SLO3 auxiliary subunit LRRC52 controls gating of sperm KSPER currents and is critical for normal fertility

Abstract

Following entry into the female reproductive tract, mammalian sperm undergo a maturation process termed capacitation that results in competence to fertilize ova. Associated with capacitation is an increase in membrane conductance to both Ca 2+ and K + , leading to an elevation in cytosolic Ca 2+ critical for activation of hyperactivated swimming motility. In mice, the Ca 2+ conductance (alkalization-activated Ca 2+ -permeable sperm channel, CATSPER) arises from an ensemble of CATSPER subunits, whereas the K + conductance (sperm pH-regulated K + current, KSPER) arises from a poreforming ion channel subunit encoded by the slo3 gene (SLO3) subunit. In the mouse, both CATSPER and KSPER are activated by cytosolic alkalization and a concerted activation of CATSPER and KSPER is likely a common facet of capacitation-associated increases in Ca 2+ and K + conductance among various mammalian species. The properties of heterologously expressed mouse SLO3 channels differ from native mouse KSPER current. Recently, a potential KSPER auxiliary subunit, leucine-rich-repeat-containing protein 52 (LRRC52), was identified in mouse sperm and shown to shift gating of SLO3 to be more equivalent to native KSPER. Here, we show that genetic KO of LRRC52 results in mice with severely impaired fertility. Activation of KSPER current in sperm lacking LRRC52 requires more positive voltages and higher pH than for WT KSPER. These results establish a critical role of LRRC52 in KSPER channels and demonstrate that loss of a non-pore-forming auxiliary subunit results in severe fertility impairment. Furthermore, through analysis of several genotypes that influence KSPER current properties we show that in vitro fertilization competence correlates with the net KSPER conductance available for activation under physiological conditions. sperm fertility | KSPER | SLO3 channels | auxiliary subunits U pon entry into the female reproductive tract, mammalian sperm undergo a sequence of maturational steps, collectively termed capacitation, to become competent to fertilize an egg (1, 2). Two important components of this process, thought to be shared among mammalian species, are cytosolic alkalization (3-5) and then an associated increase in cytosolic Ca 2+ (6, 7). These events are coupled with changes in ionic fluxes in sperm membrane. Over the past 10 y, the application of patch-clamp recording to individual sperm (8) has allowed identification of ionic currents that respond to alkalization and/or Ca 2+ (9-12). In mouse sperm, alkalization leads to activation of two spermspecific channels, the Ca 2+ -permeable CATSPER channel (8-10, 13) and the K + -permeable KSPER K + channel (14, 15). KSPER and CATSPER currents are also present in human sperm (16-18), although intriguingly there seem to be differences in regulation of each channel type between mice and humans (11,12,17).Despite the species-specific differences in the details of their regulation, KSPER and CATSPER are of central importance in sperm function and fertility in both humans and mice. In mouse spe...

Epilepsy-Related Slack Channel Mutants Lead to Channel Over-Activity by Two Different Mechanisms

“…From published work, both loss- and gain-of-function potassium channel mutants had been linked to epilepsy. Among them, loss-of-function of Kv1.1, Kv1.2, Kv4.2 and Kv7.1, Kv7.2 potassium channels are associated with epilepsy (Brew et al, 2007; D’Adamo et al, 2013; Smart et al, 1998; Wang et al, 2015; Zeng et al, 2015). On the other hand, gain-of-function of the BK and Slack channel mutants are also linked with Epilepsy (Barcia et al, 2012; Du et al, 2005; Yang et al, 2010).…”

International Union of Basic and Clinical Pharmacology. C. Nomenclature and Properties of Calcium-Activated and Sodium-Activated Potassium Channels

“…When expressed in oocytes, the mouse channel is voltage dependent and sensitive to pH, being activated by alkalinization and suppressed by acidification (Schreiber et al, 1998;Zhang et al, 2006a,b). K Ca 5.1 is expressed selectively in sperm cells, and its properties are regulated by LRRC52, a testis-specific accessory subunit (Schreiber et al, 1998;Leonetti et al, 2012;Zeng et al, 2015). Evidence strongly suggests that it corresponds to the large-conductance potassium channel that can be recorded from mature sperm.…”

Modulation of BK Channel Function by Auxiliary Beta and Gamma Subunits

“…It will be important to determine whether γ2–4 subunits also play any functional or physiological role in BK channel modulation in vivo. The mouse γ2 subunit has been found to function as an accessory subunit of the sperm- specific mouse Slo3 channels (Yang et al, 2011), and its ablation in mice was recently found to cause a severe fertility impairment (Zeng et al, 2015). It will be intriguing to determine whether in any stage of germ cells the γ2 subunit also modulates BK channels and whether Slo3 and BK channels can form functional heterotetrameric channels.…”