Mechanotransduction mechanisms of ovarian aging

Aging is a universal process that affects all tissues and leads to their deterioration. Each tissue has specific aging kinetics, and the female reproductive system is the first to age. Female reproductive aging is associated with a decrease in oocyte quality and quantity as well as a reduction in the ovarian hormones estrogen and progesterone, which accelerates women physiologic aging. Reproductive transitions, such as reproductive aging, is a priority of the Fertility and Infertility branch of the National Institutes of Health, and thus my proposed research is tightly aligned with the mission of the Eunice Kennedy Shriver National Institute of Child Health and Human Development. A major contributor to the reduction of female reproductive performance with advance reproductive age is the decrease in oocyte quality due to an increase in oocyte aneuploidy, but our work and others have demonstrated that other factors might contribute to the age-associated reduction in oocyte quality. Physical cues from the tissue environment are major regulators of cell behavior. In the ovary, stiffness is relevant for normal follicle development but also associated with pathological conditions. In mice, stiff environments keep primordial follicles dormant, however ovarian stiffness is also a marker of polycystic ovarian syndrome in humans. In my postdoctoral work I explored the biomechanical properties of the mammalian ovary with advance reproductive age. To do so, I pioneered the use of instrumental indentation to measure the stiffness of the ovary and I found that mice ovaries become significantly stiffer with advanced reproductive age. My work on ovarian stiffness laid the foundation of this proposal to identify the effects and mechanism of tissue biomechanics on follicle quality. Having set up a system to interrogate the biomechanics of the ovary, I can now explore the spatial and temporal changes of the ovarian biomechanics. In this project, I will test the overarching hypothesis that the age-associated and spatially-dependent increase in ovarian stiffness creates a physical environment that impacts follicle development and oocyte quality through activation of mechanotransduction pathways in the follicle. This hypothesis will be tested in three specific aims. First, I will determine the subcellular features that define ovarian stiffness by performing a 3D spatio-temporal architecture map of the ovarian stiffness in an age and estrous dependent manner. Second, I will investigate how stiffness affects follicle development and oocyte competency at the transcriptional and cellular level. I will establish an in vitro system which enables precise control of the physical environment. Third, I will explore the mechanism by which the follicle integrates the physical cues and whether the dysregulation of this mechanism accelerates reproductive aging. I will investigate whether follicles from reproductively young and old mice have the same capacity to respond to physical cues through the activation of mechanotransduction pathways, focusing on YAP1. These studies will be complemented with in vitro loss-of-function approaches and a YAP1 engineered animal model. This study will open exciting avenues of research in understanding the role of biomechanics on female fertility.