Across species, sexual development and fertility are dependent on cell death events. In developing ovaries and testes in mammals, massive death of germ cells (precursors of sperm and eggs) occurs during a fetal attrition event that is presumed to prevent overproliferation and select for highest quality cells. Cell death is also observed in males during embryonic regression of structures that form the female reproductive tract, and morphogenesis of the pituitary gland, which regulates gonadal sex hormone production. Surprisingly, inhibition of apoptosis results in male-specific infertility in mice, but it is not understood why this occurs or how cell death is regulated throughout male sexual development. The goal of my research is to understand regulation of apoptosis along the hypothalamic-pituitary-gonadal (HPG) axis throughout male sexual development, and why disruption of apoptosis causes infertility. Specifically, this proposal aims to map apoptotic sensitivity in normal testicular germ cells, and to find evidence of apoptotic misregulation in reproductive tissues in infertile males.
In Aim 1, the apoptotic vulnerability of germ cells at different stages of development and differentiation will be determined using functional cell death-predictive assays and testicular irradiation to induce germ cell death.
In Aim 2, the requirement of apoptosis in male sex differentiation will be investigated by analyzing embryonic reproductive tract development and adult HPG axis signaling in genetic models of apoptosis insufficiency. Testicular germ cell transplantation will be used to establish contribution of germline vs. somatic testicular cell apoptosis dysregulation to male infertility. These findings will support identification of targeted treatments for disorders of sexual development or cytotoxic exposures affecting developing children, which lead to poor reproductive outcomes as adults. The training plan for the proposed fellowship will further develop expertise in molecular and developmental biology approaches, and address conceptual and technical inexperience in other disciplines of reproductive science, including endocrinology and epidemiology. It will also provide the opportunity to move from zebrafish to mice as a model of disease and development. This will be achieved by continuing education in biostatistics, training with a co-sponsor, and utilizing an interdisciplinary scientific advisory committee to oversee experimental design and data analysis. Responsible conduct of research training will also be undertaken in Year 1. The Harvard School of Public Health, which is committed to the multi-faceted study of reproductive health and infertility, will strongly support this research and training plan with imaging and analytical facilities as well as oversight of established faculty in the field. The laboratory of Kristopher Sarosiek, which excels at functional assays of apoptosis, will enable development of a unique and rigorous research program that bridges sexual development and the molecular biology of cell death in order to uncover mechanisms driving male infertility.
Infertility affects approximately 15% of couples and 9% of men and global incidence is increasing, representing a major public health issue that has limited and often cost-prohibitive treatment options. Although the mechanisms are unclear, infertility is frequently associated with hormonal disorders, environmental toxicant exposures or cancer treatment, each of which are known to induce cell death in certain contexts. This proposal seeks to determine whether apoptotic misregulation represents a central mechanism driving male infertility, and identify death-resistant stages of germ cell differentiation that can be leveraged for fertility preservation in children exposed to cytotoxic stressors.
