post-translational protein modification and functional proteomics, as described in more detail below. So far, 2DE has been the method of choice for profiling cell culture models of aging or aging tissue (Dierick et al., 2002a; Gromov et al., 2002; Benvenuti et al., 2002a; 2002b) and the effect of environmental stresses (Dierick et al., 2002b; 2002c). Chang et al. have characterized the reproducibility and sensitivity of proteomic analysis of mitochondrial proteins from aged mouse skeletal muscle, suggesting that a sample size of 10 animals will be sufficient to detect a 100% difference in 97% of the 505 mito-chondrial proteins resolved in their 2D electrophoresis separation (Chang et al., 2003). The senescent-accelerated mouse represents a convenient animal model for the proteomic characterization of aging and age-dependent pathologies. Cho et al. compared the liver proteome of the senescence-prone strain SAMP8 (senescence-accelerated mouse senescence prone) with that of the senescent-resistant SAMR1 (senescence-accelerated mouse senescence-resistant) and detected age-dependent changes of 64 proteins between both strains, whereas 18 proteins showed age-dependent changes in both SAMP8 and SAMR1 mice (Cho et al., 2003). Surprisingly, Poon et al. quantified age-dependent changes between 12- and 4-month-old SAMP8 for only five brain proteins (Poon et al., 2004). Proteomic analysis revealed a gender-specific alteration in the age-dependent relative expression of glycolytic and mitochondrial cardiac proteins in monkeys (Yan et al., 2004). A limited proteomic analysis was also presented for the Hutchinson-Gilford Progeria Syndrome (Robinson et al., 2003). This premature aging disease is associated with mutations in the gene for lamin; a comparison of lamin expression levels between 10 and 13 years old progeria patients with their age-matched controls showed significantly reduced lamin levels. Moreover, the lamin of the progeria patients displayed ca. 0.3 units more basic pI value, consistent with the loss of a C-terminal phosphorylation site. The proteome of human cerebrospinal fluid (CSF) was profiled as part of an ongoing search for biomarkers of age-dependent pathologies (Zhang et al., 2005). Using shotgun pro-teomics in conjunction with the ICAT methodology, a series of proteins changing between 20 and 100% between the CSF of young and old donors was monitored, and, for specific proteins, these changes were confirmed by complementary Western blot analysis. An important aspect of these proteomic experiments is the elimination of highly abundant proteins such as albumin and immunoglobulin prior to the analysis, which was achieved with sequential precipitation of CSF proteins by an organic solvent, acetonitrile.
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