Retroviral gene expression as a possible biomarker of aging

We examined effects of aging on endogenous retrovirus gene expression of mouse lymphocytes with a hypothesis that it may be a useful biomarker of aging. Mice have endogenous murine leukemia viruses (MuLVs) in their chromosomes. We detected the gene expression of long terminal repeats (LTRs) of MuLVs. Brains, livers and spleens were taken from young (3 months old) and old (27 months old) male C57BL/6 mice. In addition to these control (C) mice, we also determined gene expression in dietary restricted (DR) mice, in which rates of aging are known to be slowed. RNA was extracted from the tissues and converted into cDNA. The MuLV-LTR portion of cDNA was amplified by polymerase chain reaction (PCR). The PCR products were analyzed by agarose gel electrophoresis. Gene expressions of young mice were found to be tissue-specific. Expressed LTRs from brains, livers and spleens were that of 370 base-pairs (bp), those of 370 and 620 bp, and those of 370, 400 and 620 bp, respectively. Old mice of C group, however, decreased tissue specificity: expressed LTRs became those of 370-400 bp in any tissues. In contrast the tissue specific gene expression was conserved in old DR mice which had to get prolonged life span and decreased lymphoma incidence. Thereby, gene expression of endogenous retroviruses appears to change during aging and to be modifiable by life-prolonging DR. It may be therefore used as a biomarker of aging in mice. Humans are known to have similar gene elements like MuLV. The present findings demonstrate a possibility of application of endogenous gene expressions to the epidemiology of aging.