Butyl benzyl phthalate reprotoxicity in C. elegans: understanding sexual dimorphism and the effects of mixtures

Abstract

"Infertility has been increasing globally and has been recognized as a public health issue. Although multiple factors contribute to infertility, the rise in heavily industrialized products and the chemicals used in their manufacture cannot be overlooked. Endocrine-disrupting chemicals (EDCs) are substances that alter hormone signaling, levels, and metabolism and are commonly found in consumer products. EDCs have been linked to a range of reproductive health effects in both males and females across multiple species; however, their mechanisms of action remain incompletely understood. Studying EDCs requires an interdisciplinary approach, as human studies make mechanistic assessment difficult, in vitro systems lack whole-organism context, and mammalian models are often time-consuming and costly. Caenorhabditis elegans is a genetically tractable model organism with a well-characterized meiotic program, a rapid life cycle, and robust reproductive capacity, and it has been shown to be predictive of EDC-induced reproductive toxicity in other species. Here, I describe investigations of the plasticizer and EDC butyl benzyl phthalate (BBP) in the male germline of C. elegans, both as a single toxicant and as part of a mixture of six phthalates identified in human maternal urine samples. Previous work from the Colaiácovo group demonstrated that BBP increases germline DNA double-strand breaks (DSBs), activates a p53-dependent checkpoint in late meiotic prophase I, alters meiotic progression, and induces chromosome morphology defects in oocytes at diakinesis. In Chapter 2, I characterize the reprotoxicity of BBP in the male germline using microscopy and genetic tools to investigate sexually dimorphic responses to this chemical perturbation. I determined that BBP concentrations of 1 and 100 µM elicit the strongest responses, differing from those observed in female studies. Notably, these two doses produce divergent effects: 1 µM BBP reduces the mitotic index, whereas 100 µM BBP increases it. The lower dose increases DSBs in early meiotic prophase I, while the" "higher dose induces more DSBs in late meiotic prophase I. Both concentrations disrupt meiotic progression and relax control of crossover designation. In Chapter 3, we begin assessing a mixture of six phthalates (PMix) derived from maternal urine samples from the Illinois KIDS (iKIDS) study. This mixture induces germ cell apoptosis and abnormal germline chromosome morphology in hermaphrodite C. elegans. To dissect the contribution of individual phthalates within the mixture, we performed a high-throughput screen leveraging C. elegans genetic tools to assess X-chromosome nondisjunction in embryos from adults exposed to PMix lacking individual components. We found that PMix induces X-chromosome nondisjunction in adult hermaphrodites and that this effect is likely driven in large part by DEP and BBP. Collectively, this dissertation establishes BBP as a reprotoxic compound with sexually dimorphic effects in C. elegans, highlighting the importance of investigating EDC mechanisms in both sexes across species and demonstrating that individual compounds can significantly influence outcomes within physiologically relevant chemical mixtures."