Semen amyloids participate in spermatozoa selection and clearance

Area of Science:

• Reproductive biology
• Biochemistry
• Immunology

Background:

• Semen contains amyloid fibrils, unlike other human fluids, which are known to enhance HIV infection.
• The natural function of these semen amyloid fibrils has remained largely unknown.
• Similarities between viral fusion and gamete fusion prompted investigation into their role in fertilization.

Purpose of the Study:

• To investigate the natural function of amyloid fibrils present in human semen.
• To determine the effect of semen amyloid fibrils on sperm function and fertilization.
• To explore the role of these fibrils in the female reproductive tract (FRT) environment.

Main Methods:

• Comparative analysis of sperm-macrophage interactions with and without semen fibrils.
• Assessment of fertilization rates in the presence of purified semen amyloid fibrils.
• Microscopic examination of sperm behavior and viability post-semen exposure.

Main Results:

• Semen amyloid fibrils were found to inhibit fertilization by causing sperm immobilization.
• Immobilized sperm, particularly damaged or apoptotic ones, were more rapidly phagocytosed by macrophages.
• This process suggests a mechanism for sperm selection and clearance of poor-quality sperm in the FRT.

Conclusions:

• Amyloid fibrils in semen play a role in reproduction by facilitating the clearance of suboptimal sperm.
• These fibrils may contribute to sperm selection by enhancing the removal of damaged sperm by macrophages.
• The findings reveal a novel function for semen amyloid fibrils beyond their known association with HIV infection.