Fig. 5.

Livers of old mice fail to increase SIRT1 after PH because of repression of the SIRT1 promoter by the C/EBPβ-HDAC1 complex. (A) Levels of SIRT1 mRNA in the livers of young and old mice after PH. Real-time PCR was performed with total RNA isolated at different time points after PH, and levels of SIRT1 mRNA were determined as ratios to β-actin. n = 5. *P < 0.05, old versus young; ^#P <0.05, after PH versus before PH. (B) Expression of C/EBPβ and HDAC1 in young and old mice after PH. Bottom images show levels of C/EBPβ-LAP and HDAC1 as ratios to β-actin. (C) Livers of old mice contain high amounts of C/EBPβ-HDAC1 complexes after PH. Amounts of HDAC1 and C/EBPβ-LAP were determined in C/EBPβ IPs. IgG: heavy chains of IgG. Bottom image shows ratios of HDAC1 to C/EBPβ-LAP in C/EBPβ IPs. (D) C/EBPβ activates the SIRT1 promoter in the livers of young mice, whereas the C/EBPβ-HDAC1 complex represses the promoter in the livers of old mice. The ChIP assay was performed with the SIRT1 promoter, as described in the legend to Fig. 3. (E) Levels of C/EBPβ on the SIRT1 promoter at 0 and 36 hours after PH, showing PCR signals after different numbers of cycles of PCR reaction using C/EBPβ IPs from young livers at 0 and 36 hours after PH.