Small RNAs in semen are useful biomarkers to determine the origin of azoospermia

Assisted reproduction for male infertility allowed most infertile patients to become fathers by isolating viable sperm from semen for in vitro fertilization with intracytoplasmic sperm injection (IVF-ICSI). In azoospermia, characterized by the absence of sperm in the semen, patients can only benefit from the IVF-ICSI procedure with sperm obtained from a testicular biopsy. This affectation occurs as a result of either an obstruction in the male reproductive tract (obstructive azoospermia with preserved spermatogenesis) or a severe failure in sperm production (secretory azoospermia), with few or no sperm in the testicle. Suffering from one or another azoospermia type determines the possibility to obtain sperm from a testicular biopsy, and having non-invasive biomarkers to discriminate the origin of azoospermia before performing the biopsy is essential to avoid unnecessary biopsies.

Semen contains a unique concentration of small RNAs that act as regulators of proteins involved in fertilization expression. These small RNAs, such as microRNAs (miRNAs), piRNAs, and tsRNAs among others, are mostly contained in structures called extracellular vesicles. Since some of these vesicles originate at the testicle, alterations in the levels of small-sized RNAs in the semen would be expected, which would reveal the presence of spermatogenesis disorders and their severity. A study by the Human Molecular Genetics group at IDIBELL, led by Dr. Sara Larriba, in collaboration with Dr. Lluís Bassas from Fundació Puigvert and Dr. Lauro Sumoy from IGTP, proposed an exhaustive study of the small RNA levels in the extracellular vesicles of the semen of azoospermic individuals. The objective was to select non-invasive biomarkers with diagnostic and prognostic utility, which allow the identification of individuals with a real possibility of recovering sperm from a testicular biopsy, necessary for assisted reproduction treatment.

Using RNA sequencing techniques, the team of scientists showed that alterations in the expression levels of certain RNAs in semen vesicles could be used, individually or in combination, as biomarkers for azoospermia. Among them, miRNAs and their variants stand out in terms of numbers and differences in expression, which makes them valuable molecular markers with great potential as a diagnostic tool to determine the origin of azoospermia. Other RNAs such as tsRNAs, although they are very abundant in semen vesicles, did not show utility as biological markers for the presence of spermatozoa in the testis.

Although more studies are needed, the availability and adoption of such non-invasive molecular biomarkers would represent a great improvement in reproductive treatment decision protocols for azoospermia in clinical practice.

The Bellvitge Biomedical Research Institute (IDIBELL) is a biomedical research center created in 2004. It is participated by the Bellvitge University Hospital and the Viladecans Hospital of the Catalan Institute of Health, the Catalan Institute of Oncology, the University of Barcelona and the City Council of L’Hospitalet de Llobregat.

IDIBELL is a member of the Campus of International Excellence of the University of Barcelona HUBc and is part of the CERCA institution of the Generalitat de Catalunya. In 2009 it became one of the first five Spanish research centers accredited as a health research institute by the Carlos III Health Institute. In addition, it is part of the “HR Excellence in Research” program of the European Union and is a member of EATRIS and REGIC. Since 2018, IDIBELL has been an Accredited Center of the AECC Scientific Foundation (FCAECC).