SPINK3-sperm interaction determines a stable sperm subpopulation with intact CatSper channel

Abstract

Sperm capacitation involves proteolytic remodeling of membrane proteins, including components of the CatSper calcium channel, which is essential for hyperactivation and male fertility. Here, we identify the seminal protease inhibitor SPINK3, a known decapacitation factor that suppresses premature capacitation in the female tract, as the first physiological inhibitor of CATSPER1 processing. In mouse sperm, SPINK3 blocks capacitation-induced CATSPER1 cleavage, preserving a subpopulation with intact CatSper channels and lacking pTyr development in the flagellum. SPINK3 localizes to the outer surface of the sperm principal piece membrane in a CatSper-dependent but non-quadrilateral pattern, stabilizes membrane organization, and delays cholesterol efflux. These results reveal SPINK3 as a multifunctional regulator of capacitation, shaping sperm subpopulations in the female reproductive tract. SIGNIFICANCE STATEMENTThis study unveils a novel physiological regulator from the male reproductive tract, SPINK3, which extracellularly controls the processing of CATSPER1, a key subunit of the CatSper calcium channel essential for sperm capacitation in mice. We show that SPINK3 binds to the sperm surface and prevents the processing of CATSPER1 during capacitation. SPINK3-sperm interaction is dependent on the presence of the sperm-specific CatSper channel. Our findings reveal that SPINK3 stabilizes sperm membranes providing new insights into the molecular regulation of sperm function and fertility. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=194 HEIGHT=200 SRC="FIGDIR/small/672324v3_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@164c737org.highwire.dtl.DTLVardef@1531499org.highwire.dtl.DTLVardef@16d7abaorg.highwire.dtl.DTLVardef@945453_HPS_FORMAT_FIGEXP M_FIG C_FIG