Seminal-Plasma-Mediated Effects on Sperm Performance in Humans

Abstract

Seminal plasma (SP) plays a crucial role in reproduction and contains a large number of proteins, many of which may potentially modify sperm functionality. To evaluate the effects of SP identity and its protein composition on human sperm function, we treated the sperm of several males with either their own or multiple foreign SPs in all possible sperm-SP combinations (full-factorial design). Then we recorded sperm motility and viability in these combinations and investigated whether the sperm performance is dependent on sperm and SP identity (or their interaction). Finally, we studied whether the above-mentioned sperm traits are affected by the abundance of three SP proteins, dipeptidyl peptidase-4 (DPP4), neutral endopeptidase (NEP), and aminopeptidase N (APN). The identity of the SP donor affected sperm swimming velocity, viability, and the proportion of hyperactivated sperm, but males' own SP was not consistently more beneficial for sperm than foreign SPs. Furthermore, we show that sperm performance is also partly affected by the interaction between sperm and SP donor. Finally, we found that DPP4 and NEP levels in SP were positively associated with sperm swimming velocity and hyperactivation. Taken together, our results highlight the importance of seminal plasma as a potential source of biomarkers for diagnostics and therapeutic interventions for male-derived infertility.

Keywords: fertilization; infertility; protein; reproduction; seminal plasma; sperm.

Figure 1

Sperm swimming velocity in different sperm treatments (control, foreign seminal plasma, and own seminal plasma) at both time points (30 min and 90 min). Bolded horizontal lines in each box plot denote median values and boxes extend from the 25th to the 75th percentile of the distribution of values. Vertical lines show the minimum and maximum values of the data. SP = seminal plasma.

Figure 2

Sperm swimming velocity (VCL) in SP-treated sperm samples. Sperm VCL is scaled to a mean of zero (dashed line, see methods for details) to enable male-to-male comparison at 30 min (A) and 90 min (B) time points. Each male (1–9) is represented in a separate panel and the SPs used for sperm treatments are indicated by different colors.

Figure 3

Presence of proteins of interest (above) and their loading controls (below) in seminal plasma samples. Western blot was used to determine the level of APN (A), DPP4 (B), and NEP (C) (males indicated by numbers 1–9). The position of the molecular weight standard (kDa) is shown on the right side of each panel. The blots shown here represent two other replicates based on a visual inspection of all the blots (n = 3 replicates, in total).

Figure 4

The association between sperm swimming velocity (VCL) and the abundance of DPP4 and NEP in SP samples: DPP4 30 min (A), DPP4 90 min (B), NEP 30 min (C), and NEP 90 min (D). Data points represent fitted values obtained from the LMM. Sperm donors are indicated by different colors and the black line represents the average slope across all males. Levels of DPP4 and NEP (x-axis) are shown as arbitrary unit values.

Figure 5

Functional enrichment (A) and network map (B) of the interactive proteome of DPP4, NEP, and APN in humans. Interactive proteins are based on the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) with high confidence interactions (see methods for details). Proteins inputted to the tool are indicated in blue and the proteins belonging to the integrin superfamily are marked in red. The source of interactions is indicated using colored lines: light blue stands for “curated databases”, purple refers to “experiments”, light green indicates “textmining”, and dark gray implies “co-expression” of proteins. FDR = false discovery rate.