Genetic, Cellular, and Molecular Mechanisms Underlying Reduced Sperm Motility

PROJECT SUMMARY Male factors contribute to fertility issues for 50% of infertile couples, but women bear most of the burden of in- fertility treatment. Despite a 50% global decline in sperm count and motility over the past 50 years, the molecu- lar pathogenicity of male infertility is incompletely understood, hindering progress toward potential treatments for men. Since ~10% of the genome is involved in the regulation of fertility, most unexplained male infertility is predicted to have a genetic basis. Advances in assisted reproductive technologies have allowed these genetic defects leading to male infertility to be passed on to future generations, emphasizing the urgent need for im- proved ways to diagnose and treat affected individuals. Consanguineous families offer a unique lens for com- paring genetic differences between infertile and fertile men with similar genetic backgrounds. As such, family- based studies combined with advanced genetic tools such as whole exome sequencing can dramatically im- prove the assessment of causal relationships between specific genes and male infertility. Male infertility by reduced sperm motility presents ~80% of the infertile male patients. The overall objec- tive of the proposed studies is to break new ground in understanding the genetic basis and cellular and molec- ular mechanisms underlying reduced sperm motility in male infertility. We seek to capitalize our unique access to sixteen, large consanguineous Pakistani families with abnormal semen parameters and our team’s expertise in mouse genetics, proteogenomics, molecular and cutting-edge imaging tools such as cryo-electron tomogra- phy. Our preliminary analysis has identified three novel genetic mutations, one from each of these families, demonstrating effective gene discovery. These genes encode proteins associated with distinct flagellar appa- ratus that requires high-resolution imaging. To elucidate normal function, molecular pathogenicity, and struc- tural information from intact sperm flagella, we have newly established mouse models that mimic the human mutation or abrogate the gene expression and express a tagged transgene. Our central hypothesis is that mu- tations that lead to subtle abnormalities in the flagellar apparatus can cause obvious motility defects without compromising overall flagellar morphology. To test this hypothesis, we will pursue three specific aims. In Aim 1, we will identify and characterize mutations underlying reduced sperm motility. In Aim 2 and 3, we will eluci- date the normal function and molecular pathogenesis of two causal genes that encode proteins associated with the axonemal radial spokes and the annulus at multiscale levels. Our proposed research will provide novel fun- damental insights into the complex molecular mechanisms that underlie flagella dysfunction and a deeper mechanistic understanding of the intricate regulation of sperm motility at high resolution. The results of our studies will create new opportunities for diagnostic genetic testing and evaluating prognosis in assisted repro- ductive medicine.