Age Related Expression Patterns of Mouse Liver Nuclear Proteins.

Previously we reported the discovery of the ASE/AIE-type age related regulatory mechanism of gene expression, the first molecular mechanism for age dimension homeostasis (Kurachi et al, Science 1999; Zhang et al, J Biol Chem 2002; Kurachi & Kurachi J Thromb Haemost 2005). Here we report a comprehensive analysis of the age associated changes of mouse liver nuclear proteins, an experimental model for studying the dynamic regulatory mechanisms of the age-dimension homeostasis. Liver nuclei obtained from mice (C57BL/6xSJL, male) at 1, 3, 6, 12, 18 and 21 months of age (n=10–20/age) were used for preparing protein extracts. The protein extracts were then subjected to 2-dimensional polyacrylamide gel electrophoresis (2D-PAGE) (pH range of 4–11) and protein identification by MALDI-TOF/MS. As analyzed by the PDQuest program combined with Mascot Protein Identifier, out of over 5000 protein spots identified by 2D-PAGE, approximately 2800 protein spots were found unique including isomers. Intensity changes of these protein spots along the age axis were determined and analyzed in details with the PDQuest software. Twelve proteins were found to show no significant changes in their intensity throughout the life-span (smaller than 20% fluctuation). Besides some complex patterns, at least 6 unique age-related patterns were found, including those of puberty-onset increase, puberty-onset decrease, puberty-onset increase up to 6 months of age followed by decrease, unique increase only at around 12 months of age, ageing associated increase or decrease. Age related pattern changes were observed for some isomers among many, which were likely generated by differential posttranslational modifications or conformational changes. These findings support that in addition to the ASE/AIE type mechanism, there exist multiple novel age-dimension regulatory mechanisms, and their various combinations are responsible for producing complex and subtle age related regulatory patterns for a large number of genes. This is the first comprehensive analysis of the liver nuclear proteins in relation to age, and would provide a valuable basis for studying many age related phenomena, diseases as well as epigenetic effects.