The diverse reproductive roles of Ubiquitin C-Terminal Hydrolase L1: a model to understand the role of oocyte quality in neurodegeneration, aging, and beyond

Abstract Authors: Morgan Woodman-Sousa¹, Heather Valera¹, Julia McAdams², Meghan Ozcan³, Karine Matevossian⁴, & Kathryn J. Grive^2,5.

1. Molecular Biology, Cell Biology, and Biochemistry Graduate Program, Brown University, Providence, RI 02906
2. Program in Women's Oncology, Women & Infants Hospital of Rhode Island, Providence, RI 02903
3. Division of Reproductive Endocrinology and Infertility, Wright State University, Dayton, Ohio 45433
4. Fertility Centers of Illinois, Glenview, IL 60026
5. Department of Obstetrics and Gynecology, The Warren Alpert Medical School of Brown University, Providence, RI 02903

Abstract Text: Our laboratory has identified Ubiquitin C-Terminal Hydrolase L1 (UCHL1) as highly enriched in both mouse and human oocytes throughout the reproductive lifespan, with essential roles in regulation of female reproductive health. UCHL1 is a Ubiquitin Proteasome Pathway (UPP) regulator responsible for modulating monoubiquitin and hydrolyzing ubiquitinated precursor proteins to facilitate protein turnover and abundance, or proteostasis. The specific roles of UPP regulators like UCHL1 in maintaining healthy oocyte proteostasis throughout the female reproductive life remain understudied and currently, no studies have linked the molecular underpinnings of the UPP to ovarian aging. 

We have found that female UCHL1 global knockout mice exhibit severe subfertility, altered folliculogenesis, and systemic endocrine dysfunction. Furthermore, quantitative proteomics of UCHL1 knockout oocytes revealed significant changes in many oocyte-critical peptides including Zona Pellucida Proteins 2 and 3 (ZP2 and ZP3, and p=0.0066 and p=0.0031 respectively). Using an oocyte-specific conditional UCHL1 knockout, we have begun to elucidate how oocyte-expressed UCHL1 impacts not only oocyte quality and ovarian function but also overall endocrine health, hypothalamic-pituitary-gonadal (HPG) axis function, and reproductive aging. Oocyte-specific loss of UCHL1 is associated with dramatic aberrations in, and thickening of, the zona pellucida, a feature linked to poor oocyte quality and poor IVF outcomes in humans, as well as observed in women of advanced maternal age. Additional preliminary data from the lab suggests that oocyte-specific ablation of UCHL1 results in increased rates of granulosa cell apoptosis and dramatically alters granulosa cell transcriptomes, as well as oocyte and granulosa cell proteomes. Interestingly, oocyte-specific ablation of UCHL1 also dramatically alters the brain transcriptome and blood brain barrier integrity, further suggesting that this oocyte-specific factor can influence the HPG axis and systemic health.

We are now also investigating secreted UCHL1 as a potential biomarker of the ovarian reserve. Currently, oocyte abundance in human patients is indirectly measured by evaluating Anti-Müllerian Hormone produced by ovarian somatic cells and/or Follicle Stimulating Hormone produced by the pituitary gland. Excitingly, we have observed increased serum concentrations of UCHL1 in females compared to age-matched males, in both mice and adult humans, suggesting a female-specific source of this circulating signature. Additionally, we have observed decreased serum UCHL1 in mouse models of diminished ovarian reserve, as well as in our oocyte-specific UCHL1 knockout females, definitively establishing the oocyte as the primary source of circulating UCHL1 in healthy individuals. Utilizing UCHL1 as a novel oocyte-specific marker of the ovarian reserve provides a direct method for tracking both the quantity and quality of the ovarian reserve throughout a woman's life, and could represent the first putative biomarker of ovarian aging specific to the gametes. Our laboratory has also shown that UCHL1 is highly abundant in human follicular fluid. We are now analyzing human follicular fluid and serum samples collected from patients undergoing In Vitro Fertilization, with the aim to determine the association between secreted UCHL1 levels and female infertility diagnoses, with the potential to establish UCHL1 as a marker for specific infertility conditions.

Together, this work emphasizes the ways in which oocyte-autonomous molecules can influence not only intrinsic elements of oocyte quality, but also overall ovarian function and reproductive health. Ultimately, this work will enhance efforts to understand and preserve the essential ovarian reserve that is critical for female fertility, longevity, and overall quality of life.