| MicroRNAs (miRNAs) are a class of short, non-coding RNAs that bind mRNAs through partial base-pair complementarity with their target genes, resulting in post-transcriptional repression of gene expression. miRNAs control aging-related functions such as metabolism and lifespan through regulation of genes in insulin signaling, mitochondrial respiration and protein homeostasis.;I have developed a network analysis of aging-associated miRNAs connected to transcription factors PHA-4/FOXA and SKN-1/Nrf, which are both necessary for dietary restriction (DR)-induced lifespan extension in the nematode Caenorhabditis elegans (C. elegans). The network analysis has revealed extensive regulatory interactions between PHA-4, SKN-1 and miRNAs and points to two aging-associated miRNAs, miR-71 and miR-228, as key nodes of this network. I have shown that miR-71 and miR-228 are critical for the response to dietary restriction in C. elegans. Dietary restriction induces the expression of miR-71 and miR-228, and the regulation of these miRNAs depends on PHA-4 and SKN-1. In turn, I have shown that PHA-4 and SKN-1 are negatively regulated by miR-228, while miR-71 represses PHA-4. This network fine-tunes the DR-response in C. elegans to promote longevity.;I have also studied early-life differences in organismal robustness in individual C. elegans and examined the utility of miRNAs as aging biomarkers. I quantitatively examined C. elegans reared individually in a novel apparatus and observed throughout their lives. I identified three miRNAs in which early-adulthood expression patterns individually predict up to 47% of lifespan differences. Though expression of each increases throughout this time, mir-71 and mir-246 correlate with lifespan, while mir-239 anti-correlates. Two of these three miRNA "biomarkers of aging" act upstream in insulin/IGF-1--like signaling (IIS) and other known longevity pathways; thus, I have inferred that these miRNAs not only report on but also likely determine longevity.;As miRNAs and aging genetic pathways are conserved from nematodes to humans, it may also be that miRNAs function as aging biomarkers in a similar manner in humans. To test this hypothesis, I measured miRNA levels from human blood samples taken at ages 50, 55, and 60 from individuals with documented lifespans. In particular, there is a significant and reproducible correlation between lifespans of the 16 individuals in the pilot study and expression levels of six miRNAs in the serum samples. I concluded that the expression profiles of these six miRNAs may be useful biomarkers for aging. Bioinformatics predictions and network analyses indicate numerous aging-associated functions of possible targets of these miRNAs.;In this thesis, I present my findings on these topics, and I discuss future approaches that can be used to investigate the mechanisms by which miRNAs govern aging processes. |
