Kcnj16 (Kir5.1) Gene Ablation Causes Subfertility and Increases the Prevalence of Morphologically Abnormal Spermatozoa

Abstract

The ability of spermatozoa to swim towards an oocyte and fertilize it depends on precise K+ permeability changes. Kir5.1 is an inwardly-rectifying potassium (Kir) channel with high sensitivity to intracellular H+ (pHi) and extracellular K+ concentration [K+]o, and hence provides a link between pHi and [K+]o changes and membrane potential. The intrinsic pHi sensitivity of Kir5.1 suggests a possible role for this channel in the pHi-dependent processes that take place during fertilization. However, despite the localization of Kir5.1 in murine spermatozoa, and its increased expression with age and sexual maturity, the role of the channel in sperm morphology, maturity, motility, and fertility is unknown. Here, we confirmed the presence of Kir5.1 in spermatozoa and showed strong expression of Kir4.1 channels in smooth muscle and epithelial cells lining the epididymal ducts. In contrast, Kir4.2 expression was not detected in testes. To examine the possible role of Kir5.1 in sperm physiology, we bred mice with a deletion of the Kcnj16 (Kir5.1) gene and observed that 20% of Kir5.1 knock-out male mice were infertile. Furthermore, 50% of knock-out mice older than 3 months were unable to breed. By contrast, 100% of wild-type (WT) mice were fertile. The genetic inactivation of Kcnj16 also resulted in smaller testes and a greater percentage of sperm with folded flagellum compared to WT littermates. Nevertheless, the abnormal sperm from mutant animals displayed increased progressive motility. Thus, ablation of the Kcnj16 gene identifies Kir5.1 channel as an important element contributing to testis development, sperm flagellar morphology, motility, and fertility. These findings are potentially relevant to the understanding of the complex pHi- and [K+]o-dependent interplay between different sperm ion channels, and provide insight into their role in fertilization and infertility.

Ion Channels of Spermatozoa: Structure, Function, and Regulation Mechanisms

“…The flux of calcium (Ca 2+ ) and bicarbonate (HCO 3 − ) across the sperm-plasma membrane has been extensively reported, due to the relevance of both ions as second messengers triggering sperm capacitation and hyperactivation in the female tract [ 1 ]. However, other ions such as potassium (K + ), sodium (Na + ), chloride (Cl − ) and hydrogen (H + ) are also relevant to male fertility, since they are implicated in the regulation of internal pH (pH i ) and/or the plasma membrane potential (Em) not only during sperm capacitation ( Figure 1 ) [ 2 , 3 , 4 ], but also throughout the spermiogenesis and epididymal maturation and upon ejaculation [ 4 , 5 ]. Most studies on ion channels are performed in mature sperm of mammalian species, specially from humans and rodents, and little data exist on their physiological role during germ cell differentiation and maturation.…”

“…The plasma membrane of mature sperm contains a high diversity of ion transporters belonging to different protein families and showing different ion affinity, regulation mechanisms, and functional multiplicity [ 6 ]. The absence or dysfunction of even a single channel type may result in male subfertility [ 5 , 7 , 8 ] or affect sperm cryotolerance [ 9 ]; moreover, some ion channels can be used as contraception targets [ 8 , 10 ].…”

“…Most of the original research included in this special issue focuses on the physiological role of K + and H + transporters in mammal sperm physiology. In these species, the sperm plasmalemma contains different K + transporters, such as voltage-gated potassium channels (K v ), inward-rectifier potassium channels (K ir ), calcium-activated potassium channels (K Ca ), and tandem-pore-domain potassium channels (KCNK) [ 3 , 5 , 9 ]. Poli et al [ 5 ] performed an excellent study on the expression and function of Kir4.1 and Kir5.1 channels in mature sperm cells from mice.…”

“…In these species, the sperm plasmalemma contains different K + transporters, such as voltage-gated potassium channels (K v ), inward-rectifier potassium channels (K ir ), calcium-activated potassium channels (K Ca ), and tandem-pore-domain potassium channels (KCNK) [ 3 , 5 , 9 ]. Poli et al [ 5 ] performed an excellent study on the expression and function of Kir4.1 and Kir5.1 channels in mature sperm cells from mice. Kir family includes different subfamilies (Kir1.0-Kir7.0) of inwardly rectifying K + transporters channels, which are expressed in several cell types and are implicated in the maintenance of membrane potential (Em) and cellular excitability.…”

“…Immunofluorescent approaches demonstrated the presence of Kir5.1 in the plasma membrane of mature sperm cells, but they did not indicate the presence of Kir.4.1 in the same cells. Interestingly, the deletion of Kir5.1 gene led to impaired sperm motility and fertility, but also reduced testicular development, thus highlighting the relevance of this channel in sperm-cell differentiation and function [ 5 ]. In their comprehensive research, Noto et al [ 3 ] analysed the relevance of K + transport across the plasma membrane during in vitro capacitation of pig sperm, by incubating sperm cells in the capacitation medium in either the presence or absence of a general blocker of K + channels or a specific blocker of Ca 2+ -activated K + (K Ca ) channels.…”