Capacitation-associated alkalization in human sperm is differentially controlled at the subcellular level

Abstract

Capacitation in mammalian sperm involves the accurate balance of intracellular pH (pH i), but the mechanisms controlling this process are not fully understood, particularly regarding the spatiotemporal regulation of the proteins involved in pH i modulation. Here, we employed an image-based flow cytometry technique combined with pharmacological approaches to study pH i dynamics at the subcellular level during capacitation. We found that, upon capacitation induction, sperm cells undergo intracellular alkalization in the head and principal piece regions. The observed localized pH i increases require the initial uptake of HCO 3 − , which is mediated by several proteins acting consistently with their subcellular localization. Hv1 proton channel (also known as HVCN1) and cAMP-activated protein kinase (protein kinase A, PKA) antagonists impair alkalization mainly in the principal piece. Na + /HCO 3 − cotransporter (NBC) and cystic fibrosis transmembrane regulator (CFTR) antagonists impair alkalization only mildly, predominantly in the head. Motility measurements indicate that inhibition of alkalization in the principal piece prevents the development of hyperactivated motility. Altogether, our findings shed light on the complex control mechanisms of pH i and underscore their importance during human sperm capacitation. This article has an associated First Person interview with the first author of the paper.

Conserved Mechanism of Bicarbonate-Induced Sensitization of CatSper Channels in Human and Mouse Sperm

“…Our results are consistent with others’ observations that the sAC and PKA pathways are important in regulating sperm capacitation in many species and that these pathways act, at least in part, by regulating pH i ( Puga Molina et al, 2017 ; Chavez et al, 2019 ; Matamoros-Volante and Trevino, 2020 ; Balbach et al, 2021 ). Carlson et al showed no changes in pH i induced by HCO 3 – in mouse sperm.…”

“…Several studies have revealed that HCO 3 – raises sperm intracellular pH (pH i ) ( Demarco et al, 2003 ; Chavez et al, 2019 ; Matamoros-Volante and Trevino, 2020 ) and that HCO 3 – can activate CatSper channels in mouse sperm ( Orta et al, 2018 ). Therefore, we investigated whether the [Ca 2+ ] i changes induced by HCO 3 – were due to a change in pH i .…”

Structure and Function of Ion Channels Regulating Sperm Motility—An Overview

“…The information on the role of chloride channels (and transporters) in spermatozoa is rather scarce when compared to other ion channels. Nevertheless, in sperm cells, they seem to support events such as the hyperpolarization of the plasma membrane [82], the alkalization of cytosolic environments [83,84] and cAMP/PKA-induced protein phosphorylation [84]. All of these processes are typical features of sperm capacitation.…”

HVCN1 Channels Are Relevant for the Maintenance of Sperm Motility During In Vitro Capacitation of Pig Spermatozoa

“…Sperm capacitation is characterized by a set of physiological changes preparing the male gamete for fertilization [1]. These physiological changes include increased beat frequency and curvilinear motility, intracellular pH (pH i ) alkalinization, rise in intracellular calcium levels, augmented membrane lipid disorder and tyrosine phosphorylation of specific proteins, which are required for sperm to trigger acrosomal exocytosis [1][2][3][4][5][6][7][8]. Several channels are implicated in the increase of pH i during capacitation and acrosomal reaction in mammalian spermatozoa, including HCO 3 − membrane transporters, Na + -H + exchangers (NHEs), monocarboxylate transporters (MCTs) and voltage-gated proton channels (HVCN1) [9,10].…”