Early activation of sperm by HCO3− is regulated hormonally in the murine uterus

Abstract

Sperm deposited in the female genital tract receive signals for capacitation. Past work indicates that HCO(3) (-) is the initiating signal that the female reproductive tract contains the HCO(3) (-) -permeant anion channel cystic fibrosis transmembrane conductance regulator (CFTR) and that mutations in CFTR cause subfertility in both sexes. In this study, we examined whether CFTR controls uterine HCO(3) (-) content and sperm responses to it. Both CFTR protein and mRNA were absent in prepubertal murine uterus, but appeared in pubertal and adult tissues. Thus, CFTR is upregulated during development. Uterine CFTR mRNA additionally increased upon induced oestrus, most abundantly in uterus body and distal horns. Uterine fluid of oestrous females contained two-, and nearly fourfold more HCO(3) (-) than that of dioestrous and prepubertal animals, correlating with increased CFTR expression. For sperm incubated in and recovered from prepubertal uteri, flagellar beat frequency was no different from that before incubation. However, for sperm recovered from dioestrous and oestrous uteri, beat frequency was two- and fourfold higher, respectively. Thus, uterine HCO(3) (-) content may have physiological consequences for sperm motility. The male reproductive tract showed no regional distributions or developmental dependence of CFTR expression. Although the sperm flagellum showed CFTR immunoreactivity, CFTR blockers GlyH-101 or CFTR(inh) -172 did neither diminish HCO(3) (-) -evoked increases in sperm motility nor protein tyrosine phosphorylation. Our results indicate that in the uterus, both CFTR expression and the supply of HCO(3) (-) are upregulated hormonally. We propose that these changes coordinate ovulation with increases in sperm motility and promote other components of capacitation by pathways that do not require CFTR in sperm.

Participation of the Cl−/HCO3− Exchangers SLC26A3 and SLC26A6, the Cl− Channel CFTR, and the Regulatory Factor SLC9A3R1 in Mouse Sperm Capacitation1

“…These findings suggest that SLC26A3 and CFTR are part of a complex where, as previously reported [17,18,52], each transporter activity affects the other. Interestingly, inhibition of CFTR [8,41] and SLC26 (this work, data not shown) do not affect tyrosine phosphorylation. This result was not unexpected, since it is likely that capacitation-associated events are not necessarily correlated or connected.…”

“…Experiments using specific CFTR inhibitors strongly suggest that this channel participates in the capacitation-associated hyperpolarization and the AR [9,10], although its inhibition does not affect tyrosine phosphorylation [8,41]. In many cell types, there are interrelationships between the transport of Cl À and HCO 3 À [7, 8,42].…”

CFTR/ENaC-dependent regulation of membrane potential during human sperm capacitation is initiated by bicarbonate uptake through NBC

“…This transport may occur when sperm are exposed to higher HCO 3 -concentrations in the seminal plasma at the time of ejaculation or while migrating to the site of fertilization in the female reproductive tract. In this regard, it was reported that uterine secretions of oestrous female mice contained higher HCO 3 -concentration compared to those in dioestrous (47). This increase correlates with CFTR expression indicating that this channel is upregulated hormonally (47).…”

“…In this regard, it was reported that uterine secretions of oestrous female mice contained higher HCO 3 -concentration compared to those in dioestrous (47). This increase correlates with CFTR expression indicating that this channel is upregulated hormonally (47).…”

“…We have recently shown that CFTR is essential for the sustained HCO 3 -uptake by using two specific inhibitors of this channel which abrogated the phosphorylation of PKA substrates and in tyrosine residues. On the contrary, these inhibitors did not produce any effect on phosphorylation of PKA substrates or tyrosine residues in mouse sperm (47) since the sustained HCO 3 -transport occurs through NKCC transporters (48). Supporting this concept, inhibitors of NKCC such as bumetanide did not abolish pY in human sperm (Suppl.…”