Author ORCID Identifier
Date Available
4-24-2026
Year of Publication
2024
Document Type
Doctoral Dissertation
Degree Name
Doctor of Philosophy (PhD)
College
Medicine
Department/School/Program
Molecular and Cellular Biochemistry
Advisor
Dr. Yvonne Fondufe-Mittendorf
Abstract
Environmental exposure to heavy metals poses significant threats to human health as they are associated with various developmental and chronic pathologies such as reproductive defects and cancers. Despite their profound risks, a comprehensive understanding of their disease-causing mechanisms is lacking. Most studies point to reactive oxygen species-induced DNA damage; however, their mutagenic potential is relatively weak suggesting the involvement of alternative mechanisms. One important, yet underexplored mechanism, is their ability to rewire the epigenome via DNA methylation and histone variant incorporation, leading to aberrant gene regulatory networks.
This study investigates the epigenetic mechanisms targeted by two ubiquitous heavy metals with consequences in sperm and cancer state chromatin architecture. We first examine the role of cadmium (Cd), known to cause DNA methylation changes, during developmental reprogramming. Unlike the majority of studies which focus on the effects of maternal exposure, we focus on the paternal effect of Cd on sperm biology with potential consequences for fertility. We exposed mice to low dose Cd and measured the methylation state in the sperm. Using Reduced Representation Bisulfite Sequencing (RRBS), we identify 1788 differentially methylated sites occurring at specific regulatory regions of genes involved in development and spermatogenesis. Interestingly, these changes to the sperm methylome targeted not only transcription initiation but also how these genes are spliced, suggesting that Cd might mediate protein diversity in instigating defects in spermatogenesis.
Another pervasive heavy metal is inorganic arsenic (iAs), which is mostly known to alter the DNA methylation and histone post-translational modifications (PTMs) landscape. We previously showed that iAs also induces differential expression of several hitherto unknown histone H2B variants in bronchial epithelial (BEAS-2B) cells, though the exact function of this dysregulation remains unclear. Generally, histone variants are recruited at specific times and places for particular functions. We find that H2B variants are overexpressed across cancers in a cell-type specific manner, and despite high protein sequence conservation, they exhibit unique mutational signatures. However, the basic understanding of how they distinctly alter nucleosome structure and stability for gene expression misregulation is unknown. Using biochemical and biophysical in vitro studies, we show that the incorporation of these variants impact nucleosome accessibility and integrity which can be propagated to higher order chromatin structure. Finally, we explore their regulatory roles using tagged H2B variant cell lines. We find that their overexpression induce changes in genomic accessibility and differential genomic binding, correlating with altered cancer gene expression programs.
This work enhances our view into the complex interplay between environmental factors and epigenetic programming affecting development and disease state. We present a novel role of Cd in possibly influencing paternal inheritance. Additionally, our novel finding of how histone H2B variants orchestrate changes in chromatin architecture adds to the diversity of chromatin regulators in normal biology and carcinogenesis. These studies, therefore, provide a foundational framework in chromatin biology that can be explored for potential biomarkers and therapeutic development.
Digital Object Identifier (DOI)
https://doi.org/10.13023/etd.2024.59
Funding Information
National Institute of Environmental Sciences (NIEHS) grants
- R01ES024478 (2015),
- R01ES031846 (2022),
- R01ES034253 (2022) to Y.F.M.
- P30 ES026529; “UK-CARES” (2018)
Recommended Citation
Saintilnord, Wesley, "EMERGING CHROMATIN REGULATORS IN RESPONSE TO HEAVY METAL EXPOSURE" (2024). Theses and Dissertations--Molecular and Cellular Biochemistry. 73.
https://uknowledge.uky.edu/biochem_etds/73
Included in
Biochemistry Commons, Environmental Health Commons, Molecular Biology Commons, Toxicology Commons
