Cambios en la expresión de los genes involucrados en el ciclo celular y apoptosis durante el destete en la glándula mamaria de rata lactante. Papel del GSH.

Abstract

In the lactating mammary gland, weaning produces mitochondrial cytochrome c release and nuclear DNA fragmentation. This is followed by a significant decrease in milk production and the decline of lactation. Weaning for 2h produces an early induction of p53, whereas c-Jun and JNK are elevated after 24h of weaning. The expression of p21cip1 and p27kip1, both cyclin-dependent kinase inhibitors, is significantly higher in weaned rats when compared to control lactating rats. All the changes mentioned above also happen in the lactating mammary gland when PPG, an inhibitor of the liver trans-sulfuration pathway, is administered. This effect is partially reversed by N-acetylcysteine (NAC) administration. The administration of buthionine sulfoximine (BSO), an irreversible inhibitor of ?-glutamyl cysteine synthetase, to lactating rats produces a decrease in GSH levels and changes in protein levels and gene transcripts similar to the rats with impaired trans-sulfuration pathway. These data suggest that the intertissue flux of glutathione is an important mechanism of L-cysteine delivery to the lactating mammary gland and emphasizes the importance of this physiological event to maintain gene expression required to keep lactation. Once characterized the apoptosis in the mammary gland we used this model to study in vivo the role of nitric oxide during cell death. The three isoforms of the nitric oxide synthase (NOS) are constitutively present in the acini of the lactating mammary gland. The amount of iNOS and NO production are increased during weaning when compared to control lactating glands, but the protein levels of the eNOS isoform are diminished. Western blot analysis demonstrated that protein nitration was increased in the weaned mammary gland, althought limited to a few specific tyrosine-nitrated proteins. A decrease of GSH in the mammary tissue at the peak of lactation partially mimics these findings and emphasizes the role of NO as a potential signal that triggers involution.