Javier Bartolomé-Nebreda

The incidence of sperm DNA fragmentation (SDF) in the ejaculate has garnered increasing attention in recent years due to its negative impact on reproductive outcomes. SDF involves two primary types of damage to the canonical double helix of DNA: single-strand breaks and double-strand breaks. Both of these can occur throughout the entire process of gametogenesis. Determining the precise causes of elevated SDF remains challenging, as it is influenced by a wide range of physiological processes and environmental factors. This review comprehensively explores the mechanisms underlying SDF, with a particular emphasis on the critical role of deoxyribonucleases (DNases) across different stages of male gamete development, as well as their relevance in assisted reproductive technologies (ART).

In this clinical era of intracytoplasmic sperm injection (ICSI), where a single spermatozoon is chosen for fertilization, the diagnostic functionality of the classical parameters typically associated with fertilization, such as sperm concentration, sperm motility, acrosome integrity, and mitochondria, is perhaps becoming less critical. In contrast, the contribution of sperm DNA quality to our understanding of the impact of male fertility within the context of ICSI is gaining increasing interest and importance. Even with respect to natural conception, high levels of sperm DNA fragmentation (SDF) in the ejaculate can adversely affect reproductive outcomes. However, the precise origin of SDF pathology in sperm cells is often ambiguous and most likely to be multifactorial. Hence, the genetic makeup of an individual, unbalanced REDOX processes, enzymatic activity, environmental and lifestyle factors, and even damage during sperm handling in the laboratory all operate in a unique and often synergistic manner to produce or induce sperm DNA damage. Surprisingly, the contribution of active enzymes as potential agents of SDF has received much less attention and, therefore, is likely to be underrated. This review highlights the roles of different enzymes related to the degradation of sperm DNA as possible effectors of DNA molecules in spermatozoa.