Epigenetic biomarkers in male infertility and its potential use in assisted reproductive technology

Infertility is considered a serious concern, and it is estimated that between 48 million couples and 186 million individuals in the developing world suffer from infertility at reproductive age. The WHO defined infertility as a disease of the reproductive system defined by the failure to achieve a clinical pregnancy after a period of 12 months or more of regular unprotected sexual intercourse. Infertility has been attributed to a plethora of causes from either male or female origin. External factors such as lifestyle and sexual transmission diseases are associated to infertility-environmental interactions and epigenetic alterations are unravelling novel causes of infertility, previously classified as unexplained “idiopathic” infertility. Focusing on male infertility, it is quite important to elaborate a comprehensive diagnose of the patient, and to investigate what is affecting his reproductive capacity. Male factor can involve anatomical defects, immunological factors, ejaculatory failure, urogenital tract infections, sexual transmission diseases, increased scrotal temperature, environmental toxicity, gametogenesis dysfunction, genetic and epigenetic defects. Assessment of the sperm quality, by evaluating parameters such as sperm count, motility or morphology, is one of the most important steps in the evaluation of male partner in infertile couples. However, sperm exams have a limited diagnostic potential, and t of time the exact causes for male infertility are not always known. Currently we know that spermatozoa are cargo of epigenetic information including altered DNA methylation patterns, altered protamine:histone ratio, histone variants, histone post-translational modifications (histone PTMs), and noncoding RNA, which tremendous impact in fertility, pregnancy outcome, and embryo development. This chapter reviews sperm epigenome, potential epigenetic mechanisms in spermatozoa and their impact on male reproductive potential and its use to predict assisted reproductive techniques (ART) outcome.