Date Published: March 23, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Kyung‐Won Min, Richard W. Zealy, Sylvia Davila, Mikhail Fomin, James C. Cummings, Daniel Makowsky, Catherine H. Mcdowell, Haley Thigpen, Markus Hafner, Sang‐Ho Kwon, Constantin Georgescu, Jonathan D. Wren, Je‐Hyun Yoon.
Gene expression is dynamically regulated in a variety of mammalian physiologies. During mammalian aging, there are changes that occur in protein expression that are highly controlled by the regulatory steps in transcription, post‐transcription, and post‐translation. Although there are global profiles of human transcripts during the aging processes available, the mechanism(s) by which transcripts are differentially expressed between young and old cohorts remains unclear. Here, we report on N6‐methyladenosine (m6A) RNA modification profiles of human peripheral blood mononuclear cells (PBMCs) from young and old cohorts. An m6A RNA profile identified a decrease in overall RNA methylation during the aging process as well as the predominant modification on proteincoding mRNAs. The m6A‐modified transcripts tend to be more highly expressed than nonmodified ones. Among the many methylated mRNAs, those of DROSHA and AGO2 were heavily methylated in young PBMCs which coincided with a decreased steady‐state level of AGO2 mRNA in the old PBMC cohort. Similarly, downregulation of AGO2 in proliferating human diploid fibroblasts (HDFs) also correlated with a decrease in AGO2 mRNA modifications and steady‐state levels. In addition, the overexpression of RNA methyltransferases stabilized AGO2 mRNA but not DROSHA and DICER1 mRNA in HDFs. Moreover, the abundance of miRNAs also changed in the young and old PBMCs which are possibly due to a correlation with AGO2 expression as observed in AGO2‐depleted HDFs. Taken together, we uncovered the role of mRNA methylation on the abundance of AGO2 mRNA resulting in the repression of miRNA expression during the process of human aging.
Toward the goal of increasing human lifespan of humans, there is great interest in identifying the underlying molecular causes behind the age‐associated loss of physiological functions and rise in pathologies. Recent studies using high‐throughput RNA sequencing technology have revealed that the expression of mammalian mRNAs changes extensively during the aging process (Baumgart et al., 2016; White et al., 2015). The dynamic expression of mRNAs is mainly governed by transcription and decay via their interactions with trans‐regulatory factors (e.g., RNA‐binding proteins and noncoding RNAs) and cis‐regulatory elements (specific sequences on mRNAs for RNA‐binding protein interaction, miRNA targeting, RNA modification, etc.) (Grosswendt et al., 2014; Wang & He, 2014; Yoon, Abdelmohsen & Gorospe, 2013; Yoon et al., 2014).
Our study reveals an m6A methylation profile of human aging, regulation of AGO2 mRNA stability via its methylation, and changes in miRNA profiles of PBMCs. Our findings above suggest that 1) miRNA abundance is regulated by AGO2 mRNA stability modulation, 2) the stabilization of AGO2 mRNA is methylation‐dependent, and 3) AGO2 mRNA decay contributes to senescence and aging.