Terpenoid synthesis pathway defects in mitofusin knockouts. (A) Scheme of the mevalonate pathway in mammals. Red, proteins down-regulated according to SILAC-based protein quantification performed with Mfn1 and Mfn2 knockout MEFs; blue, not affected; gray, not detected. *, COQ2 protein level was determined by Western blot analysis. (B) Quantitative proteomic analysis of two independent batches of control and Mfn2 knockout MEFs using SILAC analysis. Negative values indicate down-regulation of the protein in Mfn2 knockout relative to control MEFs. (C) Transcript levels of different enzymes involved in the terpenoid and coenzyme Q synthesis pathways determined by qRT-PCR with total RNA extracted from control (white bars) and Mfn2 knockout (black bars) hearts (n = 5 pairs of mice). (D) Terpenoid metabolites content of whole heart extracts isolated from control (white bars, n = 12 samples), Mfn1 knockout (gray bars, n = 7 samples), and Mfn2 knockout (black bars, n = 6 samples). Error bars indicate ±SEM. *, P < 0.05; **, P < 0.01; ***, P < 0.001.