Dissertation

Cellular Senescence, Circadian Rhythmicity, and Aging

Jachim, Sarah Katherine

2023

Overview

Age is the primary risk factor for most chronic diseases in developed countries, including cancer, diabetes, neurodegeneration, and cardiovascular disease. Over the past century, there has been an unprecedented rise in human life expectancy. In 1900 only 3.1 million people in the US were aged 65 and older, but that number increased to 55.8 million people in 2020. While this change reflects technological and medical advancements which promote longevity, population aging poses new challenges. In light of population aging and the strong association between aging and chronic disease, there is substantial interest in understanding fundamental molecular mechanisms of aging to guide the development and implementation of interventions.The purpose of this dissertation is to evaluate two fundamental hallmarks of aging, cellular senescence and circadian dysregulation. Hallmarks of aging are distinct, but also interrelated and by studying the interplay between senescence and circadian rhythms in the context of aging, we provide novel insight into these fundamental mechanisms of aging.In Chapter 2, I describe the investigation of BMAL1, a pioneer transcription factor and master regulator of the molecular circadian clock, and its role in the senescence program. We demonstrate that BMAL1 is significantly upregulated in senescent cells and has altered rhythmicity compared to non-senescent cells. Through BMAL1-ChIP-seq, we show that BMAL1 is uniquely localized to genomic motifs associated with AP-1 in senescent cells. Integration of BMAL1-ChIP-seq data with RNA-seq revealed that BMAL1 presence at AP-1 motifs is associated with active transcription. Finally, we showed that BMAL1 contributes to AP-1 transcriptional control of key features of the senescence program, including altered regulation of cell survival pathways, and confers resistance to drug-induced apoptosis. Overall, these results highlight a previously unappreciated role of the core circadian clock component BMAL1 on the molecular phenotype of senescent cells.In Chapter 3, I describe a study which was designed to evaluate the impacts of a circadian rhythmicity-directed, late-life endurance exercise intervention in both male and female aged mice. We measured improvements in several readouts of late-life health, including improved physical and metabolic performance in exercised mice compared to matched sedentary control mice, and note substantial sex-based differences in these measures. Ongoing molecular analyses of exercised and sedentary aged mice will continue to explore the potential for circadian rhythmicity-directed exercise as a scalable intervention to modulate aging.Given the importance of senescent cells in contributing to tissue function and disease in aging, and the fact that there is no one standalone marker for senescent cells, in Chapter 4, we sought to characterize the senescence-associated secretory phenotype unique to different senescent cells. Through multiplexed proteomic identification of secreted factors, we demonstrate significant cell-type specific differences. This work also showed the potential for these factors to be used as a non-invasive readout of senescent cell burden in clinical population, and as biomarkers for clinically relevant health outcomes.Expanding on the challenge of identification of senescent cells, in Chapter 5, we utilize a new approach: unbiased cell culture selections to identify senescent cell-specific folded DNA aptamers from vast libraries of trillions of random DNAs. Through this approach, we identified candidate DNA aptamers which bind with high specificity to senescent cells over non-senescent control cells and have begun validation of molecular targets of these candidates. This proof-of-concept study supports the potential for DNA aptamer technology in selective labeling and biomarker discovery in the context of senescence.Together, this thesis provides insight into aspects of cellular senescence, circadian rhythmicity, and aging. Integration of in vitro studies of senescence and circadian rhythmicity, with in vivo studies in an aging context will provide further insight into how these different systems interact and drive the biology of aging. The growing concern of population aging has resulted in substantial demand for basic and clinical research that will facilitate targeting of fundamental mechanisms of aging, and in this dissertation, we sought to expand upon existing work on the interplay between cellular senescence and circadian rhythmicity in the context of aging.

• Publisher: ProQuest Dissertations & Theses
• Subject: Aging / Biochemistry / Cellular biology / Molecular biology
• ISBN: 9798380375559