Figure 2: Induction of mitochondrial biogenesis by quercetin is regulated by activation of HO-1. (a) Expression levels of HO-1 mRNA and protein were determined after HepG2 cells were exposed for indicated times (0, 0.5, 1, 3, 5 h) and with the indicated concentrations (0, 5, 10, 15, 25 μM) of quercetin. Expressions of HO-1 mRNA and protein were determined by RT-PCR and Western blotting. GAPDH and β-actin served as the standards, respectively. (b–d) HepG2 cells were exposed to 15 μM of quercetin for 3 h with or without 20 μM of SnPP. (b) Expressions of PGC-1, NRF-1, and TFAM mRNA were determined by RT-PCR. (c) Expression of COXIV protein was determined by Western blotting. (d) Expression of mtDNA content was quantified by real-time PCR. Relative amounts of mtDNA and nDNA contents were compared. Results are expressed as mean ± SE of three independent experiments, and representative data are shown. * compared with untreated control group; compared with cells treated with quercetin alone.