Clusterin expression and distribution in spermatozoa as predictor of male fertility

Clusterin (CLU), one of the main glycoproteins in mammalian semen and the male reproductive tract, plays a role in spermatogenesis and sperm maturation. Given the poor reliability of classic seminal studies in determining male-fertilizing capacity and the differences in CLU abundance between normal and abnormal spermatozoa, we investigated the potential value of mRNA-CLU levels and protein distribution in spermatozoa as markers of sperm quality and predictors of male fertility. This multicenter study included 90 patients undergoing in vitro fertilization (IVF) treatment with their partners, and a control group of 36 fertile males with normal seminograms. We assessed the relationship between IVF treatment outcomes, seminogram variables, mRNA-CLU levels by quantitative real-time-PCR and CLU distribution by immunostaining in spermatozoa. Our study reveals CLU staining in the acrosome (p = 0.002, OR 14.8, 95% CI: 2.7–79.3) and mRNA-CLU levels (p = 0.005, OR 10.85, 95% CI: 2.0–57.4) as independent risk factors for pregnancy failure, irrespective of traditional seminogram variables. Additionally, our results suggest that CLU, and specially its secreted isoform, constitutes a component of the protein pool that human spermatozoa can produce during its maturation process, exhibiting a variable abundance and distribution in spermatozoa from fertile men compared to those in patients with altered seminograms and infertile patients with normal seminograms. Our study is the first to identify mRNA-CLU levels and CLU immunostaining in the spermatozoa acrosome as independent risk factors for pregnancy failure, with distribution patterns correlating with sperm maturity and seminogram alterations.