Particulate Adenylate Cyclase Plays a Key Role in Human Sperm Olfactory Receptor-mediated Chemotaxis

Abstract

Human sperm chemotaxis is a critical component of the fertilization process, but the molecular basis for this behavior remains unclear. Recent evidence shows that chemotactic responses depend on activation of the sperm olfactory receptor, hOR17-4. Certain floral scents, including bourgeonal, activate hOR17-4, trigger pronounced Ca 2؉ fluxes, and evoke chemotaxis. Here, we provide evidence that hOR17-4 activation is coupled to a cAMP-mediated signaling cascade. Multidimensional protein identification technology was used to identify potential components of a G-protein-coupled cAMP transduction pathway in human sperm. These products included various membrane-associated adenylate cyclase (mAC) isoforms and the G olf -subunit. Using immunocytochemistry, specific mAC isoforms were localized to particular cell regions. Whereas mAC III occurred in the sperm head and midpiece, mAC VIII was distributed predominantly in the flagellum. In contrast, G olf was found mostly in the flagellum and midpiece. The observed spatial distribution patterns largely correspond to the spatiotemporal character of hOR17-4-induced Ca 2؉ changes. Behavioral and Ca 2؉ signaling responses of human sperm to bourgeonal were bioassayed in the presence, or absence, of the adenylate cyclase antagonist SQ22536. This specific agent inhibits particulate AC, but not soluble AC, activation. Upon incubation with SQ22536, cells ceased to exhibit Ca 2؉ signaling, chemotaxis, and hyperactivation (faster swim speed and flagellar beat rate) in response to bourgeonal. Particulate AC is therefore required for induction of hOR17-4-mediated human sperm behavior and represents a promising target for future design of contraceptive drugs.

β-Arrestin2-Mediated Internalization of Mammalian Odorant Receptors

“…Images were acquired from up to 15 cells in a randomly selected field of view, and integrated fluorescence ratios (F 340 /F 380 ratio) were measured. Cells were exposed to either 100 or 500 M amylbutyrat, which are typical concentrations used for heterologously expressed ORs (Saito et al, 2004;Spehr et al, 2004;Katada et al, 2005). Exposure to amylbutyrat was accomplished using a specialized microcapillary application system.…”

Phosphodiesterase 11 (PDE11) regulation of spermatozoa physiology

“…Moreover, the mAC-specific inhibitor, SQ22536, prevented spermatozoan Ca 2 þ signaling, chemotaxis and hyperactivation. 34 Consistent with these studies, PDE11 À/À mice were grossly normal, but the sperm from PDE11 À/À mice had reduced forward progression, suggesting that sperm from PDE11 À/À mice, too, may fail to fertilize oocytes.…”

Human sperm pattern of movement during chemotactic re-orientation towards a progesterone source

“…24,25 Conversely, in internal-fertilizing species, such as humans, only ,10% of cells are capable of a chemotactic response while swimming towards the source of an attractant (positive gradient), whereas there is no evidence of a visible change in the pattern of movement. [2][3][4]6,16,26 In fact, in our system, the cells that chemotactically swam from W1 (containing spermatozoa) to W2 (containing progesterone) could not be distinguished from the nonchemotactic cells according to the patterns of movement. These features of mammalian sperm chemotaxis make it technically difficult to identify an individual chemotactic cell.…”

“…Therefore, sperm chemotaxis determination is currently limited to a population analysis, and the results are mostly expressed as the percentage of cells oriented towards the attractant source; 3,27 however, human spermatozoa are able to return to the source of bourgeonal (negative gradient) with asymmetrical movements of the flagella. 16 This observation directed us to study the sperm behaviour of those cells that return to the source of a physiological attractant candidate, such as progesterone.…”

“…1 Nonetheless, in a study where bourgeonal was used as an attractant, a few spermatozoa swam away from the attractant source and then suddenly turned back, apparently owing to an asymmetrical movement of the flagellum. 16 Interestingly, this sperm behaviour, which has been observed only with bourgeonal, has not been fully described. By contrast, human spermatozoa that have been exposed to a temporal gradient of progesterone show an increase in curvilinear velocity and lateral head displacement, with a decrease in swimming linearity.…”