A selective inhibitor of the sperm-specific potassium channel SLO3 impairs human sperm function

Abstract

To fertilize an oocyte, the membrane potential of both mouse and human sperm must hyperpolarize (become more negative inside). Determining the molecular mechanisms underlying this hyperpolarization is vital for developing new contraceptive methods and detecting causes of idiopathic male infertility. In mouse sperm, hyperpolarization is caused by activation of the sperm-specific potassium (K + ) channel SLO3 [C. M. Santi et al. , FEBS Lett. 584 , 1041–1046 (2010)]. In human sperm, it has long been unclear whether hyperpolarization depends on SLO3 or the ubiquitous K + channel SLO1 [N. Mannowetz, N. M. Naidoo, S. A. S. Choo, J. F. Smith, P. V. Lishko, Elife 2 , e01009 (2013), C. Brenker et al. , Elife 3 , e01438 (2014), and S. A. Mansell, S. J. Publicover, C. L. R. Barratt, S. M. Wilson, Mol. Hum. Reprod. 20 , 392–408 (2014)]. In this work, we identified the first selective inhibitor for human SLO3—VU0546110—and showed that it completely blocked heterologous SLO3 currents and endogenous K + currents in human sperm. This compound also prevented sperm from hyperpolarizing and undergoing hyperactivated motility and induced acrosome reaction, which are necessary to fertilize an egg. We conclude that SLO3 is the sole K + channel responsible for hyperpolarization and significantly contributes to the fertilizing ability of human sperm. Moreover, SLO3 is a good candidate for contraceptive development, and mutation of this gene is a possible cause of idiopathic male infertility.

The SLC9C2 Gene Product (Na+/H+ Exchanger Isoform 11; NHE11) Is a Testis-Specific Protein Localized to the Head of Mature Mammalian Sperm

“…The SLO3 K + channel has previously been shown to be essential for mediating the hyperpolarization observed in capacitated mouse sperm [ 56 ]. A recent study utilized a novel specific inhibitor of the human SLO3 K + channel, VU0546110, that prevented human sperm from hyperpolarizing and undergoing hyperactivated activity, and prevented the Ca 2+ - or progesterone-induced acrosome reaction [ 57 ]. Interestingly, a study using human sperm found no evidence of alkalization of either the sperm head or flagellum in response to valinomycin-induced hyperpolarization [ 26 ], suggesting a potential different role of NHE10 and/or NHE11 in human sperm as compared to sea urchin sperm, in which the suSLC9C protein was shown to be responsible for the hyperpolarization-evoked alkalization in response to speract stimulation [ 19 ].…”

Sperm Toolbox – A selection of small molecules to study human spermatozoa

“…This work represents the first version of the STB. Future revisions could contain newly published compounds modulating functions in spermatozoa e.g., a sAC inhibitor TDI-11861 (Balbach et al, 2023), a CatSper inhibitor RU1968 (Schierling et al, 2023), a SLO3 inhibitor (Lyon et al, 2023) or other contributions from the research community. In addition, the STB could present an important resource for testing and benchmarking newly developed drug screening assay.…”

SLO3 in the fast lane: The latest male contraceptive target with a promising small-molecule inhibitor

“…Only in the last 5 y have a handful of potential drugs emerged, such as EP055 against EPPIN ( 1 ), CDD-1102 against BRDT ( 2 ), triptonide against JUP/SPEM1 ( 3 ), and YCT529 against RARA ( 4 ). Now, a new molecule has been added to this short list: VU0546110 ( 5 ), a small molecule that inhibits Slowpoke Homolog 3 (SLO3), an ion channel specific to sperm. Because SLO3 channels are absent from women ( 6 ), they have the added benefit of being targetable by nonhormonal unisex contraceptives and, therefore, have an easier regulatory pathway to market.…”

“…Lyon et al. ( 5 ) identify VU0546110, a potent small-molecule inhibitor of SLO3, through screening of a chemical library of 50,240 compounds ( 5 ). They show that VU0546110 exerts its effect on human sperm by blocking SLO3 and inhibiting hyperpolarization ( 5 ).…”

“…( 5 ) identify VU0546110, a potent small-molecule inhibitor of SLO3, through screening of a chemical library of 50,240 compounds ( 5 ). They show that VU0546110 exerts its effect on human sperm by blocking SLO3 and inhibiting hyperpolarization ( 5 ). Based on IC50 values reported by Lyon et al., VU0546110 has 46-fold selectivity to SLO3 over Slowpoke Homolog 1 (SLO1; encoded by the KCNMA1 gene), its closest paralog with ~40% sequence similarity.…”