Figure 4. SPD prevents age-associated depletion in myocardial polyamines and alterations of SIRT1/PGC-1α signaling pathway proteins. Representative immunoblot bands for ODC, SSAT, and p21 (A), and for SIRT1, PGC-1α, NRF1, NRF2, and TFAM (B) in myocardium from 3-, 6-, 12- and 24-month-old rats. GAPDH was used as loading control. (n = 10). * P < 0.05 vs. 3 months, ** P < 0.01 vs. 3 months. (C) Correlation between ODC and (a) SIRT1, (b) PGC-1α, (c) NRF1, (d) NRF2, and (e) TFAM in cardiac tissue from rats of different ages. (D) Correlation between SSAT and (a) SIRT1, (b) PGC-1α, (c) NRF1, (d) NRF2, and (e) TFAM in cardiac tissue from rats of different ages (n = 10). (E) Representative immunoblot bands for SIRT1, PGC-1α, NRF1, NRF2, and TFAM in the myocardium of young (3 months of age), old (24 months of age), and SPD-treated (6 weeks) old rats. (n = 4). # P < 0.05 vs. young, ## P < 0.01 vs. young, * P < 0.05 vs. old, ** P < 0.01 vs. old. (F, G) Expression of SIRT1, PGC-1α, NRF1, NRF2, and TFAM measured by western blot in NRMCs treated with 0, 2.5, 5, 10, or 20 μM SPD for 24 h (F) or 10 μM SPD for 0, 6, 12, 24, and 48 h (G). Quantification of protein expression is shown on the right-hand side of the graphs (n = 4). * P < 0.05 vs. control, ** P < 0.01 vs. control.