Deubiquitinating Enzymes as Targets for Male Contraception

The central goal of this project is to identify and characterize small molecule inhibitors of ubiquitin specific peptidase 51 (USP51), a deubiquitinating (DUB) enzyme exclusive to sperm, as a means to develop a reversible, nonhormonal male contraceptive. The ubiquitin system is fundamental to ensure protein turnover within mammalian cells. Ubiquitin-activating enzymes, ubiquitin-conjugating enzymes and ubiquitin protein ligases catalyze the attachment of ubiquitin molecules to proteins, a process that targets them to the proteasome for degradation. DUBs catalyze the removal of ubiquitin to facilitate their recycling. We have identified USP51 to be specifically expressed in late elongating spermatids and epididymal sperm. USP51 depletion in mice using Vivo-Morpholinos results in male infertility due to a complete block of sperm motility. Our overall hypothesis is that small molecules existing in nature or modified in the laboratory will effectively and reversibly inhibit USP51 function in epididymal sperm, and will successfully be developed into male contraceptives. We will pursue the following Specific Aims to address this hypothesis: 1.) Use high throughput screening and virtual screening to identify hit compounds that inhibit DUB activity in sperm. 2.) Analyze hit/lead compounds for USP51 specificity over other DUB family members. 3.) Assess the exposure of sperm, testes/epididymides, and animals to candidate USP51 inhibitor compounds for efficacy and reversibility. These studies will advance our basic understanding of spermatogenesis and sperm function, as well as provide the potential for developing new contraceptive agents that reversibly inhibit a critical sperm enzyme.