Mechanisms of Transcriptome Aging Figure 9. Clusterin (Clu) expression is altered by aging in human and mouse organs and Clu expression is decreased in long-lived Pit1(dw/dw) mice (liver and hippocampus). Plots (A) and (B) display the expression of human clusterin (CLU) relative to age, where each open circle indicates the microarray-based expression estimate in sun-protected skin from an individual female or male. Red lines correspond to the least squares estimate for the regression of expression versus subject age, and blue lines represent the same regression but obtained using the Loess procedure. Panel (C) displays mean microarray-based expression levels of mouse Clu (61 standard error) in tail skin from young (5 month) and old (30 months) CB6F1 mice (n = 5 per group). Panels (D)–(G) display average expression of mouse Clu in mice from three age groups (5 months, 17 months and 30 months) and from both sexes (n = 5–6 mice for each sex/age combination; RT-PCR with 18S ribosomal RNA used as an internal control gene for calculation of relative expression). Each panel (D)–(G) displays the mean expression levels in each group (6 one standard error) normalized to the average expression level of the young (5 month) female group. For each sex, the average expression of middle-aged (17 month) and old groups (30 months) was compared to that of the young group (5 months). A red star indicates a significant difference relative to the youngest group of the same sex (P,0.05; two-sided two-sample t-test). A blue star is used to indicate a significant difference based upon a two-sample non-parametric statistical test (P,0.05; either Wilcoxon or Kruskal-Wallis rank sum test). Panels (H) and (I) display average expression of mouse clusterin (Clu) in long-lived Pit1(dw/dw) dwarf mice as compared to littermate controls with normal phenotypes (n = 6 per genotype; males; six months of age; Actb was used as an internal reference for calculation of relative expression). doi:10.1371/journal.pone.0033204.g009 PLoS ONE | www.plosone.org 12 March 2012 | Volume 7 | Issue 3 | e33204