Homozygous mutation in SLO3 leads to severe asthenoteratozoospermia due to acrosome hypoplasia and mitochondrial sheath malformations

Abstract

Background Potassium channels are important for the structure and function of the spermatozoa. As a potassium transporter, the mSlo3 is essential for male fertility as Slo3 knockout male mice were infertile with the series of functional defects in sperm cells. However, no pathogenic variant has been detected in human SLO3 to date. Here we reported a human case with homozygous SLO3 mutation. The function of SLO3 in human sperm and the corresponding assisted reproductive strategy are also investigated. Methods We performed whole-exome sequencing analysis from a large cohort of 105 patients with asthenoteratozoospermia. The effects of the variant were investigated by quantitative RT-PCR, western blotting, and immunofluorescence assays using the patient spermatozoa. Sperm morphological and ultrastructural studies were conducted using haematoxylin and eosin staining, scanning and transmission electron microscopy. Results We identified a homozygous missense variant (c.1237A > T: p.Ile413Phe) in the sperm-specific SLO3 in one Chinese patient with male infertility. This SLO3 variant was rare in human control populations and predicted to be deleterious by multiple bioinformatic tools. Sperm from the individual harbouring the homozygous SLO3 variant exhibited severe morphological abnormalities, such as acrosome hypoplasia, disruption of the mitochondrial sheath, coiled tails, and motility defects. The levels of SLO3 mRNA and protein in spermatozoa from the affected individual were reduced. Furthermore, the acrosome reaction, mitochondrial membrane potential, and membrane potential during capacitation were also afflicted. The levels of acrosome marker glycoproteins and PLCζ1 as well as the mitochondrial sheath protein HSP60 and SLO3 auxiliary subunit LRRC52, were significantly reduced in the spermatozoa from the affected individual. The affected man was sterile due to acrosome and mitochondrial dysfunction; however, intra-cytoplasmic sperm injection successfully rescued this infertile condition. Conclusions SLO3 deficiency seriously impact acrosome formation, mitochondrial sheath assembly, and the function of K+ channels. Our findings provided clinical implications for the genetic and reproductive counselling of affected families.

The Role of Sperm Membrane Potential and Ion Channels in Regulating Sperm Function

“…It has been suggested that human KSper can be mediated by SLO1 [ 90 ], by both SLO1 and SLO3 [ 40 , 83 , 91 ] or by a human-specific SLO3 variant [ 15 , 24 , 84 , 119 ]. In this context, a recent study described a human case of male infertility in which a homozygous mutation in SLO3 causes severe asthenoteratozoospermia due to acrosome hypoplasia and mitochondrial sheath malformations [ 94 ]. Additionally, the differential characteristic of human KSper may be due to association with specific auxiliary subunits, which can produce profound changes in SLO channel gating properties [ 85 , 95 , 99 ].…”

Sperm Ion Transporters and Channels in Human Asthenozoospermia: Genetic Etiology, Lessons from Animal Models, and Clinical Perspectives

“…Only recently, the screening of sub-fertile patients enrolled in ART confirmed the involvement of hSLO3 mutations in human asthenoteratozoospermia [ 48 ]. Indeed, a Chinese patient carrying the homozygous missense variant p.Ile413Phe showed male infertility due to impaired acrosome formation, mitochondrial dysfunction, altered membrane potential during capacitation and reduced sperm motility.…”

Iberiotoxin and clofilium regulate hyperactivation, acrosome reaction, and ion homeostasis synergistically during human sperm capacitation

“…Geng et al found that human SLO3 is rapidly evolving and natural genetic variation (C382R) shows enhanced Ca 2+ sensitivities (Geng et al, 2017). Recently, Lv et al found an asthenoteratozoospermia case with SLO3 homozygous mutation, which leads to infertility, suggesting that functional SLO3 is indispensable for human fertility (Lv et al, 2022). Therefore, it has been confirmed that SLO3 plays important roles in human sperm.…”