Ca2+ signals generated by CatSper and Ca2+ stores regulate different behaviors in human sperm

Area of Science:

• Reproductive Biology
• Sperm Physiology
• Calcium Signaling

Background:

• Sperm motility is regulated by intracellular calcium ([Ca2+]) signaling.
• Sperm must exhibit different behaviors for successful fertilization.

Purpose of the Study:

• To investigate how distinct Ca2+ signaling pathways influence human sperm motility.
• To differentiate the roles of CatSper and intracellular Ca2+ stores in sperm function.

Main Methods:

• Activation of CatSper using progesterone or altered pH.
• Mobilization of intracellular Ca2+ stores with thimerosal.
• Assessment of sperm hyperactivation and penetration through methylcellulose.
• Pharmacological inhibition of CatSper using NNC55-0396.

Main Results:

• CatSper activation elevated [Ca2+]i but did not induce hyperactivation; it enhanced penetration into methylcellulose.
• Thimerosal treatment induced strong hyperactivation, independent of CatSper.
• 4-Aminopyridine modulated both pH and intracellular Ca2+, inducing hyperactivation and enhancing methylcellulose penetration.
• Hyperactivation induced by 4-aminopyridine was CatSper-insensitive, while methylcellulose penetration was partially sensitive.

Conclusions:

• Distinct Ca2+ signaling pathways differentially regulate human sperm motility.
• CatSper activation is primarily involved in penetration, not hyperactivation.
• Mobilization of intracellular Ca2+ stores is essential for inducing hyperactivation.
• Capacitation and cumulus factors may regulate Ca2+ store sensitivity, influencing sperm behavior.