Temperature and Polyamines: Their Roles in CatSper Regulation and Sperm Fertility

SUMMARY For successful fertilization in vivo, mammalian sperm must first undergo capacitation, a maturation step that enables hyperactive motility and acrosomal exocytosis. Hyperactive motility is triggered by calcium influx through the sperm-specific calcium channel CatSper, but premature CatSper activation can lead to calcium overload, channel degradation, and loss of fertilizing capacity. To prevent this, CatSper must remain inactive until sperm reach the oviduct. Prevention of premature CatSper activation in the male reproductive tract has long been attributed to acidic epididymal pH, which inhibits CatSper. However, the factors that prevent CatSper activation before sperm reach epididymis and after they leave it remain unknown. Based on our recently published study in a murine model, this project will test the central hypothesis that human CatSper activation is regulated within the male and female reproductive tracts by four key factors: pH, temperature, polyamines, and progesterone. In this model, the low temperature of the testis and the acidic pH of the epididymis maintain CatSper in a closed state. When sperm mix with seminal plasma, they encounter polyamines, which further inhibit CatSper activity, even as the sperm travel through the warm and slightly alkaline environment of the cervix and oviduct. During sperm capacitation in the oviduct, and after prolonged exposure to oviductal fluids, polyamines dissociate from sperm. At this stage, CatSper is activated by high temperature, alkaline pH, and factors released by the ovulated egg, such as progesterone. This hypothesis will be tested in three specific aims. Aim 1 is to define the mechanism by which CatSper is regulated by temperature in human sperm. This aim will test the hypothesis that temperature alters human CatSper activity by influencing its voltage gating, pH- and progesterone- sensitivity. Aim 2 is to determine the effect of these four factors on CatSper impact on sperm motility and intracellular calcium concentrations in both murine and human sperm. These two aims test the hypothesis that the seminal plasma components inactivate CatSper and greatly reduce its temperature sensitivity, thereby protecting CatSper from activation until sperm reach the oviduct. Aim 3 is to determine the molecular mechanisms underlying infertility in patients with varicocele. This aim will test the hypothesis that, in patients with varicocele, high testicular temperature, lack of acidic pH, and absence of protective polyamines mimic conditions that sperm normally only encounter in the oviduct. Thus, sperm CatSper is prematurely activated in the testis, leading to calcium overload and shortened sperm life span. Completion of these aims will rely on the unique abilities of the investigators’ laboratories to conduct electrophysiological measurements, motility analysis, and calcium imaging in mouse and human sperm. The proposed work will reveal key physiological regulators of CatSper, and may reveal the molecular mechanism underlying infertility in patients with varicocele. Project Number: 1R01HD119961-01A1 | Fiscal Year: 2026 | NIH Institute/Center: Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) | Principal Investigator: Polina Lishko (+1 co-PI) | Institution: WASHINGTON UNIVERSITY, SAINT LOUIS, MO | Award Amount: $619,913 | Activity Code: R01 | Study Section: Cellular, Molecular and Integrative Reproduction Study Section[CMIR] View on NIH RePORTER: https://reporter.nih.gov/project-details/11391862