Influence of Post-transcriptional Gene Regulation on Cell Senescence and Aging

National Institute On Aging

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Abstract

Changes in gene expression patterns are a hallmark of the aging process. Important insight into the mechanisms controlling such gene expression programs has come from the study of replicative senescence of cultured cells (eg, human diploid fibroblasts), which recapitulates many features of cells from aging individuals. This Project has traditionally studied changes in RNA-binding protein (RBP) expression and function during replicative senescence. It has also examined the influence of RBPs in replicative senescence by interventions to elevate or reduce RBP levels, followed by the analysis of changes in senescence-associated mRNA expression patterns. We have studied if a given RBP binds a senescence-associated mRNA using a variety of in vitro binding assays (e.g., pulldown using biotinylated RNA segments and antisense oligomers) and assays to measure binding of endogenous molecules ribonucleoprotein immunoprecipitation (RIP) or crosslinking IP (CLIP). In recent years, we have included the analysis of noncoding RNAs microRNAs (mi)RNAs, long noncoding (lnc)RNAs, and circular (circ)RNAs that influence senescence and aging. To investigate RBP and ncRNAs function during senescence, we employ approaches such as silencing of the RBP or ncRNA, overexpression of the same, analysis or mutant RBPs/ncRNAs, and RBP/ncRNA-associated RNA identification (using microarrays, RNAseq, Oxford Nanopore, and RT-qPCR analyses). We have adopted tissue microarrays to identify senescent cells and detect RBP expression in tissues as a function of senescence and aging. To investigate whether RBPs and ncRNAs affect the stability of target mRNAs during senescence, we measure the steady-state levels and half-lives of the mRNAs of interest as a function of RBP/ncRNA abundance. We investigate whether RBPs and ncRNAs affect the translation of target mRNAs by studying the relative association of the mRNA with translating polysomes and by quantifying the nascent translation rates of the encoded proteins. We also employ reporter constructs to gain additional insight into the processes modulated by the RBPs and ncRNAs and use various senescence-associated markers to examine changes in the senescence phenotype. Over the past 12 months, this Project has continued to examine changes in gene expression programs that occur in human tissues as part of physiologic aging. Much of our effort in this Project has been directed at understanding how proteins of different types (including RBPs) and ncRNAs affect the process of cellular senescence, which is increasingly recognized as underlying age-related changes in tissue physiology and pathology. The studies in this Project examine the proteins and RNAs that modulate cellular senescence and the consequences of their influence on the senescent phenotype. Among the cell systems used for these studies, human diploid fibroblasts have been particularly informative. With increasing evidence that senescent cell accumulation in aging tissues is linked to age-associated diseases and declining function, we have initiated efforts to remove senescent cells selectively. We reported that acid ceramidase levels increase in senescent cells and contribute to the senescent phenotype (Munk et al., Aging, 2020). We identified systematically p16 and p21positive cells in tissue arrays designed to include normal organs (skin, brain, liver, spleen, intestine, lung, muscle, etc) from persons across a broad spectrum of ages and found that different organs display different levels of the senescent proteins p16 and p21 as a function of age (Idda et al., Aging 2020). We identified miR-340-3p as triggering senescence by reducing the abundance of lamin B receptor (LBR) (Herman et al., Nucleic Acids Research, 2021), and reviewed noncoding RNAs modulating telomere homeostasis in senescence and aging (Rossi and Gorospe, Trends in Molecular Medicine, 2020) and the role of MAPKs in senescence (Anerillas et al., Geroscience, 2020). Experiments are underway to identify other senescence-associated membrane markers, as well as RNA markers (coding and noncoding) of senescence.