Decreased expression level of apoptosis-related genes and/or proteins in skeletal muscles, but not in hearts, of growth hormone receptor knockout mice

The long-lived growth hormone (GH) receptor knockout (GHRKO; KO) mice are GH-resistant due to targeted disruption of the GH receptor (Ghr) gene. Apoptosis is a physiological process in which cells play an active role in their own death and is a normal component of the development and health of multicellular organisms. Aging is associated with the progressive loss of strength of skeletal and heart muscles. Calorie restriction (CR) is a well-known experimental model to delay aging and increase lifespan. The aim of the study was to examine the expression of the following apoptosis-related genes: caspase3, caspase-9, caspase-8, bax, bcl-2, Smac/DIABLO, p53 and cytochrome c1 (cyc1) in the skeletal muscles and hearts of female normal and GHRKO mice, fed ad libitum or subjected to 40% CR for six months, starting at two months of age. Moreover, skeletal muscle caspase-3, caspase-9, caspase-8, bax, bcl-2, Smac/DIABLO, Apaf-1, bad, phospho-bad (pbad), phospho-p53 and cytochrome c (cyc) protein expression levels were assessed. Expression of caspase-3, caspase-9, bax and Smac/DIABLO genes and proteins was decreased in GHRKO's skeletal muscles. The Apaf-1 protein expression also was diminished in this tissue. In contrast, bcl-2 and pbad protein levels were increased in skeletal muscles in knockouts. No changes were demonstrated for the examined genes' expression in GHRKO's hearts except for the increased level of cyc1 mRNA. CR did not alter the expression of the examined genes and proteins in skeletal muscles of knockouts versus normal (N) mice. In heart homogenates, CR increased caspase-3 mRNA level as compared with ad libitum mice. Decreased expression of certain proapoptotic genes and/or proteins may constitute the potential mechanism of prolonged longevity in GHRKO mice, protecting these animals from aging; this potential beneficial mechanism is not affected by CR.