We found that lin-4 mutants have short lifespans, while lin-4 over-expression extends lifespan and slows aging [1]. This was the first report of a role for miRNAs in regulating lifespan, and led to an intense study in my lab of roles for miRNAs in aging. Initially, we performed high throughput sequencing to identify miRNA expression patterns during C. elegans aging (the first use of this approach in the field). In addition to the approximately 50 known miRNAs with expression changes during aging, we identified about the same number of novel miRNAs. We showed that multiple miRNAs control C. elegans aging, via analysis of deletion and over-expression of miRNAs that increased/decreased over time [2, 3]. Remarkably two miRNAs (miR-71 and miR-239) regulate aging in opposite directions but through the same pathway, insulin signaling. In future work we will determine what regulates these miRNA and how they function in insulin signaling, with the goal of understanding and manipulating such signaling in mammals.
Further, isogenic C. elegans reared in identical conditions show a large variation in lifespan, from 1 week to 3 weeks. Currently very few “biomarkers of aging”, which predict future lifespan, are known. Since both miR-71 and miR-239 miRNAs increase expression in early adulthood, weeks before the animals die, we tested whether their expression levels in young adults could predict future lifespan. To do this we developed a unique “lab on a chip” method to culture and observe single C. elegans from hatching to death. We observed physiological and gene expression parameters in individual animals as they aged and then correlated early-life measurements with each animal’s final lifespan. We found that the best, and earliest, single predictor of future longevity was miR-71 expression [4]. This demonstrates that miRNAs may be useful biomarkers of longevity, perhaps even in humans, which we are planning to test in the near future.
Future work: Our work has revealed about 100 miRNAs that change expression during aging in C. elegans[2, 3]. We are currently employing a bioinformatics approach to mine the modENCODE database (to which we are a contributor) to place these miRNAs into pathways, and to formulate hypotheses to test biologically. For example, do known aging genes regulate these miRNAs, or vice-versa? Might they cause aging phenotypes when knocked out? In particular, we would like to isolate and characterize mutant alleles of novel, age-enriched miRNAs.
We have examined miRNA expression during mammalian aging and identified many novel miRNAs found enriched in old mice. We would like to test if a select few of these result in aging phenotypes when knocked out or over expressed in the mouse: e.g. does the lin-4 homologue, mir-125, determine mouse lifespan? We hope to move our analysis of aging from C. elegans to mammals in much the same way as we successfully transitioned the analysis of miRNAs and cancer.
As above, we demonstrated that miRNAs can predict future longevity in C. elegans [4]. We are collaborating with NIA investigators to screen miRNAs from (human) individuals enrolled in the Baltimore Longitudinal Study of Aging (BLSA) to determine if serum miRNA levels offer the same predictive value in humans. Since miRNAs are stable in serum, this work may identify important and easily measured biomarkers of aging in humans.