RNA surveillance-an emerging role for RNA regulatory networks in aging

Abstract

In this review, we describe recent advances in the field of RNA regulatory biology and relate these advances to aging science. We introduce a new term, RNA surveillance, an RNA regulatory process that is conserved in metazoans, and describe how RNA surveillance represents molecular cross-talk between two emerging RNA regulatory systems-RNA interference and RNA editing. We discuss how RNA surveillance mechanisms influence mRNA and microRNA expression and activity during lifespan. Additionally, we summarize recent data from our own laboratory linking the RNA editor, ADAR, with exceptional longevity in humans and lifespan in Caenorhabditis elegans. We present data showing that transcriptional knockdown of RNA interference restores lifespan losses in the context of RNA editing defects, further suggesting that interaction between these two systems influences lifespan. Finally, we discuss the implications of RNA surveillance for sarcopenia and muscle maintenance, as frailty is a universal feature of aging. We end with a discussion of RNA surveillance as a robust regulatory system that can change in response to environmental stressors and represents a novel axis in aging science.

Figure 1. RNA surveillance genes

Composition of the RNA interference and RNA editing machinery with orthologues in vertebrates, nematodes and plants.

Figure 2. Schematic of RNA regulatory pathways

a) RNA interference (RNAi) pathway and, b) RNA editing (RNAe) pathway.

Figure 3. Age trend in microRNA expression during normal aging in mice

Brain tissue from young (3 months), adult (one year) and old (2 year) mice (C57BL6), left to right, was harvested and total RNA used to evaluate expression of 380 microRNAs using an Illumina chip platform. Hierarchical clustering was conducted yielding 8 clusters (see left of dendrogram), with clusters 1 and 2 displaying high expression in young, declining with age; and clusters 5 and 6 displaying low expression in young, increasing with age.

Figure 4. Effects of ADAR on lifespan in C.elegans

a) Lifespan using mutant strains for adr-1;adr-2 in the context of dsRNA mediated gene inactivation of daf-2. Note decline in lifespan due to adr-1; adr-2 compared with N2 wildtype. Also note increases in lifespan of both N2 and adr-1; adr-2 in the presence of dsRNA for daf-2. days) b) Lifespan using mutant strains for adr-1;adr-2 and adr-1; adr-2; rde-1 (grey solid) demonstrate declines in lifespan using mutant strains and full rescue of lifespan in an RNAi defective (rde-1) background. To synchronize worms for lifespan, eggs were isolated (N2, adr-1, adr-2, adr-1;adr-2, rde-1, rde-4, adr-1;adr-2;rde-1) and synchronized by hatching overnight in the absence of food at 20C. Synchronized L1 larvae were counted and plated (10 worms/plate, n=60) on Escherichia coli bacterial lawns (OP50) on NGM media and allowed to develop to L4-stage larvae at 20C. 5-fluorodeoxyuridine (FudR) solution was added to a final concentration of 0.1mg/ml to prevent reproduction. Worms were kept at 20C and lifespan monitored by counting on alternate days. The daf-2 dsRNA -expressing bacteria were grown overnight in LB with 50 ug/ml ampicillin and then seeded onto RNAi NGM plates containing 5 mM isopropylthiogalactoside (IPTG). The RNAi bacteria were induced overnight at room temperature for dsRNA expression. About 30 synchronized L4-stage animals were added to each well and allowed to develop to adults, followed by the addition of FudR. Worms were kept at 20C, and their lifespan was monitored. c) Model interpretation of the lifespan data; wherein RNAe protects from RNAi mediated target RNA degradation.

Figure 5. Schematic of Myogenic program

Figure 6

Decline in human muscle satellite cell division with age (adapted from (Renault et al., 2000)).