Tissue-specific and age-dependent expression of protein arginine methyltransferases (PRMTs) in male rat tissues

Protein arginine methyltransferases (PRMTs) generate asymmetric and symmetric dimethyl-arginines by catalyzing the transfer of methyl groups from s-adenosyl-l-methionine to arginines in target proteins. Previously, we observed that the expression and activity of PRMTs were significantly down-regulated in replicatively senescent fibroblasts compared to young fibroblasts. In this study, we determined the level of three PRMT family members (PRMT1, PRMT4, and PRMT5) and the arginine methylation status in eight tissues from 6- and 24-month-old rats. We observed tissue-specific down-regulation of individual PRMT members in testis, thymus, kidney, lung, and heart from 24-month-old as compared to 6-month-old rats. Specifically, we observed reduced levels of PRMT1 in thymus and lung, reduced levels of PRMT4 in testis, thymus, and hearts, and reduced levels of PRMT5 in all five tissues. PRMT enzyme activity on histones generally correlated with PRMT expression. Furthermore, we observed a reduction in asymmetric and symmetric dimethylation on proteins in aged thymus and lung, and a reduction in symmetric dimethylation in aged testes relative to the testes harvested from young rats. These results suggest that individual PRMT proteins have tissue-specific functions and are regulated in a tissue-specific and age-dependent manner.