Cholesterol inhibitory effects on human sperm-induced acrosome reaction

Area of Science:

• Human reproductive biology
• Sperm physiology
• Molecular mechanisms of fertilization

Background:

• Progesterone (P4) is known to induce acrosome reactions in mammalian sperm.
• Cholesterol is recognized as a significant inhibitor of the acrosome reaction.
• Understanding cholesterol's role is crucial for reproductive science.

Purpose of the Study:

• To investigate the in vitro effects of exogenous cholesterol on human sperm acrosome reactions.
• To elucidate the mechanism by which cholesterol interferes with P4- and db-cAMP-induced acrosome reactions.
• To examine the P4 surface receptor status during capacitation and its relationship with cholesterol and acrosome reaction inducers.

Main Methods:

• Human sperm were exposed to P4 or db-cAMP with or without varying concentrations of cholesterol.
• Beta-sitosterol, a plant-based cholesterol analogue, was used for comparison.
• Progesterone surface receptor exposure was quantified using P4-FITC-BSA.

Main Results:

• Cholesterol significantly inhibited both P4- and db-cAMP-induced acrosome reactions.
• Inhibition by cholesterol was dose-dependent and noncompetitive, independent of P4 concentration.
• Beta-sitosterol mimicked cholesterol's inhibitory effects.
• Cholesterol blocked the appearance of the P4 surface receptor, crucial for P4 binding.

Conclusions:

• Cholesterol inhibits the acrosome reaction by altering sperm plasma membrane structure, hindering P4 receptor exposure.
• This noncompetitive inhibition mechanism impacts sperm function and fertilization potential.
• Findings provide insights into sperm-cholesterol interactions and their role in male fertility.