, and gels were incubated in complex I (CI)- or complex IV (CIV)-specific substrate solutions. M, monomeric CIV. (C) Relative mtDNA levels in the hippocampus of 18-wk-old mice. Total DNA was isolated from the hippocampus of mice of the indicated genotype and analyzed by quantitative real-time PCR analysis using mtDNA- and nuclear DNA–specific primers (n = 3). *, P≤ 0.05; **, P < 0.01. Error bars indicate SD. (D) Steady-state levels of respiratory chain complex subunits in Phb2^NKO and Phb2^NKOOma1^ko/ko mice. Immunoblot analysis of hippocampal mitochondria isolated from 18-wk-old mice using the indicated antibodies.