Gene expression in aging kidney and pituitary

Gene expression in aging kidney and pituitary was determined by subtractive hybridization, DNA microarrays and RT-PCR. Kidneys and pituitary were removed from 10- and 30-month-old female WAG/Rij rats, which were free from chronic progressive nephrosis and had a low incidence of pituitary tumors with age. From 350 cDNA fragments isolated by subtractive hybridization, just one showed a more than twofold change in expression between 10 and 30 months. The use of a specific microarray with 4050 rodent genes also failed to detect downregulation lower than 0.5 or upregulation larger than 2.0 in aging rat kidney. Similarly, mRNA content for vasopressin V2 and V1 receptors, aquaporin 2 and 3, and adenylyl cyclase type VI was not significantly modified with age as determined by RT-PCR. In contrast, microarray analysis of pituitary mRNA expression showed upregulation of 11 genes with ratios equal to or greater than 2.0 and downregulation of 6 genes with ratios equal to or less than 0.5. Two cDNA sequences of unknown genes from the kidney subtractive library were part of the age-related up- and downregulated genes of the pituitary. Other genes were mainly related to cell differentiation, control of homeostasis, cellular signaling, endoplasmic reticulum trafficking and metabolism. These data indicated that mRNA expression is barely modified in aging kidney free from chronic progressive nephrosis, at least in the 0.5-2.0 range, in contrast to pituitary. They also suggest that the downregulation of proteins reported in aging kidneys free from gross disease is related to post-transcriptional changes.