A sperm-specific Na ⁺ /H ⁺ exchanger (sNHE) is critical for expression and in vivo bicarbonate regulation of the soluble adenylyl cyclase (sAC)

Abstract

We previously identified a sperm-specific Na ؉ /H ؉ exchanger (sNHE) principally localized to the flagellum. Disruption of the sNHE gene in mice resulted in absolute male infertility associated with a complete loss of sperm motility. Here, we show that the sNHE-null spermatozoa fail to develop the cAMP-dependent protein tyrosine phosphorylation that coincides with the functional maturation occurring upon incubation in capacitating conditions in vitro. Both the sperm motility defect and the lack of induced protein tyrosine phosphorylation are rescued by the addition of cell-permeable cAMP analogs, suggesting that cAMP metabolism is impaired in spermatozoa lacking sNHE. Our analyses of the bicarbonate-dependent soluble adenylyl cyclase (sAC) signaling pathway in sNHE-null sperm cells reveal that sNHE is required for the expression of full-length sAC, and that it is important for the bicarbonate stimulation of sAC activity in spermatozoa. Furthermore, both codependent expression and coimmunoprecipitation experiments indicate that sNHE and sAC associate with each other. Thus, these two proteins appear to be components of a signaling complex at the sperm flagellar plasma membrane. We propose that the formation of this complex efficiently modulates intracellular pH and bicarbonate levels through the rapid and effective control of sAC and sNHE activities to facilitate sperm motility regulation.cAMP ͉ sperm motility

Flagellar ion channels of sperm: similarities and differences between species

“…The fact that sNHE −/− sperm motility could be rescued by application of membrane permeable cAMP analogues has suggested that absence of sACY was perhaps the cause of the infertile phenotype [111]. An intriguing model was recently proposed [112] suggesting that sNHE may function as hyperpolarization activated proton extrusion mechanism since it possesses a putative voltage sensor [108,110,111,113].…”

Traditional and emerging roles for the SLC9 Na+/H+ exchangers

“…When transfected in NHE-null fibroblasts, full length sperm NHE expressed poorly. A chimeric construct with the first transmembrane domain of sperm NHE replaced by that of NHE1, however, exhibited improved expression at the plasma membrane and measurable NHE activity, suggesting that sperm NHE was indeed a functional NHE [169]. Sperm NHE KO males are infertile, and display severly diminished sperm motility but normal sperm numbers and morphology [170].…”

“…Addition of ammonium chloride and cell-permeant cAMP analogues partially rescued the motility and fertility defects observed in KO sperm. Loss of sperm NHE resulted in a complete loss of full length bicarbonate-sensitive soluble adenylate cyclase (sAC) with greatly reduced bicarbonate-stimulated sAC activity [169]. sAC and sperm NHE were shown to physically interact with each other, forming a signaling complex at the sperm flagellar plasma membrane that seems to be vital for control of intracellular bicarbonate and cAMP levels, both of which are of great importance for sperm capacitation and motility [169].…”

Compartmentalization of Distinct cAMP Signaling Pathways in Mammalian Sperm

“…In sperm, we can add to this list the testis-specific Na ϩ -H ϩ exchanger that contains a putative consensus sequence for cAMP binding (71). As mentioned, immunofluorescence localization of G␣ s subunit suggests that the tmAC signaling pathway is present in the sperm plasma membrane surrounding the anterior acrosome.…”