Suppression of apoptosis by calorie restriction in aged kidney

Programmed cell death by apoptosis is regarded as an organism's protective mechanism against the accumulation of defective cells. Apoptotic activity is shown to be elevated in most aged tissues, and its intracellular regulation is intricately manipulated by mitochondria. In this study, to determine the progression of apoptosis during aging, we investigated the expression of several key apoptosis-related markers in kidney of 12- and 24-month-old rats. Mitochondrial damage was detected by lipid peroxidation and Western blot analysis in several target apoptotic proteins in aged rat kidney. Our results showed that the expression levels of a pro-apoptotic Bax protein, was significantly enhanced at the age of 24 months, while an anti-apoptotic protein, Bcl-2, was reduced in the aged rat kidney. We also found that the cytosolic cytochrome c level was significantly increased in the aged kidney. However, these age-related changes were reversed by calorie restriction (CR), exhibiting its modulatory action on apoptotic activity. Furthermore, caspase-3 activation was markedly increased in kidney of 24-month-old rats fed ad libitum (AL), as indicated by the cleaved, active form of caspase-3 (17-19 kDa), which we found was replaced with the procaspase (32 kDa) in the CR rats of both age groups. We also found that a cleaved active form (85 kDa) of poly (ADP-ribose) polymerase (116 kDa inactivated form), which serves as a nuclear substrate for active caspase-3, was increased in aged AL kidney and was blunted by CR. In addition, to investigate the oxidative status in aged kidney, we measured and compared the malondialdehyde (MDA) and 4-hydroxynonenal (HNE) levels in aged AL and CR rat kidneys. Our results showed increased MDA and HNE levels in aged AL rats, while these levels were markedly lower in CR rats, even at 24 months. These results indicate that the kidneys of rats fed ad libitum are under the influence of high oxidative stress compared to CR rats. Thus, our present data strongly suggest that the apoptotic activity observed in the aged kidney is likely modulated by the age-related oxidative status, and reversed by CR as a result of its anti-oxidative and anti-aging actions.