The role of spermatozoa-zona pellucida interaction in selecting fertilization-competent spermatozoa in humans

Front Endocrinol (Lausanne). 2023 Mar 20:14:1135973. doi: 10.3389/fendo.2023.1135973. eCollection 2023.


Human fertilization begins when a capacitated spermatozoon binds to the zona pellucida (ZP) surrounding a mature oocyte. Defective spermatozoa-ZP interaction contributes to male infertility and is a leading cause of reduced fertilization rates in assisted reproduction treatments (ARTs). Human ejaculate contains millions of spermatozoa with varying degrees of fertilization potential and genetic quality, of which only thousands of motile spermatozoa can bind to the ZP at the fertilization site. This observation suggests that human ZP selectively interacts with competitively superior spermatozoa characterized by high fertilizing capability and genetic integrity. However, direct evidence for ZP-mediated sperm selection process is lacking. This study aims to demonstrate that spermatozoa-ZP interaction represents a crucial step in selecting fertilization-competent spermatozoa in humans. ZP-bound and unbound spermatozoa were respectively collected by a spermatozoa-ZP coincubation assay. The time-course data demonstrated that ZP interacted with a small proportion of motile spermatozoa. Heat shock 70 kDa protein 2 (HSPA2) and sperm acrosome associated 3 (SPACA 3) are two protein markers associated with the sperm ZP-binding ability. Immunofluorescent staining indicated that the ZP-bound spermatozoa had significantly higher expression levels of HSPA2 and SPACA3 than the unbound spermatozoa. ZP-bound spermatozoa had a significantly higher level of normal morphology, DNA integrity, chromatin integrity, protamination and global methylation when compared to the unbound spermatozoa. The results validated the possibility of applying spermatozoa-ZP interaction to select fertilization-competent spermatozoa in ART. This highly selective interaction might also provide diagnostic information regarding the fertilization potential and genetic qualities of spermatozoa independent of those derived from the standard semen analysis.

Keywords: DNA integrity; HSPA2; SPACA3; human spermatozoa; methylation; protamination; sperm selection; zona pellucida.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Fertilization
  • Humans
  • Male
  • Semen / metabolism
  • Sperm-Ovum Interactions*
  • Spermatozoa / metabolism
  • Zona Pellucida* / metabolism

Grants and funding

This work was supported in part by the Health and Medical Research Fund, the Food and Health Bureau, The Government of the HKSAR (07182446), the High Level-Hospital Program, Health Commission of Guangdong Province, China (HKUSZH201902015), and HKU-SZH Fund for Shenzhen Key Medical Discipline (SZXK2020089).