The infertility is a social disease concerning about 10-18% of couples. It is estimated that male factor determines 40-60% of all couples’ infertility cases. It became clear that numerous factors, that can be reciprocally related between each other and which disturbances are being observed in males with reproductive failures, pays attention to the complexity of the problem. Beside of a variety of known molecular and environmental factors, also the light should be shed on so-called epigenetic factors, which are non-genetic modifications of the genome. Among them the methylation of sperm DNA and methylation/acetylation of the sperm histones seems to play crucial role in proper spermatogenesis and embryo development. Another non-genetic factor is the positioning of chromosomes within sperm nucleus, what means the defined localization of particular chromosomes. Spermatozoa characterizes unique nuclear packaging of the chromatin, thus the chromosomes’ positions are also specific. It is known that in men with various disturbances of fertility the nuclear organization is changed. There are also evidences that epigenetic changes are prone both to: genetics, as well as for environmental factors. What is interesting, relative interaction between them may work as a cause or a reason of disturbances in male fertility.
The research tasks of the Group are based on a comprehensive experimental approach to spermatozoa of males with oligozoospermia, as well as of chromosomal aberrations carriers, taking into account the characteristics of both: the genetic and epigenetic content of the sperm cell important for the course of spermatogenesis. Simultaneous evaluation of all the above-mentioned parameters may be a stimulus to develop new tests assessing both the structural and regulatory layer of the sperm genetic material.
Currently, the Group implements the research tasks following epigenetic and cytogenetic aspects of human spermatozoa from males with reproductive failures following the research projects:
- ‘Cytogenetic and molecular analyses of positioning of human sperm chromosomes, including: sperm chromatin integrity, epigenetic marks, karyotyping and sperm fractioning’ SONATA BIS NCN, no. 2020/38/E/NZ2/00134
The main purpose of the Project is to determine how the positions of the chromosomes within human sperm nucleus may be altered depending on: the state of fertility, karyotype, chromatin integrity status, epigenetic variations within DNA or histones, and between members of the same family, incl. various fractions of sperm cells. The novelty of the Project is that all analyses will be done sequentially on the same individual sperm cells, what means that the positioning of the chromosomes will be prepared in particular single spermatozoa, cell by cell, with known and documented: genotype, chromatin integrity state, and epigenetic marks level/change. Tests will be performed in males with normal karyotype (control, fertile vs. infertile from the same family, i.e. brothers), and with chromosomal abnormalities but phenotypically normal (i.e. carriers of chromosomal translocations). All tests will be performed on various sperm fractions: sperm with good motility, mature chromatin, and defined fertilization potential.
Carriership of balanced chromosomal rearrangements (CR) can be called: a ‘hidden biological bomb’, because aberrations frequently do not affect carriers’ phenotype, contrary to its negative influence on spermatogenesis. CR carriers may be at risk for abnormal pregnancy and/or offspring with developmental disabilities, because of the production of genetically unbalanced gametes during improper meiotic segregation. It is important, especially in the context of IVF techniques, where only visual evaluation of sperm motility and morphology is performed when selecting sperm cell for IVF procedure.
- ‘Analysis of DNA methylation pattern in spermatozoa of infertile men with oligozoospermia’ SONATA NCN, no. 2015/17/D/NZ5/03442
The purpose of the Project is to delineate methylation pattern for selected genes in DNA from spermatozoa of infertile men with diagnosed oligozoospermia (low sperm count in ejaculate). It is assumed that spermatozoa of oligozoospermic males may have changed methylation patterns of genes that are crucial for spermatogenesis, what may influence their fertility status. Moreover, in spermatozoa of oligozoospermic males also other genomic elements may be disrupted, including: sperm chromatin integrity (deprotamination and DNA fragmentation) and higher sperm aneuploidy level. The purpose of the Project is carrying out via complex characterization of spermatozoa from infertile males with oligozoospermia, including: (i) methylation pattern analysis of sperm DNA in promotor sequences for selected genes (gene panel and/or whole methylome sequencing), (ii) global methylation analysis of sperm DNA, followed by analysis of methylation and acetylation of selected histones’ residues, followed by their immunolocalization within human sperm nuclei, (iii) sperm chromatin integrity analysis, (iv) analysis of aneuploidy level for selected chromosomes in spermatozoa.
Diagnostics of oligozoospermia has been developed to some level. However, standard sperm analysis and hormonal evaluation is not sufficient for delineation of the reasons and mechanisms that may underlie infertility at the molecular level. It is important especially in intricated cases. We anticipate that undertaken evaluation will show us the effect of changed/disrupted methylation pattern of selected genes that possibly may be linked with oligozoospermia. Achieved results will also greatly supplement the field of epigenetic factors’ research in a context of male reproductive failures, especially a list of genes which change of methylation pattern makes sperm count in ejaculate vulnerable to deterioration. A proposed experimental panel is also the first complex research approach for oligozoospermia molecular background, supported with suggested linkage between methylation and acetylation patterns, chromatin integrity, and sperm aneuploidy status. Potential benefit of this Project will facilitate the development of new diagnostic procedures, leading to greater improvement of the prognosis for assisted reproductive medicine where the risk of transmitting of genetic defects to offspring is of a great concern.