One outstanding question in the study of the aging process is whether gene
expression changes related to age are similar among differing tissues such as
the kidney and muscle. Changes in gene expression as a function of age have
been previously studied in human calf muscle using U133 Affymetrix DNA Chips
(Welle et al., 2003); therefore, the kidney and muscle aging expression datasets
may be directly compared. We obtained the muscle dataset from the GEO database.
To compare age-regulation in the kidney and muscle, we queried whether the 447 genes identified as age-regulated in the kidney were similarly age-regulated in the muscle. We determined regression coefficients for the 447 genes in the muscle dataset using multiple regression, in a manner similar to the kidney dataset. For each of the 447 genes, we plotted regression slope in kidney against regression slope in muscle (Sup. Fig. 1), and found an overall Pearson correlation of 0.085 (p < 0.004). A Pearson correlation value of 0.085 implies that 0.72% of the variance in the muscle regression coefficients is due to variance in the associated kidney regression coefficients. We note that the muscle dataset had a small sample size (n=16), which may not be large enough to sufficiently detect similarity in age-regulation with the kidney. Future studies employing a larger number of muscle samples will be needed to more clearly discern whether there is overlap in age regulation of between kidney and muscle.