Sirt1 is down-regulated in cardiomyocytes from patients with advanced heart failure. Atrial myocardial homogenates were prepared from the recipient and donor heart sample. (A) Expression of Sirt1 and tubulin was evaluated by immunoblots. The level of donor heart is expressed as 1. H9c2 cells treated with Ad-Sirt1 was used as a positive control. (B) Atrial myocardial sections from the recipient and donor patients were subjected to hematoxylin-eosin staining (upper) and immunostaining (lower) with anti-troponin C antibody (red), anti-Sirt1 antibody (green), and DAPI (blue). The number of Sirt1 positive nuclei/total nuclei of donor heart is expressed as 1. (C) The ventricular myocardial sections of hearts from old (15 months) and young (3 months) mice were subjected to immunostaining with anti-Sirt1 antibody (green) and DAPI (blue). The number of Sirt1 positive nuclei/total nuclei of young heart is expressed as 1.