Reduced semen quality in patients with testicular cancer seminoma is associated with alterations in the expression of sperm proteins

Abstract

Testicular cancer seminoma is one of the most common types of cancer among men of reproductive age. Patients with this condition usually present reduced semen quality, even before initiating cancer therapy. However, the underlying mechanisms by which testicular cancer seminoma affects male fertility are largely unknown. The aim of this study was to investigate alterations in the sperm proteome of men with seminoma undergoing sperm banking before starting cancer therapy, in comparison to healthy proven fertile men (control group). A routine semen analysis was conducted before cryopreservation of the samples (n = 15 per group). Men with seminoma showed a decrease in sperm motility (P = 0.019), total motile count (P = 0.001), concentration (P = 0.003), and total sperm count (P = 0.001). Quantitative proteomic analysis identified 393 differentially expressed proteins between the study groups. Ten proteins involved in spermatogenesis, sperm function, binding of sperm to the oocyte, and fertilization were selected for validation by western blot. We confirmed the underexpression of heat shock-related 70 kDa protein 2 (P = 0.041), ubiquinol-cytochrome C reductase core protein 2 (P = 0.026), and testis-specific sodium/potassium-transporting ATPase subunit alpha-4 (P = 0.016), as well as the overexpression of angiotensin I converting enzyme (P = 0.005) in the seminoma group. The altered expression levels of these proteins are associated with spermatogenesis dysfunction, reduced sperm kinematics and motility, failure in capacitation and fertilization. The findings of this study may explain the decrease in the fertilizing ability of men with seminoma before starting cancer therapy.

Keywords: male fertility; proteomics; seminoma; sperm proteins; sperm quality; testicular cancer.

Figure 1

Number of proteins identified by proteomic analysis of spermatozoa samples obtained from fertile men (control) and men with testicular cancer seminoma, and expression profile of the DEPs identified after comparative analysis between the experimental groups. DEPs: differentially expressed proteins.

Figure 2

Graphical representation of the expression levels of proteins involved in reproductive functions (ACE, ACR, ATP1A4, CCT3, HSPA2, PSME4, and SPA17) in spermatozoa samples obtained from fertile men (control) and men with testicular cancer seminoma. Results are presented as fold variation to control and expressed as mean±standard error of the mean (n = 15 per group). Statistical significance is indicated as: ^*P < 0.05, ^**P < 0.01, seminoma versus control. Representative blots for each protein are also presented. ACE: angiotensin-converting enzyme; ACR: acrosin precursor; ATP1A4: sodium/potassium-transporting ATPase subunit alpha-4; CCT3: T-complex protein 1 subunit gamma; HSPA2: heat shock-related 70 kDa protein 2; PSME4: proteasome activator complex subunit 4; SPA17: sperm surface protein Sp17.

Figure 3

Graphical representation of the protein expression levels of mitochondrial complex subunits NDUFS1, UQCRC2, and ATP5A1 in spermatozoa samples obtained from fertile men (control) and men with testicular cancer seminoma. Results are presented as fold variation to control and expressed as mean ± standard error of the mean (n = 15 per group). Statistical significance is indicated as: ^*P < 0.05, seminoma versus control. Representative blots for each protein are also presented. NDUFS1: NADH-ubiquinone oxidoreductase 75 kDa subunit; UQCRC2: cytochrome b-c1 complex subunit 2; ATP5A: ATP synthase subunit alpha.