Intergenerational Mechanisms Of Paternal Stress Transmission

Evidence that the intergenerational transmission of parental experiences can influence offspring outcomes prompts new consideration for the molecular mechanisms underlying disease risk and resilience. The role of the paternal preconception environment has been of particular interest, stimulating characterization of germ cell epigenetic marks that can respond dynamically to environmental insults and transmit this information at fertilization. Given such exciting potential for sperm epigenetic marks, how these marks are changed by the environment and subsequently impact offspring development are key questions that require investigation. In this dissertation, we address these questions using our established mouse model of paternal stress, where specific sperm microRNA altered by paternal chronic stress exposure causally reprogram offspring hypothalamic-pituitary-adrenal (HPA) stress axis reactivity and the hypothalamic transcriptome. First, we examined the role of glucocorticoids, a major component of the HPA stress response, as a signal for sperm microRNA changes. To ensure similar levels of glucocorticoids are produced in response to stress and thus are available for paternal cellular signaling, we developed an approach to confirm the stress sensitivity and reactivity of experimental mice. We next demonstrated that glucocorticoids are involved in communicating stress to the caput epididymis, a somatic tissue that secretes extracellular vesicles (EVs) to deliver microRNA from epididymal epithelial cells to maturing sperm. Using an in vitro model where we administered glucocorticoids to caput epididymal epithelial cells, we showed altered EV microRNA content and within epithelial cells, changes to histone post-translational modifications and increased glucocorticoid receptor levels, mimicking aspects of our in vivo paternal stress model. Further, we demonstrated the crucial role of caput epididymal glucocorticoid receptors in paternal stress transmission by transgenic knockdown, preventing offspring HPA axis and hypothalamic programming. In our final study, we provided evidence for the specificity of paternal stress sperm microRNA effects on embryonic brain and placental transcriptomes, indicating a tightly regulated process by which sperm microRNA are coordinated and function to influence offspring development. Together, the research presented in this dissertation provides insight into the mechanisms contributing to paternal transmission and support the paternal preconception environment as an influential factor in offspring disease risk and resilience