Glutathione-independent prostaglandin D2 synthase in ram and stallion epididymal fluids: origin and regulation.

The research article discovered that a major protein, glutathione-independent prostaglandin D2 synthase (PGDS) is present in the anterior epididymal region fluid of male sheep (rams) and horses (stallions) and decreases in concentration towards the cauda region, showing that PGDS is present throughout the male genital tract. Castration and efferent duct ligation in the ram led to a decrease in PGDS mRNA and secretion.

Research Methodology

• The research started with microsequencing after a technique called two-dimensional electrophoresis. This technique is used to separate mixtures of proteins and then identify each protein. This process revealed a major protein called glutathione-independent prostaglandin D2 synthase (PGDS) in the fluid from the anterior epididymal region of both rams and stallions.
• The researchers found that in this epididymal region, PGDS was a polymorphic compound – meaning it had multiple physical forms – with a molecular mass of roughly 30 kDa and a range of pI from 4 to 7. They also found that it constituted a substantial portion of the total luminal proteins present in this region.
• They also investigated the secretion of this protein using in vitro biosynthesis, a lab method of synthesizing organic compounds. Additionally, they studied the presence of its mRNA by Northern blot analysis, which is a method used to study gene expression.
• The researchers then utilized a specific polyclonal antibody raised against a synthetic peptide to find PGDS throughout the epididymis, confirming its continual presence from the anterior to the cauda region of the epididymis.
• Lastly, they applied castration and efferent duct ligation to the ram. These procedures led to a decrease in PGDS mRNA and protein secretion, which was able to be restored by testosterone supplementation.

Findings

• The study shows that PGDS is a protein that is present in the entire male genital tract, not just limited to a specific area.
• It was also found that both castration and blocking off the duct that carries sperm away from the testes led to a decrease in PGDS mRNA and secretion.
• Of note, PGDS mRNA was not detected in the stallion one month after castration, but the presence of it was restored once the stallion was given testosterone.
• This indicates that the production and secretion of PGDS are likely regulated by testosterone, which might suggest a critical role of this protein in the maturation and/or protection of spermatozoa. However, its exact function is still unknown.