Semen-specific miRNAs: Suitable for the distinction of infertile semen in the body fluid identification?

Non-protein coding RNA, miRNAs (microRNAs), are a class of promising molecular biomarkers for forensic body fluid identification (BFI) as their small size and tissue-specific expression manners. A number of studies have shown that semen can be distinguished from forensic-related body fluids (such as menstrual blood, venous blood, vaginal fluid, saliva, etc.) using semen-specific miRNAs through microassay screening and RT-qRCR. Infertility is becoming a global health problem, affecting 10%-15% of couples worldwide, and half of the cases are the result of male factors (Lian et al., 2009 [1]). Forensic researchers have to consider the impact of semen infertility on semen identification with a high incidence of infertility. In the present study, normal semen (NS) and four other types of infertile semen samples, including asthenospermia (AS), oligospermia (OS), azoospermia (AZ), oligospermia and asthenospermia (OSAS) semen, were collected. The expression levels of a set of semen-specific miRNA markers (miR-10a, miR-10b, miR-135a, miR-135b, miR-888 and miR-891a) were evaluated using a real-time quantitative PCR technique with a specific fluorescence-labelled TaqMan probe. The results showed the significantly high expression of these miRNAs in normal semen, and the molecules have semen specificity. Nevertheless, a distinct down-regulation in the expression of infertile samples compared with normal semen samples was observed. Moreover, differences in the results of selected optimal biomarkers between the discriminant function and two-dimensional scatter plots were also detected. The goal of the present study was to identify a small set of semen-specific miRNAs that efficiently and accurately distinguish semen (fertile and infertile) from other forensic-related body fluids. The results of the present study suggest that attention should be paid to infertile semen samples when using miRNAs to identify semen samples, for which would have a far-reaching impact on forensic identification.